Potent, selective and low-calcemic inhibitors of CYP24 hydroxylase: 24-sulfoximine analogues of the hormone 1alpha,25-dihydroxyvitamin D(3)

Discovery and Optimization of a Series of Vinyl Sulfoximine-Based Analogues as Potent Nrf2 Activators for the Treatment of Multiple Sclerosis

Multiple sclerosis (MS) is an immune-mediated neurodegenerative disease of the central nervous system (CNS), which leads to demyelination, axonal loss, and neurodegeneration. Increased oxidative stress and neurodegeneration have been implicated in all stages of MS, making neuroprotective therapeutics a promising strategy for its treatment. We previously have reported vinyl sulfones with antioxidative and anti-inflammatory properties that activate nuclear factor erythroid 2-related factor 2 (Nrf2), a transcription factor that induces the expression of cytoprotective genes against oxidative stress. In this study, we synthesized vinyl sulfoximine derivatives by modifying the core structure and determined therapeutic potential as Nrf2 activators. Among them, 10v effectively activated Nrf2 (EC50 = 83.5 nM) and exhibited favorable drug-like properties. 10v successfully induced expression of Nrf2-dependent antioxidant enzymes and suppressed lipopolysaccharide (LPS)-induced inflammatory responses in BV-2 microglial cells. We also confirmed that 10v effectively reversed disease progression and attenuated demyelination in an experimental autoimmune encephalitis (EAE) mouse model of MS.

Silver-mediated Room Temperature Reactions for the Synthesis of N-α-Ketoacyl Sulfoximines and N-α,β-Unsaturated Acyl Sulfoximines

Here, we report a silver-mediated coupling of acetylenes with sulfoximines to synthesize N-α-ketoacyl sulfoximines and N-α,β-unsaturated acyl sulfoximines. The reactions are performed under an open atmosphere using the oxidant K₂S₂O₈ and the ligand 2,2-bipyridyl. However, the fate of the product formation is controlled by the type of substrate used. The coupling between aryl acetylenes and sulfoximines afforded the N-α-ketoacylsulfoximines, while the alkyl acetylenes provided the N-α,β-unsaturated acyl sulfoximines. Controlled experiments reveal the differential reactivity patterns of substrates. The labeling ¹⁸O experiments showed that water is the source of the incoming oxygen atom for the keto group of N-α-ketoacyl sulfoximines and N-α,β-unsaturated acyl sulfoximines.

Therapeutic Potential of a Novel Vitamin D3 Oxime Analogue, VD1-6, with CYP24A1 Enzyme Inhibitory Activity and Negligible Vitamin D Receptor Binding

The regulation of vitamin D3 actions in humans occurs mainly through the Cytochrome P450 24-hydroxylase (CYP24A1) enzyme activity. CYP24A1 hydroxylates both 25-hydroxycholecalciferol (25(OH)D3) and 1,25-dihydroxycholecalciferol (1,25(OH)2D3), which is the first step of vitamin D catabolism. An abnormal status of the upregulation of CYP24A1 occurs in many diseases, including chronic kidney disease (CKD). CYP24A1 upregulation in CKD and diminished activation of vitamin D3 contribute to secondary hyperparathyroidism (SHPT), progressive bone deterioration, and soft tissue and cardiovascular calcification. Previous studies have indicated that CYP24A1 inhibition may be an effective strategy to increase endogenous vitamin D activity and decrease SHPT. This study has designed and synthesized a novel C-24 O-methyloxime analogue of vitamin D3 (VD1-6) to have specific CYP24A1 inhibitory properties. VD1-6 did not bind to the vitamin D receptor (VDR) in concentrations up to 10−7 M, assessed by a VDR binding assay. The absence of VDR binding by VD1-6 was confirmed in human embryonic kidney HEK293T cultures through the lack of CYP24A1 induction. However, in silico docking experiments demonstrated that VD1-6 was predicted to have superior binding to CYP24A1, when compared to that of 1,25(OH)2D3. The inhibition of CYP24A1 by VD1-6 was also evident by the synergistic potentiation of 1,25(OH)2D3-mediated transcription and reduced 1,25(OH)2D3 catabolism over 24 h. A further indication of CYP24A1 inhibition by VD1-6 was the reduced accumulation of the 24,25(OH)D3 , the first metabolite of 25(OH)D catabolism by CYP24A1. Our findings suggest the potent CYP24A1 inhibitory properties of VD1-6 and its potential for testing as an alternative therapeutic candidate for treating SHPT.

