Abstract 2524: Combination with vorinostat overcomes ABT-263 resistance of small cell lung cancer

Abstract

Abstract Lung cancer is the most common cause of cancer related mortality worldwide, with small cell lung cancer (SCLC) representing 15% of cases, accounting for 30,000 new cases in the US each year. While SCLC is initially a highly chemotherapy-responsive disease, relapse and progressive development of chemotherapy resistance is the rule. One promising approach to overcome the therapeutic resistance would be to utilize agents targeting molecular abnormalities regulating resistance to apoptosis. Tumor cell death induced by chemotherapy or lack of appropriate cellular survival signals is mediated by the BCL-2 family-dependent mitochondrial apoptotic pathway. We and others have shown that the pro-survival member BCL-2, as well as BCL-XL and MCL-1, is overexpressed in SCLC. BH3 mimetic antagonists have been developed to block the function of pro-survival BCL-2 family members. ABT-737 and its orally available derivative ABT-263 bind to and block BCL-2 and BCL-XL, but not MCL-1 function. Although SCLC is the only non-hematologic malignancy against which ABT-737/ABT-263 are effective as single agents, the sensitivity of SCLC to these drugs varies over a broad range in vitro and in clinical trials. We have shown in a model SCLC system that expression of Noxa, a BH3-only pro-apoptotic BCL-2 family protein, is a critical determinant of ABT-737 sensitivity, demonstrating that Noxa specifically binds to and recruits MCL-1 from the cytosol to the mitochondria. Recent integrative genome analysis in SCLC implicates histone modification as a major feature of SCLC. It has also been demonstrated that Noxa is transcriptionally activated by HDAC inhibitors. Thus, we hypothesized that alteration of histone modification by a HDAC inhibitor, vorinostat could induce Noxa to enhance cell death by ABT-737/263 treatment. We have found that combination of ABT-263 and vorinostat efficiently induces apoptosis in a variety of SCLC cell lines, even in the ABT-263 resistant cells. Cell death induced by combined treatment is Noxa- and/or BIM-dependent in some cell lines but in others appears to be mediated by an alternative mechanism. These results suggest that combination of HDAC inhibitors and BCL-2 inhibitors could be an alternative effective regimen for SCLC treatment. Citation Format: Wataru Nakajima, Mark A. Hicks, Kanika Sharma, Ngoc Le, Geoffrey W. Krystal, Hisashi Harada. Combination with vorinostat overcomes ABT-263 resistance of small cell lung cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2524. doi:10.1158/1538-7445.AM2015-2524