Pharmacokinetics of all-trans retinoic acid in pediatric patients with leukemia

Hypothesis of using albumin to improve drug efficacy in cancers accompanied by hypoalbuminemia

A common problem in many cancers is the resistance of some patients to common drugs or relapse. Hypoalbuminemia has been reported in some of resistant cancer patients.This article evaluates the usefulness of albumin in the treatment of drug-resistant cancers with hypoalbuminemia based on available evidences.Rapid metabolism and drug excretion from the body is one of the causes of drug resistance. Albumin is the major plasma protein to which almost all drugs are bound. There is some evidence that increasing drug binding to albumin has beneficial effects on drug efficacy in some cancers and cancer cells. On the other hand, some reports have shown that cancer cells can use albumin as the energy and amino acid source.We have hypothesized that in this particular group of cancers, adding albumin to a treatment regimen could have a beneficial effect on drug efficacy and dosage. In fact, excess albumin can prevent rapid metabolism of drug by increasing the fraction of albumin-bound drug, and can increase drug delivery to cancer cells due to the absorption of drug-albumin complex by cancer cells.

Opportunities and Challenges in Drug Development for Pediatric Cancers

The use of targeted small-molecule therapeutics and immunotherapeutics has been limited to date in pediatric oncology. Recently, the number of pediatric approvals has risen, and regulatory initiatives in the United States and Europe have aimed to increase the study of novel anticancer therapies in children. Challenges of drug development in children include the rarity of individual cancer diagnoses and the high prevalence of difficult-to-drug targets, including transcription factors and epigenetic regulators. Ongoing pediatric adaptation of biomarker-driven trial designs and further exploration of agents targeting non-kinase drivers constitute high-priority objectives for future pediatric oncology drug development. SIGNIFICANCE: Increasing attention to drug development for children with cancer by regulators and pharmaceutical companies holds the promise of accelerating the availability of new therapies for children with cancer, potentially improving survival and decreasing the acute and chronic toxicities of therapy. However, unique approaches are necessary to study novel therapies in children that take into account low patient numbers, the pediatric cancer genomic landscape and tumor microenvironment, and the need for pediatric formulations. It is also critical to evaluate the potential for unique toxicities in growing hosts without affecting the pace of discovery for children with these life-threatening diseases.

Physiologically Based Pharmacokinetic Model of All-trans-Retinoic Acid with Application to Cancer Populations and Drug Interactions

All-trans retinoic acid (atRA) is a front-line treatment of acute promyelocytic leukemia (APL). Due to its activity in regulating the cell cycle, it has also been evaluated for the treatment of other cancers. However, the efficacy of atRA has been limited by atRA inducing its own metabolism during therapy, resulting in a decrease of atRA exposure during continuous dosing. Frequent relapse occurs in patients receiving atRA monotherapy. In an attempt to combat therapy resistance, inhibitors of atRA metabolism have been developed. Of these, ketoconazole and liarozole have shown some benefits, but their usage is limited by side effects and low potency toward the cytochrome P450 26A1 isoform (CYP26A1), the main atRA hydroxylase. We determined the pharmacokinetic basis of therapy resistance to atRA and tested whether the complex disposition kinetics of atRA could be predicted in healthy subjects and in cancer patients in the presence and absence of inhibitors of atRA metabolism using physiologically based pharmacokinetic (PBPK) modeling. A PBPK model of atRA disposition was developed and verified in healthy individuals and in cancer patients. The population-based PBPK model of atRA disposition incorporated saturable metabolic clearance of atRA, induction of CYP26A1 by atRA, and the absorption and distribution kinetics of atRA. It accurately predicted the changes in atRA exposure after continuous dosing and when coadministered with ketoconazole and liarozole. The developed model will be useful in interpretation of atRA disposition and efficacy, design of novel dosing strategies, and development of next-generation atRA metabolism inhibitors.

