Abstract 6715: CLIC1 and CLIC4 ion channels as bioelectric targets for tumor treating fields in pediatric high-grade glioma
Authors: Griffin Michaela , Smith Paul , Khan Raheela , Basu Surajit , Smith Stuart James 
Published: April 2023

Background: High Grade Glioma is a lethal brain cancer with an average survival of 14 months. Due to the scarcity of effective treatment, and aggressive nature of the tumor, pediatric High Grade Glioma (pHGG) forms a leading cause of CNS cancer-related death in children. Optune™ is a non-invasive therapy that uses alternating electric fields - coined Tumor Treating Fields (TTFields) - to disrupt cancer cell division. Increasing evidence shows that ion channels not only regulate electrical signaling of excitable cells, but also play a crucial role in the development and progression of brain tumors. Ion channels are essential in cell cycle control, invasion and migration of cancer cells and therefore present as valuable therapeutic targets.

Methods: CLIC channel expression patterns were identified via multivariate analysis of in-house and publicly available data sets and RNA sequencing of in-house patient tissues. siRNA depletion of CLIC1 and CLIC4 was assessed using cell cycle, clonogenic, migration and proliferation assays, alone and concomitant with TTFields and or CLIC channel inhibitors, IAA94 or metformin. Whole transcriptome gene expression analysis (Human Clariom™ Array) of pHGG cells treated with TTFields was carried out. Whole cell and cell attached patch clamp protocols were used to assess ion channel activity in pHGG and normal astrocytes.

Results: Clinical correlation determined that CLIC4 and CLIC1 deficiency was associated with increased overall survival (p=&lt;0.03), with siRNA depletion propagating a reduction in the proliferation, migration and invasion of pHGG cell lines associated with cell cycle arrest. Furthermore, CLIC1 and CLIC4 deficiency exacerbated the killing capacity of TTFields, reducing clonogenic and proliferative capabilities. Concomitant application of either IAA94 or metformin, and TTFields increased the sensitivity of cells to TTFields. Whole transcriptome gene expression analysis of pHGG cell lines treated with TTFields and found that cells treated with TTFields exhibited a down-regulation in CLIC1 and CLIC4 compared to untreated cells. Furthermore, neurophysiological patch clamp experiments revealed increasingly depolarized membrane potential readings in pHGG cell lines compared to normal astrocytes, with unique ion channel activity (including chloride channel function) observed and the potential for further pharmacological exploitation.

Conclusions: These data provide rationale that genetic, electrical, and pharmacological manipulation of ion channels can reduce the capacity of childhood brain tumors to proliferate and invade. CLIC channels may be a suitable target to enhance the treatment efficacy of TTFields and help optimize this non-invasive therapy in pediatric HGG patients.

Citation Format: Michaela Griffin, Paul Smith, Raheela Khan, Surajit Basu, Stuart James Smith. CLIC1 and CLIC4 ion channels as bioelectric targets for tumor treating fields in pediatric high-grade glioma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 6715.