Inhibiting tumor growth by targeting liposomally encapsulated CDC20siRNA to tumor vasculature: therapeutic RNA interference.

Many cancer cells over express CDC20 (Cell Division Cycle homologue 20), a key cell cycle regulator required for the completion of mitosis in organisms from yeast to human. A recent in vitro study showed that specific knockdown of CDC20 expression using CDC20siRNA can significantly inhibit growth of human pancreatic carcinoma cells. However, preclinical study aimed at demonstrating therapeutic potential of CDC20siRNA in inhibiting tumor growth has just begun. Using a syngeneic C57BL/6J mouse tumor model, herein we show that intravenous administration of a 19bp synthetic CDC20siRNA encapsulated within α5β1 integrin receptor selective liposomes of pegylated RGDK-lipopeptide inhibits melanoma tumor growth. Liposomally encapsulated CDC20siRNA was found to be efficient in silencing the expression of CDC20 in tumor and endothelial cells at both mRNA and protein levels under in vitro settings. Findings in the flow cytometric studies confirmed the presence of significantly enhanced populations of the G2/M phase in cells treated with liposomally encapsulated CDC20siRNA. Immunohistochemical staining of tumor cryosections from mice treated with liposomally encapsulated fluorescently labeled siRNAs revealed tumor vasculatures targeting capabilities of the present liposomal formulations. The colocalizations of the TUNEL and VE-cadherin positive cells in tumor cryosections are consistent with tumor growth inhibition being mediated via apoptosis of the tumor endothelial cells. In summary, the presently disclosed liposomal formulation of CDC20siRNA is a promising RNA interference tool for use in anti-angiogenic cancer therapy.