Leptin serves as angiogenic/mitogenic factor in melanoma tumor growth

Background: Tumor development is angiogenesis dependent. There is evidence that leptin contributes to tumor growth. However, all the mechanisms by which leptin does this has not been clearly established. The objective of the present study was to test the hypothesis that leptin enhances melanoma tumor growth through inducing angiogenesis and cell proliferation. Materials and Methods: We injected 2 × 106 B16F10 melanoma cells subcutaneously to 32 C57BL6 mice. The mice were randomly divided into four groups of eight animals, on day 8. Two groups received twice daily intraperitoneal (i.p.) injections of either phosphate buffered saline or recombinant murine leptin (1 μg/g initial body weight). Two groups received i.p. injections of either 9F8 an anti leptin receptor antibody or the control mouse IgG at 50 μg/injection every 3 consecutive days. By the end of the 2nd week, the animals were euthanized and blood samples and tumors were analyzed. Angiogenesis and proliferation were assessed by immunohistochemical staining for CD31 and Ki-67 respectively. Results: Tumors size, capillary density, plasma levels of vascular endothelial growth factor, and the number of Ki-67-positive stained cells were significantly more in the leptin than 9F8 and both control groups (P < 0.05). Conclusion: Taken together, our findings reinforce the idea that leptin acts as an angiogenic and mitogenic factor to promote melanoma growth.