Rhodium(III)-catalyzed cascade C-H functionalization/annulation of sulfoximines with iodonium ylides for the synthesis of cyclohexanone-1,2-benzothiazines

A highly efficient Rh(III)-catalyzed cascade C-H activation/annulation of sulfoximines with iodonium ylides under metal-oxidant-free conditions has been reported. The fused cyclohexanone-1,2-benzothiazine scaffold is readily achieved with a one-pot process in this reaction. This protocol exhibits good functional group tolerance and moderate to excellent yields. Additionally, the olefination of the target product illustrates the promising usefulness of this strategy.

Practical Asymmetric Synthesis of Chiral Sulfoximines via Sulfur-Selective Alkylation

Chiral sulfoximines have recently been considered as promising bioisosteres in medicinal chemistry. However, methods for preparing chiral sulfoximines in a stereoselective manner are underdeveloped. Herein, we demonstrate an asymmetric synthesis of chiral sulfoximines through a stereospecific S-alkylation of readily accessible chiral sulfinamides under practical conditions. A key to establishing the practical conditions was the identification of the intermediate structure in our previously reported S-alkylation by X-ray crystallographic analysis.

Synthesis and Configurational Assignment of Vinyl Sulfoximines and Sulfonimidamides

Vinyl sulfones and sulfonamides are valued for their use as electrophilic warheads in covalent protein inhibitors. Conversely, the S(VI) aza-isosteres thereof, vinyl sulfoximines and sulfonimidamides, are far less studied and have yet to be applied to the field of protein bioconjugation. Herein, we report a range of different synthetic methodologies for constructing vinyl sulfoximine and vinyl sulfonimidamide architectures that allows access to new areas of electrophilic chemical space. We demonstrate how late-stage functionalization can be applied to these motifs to incorporate alkyne tags, generating fully functionalized probes for future chemical biology applications. Finally, we establish a workflow for determining the absolute configuration of enantioenriched vinyl sulfoximines and sulfonimidamides by comparing experimentally and computationally determined electronic circular dichroism spectra, enabling access to configurationally assigned enantiomeric pairs by separation.

Efficient Synthesis of Sulfur-Stereogenic Sulfoximines via Ru(II)-Catalyzed Enantioselective C-H Functionalization Enabled by Chiral Carboxylic Acid

Ru(II)-catalyzed enantioselective C-H functionalization involving an enantiodetermining C-H cleavage step remains undeveloped. Here we describe a Ru(II)-catalyzed enantioselective C-H activation/annulation of sulfoximines with α-carbonyl sulfoxonium ylides using a novel class of chiral binaphthyl monocarboxylic acids as chiral ligands, which can be easily and modularly prepared from 1,1'-binaphthyl-2,2'-dicarboxylic acid. A broad range of sulfur-stereogenic sulfoximines were prepared in high yields with excellent enantioselectivities (up to 99% yield and 99% ee) via desymmetrization, kinetic resolution, and parallel kinetic resolution. Furthermore, the resolution products can be easily transformed to chiral sulfoxides and key intermediates for kinase inhibitors.

Vitamin D Signaling in Inflammation and Cancer: Molecular Mechanisms and Therapeutic Implications

Vitamin D and its active metabolites are important nutrients for human skeletal health. UV irradiation of skin converts 7-dehydrocholesterol into vitamin D3, which metabolized in the liver and kidneys into its active form, 1α,25-dihydroxyvitamin D3. Apart from its classical role in calcium and phosphate regulation, scientists have shown that the vitamin D receptor is expressed in almost all tissues of the body, hence it has numerous biological effects. These includes fetal and adult homeostatic functions in development and differentiation of metabolic, epidermal, endocrine, neurological and immunological systems of the body. Moreover, the expression of vitamin D receptor in the majority of immune cells and the ability of these cells to actively metabolize 25(OH)D3 into its active form 1,25(OH)₂D3 reinforces the important role of vitamin D signaling in maintaining a healthy immune system. In addition, several studies have showed that vitamin D has important regulatory roles of mechanisms controlling proliferation, differentiation and growth. The administration of vitamin D analogues or the active metabolite of vitamin D activates apoptotic pathways, has antiproliferative effects and inhibits angiogenesis. This review aims to provide an up-to-date overview on the effects of vitamin D and its receptor (VDR) in regulating inflammation, different cell death modalities and cancer. It also aims to investigate the possible therapeutic benefits of vitamin D and its analogues as anticancer agents.

