Impact of CYP24A1 overexpression on growth of colorectal tumour xenografts in mice fed with vitamin D and soy.

Julia Höbaus,Samawansha Tennakoon,Enikö Kállay,Doris M Hummel,Rodrig Marculescu,Walter Berger,Charlotte Groeschel,Ursula Thiem,Abhishek Aggarwal,Petra Heffeter

doi:10.1002/ijc.29717

Abstract

Our previous studies showed that the 1,25‐dihydroxyvitamin D (1,25‐D3) catabolizing enzyme, 1,25‐dihydoxyvitamin D 24 hydroxylase (CYP24A1) was overexpressed in colorectal tumours and its level correlated with increased proliferation. We hypothesised that cells overexpressing CYP24A1 have growth advantage and a diet rich in vitamin D and soy would restore sensitivity to the anti‐tumourigenic effects of vitamin D. Soy contains genistein, a natural CYP24A1 inhibitor. To determine causality between CYP24A1 and tumour growth, we established xenografts in male SCID mice with HT29 cells stably overexpressing either GFP‐tagged CYP24A1 or GFP. Mice were fed with either high (2500 IU D3/kg) or low vitamin D (100 IU D3/kg) diet in the presence or absence of soy (20% diet). In vitro, cells overexpressing CYP24A1 grew faster than controls. 1,25‐D3, the active vitamin D metabolite, reduced cell number only in the presence of the CYP24A1 inhibitor VID400. Regardless of the amount of vitamin D in the diet, xenografts overexpressing CYP24A1 grew faster, were heavier and more aggressive. Soy reduced tumour volume only in the control xenografts, while the tumours overexpressing CYP24A1 were larger in the presence of dietary soy. In conclusion, we demonstrate that CYP24A1 overexpression results in increased aggressiveness and proliferative potential of colorectal tumours. Irrespective of the dietary vitamin D3, dietary soy is able to increase tumour volume when tumours overexpress CYP24A1, suggesting that combination of vitamin D3 and soy could have an anti‐tumourigenic effect only if CYP24A1 levels are normal.

Highlights

The prohormone vitamin D3 is biologically inert and requires two hydroxylation steps in the liver and kidney to form the physiologically active 1,25-dihydroxyvitamin D3 (1,25-hydroxyvitamin D3 (25-D3))
HT29 cells are characterized by low basal expression of CYP24A1, which is highly inducible upon treatment with 1,25-D3
On mRNA level, basal expression of CYP24A1 was very low in HT29CYP24A1-GFP cells to control levels (HT29GFP) cells and the parental cell line HT29, while it was significantly higher in the CYP24A1-GFPtransfected cells (Figs. 1a and 1b)

Summary

Introduction

The prohormone vitamin D3 is biologically inert and requires two hydroxylation steps in the liver and kidney to form the physiologically active 1,25-dihydroxyvitamin D3 (1,25-D3).. Vitamin D3 supplementation is linked to reduced tumour growth in the colon, but colorectal tumours may overexpress the vitamin-D-degrading enzyme CYP24A1, potentially undermining the benefits of vitamin D intake. We show that in a mouse xenograft model, CYP24A1 overexpression confers growth advantage to colorectal tumours, regardless of vitamin D intake. Combination of dietary vitamin D and soy increases volume and weight of tumours overexpressing CYP24A1. The findings warrant exploration of the effects of specific CYP24A1 inhibitors in CYP24A1-overexpressing colorectal tumours. Colonocytes express the vitamin D receptor (VDR), the vitamin D-metabolizing enzyme CYP27B1 as well as the vitamin D-degrading enzyme, 1,25-dihyroxyvitamin D-24 hydroxylase (CYP24A 1).[5,6] The latter is an inner mitochondrial membrane enzyme[7] and is a 1,25-D3 target gene. Its expression is rapidly increased in the presence of 1,25-D3.8

Methods

Results

Conclusion