Synthesis and enzyme-specific activation of carbohydrate-geldanamycin conjugates with potent anticancer activity

Geldanamycin (GA) is a potent anticancer antibiotic that inhibits Hsp90. Its potential clinical utility is hampered by its severe toxicity. To alleviate this problem, we synthesized a series of carbohydrate - geldanamycin conjugates for enzyine-specific activation to increase tumor selectivity. The conjugation was carried out at the C-17-position of GA. Their anticancer activity was tested in a number of cancer cell lines. The enzyme-specific activation of these conjugates M ion was evaluated with beta-galactosidase and beta-glucosidase. Evidently. glycosylation of C-17-pasition converted GA to an inactive prodrug before enzyme cleavage. Glucose-GA, as positive control, showed anticancer activity with IC50 of 70.2- 380.9 nM in various cancer cells by beta-glucocsidase activation inside of the tumor cells, which was confirmed by 3-fold inhibition using beta-glucasidase. specific inhibitor [2,5-dihydroxyniethy-3,4-dihydroxypyrrolidine (DMDP)]. Compared to glucose- GA, galactose- and lactose-GA conjugates exhibited much less activity with IC50 greater than 8000-25 000 nM. However, when galactose- and lactose-GA, were incubated with beta-galactosidase in the cells, their anticancer activity was enhanced by 3- to 40-fold. The results suggest, that GA can be inactivated by glycosylation of C-17-position and reactivated for anticancer activity by beta-galactosidase. Therefore, galactose-GA can be exploited in antibody-directed enzyme prodrug therapy (ADEPT) with beta-galactosidase for enzyme-specific activation in tumors. to increase tumor selectivity.