Compound 4a induces paraptosis in liver cancer through endoplasmic reticulum stress mediated by the calreticulin protein.

Background and purpose: Emerging evidence has highlighted that paraptosis may be an effective strategy for treating liver cancer. In our previous studies, Compound 4a induced paraptosis in cancer cells. Here, the characteristics of Compound 4a-induced paraptosis were further revealed and, for the first time, the target and related molecular mechanisms of Compound 4a-induced paraptosis in liver cancer were defined.

Experimental approach: The effects and mechanism of Compound 4a in liver cancer cells were studied in in vitro and in vivo (BALB/c-nude xenograft model) experiments, and the targets of Compound 4a that trigger paraptosis were identified and confirmed via mass spectrometry-based drug affinity responsive target stability (DARTS) analyses, siRNA experiments and a cellular thermal shift assay (CETSA). The function and distribution of calreticulin (CRT) protein were detected via Cal-520 AM and immunofluorescence staining, respectively.

Key results: Compound 4a effectively induced paraptosis-like cell death in liver cancer, both in vitro and in vivo, and its effect was comparable with the first-line anti-liver cancer drug oxaliplatin but with a higher safety profile. We identified the CRT protein as a target of Compound 4a, which caused cellular endoplasmic reticulum stress (ERS) and calcium overload. CRT knockdown weakened the anti-liver cancer activity of Compound 4a, which may be related to the inhibition of paraptosis.

Conclusion: Compound 4a represents a potentially safe and effective agent for the treatment of liver cancer. The characteristics of Compound 4a-triggered paraptosis was clarified and a unique function of CRT in paraptosis was revealed.