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International Journal of Research in Pharmacy and Biosciences

Volume 2, Issue 5,June 2015, PP 1-18

ISSN 2394-5885 (Print) & ISSN 2394-5893 (Online)

*Address for correspondence

[email protected]

International Journal of Research in Pharmacy and Biosciences V2 ● I5 ● June 2015 1

Recent Advances in the Development of Anti-tuberculosis Drugs

Acting on Multidrug-Resistant Strains: A review

Amanuel Godebo*1

, Abiy H/woldi2, Alemayehu Toma

3

1Department of Pharmacology, School of Medicine, College of Health Sciences, Addis Ababa University, Addis

Ababa, Ethiopia

2Department of Pharmacology, School of Medicine, College of Health Sciences, Addis Ababa University, P. O.

Box 9086, Addis Ababa, Ethiopia 3Pharmacology Department, School of Medicine, Hawassa University, Hawassa, Ethiopia

ABSTRACT

Despite over a century of drug development research, tuberculosis remains a major public health problem with a

leading cause of infectious death worldwide. The reality of being deadly is the result of decades of neglect for

an important infectious disease, lack of resources for national TB control programs, poor case detection and

inadequate/inappropriate therapy in high-burden countries. At present time, the outcome of treatment protocol

for MDR-TB is not intrinsically satisfactory, and it is lengthy in duration (18 – 24 months) although the

treatment regimen consists of at least four drugs with different mechanism of action. Hence, new drugs are

urgently needed to shorten and improve the treatment course in drug resistant TB, and to minimize the

occurrence of new infections and death to zero level. Nowadays, various novel investigational drugs, such as

bedaquine (TMC207) [approved for use by FDA and WHO Expert Group], nitroimidazoles (PA-824, OPC-

67683), diamines (SQ109), oxazolidinones(Linezolid, PNU-100480 (Sutezolid), ADZ5847), pyrroles (LL3858)

and fluoroquinolones (moxifloxacin and gatifloxacin), have entered various clinical trial phases and on progress

to be developed for the treatment of MDR-TB. However, new targets should be further identified and

discovered that can kill the viable MTB in the latent phase and prevent the occurrence of resistance in bacterial

cells. Finally, it is crucial to boost the connection between different parties, like research and development

institutes, industries, drug control authorities, and international policy-making bodies to make the future bright

and convey the optimum therapy for the patients who are suffering from TB.

Keywords: Tuberculosis, MDR-TB, treatment protocol, new targets, challenges.

INTRODUCTION

Background

Tuberculosis (TB) remains a major global health problem. It causes ill-health among millions of

people each year and ranks as the second leading cause of death from an infectious disease

worldwide, after the human immunodeficiency virus (HIV). According to World Health Organization

(WHO) global TB report 2012, there were almost 9 million new cases in 2011 and 1.4 million TB

deaths. Besides, the emergence of drug-resistance is becoming a major threat to global TB care and

control. WHO estimates that around 310,000 multidrug-resistant tuberculosis (MDR-TB) cases

occurred among notified TB patients in 2011.1The increasing emergence of drug resistant TB, and

HIV infection, which compromises host defense and allows latent infection to reactivate TB, pose

further challenges for effective control of the disease. Moreover, TB treatment is remarkably lengthy

(takes 6–9 months) with significant toxicity, which creates poor patient compliance resulting in a

frequent cause for selection of drug resistant and often deadly MDR-TB bacteria.2To tackle this

situation, multiple approaches will need to be implemented simultaneously, combining the efforts of

government, academic and industrial entities. These approaches include increased funding for

research in antibiotic resistance and drug development for TB, development of methods for protecting

the efficacy of existing drugs, and prioritization for making use of current non-TB drugs for TB

treatment.3

Amanuel Godebo et al. “Recent Advances in the Development of Anti-tuberculosis Drugs Acting on

Multidrug-Resistant Strains: A Review”

2 International Journal of Research in Pharmacy and Biosciences V2 ● I5 ● June 2015

Current treatment regimens for MDR-TB are far from satisfactory: the overall duration is 20 months

or more, requiring daily administration of drugs that are more toxic and less effective than those used

to treat drug-susceptible TB, and have a high cost. Among MDR-TB patients started on treatment

globally in 2009, only 48% were treated successfully, largely as a result of a high frequency of patient

deaths (15%) and loss to follow-up (28%), which is commonly associated with adverse drug

reactions, among other factors. New drugs that would help build a better, safer, less toxic, shorter and

cheaper regimen are therefore urgently needed to reduce patient suffering and mortality.4It has been

over 40 years since a new drug for tuberculosis has been discovered.5 Therefore, the development of

innovative, effective drug combinations should also be encouraged to diversify therapeutic choices,

especially those for drug resistant TB cases. Emphasis, however, should be placed on compounds that

attack non-traditional targets, as to lower the risk for acquired drug resistance mechanisms.3

Epidemiology

Globally in 2011, there were an estimated 630,000 cases of MDR-TB (range, 460 000–790 000)

among the world’s 12 million prevalent cases of TB, in which 3.7% of new cases and 20% of

previously treated cases were anticipated. Almost 60% of these cases were in India, China and the

Russian Federation. While the number of cases of MDR-TB notified in the 27 high MDR-TB burden

countries is increasing and reached almost 60,000 worldwide in 2011, this is only one in five (19%) of

the notified TB patients estimated to have MDR-TB.1

TREATMENT AND MANAGEMENT OF MDR-TB

The current MDR-TB epidemic is the result of decades of neglect for an important infectious disease,

lack of resources for national TB control programs, poor case detection and inadequate/inappropriate

therapy in high-burden countries. Initial outbreaks of MDR-TB in developed countries were

associated with very high mortality rates both in HIV-negative and HIV-coinfected patients.

Optimization of treatment regimens together with rapid diagnosis and drug susceptibility testing

(DST) for first- and second-line drugs, greatly improved the clinical outcome. However, in

developing countries, the prognosis is still largely poor due to inadequate laboratory support that is

critical for successful management of MDR-TB patients.6

Treatment of drug-resistant TB requires a combination various anti-TB drugs with different

mechanisms of action. Traditionally, the classes of anti-TB drugs have been divided into first- and

second-line drugs as briefly explained in Table 1. Besides, there are some other agents with unclear

efficacy (not recommended for routine use) being used for the treatment of MDR-TB and XDR-

TB.7For MDR treatment, anti-TB drugs are grouped according to efficacy, experience of use and drug

class, as shown in Table 2. All the first-line anti-TB drugs are in Group 1, except streptomycin (SM),

which is classified with the other injectable agents in Group 2. All the drugs in Groups 2–5 (except

SM) are second-line, or reserve drugs. Treatment regimens should consist of at least four drugs with

either certain, or almost certain, effectiveness. Each dose in an MDR regimen is given as directly

observed therapy (DOT) throughout the treatment.8

Table1. Some of Anti-TB drugs with their category and mechanism of action

Drug Name Category Route Chemical Description Mechanism of Action

Isoniazid (INH) 1st line Oral Nicotinic acid

hydrazide

Inhibits mycolic acid synthesis

Rifampin/rifampicin

(RIF)

1st line Oral Rifamycin derivative Inhibits RNA synthesis by

targeting RNA polymerase

Pyrazinamide (PZA) 1st line Oral Nicotinamide

derivative

Inhibits cell membrane synthesis

Ethambutol (EMB) 1st line Oral Ethylene di-imine di-

1-butanol

Inhibit cell wall synthesis

Streptomycin (SM) 1st line Injectable Aminoglycoside Inhibits protein synthesis

Rifabutin (Rfb)

/Rifapentine

2nd line Oral Rifamycin derivative Inhibits RNA synthesis by

targeting RNA polymerase

Amikacin (Am) 2nd line Injectable Aminoglycoside Inhibits protein synthesis

Kanamycin (Km) 2nd line Injectable Aminoglycoside Inhibits protein synthesis

Capreomycin (Cm) 2nd line Injectable Cyclic peptide Inhibits protein synthesis

Ofloxacin (Ofx) 2nd line Oral Fluoroquinolone Inhibits DNA synthesis and




supercoiling by targeting

toposiomerase

Levofloxacin (Lfx) 2nd line Oral Fluoroquinolones Inhibits DNA synthesis and


toposiomerase

Moxifloxacin (MFX) 2nd line Oral Fluoroquinolones Inhibits DNA synthesis and


toposiomerase

Ethionamide (Eto) 2nd line Oral Isonicotinic acid

derivative


Protionamide (Pto) 2nd line Oral Isonicotinic acid

derivative


Cycloserine (Cs) 2nd line Oral D-Cycloserine Inhibits cell wall synthesis

Paraaminosalicylicacid

(PAS)

