# Opposing Calcium-Dependent Effects of GsMTx4 in Acute Lymphoblastic Leukemia: In Vitro Proliferation vs. In Vivo Survival Advantage

## TL;DR

GsMTx4 affects calcium levels in leukemia cells differently in lab tests and living mice, suggesting calcium signaling could be a new target for leukemia treatment.

## Contribution

The study reveals opposing effects of GsMTx4 on calcium signaling and leukemia progression in vitro versus in vivo.

## Key findings

- GsMTx4 increases calcium levels and promotes leukemia cell proliferation in vitro.
- GsMTx4 reduces cytosolic calcium and extends survival in leukemia mice models.
- Calcium signaling is identified as a key vulnerability in leukemia progression.

## Abstract

Mechanogated (MG) ion channels play a crucial role in mechano-transduction and immune cell regulation, yet their impact on blood cancers, particularly acute lymphoblastic leukemia (ALL), remains poorly understood. This study investigates the pharmacological effects of GsMTx4, an MG channel inhibitor, in human ALL cells both in vitro and in vivo. Unexpectedly, we found that GsMTx4 remarkably increased basal calcium (Ca2+) levels in ALL cells through constitutive Ca2+ entry and enhanced store-operated Ca2⁺ influx upon thapsigargin stimulation. This increase in basal Ca2+ signaling promoted ALL cell viability and proliferation in vitro. Notably, chelating intracellular Ca2+ with BAPTA-AM reduces GsMTx4-mediated leukemia cell viability and proliferation. However, in vivo, GsMTx4 decreases cytosolic Ca2+ levels in Nalm-6 GFP⁺ cells isolated from mouse blood, effectively countering leukemia progression and significantly extending survival in NSG mice transplanted with leukemia cells (median survival: GsMTx4 vs. control, 37.5 days vs. 29 days, p = 0.0414). Our results highlight the different properties of GsMTx4 activity in in vitro and in vivo models. They also emphasize that Ca2+ signaling is a key vulnerability in leukemia, where its precise modulation dictates disease progression. Thus, targeting Ca2+ channels could offer a novel therapeutic strategy for leukemia by exploiting Ca2+ homeostasis.