Ligand-Free, Quinoline N-Assisted Copper-Catalyzed Nitrene Transfer Reaction To Synthesize 8-Quinolylsulfimides

An efficient copper-catalyzed, quinolyl N-directed nitrene transfer reaction to 8-quinolylsulfides was described. A variety of 8-quinolylsulfimides with different functional groups were synthesized in moderate to high yields. The obtained 8-quinolylsulfimides were proved to be promising novel type of bidentate ligands in Pd(II)-catalyzed allylic alkylation.

Rhodium(III)-Catalyzed C-H Alkynylation of N-Methylsulfoximines

A rhodium(III)-catalyzed direct C-H alkynylation of a wide range of N-methylsulfoximines with (bromoethynyl)triisopropylsilane has been developed. This protocol is compatible with both (S,S)-diaryl sulfoximines and (S,S)-alkyl aryl sulfoximines, and shows mild conditions, and good functional group tolerance. The synthetic utility of this method has been demonstrated by subsequent various transformations of the products.

Human uterine leiomyoma contains low levels of 1, 25 dihdroxyvitamin D3, and shows dysregulated expression of vitamin D metabolizing enzymes

OBJECTIVES

To evaluate tissue concentration of 1, 25 dihydroxyvitamin D3, and gene expression level of CYP27B1 that codes for 1-α hydroxylase (vitamin D activating enzyme), and CYP24A1 that codes for 24-hydroxylase (vitamin D catabolizing enzyme) in human uterine leiomyoma (ULM), its adjacent myometrium (Myo-F), and normal myometrium (Myo-N).

STUDY DESIGN

Levels of 1, 25 dihydroxyvitamin D3 were measured using HPLC and Diode detectors whereas CYP27B1, and CYP24A1 expressions were assessed using Real-Time PCR in ULM, Myo-F, and Myo-N. Non-parametric statistics were used.

RESULTS

ULMs contained significantly less 1, 25 dihydroxy vitamin D3 compared to Myo-F (3.0, IQR: 1.0-9.0 versus 6.0, IQR: 3.0-13.0 μg/ kg, P value is 0.03). No significant difference was detected between ULM and Myo-N, or Myo-F and Myo-N. Intratumoral level of the active form of vitamin D did not differ according to the type of ULM (submucous or interstitial/subserous), or to the ULM volume. CYP27B1 was expressed in ULM (2.17, IQR: 0.65-4.9), Myo-F (4.94, IQR: 1.04-22.59), and Myo-N (0.99, IQR: 0.49-1.71) to a comparable level. CYP24A1 expression was significantly higher in ULM compared to Myo-N (2.00, IQR: 0.69-10.77 versus 0.22, IQR: 00- 0.96, respectively, P value is 0.04).

CONCLUSIONS

Human ULMs contain significantly lower 1, 25 dihydroxyvitamin D3 than its adjacent myometrium. ULM, Myo-F, and Myo-N express CYP27B1 and CYP24A1. ULMs express significantly higher level of CYP24A1 than normal myometrium indicating that over expression of 24-hydroxylase is a mechanism by which ULMs sustain a relative state of hypovitaminosis D.

Cp*Ir(iii)-catalyzed C–H/N–H functionalization of sulfoximines for the synthesis of 1,2-benzothiazines at room temperature

The first Cp*Ir(iii)-catalyzed C–H/N–H bond functionalization of sulfoximines with α-diazocarbonyl compounds has been developed for the synthesis of 1,2-benzothiazines under redox-neutral conditions at room temperature.

Vitamin D Receptor Signaling and Cancer

The vitamin D receptor (VDR) binds the secosteroid hormone 1,25(OH)₂D₃ with high affinity and regulates gene programs that control a serum calcium levels, as well as cell proliferation and differentiation. A significant focus has been to exploit the VDR in cancer settings. Although preclinical studies have been strongly encouraging, to date clinical trials have delivered equivocal findings that have paused the clinical translation of these compounds. However, it is entirely possible that mining of genomic data will help to refine precisely what are the key anticancer actions of vitamin D compounds and where these can be used most effectively.

Synthesis of NH-sulfoximines from sulfides by chemoselective one-pot N- and O-transfers

Direct synthesis of NH-sulfoximines from sulfides has been achieved through O and NH transfer in the same reaction, occurring with complete selectivity.

