Screening of promising chemotherapeutic candidates against human adult T-cell leukemia/lymphoma from plants: active principles from Physalis pruinosa and structure–activity relationships with withanolides

Adult T-cell leukemia/lymphoma (ATL) is a peripheral T-cell malignancy caused by human T-cell lymphotropic virus type I (HTLV-1). Clinical manifestations of ATL range from smoldering to chronic, lymphoma and acute subtypes. Patients with acute and lymphoma-type ATL require therapeutic intervention. Conventional chemotherapeutic regimens used against other malignant lymphoma have been administered to ATL patients, but the therapeutic outcomes of acute and lymphoma-type ATL remain very poor. In this study, 214 extracts from 162 plants belonging to 65 families were screened for the purpose of elucidating the anti-proliferative effect against HTLV-1-infected T-cell lines. Extracts from aerial parts of Physalis pruinosa showed potent inhibitory effect. We isolated five withanolides from the extracts by activity-guided fractionation and examined the structure–activity relationships. The presence of a 5β,6β-epoxy function is suggested to be essential for the activity, and the most active principle showed selective toxicity to HTLV-1-infected T-cell lines.