(a) Effect of 6-thioguanine on blood ionized-calcium concentrations in male athymic nude mice bearing RWGT2 cells. Treatment with 6-thioguanine (10 mg/kg/day subcutaneously) was begun on day 11, after hypercalcemia became evident. Vertical arrows indicate the days of treatment. Final blood samples were obtained 1–2 hours after the fourth dose of 6-thioguanine was given. (b) Effect of 6-thioguanine on serum PTHrP concentrations in male athymic nude mice bearing RWGT2 cells. Treatment with 6-thioguanine (10 mg/kg/day subcutaneously) was begun on day 11, after hypercalcemia became evident. Vertical arrows indicate the days of treatment. Final blood samples were obtained 1–2 hours after the fourth dose of 6-thioguanine was given. (c) Effect of 6-thioguanosine on blood ionized-calcium concentrations in male athymic nude mice bearing RWGT2 cells. Treatment with 6-thioguanosine (10 mg/kg/day subcutaneously) was begun on day 11, after hypercalcemia became evident. Vertical arrows indicate the days of treatment. Final blood samples were obtained 1–2 hours after the fourth dose of 6-thioguanosine was given. (d) Effect of 6-thioguanosine on serum PTHrP concentrations in male athymic nude mice bearing RWGT2 cells. Treatment with 6-thioguanosine (10 mg/kg/day subcutaneously) was begun on day 11, after hypercalcemia became evident. Vertical arrows indicate the days of treatment. Final blood samples were obtained 1–2 hours after the fourth dose of 6-thioguanosine was given. Values in all panels represent means ± SEM (n = 5 per group). *P < 0.05.