Triple-negative breast cancer (TNBC) is associated with high grade, metastatic phenotype, younger patient age, and poor prognosis. The discovery of an effective anti-TNBC agent has been a challenge in oncology. In this study, fifty-eight ester derivatives (DETDs) with a novel sesquiterpene dilactone skeleton were organically synthesized from a bioactive natural product deoxyelephantopin (DET). Among them, DETD-35 showed potent antiproliferative activities against a panel of breast cancer cell lines including TNBC cell line MDA-MB-231, without inhibiting normal mammary cells M10. DETD-35 exhibited a better effect than parental DET on inhibiting migration, invasion, and motility of MDA-MB-231 cells in a concentration-dependent manner. Comparative study of DETD-35, DET and chemotherapeutic drug paclitaxel (PTX) showed that PTX mainly caused a typical time-dependent G2/M cell-cycle arrest, while DETD-35 or DET treatment induced cell apoptosis. In vivo efficacy of DETD-35 was evaluated using a lung metastatic MDA-MB-231 xenograft mouse model. DETD-35 significantly suppressed metastatic pulmonary foci information along with the expression level of VEGF and COX-2 in SCID mice. DETD-35 also showed a synergistic antitumor effect with PTX in vitro and in vivo. This study suggests that the novel compound DETD-35 may have a potential to be further developed into a therapeutic or adjuvant agent for chemotherapy against metastatic TNBC.
The androgen receptor (AR) is the main driver in the development of castration-resistant prostate cancer, where the emergence of AR splice variants leads to treatment-resistant disease. Through detailed molecular studies of the marine alkaloid manzamine A (MA), we identified transcription factor E2F8 as a previously unknown regulator of AR transcription that prevents AR synthesis in prostate cancer cells. MA significantly inhibited the growth of various prostate cancer cell lines and was highly effective in inhibiting xenograft tumor growth in mice without any pathophysiological perturbations in major organs. MA suppressed the full-length AR (AR-FL), its spliced variant AR-V7, and the AR-regulated prostate-specific antigen (PSA; also known as KLK3) and human kallikrein 2 (hK2; also known as KLK2) genes. RNA sequencing (RNA-seq) analysis and protein modeling studies revealed E2F8 interactions with DNA as a potential novel target of MA, suppressing AR transcription and its synthesis. This novel mechanism of blocking AR biogenesis via E2F8 may provide an opportunity to control therapy-resistant prostate cancer over the currently used AR antagonists designed to target different parts of the AR gene.