Our previous research demonstrated that SIC-19, an innovative inhibitor of salt-inducible kinase 2 (SIK2), effectively reduces SIK2 protein levels through the ubiquitin-proteasome pathway and exhibits synthetic lethal effects with poly ADP-ribose polymerase (PARP) inhibitors in ovarian cancer. However, the role of SIC-19 in triple-negative breast cancer (TNBC) and pancreatic cancer (PC) remains poorly defined. This study aims to investigate whether SIC-19 combined with PARP inhibitors can induce synthetic lethal effects in TNBC and PC.

Cell lines with high SIK2 expression were identified through Western blot analysis. The combination’s impact was evaluated using Cell Counting Kit-8 (CCK8), clone formation, and apoptosis assays, as well as in vivo xenograft models.

Our findings indicated that the IC50 of SIC-19 was inversely correlated with endogenous SIK2 expression in TNBC and PC cell lines. SIC-19 modulates the homologous recombination repair pathway by suppressing levels of RAD50-pS635, thereby enhancing the sensitivity of TNBC and PC cells, as well as xenografts, to PARP inhibitors.

These results underscore the potential of combining PARP inhibitors in combination with SIK2 inhibitors as a novel therapeutic approach to increase PARP inhibition’s effectiveness in treating TNBC and PC. This innovative combination therapy represents a promising approach for overcoming resistance mechanisms and improving the outcomes for patients with these challenging malignancies.