Proopiomelanocortin (POMC) is the precursor of

various anti-inflammatory peptides including α-melanocyte-stimulating hormone (α-MSH). We have recently demonstrated the potential of systemic POMC expression via adenovirus gene transfer suppresses the growth of primary B16-F10 melanoma and prolongs the survival of tumor-bearing mice. In this study, we investigated whether POMC gene transfer also held promise for management of metastatic melanoma. In cell cultures, POMC gene delivery potently inhibited the motility and invasiveness of B16-F10 melanoma cells. Such inhibition was correlated with the reduced Rho activity and downregulation Erlotinib in vivo of Rho-ROCK signaling proteins including RhoA, RhoB, ROCK-I and ROCK-II. Besides, POMC gene transfer also disrupted the epithelial-mesenchymal transition (EMT) of melanoma cells through E-cadherin up-regulation and α-SMA

down-regulation. To evaluate the anti-metastatic efficacy in vivo, C57BL/6 mice were intravenously administrated with luciferase-engineered B16-F10 cells at day 1, treated with adenovirus vectors at day 2, and monitored for development of lung metastasis at day 14 BAY 57-1293 ic50 by counting lung foci and bioluminescence. It was found that POMC-treated mice exhibited significant reduction in lung metastasis. Therefore, the present study demonstrated for the first time the anti-metastatic potential of peripheral POMC expression for control of metastatic melanoma via perturbing EMT and Rho/ROCK pathways. Poster No. 209 Denileukin Diftitox Selectively Depletes Regulatory T Cells and Inhibits Tumor Growth in Syngeneic Tumor Models Mary Vermeulen 1 , Lana Parent1, Nanding Zhao1, Diana Liu1, Sally Ishizaka1, Matthew Mackey1, Natalie

Twine1, Judith Oestreicher1, Bruce Littlefield1 1 Eisai Research Institute, Andover, MA, USA Denileukin diftitox (DD; ONTAK® Ribonucleotide reductase – Eisai Inc.), a recombinant fusion protein that combines IL-2 with the membrane and catalytic domains of diphtheria toxin, binds to and potently kills cells that express the IL-2 receptor (IL-2R). One component of that receptor is CD25. High level IL-2R expression is a characteristic of immunosuppressive regulatory T lymphocytes (Tregs), which many types of solid tumors are known to utilize for immune evasion. We found that a 1–2 hour exposure to DD dose-dependently depleted CD4+CD25+FoxP3+ murine splenocytes or CD4+CD25hiFoxP3+ human blood leukocytes in vitro, while largely sparing CD4+CD25- splenocytes. The same brief DD exposure that led to depletion of Tregs (as measured by flow cytometry) also inhibited suppressive activity of murine Tregs (as measured by suppression of [3H]thymidine uptake) towards stimulated non-Treg T cells. In vivo exposure to DD at 4.5 µg/mouse (Q7dx2) led to stasis of established subcutaneous CT26 colon tumors in BALB/c mice. Of interest, we also found that DD at 4.5 µg/mouse (Q7dx2) was completely without anti-tumor effect towards CT26 tumors if tumors were implanted in immunocompromised nude mice.