Anti-apoptotic Protein BCL-XL As A Therapeutic Vulnerability In Gastric Cancer

Objective:New therapeutic targets are needed to improve the outcomes for gastric cancer(GC)patients with advanced disease.Evasion of programmed cell death(apoptosis)is a hallmark of cancer cells and direct induction of apoptosis by targeting the pro-survival BCL2 family proteins represents a promising therapeutic strategy for cancer treatment.Therefore,understanding the molecular mechanisms underpinning cancer cell survival could provide a molecular basis for potential therapeutic interventions.Here we explored the role of BCL2L1 and the encoded anti-apoptotic BCL-XL in GC,aims to provide a new targeted therapy strategy for gastric cancer.Methods:Using Droplet Digital PCR(ddPCR)technology to investigate the DNA amplification of BCL2L1 in GC samples and GC cell lines;The sensitivity of GC cell lines to selective BCL-XL inhibitors A1155463,A1331852,pan-inhibitor ABT-263,and VHL-based PROTAC-BCL-XL was analyzed using(CellTiter-Glo)CTG assay in vitro;Western Blot(WB)was used to detect the protein expression of BCL2 family members in GC cell lines and the manner in which PROTAC-BCL-XL kills GC cells;Co-Immunoprecipitation(CoIP)was used to investigate the mechanism of A13 31852 and ABT-263 kills GC cell lines;DDPCR,WB,and real-time PCR(RTPCR)were used to investigate the correlation between DNA,RNA,protein levels and drug activity.Results:(1)A subset of GC cell lines relies on BCL-XL for survival.(2)In gastric cancer cell lines,BCL-XL inhibitors A1155463 and A1331852 are more sensitive than pan BCL2 family inhibitor ABT263,indicated that ABT-263 is not an optimal inhibitor of BCL-XL.(3)VHL-based PROTAC-BCL-XL DT2216 appears to be active in GC cells.(4)DT2216 induces apoptosis of gastric cancer cells in a time-and dose-dependent manner through the proteasome pathway.(5)BCL-XL protein level predicts the response of GC cells to BCL-XL targeting therapy.(6)BCL2L1 gene CNVs do not reliably predict BCL-XL expression.Conclusions:We identified BCL-XL as a promising therapeutic target in a subset of GC cases with high levels of BCL-XL protein expression.Functionally,we demonstrated that both selective BCL-XL inhibitors and VHL-based PROTAC BCL-XL can potently kill GC cells that reliant on BCL-XL for survival.However,we found that BCL2L1 copy number variations(CNVs)cannot reliably predict BCL-XL expression,but that BCL-XL protein level serves as a useful biomarker predicting the sensitivity of GC cells to BCL-XL-targeting compounds.Taken together,our study pinpointed BCL-XL as potential druggable target for specific subsets of GC.