Effect of 6-thioguanine and 6-thioguanosine on osteoclast number per millimeter of tumor per bone. Data represent histomorphometric analysis of hindlimbs from mice with osteolytic lesions. MDA-MB-231 tumor cells were inoculated on day 0. Treatment with either 6-thioguanine or 6-thioguanosine (1.0 mg/kg/day subcutaneously) was begun on the following day. Measurements are of the number of osteoclasts per millimeter of tumor adjacent to bone (tumor–bone interface) from the midsections of tibias and femurs of mice. Values represent means ± SEM (n = 5 per group). 6-TG, 6-thioguanine; 6-TGu, 6-thioguanosine. *P < 0.05.