Diet-derived 25-hydroxyvitamin D3 activates vitamin D receptor target gene expression and suppresses EGFR mutant non-small cell lung cancer growth in vitro and in vivo

Epidemiologic studies implicate vitamin D status as a factor that influences growth of EGFR mutant lung cancers. However, laboratory based evidence of the biological effect of vitamin D in this disease is lacking. To fill this knowledge gap, we determined vitamin D receptor (VDR) expression in human lung tumors using a tissue microarray constructed of lung cancer cases from never-smokers (where EGFR gene mutations are prevalent). Nuclear VDR was detected in 19/19 EGFR mutant tumors. Expression tended to be higher in tumors with EGFR exon 19 deletions than those with EGFR L858R mutations. To study anti-proliferative activity and signaling, EGFR mutant lung cancer cells were treated with the circulating metabolite of vitamin D, 25-hydroxyvitamin D3 (25D3). 25D3 inhibited clonogenic growth in a dose-dependent manner. CYP27B1 encodes the 1α-hydroxylase (1αOHase) that converts 25D3 to the active metabolite, 1,25-dihydroxyvitamin D3 (1,25D3). Studies employing VDR siRNA, CYP27B1 zinc finger nucleases, and pharmacologic inhibitors of the vitamin D pathway indicate that 25D3 regulates gene expression in a VDR-dependent manner but does not strictly require 1αOHase-mediated conversion of 25D3 to 1,25D3. To determine the effects of modulating serum 25D3 levels on growth of EGFR mutant lung tumor xenografts, mice were fed diets containing 100 or 10,000 IU vitamin D3/kg. High dietary vitamin D3 intake resulted in elevated serum 25D3 and significant inhibition of tumor growth. No toxic effects of supplementation were observed. These results identify EGFR mutant lung cancer as a vitamin D-responsive disease and diet-derived 25D3 as a direct VDR agonist and therapeutic agent.

Metal-Free, Phosphonium Salt-Mediated Sulfoximination of Azine N-Oxides: Approach for the Synthesis of N-Azine Sulfoximines

Herein, we report a simple and metal-free method for the synthesis of N-azine sulfoximines by the nucleophilic substitution of azine N-oxides with NH-sulfoximines. The present method works at room temperature with wide functional group compatibility and gives several unprecedented N-azine sulfoximines. The reaction conditions were also found suitable with enantiopure substrates and furnished products without any racemization. It also finds an application in the sulfoximination of azine-based functional molecules such as 2,2'-bipyridine, 1,10-phenanthroline, and quinine.

Recent Trends in Copper-Catalyzed C-H Amination Routes to Biologically Important Nitrogen Scaffolds

Nitrogen-containing heterocycles have found remarkable applications in natural product research, material sciences, and pharmaceuticals. Although the synthesis of this interesting class of compounds attracted the interest of generations of organic chemists, simple and straightforward assembly methods based on transition-metal catalysis have regularly been elusive. The recent advancements in the development of C-H functionalization have helped in accomplishing the synthesis of a variety of complex heterocycles from simple precursors. This Focus Review summarizes the recent advances in one particular field: the copper-catalyzed C-N bond formation reactions via C-H bond functionalization to furnish a comprehensive range of nitrogen heterocycles. Applicability and synthetic feasibility of a particular reaction represent major requirements for the inclusion in this review.

Synthesis of N-Imidoyl and N-Oxoimidoyl Sulfoximines from 1-Alkynes, N-Sulfonyl Azides, and Sulfoximines

N-Imidoylation of sulfoximines is developed from a Cu-catalyzed three-component reaction from 1-alkynes, N-sulfonyl azides, and sulfoximines in THF at room temperature under air. In addition, N-oxoimidoylation of sulfoximines is accessed from a Cu-catalyzed three-component reaction from 1-alkynes, N-sulfonyl azides, and sulfoximines in THF at room temperature followed by a Cu-catalyzed oxidative reaction at 50 °C under air, producing N-oxoimidoyl sulfoximines.

