Inhibition of Trypanosoma brucei brucei peptidyl transferase activity by sparsomycin analogs and effects on trypanosome protein synthesis and proliferation.

Peptidyl transferase activity of Trypanosoma brucei brucei polyribosomes was competitively inhibited by analogs of sparsomycin (Ki = 1-100 microM). The analogs were also potent inhibitors of [3H]-leucine and [3H]mannose incorporation into the proteins of intact trypanosomes with little or no effect on overall respiratory rate, suggesting a specific site of action for these analogs on protein synthesis. The peptidyl transferase inhibitors were effective at low concentrations at limiting the proliferation of trypanosomes both in vitro and in vivo. The potency of the compounds as inhibitors of cell proliferation was positively correlated with their efficacy as inhibitors of peptidyl transferase activity. One compound, MDL 20828 (1 mg/kg), increased the survival time of T. b. brucei-infected mice 4-fold in the absence of any overt drug toxicity to the hosts.