Treatment of myelodysplastic syndromes with orally administered N-(2S, 3R)-3-amino-2-hydroxy-4-phenylbutyryl-L-leucine (ubenimex)

N-(2S, 3R)-3-amino-2-hydroxy-4-phenylbutyryl-L-leucine (ubenimex) was administered orally, to patients with myelodysplastic syndromes (MDS) and acute leukemia derived from MDS, in a multi-institute study. Out of 77 patients evaluated, one achieved a complete remission, three a good response and two a partial response while 71 failed to respond to a daily oral administration of 30 mg ubenimex. The overall response rate was 7.8% (95% confidence limits; 3.6-16.0%); 7.0% (3.0-15.4%) in 71 MDS and 16.6% (3.0-56.3%) in acute six leukemias derived from MDS. Responses continued for six to 24 (median 10.5) weeks. No serious hematologic, biochemical or clinical toxicity was encountered, except for gastro-intestinal (GI) toxicity in one patient. The present study demonstrated ubenimex not to be generally beneficial for patients with MDS, and not to be recommended as a standard treatment for the disease.