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Highlights • During PDAC development CYP24A1 levels are reduced in the endocrine islets. • During malignant transformation pancreatic ducts accumulate CYP24A1 protein. • CYP24A1 expression correlates with VDR in CP patients, but not in PDAC patients. • CYP24A1 overexpressing tumors are highly proliferative. • CaSR and VDR are co-expressed in the endocrine cells of the islets., The vitamin D system is deregulated during development and progression of several cancer types. Data on the expression of the vitamin D system in the diseased pancreas are missing. The aim of this study was to investigate the expression of the vitamin D receptor (VDR), 1,25-dihydroxyvitamin D3 24-hydroxylase (CYP24A1), and the calcium-sensing receptor (CaSR), a vitamin D target gene, in the different regions of the pancreas in patients with chronic pancreatitis (n = 6) and pancreatic ductal adenocarcinomas (PDAC) (n = 17). We analyzed the expression of these genes at mRNA and protein level with quantitative real-time RT-PCR and immunostaining. mRNA expression of CYP24A1 and VDR was significantly increased in tumors compared with the adjacent non-tumorous tissue (p

Highlights ► Comparative oncological trials could speed up the development of novel therapies. ► Modeling revealed that human and canine ErbB-1 and ErbB-2 molecules are highly conserved. ► The canine ErbB molecules harbour epitopes for cetuximab and trastuzumab antibodies and indeed transmitted growth inhibitory signals. ► This knowledge opens up perspectives for comparative immunotherapy trials with canine cancer patients., To facilitate comparative oncology trials we compared the biological and molecular homologies of canine (dog; Canis lupus familiaris) and human tumor-associated antigens ErbB-1 and -2. Further, we investigated whether they could serve as targets for anti-ErbB-1 (cetuximab) and anti-ErbB-2 antibodies (trastuzumab), which are highly relevant in human clinical oncology. Immunohistochemistry of canine mammary cancer showed ErbB-1 overexpression in 3/10 patients and ErbB-2 in 4/10. We report 91% amino acid homology for ErbB-1 and 92% for ErbB-2 between canine and human molecules. Modeling of canine on human ErbB-1 revealed that the cetuximab epitope only differs by 4 amino acids: Lys443 is replaced by Arg, Ser468 by Asn, Gly471 by Asp, and Asn473 by Lys in canines. The trastuzumab binding site is identical in human and canine ErbB-2 apart from a single amino acid change (Pro557 to Ser). Binding of cetuximab and trastuzumab to canine mammary carcinoma cells CF33, CF41, Sh1b and P114 was confirmed by flow cytometry. Both antibodies significantly inhibited canine tumor cell proliferation partly due to growth arrest in G0/G1 phase. We explain the lower efficiency on the tested canine than on human SKBR3 and A431 cells, by a 2-log lower expression level of the canine ErbB-1 and -2 molecules. Our results indicate significant homology of human and canine Erb-1 and -2 tumor associated antigens. The fact that the canine homologues express the cetuximab and trastuzumab epitopes may facilitate antibody-based immunotherapy in dogs. Importantly, the striking similarities of ErbB-1 and -2 molecules open up avenues towards comparative strategies for targeted drug development.

Sporadic colorectal cancer develops as a multistep process during decades of latency. Multiple factors, in particular nutrition, influence progression. Both nutritional calcium and soy are known to reduce sporadic cancer incidence. Soy contains high levels of phytoestrogens. Among them genistein is recognized as an antioxidant and cell-cycle inhibitor. However, timing and length of consumption of genistein as well as gender- and colon site‐specific activity may result in beneficial or detrimental effects. We therefore evaluated the effect in mice of a basic AIN76A diet containing 20% soy as main protein source fed for 1 or 2 generations. In another set of animals, normal calcium levels (0.5%) were replaced by low calcium (0.04%) with or without supplementation of genistein (0.04%). Expression of the vitamin D receptor, cyclooxygenase (COX)-2, proapoptotic Bak and antiapoptotic Bcl-2 protein, as well as estrogen receptor (ER)-a and ER-b mRNA were evaluated. Results were identical whether soy was fed for 1 or 2 generations. Soy decreased Bak and increased COX-2 and ER-a expression site-specifically in female mice. Vitamin D receptor protein was reduced only in males. In animals fed 0.04% dietary calcium, COX-2 protein was increased mainly in females, but supplementation of genistein to the diet lowered COX-2 expression significantly in both genders. Our results suggest that genistein counteracts the induction of a marker of colonic premalignancy by low nutritional calcium in both genders. However, soy itself enhances COX-2 and reduces Bak, but only in females. This suggests detrimental activity of an unknown component of soy triggered by a high-estrogen background. J. Nutr. 137: 211S‐215S, 2007.