2nd line Oral Para-amino salicylic

acid

Inhibit folate biosynthesis

Table2.Groups of Drugs to Treat MDR-TB

Group Class Drugs

Group 1

First-line oral agents

Pyrazinamide (PZA)

Ethambutol (EMB)

Rifabutin (RFB)

Group 2

Injectable Agents

Kanamycin (Km)

Amikacin (Am)

Capreomycin (Cm)

Streptomycin (SM)

Group 3

Fluoroquinolones

Levofloxacin (lfx)

Moxifloxacin (mfx)

Ofloxacin (ofx)

Group 4

Oral bacteriostatic second-line

agents

Para-aminosalicylic acid (PAS)

Cycloserine (Cs)

Terizidone (Trd)

Ethionamide (Eto)

Protionamide (Pto)

Group 5

Agents with unclear role in

treatment of drug resistant-TB

Clofazimine (Cfz)

Linezolid (Lzd)

Amoxicillin/Clavulanate (Amx/clv)

Thioacetazone (Thz)

Imipenem/Cilastatin (Ipm/Cln)

High-dose isoniazid (high-dose H)

Clarithromycin (Clr)

Programmatic approaches to MDR-TB treatment depend in part on the type of laboratory method

(Conventional and Rapid DST) used to confirm MDR-TB, as shown in Table 3. Once MDR-TB is

confirmed, patients can be treated with: a standard MDR-TB regimen (standardized approach); or an

individually tailored regimen, based on DST of additional drugs, as shown in Table 4.8

Table1. MDR-TB Treatment Strategies Depending on Laboratory Method to Confirm MDR-TB

Laboratory Method DST Result Treatment Approach

Conventional method to

detect MDR-TB

While awaiting DST results for

isoniazid, rifampicin; MDR-TB

is suspected

Empirical treatment with MDR-TB regimen

Once MDR-TB is confirmed

Continue standard MDR-TB regimen or

Change to individualized MDR-TB regimen

(once susceptibility testing for second-line

drugs is available).

Rapid method to detect

MDR (takes around 1–2

days to detect MDR-TB)

Once MDR-TB is confirmed

Standard MDR-TB regimen or

Individualized MDR-TB regimen (once

susceptibility testing for second-line drugs is

available).




Table2. Potential regimens for the treatment of patients with MDR-TB

Pattern of Drug

Resistance

Suggested Regimen (Daily Unless Otherwise Stated) Duration of Treatment

(months)

INH (± SM) RIF, PZA, EMB (a fluoroquinolone may strengthen the

regimen for patients with extensive disease)

6

RIF INH, EMB, fluoroquinolones, supplemented with PZA for

the first 2 months (an Injectable Agents may be included

for the first 2-3 months for patients with extensive disease)

12-18

INH, RIF (± SM) Fluoroquinolones, PZA, EMB, Injectable Agents (±

alternative agent)

18-24

INH, RIF (± SM)

and EMB

Fluoroquinolones, PZA, Injectable Agents, and two

alternative agents

24

INH, RIF (± SM)

and PZA

Fluoroquinolones, EMB, Injectable Agents, and two

alternative agents

24

Drug Candidates and New Drugs Invented to Treat MDR-TB

New drugs are urgently needed to get to zero deaths, zero new infections, and zero stigma and

suffering from TB. While TB has been curable for decades, existing drugs have to be taken for

months or even years.9 New anti-TB drugs are needed for three main reasons: firstly, to shorten or

otherwise simplify treatment of TB caused by drug-susceptible organisms; secondly, to improve

treatment of drug-resistant TB, and thirdly, to provide more efficient and effective treatment of latent

TB infection.10 Consequently, the landscape of TB drug development has evolved dramatically over

the past ten years, and novel drugs are entering Phase III trials for the treatment of MDR-TB.5 Within

a rational and well-funded infrastructure for conducting multinational large clinical trials, the

importance of the development of new sterilizing drugs that target persistent bacteria and shorten TB

therapy must be intensely promoted by the medical and TB patient advocacy communities.11

Bedaquiline (Diarylquinoline TMC207, R207910)

Bedaquiline [formerly named as TMC20712 or R20791013] is the first new drug from a new drug class

to treat TB to be approved by the United States Food and Drug Administration (FDA) in over 40

years 14, whose chemical structure is seen in Fig. 1.15The drug, to be called Sirturo, was discovered by

scientists at Janssen, the pharmaceuticals unit of Johnson and Johnson, and is the first in a new class

of drugs that aims to treat the drug-resistant strain of the disease.16As a result, the Expert Group

suggested that, as an interim recommendation, bedaquiline may be added to a WHO-recommended

regimen in MDR-TB adult patients under the following conditions: when an effective treatment

regimen containing four second-line drugs in addition to PZA according to WHO recommendations

cannot be designed; and when there is documented evidence of resistance to any fluoroquinolone in

addition to multidrug resistance.4

TMC207 is a first-in-class diary lquinolone compound with a novel mechanism of action 17 and

exhibits excellent activity against drug susceptible, MDR and XDR mycobacterium strains, with no

cross-resistance to current first-line drugs. It appears that TMC207 has greater potency against

mutated drug resistant strains than to fully susceptible isolates, suggesting a unique mechanism of

action. Whilst TMC207-resistant strains have appeared, they remain fully susceptible to other anti-TB

drugs such as RIF, INH, SM and EMB. Diarylquinoline TMC207 seems to act by inhibiting the ATP

synthase, leading to ATP depletion and pH imbalance.12

Figure1.Chemical Structure of bedaquiline (TMC207)




Moreover, diarylquinoline TMC207 has potent bactericidal activity in the established infection in

murine TB model.13Besides, oral once daily administration of TMC207 has bactericidal activity at a

dose of 400 mg when administered as mono-therapy for 7 days in patients with pulmonary TB.

Compared to INH and RIF, the bactericidal activity of 400 mg of TMC207 started later but was of

similar magnitude on days 4 to 7. Serious adverse effects related to the study drug did not occur.18

TMC207 has bactericidal and sterilizing activity against Mycobacterium tuberculosis (MTB) and

other mycobacterial species but little activity against other bacteria.19

Substitution of RIF, INH or PZA with diarylquinoline TMC207 accelerated activity leading to

complete culture conversion after 2 months of treatment. In particular, the TMC207-INH-PZA and

TMC207-RIF-PZA combinations cleared the lungs of TB in all the mice after two months.

Diarylquinoline TMC207 has been also tested in various combination with the second line drugs

amikacin, PZA, MFX and ethionamide in mice infected with the drug susceptible virulent MTB strain

H37Rv. Diarylquinoline containing regimen were more active than the current recommended regimen

for MDR-TB amikacin-PZA-MFX-ethionamide and culture negativity of the both lungs and spleens

was reached after 2 months of treatment in almost every case.13

As preliminary stage 1 data from a double-blind, placebo-controlled, randomized Phase II trial 19 and

2-years followed up results revealed on the randomized placebo-controlled study 20 confirm the

significant bactericidal activity of TMC207/bedaquiline in patients treated for MDR-TB. In both

studies there is a reduced time to culture conversion and a higher number of culture conversions after

8 weeks of a standard background regimen plus TMC207 in patients with MDR-TB. The compound

was safe and well tolerated over the 8-week treatment period. The emergence of drug resistance was

substantial and may have been reduced by the concurrent administration of bedaquiline.19, 20

Nitroimidazoles (PA-824 and OPC-67683)

Another class of compounds that has been the subject of considerable interest because of their

potential in TB therapy is the nitroimidazoles. Currently, two nitroimidazoles,the nitroimidazo-

oxazine PA824, which is being developed by the TB Alliance, and the dihydroimidazooxazole

OPC67683, which is being developed by Otsuka Pharmaceutical, are in clinical development. This

class of compounds possessed antimicrobial activity. However, when the lead compound (CGI-

17341) was found to be mutagenic in the Ames assay, further development was halted.21

PA-824

PA-824 is a promising new compound, with the chemical name (S)-2-nitro-6-(4-(trifluoromethoxy)

benzyloxy)-6,7-dihydro-5H-imidazo[2,1-b][1,3], as shown on Fig. 2, 22for the treatment of TB that is

currently undergoing human trials. Like its progenitors, metronidazole and CGI-17341, PA-824 is a

pro-drug of the nitroimidazole class, requiring bio-reductive activation of an aromatic nitro group to

exert an anti-tubercular effect. And it was confirmed that resistance to PA-824is most commonly

mediated by loss of a specific glucose-6-phosphate dehydrogenase (FGD1) or its deazaflavin cofactor

