Abstract 977: Mcl-1 levels critically determines the sensitivities of human colon cancer cells to APG1244, a novel Bcl-2 and Bcl-XLinhibitor, that induces Bax- and caspase-8- dependent apoptosis

Abstract

Abstract Colorectal cancer (CRC) is the third leading cause of cancer-related deaths worldwide due to its poor prognosis. Most of the patients receive surgical resection when diagnosed as CRC, whereas the recurrence rate is very high. Therefore, additional treatment options, such as targeted therapy, are still urgently needed. The novel BH3 mimetic, APG1244 (a prodrug for APG1252), is a highly potent Bcl-2 and Bcl-XL dual inhibitor and being tested in clinical trials as a potential cancer therapeutic agent. The current study focuses on demonstrating the therapeutic efficacies of APG1244 against colorectal cancer and understanding the underlying mechanisms. A panel of CRC cell lines with different levels of Bcl-2, Bcl-XL and Mcl-1 possessed different sensitivities to APG1244. APG1244 effectively decreased the survival of CRC cell lines, particularly those expressing relative low levels of Mcl-1, with induction of apoptosis. High levels of Mcl-1 in these cell lines were significantly correlated to decreased sensitivity to APG1244. APG1244, when combined with a Mcl-1 inhibitor, synergistically decreased the survival and induced apoptosis of APG1244-insensitive cell lines with high levels of Mcl-1. This combination could further decreased the survival and enhanced apoptosis even in the cell lines with relatively low levels of Mcl-1, whereas enforced expression of ectopic Mcl-1 in these cells abrogated APG1244's effects on decreasing cell survival and inducing apoptosis, which can be reversed by Mcl-1 inhibition. In our study, it appears that APG1244 quickly activated caspase-8 and caspase-3 and induced PARP cleavage with induction of cytochrome C and Smac release from mitochondria. Deficiency of Bax, Smac, Bim or PUMA, but not FADD, in CRC cells protected (BAX-KO) or partially protected cells from APG1244-induced apoptosis, indicating that APG1244 induces Bax-dependent apoptosis. Furthermore, blockage of caspase-8 with a caspase-8 specific inhibitor abolished cleavage of caspase-3 and PARP including attenuation of cytochrome C and Smac release induced by APG1244, suggesting a caspase-8-dependent mechanism. The current study thus demonstrates the potential of APG1244 as a monotherapy in the treatment of CRC, particularly those with low Mcl-1 expression, or in combination with a Mcl-1 inhibitor for CRC treatment, warranting further evaluation in vivo and in the clinic. Citation Format: Weilong Yao, Shi-Yong Sun. Mcl-1 levels critically determines the sensitivities of human colon cancer cells to APG1244, a novel Bcl-2 and Bcl-XLinhibitor, that induces Bax- and caspase-8- dependent apoptosis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 977.