Dendritic cells (DCs) are sentinels of the immune system for antigen recognition and uptake, as well as presentation to naïve T cells for stimulation or priming. Internalization and endocytic degradation of allergens by DCs are important steps required for T cell priming. In the current study we investigated binding and internalization of purified recombinant non-glycosylated grass pollen allergen, Phl p 5, and natural non-specific lipid transfer protein from sunflower, SF-nsLTP to human monocyte derived dendritic cells (MoDCs). Colocalization of Phl p 5 with low affinity (CD23) or high affinity receptor (FcεRI) was investigated by immunofluorescence staining. Likewise, localization of the allergens in early (EE) and late endosomes (LE) was detected by co-staining for early endosome antigen (EEA1) and lysosomal-associated membrane protein 1 (LAMP1). In our experimental setting we could demonstrate that Phl p 5 as well as SF-nsLTP bound to MoDCs from both, grass pollen allergic and non-allergic individuals. Competitive allergen uptake experiments demonstrated non-preferential and simultaneous uptake of Phl p 5 and SF-nsLTP by MoDCs. No overlap of signals from Phl p 5 and CD23 or FcεRI was detectable, excluding IgE-mediated uptake for this allergen. Both allergens, Phl p 5 and SF-nsLTP, were localized in early and late endosomes. The present study applied a set of methods to assess the allergen uptake by MoDCs in an in vitro model. No qualitative and quantitative differences in the allergen uptake of both, Phl p 5 and SF-nsLTP were detected in single and competitive assays.

The antimitotic, prodifferentiating, and proapoptotic steroid hormone, 1alpha,25-dihydroxyvitamin D(3) [1alpha,25-(OH)(2)D(3)], at supraphysiological levels has potential for tumor therapy. However, epithelial cells from tumor-prone organs such as colon, prostate, and breast express not only the vitamin D receptor, but also vitamin D hydroxylases. In contrast to normal cells, malignant cells have high basal levels of the hydroxylase 25-hydroxyvitamin D(3)-24-hydroxylase (CYP24) and, in addition, have the potential to induce CYP24 in response to 1alpha,25-(OH)(2)D(3). Because 24-hydroxylation by CYP24 would rapidly degrade the steroid hormone in the course of therapy, the enzyme activity in tumor cells should be inhibited. We demonstrate that a 24-phenylsulfone analog of 1alpha,25-(OH)(2)D(3), KRC-24SO(2)Ph-1 (S-4a), rapidly and potently inhibits 24-hydroxylase activity in human tumor cells derived from colon, prostate, and mammary gland. Although enzymatic inhibition is a consequence of direct interaction, S-4a as a vitamin D analog apparently binds to the vitamin D receptor and induces CYP24 mRNA, which, however, is not translated into increased enzymatic activity. 25-Hydroxyvitamin D(3)-1alpha-hydroxylase expression is not affected at all by S-4a. When both 1alpha,25-(OH)(2)D(3) and S-4a are added to the cell culture, transcription of CYP24 is increased, possibly because of an increase in the half-life of the hormone. The colon cell line COGA-13 has very high levels of CYP24 and is, therefore, resistant to the action of vitamin D. Yet, S-4a imparts antimitotic activity to 1alpha,25-(OH)(2)D(3) and may therefore constitute a therapeutic to stimulate the antiproliferative potential of vitamin D-based antitumor activity.

Unimpaired vitamin D action has been implicated in human cancer prevention. We have previously demonstrated the effectiveness of 1 alpha-dihydroxyvitamin D3 (1,25-D3) to reduce proliferation and increase differentiation in human colon cancer cells. The aim of this study was to investigate, on the one hand, expression of the vitamin D receptor (VDR) and of 25-hydroxyvitamin D(3)-1 alpha-hydroxylase (1 alpha-hydroxylase) in human normal and malignant colonic tissue and, on the other hand, to determine consequences of reduced or lacking VDR action in a VDR knockout mouse model. In low-grade malignancies of the human colon we found increased VDR and 1 alpha-hydroxylase mRNA expression. However, in late-stage high-grade tumors the vitamin D system is severely compromised. In the mouse colon we found an inverse relationship between VDR levels and proliferation in colon descendens, a tissue known to be specifically affected by nutrients during carcinogenesis. Expression of 8-hydroxy-2'-deoxyguanosine (8-OHdG), a marker of oxidative DNA damage, was significantly augmented with complete loss of VDR. These data suggest that genomic 1,25-D(3) action is necessary to protect against nutrition-linked hyperproliferation and oxidative DNA damage.