F420, which together provide electrons for the reductive activation of this class of molecules.23 PA-824

has substantial bactericidal activity during both the initial and the continuation phases of treatment in

an experimental murine TB model. The minimal effective dose and minimal bactericidal dose were

12.5 mg/kg and 100 mg/kg, respectively. At a dose of 100 mg/kg/day, the bactericidal activity of PA-

824 approaches that of INH at the equipotent dosage of 25 mg/kg/day for humans.24

Figure2. Structural formula of investigational product: PA-824

In the randomized study, PA-824 appeared safe and well tolerated during 14 days of once-daily

dosing in drug-sensitive, sputum smear-positive, adult pulmonary tuberculosis (PTB) patients at

dosages of 200 to 1,200 mg/day. The number of adverse events was low and the severity of events

mostly mild or moderate. PA-824 also showed to have a substantial and linear early bactericidal




activity (EBA) over 14 days comparable to that of the existing first-line TB treatment agents. The

extended EBA of PA-824 suggests that this drug may have sterilizing activity in human PTB and as

such could contribute importantly to the sterilizing and treatment shortening ability of a MDR-TB

treatment regimen.25In another study done on 58 healthy subjects, the safety, tolerability, and

pharmacokinetics of PA-824 were evaluated in two escalating-dose clinical studies, one a single-dose

study and the other a multiple-dose study (up to 7 days of daily dosing). In subjects dosed with PA-

824 in these studies, the drug candidate was well tolerated, with no significant or serious adverse

events.26

The bicyclic nitroimidazole PA-824 has a very complex mechanism of action active against both

replicating and hypoxic, non-replicating MTB. Microarray analysis of the mode of action of PA-824

showed a puzzling mixed effect both on genes responsive to both cell wall inhibition (like INH) and

respiratory poisoning (like cyanide). The aerobic killing mechanism of this drug appears to involve

inhibition of cell wall mycolic acid biosynthesis through unknown molecular mechanism. Whereas in

the case of respiratory poisoning, PA-824 acts directly as nitric oxide (NO) donor, and that NO

release from various PA-824 derivatives correlated well with the anaerobic killing of MTB. Thus, PA-

824 acts as a “suicide bomb” releasing toxic NO within mycobacterial cells and NO possibly reacts

with cytochromes/ cytochrome oxidase to interfere with the electron flow and ATP homeostasis under

hypoxic non-replicating conditions.27

Based on the study done inevaluating 3-drug combinations composed of TMC207, PZA, PA-824,

MFX; and rifapentine, TMC207 plus PZA plus either rifapentine or MFX was the most effective,

curing 100% and 67% of the mice treated, respectively, in 2 months of treatment. Four months of the

first-line regimen did not cure any mice, whereas the combination of TMC207, PA-824, and MFX

cured 50% of the mice treated. The results reveal new building blocks for novel regimens with the

potential to shorten the duration of treatment for both drug-susceptible and drug-resistant TB,

including the combination of TMC207, PZA, PA-824, and a potent fluoroquinolone.28

The murine model for TB has been informative in the development of multi component drug

regimens. In the studies with aerosol infection of mice with TB, PA-824 showed significant

bactericidal activity both alone and when substituted for INH as part of a standard regimen. This

finding was supported by pharmacokinetic data that suggested that PA-824 did not significantly affect

concentrations of RIF, INH and PZA.29In other study, testing of the PA-824, MFX and PZA

combination revealed that the triple combination cured mice more rapidly than the current first-line

regimen components of RIF, INH and PZA. MFX has potent in vitro activity against TB and

improves culture conversion in early TB treatment. 30

OPC-67683

Figure3. Chemical Structure of OPC-67683

A more recently discovered nitroimidazole, OPC67683, is a dihydroimidazo-oxazole under

development by Otsuka Pharmaceutical specifically for the treatment of TB. After undergoing single-

and multiple-dose trials in normal volunteers, the compound is presently being tested in patients in an

EBA trial. OPC67683 has extremely potent in vitro and in vivo activity against MTB.31 OPC-67683,

as its structure shown on Fig. 3 32, is a pro-drug and requires activation by MTB for activity;

experimentally isolated OPC-67683-resistant mycobacteria did not metabolize the compound and a

mutation in the MTB Rv3547 gene (responsible for activating PA-824) among the resistant organisms

suggests that this enzyme is involved in activating OPC-67683. The compound has been shown to

inhibit mycolic acid biosynthesis and kill MTB in vitro.33

In a mouse model of chronic infection, the efficacy of OPC67683 was superior to that of currently

used TB drugs. The effective plasma concentration was 0.1mg/mL, which was achieved with an oral

dose of 0.625 mg/kg, confirming the remarkable in vivo potency of the compound. Besides, OPC-

67683 showed no cross-resistance with any of the currently used anti-TB drugs.34 OPC-67683 showed




dose-dependent killing of drug-tolerant clinical strains of MTB that was superior to INH and

equivalent to RIF, the most strongly sterilizing TB drug. To the extent that findings in the mouse

model indicate potential sterilizing activity in human TB.35The eradication rate of a new regimen

containing OPC-67683 was compared with that of the standard regimen. The OPC-67683-containing

regimen exerted a rapid and consistent reduction during the first 3 months. At 3 months after the start

of treatment, only one colony was detected in one of the six animals; at 4 months, no colonies were

detected in any of the six animals. In contrast, at 6 months for the standard regimen, colonies were

detected in four out of five mice. These results suggest that a new regimen containing OPC-67683

could dramatically reduce the treatment duration by at least 2 months.33

Diamine(SQ-109)

Sixty-nine 1,2-ethylenediamines were re-tested for in vitro activity against MTB H37Rv in a micro-

broth dilution assay. For compound SQ109, its structure shown on Fig. 4 36, the best minimum

inhibitory concentration (MIC) of 1.56µM was determined, selectivity index of 16.7 and 99%

inhibition activity against intracellular bacteria, demonstrated potency in vivo and limited toxicity in

vitro and in vivo. SQ109 was also tested against Erdman and single drug resistant strains of MTB and

demonstrated significant activity: Erdman (0.7µM), ethambutol-resistant (1.4µM in Alamar Blue,

0.99µM in the BACTEC), INH-resistant (1.4µM), RIF-resistant (≤0.7µM). The fact that SQ109 works

against an EMB-resistant strain suggests different specific target, mechanism of action and/or

different activation pathways for SQ109 and EMB.37

Figure4. Chemical Structure of SQ109

The efficacy of SQ109 against MTB was demonstrated through in vitro macrophage model followed

by further testing in an in vivo animal model. Both models were infected with the same MTB strain

H37Rv. SQ109 exhibited both in vitro antimicrobial activity against MTB strain H37Rv grown inside

the host murine macrophage cells (i.e. its ability to penetrate into macrophage phagosome, where

MTB replicates) and in vivo antimicrobial activity on the mouse model inoculated with the H37Rv.

The activity of SQ109 in this regard was comparable to that of INH in the macrophage test system,

but superior over that of EMB.36

SQ109 interacts synergistically with INH and RIF, two of the most important front-line TB drugs.

SQ109 at 0.5 of its MIC demonstrated strong synergistic activity with 0.5 fraction of MIC INH and as

low as 0.1fraction of MIC RIF in inhibition of MTB growth. Additive effects were observed between

SQ109 and SM, but neither synergy nor additive effects were observed with the combination of

SQ109 with EMB or PZA. The synergy between SQ109 and RIF was also demonstrated using RIF-

resistant strains; SQ109 lowered the MIC of RIF for these drug-resistant strains.38 Substitution of the

new diamine antibiotic SQ109 for EMB in a mouse model of chronic TB improved efficacy of

combination drug therapy with first-line TB drugs RIF and INH, with or without PZA: at 8 weeks,

lung bacteria were 1.5log10 lower in SQ109-containing regimens.39

The combination of SQ109 with TMC207 improved an already excellent TMC207 MIC for MTB

H37Rv by 4- to 8-fold, improved the rate of killing of bacteria over the rate of killing by each single

drug, and enhanced the drug post antibiotic effect by 4 h. In no instance, antagonistic activities with

the combination of SQ109 and TMC207 were observed.40 In another study, the two investigational

drugs being developed for the treatment of TB, SQ109 and PNU-100480, combinations were additive

and improved the rate of MTB killing over individual drugs. It showed an overall lack of antagonism

between SQ109 and PNU-100480 in the range of expected therapeutic drug concentrations.41

Oxazolidinone[Linezolid, PNU-100480(Sutezolid) and AZD5847]

