Abstract PS4-39: Efficacy of combined CDK4/6 inhibitor and PARP inhibitor in the treatment of BRCA1 mutant triple negative breast cancer

Abstract

Abstract Background: PARP inhibitors (PARPi) benefit only a fraction of breast cancer with BRCA mutation, and are even more limited in triple negative breast cancer (TNBC), due to clinical primary and acquired resistance. Here we found that the efficacy of PARPi in TNBC can be expanded with CDK4/6 inhibitors (CDK4/6i). Methods: We screened sensitive and resistant PARPi cell lines from existing TNBC cell lines and cultured PARPi-resistant strains by gradient concentration increase method. The effects of PARP inhibitor Olaparib and CDK4/6 inhibitor Palbociclib on TNBC cells lines were examined in vitro and in vivo. Combination index (CI) was used to evaluate the synergistic effects of drug combination. Results: We screened out the cell line MDA-MB-436, which was the most sensitive to PARPi, and the cell lines HCC1937 and SUM149, which were relatively resistant to PARPi, all of which were BRCA1 mutants. We demonstrated for the first time that the combination of PARPi and CDK4/6i has synergistic effects against some TNBCs both in vitro and in vivo, and was verified by CI<0.9. Further experiments confirmed that PARPi combined with CDK4/6i inhibited cell proliferation and migration, and increased apoptosis and DNA damage. In the PARPi sensitive BRCA-/TNBC cell (MDA-MB-436), the inhibitory effect of monotherapy PARPi was obvious; In the PARPi resistant BRCA-/TNBC cells (HCC1937 and SUM149), CDK4/6i was added to achieve significant growth inhibition. In the timing of medication, PARPi followed by CDK4/6i had better inhibitory effect.Conclusions: In some BRCA-/ TNBCs, PARPi combined with CDK4/6i had a synergistic effect. Even in PARPi-resistant cells, combined treatment could enhance the efficacy and might reverse the drug resistance to some extent. The combination index index of HCC1937 at different drug concentrations (uM)The combination index index of HCC1937 at different drug concentrations (uM)OlaparibPalbociclib25.0016.6711.117.414.943.292.191.460.980.65P-25.000.459110.668320.866540.869640.993450.989890.97841.003221.073741.00809P-20.000.537090.851131.022651.149561.231561.270271.189071.145021.14811.25795P-15.000.594121.018141.134481.056960.928140.955670.889760.842040.81060.81348P-10.000.475540.860580.77190.717480.62330.615880.561390.52960.510250.49752P-5.000.509450.762230.746560.683340.56030.499410.467390.41490.390670.37502P-2.500.573130.706410.714750.661230.519270.455960.350980.29340.319310.2756 Citation Format: Xiuzhi Zhu, Li Chen, Zhonghua Wang. Efficacy of combined CDK4/6 inhibitor and PARP inhibitor in the treatment of BRCA1 mutant triple negative breast cancer [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS4-39.