It is interesting that a number of bisindole alkaloids (taburnaemine A, etc., Table 1) isolated from Tabernaemontana corymbosa showed antiproliferative activity (IC50 2.6–9.8 μM) against several human cancer cell lines, including A-549, the triple-negative breast cancer (TNBC) cell line (MDA-MB-231, a highly metastatic cancer that lacks efficient targeted chemotherapy), ER+/PR+ breast cancer (MCF-7), KB and KB-VIN cells [37]. This evidence concerns the gene ESR1 and cancer.