Complete regression of established subcutaneous B16 murine melanoma tumors after delivery of an HIV-1 Vpr-expressing plasmid by in vivo electroporation.

Novel therapies and delivery methods directed against malignancies such as melanoma, and particularly metastatic melanoma, are needed. The HIV-1 accessory protein Vpr (viral protein R) has previously been demonstrated to induce G2 cell cycle arrest as well as in vitro growth inhibition/killing of a number of tumor cells by apoptosis. In vivo electroporation has been utilized as an effective delivery method for pharmacologic agents and DNA plasmids that express "therapeutic" proteins and has been targeted to various tissues, including malignant tumors. For the study reported here, we hypothesized that intratumoral delivery of a Vpr expression plasmid through in vivo electroporation would induce apoptosis and growth attenuation or regression of melanoma tumors. Established subcutaneous B16.F10 melanoma tumors were injected intratumorally with a Vpr-expressing (either 25 or 100 microg) plasmid, followed by electroporation, on day 0 (i.e., when tumors had attained an appropriate size) and day 4. Treatment with 25 or 100 microg of the Vpr-expressing plasmid resulted in complete tumor regression with long-term survival in 14.3 and 7.1% of the mice, respectively. In addition, electroporative delivery of the Vpr-expressing plasmid was shown to induce apoptosis in tumors after intratumoral injection. This is the first report demonstrating the ability of Vpr, when delivered as a DNA expression plasmid with in vivo electroporation, to attenuate melanoma lesion growth and induce complete tumor regression coupled with long-term survival of mice in a highly aggressive and metastatic solid tumor model.