Inhibition of Galectin-1 impairs cancer growth and reshapes the tumor microenvironment in Cancer of Unknown Primary

Cancer of Unknown Primary (CUP) is a highly aggressive metastatic malignancy associated with poor prognosis and limited therapeutic options, underscoring the urgent need to identify novel actionable therapeutic targets (1). Galectin-1 (Gal-1), a multifunctional β-galactoside-binding lectin, has emerged as a key regulator of tumor progression by promoting immune evasion, angiogenesis, extracellular matrix remodeling, and stromal reprogramming across multiple cancer types (2). However, its functional role and therapeutic potential in CUP remain largely unexplored. To investigate Gal-1 functional role, we employed patient-derived CUP agnospheres xenografted into immunodeficient mice (CUP-PDX), a clinically relevant preclinical model that faithfully recapitulates the molecular and metastatic features of CUP patients (3). Patient-derived melanoma xenografts were analyzed as a reference due to their known high expression of Gal-1. However, RNA sequencing revealed that LGALS1 expression was significantly higher in CUP-PDX than in melanoma models, demonstrating a marked enrichment of Gal-1 in CUP. Pharmacological inhibition of Gal-1 with OTX008 resulted in a dose-dependent suppression of patient-derived agnosphere proliferation in vitro. Notably, systemic administration of OTX008 significantly inhibited tumor growth in CUP-PDX-bearing mice, demonstrating robust antitumor activity in vivo. Mechanistically, Gal-1 blockade induced profound remodelling of the tumor microenvironment. OTX008 treatment markedly reduced the infiltration of immunosuppressive M2-like macrophages while promoting the accumulation of pro-inflammatory M1-like macrophages, indicative of a shift toward an antitumor immune microenvironment. In parallel, Gal-1 inhibition promoted vascular normalization, as evidenced by increased pericyte coverage of tumor blood vessels, and significantly reduced intratumoral hypoxia. Collectively, these findings demonstrate that Gal-1 inhibition exerts multifaceted antitumor effects in CUP by simultaneously targeting tumor cell survival and multiple stromal components of the tumor microenvironment. Our study identifies Gal-1 as a previously unrecognized therapeutic vulnerability in CUP and provides compelling preclinical evidence supporting the evaluation of Gal-1 inhibitors as part of future combination therapeutic strategies aimed at improving clinical outcomes for patients with this highly aggressive disease.