The oxazolidinones represent a novel class of antibacterial agents whose mechanism of action appears

to be inhibition of protein synthesis by binding to the 50S ribosomal subunit at a site close to the




site(s) to which chloramphenicol and lincomycin bind but that the oxazolidinones are mechanistically

distinct from these two antimicrobial agents.42 Two oxazolidinones, PNU-100480 and linezolid, have

promising anti-MTB activities in the murine test system.43 AZD5847 also showed anti-mycobacterial

activity.44

Linezolid

Linezolid, its structure shown on Fig. 4 45, is the first oxazolidinone to be developed and introduced in

clinical use. In vitro studies have shown good activity against different species of mycobacteria,

including resistant strains. The linezolid MIC to inhibit the growth of 90% of organisms for MTB is in

the range of 1–2 µg.L-1.46 Linezolid has modest EBA against rapidly dividing tubercle bacilli in

patients with cavitaryPTB during the first 2 days of administration, but little extended EBA.47

Figure5. Structural formula of Linezolid

Linezolid is a valid alternative in patients with MDR-TB. Its anti-mycobacterial activity sharply

increases the efficacy of other second-line therapies. However, the most limiting problem related to

the prolonged use of linezolid in MDR-TB is toxicity, mainly anemia and peripheral neuropathy.48 As

a result, it is recommended to use it with caution, in a dose never exceeding 600 mg, once a day, in

patients with MDR-TB and XDR-TB, who have few other drug options.49 Overall, the available data

suggest that linezolid is a potentially useful drug in treating the significant proportion of MDR-TB

patients in whom second-line regimens fail or who are infected with TB strains with such significant

resistance as not to allow the formulation of an appropriate second-line regimen using recommended

drugs.50

In the study done from 2003-2007, 30 patients received linezolid therapy at a dosage of 600 mg once

daily (2 received intermittent or lower-dose therapy because of low body weight). Of the 30 patients,

22 successfully completed treatment. Among patients who completed treatment, there was no relapse

during a mean follow-up of 1.5 years. All 29 patients with PTB achieved culture conversion, at a

median time of 7 weeks. Five additional patients continued to receive treatment and were tolerating

linezolid well at data censure. Two patients defaulted, and one experienced treatment failure, with an

isolate with the same susceptibility pattern as the initial episode of MDR-TB.51In another study

involving 39 patients with XDR pulmonary tuberculosis who had not had a response to any standard

treatment regimen for 6 months or more, the immediate addition of linezolid at a dose of 600 mg per

day to the ongoing background treatment regimen had a significant beneficial effect on the time to

sputum-culture conversion on solid medium, as compared with the delayed addition of linezolid at the

same dose. During the first 6 months, 34 of the 39 patients (87%) had confirmed culture conversion,

at a median of 76 days. 52 Even though, the role of linezolid in the treatment of MDR-TB and XDR-

TB has been considered controversial, an aggressive, comprehensive management programme using

linezolid along with other drugs can favorably treat significant number of patients with XDR-TB or

pre-XDR-TB.53

PNU-100480 (Sutezolid)

Figure 6.Structure of PNU-100480 (Sutezolid)




Another oxazolidinone, named as PNU-100480, its structure shown on Fig. 6 45, has been

demonstrated to have more potent bactericidal activity in vitro and in a murine TBmodel. Moreover,

the incorporation of PNU-100480 dramatically improved the bactericidal activities of regimens

containing current first-line anti-TB drugs and MFX. For instance, the addition of PNU-100480 (100

mg/kg/day) to the standard regimen of RIF, INH, and PZA resulted in an additional 2.0-log10-unit

reduction in lung CFU counts during the first 2 months of treatment. The combination of PNU-

100480, MFX, and PZA, which doesn’t contain either RIF or INH, was also more active than RIF,

INH, and PZA.54 PNU-100480 also advances further sterilizing activity to the first-line regimen that is

capable of shortening the duration of treatment necessary for cure.55

In the study done on health volunteers, PNU-100480 was well tolerated, showed proportional

increases in exposure to 1000 mg, adequately and predictably absorbed, and exhibited superior

bactericidal activity compared with line zolid, independent of peak drug concentrations.56,57In another

study, the duration of dosing of PNU-100480 was extended to better appreciate potential

oxazolidinone toxicities due to mitochondrial protein synthesis inhibition. No significant untoward

hematologic effects were observed when it was dosed at doses of 600 mg twice daily. Besides, it

shows additive or synergistic activity when it is added to standard doses of PZA.57PNU-100480,

TMC207, PA-824, SQ109, and PZA were examined singly and in various combinations, against

intracellular MTB, using whole blood culture (WBA). Combinations of PNU-100480, TMC207, and

SQ109 were fully additive, whereas those including PA-824 were less than additive or antagonistic.

The most active regimens, including PNU-100480, TMC207, and SQ109, were predicted to have

cumulative activity comparable to standard TB therapy.58 Susceptibility of clinical MTB isolates to

PNU-100480 and linezolid was evaluated. The isolates had various susceptibilities to INH, RIF,

EMB, and SM. The mean MIC for PNU-100480 was 3.2 times lower than that for linezolid.

Therefore, PNU-100480 is a promising candidate to be developed further as an adjunct in the

treatment of MDR-TB and XDR-TB.59

AZD5847

A little further behind in development, AstraZeneca are developing an oxazolidinone, AZD5847.

Healthy volunteer tolerability and pharmacokinetic studies were recently completed but results are not

yet available. A phase II EBA study is in development.60AZD5847, its structure shown on fig. 7 45,

was originally intended as a broad-spectrum antibiotic, but has now been repurposed as an anti-TB

agent.61 It is well recognized that with linezolid, treatment periods longer than 14 days may result in

hematological adverse effects and since treatment for TB is considerably longer than 14 days, the

degree and severity of this off-target activity with the next-generation oxazolidinone agents will be

the key for their development.62

Figure7.Chemical Structure of AZD5847

Pyrrole (LL-3858)

The anti-TB activity of the pyrrole class was first described in 1998. BM212, the most potent pyrrole

derivative studied so far, can be used as a lead for the preparation of new and more efficacious anti-

mycobacterial drugs, with MIC that ranged from 0.7 to 1.5 mg/mL against several strains of MTB

including the resistant strains.63 The mycobacterial target of LL3858, its structure shown on fig. 7 64,

is not yet known having a MIC range of 0.06–0.5 mg/mL that was not affected by resistance to INH

and RIF. Additive activity in combination with first line drugs in the murine model was also

described. The target probably differs from the targets of currently used drugs.65




Figure 8: Chemical Structure of LL3858

Fluoroquinolones (Gatifloxacin and Moxifloxacin)

Of the new compounds being tested for their efficacy in TB treatment, the fluoroquinolones are the

first novel drugs since the development of rifamycins to have been shown to have significant activity

against MTB.66 Currently fluoroquinolones are used as anti-tuberculous agents in MDR-TB and, to a

lesser extent, in the case of severe adverse reactions to the conventional anti-TB regimen.

Fluoroquinolones are not included at present in the first-line treatment of TB, although that might

change in the future, in order to shorten treatment duration. The newer fluoroquinolones, MXF and

gatifloxacin have been shown to exert better activity and are associated with a lower probability of

emergence of resistance.67

Moxifloxacin (MFX)

The excellent in vitro activity of MXF translates into activity in the human host. Moxifloxacin, its

structure shown on fig. 9 64, joins the small number of highly bactericidal anti-TB drugs and may

contribute to the development of more effective regimens.68The results of a comprehensive preclinical

evaluation of the safety of MFX are consistent with those reported for other fluoroquinolones. Most of

the findings (e.g. arthrotoxicity in juvenile animals and CNS toxicity) that have led to restrictions in

the use of quinolones in general have also been observed with MFX.69

Besides,MFX has a good EBA

against MTB in patients with drug-susceptible TB. Its extended EBA activity from days 2 to 7, a

putative surrogate marker of sterilizing activity, may be slightly higher than for INH.70

Figure 9: Chemical Structure of Moxifloxacin

In one experimental study, the substitution of MFX for INH in the standard regimen revealed the

dramatic increase in potency and appeared to have the greatest potential to shorten the course of TB

therapy to 4 months or less.71 In contrast, substitution of MFX for EMB in the standard regimen did

not have an effect on 2-months sputum culture status but did result in a higher frequency of negative

cultures at earlier time points among patients with smear-positive PTB. Therefore, MFX has

sterilizing activity, but insufficient activity when used in the manner evaluated in this trial (i.e., added

to INH, RIF, and PZA) to support treatment shortening based on the surrogate marker of 2-months

culture conversion.72

Gatifloxacin

Gatifloxacin, its chemical structure shown on Fig. 10 64, has excellent EBA, only slightly less than for

