Targeting Rac1 as a therapeutic vulnerability in T-cell lymphomas

T-cell lymphomas (TCL) are aggressive and heterogeneous neoplasms with limited therapeutic options and poor prognosis, underscoring the need for novel molecular targets. Here, we investigated Rac1, a Rho GTPase that regulates cytoskeletal dynamics, migration, and survival pathways, as a potential therapeutic vulnerability in TCL. Its central role in these tumor-promoting processes suggests that Rac1 inhibition could represent an innovative strategy to limit lymphoma growth and dissemination. We first evaluated the anti-lymphoma activity of the pharmacological Rac1 inhibitor 1A-116 in a panel of TCL cell lines (EL4, CUTLL1, OCI-Ly12, OCI-Ly13.2, HuT78, MJ, Karpas299). Cell viability was assessed by luminescence assay, and apoptosis by caspase-3/7 activity after 48 h of treatment. We found that 1A-116 markedly reduced cell viability in all models (p<0.01), with IC₅₀ values ranging from 20 to 250 µM, and induced a 60-200% increase in caspase activity (p<0.05). Basal Rac1 expression was elevated compared with healthy murine lymph node controls, showing a 30-60% increase across cell lines (p<0.05). Consistently, basal phosphorylated PAK 1-3 levels, an indicator of Rac1 pathway activation, were significantly higher in most lines, except for HuT78 and Karpas299, the most resistant cells to Rac1 inhibition. To further validate the therapeutic potential of Rac1 targeting, we used a syngeneic mouse model bearing subcutaneous EL4 tumors. Daily intraperitoneal injections of 1A-116 (20 mg/kg) for nine consecutive days significantly reduced tumor growth, showing an average 80% reduction in tumor area under the curve (p=0.0071) and a 79% decrease in final tumor volume (p=0.0175), with no overt signs of toxicity. Finally, analysis of three independent TCL RNA-seq datasets (GSE113113, GSE168508, GSE58445) showed that increased expression of Rac1 activators such as VAV1 and TIAM2, and downstream effectors such as PAK2 and GSK3 correlates with advanced disease and poorer survival (p<0.05). In line with these findings, Rac1 immunostaining in 14 TCL biopsies revealed positive expression in all cases, underscoring the clinical relevance of Rac1 signaling in TCL. Together, these results identify Rac1 as a key molecular driver in TCL and establish its pharmacological inhibition as a promising and translationally relevant therapeutic strategy. Our study provides a strong rationale for further evaluation of Rac1 inhibitors, either alone or in combination regimens, to improve treatment outcomes in patients with T-cell lymphomas. Overall, these data identify Rac1 signaling as a promising target that may expand the currently limited treatment landscape for these aggressive malignancies.