validation of nanodot array luminometric immunoassay: an assay for the simultaneous measurement of...
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Validation of nanodot array luminometric immunoassay:
An assay for the simultaneous measurement
of tumour markers
Laura WainwrightQueen Alexandra Hospital, Portsmouth
Potential uses
•Screening of general/at risk populations•Differential diagnosis in patients displaying symptoms•Clinical staging of cancer•Estimation of tumour volume•Prognostic indicator of disease progression•Detecting recurrence of cancer•Monitoring response to therapy
Tumour markers
CEA Colorectal cancer; post-operative surveillance and during chemotherapy
Breast cancer; detection of metastasis and during chemotherapy in advanced disease
CA 15-3 Breast cancer; detection of recurrence and during chemotherapy of advanced disease
CA 125 Ovarian cancer; differential diagnosis of pelvic masses, post- operative surveillance and during chemotherapy
CA 19-9 Pancreatic cancer; monitoring chemotherapy and detecting recurrence
-hCG Germ cell tumours and gestational trophoblastic disease; diagnosis, staging, monitoring treatment and prognosis
Multiple markers
•Use several markers to increase specificity and sensitivity of detection/distinguishing malignancy from non-malignancy•hCG, LDH and AFP should be used to monitor NSGCT•EGTM recommends measurement of CA 15-3 and CEA in breast cancer follow-up•Literature surrounding breast and ovarian cancer is mixed
Multiplex Immunoassay
•Theory: uses less reagent, faster, needs less sample•Dots of immobilised Ab on a planar surface = mini-ELISA•Arrays of capture Ab on 96-well plates/glass slides•Literature examples: cytokines and tumour markers.•CVs up to 40 %: imprecision generally a problem
NALIANanodot Array Luminometric
Immunoassay
Vacuum Manifold
well
capture Ab
Agdetection Abbiotin
SA-HRP
Aims
•Validate the markers currently on the array (CEA, CA 125, CA 15-3, CA 19-9)•Optimise and validate -hCG onto the array•Compare with current routinely used assays (DxI, Kryptor)•Look at how many of these markers are raised in breast and ovarian cancer
•Set up -hCG assay as a standard ELISA•Transfer it to NALIA•Run all 5 assays together on NALIA -exp with blocking, exposure time and background subtraction -changes to existing assay protocol
•Run samples, standard curve and 2 levels of control in triplicate•100 samples per marker for method comparison
First…
Standard curves
•Intra- and inter-plate CVs: 44.5-114.1 %
LOD
CEA (ng/mL) 3.9
CA 125 (U/mL) 73.7
CA 15-3 (U/mL) 235.9
CA 19-9 (U/mL) 2621.8
Free -hCG (ng/mL)
116.5
% Recovery
CEA 121-208
CA 125 8-67
CA 15-3 312-4901
CA 19-9 -868-3746
Free -hCG 73-977
•Cross-reactivity: Difficult to interpret due to high CVs and LODs
•LOD and recovery:
Scatter Plots + Spearman Rank Correlation
0
7000
14000
21000
28000
35000
0 7000 14000 21000 28000 35000
NALIA (U/mL)
DxI
(U/m
L)
CA125
0.510
0
700
1400
2100
2800
3500
0 700 1400 2100 2800 3500
NALIA (U/mL)
DxI
(U/m
L)
CA 15-3
0.499
0
300
600
900
1200
0 500 1000
NALIA (ng/mL)
DxI
(ng/
mL)
CEA
0.549
0
2000
4000
6000
0 2000 4000 6000
NALIA (U/mL)
DxI
(U
/mL
)
CA 19-9
-0.139
0
50
100
150
200
250
300
0 100 200 300
NALIA (ng/mL)
Kry
ptor
(ng/
mL)
Free -hCG
0.172
•Signed rank sum test: NALIA has a +ve bias•Bland and Altman plots show the same
Dotting CVs•Dot plates with biotinylated BSA•Calculate inter-well and inter-plate CVs from the raw data to determine how spot density varies•Within well: 19.1 %•Within plate: 24.8 %•Occurs randomly over the plate
well
BSAbiotin
SA-HRP
So…•Not ready for routine use•CEA, then CA 125 were the best of the five
Drawbacks of NALIA
•Main problem: very high assay CVs - dotting inconsistencies - buffer flow variations over the plate when in manifold - differing viscosities of serum samples - uneven well-emptying during incubations - manual process for conversion of image data to numerical format•Very low S/N ratio•Data acquisition process not practical for routine use•Very time consuming and labour-intensive
Future
•Much additional work needs to be performed
- sort out previously mentioned problems- reagent stability- effect of lot number change
•Need more research into the use of multiple markers•Requesting tests just because they are there will not improve patient care•Temptation to use array-based assays as a cancer “screen”
Acknowledgements
Guy GabrielIan Cree
Helen SmithTORC lab members
Bernie Higgins