Vitamin D3 enhances the tumouricidal effects of 5-Fluorouracil through multipathway mechanisms in azoxymethane rat model of colon cancer

Background: vitamin d3 and its analogues have recently been shown to enhance the anti-tumour effects of 5-fluorouracil (5-fu) both in vitro and in xenograft mouse model of colon cancer. this study measured the potential mechanism(s) by which vitamin d3 could synergise the tumouricidal activities of 5-fu in azoxymethane (aom) rat model of colon cancer. methods: seventy-five male wistar rats were divided equally into 5 groups: control,aom,aom-treated by 5-fu (5-fu),aom-treated by vitamin d3 (vitd3),and aom-treated by 5-fu∈+∈vitamin d3 (5-fu/d). the study duration was 15 weeks. aom was injected subcutaneously for 2 weeks (15 mg/kg/week). 5-fu was injected intraperitoneally in the 9th and 10th weeks post aom (8 total injections were given: 12 mg/kg/day for 4 successive days,then 6 mg/kg every other day for another 4 doses) and oral vitamin d3 (500 iu/rat/day; 3 days/week) was given from week 7 post aom till the last week of the study. the colons were collected following euthanasia for gross and histopathological examination. the expression of β-catenin,transforming growth factor-β1 (tgf-β1),tgf-β type 2 receptor (tgf-βr2),smad4,inducible nitric oxide synthase (inos),and heat shock protein-90 (hsp-90) proteins was measured by immunohistochemistry. in colonic tissue homogenates,quantitative rt-pcr was used to measure the mrna expression of wnt,β-catenin,dickkopf-1 (dkk-1) and cyclooxygenase-2 (cox-2) genes,while elisa was used to measure the concentrations of tgf-β1,hsp-90 and cox-2 proteins. results: monotherapy with 5-fu or vitamin d3 significantly decreased the number of grown tumours induced by aom (p∈<∈0.05); however,their combination resulted in more significant tumouricidal effects (p∈<∈0.05) compared with monotherapy groups. mechanistically,vitamin d3/5-fu co-therapy significantly decreased the expression of wnt,β-catenin,inos,cox-2 and hsp-90 and significantly increased the expression of dkk-1,tgf-β1,tgf-βr2,smad4 (p∈<∈0.05),in comparison with their corresponding monotherapy groups. conclusions: vitamin d3 and 5-fu synergise together and exhibit better anticancer effects by modulating wnt/β-catenin pathway,tgf-β1 signals,inos,cox-2 and hsp-90. further studies are required to illustrate the clinical value of vitamin d supplementation during the treatment of colon cancer with 5-fu in human patients. © 2015 refaat et al. this is an open access article distributed under the terms of the creative commons attribution license.