Abstract B18: Non-thermal plasma, tirapazamine, and gap junctions: A novel approach to melanoma therapy through ROS induction

Abstract

Abstract Melanoma cells typically have high levels of superoxide anion which may increase their susceptibility to cell death by reactive oxygen species (ROS). We have used this information to establish a system whereby melanoma cells are saturated with ROS through treatment with non-thermal plasma (NTP). NTP is formed from a mixture of highly charged helium and atmospheric gases to emit a total of 45 molecular species, many of which are ROS. We have recently demonstrated that NTP causes selective apoptotic cell death of melanoma cells as compared to normal skin keratinocytes when plated in co-culture. Since tumors flourish under low oxygen (hypoxic) conditions, we tested the effects of NTP under hypoxia. In order to enhance the effects of NTP, we combined this therapy with the experimental anticancer drug, tirapazamine, which promotes cell toxicity through DNA damage only under hypoxic conditions. The question then remains as to how to increase the target area of melanoma therapy. Our previous studies have demonstrated that gap junctions act via the bystander effect to enable the passage of cell-death promoting signals by NTP. We utilized stably transfected 1205Lu metastatic melanoma cells that express three different levels of gap junctions: endogenous low levels, increased levels through expression of connexin 43, or an absence of gap junctions due to expression of a dominant negative mutant connexin 43. We have shown that the cells with the mutant connexin 43 showed increased invasive potential as well as enhanced expression of HIF1α. The combination therapy with NTP and tirapazamine under hypoxic conditions caused a synergistic effect which increased cell death in all cells, yet was most apparent in the 1205Lu cells overexpressing the functional gap junctions. In addition, the target area of the NTP torch was dramatically increased under these conditions. This suggests that the ROS generated by NTP and tirapazamine induced the bystander effect and promoted the spreading of cell death signals well beyond the area of the plasma treatment. These results are indicative a novel future approach to melanoma therapy through selective ROS induction and modification of gap junction phenotype. Citation Format: Shoshanna N. Zucker, Cory Higley, Zethan Koch, Haneesha Goli, Peter Casey, Akeem Francis, Kevin Burke, Jennifer Zirnheld. Non-thermal plasma, tirapazamine, and gap junctions: A novel approach to melanoma therapy through ROS induction. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Melanoma: From Biology to Therapy; Sep 20-23, 2014; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(14 Suppl):Abstract nr B18.