Apoptosis regulators of the Bcl‐2 family play a key role in chemoresistance of cholangiocarcinoma organoids

Cholangiocarcinoma (CCA) is a rare but devastating liver cancer which is commonly diagnosed at a late stage and often resistant to chemotherapy. Bcl-2 family members, which control apoptotic cell death, are known to be involved in the chemoresistance of some cancer types. This study investigated the role of Bcl-2 family members in the chemoresistance of cholangiocarcinoma organoids (CCAOs) in both undifferentiated and matured branching phenotypes (BRCCAOs). Patient-derived CCAOs and BRCCAOs were cultured to assess chemoresistance to an FDA-approved anticancer drug panel by testing cell viability using ATP quantification and apoptotic cell death by cleaved caspase 3 staining. More specifically, sensitivity to the first-line drug gemcitabine was tested in combination with Bcl-2 family inhibitors or activators. We found that in gemcitabine-resistant CCAOs, inhibition of Bcl-xl could overcome gemcitabine resistance and induce apoptotic cell death. Although inhibition of Mcl-1 or activation of Bax induced spontaneous cell death, this could not overcome gemcitabine resistance. The BRCCAOs, which mimic tumor architecture better than CCAOs, show broader chemoresistance to anticancer drugs. Of note, in the resistant BRCCAOs, Bcl-xl inhibition could restore gemcitabine sensitivity. In conclusion, this study shows that targeting Bcl-xl can overcome chemoresistance to gemcitabine in CCA organoids. CCAOs and BRCCAOs provide good preclinical models for testing new drug combinations and assessing personalized therapeutic approaches.