İlknur Keskin, Begüm Şahin, Aziz Bülbül, Mustafa Çakır, Mervenur Yavuz, Muhammet Volkan Bülbül, Turan Demircan
Colon cancer remains a leading cause of cancer-related deaths, and drug repurposing offers a promising strategy to identify new therapies. Hydroquinidine (HQ), a class I antiarrhythmic agent, has recently been suggested to possess anticancer properties; however, its preclinical safety and efficacy in colorectal cancer are not well defined. The safety of HQ was evaluated in Wistar rats following OECD guidelines. Rats received daily intraperitoneal doses (2.5-25 mg/kg) for 90 days, with hematological, biochemical, and histopathological assessments performed. HQ was well tolerated up to 12.5 mg/kg, whereas 25 mg/kg caused signs of hepatotoxicity without lethality. A 1,2-dimethylhydrazine-induced colorectal cancer model was then used to assess HQ at safe doses (6.25 and 12.5 mg/kg) compared with cisplatin. Tissue histopathology and selected molecular markers associated with inflammation, apoptosis, epithelial-mesenchymal transition, and PI3K/AKT/mTOR pathway activity were analyzed. In the DMH-induced colon cancer model, HQ improved colonic tissue architecture and was associated with lower histopathological scores compared with untreated tumor controls. HQ also modulated tumor-associated markers by reducing IL-6 immunoreactivity, increasing caspase-3 expression, enhancing E-cadherin immunoreactivity, and decreasing vimentin expression. Moreover, HQ was associated with reduced immunoreactivity of mTOR pathway-related markers, suggesting attenuation of pathway activation in this experimental context. Overall, HQ showed an acceptable safety profile at the selected doses and exerted favorable histopathological and molecular modulatory effects, supporting further investigation as a potential repurposing candidate.