Amygdalin (Laetrile) and prunasin beta-glucosidases: distribution in germ-free rat and in human tumor tissue.

Amygdalin, the gentiobioside derivative of mandelonitrile commonly referred to as Laetrile, is presently under intensive investigation as a potential cancer chemotherapeutic agent. Because of this interest, we investigated the activity of beta-glucosidases that cleave glucose from amygdalin and from prunasin (mandelonitrile monoglucoside) in tissues from germ-free rats and in normal and neoplastic human tissues. Rat and human small intestinal mucosa contain high levels of activity of glucosidases that act on both of these cyanogenic glucosides. Release of glucose from these compounds was not detected in any of the human neoplastic tissues examined in the present study. These observations are consistent with reports of cyanide toxicity through the oral use of amygdalin or prunasin and pose serious questions concerning the alleged tumoricidal effect of amygdalin.