Abstract B32: A novel combination therapy for metastatic melanoma potentiates a gap junction positive feedback mechanism
Authors: Bagati Archis , Koch Zethan , Hutcherson Timothy C. , Pechette Joseph , Dianat Hossein , Higley Cory , Chiu Lisa , Song Yesul , Shah Jay , Chazen Elana , Nicolais Andrew , Casey Peter , Thompson Kyle , Nikiforov Mikhail A. , Zirnheld Jennifer , Zucker Shoshanna N. 
Published: June 2022

Abstract
We have developed a novel approach for treating melanoma by selectively targeting cancer cells with reactive oxygen species (ROS). This combination therapy incorporates ROS generated by 1) nonthermal plasma (NTP) that emits a multitude of ROS and 2) SR-4233 (TPZ) that undergoes a chemical change to become a ROS only in conditions of hypoxia. The results show an additive to synergistic effect of the combination therapy as compared to each agent individually. Since gap junctions promote the intercellular communication of small molecules up to 1 kDa, we assessed the effect of this combination therapy on metastatic melanoma with functional and nonfunctional gap junctions. We utilized 1205Lu metastatic melanoma cells expressing an empty vector, overexpressing a wild-type Cx43, or a dominant negative variant. The results demonstrated that NTP induced a highly localized cell death in the target area whereas TPZ partially reduced viability over the total surface area. However, when the combination of NTP/TPZ therapy was delivered, complete cell death was observed across the entire plate, specifically in the cells expressing high gap junctions. Similarly, in vivo studies of human metastatic melanoma in a mouse tumor model demonstrated a 90% reduction in tumor volume when treated with the combination of NTP/TPZ in high gap junction expressing tumors. Treatment with NTP/TPZ increased expression of genes activated by apoptosis and oxidative stress while decreasing genes related to cell migration. Microarray analysis also demonstrated a high induction of interleukins and cytokines, indicative of the potential for an immune response. In addition, the transcription factor, HIF1α, known to promote tumor progression, was decreased only under the conditions of NTP/TPZ with high gap junctions. Interestingly, the connexin protein, Cx26, was upregulated following treatment with NTP/TPZ, and the associated gap junctions were shown to maintain functionality during the onset of treatment. Therefore, we conclude that gap junctions both increase the efficacy of NTP/TPZ and are induced by the therapy, thus promoting a positive feedback mechanism of tumoricidal activity. Our unique approach to ROS induction in melanoma cells with NTP/TPZ shows preclinical efficacy, suggesting potential as a novel cancer treatment.
Citation Format: Archis Bagati, Zethan Koch, Timothy C. Hutcherson, Joseph Pechette, Hossein Dianat, Cory Higley, Lisa Chiu, Yesul Song, Jay Shah, Elana Chazen, Andrew Nicolais, Peter Casey, Kyle Thompson, Mikhail A. Nikiforov, Jennifer Zirnheld, Shoshanna N. Zucker. A novel combination therapy for metastatic melanoma potentiates a gap junction positive feedback mechanism [abstract]. In: Proceedings of the AACR Special Conference on Melanoma: From Biology to Target; 2019 Jan 15-18; Houston, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(19 Suppl):Abstract nr B32.