K-252b is an indolocarbazole isolated from the actinomycete Nocardiopsis and is a PKC inhibitor. K-252b can be used to inhibit extracellular kinases of cells in culture because it can’t pass through the cell membrane freely.
Rebeccamycin is an antitumor antibiotic+ inhibits DNA topoisomerase I. Rebeccamycin appears to exert its primary antineoplastic effect by poisoning topoisomerase I. It also has a negligible effect on protein kinase C and topoisomerase II.