Pharmacogenomics of Drug Metabolizing Enzymes and Transporters: Relevance to Precision Medicine

Pharmacogenetics: An Important Part of Drug Development with A Focus on Its Application

Since the human genome project in 2003, the view of personalized medicine to improve diagnosis and cure diseases at the molecular level became more real. Sequencing the human genome brought some benefits in medicine such as early detection of diseases with a genetic predisposition, treating patients with rare diseases, the design of gene therapy and the understanding of pharmacogenetics in the metabolism of drugs. This review explains the concepts of pharmacogenetics, polymorphisms, mutations, variations, and alleles, and how this information has helped us better understand the metabolism of drugs. Multiple resources are presented to promote reducing the gap between scientists, physicians, and patients in understanding the use and benefits of pharmacogenetics. Some of the most common clinical examples of genetic variants and how pharmacogenetics was used to determine treatment options for patients having these variants were discussed. Finally, we evaluated some of the challenges of implementing pharmacogenetics in a clinical setting and proposed actions to be taken to make pharmacogenetics a standard diagnostic tool in personalized medicine.

Alterations in the gene expression of drug and arachidonic acid-metabolizing Cyp450 in the livers of controlled and uncontrolled insulin-dependent diabetic mice

BACKGROUND

Diabetic patients have lower capacity to metabolize drugs in comparison to normal people. Therefore, the present study aimed to investigate the alterations in gene expression of drug and arachidonic acid metabolizing cytochrome p450s (cyp450s) in the livers of controlled (CDM) and uncontrolled (UDM) insulin-dependent diabetic mice.

METHODS

Balb/c mice were treated with single dose of streptozocin (240 mg/kg) to induce diabetes and compared with control group, which was treated with citric buffer (pH =4.5). After 3 days, the blood glucose level was measured to confirm the induction of diabetes. Normalization of blood glucose level in diabetic mice was achieved after 0.1 mL/kg Mixtard® insulin therapy for more 5 days. Then, the mice livers were isolated to extract RNA and convert it to cDNA. The gene expression of 14 genes, which play a major role in drug and arachidonic acid metabolism, were measured using quantitative real-time polymerase chain reaction technique.

RESULTS

It was found that the gene expression was downregulated (ANOVA test, P-value <0.05) in the livers of UDM mice. The most downregulated genes were cyp4a12, cyp1a2, and slc22a1 with more than 10-fold reduction. The livers of CDM mice showed significantly (P-value <0.05) higher levels of mRNA than UDM mice, but still lower than the non-diabetic mice.

CONCLUSION

This study concluded that hepatic gene expression of drug metabolizing and arachidonic acid- cyp450 enzymes is reduced in insulin-dependent diabetic mice, which can explain, at least in part, the variation in drug and fatty acid metabolism between normal and diabetic patients.

Clinical significance of CYP2C19 polymorphisms on the metabolism and pharmacokinetics of 11β-hydroxysteroid dehydrogenase type-1 inhibitor BMS-823778

AIMS

BMS-823778 is an inhibitor of 11β-hydroxysteroid dehydrogenase type-1, and thus a potential candidate for Type 2 diabetes treatment. Here, we investigated the metabolism and pharmacokinetics of BMS-823778 to understand its pharmacokinetic variations in early clinical trials.

METHODS

The metabolism of BMS-823778 was characterized in multiple in vitro assays. Pharmacokinetics were evaluated in healthy volunteers, prescreened as CYP2C19 extensive metabolizers (EM) or poor metabolizers (PM), with a single oral dose of [¹⁴ C]BMS-823778 (10 mg, 80 μCi).

RESULTS

Three metabolites (<5%) were identified in human hepatocytes and liver microsomes (HLM) incubations, including two hydroxylated metabolites (M1 and M2) and one glucuronide conjugate (M3). As the most abundant metabolite, M1 was formed mainly through CYP2C19. M1 formation was also correlated with CYP2C19 activities in genotyped HLM. In humans, urinary excretion of dosed radioactivity was significantly higher in EM (68.8%; 95% confidence interval 61.3%, 76.3%) than in PM (47.0%; 43.5%, 50.6%); only small portions (<2%) were present in faeces or bile from both genotypes. In plasma, BMS-823778 exposure in PM was significantly (5.3-fold, P = 0.0097) higher than in EM. Furthermore, total radioactivity exposure was significantly higher (P < 0.01) than BMS-823778 exposure in all groups, indicating the presence of metabolites. M1 was the only metabolite observed in plasma, and much lower in PM. In urine, the amount of M1 and its oxidative metabolite in EM was 7-fold of that in PM, while more glucuronide conjugates of BMS-823778 and M1 were excreted in PM.

