Significant augmentation of pro-apoptotic gene therapy by pharmacologic bcl-xl down-regulation in mesothelioma

The ratio of pro-apoptotic (PAP) and anti-apoptotic (AAP) bcl-2 proteins, i s important in apoptosis regulation. We sought to determine if inhibition o f the AAP bcl-xl by sodium butyrate (SB) would augment apoptotic cellular d eath in mesothelioma when combined with adenoviral pro-apoptotic gene thera py (PAGT) by simultaneously increasing PAP and decreasing AAP in these cell s. Human mesothelioma cell lines were exposed to AdBax, AdBak, Adp53, and S B alone as well as all vectors combined with SB at varying doses and time p oints. Cell death was assessed, and apoptosis evaluated by morphology and F ACS. Isobologram analysis evaluated additive or synergistic effect. Cellula r death and apoptosis were augmented by PAGT/SB combinations compared to mo notherapy. Following AdBax/SB and AdBak/SB, a decrease of the AAP bcl-xl wa s noted in combination with increases in PAP bax and bak. By isobologram an alysis, additive or synergistic cell killing was noted with both combinatio ns. SB treatment did not significantly augment cell killing or apoptosis in combination with Adp53. PAGT/SB was more effective than monotherapy in ind uction of apoptotic cell death. Synergy may be due to the ability of SB to decrease bcl-xl with marked increases in PAP engendered by PAGT. Combinatio n therapy with agents that down-regulate AAP in addition to PAGT may prove useful clinically.