Design, synthesis and structural exploration of novel fluorinated dabigatran derivatives as direct thrombin inhibitors

Twenty-one fluorinated dabigatran derivatives were designed based on the bioisosteric principle. All derivatives were synthesised and evaluated for their thrombin inhibitory activity in vitro. Among these compounds, 14h, 14m, 14s and 14t were potent and the activity was in the range of reference drug, dabigatran. Three structural changes were introduced in these 21 compounds to elucidate the structure-activity relationship of the drugs. In addition, prodrugs of compounds 14h and 14s were developed to investigate their anticoagulant activities in vivo. In these experiments, compound 16 showed a fairly strong inhibitory effect on thrombin-induced platelet aggregation, and demonstrated potent activity for inhibiting arteriovenous thrombosis with an inhibition rate of (73 ± 6) %, which was comparable to that of dabigatran etexilate (76 ± 2) %. Moreover, molecular docking studies were performed to understand the binding interactions of active compounds 14h, 14s and 14t with thrombin protein (PDB ID:1KTS). Contour maps obtained from the 3D-QSAR model are meaningful in designing more active molecules to act as direct inhibitors of thrombin.

19-Norvitamin D analogs for breast cancer therapy

The active form of vitamin D3, 1α,25-dihydroxyvitamin D3 (1α,25(OH)2D3 or calcitriol), is known to inhibit the proliferation and invasiveness of many types of cancer cells, including breast, colon, pancreatic, prostate, and liver cancer cells. These findings support the use of 1α,25(OH)2D3 for the treatment of these types of cancer. However, 1α,25(OH)2D3 can cause hypercalcemia, so analogs of 1α,25(OH)2D3 that are less calcemic but exhibit more potent anti-tumor activity would be good candidates as therapeutic agents. Therefore, a series of 19-norvitamin D analogs, in which the methylidene group on C19 is replaced with 2 hydrogen atoms, have been synthesized by several laboratories. In our laboratory, we have designed and synthesized a series of 2α-functional group substituted 19-norvitamin D3 analogs and examined their anti-proliferative activity. Among them, 2α- and 2β-(3-hydroxypropyl)-1α,25-dihydroxy-19-norvitamin D3 (MART-10 and MART-11) were found to be the most promising. Here, we review the rationale and approaches for the synthesis of different 19-norvitamin D analogs, and the pre-clinical studies using these analogs in breast cancer cells, in particular, we chose MART-10 for its potential application to the prevention and treatment of breast cancer.

The novel purification and biochemical characterization of a reversible CYP24A1:adrenodoxin complex

Novel paradigms for CYP24A1 inhibitor development are needed to circumvent existing efficacy and toxicity issues related to human therapeutics in this class. We hypothesize that improved structural knowledge of CYP24A1 in complex with natural substrates, inhibitors and/or its redox partner protein, adrenodoxin (Adx) is required to facilitate the next generation of CYP24A1 inhibitor design. To this end, we have developed truncated expression constructs for both rat CYP24A1 (Δ51) and bovine Adx (Δ108), which allow us to purify a stable and reversible state of the CYP24A1:Adx complex, for use in ongoing X-ray crystallographic studies. Spectral characterization of the reversible complex revealed that Adx binding enhanced the stability of the enzyme-substrate complex, despite lowering the ligand binding affinity of the free enzyme, for 1,25(OH)2D2, over 9-fold. Truncation of CYP24A1's flexible N-terminus (Δ51) improved the enzyme's ability to recruit substrate, without altering Adx's ability to stabilize the ligand-bound form. We also found that several common crystallization detergents, including CHAPS, inhibit ligand binding to the CYP24A1:Adx complex at concentrations well below their reported critical micelle concentration (CMC) values. Ultimately, this research provides a useful platform and framework for the study of conformationally complex, membrane-protein complexes, in the ligand-bound state.

Inhibition of protein kinase CK2 reduces Cyp24a1 expression and enhances 1,25-dihydroxyvitamin D(3) antitumor activity in human prostate cancer cells

Vitamin D has broad range of physiological functions and antitumor effects. 24-Hydroxylase, encoded by the CYP24A1 gene, is the key enzyme for degrading many forms of vitamin D including the most active form, 1,25D(3). Inhibition of CYP24A1 enhances 1,25D(3) antitumor activity. To isolate regulators of CYP24A1 expression in prostate cancer cells, we established a stable prostate cancer cell line PC3 with CYP24A1 promoter driving luciferase expression to screen a small molecular library for compounds that inhibit CYP24A1 promoter activity. From this screening, we identified, 4,5,6,7-tetrabromobenzimidazole (TBBz), a protein kinase CK2 selective inhibitor as a disruptor of CYP24A1 promoter activity. We show that TBBz inhibits CYP24A1 promoter activity induced by 1,25D(3) in prostate cancer cells. In addition, TBBz downregulates endogenous CYP24A1 mRNA level in TBBz-treated PC3 cells. Furthermore, siRNA-mediated CK2 knockdown reduces 1,25D(3)-induced CYP24A1 mRNA expression in PC3 cells. These results suggest that CK2 contributes to 1,25D(3)-mediated target gene expression. Finally, inhibition of CK2 by TBBz or CK2 siRNA significantly enhances 1,25D(3)-mediated antiproliferative effect in vitro and in vivo in a xenograft model. In summary, our findings reveal that protein kinase CK2 is involved in the regulation of CYP24A1 expression by 1,25D(3) and CK2 inhibitor enhances 1,25D(3)-mediated antitumor effect.

