Amphotericin B: a novel class of antiscrapie drugs.

Amphotericin B (AmB) has been able to lengthen the incubation period of intracerebrally (ic) scrapie-injected hamsters to 45 d. This article reports a linear relationship between AmB doses and the duration of the incubation periods of ic-treated animals compared with controls, a greater effect of AmB treatment administered 2 w before or the same day of ic scrapie incubation, and the ineffectiveness of mepartricin, an AmB analogue, in prolonging the incubation period of ic scrapie-injected hamsters. The beneficial effect of AmB appears due to a delay in the replication of the scrapie agent in the brain of infected hamsters. Moreover, AmB suppresses scrapie replication in the spleen of treated animals. Three hypotheses may explain these results: (1) AmB alters a hypothetical scrapie receptor, preventing the entry of the agent into central nervous system (CNS) target cells; (2) AmB interferes with mechanisms involved in scrapie replication; (3) AmB prevents the formation and accumulation of a scrapie-specific amyloid protein responsible for the disease. Whatever the mechanism of action, AmB is the only currently available drug to modify experimental CNS scrapie infection, so AmB is proposed as a novel class of antiscrapie drugs.