Twenty-four patients were treated in three dose tiers of 8 patients each, utilizing a unique statistical design, so that within each group, patients were randomized in blocks of 4 to receive loxoribine initially and then placebo 4 weeks later--a sequence that was reversed in the remaining 4 patients. In 23 courses of loxoribine and 20 courses of placebo, toxicity was mild and infrequent at all dose tiers (1 mg/kg, 5 mg/kg and 10 mg/kg.

Leukemic B cells from a majority of patients with chronic lymphocytic leukemia (CLL) enter the cell cycle upon stimulation in vitro with loxoribine (1mM). In the absence of added costimulants, a proportion of these cells become activated and undergo DNA synthesis and mitosis accompanied by a marked increase in expression of an array of cell surface activation antigens. The resultant activated B-CLL cells exhibit greatly enhanced sensitivity to cycle-active cytotoxic drugs.