Anorectal and urinary anomalies and aberrant retinoic acid metabolism in cytochrome P450 oxidoreductase deficiency

CONTEXT

Cytochrome P450 oxidoreductase (POR) is an electron donor for all microsomal P450 enzymes including CYP26 involved in inactivation of all-trans retinoic acid (atRA). Although previous studies in Por knockout mice suggest that atRA accumulation is relevant to various posterior organ abnormalities, a systematic analysis has not been performed for anorectal and urinary anomalies in patients with POR deficiency (PORD).

OBJECTIVE

To report the frequencies of anorectal and urinary anomalies and plasma atRA values in PORD patients.

PATIENTS

We studied 37 Japanese patients with PORD, consisting of 15 homozygotes for R457H (group A), 15 compound heterozygotes for R457H and one apparently null mutation (group B), and seven patients with other combinations of mutations (group C). Since R457H is a severe hypomorphic mutation, the residual POR function is predicted to be higher in group A than in group B.

RESULTS

Imperforate anus was observed in four patients (10.8%) and vesicoureteral reflux was found in three patients (8.1%), with no significant difference in the frequencies of such anomalies between groups A and B. In addition, a complex urogenital malformation including penile agenesis was identified in one patient. Plasma atRA values were above the reference range in nine of 12 patients examined, and were similar between groups A and B and between patients with and without anomalies.

CONCLUSIONS

The results imply that aberrant atRA metabolism due to CYP26 deficiency underlies various anorectal and urinary anomalies in patients with PORD. Clinical phenotypes may be primarily determined by maternal oral retinol intake during pregnancy, and plasma atRA values may be largely influenced by the amount of postnatal oral retinol intake in such patients.

All-trans-retinoic acid inhibits the development of mesangial proliferative glomerulonephritis in interleukin-6 transgenic mice

All-trans-retinoic acid (ATRA), a vitamin A derivative, was reported to suppress the interleukin-6 (IL-6) production and to downregulate the IL-6 receptor (IL-6R) and/or its signal transducer glycoprotein 130. We investigated the in vivo antinephritic effect of ATRA on IL-6 transgenic mice which had developed mesangial proliferative glomerulonephritis (PGN) as well as its in vitro inhibitory effect on the proliferation of rat mesangial cells. In vivo experiments on IL-6 transgenic mice showed that ATRA administration suppressed proteinuria and hematuria and reduced the IL-6 concentrations; furthermore, histological examination demonstrated that it improved PGN. In vitro experiments using rat mesangial cells demonstrated that ATRA inhibited cell growth in a dose-dependent manner within a range from 10(-4) to 10(-6) M. This inhibition by ATRA was partially counteracted by the addition of IL-6. RT-PCR assay results showed that ATRA also reduced IL-6R, but not the glycoprotein 130 expression in mesangial cells. These findings indicate that, by blocking of the IL-6 function, ATRA may be therapeutically effective in PGN.

Pharmacology of all-trans-retinoic acid in children with acute promyelocytic leukemia

BACKGROUND

Due to severe side effects in virtually all children treated with a standard dose of 45 mg/m(2)/day all-trans-retinoic acid (ATRA) for acute promyelocytic leukemia (APL) the AML-BFM study group reduced the dosage to 25 mg/m(2)/day. For the lack of data on the use of ATRA at this dosage in children with APL, the study group further decided to evaluate the pharmacokinetics and metabolism of ATRA in children.

PROCEDURE

Twenty-three pharmacokinetic and metabolic profiles of ATRA were studied in 14 children (aged 0.9-18.4 years) with APL. Eleven plasma samples were collected over a period of 8 hr and analyzed for ATRA and its metabolites by high-performance liquid chromatography.

RESULTS

Peak plasma concentrations of ATRA were characterized by wide interpatient variability (range: 28.6-513.0 nM). Compared to adults the same metabolic pathways were observed in children. Even though peak plasma concentrations were in the lower range of those considered effective in vitro, ATRA side effects, notably neurotoxicity, still required dose reduction, treatment break, or drug withdrawal in eight patients. In this small number of patients, neurotoxicity could not be related to age or any specific level of ATRA or metabolites in the plasma. Plasma concentrations of vitamin A, however, were significantly higher in those patients, who developed signs of neurotoxicity (P = 0.03, Mann-Whitney Rank Sum test).

