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Translational research with small animal IGRT

Andrew Hope, MD

Staff Radiation OncologistRadiation Medicine ProgramPrincess Margaret Hospital

Assistant ProfessorDepartment of Radiation Oncology

University of Toronto

“Good” models for translational research

• Should assess both tumor control and normal tissue effects– Relevant tumor model

• Orthotopic tumor• Carcinogenesis

– Normal tissue endpoints in conjunction with tumor

• Longitudinal studies with non-invasive endpoints

• Physiologic measures• Imaging

µµµµCT µµµµSPECT µµµµPET MR – 7T

Pre-clinical imaging modalities

Gruene et al., Gamma Medica, Nature Medicine

µµµµUS µµµµOptical

Pre-clinical imaging modalities

Images courtesy of Visualsonics, Xenogen

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Biologic variation is a significant factor in the clinic

• Inherent radiosensitivityand/or response to treatment may be as important as the dose itself

• Small animal irradiation can minimize biologic variation– inbred strains

• Evaluation of radiotherapy, chemotherapy, and biologic agents without confounding genetic heterogenity

Yuan et al., JCO, 2009

A challenging problem

• Glioblastoma– Very poor long-term

prognosis – Radiotherapy alone

insufficient– Some improvements with

addition of temozolomide(~10% OS @ 5y)

• New treatments required– Novel targets continuously

being explored– How to test to see if they

improve outcomes?

Stupp, R. et al. N. Engl. J. Med 352, 987-996(2005).

A potential target

• Many brain tumors gliomas express CXCR4– G-protein coupled receptor

that drives cAMP levels

• Inhibition of CXCR4 with targeted agents slows tumor growth– Multiple cell lines

• Possible target for further clinical exploration?

Rubin, J.B. et al. Proc. Natl. Acad. Sci. U.S.A 100, 13513-13518(2003).

An exploitable mechanism

• Tumors drive cAMP down via CXCL12/CXCR4 to sustain growth

• CXCR4 suppression elevates cAMP– Elevated cAMP suppresses

tumor growth

• Rolipram (generic drug) elevated cAMP as well as more expensive ‘targeted’agent

Yang, L. et al. Cancer Res 67, 651-658(2007).

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An in vivo model

• Intracranially implanted bioluminescent tumors– U87-luc/NCR nude

• Growth can be tracked longitudinally with non-invasive imaging

• Tumor growth is slowed, but not halted

• What’s the next step?

Yang, L. et al. Cancer Res 67, 651-658(2007).

A rationale for pre-clinical IGRT

• High RT doses are needed to effectively treat brain tumors

• Concurrent chemotherapy with temozolomide is the current standard of care

• High RT doses in previous mouse model attempts was poorly tolerated– Adjacent critical structures! (Pharynx, esophagus, eye)– Concurrent chemotherapy

microRTmicroRTP

Kiehl, E.L. et al. Med Phys 35, 4735-4743(2008).

Experimental schema

• RT – 30 Gy / 6 (pragmatic, ~66 Gy equiv)• Temozolomide (21 mg/kg/d x 5d per month)• Rolipram (5mg / kg continuously)

RT: 6x5Gy MWFx2

TMZ TMZTMZ TMZ

Rolipram

Imaging Imaging Imaging Imaging Imaging Imaging

Goldhoff, P. et al. Clin Cancer Res 14, 7717-7725(2008).

An important observation in vivo

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A translatable result?

Goldhoff, P. et al. Clin Cancer Res 14, 7717-7725(2008).

Bench to mouse… to clinic?

• Translational path– From basic science observation– Clinical relevant (staining patient samples)– Shown to be effective alone in vivo– When added to ‘standard’ therapy in vivo cured

tumors

• Next stop…. the clinic?– Novel agent in trials of pediatric patients with

unresectable (and universally fatal) brain stem gliomas

A related clinical problem

• Radiation necrosis– Imaging methods currently don’t clearly differentiate from tumor– TMZ addition appears to make this effect more common

• Up to 10% rate

– Biopsy is usually required to prevent futile re-operation

Peca, C. et al. Clin Neurol Neurosurg 111, 331-334(2009).

An in vivo normal tissue model

• Using a micro-IGRT device, sub-totally irradiate murine brain– 60 Gy / 10 fractions

• Monitor with small animal MR

Jost, S.C. et al. Intl J Rad Onc Bio Phys In press,

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Jost, S.C. et al. Intl J Rad Onc Bio Phys In press,

Contrast-enhanced, T1-weighted, gradient-echo images

T2-weighted spin-echo images

2 months 4 months 6 months

Histology confirms necrosis

Jost, S.C. et al. Intl J Rad Onc Bio Phys In press,

Mouse Human

Tools for translation research• Orthotopic tumor and normal tissue models

– Biologic (targeted) agents– Chemotherapy– Timing– Combinations

• Modeling outcomes– Modulate dose to adjust TCP and NTCP – Model uncomplicated control

• Imaging questions– Novel imaging methods and modalities (PET tracers,

MR sequences, etc) • Imaging biomarkers to distinguish tumor from necrosis

• Therapy questions– Hypoxia targeting?– Sub-volume boosts to ‘resistant’ areas

Garbow et al., Clin Can Res 2008

Carcinogenesis models

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Respiratory correlated small animal CBCT and 4D IGRT

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Moseley D., Lindsay, P. 2009

Endpoints: Pre-clinical and Clinical

• Clinical– Symptoms– Histology – Laboratory– Physiology– Imaging

• Anatomic

• Functional

– Tumor endpoints

• Pre-clinical

– Histology– Laboratory– Physiology– Imaging

• Anatomic

• Functional

– Tumor endpoints

Site3-WBP1:Flow WB FDP:Time

4.323.4562.5921.7280.8640

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Conclusions• Potential for exploration with small

animal IGRT is immense– Internal normal control tissue for

experiments

• Many issues to consider for each potential application

– Biology• Species/strain• Tumor model• Endpoints

– Radiotherapy• Fractionation• Dose distribution• Motion• Validation

– Drugs• Timing• Sequencing

Acknowledgements:Washington University in St. Louis

• Daniel Low• Strahinja Stojadinovic• Enrique Izaguirre• Simon Powell• Joseph Deasy• Issam El Naqa• Jeffrey Bradley• Sasa Mutic• James Alaly• Divya Khullar• Aditya Aapte• Kate Malinowski• Erich Kiehl• And many more…

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Acknowledgements:Princess Margaret Hospital

• Patricia Lindsay• David Jaffray• Dick Hill• Amudha Venugopal• Steve Ansell• Salomeh Jelveh• Doug Moseley• James Chow• Graham Wilson• Precision X-ray, Inc.• (many more)