Selective antitumor and apoptosis‑inducing effects of the Src inhibitor PP1 in human tongue squamous cell carcinoma cells

Src phosphorylation (activation) is associated with the proliferation and survival of numerous human cancer cells. The role of Src phosphorylation and expression, as well as its pharmacological inhibition by PP1, a Src inhibitor, in the growth of oral squamous cell carcinoma (OSCC), remain unclear. The present study explored whether Src is expressed and phosphorylated in HSC‑3 human oral cancer cells and whether PP1 treatment affects the proliferation of these cells. Src was found to be highly expressed and phosphorylated in HSC‑3 human oral cancer cells. Notably, treatment with PP1 at 10 µM significantly reduced cell proliferation and induced apoptosis, evidenced by DNA fragmentation, caspase‑9 and ‑8 activation, and poly(ADP‑ribose) polymerase cleavage. Mechanistically, PP1 not only inhibited Src phosphorylation but also disrupted a broad network of oncogenic pathways, including EGFR, JAK2, STAT‑3, PKB and ERK‑1/2 in HSC‑3 cells. Furthermore, PP1 induced markers of ER stress and inhibited protein translation, as shown by increased eIF‑2α phosphorylation and decreased S6 phosphorylation. The critical role of Src was confirmed by pharmacological inhibition and further validated when small interfering RNA‑mediated knockdown mimicked the anti‑proliferative effects of PP1. Importantly, these potent anticancer effects were conserved in another OSCC cell line (YD‑10B) and, were validated in vivo, where PP1 suppressed tumor growth in a zebrafish xenograft model. Collectively, these findings suggest that PP1 exerts strong anticancer effects on human oral cancer by simultaneously inhibiting Src activity and disrupting a network of associated oncogenic pathways (EGFR, STAT‑3, PKB and ERK‑1/2).