Anti-oxidant treatment enhances anti-tumor cytotoxicity of (-)-gossypol.
We showed that tumor cells with wild-type p53 and high levels of Bcl-x(L) are cisplatin resistant but are induced to undergo apoptosis by (-)-gossypol, making this a promising agent for overcoming cisplatin resistance. However, some cells in a population with this phenotype are not killed and continue to survive. Conversely, tumor cells with low Bcl-x(L) expression and either wild type or mutant p53 are relatively cisplatin sensitive and do not exhibit such high levels of apoptosis. However, these do undergo progressive loss of viability after (-)-gossypol that may not be tumor specific. We sought to elucidate the basis for these observations using cDNA microarray analysis of (-)-gossypol treated cisplatin sensitive and resistant cells. Genes in the reactive oxygen species (ROS) pathway were highly upregulated in response to (-)-gossypol. The upregulation was of much greater magnitude in cisplatin sensitive than resistant cells. Staining with an oxidation reporter dye confirmed differential induction of ROS in tumor cells with low Bcl-x(L). As (-)-gossypol is known to undergo oxidative metabolism in vivo, ROS generation may be responsible for both off-target cytotoxicity and inactivation of the drug. In agreement with this hypothesis, oxidation of (-)-gossypol by pre-treatment with hydrogen peroxide eliminated its activity. Combined treatment with the antioxidant N-acetyl-cysteine (NAC) to block ROS increased (-)-gossypol-induced cytotoxicity to tumor but not normal cells. Furthermore, NAC increased the induction of apoptosis as measured by the sub-G(1) population, in both cisplatin sensitive and resistant cells. We postulate that concurrent treatment with antioxidant to block ROS prevents oxidative inactivation of (-)-gossypol and limits off-target toxicity allowing more potent (-)-gossypol-induced anti-tumor activity.
Sikora
Matthew J
MJ
Department of Pharmacology, University of Michigan, Ann Arbor, Michigan, USA.
Bauer
Joshua A
JA
Verhaegen
Monique
M
Belbin
Thomas J
TJ
Prystowsky
Michael B
MB
Taylor
Joseph C
JC
Brenner
J Chad
JC
Wang
Shaomeng
S
Soengas
Maria S
MS
Bradford
Carol R
CR
Carey
Thomas E
TE
D000111:Acetylcysteine / Q000494:pharmacology; D000970:Antineoplastic Agents / Q000494:pharmacology*; D000975:Antioxidants / Q000494:pharmacology*; D002460:Cell Line; D045744:Cell Line, Tumor; D002470:Cell Survival; D004357:Drug Synergism; D015972:Gene Expression Regulation, Neoplastic; D006072:Gossypol / Q000494:pharmacology*; D006801:Humans; D008954:Models, Biological; D009369:Neoplasms / Q000188:drug therapy*; D020411:Oligonucleotide Array Sequence Analysis; D016877:Oxidants / Q000378:metabolism; D017382:Reactive Oxygen Species
D000970:Antineoplastic Agents; D000975:Antioxidants; D016877:Oxidants; D017382:Reactive Oxygen Species; D006072:Gossypol; D000111:Acetylcysteine