Chemical formula: C₁₄H₂₀N₂O₃ Molecular mass: 264.32 g/mol PubChem compound: 5311
Vorinostat inhibits the enzymatic activity of histone deacetylases HDAC1, HDAC2 and HDAC3 (Class I) and HDAC6 (Class II) at nanomolar concentrations (IC50<86 nM). These enzymes catalyze the removal of acetyl groups from the lysine residues of proteins, including histones and transcription factors. In some cancer cells, there is an overexpression of HDACs, or an aberrant recruitment of HDACs to oncogenic transcription factors causing hypoacetylation of core nucleosomal histones. Hypoacetylation of histones is associated with a condensed chromatin structure and repression of gene transcription. Inhibition of HDAC activity allows for the accumulation of acetyl groups on the histone lysine residues resulting in an open chromatin structure and transcriptional activation. In vitro, vorinostat causes the accumulation of acetylated histones and induces cell cycle arrest and/or apoptosis of some transformed cells. The mechanism of the antineoplastic effect of vorinostat has not been fully characterized.
A randomized, partially-blind, placebo-controlled, 2-period crossover study was performed to assess the effects of a single 800-mg dose of vorinostat on the QTc interval in 24 patients with advanced cancer. This study was conducted to assess the impact of vorinostat on ventricular repolarization. The upper bound of the 90% confidence interval of the placebo-adjusted mean QTc interval change-from-baseline was less than 10 msec at every time point through 24 hours. Based on these study results, administration of a single supratherapeutic 800-mg dose of vorinostat does not appear to prolong the QTc interval in patients with advanced cancer; however the study did not include a positive control to demonstrate assay sensitivity. In the fasted state, oral administration of a single 800-mg dose of vorinostat resulted in a mean AUC and Cmax and median Tmax of 8.6±5.7 µM∙hr and 1.7±0.67 µM and 2.1 (0.5-6) hours, respectively.
In clinical studies in patients with CTCL, three of 86 CTCL patients exposed to 400 mg once daily had Grade 1 (>450-470 msec) or 2 (>470-500 msec or increase of >60 msec above baseline) clinical adverse reactions of QTc prolongation. In a retrospective analysis of three Phase 1 and two Phase 2 studies, 116 patients had a baseline and at least one follow-up ECG. Four patients had Grade 2 (>470-500 msec or increase of >60 msec above baseline) and 1 patient had Grade 3 (>500 msec) QTc prolongation. In 49 non-CTCL patients from 3 clinical trials who had complete evaluation of QT interval, 2 had QTc measurements of >500 msec and 1 had a QTc prolongation of >60 msec.
The pharmacokinetics of vorinostat were evaluated in 23 patients with relapsed or refractory advanced cancer. After oral administration of a single 400-mg dose of vorinostat with a high-fat meal, the mean ± standard deviation area under the curve (AUC) and peak serum concentration (Cmax) and the median (range) time to maximum concentration (Tmax) were 5.5±1.8 µM∙hr, 1.2±0.62 µM and 4 (2-10) hours, respectively.
In the fasted state, oral administration of a single 400-mg dose of vorinostat resulted in a mean AUC and Cmax and median Tmax of 4.2±1.9 µM∙hr and 1.2±0.35 µM and 1.5 (0.5-10) hours, respectively. Therefore, oral administration of vorinostat with a high-fat meal resulted in an increase (33%) in the extent of absorption and a modest decrease in the rate of absorption (Tmax delayed 2.5 hours) compared to the fasted state. However, these small effects are not expected to be clinically meaningful. In clinical trials of patients with CTCL, vorinostat was taken with food.
At steady state in the fed-state, oral administration of multiple 400-mg doses of vorinostat resulted in a mean AUC and Cmax and a median Tmax of 6.0±2.0 µM∙hr, 1.2±0.53 µM and 4 (0.5-14) hours, respectively.
Vorinostat is approximately 71% bound to human plasma proteins over the range of concentrations of 0.5 to 50 µg/mL.
