Synthesis, CYP24A1-Dependent Metabolism and Antiproliferative Potential against Colorectal Cancer Cells of 1,25-Dihydroxyvitamin D2 Derivatives Modified at the Side Chain and the A-Ring

Targeting Androgen, Thyroid Hormone, and Vitamin A and D Receptors to Treat Prostate Cancer

The nuclear hormone family of receptors regulates gene expression. The androgen receptor (AR), upon ligand binding and homodimerization, shuttles from the cytosol into the nucleus to activate gene expression. Thyroid hormone receptors (TRs), retinoic acid receptors (RARs), and the vitamin D receptor (VDR) are present in the nucleus bound to chromatin as a heterodimer with the retinoid X receptors (RXRs) and repress gene expression. Ligand binding leads to transcription activation. The hormonal ligands for these receptors play crucial roles to ensure the proper conduct of very many tissues and exert effects on prostate cancer (PCa) cells. Androgens support PCa proliferation and androgen deprivation alone or with chemotherapy is the standard therapy for PCa. RARγ activation and 3,5,3'-triiodo-L-thyronine (T3) stimulation of TRβ support the growth of PCa cells. Ligand stimulation of VDR drives growth arrest, differentiation, and apoptosis of PCa cells. Often these receptors are explored as separate avenues to find treatments for PCa and other cancers. However, there is accumulating evidence to support receptor interactions and crosstalk of regulatory events whereby a better understanding might lead to new combinatorial treatments.

Structure and the Anticancer Activity of Vitamin D Receptor Agonists

Vitamin D is a group of seco-steroidal fat-soluble compounds. The two basic forms, vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol), do not have biological activity. They are converted in the body by a two-step enzymatic hydroxylation into biologically active forms, 1α,25-dihydroxyvitamin D2 [ercalcitriol, 1,25(OH)2D2] and 1α,25-dihydroxyvitamin D3 [calcitriol, 1,25(OH)2D3], which act as classical steroid hormones. 1,25(OH)2D3 exerts most of its physiological functions by binding to the nuclear vitamin D receptor (VDR), which is present in most body tissues to provide support to a broad range of physiological processes. Vitamin D-liganded VDR controls the expression of many genes. High levels of 1,25(OH)2D3 cause an increase in calcium in the blood, which can lead to harmful hypercalcemia. Several analogs of 1,25(OH)2D3 and 1,25(OH)2D2 have been designed and synthesized with the aim of developing compounds that have a specific therapeutic function, for example, with potent anticancer activity and a reduced toxic calcemic effect. Particular structural modifications to vitamin D analogs have led to increased anticancer activity and reduced calcemic action with the prospect of extending work to provide future innovative therapies.

In Silico Prediction of the Metabolic Resistance of Vitamin D Analogs against CYP3A4 Metabolizing Enzyme

The microsomal cytochrome P450 3A4 (CYP3A4) and mitochondrial cytochrome P450 24A1 (CYP24A1) hydroxylating enzymes both metabolize vitamin D and its analogs. The three-dimensional (3D) structure of the full-length native human CYP3A4 has been solved, but the respective structure of the main vitamin D hydroxylating CYP24A1 enzyme is unknown. The structures of recombinant CYP24A1 enzymes have been solved; however, from studies of the vitamin D receptor, the use of a truncated protein for docking studies of ligands led to incorrect results. As the structure of the native CYP3A4 protein is known, we performed rigid docking supported by molecular dynamic simulation using CYP3A4 to predict the metabolic conversion of analogs of 1,25-dihydroxyvitamin D2 (1,25D2). This is highly important to the design of novel vitamin D-based drug candidates of reasonable metabolic stability as CYP3A4 metabolizes ca. 50% of the drug substances. The use of the 3D structure data of human CYP3A4 has allowed us to explain the substantial differences in the metabolic conversion of the side-chain geometric analogs of 1,25D2. The calculated free enthalpy of the binding of an analog of 1,25D2 to CYP3A4 agreed with the experimentally observed conversion of the analog by CYP24A1. The metabolic conversion of an analog of 1,25D2 to the main vitamin D hydroxylating enzyme CYP24A1, of unknown 3D structure, can be explained by the binding strength of the analog to the known 3D structure of the CYP3A4 enzyme.

