We have already reported the construction and evaluation of a self-bioluminescent reporter strain of E. coli with high sensititivity to the nucleoside analogue cytosine arabinoside (Ara-C) the mainstay of treatment in patients with Acute Myeloid Leukaemia (

Blood
,
106
(11), Abstr. 2473;
695a
). This rapid assay, which uses a bioluminescent biosensor to measure intracellular levels of Ara-C and its active metabolite Ara-CTP, has been utilised in leukaemic cell lines KG1a (FAB type M0) which is sensitive to Ara-C and THP-1 (FAB type M5) which is partially insensitive to Ara-C due to over expression of cytidine deaminase (cdd). It has also been used in primary cultures of AML cells from six patients with M0 (n=1), M2 (n=2), M3 (n=1) and M4 (n=2). Intracellular concentrations of Ara-C as low as 0.05 μM can be detected by an increase in light output from the bacterial biosensor. The technology is suitable for the quantitation of response to clinical Ara-C doses (between 25–100μM) in less than 8 hours. Results from the KG1a cell line with known sensitivity to Ara-C showed correlation between the rapid assay and a 3 day cytotoxicity test of Ara-C sensitivity. Preliminary tests with the six clinical marrow samples showed 100% concordance with clinical outcome within eight hours of commencing the assay (vide infra: Table 1). In newly diagnosed AML patients, only 70% are sensitive to Ara-C therapy. Interestingly, in our hands, the M3 patient was Ara-C insensitive despite the fact that, most commonly, M3 patients do not express p-glycoprotein and therefore do not require Ara-C. Our small cohort of patients were disproportionately insensitive to Ara-C and therefore had a poor outcome overall. This assay system is potentially suitable for prescreening AML samples prior to commencement of Ara-C containing chemotherapy regimens. It may also give information on relative Ara-C sensitivity thus permitting dose adjustment and prevention of unnecessary toxicity to other organs. The assay could be repeated at relapse to document clonal evolution and decide whether Ara-C can be used to achieve a second remission. Work is currently underway with an industrial partner to look at commercialisation of this assay.

TABLE 1:

Correlation between light output and clinical response in six patients with primary AML

PatientDiagnosisClinical OutcomeDifferential Light Output: cytotoxicity testBioluminescent Assay: Ara-C sensitivity
1 M0 No response 5% no 
2 M2 No Response 84% no 
3 M2 No Response 79% no 
4 M3 Remission Death 91% no 
5 M4 Complete Response 99% yes 
6 M4 No Response 62% no 
PatientDiagnosisClinical OutcomeDifferential Light Output: cytotoxicity testBioluminescent Assay: Ara-C sensitivity
1 M0 No response 5% no 
2 M2 No Response 84% no 
3 M2 No Response 79% no 
4 M3 Remission Death 91% no 
5 M4 Complete Response 99% yes 
6 M4 No Response 62% no 
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Topics:
bioluminescence, cytarabine, leukemic cells, metabolism, cytotoxicity, disease remission, arabinofuranosylcytosine triphosphate, chemotherapy regimen, complete remission, cytidine deaminase

Author notes

Disclosure: No relevant conflicts of interest to declare.

2007, The American Society of Hematology
2007
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