Staurosporine Derivatives Generated by Pathway Engineering in a Heterologous Host and Their Cytotoxic Selectivity

Two new staurosporine derivatives, staurosporines M1 and M2 (4 and 5), in addition to five previously reported metabolites (1-3, 6, and 7), were generated by the heterologous expression of engineered spc gene clusters in Streptomyces coelicolor M1146. The structures of these derivatives were determined by a combination of spectroscopic methods and CD measurement. Compounds 1, 2, 4, and 5 showed effective activities against three tumor cell lines (HCT-116, K562, and Huh 7.5), and 3 was active against HCT-116 and K562 cells. In addition, compounds 3 and 5 showed undetectable toxicity up to 100 μM toward the normal hepatic cell line LO₂. Based on the IC₅₀ values, their structure and activity relationships are discussed.