INH, and greater extended EBA.70Gatifloxacinwas evaluated alone and in combination with

ethionamide, PZA, and EMB. Ethionamide appeared to be the most promising single agent for use in




combination with ratifloxacin. Gatifloxacin-ethionamide-PZA and/or EMB would likely be an

effective regimen for treatment of MDR-TB.73

Figure10. Chemical Structure of Gatifloxacin

In the Randomized Clinical Trial that was done by substituting EMB for new drugs in the standard

regimen, the response at the end of treatment was uniformly high in all regimens, with 95% and 98%

of the patients treated with a thrice-weekly 4-month gatifloxacin and MFX regimens, respectively,

becoming culture negative at the end of treatment, compared to 97% in the standard regimen.74

New Targets Identified for the Development of Anti-TB Drugs

It is reassuring that after many years, a TB drug pipeline is now developing. Moreover, several novel

pathways essential for MTB survival are currently being explored, including the protein kinase G and

coronin 1 pathways, which have potential to serve as novel drug targets for treatment of both drug-

sensitive and drug-resistant TB. Whilst pressing on with the development of drugs and optimized

combination and usage of existing drugs at the “outcome” end of the pipeline, concerted effort is

needed to expand further the portfolio of novel drug targets and to identify novel leads.75

The discovery that focuses on commercially available drugs, such as prescribed for the treatment of

Parkinson’s disease, showed the potential to treat MDR and XDR-TB. These drugs, entacapone and

tolcapone, are predicted to bind to the enzyme InhA and directly inhibit substrate binding. The

prediction is validated by in vitro and InhA kinetic assays using tablets of Comtan, whose active

component is entacapone, with MIC for MTB approximately 260µM. Moreover, kinetic assays

indicate that Comtan inhibits InhA activity by 47.0% at an entacapone concentration of approximately

80µM. So, the active component in Comtan represents a promising lead compound for developing a

new class of anti-tubercular therapeutics with excellent safety profiles.76

Peptide-based antibiotics are attractive both to fundamental research and for their potential therapeutic

applications. They are relatively small molecules, their action is fast and lethal to a large spectrum of

pathogens, and they seem to escape many of the drug resistance mechanisms. Compared to classical

antibiotics, peptides portray a highly modular synthetic antimicrobial system. Unlike classical

antibiotics that must penetrate the target cell to act on it, antimicrobial peptides are believed to kill

target cells by destroying their membrane. Theoretically, this mode of action should severely reduce

microbial resistance and represents, therefore, a promising alternative in the treatment of raging MDR

infectious diseases.77

Mycobacterial persistence which refers to the ability of tubercle bacillus to survive in the face of

chemotherapy and/or immunity is a new approach.78 Gene products involved in mycobacterial

persistence, such as isocitratelyase (ICL),an enzyme essential for the metabolism of fatty acids79;

PcaA, required for cording and mycolic acid cyclopropane ring synthesis in the cell wall of both BCG

and MTB80; RelAMtb (ppGpp synthase), critical for the successful establishment of persistent infection

in mice by altering the expression of antigenic and enzymatic factors that may contribute to successful

latent infection 81; and Rv3133c/DosR, is a transcription factor of the two-component response

regulator class and the primary mediator of a hypoxic signal within MTB, used to control a 48-gene

regulon involved in MTB survival under hypoxic conditions82, have been identified and could be good

targets for development of drugs that target persistent bacilli.

In MTB, the energy production pathways are not well characterized. But, the findings that showed as

PZA acts by disrupting membrane potential and depleting energy in MTB lead to focus on energy

pathway as a drug target.83 Energy production or maintenance is important for the viability of

persistent non-growing tubercle bacilli in vivo. The recent discovery of the highly effective TB drug




TMC207 also highlights the importance of energy production pathways for MTB. It is likely that

energy production pathways, such as the electron transport chain, glycolytic pathways and

fermentation pathways, could be good targets for TB drug development.2

Another target is toxin-antitoxin modules. Inappropriate or uncontrolled expression of the toxin or a

decrease in the expression of antitoxin can cause bacterial cell death.84It is interesting to note that the

MTB genome has recently been found to contain at least 38 toxin-antitoxin modules including three

relBE and nine mazEF loci. RelE and MazF are toxins that cleave mRNA in response to nutritional

stress. Evidence now indicates that these loci provide a control mechanism that helps free-living

prokaryotes cope with nutritional stress.85Hence, the toxin-antitoxin modules are attractive targets in

MTB for designing drugs that either induce the production of the toxin or inhibit the expression of the

antitoxin.2

Essential mycobacterial genes can also be good targets for TB drug development. Systematic analysis

of essential genes by transposon mutagenesis and targeted knockout of specific genes are valuable

approaches to identify essential genes because whose disruption leads to non-viability of the bacilli. 3

Around one-sixth of the total number of genes (614 genes) in MTB, were found to be essential for in

vitro growth.86While 194 genes were demonstrated to be essential for in vivoMTB survival in mice. A

surprisingly large fraction of these genes are unique to mycobacteria and closely related species,

indicating that many of the strategies used by this unusual group of organisms are fundamentally

different from other pathogens.87

It has been demonstrated that the ClpP proteins ofMTB, which are essential for growth in vitro using

genetic means but its activators are effective against mycobacteria, are exciting new drug targets for

exploration using genetic and chemical validation approaches. Targeting the Clp series has the added

advantage that both inhibitors andactivators have the potential to kill the cell. Further work to develop

the acyldepsipeptides (ADEP) activator series or to identify new activators orinhibitors could lead to

the development of new drugs in the long term.88

Challenges in the Development of New Drugs

Along with the socioeconomic and host factors that underlie the serious global burden of TB, a

fundamental problem that hinders more effective TB control is the ability of MTB to persist in the host

and to develop drug resistance, often because of poor adherence to lengthy therapy.10 Despite a

resurgence of TB, development of new drugs to treat the disease has stagnated in the face of

numerous scientific and economic obstacles. Showing of the superiority of new agents constitutes the

most convincing clinical evidence of drug efficacy, but in the case of drug-sensitive disease this may

be infeasible given the high efficacy rates of existing regimens, the need for extended follow-up, and

the large number of participants required supporting statistical conclusions.89

Primarily, overall funding for TB research in general, and drug discovery in particular, remains

alarmingly inadequate. TB research is funded in competition with all other areas of biomedicine and

is clearly not receiving funds commensurate with the global dimension of the disease and the

probability that untreatable forms of TB will become increasingly widespread.90 Besides, the TB drug

market is associated with insufficient profit opportunity or investment return to instigate

pharmaceutical industries to develop new drugs.91Secondly, it is the lack of access to information,

pharmaceutical expertise, compounds, and research tools. There would be great value, for example, in

a publicly accessible database that collected thorough information about screenings of compounds and

about analyses that indicate which targets in MTB appear to be “druggable.” Considering the limited

resources for TB drug development, it is critical to avoid repetitive efforts, particularly multiple

independent journeys to a dead-end.88 However, the molecular mechanisms responsible for

mycobacterial dormancy, persistence, and drug resistance are not yet fully understood.92Thirdly, there

are a number of constraints that have companies from investing in new anti-TB drugs. The research is

expensive, slow and difficult and requires specialized facilities for handling MTB. There are few

animal models that closely mimic the human TB disease. Development time of any anti-TB drug will

be long. In fact minimum six month therapy will require with a follow up period of one year or

more.93Lastly, the challenge of TB drug Research and Development is the long timeline of clinical

trials. Phase II studies for TB drugs typically require at least two years, and pivotal trials a minimum




of three years from beginning patient enrollment to finalized study reports. Furthermore, the fact that

people must be treated with a combination of four drugs, rather than with a single drug, means that to

replace the current regimen with a totally new three- or four-drug regimen by testing the substitution

of one drug at a time into the standard regimen will require not a minimum of six years, but at least

four times six years - over two decades - just for the clinical phase of development.94

FUTURE PERSPECTIVES

A promising new era in TB drug development has begun. It is now critical to consolidate recent

progress and ensure that new drugs/regimens for treatment of all forms of TB are suitably introduced

in countries in a way that guarantees access to best treatments for all those in need and avoids

inappropriate use of new drugs.95 Moreover, one can certainly strive to discover new drugs with

improved efficacy and tolerability and with the ability to be used in new combination therapies to

shorten the current, protracted treatment duration. So, it is important to identify essential TB targets

based on the increased knowledge of the pathogen and the physiology of the disease, to develop

smarter screening assays, and to prepare sets of compounds designed to give improved leads for

antibacterial activities.45 However, it requires the wide involvement of all relevant parties (industry,

academia, drug regulatory agencies, and international policy-making agencies) who must collaborate

effectively to deliver optimal future therapies for TB.96

The emergence of multi-drug-resistant strains of MTB makes the discovery of new molecular

scaffolds a priority, and the current situation even necessitates the re-engineering and repositioning of

some old drug families to achieve effective control.97 In this condition, smaller studies may suffice if

large differences in efficacy between experimental and comparator regimens are likely. Use of

preliminary endpoints may be possible, resulting in accelerated drug approval. In a situation of dire

medical need, large potential benefits may outweigh minor risks. But most important, given the

pressing need for new drugs to treat resistant TB, this approach will bring the promise of new drugs to

an area of major public health concern.89

Finally, ways to shorten clinical trials with new TB drugs should be explored. The evaluation of

surrogate biomarkers that predict the likelihood of relapse, such as serial sputum colony counts and

molecular markers, should be incorporated into clinical trials as much as possible. Validated surrogate

markers will reduce the time it takes to assess the efficacy of new agents.91 Besides, it is important

to develop novel drugs that avoid the manifestation of drug resistance in bacterial cells.

