Population Pharmacokinetic and Pharmacogenetic Analysis of Mitotane in Patients with Adrenocortical Carcinoma: Towards Individualized Dosing.

BACKGROUND: Mitotane is the only approved treatment for patients with adrenocortical carcinoma (ACC). A better explanation for the variability in the pharmacokinetics (PK) of mitotane, and the optimization and individualization of mitotane treatment, is desirable for patients. OBJECTIVES: This study aims to develop a population PK (PopPK) model to characterize and predict the PK profiles of mitotane in patients with ACC, as well as to explore the effect of genetic variation on mitotane clearance. Ultimately, we aimed to facilitate mitotane dose optimization and individualization for patients with ACC. METHODS: Mitotane concentration and dosing data were collected retrospectively from the medical records of patients with ACC taking mitotane orally and participating in the Dutch Adrenal Network. PopPK modelling analysis was performed using NONMEM (version 7.4.1). Genotypes of drug enzymes and transporters, patient demographic information, and clinical characteristics were investigated as covariates. Subsequently, simulations were performed for optimizing treatment regimens. RESULTS: A two-compartment model with first-order absorption and elimination best described the PK data of mitotane collected from 48 patients. Lean body weight (LBW) and genotypes of CYP2C19*2 (rs4244285), SLCO1B3 699A>G (rs7311358) and SLCO1B1 571T>C (rs4149057) were found to significantly affect mitotane clearance (CL/F), which decreased the coefficient of variation (CV%) of the random inter-individual variability of CL/F from 67.0 to 43.0%. Fat amount (i.e. body weight - LBW) was found to significantly affect the central distribution volume. Simulation results indicated that determining the starting dose using the developed model is beneficial in terms of shortening the period to reach the therapeutic target and limit the risk of toxicity. A regimen that can effectively maintain mitotane concentration within 14-20 mg/L was established. CONCLUSIONS: A two-compartment PopPK model well-characterized mitotane PK profiles in patients with ACC. The CYP2C19 enzyme and SLCO1B1 and SLCO1B3 transporters may play roles in mitotane disposition. The developed model is beneficial in terms of optimizing mitotane treatment schedules and individualizing the initial dose for patients with ACC. Further validation of these findings is still required.

Differences in 5-hydroxytryptamine-3B haplotype frequencies between Asians and Caucasians.

BACKGROUND: The 5-hydroxytryptamine (5-HT3) receptor is a ligand-operated ion channel with five different receptor subunits (5-HT3A, B, C, D, and E) found in humans. Activation of 5-HT3 receptors influences various effects such as drug-induced emesis and causes behavioral problems such as anxiety, depression and cognitive disorders. To explore interethnic differences in the response to 5-HT3 antagonists, we studied haplotype frequencies in the gene encoding the 5-HT3B receptor in Asians and Caucasians. METHODS: Three single nucleotide polymorphisms (SNPs) of the 5-HT3B receptor gene, i.e., deletion AAG at the 5'-UTR position, 18792A>G at the intron position, and 46698G>A at the 3' near gene position, were selected and genotyped in 165 Indonesian cancer patients and 188 Caucasian healthy volunteers. Haplotypes were set with gPlink, whereas the differences in haplotype frequencies between Indonesians and Caucasians were compared using multivariate analysis. RESULTS: The haplotype profiles based on the deletion AAG, 18792A>G and 46698G>A were AAGAA, AAGAG, AAGGG, and deletion AG in both Indonesians and Caucasians. The frequency of the AAGAG haplotype was 54.8% in Indonesians and 39.9% in Caucasians (p<0.05). The frequency of the AAGGG haplotype was 14.3% in Indonesians and 29.3% in Caucasians. Moreover, there were significant differences in the frequencies of haplotype pairs between Indonesians and Caucasians (p<0.001). CONCLUSION: Indonesian cancer patients had significantly different AAGAG and AAGGG haplotype frequencies of the gene encoding the 5-HT3B receptor compared to healthy Caucasians. This finding could be useful for understanding interethnic differences in the response to drugs targeting the 5-HT3B receptor in cancer-treatment-related emesis.

Association of ABCB1, 5-HT3B receptor and CYP2D6 genetic polymorphisms with ondansetron and metoclopramide antiemetic response in Indonesian cancer patients treated with highly emetogenic chemotherapy.

OBJECTIVE: Suboptimal treatment of chemotherapy-induced nausea and vomiting and unsatisfactory response to antiemetic drugs cause impairment of cancer patient's daily functioning. This study was aimed to investigate the association of selected germline polymorphisms with ondansetron and metoclopramide response in Indonesian cancer patients treated with highly emetogenic chemotherapy. METHODS: We enrolled 202 chemotherapy naïve patients treated with cisplatin at a dosage of ≥50 mg/m(2) as monotherapy or as combined chemotherapy. Ondansetron 8 mg and dexamethasone 8 mg intravenously were the standard antiemetic therapy for prevention of acute chemotherapy-induced nausea and vomiting. Metoclopramide 10 mg orally, three times per day as fixed prescription, was given until 5 days after chemotherapy to prevent delayed chemotherapy-induced nausea and vomiting. Primary and secondary outcomes were the occurrence of chemotherapy-induced nausea and vomiting in the acute and delayed phase. The following single-nucleotide polymorphisms were determined in ABCB1: rs1045642, rs2032582 and rs1128503; in 5-HT3B-R: rs45460698, rs4938058 and rs7943062; and in CYP2D6: rs16947 (CYP2D6 2), rs3892097 (CYP2D6 4) and rs1065852 (CYP2D6 10) using Taqman assays. RESULTS: During the acute phase, 21.8 and 30.2% patients experienced Grade 3 and 4 nausea and vomiting, respectively, whereas 38.6% patients experienced nausea and/or vomiting in the delayed phase. Carriers of the CTG haplotype of the ABCB1 gene experienced Grade 3 and 4 chemotherapy-induced nausea and vomiting more often than other haplotypes in the delayed phase (P< 0.05). No associations were found with the 5-HT3B receptor haplotypes and CYP2D6-predicted phenotypes. CONCLUSIONS: Our study shows that in Indonesian cancer patients treated with highly cytostatic emetogenic, carriership of the CTG haplotype of the ABCB1 gene is related to an increased risk of delayed chemotherapy-induced nausea and vomiting.