Impact of insulin on doxorubicin-induced rat host toxicity and tumor regression

To test whether the anorexia and host depletion following doxorubicin chemotherapy can be improved by concomitant insulin therapy, 70 F344 rats were divided equally between tumor-bearing (TB) and non-tumor-bearing (NTB) groups and studied for food intake, host weight, and tumor size changes. Sarcoma fragments were implanted s.c. in TB rats and 18 days later all rats received an i.v. dose of doxorubicin (8 mg/kg). The following day TB and NTB rats were randomized to receive neutral protaminehagedorn insulin (2 units/100 g/24 h) or normal saline until food intake returned to normal. Following doxorubicin administration food intake and host weight declined in an identical pattern in both NTB and TB rats treated with saline. However, beginning on day 6 insulin-treated TB and NTB rats ate significantly more than saline-treated controls. Insulin-treated animals returned to normal food intake levels in 50% less time than controls. This improved food intake resulted in an improved host mass beginning also on day 6 for both TB and NTB rats. In addition, it appeared that insulin treatment significantly improved the tumor shrinkage initiated by doxorubicin. Following doxorubicin, insulin-treated TB rats had a greater reduction of tumor size (10.6 +/- 1.2 cm3) compared to saline-treated rats (6.6 +/- 0.8 cm3, P less than 0.01). To further characterize the effect of insulin and/or doxorubicin on tumor growth, the experiment was repeated in the same manner except for two additional TB groups: saline- and insulin-treated tumor bearers with treatment beginning 19 days after tumor implant. Rats treated with doxorubicin had a significant reduction in tumor size compared to rats not treated with doxorubicin (P less than 0.001). Insulin alone did not affect tumor growth, but insulin plus doxorubicin significantly decreased tumor size compared to doxorubicin alone (P less than 0.01). In a second experiment using 80 rats insulin treatment had no apparent effect on reduction of peripheral blood counts including white blood cells, neutrophils, lymphocytes, platelets, and hematocrit induced by doxorubicin in either NTB or TB rats. Insulin given 24 h previously had minimal effect on plasma glucose. The marked improvement in food intake and host weight, as well as additional tumor reduction with exogenous insulin following doxorubicin, suggests that insulin may have a role in reversal of doxorubicin host nutritional toxicity and perhaps improvement of antitumor efficacy.