Up-regulation of antioxidant enzymes and coenzyme Q₁₀in a human oral cancer cell line with acquired bleomycin resistance

Abstract

Bleomycin (BLM) is an anti-cancer drug that can induce formation of reactive oxygen species (ROS). To investigate the association between up-regulation of antioxidant enzymes and coenzyme Q(10) (CoQ(10)) in acquired BLM resistance, one BLM-resistant clone, SBLM24 clone, was selected from a human oral cancer cell line, SCC61 clone. The BLM resistance of SBLM24 clone relative to a sub-clone of SCC61b cells was confirmed by analysis of clonogenic ability and cell cycle arrest. CoQ(10) levels and levels of Mn superoxide dismutase, glutathione peroxidase 1, catalase and thioredoxin reductase 1 were augmented in SBLM24 clone although there was also a mild increase in the expression of BLM hydrolase. Suppression of CoQ(10) levels by 4-aminobenzoate sensitized BLM-induced cytotoxicity. The results of suppression on enhanced ROS production by BLM and the cross-resistance to hydrogen peroxide in SBLM24 clone further demonstrated the development of adaptation to oxidative stress during the formation of acquired BLM resistance.

Resistance to Bleomycin in Cancer Cell Lines Is Characterized by Prolonged Doubling Time, Reduced DNA Damage and Evasion of G2/M Arrest and Apoptosis

“…This may be due to reduced cellular uptake of BLM, and/or enhanced BLM elimination/detoxification, mediated by cell surface receptors or transporters [31], antioxidant molecules/enzymes that reduce BLM-generated ROS [11,32]; or enzymes that inactivate BLM [33,34]. Future studies need to further study these mechanisms.…”

“…BLM was found to induce G2/M cell cycle arrest in cancer cell lines [10,11]. This may be explained by a G2/M checkpoint response to DNA damage.…”

“…Although the mechanism of BLM-resistance is unclear, several possibilities have been put forward, including: (a) altered BLM intake and efflux [14,15]; (b) elevated antioxidant level [5,11]; (c) enhanced repair ability for BLM-induced DNA damage [14,16,17]; and (d) increased metabolism (inactivation) of BLM [17–19]. …”

Action of bleomycin is affected by bleomycin hydrolase but not by caveolin-1

“…In the cell lines we studied, the expression of hCT2 mRNA was not detected by RT-PCR (data not shown), ruling out its involvement in bleomycin action. Accumulation data showed that resistance to bleomycin was due to repair enzymes, overexpression of antioxidant enzymes and antioxidant Q10 (30,41). Evaluating all factors reported for prediction of sensitivity to bleomycin is under way in our laboratory.…”

“…It is helpful to explain the reason why induction of bleomycin resistance led to increased BLH activity (29,30). BLH may be a response protein to resist cytotoxicity of bleomycin.…”