Effect of 2-(4-aminophenylmethyl)-6-hydroxy-3,4-dihydronaphthalen-1(2H)-one on all-transand 13-cis-retinoic acid levels in plasma quantified by high perfomance liquid chromatography coupled to tandem mass spectrometry

2-(2-Methylfuran-3-carboxamido)-3-phenylpropanoic acid, a potential CYP26A1 inhibitor to enhance all-trans retinoic acid-induced leukemia cell differentiation based on virtual screening and biological evaluation

To develop new CYP26A1 inhibitors, a three-cycle virtual screening was carried out based on the constructed homology model of human CYP26A1 using Dock, Fred, Gold and AutoDock. Twenty-two compounds exhibited high scores and reasonable binding modes in molecular docking were purchased from Specs Company. Eighteen compounds were tested their abilities to enhance ATRA-induced differentiation in human acute promyelocytic leukemia NB4 cells. Eight of them enhanced the ability of ATRA to induce differentiation at concentrations of 0.5 and 1 μM. Among these compounds, 2-(2-methylfuran-3-carboxamido)-3-phenylpropanoic acid (S8) is of most effective in blocking ATRA breaking down in NB4 cells based on the LC-MS/MS assay.

Quantification of retinoid concentrations in human serum and brain tumor tissues

Retinoic acid signaling is essential for central nervous system (CNS) differentiation and appears to be impaired in tumors. Thus far, there are no established methods to quantify relevant retinoids (all-trans-retinoic acid, 9-cis-retinoic acid, 13-cis retinoic acid, and retinol) in human brain tumors. We developed a single step extraction and quantification procedure for polar and apolar retinoids in normal tissue, lipid-rich brain tumor tissues, and serum. This quantification procedure is based on high performance liquid chromatography (HPLC) with diode-array detection (DAD) using all-trans-acitretin as an internal standard and extraction by liquid-liquid partition with ethyl acetate and borate buffer at pH 9. Recovery with this extraction procedure was higher than earlier (two-step) liquid-liquid extraction procedures based on hexane, NaOH, and HCl. The overall quantification procedure was validated according to Food and Drug Administration (FDA) guidelines and fulfilled all criteria of accuracy, precision, selectivity, recovery, and stability. The overall method accuracy varied between -5.6% and +5.4% for serum and -3.8% and +6.2% for tissues, and overall precision ranged from 3.1% to 6.9% for serum and 2.1% to 8.3% for tissues (%CV batch-to-batch). The lower limit of quantification for all compounds in tumor tissue (and serum) was 3.9 ng g(-1) (ng mL(-1)). Using this assay, photodegradation of the retinoids was evaluated and endogenous polar and apolar retinoids were quantified in sera and brain tumor tissues of patients and compared with serum and tonsil tissue concentrations of controls. It may thus serve as a suitable method for the characterization of retinoid uptake and metabolism in the respective compartments.

Retinoic acid metabolism blocking agents (RAMBAs) for treatment of cancer and dermatological diseases

The naturally occurring retinoids and their synthetic analogs play a key role in differentiation, proliferation, and apoptosis, and their use/potential in oncology, dermatology and a variety of diseases are well documented. This review focuses on the role of all-trans-retinoic acid (ATRA), the principal endogenous metabolite of vitamin A (retinol) and its metabolism in oncology and dermatology. ATRA has been used successfully in differentiated therapy of acute promyelocytic leukemia, skin cancer, Kaposi's sarcoma, and cutaneous T-cell lymphoma, and also in the treatment of acne and psoriasis. However, its usefulness is limited by the rapid emergence of acquired ATRA resistance involving multifactoral mechanisms. A key mechanism of resistance involves ATRA-induced catabolism of ATRA. Thus, a novel strategy to overcome the limitation associated with exogenous ATRA therapy has been to modulate and/or increase the levels of endogenous ATRA by inhibiting the cytochrome P450-dependent ATRA-4-hydroxylase enzymes (particularly CYP26s) responsible for ATRA metabolism. These inhibitors are also referred to as retinoic acid metabolism blocking agents (RAMBAs). This review highlights development in the design, synthesis, and evaluation of RAMBAs. Major emphasis is given to liarozole, the most studied and only RAMBA in clinical use and also the new RAMBAs in development and with clinical potential.

Novel tetralone-derived retinoic acid metabolism blocking agents: synthesis and in vitro evaluation with liver microsomal and MCF-7 CYP26A1 cell assays

The potent inhibitory activity of novel 2-benzyltetralone and 2-benzylidenetetralone derivatives vs liver microsomal retinoic acid metabolizing enzymes and a MCF-7 CYP26A1 cell assay is described. In the liver microsomal assay, the 2-biphenylmethyl-6-hydroxytetralone derivatives 16a and 16b were found to be potent inhibitors (IC50 = 0.5 and 0.8 microM) compared with the broad spectrum P450 inhibitor ketoconazole and the retinoid mimetic R115866 (IC50 = 18.0 and 9.0 microM, respectively). In the MCF-7 CYP26A1 cell assay, the 2-(4-hydroxybenzyl)-6-methoxytetralone 5 and unsaturated benzylidene precursor 6 were found to be the most potent (IC50 = 7 and 5 microM, respectively), which was comparable with liarozole (7 microM) but considerably less active than R115866 (IC50 = 5 nM). With a CYP26A1 homology model, the tetralones were shown to be positioned in a hydrophobic tunnel with additional interactions, e.g., transition metal coordination and hydrogen-bonding interactions with GLY300, observed for the potent 4-hydroxyphenyl substituted inhibitors.