Supplemental table S1 shows siRNA sequences. Table S2 shows primer sequences used for RTPCR. Figure S1 shows sensitivity of various cells to olaparib. Figure S2 shows the effect of olaparib on ALDHbr population. Figure S3 shows expression of ALDH isoforms at mRNA level. Figure S4 shows mRNA level of ALDH isoforms in PARPi-resistance cancer cells. Figure S5 shows the effect of ALDH1A1 expression on the sensitivity of EOC cells to olaparib. Figure S6 shows DNA repair ability in ALDH+ cells. Figure S7 shows the effect of ALDH1A1 on homologous recombination repair. Figure S8 shows the effect of NCT-501 on cell viability and ALDH activity. Figure S9 shows BRCA2 expression in various EOC cells. Figure S10 shows the combined effect of olaparib and NCT-501 on BRCA2-wt cells. Figure S11 shows the effect of NCT-501 on DNA repair in PARPi-resistant cells.
ARTICLE ABSTRACT
Poly (ADP-ribose) polymerase (PARP) inhibitors (PARPi) are approved to treat recurrent ovarian cancer with BRCA1 or BRCA2 mutations, and as maintenance therapy for recurrent platinum-sensitive ovarian cancer (BRCA wild-type or mutated) after treatment with platinum. However, the acquired resistance against PARPi remains a clinical hurdle. Here, we demonstrated that PARP inhibitor (olaparib)–resistant epithelial ovarian cancer (EOC) cells exhibited an elevated aldehyde dehydrogenase (ALDH) activity, mainly contributed by increased expression of ALDH1A1 due to olaparib-induced expression of BRD4, a member of bromodomain and extraterminal (BET) family protein. We also revealed that ALDH1A1 enhanced microhomology-mediated end joining (MMEJ) activity in EOC cells with inactivated BRCA2, a key protein that promotes homologous recombination (HR) by using an intrachromosomal MMEJ reporter. Moreover, NCT-501, an ALDH1A1-selective inhibitor, can synergize with olaparib in killing EOC cells carrying BRCA2 mutation in both in vitro cell culture and the in vivo xenograft animal model. Given that MMEJ activity has been reported to be responsible for PARPi resistance in HR-deficient cells, we conclude that ALDH1A1 contributes to the resistance to PARP inhibitors via enhancing MMEJ in BRCA2−/− ovarian cancer cells. Our findings provide a novel mechanism underlying PARPi resistance in BRCA2-mutated EOC cells and suggest that inhibition of ALDH1A1 could be exploited for preventing and overcoming PARPi resistance in EOC patients carrying BRCA2 mutation.
