Combined treatment of colorectal cancer cell lines with aspirin and bortezomib
14562 Background: The ubiquitin-Proteasome system (UPS) has emerged as an important proteolytic system for the regulation of a wide range of cellular functions. Key determinants of carcinogenesis, are regulated in multiple levels by UPS. Proteasome inhibition by the boronic containing molecule bortezomib is already in use for the treatment of multiple myeloma and is in various phases of investigation for other malignancies. Cox inhibitors such as NSAIDs have been shown to inhibit the growth of colorectal cancer cells in vitro and polyp formation in vivo. Methods: HT-29 and HCT116 colorectal cancer cell lines were treated with aspirin (ASA), bortezomib and their combination. MTT assay was used to evaluate the effect of treatment on cell proliferation compared to controls. Cox activity and proteasome activity were measured with colorimetric methods. The effect of drug treatments on specific proteins expression was assayed by western blotting. Results: Both cell lines are inhibited by ASA and bortezomib and their proliferation is further inhibited by the combination of the two drugs. In HT-29 cells both ASA and bortezomib inhibit proteasome and their combination has additive effect in this inhibition. In contrast in HCT116 cells ASA-mediated inhibition is accompanied by increased proteasome activity while bortezomib-mediated growth inhibition is accompanied as expected by proteasome inhibition. ASA-mediated inhibition is not Cox-mediated since no Cox activity was detected in either cell line. Cell cycle inhibitor p27 expression is induced in HCT116 cells by bortezomib while ASA fails to do so. In HT29 cells p27 is expressed at baseline and does not change significantly by treatments. Conclusion: The combination of ASA and bortezomib inhibited the proliferation of both cell lines more than either drug alone in a Cox-independent way. ASA had opposite effects on proteasome activity in the two lines. p27 induction may mediate at least partially the anti-proliferative effect of bortezomib in HCT116 cells. Further studies are in progress to determine other molecular components of the cellular processes taking place during treatment by the combination of these drugs in order to better understand their mechanism of action and thus explore their potential therapeutic use. No significant financial relationships to disclose.