Antitumor Compounds From Halophilic <i>Streptomyces violaceorubidus</i> M4 Against Triple‐Negative Breast Cancer

Triple-negative breast cancer (TNBC) is an aggressive form of breast cancer characterized by the absence of estrogen and progesterone receptors and minimal HER2 expression, restricting the available treatment options. Actinobacteria have emerged as promising sources of anticancer compounds because of their remarkable ability to produce beneficial compounds. This study aimed to evaluate the antitumor effects of the halophilic Streptomyces violaceorubidus M4 extract on TNBC both in vitro and in vivo. The extracted compounds were analyzed by LC-MS. MTT and annexin-PI assays were used to assess the apoptosis-inducing effects of the compounds on MDA-MB-231 and MCF-10A cells. The expression of apoptosis-related BAX, BCL2, P53, CASPASE-8, and CASPASE-9 genes was analyzed using Real-time PCR. A TNBC mouse model was established using 4T1 cell transplantation, and the animals received the extract intravenously for 21 days. S. violaceorubidus M4 contained bioactive compounds, including amino acids, carboxylic acids, coumarins, isoflavones, phosphatidylcholine, tetrahydroxyanthraquinone, and flavonoids. The extract demonstrated selective cytotoxicity against MDA-MB-231 cells, with an IC50 of 48.04 μg/mL after 48 h, while the IC50 for MCF-10A cells was 132 μg/mL. The reduction in Cas-9 expression alongside the elevation of Cas-8 and P53 expression suggests the participation of the extrinsic pathway in the process of apoptosis. Histopathological evaluation of tumor tissues from mouse models showed that the extract injection reduced the number of mitotic cells, nuclear pleomorphism, and angiogenesis in tumor tissue. This study suggests that S. violaceorubidus M4 has a pronounced anticancer effect on TNBC and can be considered for the production of anticancer substances.