Non-thermal plasma induction of preprogrammed cell death in monocytic leukemia cells

The need for new and effective mechanisms to induce programmed cellular death (apoptosis) in cancerous cells is of great importance in cancer research. Application of direct as well as indirect exposure of plasma for cancer research is still in the exploratory stage and there remain several unanswered questions. We have developed a portable non-thermal resistive barrier based air plasma source that can be operated in both direct and indirect exposure modes [1]. We are investigating the effects of indirect exposure of non-thermal air plasma on monocytic leukemia cancer cells (THP-1) and deciphering the mechanisms that modulate cellular induction of apoptosis. The phenotypes of interest were cells demonstrating death morphologies of apoptosis or necrosis. This is important since cells undergoing necrosis can initiate an inflamed immune response that can be detrimental to a treated individual. The type of morphological cell death that occurred in THP-1 for various plasma treatment dosages (plasma power, flow and distance) was investigated and the results will be reported. We were able to demonstrate a preference for apoptosis in plasma treated THP-1 cells under particular plasma parameters and dosage levels. The THP-1 cells were identified as apoptotic utilizing a fluorescent dye conjugated with annexin V followed by identification of the cells through fluorescent microscopy and flow-cytometry diagnostics. Further, DNA fragmentation assays, for late detection of apoptosis, correlated with are fluorescence data demonstrating patterns of apoptotic events. However, the data also revealed that higher plasma dosages presented with undesired necrotic morphologies in the THP-1 cells. The presented variabilities in the death morphologies by plasma treated THP-1 cells signify the need for further investigation on the cellular mechanisms induced by the indirect plasma exposure. Along with taking into account other death processes such as autophagy, a catabolic process involving- the degradation of a cell´s own components through the lysosomal machinery. The results obtained from this research indicate great potential for the use of our portable non-thermal resistive barrier based indirect plasma treatment method as an inexpensive and less invasive method for treating leukemia and other cancerous lesions.