A novel sequential treatment of palbociclib enhances the effect of cisplatin in RB-proficient triple-negative breast cancer
Abstract Background: Triple-negative breast cancer (TNBC) is a highly aggressive malignancy lack of sensitivity to chemo-, endocrine and targeted therapy. CDK4/6 inhibitors, combined with endocrine therapy, have been proven to be effective in postmenopausal women with HR-positive, HER2-negative advanced or metastatic breast cancer. So we investigated that whether CDK4/6 inhibitor palbociclib (PD) could enhance effects of cisplatin (CDDP) on TNBC.Methods: The effects of different drug regimens of PD and CDDP on MDA-MB-231 and RB-knockdown MDA-MB-231 (sh-MDA-MB-231) cells were assessed in vitro and vivo. MDA-MB-468 and RB-overexpression MDA-MB-468 cells were used to assess the effect of PD-CDDP regimen in vitro. Immunoblotting illustrated cyclin D1/RB/E2F axis signaling pathway.Results: PD induced G1 phase cell cycle arrest in MDA-MB-231 cell line. However, synchronous treatment with PD and CDDP for 24h, PD used for 24h and then followed by CDDP or CDDP used for 24h and then followed by PD all had no influence on cell apoptosis of MDA-MB-231 cells. We further investigated the effect of PD or CDDP withdrawal on sequential treatment and found that PD used for 48h and then withdrawn for 48h followed by CDDP (PD-CDDP) could significantly increase apoptosis, inhibit cell viability and colony formation of MDA-MB-231 cells, while in other regimens PD and CDDP represented additive or antagonistic response. Preferential use of PD could increase DNA damage by CDDP as measured through γH2AX. These findings above were negative in sh-MDA-MB-231 cells and cell function experiments of MDA-MB-468 and RB-overexpression MDA-MB-468 cells could draw similar conclusions, which indicated that PD enhanced the sensitivity of TNBC cells to CDDP in a RB dependent manner. In vivo, this combination treatment inhibited tumor growth and Ki-67 expression compared with single drug treatments in MDA-MB-231 xenograft models. Western blotting analysis presented that PD enhanced sensitivity to CDDP through CDK4/6-cyclin D-RB-E2F pathway. Conclusions: Pre-treatment with PD synchronized tumor cell cycle through CDK4/6-cyclin D1-RB-E2F pathway, which could increase anti-tumor effect of CDDP. PD-CDDP might be an effective treatment for RB-proficient TNBC patients.