CONCLUSIONS

Considering the low plasma concentrations and the persistence of toxicity in spite of dose reduction intermittent dosing schedules might be considered as an alternative to further dose reduction of ATRA in the treatment of APL especially in children, who might be at risk of ATRA-induced neurotoxicity.

Mutations in the E-Domain of RARα Portion of the PML/RARα Chimeric Gene May Confer Clinical Resistance to All-transRetinoic Acid in Acute Promyelocytic Leukemia

The binding of all-trans retinoic acid (ATRA) to the ligand-binding region in the E-domain of retinoic acid receptor-α (RARα) modifies the transcriptional activity of RARα protein. ATRA probably induces differentiation of acute promyelocytic leukemia (APL) cells by binding to the E-domain of the RARα portion (RARα/E-domain) of PML/RARα chimeric protein. Therefore, molecular alteration in the RARα/E-domain of the chimeric gene is one mechanism by which patients with APL may acquire resistance to ATRA therapy. In this study using reverse transcription-polymerase chain reaction and single-strand conformation polymorphism, DNA segments amplified from the RARα/E-domain in fresh APL cells of 23 APL patients (8 males and 15 females from 4 to 76 years of age) were screened for mutations. Of those patients, 3 patients (1 with de novo and 2 with relapse) had clinical resistance to ATRA therapy. We found mutations in the RARα/E-domain of PML/RARα chimeric gene exclusively in the 2 patients who exhibited ATRA-resistance at relapse, whereas the mutations were not detected at their initial onset. Interestingly, these patients received a prolonged or intermittent administration of ATRA before relapse with ATRA-resistance. The mutations lead to the change of amino acid in the ligand-binding region of RARα/E-domain, Arg272Gln, or Met297Leu according to the amino acid sequence of RARα, respectively. Further study demonstrated that the in vitro ligand-dependent transcriptional activity of the mutant PML/RARα protein was significantly decreased as compared with that of wild-type PML/RARα. These findings suggest that mutations in the RARα/E-domain of the PML/RARα chimeric gene may confer clinical resistance to ATRA therapy in patients with APL.

Mutations in the E-Domain of RARα Portion of the PML/RARα Chimeric Gene May Confer Clinical Resistance to All-transRetinoic Acid in Acute Promyelocytic Leukemia

The binding of all-trans retinoic acid (ATRA) to the ligand-binding region in the E-domain of retinoic acid receptor-α (RARα) modifies the transcriptional activity of RARα protein. ATRA probably induces differentiation of acute promyelocytic leukemia (APL) cells by binding to the E-domain of the RARα portion (RARα/E-domain) of PML/RARα chimeric protein. Therefore, molecular alteration in the RARα/E-domain of the chimeric gene is one mechanism by which patients with APL may acquire resistance to ATRA therapy. In this study using reverse transcription-polymerase chain reaction and single-strand conformation polymorphism, DNA segments amplified from the RARα/E-domain in fresh APL cells of 23 APL patients (8 males and 15 females from 4 to 76 years of age) were screened for mutations. Of those patients, 3 patients (1 with de novo and 2 with relapse) had clinical resistance to ATRA therapy. We found mutations in the RARα/E-domain of PML/RARα chimeric gene exclusively in the 2 patients who exhibited ATRA-resistance at relapse, whereas the mutations were not detected at their initial onset. Interestingly, these patients received a prolonged or intermittent administration of ATRA before relapse with ATRA-resistance. The mutations lead to the change of amino acid in the ligand-binding region of RARα/E-domain, Arg272Gln, or Met297Leu according to the amino acid sequence of RARα, respectively. Further study demonstrated that the in vitro ligand-dependent transcriptional activity of the mutant PML/RARα protein was significantly decreased as compared with that of wild-type PML/RARα. These findings suggest that mutations in the RARα/E-domain of the PML/RARα chimeric gene may confer clinical resistance to ATRA therapy in patients with APL.