Diarylsulfonylurea (DSU) antitumor agents represent a new class of oncolytic compounds with an unknown, potentially novel, mechanism of action. At high concentrations of several of these agents, cytotoxicity appears to be a consequence of uncoupling of mitochondria. However, the mechanism of action at pharmacologically achievable concentrations is unknown. To further study these agents a subline of human colon carcinoma. GC3/c1, was selected for resistance to N-(5-indanylsulfonyl)-N'-(4-chlorophenyl)urea (ISCU) (Sulofenur). This clone (designated LYC5) was stably resistant for 2 years in the absence of selection pressure and was characterized for cross-resistance to other antitumor DSU and therapeutically used oncolytic agents. LYC5 was cross-resistant to six of seven DSU analogues examined when cells were exposed to drugs for 7 days. However, the degree of resistance was inversely related to the potency of the individual DSU against the parental GC3/c1 clone. Consequently, against LYC5 cells there was a relatively narrow range for concentrations inhibiting colony formation by 50% (4-fold), compared with that in GC3/c1 cells (12-fold range). With a single exception, each DSU examined caused uncoupling of oxidative phosphorylation in isolated mitochondria at 50 μM, and data suggest that cytotoxicity in LYC5 cells may be a consequence of mitochondrial impairment. In contrast, LYC5 cells were collaterally sensitive to the mitochondrial toxins rotenone, antimycin, and oligomycin, by 11.4-, 7.2-, and 36.9-fold respectively. LYC5 cells were also collaterally sensitive to vincristine (7.7-fold), Actinomycin D (5.9-fold), and rhodamine-123 (10.5-fold), agents associated with P-glycoprotein (Pgp)- mediated multidrug resistance (MDR). LYC5 cells were slightly more sensitive to Melphalan and doxorubicin (2.8- and 2.3-fold, respectively) but not to cisplatin or dideazatetrahydrofolic acid. Collateral sensitivity to vincristine and Actinomycin D was consistent with decreased Pgp levels in LYC5 cells. Immunohistochemical staining and Western blotting with anti-Pgp antibodies indicated an 8-fold reduction in Pgp levels in LYC5 cells, relative to expression in parental GC3/c1 cells. Consequently, association of mitochondrial toxins with resistance in MDR KB8-5 cells was examined in the presence or absence of the MDR-reversing agent verapamil. KB8-5 cells had equal or greater sensitivity, compared with parental KB3-1 cells, to rotenone, antimycin, and oligomycin and also to each DSU analogue examined. In addition, verapamil tended to have a protective effect against these mitochondrial toxins. It is thus concluded that these toxins are probably not part of the Pgp-mediated MDR phenotype and that collateral sensitivity of LYC5 cells to mitochondrial toxins is not a consequence of decreased Pgp expression. In contrast to results obtained with KB cells, verapamil significantly potentiated the toxicity of each mitochondrial toxin in GC3/c1 cells by approximately 5-fold, such that in the presence of verapamil GC3/c1 and LYC5 cells had similar sensitivities to rotenone and antimycin. Verapamil had significantly less effect in potentiating the cytotoxicity of mitochondrial toxins in LYC5 cells (<2-fold). Results suggested that resistance to DSU and collateral sensitivity to mitochondrial toxins may be linked and may be related to the mechanism of action of DSU at pharmacologically achievable concentrations. To test this, hybrids between GC3/c1 and LYC5 cells were made and tested for resistance to ISCU and mitochondrial toxins. Results demonstrated that resistance to ISCU was a recessive trait, as was collateral sensitivity to rotenone, antimycin, and oligomycin.
|Original language||English (US)|
|Number of pages||9|
|State||Published - Jan 1 1994|
ASJC Scopus subject areas
- Molecular Medicine