Genomic analysis and selective small molecule inhibition identifies BCL-XL as a critical survival factor in a subset of colorectal cancer

Abstract

BackgroundDefects in programmed cell death, or apoptosis, are a hallmark of cancer. The anti-apoptotic B-cell lymphoma 2 (BCL-2) family proteins, including BCL-2, BCL-XL, and MCL-1 have been characterized as key survival factors in multiple cancer types. Because cancer types with BCL2 and MCL1 amplification are more prone to inhibition of their respectively encoded proteins, we hypothesized that cancers with a significant frequency of BCL2L1 amplification would have greater dependency on BCL-XL for survival.MethodsTo identify tumor subtypes that have significant frequency of BCL2L1 amplification, we performed data mining using The Cancer Genome Atlas (TCGA) database. We then assessed the dependency on BCL-XL in a panel of cell lines using a selective and potent BCL-XL inhibitor, A-1155463, and BCL2L1 siRNA. Mechanistic studies on the role of BCL-XL were further undertaken via a variety of genetic manipulations.ResultsWe identified colorectal cancer as having the highest frequency of BCL2L1 amplification across all tumor types examined. Colorectal cancer cell lines with BCL2L1 copy number >3 were more sensitive to A-1155463. Consistently, cell lines with high expression of BCL-XL and NOXA, a pro-apoptotic protein that antagonizes MCL-1 activity were sensitive to A-1155463. Silencing the expression of BCL-XL via siRNA killed the cell lines that were sensitive to A-1155463 while having little effect on lines that were resistant. Furthermore, silencing the expression of MCL-1 in resistant cell lines conferred sensitivity to A-1155463, whereas silencing NOXA abrogated sensitivity.ConclusionsThis work demonstrates the utility of characterizing frequent genomic alterations to identify cancer survival genes. In addition, these studies demonstrate the utility of the highly potent and selective compound A-1155463 for investigating the role of BCL-XL in mediating the survival of specific tumor types, and indicate that BCL-XL inhibition could be an effective treatment for colorectal tumors with high BCL-XL and NOXA expression.

Computationally designed high specificity inhibitors delineate the roles of BCL2 family proteins in cancer

“…Inhibiting a single pro-survival homolog had little effect on short-term survival; only SW48 cells showed greater than a 50% decrease in viability after treatment with A-1331852, consistent with a previous study showing SW48 is sensitive to Bcl-xL inhibition (Zhang et al, 2015; Figure 9A). Combined inhibition of both Mcl-1 and Bcl-xL caused nearly complete cell death after 24 hr in all colon cancers except HCT-116; further analyses showed that αMCL1-mediated Mcl-1 inhibition strongly sensitizes most colon cancers to A-1331852 (and to a lesser extent ABT-263), with a 4.6-fold or greater decrease in EC 50 values observed in all cell lines except HCT-116 (Figure 9—figure supplement 1A–B).…”

“…In previous studies, colon cancers showed a variable response to small-molecule-mediated Bcl-xL inhibition, and RNAi experiments identified Mcl-1 as a resistance factor (Zhang et al, 2015). To determine whether the Mcl-1 antagonism could render colon cancers sensitive to Bcl-xL neutralization and assess the influence of other pro-survival homologs on survival, we modified a panel of seven colon cancer lines to inducibly express either αMCL1 or αBFL1, and treated them with small molecules to selectively inhibit Bcl-2 (ABT-199), Bcl-xL (A-1331852), or Bcl-2 and Bcl-xL simultaneously (ABT-263).…”

Bcl-xL is an oncogenic driver in colorectal cancer

“…24, 25 Furthermore, Bcl-x L has been identified as a critical survival factor utilizing frequent genomic alterations in a subset of CRCs. 26 …”

How to unleash mitochondrial apoptotic blockades to kill cancers?

“…Anti-apoptotic proteins include at least BCL-2, BCL-xL, MCL-1, BCL-w and BFL-1. High expression of anti-apoptotic proteins, especially BCL-211, 12, 13, 14, BCL-xL 15 and MCL-116, 17, 18, 19, 20, has been shown in various types of cancers, and they play important roles in tumorigenesis in different tumor models 9, 21, 22, 23, 24, 25. Pro-apoptotic proteins can be further divided into two subgroups, including multi-domain proteins, like the death effectors/executioners BAX and BAK; and BH3-only proteins, like activators BIM, BID and PUMA, or sensitizers including BAD, NOXA, HRK and BMF.…”