Cytotoxicity and Mechanism of Action of the Marine-Derived Fungal Metabolite Trichodermamide B and Synthetic Analogues

The trichodermamides are modified dipeptides isolated from a wide variety of fungi, including <i>Trichoderma virens</i>. Previous studies reported that trichodermamide B (<b>2</b>) initiated cytotoxicity in HCT-116 colorectal cancer cells, while trichodermamide A (<b>1</b>) was devoid of activity. We recently developed an efficient total synthesis for the trichodermamides A–C (<b>1</b>–<b>3</b>). Multiple intermediates and analogues were produced, and they were evaluated for biological effects to identify additional structure–activity relationships and the possibility that a simplified analogue would retain the biological effects of <b>2</b>. The antiproliferative effects of 18 compounds were evaluated, and the results show that <b>2</b> and four other compounds are active in HeLa cells, with IC₅₀ values in the range of 1.4–21 μM. Mechanism of action studies of <b>2</b> and the other active analogues revealed different spectra of activity. At the IC₈₅ concentration, <b>2</b> caused S-phase accumulation and cell death in HeLa cells, suggesting response to DNA double-strand breaks. The analogues did not cause S-phase accumulation or induction of DNA damage repair pathways, consistent with an alternate mode of action. The mechanistic differences are hypothesized to be due to the chlorohydrin moiety in <b>2</b>, which is lacking in the analogues, which could form a DNA-reactive epoxide