Vitamin D/VDR in the pathogenesis of intervertebral disc degeneration: Does autophagy play a role?

To date, the underlying mechanisms involved intervertebral disc degeneration (IDD) remain unclear, which has hindered the development of molecular biological therapy for IDD. Autophagy is vital for intracellular quality control and metabolic balance in intervertebral disc cells. Hence, autophagy homeostasis is important. Emerging evidence has implicated vitamin D (VD) and the vitamin D receptor (VDR) in IDD progression because of their effects on different autophagy steps. However, the results of clinical trials in which VD supplementation was assessed as a treatment for IDD are controversial. Furthermore, experimental studies on the interplay between VD/VDR and autophagy are still in their infancy. In view of the significance of the crosstalk between VD/VDR and autophagy components, this review focuses on the latest research on VD/VDR modulation in autophagy and investigates the possible regulatory mechanisms. This article will deepen our understanding of the relationship between VD/VDR and autophagy and suggests novel strategies for IDD prevention and treatment.

Vitamin D Analogs Regulate the Vitamin D System and Cell Viability in Ovarian Cancer Cells

BACKGROUND

Ovarian cancer (OC) is one of the most lethal cancers in women. The active form of vitamin D₃, 1,25-dihydroxyvitamin D₃ (1,25D₃, calcitriol) has anticancer activity in several cancers, including ovarian cancer, but the required pharmacological doses may cause hypercalcemia. We hypothesized that newly developed, low calcemic, vitamin D analogs (an1,25Ds) may be used as anticancer agents instead of calcitriol in ovarian cancer cells.

METHODS

We used two patient-derived high-grade serous ovarian cancer (HGSOC) cell lines with low (13781) and high (14433) mRNA expression levels of the gene encoding 1,25-dihydroxyvitamin D₃ 24-hydroxylase CYP24A1, one of the main target genes of calcitriol. We tested the effect of calcitriol and four structurally related series of an1,25Ds (PRI-1906, PRI-1907, PRI-5201, PRI-5202) on cell number, viability, the expression of CYP24A1, and the vitamin D receptor (VDR).

RESULTS

CYP24A1 mRNA expression increased in a concentration-dependent manner after treatment with all compounds. In both cell lines, after 4 h, PRI-5202 was the most potent analog (in 13781 cells: EC₅₀ = 2.98 ± 1.10 nmol/L, in 14433 cells: EC₅₀ = 0.92 ± 0.20 nmol/L), while PRI-1907 was the least active one (in 13781 cells: EC₅₀ = n/d, in 14433 cells: EC₅₀ = n/d). This difference among the analogs disappeared after 5 days of treatment. The 13781 cells were more sensitive to the an1,25Ds compared with 14433 cells. The an1,25Ds increased nuclear VDR levels and reduced cell viability, but only in the 13781 cell line.

CONCLUSIONS

The an1,25Ds had different potencies in the HGSOC cell lines and their efficacy in increasing CYP24A1 expression was cell line- and chemical structure-dependent. Therefore, choosing sensitive cancer cell lines and further optimization of the analogs' structure might lead to new treatment options against ovarian cancer.

Development of In Vitro and In Vivo Evaluation Systems for Vitamin D Derivatives and Their Application to Drug Discovery

We have developed an in vitro system to easily examine the affinity for vitamin D receptor (VDR) and CYP24A1-mediated metabolism as two methods of assessing vitamin D derivatives. Vitamin D derivatives with high VDR affinity and resistance to CYP24A1-mediated metabolism could be good therapeutic agents. This system can effectively select vitamin D derivatives with these useful properties. We have also developed an in vivo system including a Cyp27b1-gene-deficient rat (a type I rickets model), a Vdr-gene-deficient rat (a type II rickets model), and a rat with a mutant Vdr (R270L) (another type II rickets model) using a genome editing method. For Cyp27b1-gene-deficient and Vdr mutant (R270L) rats, amelioration of rickets symptoms can be used as an index of the efficacy of vitamin D derivatives. Vdr-gene-deficient rats can be used to assess the activities of vitamin D derivatives specialized for actions not mediated by VDR. One of our original vitamin D derivatives, which displays high affinity VDR binding and resistance to CYP24A1-dependent metabolism, has shown good therapeutic effects in Vdr (R270L) rats, although further analysis is needed.