Combination with vorinostat overcomes ABT-263 (navitoclax) resistance of small cell lung cancer

Small cell lung cancer (SCLC) is an aggressive tumor type with high mortality. One promising approach for SCLC treatment would be to utilize agents targeting molecular abnormalities regulating resistance to apoptosis. BH3 mimetic antagonists, such as ABT-737 and its orally available derivative ABT-263 (navitoclax) have been developed to block the function of pro-survival BCL-2 family members. The sensitivity of SCLC to these drugs varies over a broad range in vitro and in clinical trials. We have previously shown that the expression of Noxa, a BH3-only pro-apoptotic BCL-2 family protein, is a critical determinant of sensitivity to ABT-737. Thus, pharmacological up-regulation of Noxa could enhance cell death induced by the BH3 mimetics. We find that the combination of ABT-263 and a HDAC inhibitor, vorinostat, efficiently induces apoptosis in a variety of SCLC cell lines, including ABT-263 resistant cell lines. Cell death induced by combined treatment is Noxa- and/or BIM-dependent in some cell lines but in others appears to be mediated by down-regulation of BCL-X-L and release of BAK from BCL-X-L and MCL-1. These results suggest that combination of HDAC inhibitors and BCL-2 inhibitors could be an alternative and effective regimen for SCLC treatment.