Control programs that implemented have also been less effective than expected in reducing the

occurrence of TB transmission, mainly because patients are not diagnosed and cured quickly

enough.98

CONCLUSION

In the past ten years, the development of anti-TB drugs were extremely increasing and expecting to

improve the current treatment protocol to life saving and optimum status. Consequently, the death and

being infectious resulted from TB will stop or exponentially decrease in near future. However, to

reach this level, it needs hand-to-hand work of different sectors that are responsible for the

development of new drugs. In addition, the research area should look for the potential targets that can

bring paradigm shift in the history of treatment of TB.

REFERENCES

[1] World Health Organization (WHO). Global Tuberculosis Report 2012; WHO Press, World

Health Organization: Geneva, Switzerland, 2012.

[2] Zhang Y, Post-Martens K, Denkin S. New drug candidates and therapeutic targets for

tuberculosis therapy. Drug Discovery Today. 2006; 11:21-27.

[3] Pham T, Nguyen T, Nguyen L. Targeting Drug Resistance Mechanisms in Mycobacterium

tuberculosis. J Anc Dis Prev Rem. 2013;1(4):1-2.

[4] World Health Organization (WHO). The use of bedaquiline in the treatment of multidrug-

resistant tuberculosis, Interim Policy Guidance. WHO Press, World Health Organization:

Geneva, Switzerland, 2013.




[5] Anishetty S, Pulimi M, Pennathur G. Potential drug targets in Mycobacterium tuberculosis

through metabolic pathway analysis. ComputBiol Chem.2005;29(5):368-378.

[6] Ahmad S, Mokaddas E. Recent advances in the diagnosis and treatment of multidrug-resistant

tuberculosis. Respiratory Medicine CME. 2010;3:51-56.

[7] World Health Organization (WHO). Guidelines for the programmatic management of drug-

resistant tuberculosis: Emergency Update 2008. WHO Press, World Health Organization:

Geneva, Switzerland 2008.

[8] World Health Organization (WHO). Treatment of Tuberculosis Guidelines. Fourth Edition.

WHO Press, World Health Organization: Geneva, Switzerland, 2010.

[9] Orenstein EW, Basu S, Shah S, et al. Treatment outcomes among patients with multidrug-

resistant tuberculosis: systemic review and meta-analysis. Lancet Infect Dis. 2009; 9(3):153–

161.

[10] American Thoracic Society, CDC, and Infectious Disease Society of America. Treatment of

tuberculosis. MMWR. 2003;52(RR11):1-77.

[11] Conde MB, Silva JRL. New Regimens for Reducing the Duration of Treatment of Drug-

Susceptible Pulmonary Tuberculosis. Drug Dev Res. 2011;72(6):501–508.

[12] Andries K, Verhasselt P, Guillemont J, et al.A diarylquinoline drug active on the ATP synthase

of Mycobacterium tuberculosis. Science. 2005;307:223-227.

[13] Lounis N, Veziris N, Chauffour A, et al. Combinations of R207910 with drugs used to treat

MDR-TB have the potential to shorten treatment duration. Antimicrob Agents

Chemother.2006;50:3543–3547.

[14] Lessem E, McKenna L. An Activist’s Guide to Bedaquiline (Sirturo). Treatment Action Group.

February 2013.

[15] Gaurrand S, Desjardins S, Meyer C, et al. Conformational analysis of R207910, a new drug

candidate for the treatment of tuberculosis, by a combined NMR and molecular modeling

approach.Chem. Biol. Drug Des. 2006;68:77–84.

[16] Mahajan R. Bedaquiline: First FDA-approved tuberculosis drug in 40 years. Int J App Basic Med

Res. 2013;3:1-2.

[17] Matteelli A, Carvalho ACC, Dooley KE, et al.TMC207: the first compound of a new class of

potent anti-tuberculosis drugs. Future Microbiol. 2010;5(6):849–858.

[18] Rustomjee R, Diacon AH, Allen J, et al. Early Bactericidal Activity and Pharmacokinetics of the

Diarylquinoline TMC207 in Treatment of Pulmonary Tuberculosis.Antimicrob. Agents

Chemother. 2008;52(8):2831-2835.

[19] Diacon AH, Pym A, Grobudch M, et al. The diarylquinolone TMC207 for multi-drug-resistant

tuberculosis. N Engl J Med. 2009;360:2397–2405.

[20] Diacon AH, Donald PR, Pym A, et al.Randomized Pilot Trial of Eight Weeks of Bedaquiline

(TMC207) Treatment for Multidrug-Resistant Tuberculosis: Long-Term Outcome, Tolerability,

and Effect on Emergence of Drug Resistance.Antimicrob. Agents Chemother. 2012;56(6):3271-

3276.

[21] Spigelman MK. New Tuberculosis Therapeutics: A Growing Pipeline. The Journal of Infectious

Diseases. 2007;196:S28–S34.

[22] Li X, Manjunatha UH, Goodwin MB, et al. Synthesis and antitubercular activity of 7-(R)- and 7-

(S)-methyl-2-nitro-6-(S)-(4-(trifluoromethoxy)benzyloxy)-6,7-dihydro-5H-imidazo [2,1-b][1,3]

oxazines, analogues of PA-824. Bioorg Med ChemLett. 2008;18:2256-2262.

[23] Manjunatha UH, Boshoff H, Dowd CS, et al.Identification of a nitroimidazo-oxazine-specific

protein involved in PA-824 resistance in Mycobacterium tuberculosis. PNAS. 2006;103(2):431-

436.

[24] Tyagi S, Nuermberger E, Yoshimatsu T, et al.Bactericidal Activity of the Nitroimidazopyran PA-

824 in a Murine Model of Tuberculosis.Antimicrob. Agents Chemother. 2005;49(6):2289–2293.

[25] Diacon AH, Dawson R, Hanekom M, et al. Early Bactericidal Activity and Pharmacokinetics of

PA-824 in Smear-Positive Tuberculosis Patients.Antimicrob. Agents Chemother.

2010;54(8):3402–3407.

[26] Ginsberg AM, Laurenzi MW, Rouse DJ, et al. Safety, Tolerability, and Pharmacokinetics of PA-

824 in Healthy Subjects.Antimicrob. Agents Chemother. 2009;53(9):3720–3725.

http://www.ncbi.nlm.nih.gov/pubmed/16213791

http://www.ncbi.nlm.nih.gov/pubmed?term=Diacon%20AH%5BAuthor%5D&cauthor=true&cauthor_uid=22391540

http://www.ncbi.nlm.nih.gov/pubmed?term=Donald%20PR%5BAuthor%5D&cauthor=true&cauthor_uid=22391540

http://www.ncbi.nlm.nih.gov/pubmed?term=Pym%20A%5BAuthor%5D&cauthor=true&cauthor_uid=22391540




[27] Manjunatha U, Boshoff HIM, Barry CE.The mechanism of action of PA-824. Communicative &

Integrative Biology. 2009;2(3):215-218.

[28] Tasneen R, Li SY, Peloquin CA, et al.Sterilizing Activity of Novel TMC207- and PA-824-

Containing Regimens in a Murine Model of Tuberculosis.Antimicrob. Agents

Chemother.2011;55(12):5485–5492.

[29] Nuermberger E, Rosenthal I, Tyagi S, et al. Combination chemotherapy with the

nitroimidazopyran PA-824 and first-line drugs in a murine model of tuberculosis. Antimicrob

Agents Chemother. 2006;50:2621-2625.