We studied the possible regulatory effects of 1α,25-dihydroxyvitamin D3 [1α,25-(OH)2D3] on cytokine production and differentiation of subsets of CD4+ [T helper 1 (Th1) and Th2] and CD8+ [T cytotoxic 1 (Tc1) and Tc2] lymphocytes at the single cell level. PBMC from healthy donors were cultured with or without 1α,25-(OH)2D3 for up to 21 days. On days 0, 7, 14, and 21, the percentage of cytokine-producing T lymphocytes was analyzed by intracellular cytokine detection with mAb and flow cytometry. Simultaneous staining for cell surface markers allowed discrimination of CD4+ and CD8+ T cell subsets. After culture with 1α,25-(OH)2D3 (10−8 mol/L), no significant effects on the proportion of interferon-γ (IFNγ)- or interleukin-4 (IL-4)-producing cells were detected, whereas reduced frequencies of IL-2-producing cells in the CD4+ as well as in the CD8+ population were found. An increase in the low percentage of CD4+ and CD8+ T cells producing the Th2 cytokine IL-13 was noticed. Most interestingly, IL-6-producing CD4...

The extragonadal synthesis of biological active steroid hormones from their inactive precursors in target tissues is named “intracrinology.” Of particular importance for the progression of estrogen-dependent cancers is the in situ formation of the biological most active estrogen, 17beta-estradiol (E2). In cancer cells, conversion of inactive steroid hormone precursors to E2 is accomplished from inactive, sulfated estrogens in the “sulfatase pathway” and from androgens in the “aromatase pathway.” Here, we provide an overview about expression and function of enzymes of the “sulfatase pathway,” particularly steroid sulfatase (STS) that activates estrogens and estrogen sulfotransferase (SULT1E1) that converts active estrone (E1) and other estrogens to their inactive sulfates. High expression of STS and low expression of SULT1E1 will increase levels of active estrogens in malignant tumor cells leading to the stimulation of cell proliferation and cancer progression. Therefore, blocking the “sulfatase pathway” by STS inhibitors may offer an attractive strategy to reduce levels of active estrogens. STS inhibitors either applied in combination with aromatase inhibitors or as novel, dual aromatase-steroid sulfatase inhibiting drugs are currently under investigation. Furthermore, STS inhibitors are also suitable as enzyme–based cancer imaging agents applied in the biomedical imaging technique positron emission tomography (PET) for cancer diagnosis.

Extrarenal synthesis of the active vitamin D metabolite 1,25-dihydroxyvitamin-D3 (1,25-D) has been observed in cells derived from human organs prone to sporadic cancer incidence. Enhancement of the synthesizing hydroxylase CYP27B1 and reduction of the catabolic CYP24 could support local accumulation of the antimitotic steroid, thus preventing formation of tumors of e.g., colon and breast. By applying quantitative RT-PCR and HPLC it was observed that in colon-(Caco-2) and breast-(MCF-7) derived cells, 17beta-estradiol and genistein induced CYP27B1 but reduced CYP24 activity, while equol was inactive. Mammary cells express both estrogen receptors (ER) a and beta, while colon cells express mainly ERbeta, possibly explaining why MCF-7 cells were more affected. These results indicate a potential, new approach for cancer prevention by counteraction of the 1,25-D-driven negative feedback, i.e., down-regulation of CYP27B1 and up-regulation of CYP24, which prevents its own local accumulation. However, mammary cells may be more susceptible to this than colonocytes.

