Preliminary cytogenetic characterization of an AZT-resistant subclone, clone 5, of the human colon tumor cell line, HCT-15

Abstract

Stage II human trials have indicated that the combination of 3′-azido-3′-deoxythymidine (AZT) with 5-fluorouracil and leucovorin has improved efficacy in the adjuvant chemotherapy of colorectal cancer. The development of resistance to AZT has been well documented in viral metabolism, but has not been fully described in human cells. This renders the drug clinically unpredictable, limiting its chemotherapeutic utility. In order to better study the mechanism of AZT-resistance, we have developed an AZT-resistant colon cancer cell line in culture to serve as a model system.The human colon adenocarcinoma cell line, HCT-15 (American Type Culture Collection #CCL225), has been previously characterized by conventional cytogenetic studies and by fluorescent in situ hybridization (FISH). We have measured the concentration of AZT necessary to inhibit growth by 50% over 5 days (IC50) to be approximately 30 μM. AZT-resistant cell lines were derived by serial passage of HCT-15 cells in increasing concentrations of AZT until stable growth was achieved in 1000 μM AZT. The surviving cell colonies were then subcloned in soft agar. One such cell line, clone 5, was found to have eighty-fold increased resistance to AZT, with an IC50 of approximately 2500 μM AZT. We now report a preliminary characterization of the clone 5 cell line in comparison to its parent HCT-15 cell line, using conventional G-banding techniques.