CONCLUSIONS

CYP2C19 polymorphisms significantly impacted systemic exposure and metabolism pathways of BMS-823778 in humans.

Overcoming ABC transporter-mediated multidrug resistance: The dual role of tyrosine kinase inhibitors as multitargeting agents

Resistance to conventional and target specific antitumor drugs still remains one of the major cause of treatment failure and patience death. This condition often involves ATP-binding cassette (ABC) transporters that, by pumping the drugs outside from cancer cells, attenuate the potency of chemotherapeutics and negatively impact on the fate of anticancer therapy. In recent years, several tyrosine kinase inhibitors (TKIs) (e.g., imatinib, nilotinib, dasatinib, ponatinib, gefitinib, erlotinib, lapatinib, vandetanib, sunitinib, sorafenib) have been reported to interact with ABC transporters (e.g., ABCB1, ABCC1, ABCG2, ABCC10). This finding disclosed a very complex scenario in which TKIs may behave as substrates or inhibitors depending on the expression of specific pumps, drug concentration, affinity for transporters and types of co-administered agents. In this context, in-depth investigation on TKI chemosensitizing functions might provide a strong rationale for combining TKIs and conventional therapeutics in specific malignancies. The reposition of TKIs as antagonists of ABC transporters opens a new way towards anticancer therapy and clinical strategies aimed at counteracting drug resistance. This review will focus on some paradigmatic examples of the complex and not yet fully elucidated interaction between clinical available TKIs (e.g. BCR-ABL, EGFR, VEGFR inhibitors) with the main ABC transporters implicated in multidrug resistance.

LC-MS/MS quantification of sulfotransferases is better than conventional immunogenic methods in determining human liver SULT activities: implication in precision medicine

This study aims to determine whether enzyme activities are correlated with protein amounts and mRNA expression levels of five major human sulfotransferase (SULT) enzymes in 10 matched pericarcinomatous and hepatocellular carcinoma liver samples. The MRM UHPLC-MS/MS method, Western blot and RT-PCR were used along with SULT activity measurement using probe substrates. The LC-MS/MS method was specific for all five tested SULTs, whereas Western blot was specific for only two isoforms. The activities of SULT1A1, SULT1B1, SULT1E1 and SULT2A1 in 9 of 10 samples showed a significant decrease in tumor tissues relative to matched pericarcinomatous tissues, whereas the activities of SULT1A3 in 7 of 10 samples increased. The turnover numbers of SULTs did not change, except for SULT1A1. A generally high degree of correlations was observed between SULT activities and protein amounts (r² ≥ 0.59 except one), whereas a low degree of correlations was observed between SULT activities and mRNA expression levels (r² ≤ 0.48 except one). HCC reduced the SULT activities via impaired protein amounts. LC-MS/MS quantification of SULTs is highly reliable measurement of SULT activities, and may be adopted for implementing precision medicine with respect to drugs mainly metabolized by SULTs in healthy and HCC patients.

Examining How Our Shared Evolutionary History Shapes Future Disease Outcomes

Cardiometabolic diseases are major contributors to mortality and morbidity, and their burden displays global and regional disparities. Gene-environment interactions contribute to the pathogenesis of cardiometabolic diseases. Population differences in genetic structure, ancient environmental pressures that shape the human genome, and early life environmental adversities (e.g., in utero conditions) all contribute to observed disparities in global cardiometabolic diseases. The genetic and sociocultural diversity of global populations presents opportunities for discovering genomic loci that influence cardiometabolic diseases as illustrated by a few genetic, epigenetic, and population-genetic discoveries leading to notable understanding of disease mechanisms. However, African, Latin American and Hispanic, and indigenous peoples represent <4% of all genome-wide association study samples analyzed to date. Using examples of recent studies in African populations, we discuss the crucial importance of conducting genomic studies in ancestrally diverse populations to understand disease mechanisms and to prepare fertile ground for future delivery of precise health care to all individuals.