The major pathways of vorinostat metabolism involve glucuronidation and hydrolysis followed by β-oxidation. Human serum levels of two metabolites, O-glucuronide of vorinostat and 4-anilino-4-oxobutanoic acid were measured. Both metabolites are pharmacologically inactive. Compared to vorinostat, the mean steady state serum exposures in humans of the O-glucuronide of vorinostat and 4-anilino-4-oxobutanoic acid were 4-fold and 13-fold higher, respectively.
In vitro studies using human liver microsomes indicate negligible biotransformation by cytochromes P450 (CYP).
Vorinostat is eliminated predominantly through metabolism with less than 1% of the dose recovered as unchanged drug in urine, indicating that renal excretion does not play a role in the elimination of vorinostat. The mean urinary recovery of two pharmacologically inactive metabolites at steady state was 16±5.8% of vorinostat dose as the O-glucuronide of vorinostat, and 36±8.6% of vorinostat dose as 4-anilino-4-oxobutanoic acid. Total urinary recovery of vorinostat and these two metabolites averaged 52±13.3% of vorinostat dose. The mean terminal half-life (t½) was ~2.0 hours for both vorinostat and the O-glucuronide metabolite, while that of the 4-anilino-4-oxobutanoic acid metabolite was 11 hours.
Based upon an exploratory analysis of limited data, gender, race and age do not appear to have meaningful effects on the pharmacokinetics of vorinostat.
Vorinostat was not evaluated in patients <18 years of age.
The single dose pharmacokinetics of a 400 mg vorinostat dose was evaluated in patients with non-CTCL cancers with varying degrees of hepatic impairment. The mean AUC of vorinostat in patients with mild (bilirubin >1 to 1.5 × ULN or AST > ULN but bilirubin ≤ ULN) and moderate (bilirubin 1.5 to ≤3 × ULN) hepatic impairment increased by 50% compared to the AUC of vorinostat in patients with normal hepatic function. The mean vorinostat AUC in patients with severe hepatic impairment (bilirubin >3 × ULN) increased by 66% compared to the AUC of patients with normal hepatic function.
The safety of multiple daily doses of vorinostat was also evaluated in patients with non-CTCL cancers with varying degrees of hepatic impairment. The highest dose studied in mild, moderate and severe hepatic impairment was 400, 300 and 200 mg daily respectively. The incidence of Grade 3 or 4 adverse reactions was similar among the hepatic function groups. The most common Grade 3 or 4 adverse reaction was thrombocytopenia.
Reduce the dose in patients with mild to moderate hepatic impairment. There is not enough data in patients with severe hepatic impairment to recommend a dose modification.
Vorinostat was not evaluated in patients with renal impairment. However, renal excretion does not play a role in the elimination of vorinostat.
Vorinostat is not an inhibitor of CYP drug metabolizing enzymes in human liver microsomes at steady state Cmax of the 400 mg dose (Cmax of 1.2 µM vs IC50 of >75 µM). Gene expression studies in human hepatocytes detected some potential for suppression of CYP2C9 and CYP3A4 activities by vorinostat at concentrations higher (≥10 µM) than pharmacologically relevant. Thus, vorinostat is not expected to affect the pharmacokinetics of other agents. As vorinostat is not eliminated via the CYP pathways, it is anticipated that vorinostat will not be subject to drug-drug interactions when co-administered with drugs that are known CYP inhibitors or inducers. However, no formal clinical studies have been conducted to evaluate drug interactions with vorinostat.
In vitro studies indicate that vorinostat is not a substrate of human P-glycoprotein (P-gp). In addition, vorinostat has no inhibitory effect on human P-gp-mediated transport of vinblastine (a marker P-gp substrate) at concentrations of up to 100 µM. Thus, vorinostat is not likely to inhibit P-gp at the pharmacologically relevant serum concentration of 2 µM (Cmax) in humans.
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