Pharmacokinetic and Pharmacogenetic Studies of Cyclophosphamide based Chemotherapy and Tamoxifen in Ethiopian Breast Cancer Patients
| dc.contributor.advisor | Pro.Makonnen, Eyasu(Ph.D) | |
| dc.contributor.author | Ahmed, Jemal Hussien(PhD) | |
| dc.date.accessioned | 2020-12-06T08:13:09Z | |
| dc.date.accessioned | 2023-11-06T08:07:59Z | |
| dc.date.available | 2020-12-06T08:13:09Z | |
| dc.date.available | 2023-11-06T08:07:59Z | |
| dc.date.issued | 2019-01 | |
| dc.description.abstract | Introduction: Breast cancer is the most frequently diagnosed cancer among women in both developed and developing countries. Its treatment involves a multi-modality approach to eradicate residual cancer and prevent recurrent disease. Large inter-individual variations in the phamacokinetics and treatment outcome of cyclophosphamide and tamoxifen have been reported. In addition to other patient factors such as age, sex and etc, pharmacogenetic variations have been implicated to potentially influence the pharmacokinetics of anticancer drugs resulting in suboptimal effects and/or unpredictable toxicity. This thesis contributes to better increase our understanding of the implication of pharmacogentic variations in the treatment of breast cancer. Objective: The aim of this thesis was to investigate the effect of genetic polymorphism of drug metabolizing enzymes and transporter proteins on the pharmacokinetics and pharmacodynamics of cyclophosphamide and pharmacokinetics of tamoxifen metabolites among Ethiopian breast cancer patients. Methods: The study was conducted in breast cancer patients who were on CPA based chemotherapy (chemotherapy group) and on tamoxifen (tamxifen group). Drug and metabolite quantification was performed using HPLC (cyclophosphamide) or LC/MS/MS (Tam and its metabolites). Genotyping of candidate genes encoding drug metabolizing enzymes and transporter proteins, relevant to cyclophosphamide and tamoxifen metabolism and transport including CYP2B6, CYP2D6, CYP2C9, CYP2C19, CYP2J2, CYP3A5, POR, and ABCB1 and UGT2B15, was done using TaqMan TM allele specific PCR. CYP2D6 gene copy number was also determined by TaqMan TM Copy Number Assay. Among chemotherapy group, hematological toxicity (neutropenia, anemia, and thrombocytopenia) were also monitored throughout chemotherapy cycle. A population PK-PD modeling of cyclophosphamide was performed using non linear mixed effect modeling (NONMEM) software. Result: In study I, the incidence of chemotherapy induced grade 3 or 4 hematological toxicity was 51.0% (95% confidence interval (CI) = 44.54 – 57.46%). Most of the hematologic toxicities were neutropenic toxicity (50.2%). CYP2J2*7 variant allele and low baseline white blood cells count (grade 1 leukocytopenia), or low neutrophils count (grade 1 or 2 neutropenia), were associated with increased risk of grade 3 or 4 hematologic toxicity in the subsequent cycles. Patients carrying CYP2C9 *2 or *3 alleles were associated with lower incidence of hematologic toxicity. In study II, the overall actual average RDI was 81.9%. The proportion of patients who received reduced RDI < 85% of the standard/planned dose intensity was 56.6%. The independent risk predictors of reduced RDI were CYP2J2*7 allele, BMI < = 18.4 kg/m (underweight), low baseline leukocyte count, and low baseline neutrophils count. On the other hand, the odds of receiving reduced RDI was lower in patients with CYP2B6 *6/*6 genotype. In study 3, the PK analysis showed that cyclophosphamide was described by one compartment pharmacokinetic model with population clearance, and apparent volume of distribution of 5.41 L/hr and 46.5 L, respectively. The inter-individual variability (IIV) in clearance was 51% (38.9% and 49.3% for 500 and 600 mg/m 2 CPA regimen group, respectively). CYP3A5 and CYP2C9 genotypes, body surface area and cyclophosphamide dosing regimen were identified as significant predictors of PK parameters. Plasma cyclophosphamide exposure moderately and positively predicts neutropenic toxicity. In study IV, the proportion of patients with low endoxifen concentration (below 5.9 ng/mL) was 35.8%. Large inter-individual variability in endoxifen concentration and MR was observed (coefficient of variation 74.6% and 59%, respectively). An increase in CYP2D6 activity score (AS) was associated with a corresponding increment in endoxifen concentration and metabolic ratios (MR E/NDM E/NDM , MR ). ABCB1 was also significantly associated with MR E/NDM (p = 0.042) and MR E/4-HT (p = 0.015). Carriers of G allele for ABCB1 had a lower metabolic ratios for MR (0.022 vs 0.041; p = 0.042) and MR E/4-HT E/NDM (2.52 vs 3.02, p = 0.016) compared to the wild type allele (ABCB1, allele A). Moreover, CYP2D6 diplotype explained 29% of the variability in endoxifen concentration and 46% of the variability in MR Similarly, CYP2D6 phenotype explained 26.3% of the variability in endoxifen concentration and 40.9% of the variability in MR E/NDM. . In conclusion, we report high rates of chemotherapy-induced hematological toxicities causing larger proportion of patients to receive inadequate RDI. Patients carrying CYP2J2 *7 allele and with low baseline WBC or ANC are at a higher risk for chemotherapy induced hematologic toxicities and receiving reduced RDI. Such patients require prior support and close follow up during chemotherapy. CYP3A5, and CYP2C9 genotypes, CPA dosage regimen, BMI, and BSA, influence the PK of CPA. Plasma CPA exposure moderately and positively predicts neutropenic toxicity. On the other hand, CYP2D6, POR and ABCB1 explain the interindividual variations of endoxifen. Tamoxifen therapy guided by CYP2D6 genotyping in clinical practice may assist treatment decision-making for optimal patient benefit. E/NDM and MR E/4-HT 4HT/Tam | en_US |
| dc.identifier.uri | http://etd.aau.edu.et/handle/123456789/23873 | |
| dc.language.iso | en_US | en_US |
| dc.publisher | Addis Abeba University | en_US |
| dc.subject | Pharmacokinetics ,Pharmacogenetic Studies ,Cyclophosphamide ,Chemotherapy ,Tamoxifen , Ethiopian Breast Cancer Patients | en_US |
| dc.title | Pharmacokinetic and Pharmacogenetic Studies of Cyclophosphamide based Chemotherapy and Tamoxifen in Ethiopian Breast Cancer Patients | en_US |
| dc.type | Thesis | en_US |