CYP24 inhibition preserves 1α,25-dihydroxyvitamin D(3) anti-proliferative signaling in lung cancer cells

Human lung tumors aberrantly express the 1α,25-dihydroxyvitamin D(3) (1,25(OH)(2)D(3))-catabolizing enzyme, CYP24. We hypothesized that CYP24 reduces 1,25(OH)(2)D(3)-mediated transcription and allows lung cancer cells to escape its growth-inhibitory action. To test this, H292 lung cancer cells and the CYP24-selective inhibitor CTA091 were utilized. In H292 cells, CTA091 reduces 1,25(OH)(2)D(3) catabolism, significantly increases 1,25(OH)(2)D(3)-mediated growth inhibition, and increases 1,25(OH)(2)D(3) effects on induced and repressed genes in gene expression profiling studies. Pathway mapping of repressed genes uncovered cell cycle as a predominant 1,25(OH)(2)D(3) target. In H292 cells, 1,25(OH)(2)D(3) significantly decreases cyclin E2 levels and induces G(0)/G(1) arrest. A broader set of cyclins is down-regulated when 1,25(OH)(2)D(3) is combined with CTA091, and cell cycle arrest further increases. Effects of CTA091 on 1,25(OH)(2)D(3) signaling are vitamin D receptor-dependent. These data provide evidence that CYP24 limits 1,25(OH)(2)D(3) anti-proliferative signaling in cancer cells, and suggest that CTA091 may be beneficial in preserving 1,25(OH)(2)D(3) action in lung cancer.

Hershberger P. A local effect of CYP24 inhibition on lung tumor xenograft exposure to 1,25-dihydroxyvitamin D(3) is revealed using a novel LC-MS/MS assay

The vitamin D(3) catabolizing enzyme, CYP24, is frequently over-expressed in tumors, where it may support proliferation by eliminating the growth suppressive effects of 1,25-dihydroxyvitamin D(3) (1,25(OH)(2)D(3)). However, the impact of CYP24 expression in tumors or consequence of CYP24 inhibition on tumor levels of 1,25(OH)(2)D(3)in vivo has not been studied due to the lack of a suitable quantitative method. To address this need, an LC-MS/MS assay that permits absolute quantitation of 1,25(OH)(2)D(3) in plasma and tumor was developed. We applied this assay to the H292 lung tumor xenograft model: H292 cells eliminate 1,25(OH)(2)D(3) by a CYP24-dependent process in vitro, and 1,25(OH)(2)D(3) rapidly induces CYP24 expression in H292 cells in vivo. In tumor-bearing mice, plasma and tumor concentrations of 1,25(OH)(2)D(3) reached a maximum of 21.6 and 1.70ng/mL, respectively, following intraperitoneal dosing (20μg/kg 1,25(OH)(2)D(3)). When co-administered with the CYP24 selective inhibitor CTA091 (250μg/kg), 1,25(OH)(2)D(3) plasma levels increased 1.6-fold, and tumor levels increased 2.6-fold. The tumor/plasma ratio of 1,25(OH)(2)D(3) AUC was increased 1.7-fold by CTA091, suggesting that the inhibitor increased the tumor concentrations of 1,25(OH)(2)D(3) independent of its effects on plasma disposition. Compartmental modeling of 1,25(OH)(2)D(3) concentration versus time data confirmed that: 1,25(OH)(2)D(3) was eliminated from plasma and tumor; CTA091 reduced the elimination from both compartments; and that the effect of CTA091 on tumor exposure was greater than its effect on plasma. These results provide evidence that CYP24-expressing lung tumors eliminate 1,25(OH)(2)D(3) by a CYP24-dependent process in vivo and that CTA091 administration represents a feasible approach to increase tumor exposure to 1,25(OH)(2)D(3).