S-allyl mercaptocysteine (SAMC), a water-soluble component derived from garlic, has been found to exert multi-antitumor activities. This study was to investigate the responsible molecular mechanisms of SAMC in human breast cancer cell lines. Sulforhodamine B assay was used to determine cell viability, flow cytometry was applied for the analysis of cell cycle and cell apoptosis, the change of protein was detected by Western blot. It was found that SAMC exhibited an effective cell growth inhibition of human breast cancer cell lines MCF-7 (ER positive) and MDA-MB-231 (ER negative) in a dose- and time-dependent manner by inducing cell cycle arrested in G0/G1 phase, the block of cell cycle was associated with the up-regulation of p53 and p21. Furthermore, the SAMC-mediated cell cycle arrest was accompanied with promotion of apoptosis, as indicated by the changes in the nuclear morphology and expressions of apoptosis-related proteins. SAMC clearly triggered the mitochondrial apoptotic pathway as indicated by activation of Bax, decreased expression of Bcl-2 and Bcl-XL, and subsequent activation of caspase-9 and caspase-3. These results highlight the value of a continued investigation into the use of SAMC as a potential antitumor candidate for breast cancer.

Three new angucycline-type C-glycosides, grincamycins L–N (1–3), together with the known rabelomycin (4), moromycin B (5), fridamycin D (6), saquayamycin B1 (7), actinomycin X₂ (8), and actinomycin D (9), were isolated from the culture of the soil-derived Streptomyces sp. XZHG99T collected from Color desert, Dengpa District, Tibet. The structures of 1–3 were established by detailed analyses of comprehensive spectroscopic data. Compounds 1–9 exhibited significant cytotoxicity against a panel of human cancer cell lines A549, H157, MCF7, MDA-MB-231, and HepG2, while 4, 8, and 9 showed decent antibacterial activity against Mycobacterium smegmatis and Staphylococcus aureus.