Treatment of metastatic colorectal cancer : A role for Curcumin?

Colorectal cancer remains the third largest cause of mortality from cancer related death, with approximately 90% of these deaths attributed to metastatic spread of the disease. There is a need to improve chemotherapy, with the dietary polyphenol curcumin, derived from turmeric, representing a potential candidate as it possess very few side effects and it has shown efficacy in mouse models. Recent advances in our understanding of tumour development have highlighted the existence of tumour initiating cells (TIC), which possess clonogenic potential, are essential for tumour growth, and represent an important therapeutic target. This study sought to determine whether curcumin in combination with oxaliplatin+5-Fluorouracil (OX+5-FU) represented a better combination for targeting TICs, using a variety of models consisting of cells derived directly from colorectal liver metastasis (CRLM). ALDHHigh activity, CD133 and CD26 were all found to mark a spheroid forming population, a method that tests for clonogenicity and selects for TICs. Curcumin significantly reduced the number of spheroids compared to DMSO, and enhanced efficacy of OX+5-FU. The only marker to decrease after treatment was ALDHHigh activity, which was also positively associated with spheroid growth. CD26 expressing cells were identified as a possible chemo-resistant population, however, this population remained unaffected by curcumin. Ex vivo analysis using explant cultures demonstrated that curcumin could significantly decrease ki67 and increase cleaved capase-3 expression, notably enhancing the effects of oxaliplatin in a proportion of patients. A pilot study was undertaken using non-obese diabetic/severe combined immunodeficient (NOD-SCID) mice to reflect a clinical regimen, and assess in vivo whether curcumin could enhance efficacy of OX+5-FU, but the results advocate the use of higher doses as little effect was seen. Overall this body of work contributes to knowledge on propagating CRLM TICs, their expression of known TIC markers, and response to curcumin.