Purpose: How colorectal cancer develops resistance to gamma-radiation is not fully understood, but the transcription factor nuclear factor-kappaB (NF-kappaB) and NF-kappaB-regulated gene products have been proposed as mediators. Because curcumin, a component of turmeric (Curcuma longa), has been shown to suppress NF-kappaB activation, whether it can sensitize the colorectal cancer to gamma-radiation was investigated in colorectal cancer xenografts in nude mice.
Experimental design: We established HCT 116 xenograft in nude mice, randomized into four groups, and treated with vehicle (corn oil), curcumin, gamma-radiation, and curcumin in combination with gamma-radiation. NF-kappaB modulation was ascertained using electrophoretic mobility shift assay and immunohistochemistry. Markers of proliferation, angiogenesis, and invasion were monitored by immunohistochemistry and Western blot analysis.
Results: Curcumin significantly enhanced the efficacy of fractionated radiation therapy by prolonging the time to tumor regrowth (P=0.02) and by reducing the Ki-67 proliferation index (P<0. 001). Moreover, curcumin suppressed NF-kappaB activity and the expression of NF-kappaB-regulated gene products (cyclin D1, c-myc, Bcl-2, Bcl-xL, cellular inhibitor of apoptosis protein-1, cyclooxygenase-2, matrix metalloproteinase-9, and vascular endothelial growth factor), many of which were induced by radiation therapy and mediate radioresistance. The combination of curcumin and radiation therapy also suppressed angiogenesis, as indicated by a decrease in vascular endothelial growth factor and microvessel density (P=0.002 versus radiation alone).
Conclusion: Collectively, our results suggest that curcumin potentiates the antitumor effects of radiation therapy in colorectal cancer by suppressing NF-kappaB and NF-kappaB-regulated gene products, leading to inhibition of proliferation and angiogenesis.