Repurposed Biguanide Drugs in Glioblastoma Exert Antiproliferative Effects via the Inhibition of Intracellular Chloride Channel 1 Activity

Abstract

The lack of in-depth knowledge about the molecular determinants of glioblastoma (GBM) occurrence and progression, combined with few effective and BBB crossing-targeted compounds represents a major challenge for the discovery of novel and efficacious drugs for GBM. Among relevant molecular factors controlling the aggressive behavior of GBM, chloride intracellular channel 1 (CLIC1) represents an emerging prognostic and predictive biomarker, as well as a promising therapeutic target. CLIC1 is a metamorphic protein, co-existing as both soluble cytoplasmic and membrane-associated conformers, with the latter acting as chloride selective ion channel. CLIC1 is involved in several physiological cell functions and its abnormal expression triggers tumor development, favoring tumor cell proliferation, invasion, and metastasis. CLIC1 overexpression is associated with aggressive features of various human solid tumors, including GBM, in which its expression level is correlated with poor prognosis. Moreover, increasing evidence shows that modification of microglia ion channel activity, and CLIC1 in particular, contributes to the development of different neuropathological states and brain tumors. Intriguingly, CLIC1 is constitutively active within cancer stem cells (CSCs), while it seems less relevant for the survival of non-CSC GBM subpopulations and for normal cells. CSCs represent GBM development and progression driving force, being endowed with stem cell-like properties (self-renewal and differentiation), ability to survive therapies, to expand and differentiate, causing tumor recurrence. Downregulation of CLIC1 results in drastic inhibition of GBM CSC proliferation in vitro and in vivo, making the control of the activity this of channel a possible innovative pharmacological target. Recently, drugs belonging to the biguanide class (including metformin) were reported to selectively inhibit CLIC1 activity in CSCs, impairing their viability and invasiveness, but sparing normal stem cells, thus representing potential novel antitumor drugs with a safe toxicological profile. On these premises, we review the most recent insights into the biological role of CLIC1 as a potential selective pharmacological target in GBM. Moreover, we examine old and new drugs able to functionally target CLIC1 activity, discussing the challenges and potential development of CLIC1-targeted therapies.

Intracellular Chloride Channels: Novel Biomarkers in Diseases

“…In an independent study, CLIC1 partially decreased the antineoplastic effects of metformin and upregulation of CLIC1 increased drug sensitivity ; this again proves CLIC1 can be a therapeutic target for various tumors. A recent study also showed that several drugs of biguanidine class, including metformin, act via CLIC1 (Barbieri et al, 2019). Metformin is presented as a wonder drug in several pathological conditions such as diabetes, and if CLIC1 directly interacts with metformin, it could possibly provide the "elusive" mechanism of action for the drug.…”

Ion Channels as Therapeutic Targets in High Grade Gliomas

“… NaV1.1 and NaV1.6 play role in cytokines release in glial cells [ 50 , 51 ] TRPM3 GBM cell lines High expression of TRPM3 linked to decreased median survival [ 50 , 52 ] P2RX4 Human glioma High expression of P2RX4 linked to decreased median survival Silencing suppresses glioma cell growth through BDNF/TrkB/ATF4 signaling pathway [ 50 , 53 ] CLCN3 GBM cell lines Reduced expression of CLCN3 inhibits migration of GBM cells CLCN3 suppression can sensitize glioma cells to cisplatin through lysosomal dysfunction [ 54 , 55 ] CLCN6 Human Glioma Down regulated in human glioma, significantly increased risk of death. [ 54 ] CLIC1 Human Glioma GBM cell lines Glioma stem cell CLICL1 is up-regulated in human glioma, conferred poor overall survival CLIC1 silencing reduced proliferative, clonogenic, and tumorigenic capacity of stem/progenitor cells Inhibition of CLIC1 at G1/S transition by metformin is a has an antiproliferative effect in glioblastoma Biguanide inhibition impairs GSC viability, invasiveness, and self-renewal [ 54 , 56 , 57 , 58 ] CLIC4 Human Glioma GBM cell lines Down regulated in human glioma, si...…”

CLIC1 recruits PIP5K1A/C to induce cell-matrix adhesions for tumor metastasis

“…Since CLIC1 is upregulated in many types of human cancers and selectively targeted to the plasma membrane in tumor cells, it can be a promising target for the anticancer treatment of invasion and metastasis. Notably, the CLIC1 gene is highly conserved among tumors with only 2% of patients harboring missense or nonsense mutations, indicating that its role in tumorigenesis is more related to its membrane localization-associated activity than to mutations (45). Gurski et al reported that in renal cell carcinoma, CLIC1 cooperates with integrin v3 and fibronectin to stabilize invadopodia for tumor invasion by regulating myosin light chain kinase (MYLK) (46).…”