Epidemiological data suggest a protective role of calcium and vitamin D against colorectal tumor pathogenesis. 1,25-dihydroxyvitamin D 3 (1,25-D 3 ) is a key determinant of calcium homeostasis, cell proliferation and differentiation. Calcium in the intestinal lumen functions as a growth regulator and may prevent cancer by direct reduction of colonocyte proliferation. While calcium or vitamin D can counteract proliferation by itself, they could also interact if nutritional calcium were to modulate colonic vitamin D synthesis. In this paper we demonstrate that colonic and renal vitamin D hydroxylases are regulated independently. When mice were fed a modified AIN-76 diet containing low dietary calcium (0.1 or 0.04%) fecal calcium content was as low as 5% of that found in mice on a 0.9% calcium containing diet. Low fecal calcium concentration enhanced proliferating cell nuclear antigen expression in the colon mucosa and reduced that of the cyclin dependent kinase inhibitor p21. While low dietary calcium did not affect colonic expression of VDR or 25-hydroxyvitamin D 3 1α-hydroxylase (CYP27B1) mRNA, it influenced their renal expression in the expected manner by elevating the CYP27B1 expression and reducing VDR and 25-hydroxy-vitamin D 3 24-hydroxylase (CYP24) expression. In contrast, low calcium diets significantly augmented colonic CYP24 mRNA expression, but only in the ascending colon. This might result in reduced colonic accumulation of 1,25-D 3 during hyperproliferation caused by low dietary calcium and might support site-specific tumorigenesis. The important realization that low dietary calcium by itself is a risk factor for colorectal carcinogenesis and that colonic and renal vitamin D hydroxylases indeed are regulated differently from each other will provide novel approaches for colon cancer prevention.

Human colorectal cancer cells not only express the nuclear vitamin D receptor (VDR) but are also endowed with 25-hydroxy-vitamin D(3)-1alpha-hydroxylase activity and therefore are able to produce the specific ligand for the VDR, the hormonally active steroid 1alpha,25-dihydroxyvitamin D(3) (1alpha,25(OH)(2)D(3)). In the present study we show by semiquantitative reverse transcriptase polymerase chain reaction (RT-PCR) as well as by Western blotting and immunohistochemical methods, that in human large intestinal carcinomas expression of the genes encoding the 25-(OH)D(3)-1alpha-hydroxylase as well as the VDR increases in parallel with ongoing dedifferentiation in the early phase of cancerogenesis, whereas in poorly differentiated late stage carcinomas only low levels of the respective mRNAs can be detected. This indicates that, through up-regulation of this intrinsic 1alpha,25(OH)(2)D(3)/VDR system which mediates the anti-mitotic effects of the steroid hormone, colorectal cancer cells are apparently able to increase their potential for an autocrine counter-regulatory response to neoplastic cell growth, particularly in the early stages of malignancy.

481 Background: OATP-transporter proteins, such as OATP4A1, present influence cancer progression by providing compounds (hormones, prostaglandins, cyclic nucleotides, second messenger proteins, drugs) which either inhibit or stimulate tumor cells growth. Therefore, OATP expression in cancer cells and in the stroma, i.e., the microenvironment surrounding the epithelial cells can become a critical parameter. Methods: OATP4A1 was investigated in paraffin-embedded specimens from 148 patients with colorectal cancer and 20 with diverticulitis by immunohistochemistry (IHC) on an automatic quantitative microscopic image analysis system (TissuesFaxs). With the Histoquest program, the immunoreactive score (IRS), was calculated from the degree of the staining intensity and the number of OATP4A1-positive cells. To identify OATP4A1+-cells, double-immunofluorescence staining (IF) was done with antibodies against appropriate cellular markers. Results: OATP4A1 was located in the membrane and cytosol of colon cancer cells and immune cells, while membranous OATP4A1staining was seen in normal mucosa. OATP4A1 levels were higher in cancer cells in patients without tumor recurrence for up to 5 years (NR) than in patients with an early relapse (R) having IRS of 4391±231 and 3026±373 (Mean±SEM), respectively. Highest OATP4A1 levels were observed in immune cells in the tumors of Rs (IRS, 5712 ±254, while in NRs they were lower (IRS: 3549±358; p=0.05). In both groups, OATP4A1 levels in stroma cells were low (288±54 vs. 611±82). OATP4A1 expressing immune cell subtypes in cancer and diverticulitis sections were identified as CD45+ leukocytes, CD3+ T- and CD20+ B-cells, CD68+ macrophages, CD34+precursor cells. OATP4A1 was not detectable in Conclusions: High levels of OATP4A1 in immune cells in malignant and non-malignant colon disease suggest a role of the transporter in the activation of the immune system in malignant and non-malignant colon disease. Whether OATP4A1 might be a therapeutical target has to be established.

