Irisin Potentiates 5-fluorouracil Cytotoxicity in HT-29 Colon Cancer Cells through Enhanced Apoptosis and Transcriptional Modulation of Adenosine Monophosphate-activated Protein Kinase/Mammalian Target of Rapamycin Signaling.

Background: Although 5-fluorouracil (5-FU) is a standard chemotherapeutic agent for colorectal cancer (CRC), its efficacy is often limited by chemoresistance. Irisin, an exercise-induced myokine, has demonstrated anticancer potential; however, its role in CRC remains incompletely defined. Materials and Methods: Human HT-29 CRC cells were treated for 12 h with irisin (2, 20, and 200 ng/mL) alone or combined with 5-FU (50 μM). Cell cycle progression and apoptosis were assessed by flow cytometry. Expression of cell cycle regulators (CCND1, CCND3, p21, and p27), apoptotic markers (BCL2, Bcl-2-associated X protein, cytochrome c, caspase-8, caspase-9, and caspase-3), and metabolic mediators (protein kinase B [Akt], mammalian target of rapamycin [mTOR], adenosine monophosphate-activated protein kinase [AMPK], and phosphatase and tensin homolog [PTEN]) was analyzed by quantitative reverse transcription-polymerase chain reaction. Results: While 5-FU induced G0/G1 arrest with p21/p27 upregulation, irisin alone or in combination exerted minimal additional effects on cell cycle progression. In contrast, high-dose irisin (200 ng/mL) significantly increased apoptotic cell fractions and upregulated caspase-8 and caspase-3 without significant alteration of mitochondrial apoptotic gene expression. Combination treatment further enhanced apoptosis. Co-treatment also increased AMPK and PTEN mRNA levels while reducing Akt and mTOR mRNA levels. Conclusion: Under the experimental conditions used, irisin potentiated 5-FU cytotoxicity in HT-29 CRC cells primarily through enhanced apoptosis and transcriptional modulation of metabolic signaling components. These findings suggest a potential chemosensitizing role for irisin, warranting further validation at the protein and functional levels.