Received for publication August 13, 2007.
Revised June 6, 2008.
Accepted for publication June 6, 2008.

Combinatorial anti-leukemic disruption of oxidative homeostasis and mitochondrial stability by the redox reactive thalidomide CPS49 and flavopiridol

Abstract

CPS49 is a member of a recently identified class of redox-reactive thalidomide analogs that show selective killing of leukemic cells by increasing intra-cellular reactive oxygen species (ROS) and targeting multiple transcriptional pathways. Flavopiridol is a semi-synthetic flavonoid that inhibits cyclin-dependent kinases and also shows selective lethality against leukemic cells. The purpose of this study is to explore the efficacy and mechanism of action of the combinatorial use of the redox-reactive thalidomide CPS49 and the cyclin dependent kinase inhibitor flavopiridol as a selective anti-leukemic therapeutic strategy. In combination, CPS49 and flavopiridol were found to induce selective cytotoxicity associated with mitochondrial dysfunction and elevations of ROS in leukemic cells ranging from additive to synergistic activity at low micro-molar concentrations. Highest synergy was observed at the level of ROS generation with a strong correlation between cell-specific cytoxicity and reciprocal coupling of drug-induced ROS elevation with glutathione depletion. Examination of the transcriptional targeting of CPS49 and flavopiridol combinations reveals that the drugs act in concert to initiate a transcriptional program that manipulates NF-B, E2F-1 and p73 activity to promote enhanced mitochondrial instability by simultaneously elevating the expression of the pro-apoptotic factors BAX, BAD, p73 and PUMA, while depressing expression of the anti-apoptotic genes MCL1, XIAP, BCL-xL, SURVIVIN and MDM2. The co-administration of CPS49 and flavopiridol acts through coordinate targeting of transcriptional pathways that enforce selective mitochondrial dysfunction and ROS elevation and is therefore a promising new therapeutic combination that warrants further preclinical exploration.

Key words: Interleukins, NFkappaB, Signaling network analyses, Mitochondrial toxins, Oxidative stress/antioxidants, Mechanisms of cell killing/apoptosis