[30] Singh KP, Brown M, Murphy ME, et al. Moxifloxacin for tuberculosis. Lancet Infect Dis.

2012;12:176-178.

[31] Matsumoto M, Hshizume H, Tomishige T, et al. In vitro and in vivo efficacy of novel

antituberculous candidate OPC-67683 [abstract F-1462]. In: Program and abstracts of the 45th

Interscience Conference on Antimicrobial Agents and Chemotherapy (Washington, DC).

Washington, DC: American Society for Microbiology. 2005;204.

[32] Shakya N, Garg G, Agrawal B, et al. Chemotherapeutic Interventions against Tuberculosis.

Pharmaceuticals. 2012;5:690-718.

[33] Matsumoto M, Hashizume H, Tomishige T, et al. OPC-67683, a Nitro-Dihydro-Imidazooxazole

Derivative with Promising Action against Tuberculosis In Vitro and In Mice. PLoS Medicine.

2006;3(11):2131-2143.

[34] Tsubouchi H, Sasaki H, Haraguchi Y, et al. Synthesis and antituberculous activity of a novel

series of optically active 6-nitro-2,3-dihydroimidazol[2,1-b]oxazoles [abstract F-1473]. In:

Program and abstracts of the 45th Interscience Conference on Antimicrobial Agents and

Chemotherapy (Washington, DC). Washington, DC: American Society for Microbiology.

2005;207.

[35] Saliu OY, Crismale C, Schwander SK, et al. Bactericidal activity of OPC-67683 against drug-

tolerant Mycobacterium tuberculosis. J AntimicrobChemother. 2007;60:994-998.

[36] Jia L, Tomaszewski JE, Hanrahan C, et al. Pharmacodynamics and pharmacokinetics of SQ109,

a new diamine-based antitubercular drug. British Journal of Pharmacology. 2005;144:80–87.

[37] Protopopova M, Hanrahan C, Nikonenko B, et al.Identification of a new antitubercular drug

candidate, SQ109, from a combinatorial library of 1,2-ethylenediamines. J

AntimicrobChemother. 2005;56:968–974.

[38] Chen P, Gearhart J, Protopopova M, et al. Synergistic interactions of SQ109, a new ethylene

diamine, with front-line antituberculardrugsin vitro. J AntimicrobChemother. 2006;58:332–337.

[39] Nikonenko BV, Protopopova M, Samala R, et al. Drug Therapy of Experimental Tuberculosis

(TB): Improved Outcome by Combining SQ109, a New Diamine Antibiotic, with Existing TB

Drugs. Antimicrob. Agents Chemother. 2007;51(4):1563–1565.

[40] Reddy VM, Einck L, Andries K, et al. In Vitro Interactions between New Antitubercular Drug

Candidates SQ109 and TMC207. Antimicrob. Agents Chemother. 2010;54(7):2840–2846.

[41] Reddy VM, Dubuisson T, Einck L, et al. SQ109 and PNU-100480 interact to kill Mycobacterium

tuberculosis in vitro. J AntimicrobChemother. 2012;67:1163–1166.

[42] Lin AH, Murray RW, Vidmar TJ, et al. The oxazolidinoneeperezolid binds to the 50S ribosomal

subunit and competes with binding of chloramphenicol and lincomycin. Antimicrob. Agents

Chemother. 1997;41:2127–2131.

[43] Cynamon MH, Klemens SP, Sharpe CA, et al. Activities of Several Novel Oxazolidinones

against Mycobacterium tuberculosis in a Murine Model. Antimicrob. Agents Chemother.

1999;43(5):1189-1191.

[44] Reele S, Xiao AJ, Das S, Balasubramanian V, et al. Flexible Single Day Ascending Dose

(SDAD) Studies with AZD5847 Demonstrate Oral Dosing Regimens with Potential Utility for

the Treatment of Tuberculosis (TB). Infection Innovative Medicine, AstraZeneca R&D, Boston,

35 Gatehouse Drive. Waltham, MA 02451, USA.

[45] Kaneko T, Cooper C, Mdluli K. Challenges and opportunities in developing novel drugs for TB.

Future Med. Chem. 2011;3(11):1373–1400.




[46] Alcala L, Ruiz-Serrano MJ, Turegano CP, et al. In Vitro Activities of Linezolid against Clinical

Isolates of Mycobacterium tuberculosis That Are Susceptible or Resistant to First-Line

Antituberculous Drugs. Antimicrob. Agents Chemother. 2003;47(1):416-417.

[47] Dietze R, Hadad DJ, McGee B, et al. Early and Extended Early Bactericidal Activity of

Linezolid in Pulmonary Tuberculosis. Am J RespirCrit Care Med. 2008;178:1180–1185.

[48] Fortun J, Martin-Davila P, Navas E, et al.Linezolid for the treatment of multidrug-resistant

tuberculosis. J AntimicrobChemother. 2005;56:180–185.

[49] Udwadia ZF, Sen T, Moharil G. Assessment of linezolid efficacy and safety in MDR and XDR-

TB: an Indian perspective. EurRespir J. 2010;35(4):936-939

[50] Cox H, Ford N. Linezolid for the treatment of complicated drug-resistant tuberculosis: a

systematic review and meta-analysis. Int J Tuberc Lung Dis. 2012;16(4):447-454.

[51] Schecter GF, Scott C, True L, et al. Linezolid in the Treatment of Multidrug-Resistant

Tuberculosis. Clinical Infectious Diseases. 2010;50:49–55.

[52] Lee M, Lee J, Carroll MW, et al. Linezolid for Treatment of Chronic Extensively Drug-Resistant

Tuberculosis. N Engl J Med. 2012;367:1508-1518.

[53] Singla R, Caminero JA, Jaiswal A, et al. Linezolid: an effective, safe and cheap drug for patients

failing multidrug-resistant tuberculosis treatment in India. EurRespir J. 2012;39:956–962.

[54] Barbachyn M, Wishka D, Lall M, et al. Promising Antituberculosis Activity of the

Oxazolidinone PNU-100480 relative to that of Linezolid in a Murine Model. Antimicrob Agents Chemother. 2009;53(4):1314-1319.

[55] Williams KN, Brickner SJ, Stover CK, et al. Addition of PNU-100480 to First-Line Drugs

Shortens the Time Needed to Cure Murine Tuberculosis. Am J RespirCrit Care Med.

2009;180:371–376.

[56] Wallis RS, Jakubiec WM, Kumar V, et al. Pharmacokinetics and Whole-Blood Bactericidal

Activity against Mycobacterium tuberculosis of Single Doses of PNU-100480 in Healthy

Volunteers. The Journal of Infectious Diseases. 2010;202(5):745–751.

[57] Wallis RS, JakubiecW, KumarV, et al.Biomarker-Assisted Dose Selection for Safety and Efficacy

in Early Development of PNU-100480 for Tuberculosis. Antimicrob Agents Chemother. 2011;55(2): 567–574.

[58] Wallis RS, Jakubiec W, Mitton-Fry M, et al. Rapid Evaluation in Whole Blood Culture of

Regimens for XDR-TB Containing PNU-100480 (Sutezolid), TMC207, PA-824, SQ109, and

Pyrazinamide. PLoS ONE. 2012;7(1):1-7.

[59] Alffenaar JWC, van der Laan T, Simons S, et al. Susceptibility of Clinical Mycobacterium

tuberculosis Isolates to a Potentially Less Toxic Derivate of Linezolid, PNU-100480. Antimicrob Agents Chemother. 2011;55(3):1287–1289.

[60] Swindells S. New drugs to treat tuberculosis. F1000 Medicine Reports. 2012;4(12):1-7.

[61] Gravestock MB, Acton DG, Betts MJ, et al. New classes of antibacterial oxazolidinones with C-

5, methylene O-linked heterocyclic side chains. Bioorg. Med. Chem. Lett. 2003;13:4179–4186.

[62] Gerson SL, Kaplan SL, Bruss JB, et al. Hematologic effects of linezolid: summary of clinical

experience. Antimicrob. Agents Chemother. 2002;46(8):2723–2726.

[63] Deidda D, Lampis G, Fioravanti R. Bactericidal Activities of the Pyrrole Derivative BM212

against Multidrug-Resistant and Intramacrophagic Mycobacterium tuberculosis. Antimicrob.

Agents Chemother. 1998;42(11):3035-3037.

[64] Brennan PJ, Young DB, Robertson BD. Handbook of Anti-Tuberculosis Agents. Tuberculosis.

2008;88(2):126.

[65] Arora S. Eradication of Mycobacterium tuberculosis infection in 2 months with LL-3858: a

preclinical study. Int J Tuberc Lung Dis. 2004;8(11 Suppl 1):S29.

