Breast cancer is the second leading cause of cancer deaths in women worldwide and represents a highly aggressive nature with limited therapeutic options; thus, investigating novel therapeutic agents for breast cancer is much needed. In this study, we investigated the anticancer effects of a novel camptothecin derivative, CPT211, against human breast cancer.

We used hormone receptor-positive MCF-7, triple-negative (TNBC) MDA-MB-231, and HER2-positive BT-474 human breast cancer cells to examine cytotoxicity of CPT211. We measured cell viability with dose dependence of CPT211 treatments by an MTT assay and investigated the potential underlying mechanism through flow cytometric and Western blot methods. Furthermore, we evaluated the efficacy of the treatment combination of CPT211 and doxorubicin in a mouse model bearing MDA-MB-231 xenografts.

CPT211 treatment led to dose-dependent decreases in cell viability of both MCF-7 and MDA-MB-231 cells, but not BT-474 cells. Analysis of the underlying molecular mechanism revealed that CPT211 activated p53-mediated apoptosis, by triggering intrinsic and extrinsic apoptotic pathways in MCF-7 cells. Additionally, CPT211 induced apoptosis and cell cycle arrest of MDA-MB-231 cells by activating Fas/FADD/caspase-8 signaling, suggesting that CPT211-mediated MDA-MB-231 cell apoptosis may occur through an extrinsic apoptosis pathway. CPT211 treatment with doxorubicin in mice bearing MDA-MB-231 xenografts was shown to enhance caspase-8 and caspase-7 activation, resulting in significant inhibition of tumor growth.

These results indicate that Fas/FADD/caspase-8 activation plays an important role in CPT211-mediated tumor growth suppression in TNBC, and the novel camptothecin derivative, CPT211, can be exploited for specific targeted therapies and potentially improve approaches to combination treatments for human breast cancer.