n(6)-((dimethylamino)methylene)mitomycin-c and Colonic-Neoplasms

Prior studies have suggested the multifactorial nature of mitomycin C (MMC) resistance. However, the relative importance of the different resistance mechanisms is unknown.. A panel of colon cancer cell lines with levels of MMC resistance from 2- to 15-fold compared to the parent line HT-29 was produced by repeated MMC exposure. Cell survival was measured using clonogenic assay. Glutathione and related enzymes and DT-diaphorase were measured using biochemical assays. P-glycoprotein expression was measured using flow cytometry. Topoisomerase II activity was measured using the pBR322 DNA relaxation assay.. Multiple drug resistance mechanisms were altered in the resistant cell lines (glutathione reductase, glutathione peroxidase, topoisomerase II). However, the level of DT-diaphorase correlated best with the degree of MMC resistance. The importance of DT-diaphorase was confirmed by using BMY 25282, an MMC analogue which is less dependent on DT-diaphorase for activation. Resistance in the HT-29R54 cell line was 15-fold with MMC compared to 5-fold with BMY 25282. P-glycoprotein-mediated resistance does not appear important in this model.. Although MMC resistance appears to be multifactorial, the results of this study strongly suggest that DT-diaphorase is the major contributor to MMC resistance under aerobic conditions. Strategies to enhance drug activation may therefore be useful for reversing MMC resistance.

Topics: Aerobiosis; Antibiotics, Antineoplastic; ATP Binding Cassette Transporter, Subfamily B, Member 1; Cell Survival; Colonic Neoplasms; DNA Topoisomerases, Type II; Drug Resistance; Drug Resistance, Multiple; Glutathione; Glutathione Peroxidase; Glutathione Reductase; Humans; Mitomycin; Mitomycins; NAD(P)H Dehydrogenase (Quinone); Oxidation-Reduction; Tumor Cells, Cultured; Tumor Stem Cell Assay

Topics: Animals; Biotransformation; Carcinoma; Cell Line; Colonic Neoplasms; DNA; Drug Resistance; Humans; Mice; Mitomycin; Mitomycins; Neoplasm Transplantation; Structure-Activity Relationship; Transplantation, Heterologous

BMY25282, a newly designed analogue of mitomycin C (MMC) with the substitution of an amidine group at position 7 of MMC, can circumvent MMC resistance in a series of human colonic carcinoma cells that were selected for resistance to MMC (J.K.V. Willson et al., Cancer Res., 45:5281-5286, 1985). In this study MMC resistance was found to be associated with an inability of the resistant cells to activate MMC. However, both the MMC-sensitive and -resistant cells were observed to metabolize BMY25282 extensively in vitro to a reactive species capable of alkylating 4-(p-nitrobenzyl)pyridine (a trapping agent for activated drug). The results of these studies suggested that the deficient cellular reductive activating mechanism was associated with MMC resistance and that analogue BMY25282 was able to overcome this deficiency in MMC-resistant cells by virtue of its enhanced activation.

Topics: Animals; Biotransformation; Colonic Neoplasms; Drug Resistance; Humans; Microsomes, Liver; Mitomycin; Mitomycins; Oxidation-Reduction; Rats

BMY 25282, a newly designed analogue of mitomycin C (MMC), was assessed for its non-cross-resistant cytotoxic and biochemical action against MMC-resistant human colon carcinoma cells. The analogue has an amidine substituted at position 7 of MMC and has a more efficient intracellular activation to its active species than MMC. In this study we demonstrated that BMY 25282 can overcome MMC resistance in a series of previously described human colon carcinoma cells resistant to MMC (Cancer Res., 44: 5880, 1984). The non-cross-resistance of the analogue in the model was confirmed in vivo by treating tumor xenograft-bearing athymic mice with equitoxic doses of MMC or BMY 25282. We further investigated the formation of interstrand DNA cross-link (IDC) formation by BMY 25282 and MMC. MMC-sensitive cells contained 3 to 8 times as many IDCs as resistant colon carcinoma cells, while no significant differences in IDCs were found between the MMC-sensitive or -resistant cells incubated with BMY 25282. When MMC-sensitive or -resistant cells were exposed to the 70% inhibition concentration of either MMC or BMY 25282, no differences were seen with respect to IDC formation. These studies demonstrate that BMY 25282 is able to overcome MMC resistance in a series of human colon carcinoma cells and that IDC formation in the MMC-sensitive or -resistant cells parallels cytotoxicity for both MMC and the analogue.

Topics: Animals; Antineoplastic Agents; Biotransformation; Cells, Cultured; Colonic Neoplasms; DNA; Drug Resistance; Female; Humans; In Vitro Techniques; Mice; Mice, Inbred BALB C; Mitomycin; Mitomycins; Neoplasm Transplantation; Rats; Transplantation, Heterologous