430 Background: Organic anions transporters (OATPs) are important for tumor progression and therapeutic response by regulating cellular levels of hormones, second messenger proteins and drugs. OATP4A1 is a transporter of pro-inflammatory prostaglandin E2 and may contribute to cancer progression. Data on the expression of OATP4A1 and its clinical impact in primary colorectal cancer (CRC) is rare. Our study was designed to proof the overexpression of OATP4A1 in primary CRC. Methods: Frozen samples from 20 unselected CRC patients (pat) and five CRC cell lines were analyzed for OATP4A1 mRNA expression by real time PCR (mean level normalized to the calibrator, MNE). Immunohistochemistry was performed on paraffin- embedded tumor sections from 50 CRC pat., UICC 0-II (25/50 with subsequent relapse). An automatic quantitative image analysis program was applied to quantify OATP4A1 expression. Expression and intensity was correlated with clinical parameters and relapses. Results: Significant (p>0.05) higher levels of OATP4A1 mRNA were observed in 20 cancer samples as compared to adjacent non-cancerous tissue (2.44 vs. 0.46 MNE). The highest expression (9.85 MNE) was observed in a well-differentiated tumor sample. Similar high levels were observed in the COGA1A cell line, expression in the other cell lines ranged between 1.83 and 0.28 MNE. Immunoreactive staining for OATP4A1 was located in the membrane and occasionally in the cytosol of tumor cells, it was exclusively membrane located in the adjacent non-cancerous epithelial cells. The staining intensity was significantly higher in cancer cells compared to non-cancerous areas (1528±326 vs.376±218) while staining of stroma cells was only occasionally detectable. Surprisingly, the highest OATP4A1 levels were observed in immune cells (2839±381 vs.298±56). Data on the clinical impact of OATP4A1 in the early stage CRC pat. will be presented at the meeting. Conclusions: The profound expression of OATP4A1 in CRC cells and in the inflammatory infiltrates supports its implication on cancer progression. Suitability of OATP4A1 as a potential prognostic marker has to be established on a larger patient collective.

In human medicine, passive immunotherapy is a well-established tool to fight cancer. Cetuximab and trastuzumab are famous examples of effective monoclonal antibody therapies for the treatment of ErbB-1 (EGFR) overexpressing colon tumors and for ErbB-2 (HER2/neu) overexpressing metastatic breast cancer. Mammary carcinomas of dogs are the most important cause of tumor-related death in females. It is known that these tumors also express tumor markers similar to human breast cancer and that regarding the idea of comparative oncology cancer in pet dogs are a valuable model for speeding up drug development. Therefore, we aimed to investigate more closely canine ErbB-1 and ErbB-2 and the applicability of cetuximab and trastuzumab in the dog. Screenings with FDA-approved immunohistochemical diagnostic tests of canine mammary tumor samples showed 3/10 ErbB-1 and 4/10 ErbB-2 overexpression, which seems similar to the expression pattern in human breast cancer patients. Sequence analyses revealed amino acid sequence identities of 91% between human and canine ErbB-1 and 92% for ErbB-2. Modeling of those proteins showed that the human cetuximab epitope differs in only four amino acids compared to the canine counterpart and that the trastuzumab binding site is identical in human and canine ErbB-2 except for only one amino acid. Using flow cytometry analyses cetuximab and trastuzumab binding could be confirmed in four canine mammary carcinoma cell lines. Furthermore, cell viability assays showed that incubation of canine cell lines with both antibodies inhibited tumor cell proliferation, even though there are lower numbers of ErbB molecules on canine than on human cells, which was confirmed by a flow cytometry-based assay. This comparative oncology study indicates that ErbB-1 and ErbB-2 are highly conserved molecules with significant concordance in terms of structure and expression pattern between human and canine cancer. Importantly, the canine homologous molecules are susceptible to cetuximab and trastuzumab targeting, which may open up new avenues towards antibody-based immunotherapies in companion dogs and improvements in anticancer drug development. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the Second AACR International Conference on Frontiers in Basic Cancer Research; 2011 Sep 14-18; San Francisco, CA. Philadelphia (PA): AACR; Cancer Res 2011;71(18 Suppl):Abstract nr C46.

