Several small molecules that inhibit checkpoint proteins have been described in the literature, the first of which were the purine alkaloids caffeine (1) and pentoxifylline (2), which inhibit two upstream kinases, ATM and ATR (Fig. 1). 2 However, caffeine cannot be used to inhibit this pathway in human beings as the doses required cause central nervous system and cardiac toxicities. ... UCN-01 (3), one member of the indolocarbazole family, 3, 3a, 3b, 3c and 3d ...
