Inhibition of all-trans-retinoic acid metabolism by fluconazole in vitro and in patients with acute promyelocytic leukemia

Treatment With a New Synthetic Retinoid, Am80, of Acute Promyelocytic Leukemia Relapsed From Complete Remission Induced by All-trans Retinoic Acid

Differentiation therapy with all-trans retinoic acid (ATRA) has marked a major advance and become the first choice drug in the treatment of acute promyelocytic leukemia (APL). However, patients who relapse from ATRA-induced complete remission (CR) have difficulty in obtaining a second CR with a second course of ATRA therapy alone. We tested the efficacy of a new synthetic retinoid, Am80, in APL that had relapsed from CR induced by ATRA in a prospective multicenter study. Am80 is approximately 10 times more potent than ATRA as an in vitro differentiation inducer, is more stable to light, heat, and oxidation than ATRA, has a low affinity for cellular retinoic acid binding protein, and does not bind to retinoic acid receptor-γ. Patients received Am80, 6 mg/m2, orally alone daily until CR. Of 24 evaluable patients, 14 (58%) achieved CR. The interval from the last ATRA therapy was not different between CR and failure cases. The clinical response was well correlated with the in vitro response to Am80 in patients examined. Adverse events included 1 retinoic acid syndrome, 1 hyperleukocytosis, 9 xerosis, 8 cheilitis, 16 hypertriglyceridemia, and 15 hypercholesterolemia, but generally milder than those of ATRA, which all patients had received previously. Am80 is effective in APL relapsed from ATRA-induced CR and deserves further trials, especially in combination with chemotherapy.

Treatment With a New Synthetic Retinoid, Am80, of Acute Promyelocytic Leukemia Relapsed From Complete Remission Induced by All-trans Retinoic Acid

Differentiation therapy with all-trans retinoic acid (ATRA) has marked a major advance and become the first choice drug in the treatment of acute promyelocytic leukemia (APL). However, patients who relapse from ATRA-induced complete remission (CR) have difficulty in obtaining a second CR with a second course of ATRA therapy alone. We tested the efficacy of a new synthetic retinoid, Am80, in APL that had relapsed from CR induced by ATRA in a prospective multicenter study. Am80 is approximately 10 times more potent than ATRA as an in vitro differentiation inducer, is more stable to light, heat, and oxidation than ATRA, has a low affinity for cellular retinoic acid binding protein, and does not bind to retinoic acid receptor-γ. Patients received Am80, 6 mg/m2, orally alone daily until CR. Of 24 evaluable patients, 14 (58%) achieved CR. The interval from the last ATRA therapy was not different between CR and failure cases. The clinical response was well correlated with the in vitro response to Am80 in patients examined. Adverse events included 1 retinoic acid syndrome, 1 hyperleukocytosis, 9 xerosis, 8 cheilitis, 16 hypertriglyceridemia, and 15 hypercholesterolemia, but generally milder than those of ATRA, which all patients had received previously. Am80 is effective in APL relapsed from ATRA-induced CR and deserves further trials, especially in combination with chemotherapy.

Induction of cytochrome P450 3A by retinoids in rat hepatocyte culture

1. Rat hepatocytes cultured on a Matrigel matrix were exposed for 48 h to all-trans-retinoic acid, 9-cis-retinoic acid, 13-cis-retinoic acid or fenretinide. 2. Cytochrome P450 3A (CYP3A) RNA levels were increased by approximately eightfold in hepatocytes treated with the retinoids compared to control cultures. 3. CYP1A1 and CYP1A2 RNA levels were only slightly affected or unaffected by the retinoids. 4. The induction of CYP3A by these therapeutically-useful retinoids suggests that they may share a common mechanism for accelerated drug catabolism and acquired clinical resistance.

N-4-hydroxyphenylretinamide enhances retinoic acid-induced differentiation and retinoylation of proteins in the human acute promyelocytic leukemia cell line, NB4, by a mechanism that may involve inhibition of retinoic acid catabolism

All-trans-retinoic acid (RA) induces differentiation of acute promyelocytic leukemia cells both in vitro and in vivo and is an alternative to cytotoxic chemotherapy in the treatment of acute promyelocytic leukemia. However, despite a complete remission rate of about 90%, most patients relapse and are resistant to further treatment with RA. This resistance primarily is due to an increased systemic catabolism of RA. In this study we examined the catabolism of RA by the human acute promyelocytic leukemia cell line NB4 and the human myeloid leukemia cell line HL60. NB4 cells converted RA to 4-hydroxy-RA, 4-oxo-RA and more polar unidentified retinoids at a much greater rate than HL60 cells. Exposure of NB4 cells to RA induced RA catabolism. We found that 4-hydroxyphenylretinamide (4-HPR) inhibited the catabolism of RA. This inhibition was dosedependent and greater, on a molar basis, than the inhibition seen with the cytochrome P450 inhibitor, ketoconazole, or two synthetic retinoids, Ch55 and Am80. 4-HPR alone was a poor inducer of differentiation of NB4 cells. However, it markedly enhanced RA-induced differentiation and increased the level of retinoylation, the covalent binding of RA to proteins. These results suggest some retinoid analogs, including 4-HPR, may have clinical utility because of their ability to increase the biological half-life of RA.