VCOM Research Day Program Book 2023

Graduate Student Research Biomedical

03 Immune Checkpoint and DNA Damage Repair Pathways Mitigate the Effects of Irreversible Electroporation on Pancreatic Cancer

K.M. Imran 1 ; R.M. Brock 1 ; N. Alinezhadbalalami 2 ; K.N. Aycock 2 ; B. Tintera 3 ; H.A. Morrison 3 ; R.V. Davalos 2 ; I.C. Allen 3 Corresponding author: imrankhan@vt.edu

1 Graduate Program in Translational Biology, Medicine and Health, Virginia Tech 2 Department of Biomedical Engineering and Mechanics, Virginia Tech 3 Department of Biomedical Sciences and Pathobiology, VA-MD College of Veterinary Medicine

Pancreatic cancer is one of the deadliest diagnoses leaving patients with few therapeutic options. Traditional (Chemo, radio) and recent targeted immunotherapy are not very effective against pancreatic cancer. Recent research is focusing on non-targeted and combined treatment to improve patient outcome. Irreversible electroporation (IRE), a novel nonthermal ablation system, utilizes very short, high voltage electrical pulses to form micropores in cell membranes and stimulate cell death. IRE has been tested in human clinical trials for pancreatic cancer treatment with a significant improvement in progression-free survival, but not much is understood about the immunomodulatory effects of IRE and the reasons for tumor relapse. We hypothesized that, by investigating the interplay between the host immune system and tumor microenvironment, we could identify a molecular rationale for the tumor recurrence and potential co-therapy targets for IRE treatment. We have utilized Pan02 mouse pancreatic cancer cells, and a subcutaneous flank model of pancreatic cancer. Here, we show that IRE can

significantly delay cancer progression by shifting the tumor microenvironment to a pro-inflammatory state. In doing so, IRE treatment recruits cytotoxic CD8+ T-cells to the tumor sites, reduces contralateral tumor burden, and increases interferon-gamma (IFNg) levels in the serum. IFNg expression indicates activation of antitumor immunity through inflammation but within two weeks after treatment, immune cells in the tumor site reverts to the pre-treatment condition, IFNg expression reduces, tumor cells express programmed cell death-ligand 1 (PD-L1) and as a result tumor relapses. Our in vitro findings of IFNg dependent PD-L1 expression and ineffective in vivo blocking of IFNg hints feedback loop pathway involving IFNg and PD-L1 and indicates that IFNg is important for tumor cell killing but also activates anti-inflammation through initiation of PD-L1 expression. We have also found that IRE causes cell cycle arrest at G0/ G1 phase probably through cell membrane and DNA damage. Of note, DNA damage repair protein DDB1 expression coincides with tumor relapse after IRE

treatment. Our ongoing works are trying to confirm involvement of DDB1 on IRE mediated cell cycle arrest due to DNA damage by using DDB1 knockout cells and DDB1 inhibitors. Our future work would be to improve the effects of IRE by additional combination therapy methods, including PD1/PD L1 antibody immunotherapies, and small molecule inhibitors of DDB1.

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