Endogenous Nitroalkene Exploits Dependence on Autophagy-Lysosome Pathway in PARPi-Resistant TNBC
Lack of DNA double-strand break repair efficiency exquisitely sensitizes cancers to poly-ADP ribose polymerase inhibitors (PARPi). Unfortunately, resistance to PARPi poses an insurmountable challenge for patients. Mechanisms that confer insensitivity to PARPi therapy include enhanced DNA damage repair and autophagy. Natural and non-natural unsaturated fatty acid nitroalkene derivatives (NFA) show anticancer actions that sensitize TNBC cells to PARPi and other DNA-damaging treatments. We reveal that nitro-oleic acid (OA-NO2) re-sensitizes PARPi-resistant TNBC cells to PARPi. RNA-seq analysis of clinically relevant mutBRCA1 PARPi-resistant TNBC cell lines exhibited upregulation in autophagy and lysosomal pathways. Bio-orthogonal analysis identified the autophagy regulator SQSTM1/p62 as a novel OA-NO2 target, alkylating two redox-sensitive Cys residues of p62 (Cys105 and Cys113). These Cys are essential for p62 regulation of autophagy and mimicked the effects of p62 Cys105 and Cys113Ala mutants and when alkylated by OA-NO2 showed impaired p62 oligomerization, degradation, and inhibition of autophagy. Combination treatment of PARPi-resistant TNBC with a PARPi and OA-NO2 synergistically inhibited p62-associated autophagy and lysosome function. These data emphasize the clinical potential of OA-NO2 for treating PARPi-resistant TNBC patients.