Comparative oncology aims at speeding up developments for both, human and companion animal cancer patients. Following this line, carcinoembryonic antigen (CEA, CEACAM5) could be a therapeutic target not only for human but also for canine (Canis lupus familiaris; dog) patients. CEACAM5 interacts with CEA-receptor (CEAR) in the cytoplasm of human cancer cells. Our aim was, therefore, to phylogenetically verify the antigenic relationship of CEACAM molecules and CEAR in human and canine cancer. Anti-human CEACAM5 antibody Col-1, previously being applied for cancer diagnosis in dogs, immunohistochemically reacted to 23 out of 30 canine mammary cancer samples. In immunoblot analyses Col-1 specifically detected human CEACAM5 at 180 kDa in human colon cancer cells HT29, and the canine antigen at 60, 120, or 180 kDa in CF33 and CF41 mammary carcinoma cells as well as in spontaneous mammary tumors. While according to phylogenicity canine CEACAM1 molecules should be most closely related to human CEACAM5, Col-1 did not react with canine CEACAM1, -23, -24, -25, -28 or -30 transfected to canine TLM-1 cells. By flow cytometry the Col-1 target molecule was localized intracellularly in canine CF33 and CF41 cells, in contrast to membranous and cytoplasmic expression of human CEACAM5 in HT29. Col-1 incubation had neither effect on canine nor human cancer cell proliferation. Yet, Col-1 treatment decreased AKT-phosphorylation in canine CF33 cells possibly suggestive of anti-apoptotic function, whereas Col-1 increased AKT-phosphorylation in human HT29 cells. We report further a 99% amino acid similarity of human and canine CEA receptor (CEAR) within the phylogenetic tree. CEAR could be detected in four canine cancer cell lines by immunoblot and intracellularly in 10 out of 10 mammary cancer specimens from dog by immunohistochemistry. Whether the specific canine Col-1 target molecule may as functional analogue to human CEACAM5 act as ligand to canine CEAR, remains to be defined. This study demonstrates the limitations of comparative oncology due to the complex functional evolution of the different CEACAM molecules in humans versus dogs. In contrast, CEAR may be a comprehensive interspecies target for novel cancer therapeutics.

The vitamin D receptor knockout (VDR-KO) mouse presents with a skeletal phenotype typical for complete lack of genomic 1,25-dihydroxycholecalciferol effects. Our previous data from human colorectal tissue suggest that the steroid hormone and its receptor may have protective function against tumour progression. In order to investigate the relevance of the vitamin D system for pre-malignant site-directed changes in the colon, we characterized the amount and site-specific distribution of the VDR along the large intestine in wild-type (WT), heterozygote (HT) and KO mice. We also evaluated expression of proliferating cell nuclear antigen (PCNA), of cyclin D1 and the levels of 8-hydroxy-2'-deoxyguanosine (8-OHdG), a marker of oxidative stress. In colon ascendens, proliferative cells were dispersed all along the crypt and expression levels of all three markers were high in WT mice. A decrease of VDR expression did not affect expression significantly. In colon descendens, however, fewer proliferative cells were solely located in the lower third of the crypt, and an inverse relationship between VDR reduction, PCNA positivity and cyclin D1 expression was found in HT and KO mice. In parallel to enhanced proliferation a highly significant increase of 8-OHdG positivity occurred. Therefore, the sigmoid colon of VDR-KO mice, fed on an appropriate lactose/calcium-enriched diet to alleviate impaired calcium homeostasis-related phenotypic changes, is an excellent model for investigating induction and prevention of pre-malignant changes in one of the hotspots for human colorectal cancer incidence.

Soybean products are highly represented in the traditional Asian diet. Major components of soy proteins are phytoestrogens, such as isoflavones. They may be responsible for the extremely low incidence of prostate and mammary tumors and possibly also of colon cancer in countries such as China and Japan. Serum 1,25-dihydroxyvitamin D 3 level is inversely related to incidence of some cancers. Levels are determined by skin exposure to ultraviolet light or, to a minor extent, nutritional uptake and by subsequent conversion of the precursor vitamin D to the active hormone by the cytochrome P450 hydroxylases CYP27A1, CYP27B1 (responsible for synthesis) and CYP24 (responsible for catabolism) in liver and kidney. However, vitamin D synthesis is also found in colonocytes and is enhanced during incipient malignancy. This may indicate an autocrine/paracrine role for this differentiation-inducing hormone in defense against progression. We were able to demonstrate that either a single large oral dose of genistein or feeding soy protein for 4 mo elevated CYP27B1 and decreased CYP24 expression in the mouse colon. Our data therefore suggest that an inverse correlation of soy product consumption with colon tumor incidence may be consequent to enhanced colonic synthesis of the antimitotic hormone 1,25-dihydroxyvitamin D 3 .