[66] Iseman MD. Tuberculosis therapy: past, present and future. EurRespir J. 2002;36:S87-94.

[67] Manika K, Kioumis I. The role of fluoroquinolones in the treatment of Tuberculosis. Pneumon.

2008;21(4):395–401.

[68] Gosling RD, Uiso LO, Sam NE, et al. The Bactericidal Activity of Moxifloxacin in Patients with

Pulmonary Tuberculosis. Am J RespirCrit Care Med. 2003;168:1342–1345.

http://www.ncbi.nlm.nih.gov/pubmed/?term=Wallis%20RS%5Bauth%5D

http://www.ncbi.nlm.nih.gov/pubmed/?term=Jakubiec%20W%5Bauth%5D

http://www.ncbi.nlm.nih.gov/pubmed/?term=Kumar%20V%5Bauth%5D




[69] Von Keutz E, Schluter G. Preclinical Safety Evaluation of Moxifloxacin, a Novel

Fluoroquinolone. J AntimicrobChemother. 1999;43:91-100.

[70] Johnson JL, Hadad DJ, Boom WH, et al. Early and extended early bactericidal activity of

levofloxacin, gatifloxacin and moxifloxacin in pulmonary tuberculosis. Int J Tuberc Lung Dis.

2006;10(6):605–612.

[71] Nuermberger EL, Yoshimatsu T, Tyagi S, et al.Moxifloxacin-containing Regimen Greatly

Reduces Time to Culture Conversion in Murine Tuberculosis. Am J RespirCrit Care Med.

2004;169:421–426.

[72] Burman WJ, Goldberg S, Johnson JL. Moxifloxacin versus Ethambutol in the First 2 Months of

Treatment for Pulmonary Tuberculosis. Am J RespirCrit Care Med. 2006;174: 331–338.

[73] Alvirez-Freites EJ, Carter JL, Cynamon MH. In Vitro and In Vivo Activities of Gatifloxacin

against Mycobacterium tuberculosis. Antimicrob. Agents Chemother. 2002;46(4):1022-1025.

[74] Jawahar MS, Banurekha VV, Paramasivan CN, et al.Randomized Clinical Trial of ThriceWeekly

4-Month Moxifloxacin or Gatifloxacin Containing Regimens in the Treatment of New Sputum

Positive Pulmonary Tuberculosis Patients. PLoS ONE. 2013;8(7):e67030.

[75] Janssen S, Jayachandran R, Khathi L, et al. Exploring prospects of novel drugs for tuberculosis.

Drug Design, Development and Therapy. 2012; 6: 217-224.

[76] Kinnings SL, Liu N, Buchmeier N, et al. Drug Discovery Using Chemical Systems Biology:

Repositioning the Safe Medicine Comtan to Treat MultiDrug and Extensively Drug Resistant

Tuberculosis. PLoSComput Biol. 2009;5(7):1-10.

[77] Mor A. Peptide-Based Antibiotics: A Potential Answer to Raging Antimicrobial Resistance.

Drug Dev. Res. 2000;50:440–447.

[78] McDermott W. Microbial persistence. YaleJ. Biol. Med. 1958;30:257–291.

[79] McKinney JD, HönerzuBentrup K, Muñoz-Elías EJ,et al. Persistence of Mycobacterium

tuberculosis in macrophages and mice requires the glyoxylate shunt enzyme isocitratelyase.

Nature. 2000;406:735–738.

[80] Glickman MS, Cox JS, Jacobs WR. A novel mycolic acid cyclopropanesynthetase is required for

cording, persistence, and virulence of Mycobacterium tuberculosis. Mol. Cell 2000;5:717–727.

[81] Dahl JL, Kraus CN, Boshoff HIM, et al. The role of RelMtb-mediated adaptation to stationary

phase in long-term persistence of Mycobacterium tuberculosis in mice. Proc. Natl. Acad. Sci.

2003;100(17):10026–10031.

[82] Park HD, Guinn KM, Harrell MI, et al. Rv3133c/dosR is a transcription factor that mediates the

hypoxic response of Mycobacterium tuberculosis. Mol. Microbiol. 2003;48(3):833–843.

[83] Zhang Y, Wade MM, Scorpio A, et al. Mode of action of pyrazinamide: disruption of

Mycobacterium tuberculosis membrane transport and energetics by pyrazinoic acid. J.

Antimicrob. Chemother. 2003;52:790–795.

[84] Engelberg-Kulka H, Sat B, Reches M, et al. Bacterial programmed cell death systems as targets

for antibiotics. Trends Microbiol. 2004;12(2):66–71.

[85] Gerdes K, Christensen SK, Løbner-Olesen A. Prokaryotic toxin-antitoxin stress response loci.

Nat. Rev. Microbiol. 2005;3(5):371–382.

[86] Sassetti CM, Boyd DH, Rubin EJ. Genes required for mycobacterial growth defined by high

density mutagenesis. Mol. Microbiol. 2003;48(1):77–84.

[87] Sassetti CM, Rubin EJ. Genetic requirements for mycobacterial survival during infection. Proc.

Natl. Acad. Sci. U. S. A. 2003;100:12989–12994.

[88] Ollinger J, O'Malley T, Kesicki EA, etal. Validation of the essential ClpP protease in

Mycobacterium tuberculosis as a novel drug target. J Bacteriol. 2012;194(3):663-668.

[89] Sacks LV, Behrman RE. Developing new drugs for the treatment of drug resistant tuberculosis: a

regulatory perspective. Tuberculosis. 2008;88(1):S93-S100.

[90] Casenghi M, Cole ST, Nathan CF. New Approaches to Filling the Gap in Tuberculosis Drug

Discovery. PLoS Med. 2007; 4(11):1722-1725.

[91] Boogaard J, Kibiki GS, Kisanga ER, et al. New Drugs against Tuberculosis: Problems, Progress,

and Evaluation of Agents in Clinical Development. Antimicrob. Agents Chemother.

2009;53(3):849–862.

http://www.ncbi.nlm.nih.gov/pubmed?term=H%C3%B6ner%20zu%20Bentrup%20K%5BAuthor%5D&cauthor=true&cauthor_uid=10963599

http://www.ncbi.nlm.nih.gov/pubmed?term=Mu%C3%B1oz-El%C3%ADas%20EJ%5BAuthor%5D&cauthor=true&cauthor_uid=10963599

http://www.ncbi.nlm.nih.gov/pubmed?term=Christensen%20SK%5BAuthor%5D&cauthor=true&cauthor_uid=15864262

http://www.ncbi.nlm.nih.gov/pubmed?term=L%C3%B8bner-Olesen%20A%5BAuthor%5D&cauthor=true&cauthor_uid=15864262




[92] Zhang Y. Persistent and dormant tubercle bacilli and latent tuberculosis. Front. Biosci.

2004;9:1136-1156.

[93] Tomioka H, Namba K. Development of antituberculous drugs: current status and future

prospects. Kekkaku. 2006;81(12):753–774.

[94] Ginsberg AM, Spigelman M. Challenges in tuberculosis drug research and development. Nature

Medicine. 2007;13(3):290-294.

[95] Lienhardt C, Raviglione M, Spigelman M, et al. New Drugs for the Treatment of Tuberculosis:

Needs, Challenges, Promise, and Prospects for the Future. J Infect Dis. 2012;205(suppl 2):S241-S249.

[96] Lienhardt C, Vernon A, Raviglione MC. New drugs and new regimens for the treatment of

tuberculosis: review of the drug development pipeline and implications for national programmes.

Current Opinion in Pulmonary Medicine. 2010;16:186–193.

[97] Yadav P, Deolekar P, Kanase V, et al. Overview of New Anti-TB Drugs. IJPSR. 2012;3(8):2472-

2481.

[98] Shehzad A, Rehman G, Ul-Islam M, et al. Challenges in the development of drugs for the

treatment of tuberculosis. Braz J Infect Dis. 2013;17(1):74–81.

AUTHORS’ BIOGRAPHY

Alemayehu Toma Mena

As Lecturer of Pharmacology in Hawassa University, College of Medicine and

Health Science since May, 2011

Current Research Activities:

Antiglycation activities of extract of Moringa stenopetala leaves in fructose

induced protein glycation

Antidiabetic activities of aqueous ethanol and n-butanol fraction of Moringa

stenopetala leaves in streptozotocin-induced diabetic rats Under submission

Antiinflammatory activity of Moringa stenopetala leaves in carreggen in induced mice.

Evaluation of treatment outcome in antiretroviral therapy in Hawassa Referral Hospital.

recent advances in the development of anti-tuberculosis drugs … · recent advances in the...

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