Differential kinetics of drug resistance in human leukaemic cells measured by SCGE/CLSM

Abstract

Background: New analogues of DNA directed chemotherapy moieties are available for comparative efficacy testing in human neoplastic disease. In addition to MTT testing direct assessment of DNA excision repair activity after direct exposure of marrow cells may provide information on relative DNA effects in vitro.

Aims: To assess the ability of SCGE/high resolution CLSM to detect differences in drug resistance between human neoplastic cell lines in the DNA excision repair response to chemotherapy.

Methods: Eight human leukaemia samples (4 childhood, 4 adult) were exposed to 1 hour of single concentrations of daunorubicin, DaunoXome (courtesy NeXstar Pharmaceuticals Inc, USA), cyclophosphamide and 4-hydroperoxycyclophosphamide (4-HC, courtesy Dr. M. Colvin, Duke University, USA), followed by SCGE/high resolution CLSM with quantitation of total excised DNA. Differences between cases/drug moieties/exposures were analysed.

Results: Although generally equal effect dose levels for DaunoXome were lower than for standard daunorubicin, patients/individual neoplastic cells differed considerably in optimal dose levels. Conventional cyclophosphamide in comparison to 4-HC showed inconsistent results indicating considerable differences in the level of drug resistance to the conventional product.

Conclusions: Direct testing for drug resistance patterns in DNA directed drug moieties by SCGE/CLSM reveals individual variability of human malignant cell lines warranting comparison with results of MTT testing and in-vivo patient response.