Pharmacogenetics of irinotecan: clinical perspectives on the utility of genotyping

Role of pharmacogenomics in drug discovery and development

Pharmacogenetics and pharmacogenomics are two major emerging trends in medical sciences, which influence the success of drug development and therapeutics. In current times, though pharmacogenetic studies are being done extensively for research, its application for drug development needs to get started on a large scale. The major determinants of success of a new drug compound, viz safety and efficacy, have become more predictable, with the advent of pharmacogenetic studies. There is a need felt for pharmacogenomic studies, where the effects of multiple genes are assessed with the study of entire genome.Pharmacogenetic studies can be used at various stages of drug development. The effect of drug target polymorphisms on drug response can be assessed and identified. In clinical studies, pharmacogenetic tests can be used for stratification of patients based on their genotype, which corresponds to their metabolizing capacity. This prevents the occurrence of severe adverse drug reactions and helps in better outcome of clinical trials. This can also reduce attrition of drug compounds. Further, the variations in drug response can be better studied with the wider application of pharmacogenomic methods like genome wide scans, haplotype analysis and candidate gene approaches. The cost of pharmacogenetic testing has become very low, with the advent of newer high throughput genotyping systems. However, the cost of pharmacogenomic methods continues to be very high. As the treatment with several drugs is being more and more pharmacogeneticaly guided (e.g. warfarin and irinotecan), the FDA has laid down guidelines for pharmaceutical firms regarding submission of pharmacogenetic data for their drug products in labelling.

Correlation of CDA, ERCC1, and XPD polymorphisms with response and survival in gemcitabine/cisplatin-treated advanced non-small cell lung cancer patients

PURPOSE

Selecting patients according to key genetic characteristics may help to tailor chemotherapy and optimize the treatment in non-small cell lung cancer (NSCLC). Polymorphisms at the xeroderma pigmentosum group D (XPD), excision repair cross-complementing 1 (ERCC1), and cytidine deaminase (CDA) genes have been associated with alterations in enzymatic activity and may change sensitivity to the widely used cisplatin-gemcitabine regimen.

EXPERIMENTAL DESIGN

Analyses of CDA, XPD, and ERCC1 polymorphisms were done on blood samples of 65 chemotherapy-naïve, advanced NSCLC patients treated with cisplatin-gemcitabine. Furthermore, CDA enzymatic activity was evaluated by high-performance liquid chromatography analysis. Association between XPD Asp(312)Asn and Lys(751)Gln, ERCC1 C118T, and CDA Lys(27)Gln polymorphisms and response, clinical benefit, toxicity, time to progression (TTP), and overall survival (OS) was estimated using Pearson's chi(2) tests, the Kaplan-Meier method, the log-rank test, and the Cox proportional hazards model.

RESULTS

The CDA Lys(27)Lys polymorphism significantly correlated with better clinical benefit (P = 0.04) and grade > or =3 neutropenia and thrombocytopenia, as well as with longer TTP and OS (P = 0.006 and P = 0.002, respectively), whereas no significant associations were found among ERCC1 and XPD polymorphisms and both response and clinical outcome. Finally, the enzymatic activity assay showed a significant lower mean in subjects harboring the CDA Lys(27)Lys polymorphism.

CONCLUSIONS

Our data suggested the role of CDA Lys(27)Lys polymorphism as a possible predictive marker of activity, toxicity, TTP, and OS in advanced NSCLC patients treated with cisplatin and gemcitabine. These results may be explained by the lower enzymatic activity associated with the Lys(27)Lys CDA and offer a potential new tool for treatment optimization.

The multidisciplinary management of gastrointestinal cancer. The use of molecular markers in the diagnosis and treatment of colorectal cancer

Rapidly growing insights into the molecular biology of colorectal cancer led to high hopes for the identification of molecular markers to be used in optimised and tailored treatment regimens for this disorder. However, no molecular marker has yet made it into daily practice. In this review we will discuss some of the potential molecular markers, focus on the lessons learnt from marker development and identify strategies for the future.

Lopinavir–Ritonavir Dramatically Affects the Pharmacokinetics of Irinotecan in HIV Patients With Kaposi’s Sarcoma

The coadministration of protease inhibitors with anticancer drugs in the management of human immunodeficiency virus-related malignancies can cause potential drug-drug interactions. The effect of lopinavir/ritonavir (LPV/RTV) on the pharmacokinetics of irinotecan (CPT11) has been investigated in seven patients with Kaposi's sarcoma. Coadministration of LPV/RTV reduces the clearance of CPT11 by 47% (11.3+/-3.5 vs 21.3+/-6.3 l/h/m(2), P=0.0008). This effect was associated with an 81% reduction (P=0.02) of the AUC (area under the curve) of the oxidized metabolite APC (7-ethyl-10-[4-N-(5-aminopentanoic-acid)-1-piperidino]-carbonyloxycamptothecin). The LPV/RTV treatment also inhibited the formation of SN38 glucuronide (SN38G), as shown by the 36% decrease in the SN38G/SN38 AUCs ratio (5.9+/-1.6 vs 9.2+/-2.6, P=0.002) consistent with UGT1A1 inhibition by LPV/RTV. This dual effect resulted in increased availability of CPT11 for SN38 conversion and reduced inactivation on SN38, leading to a 204% increase (P=0.0001) in SN38 AUC in the presence of LPV/RTV. The clinical consequences of these substantial pharmacokinetic changes should be investigated.

A pharmacogenomics primer

The human genome project and related research initiatives have enabled the identification of a significant number of genetic variants that are predictive of drug response and outcome (pharmacogenomic biomarkers). As yet, incorporation of routine pharmacogenomic testing into clinical practice has been relatively modest. Potential barriers to adoption include a relative lack of prospective controlled trials establishing the benefits of such testing, economic constraints, and ethical concerns, among others. Clinicians considering the use of pharmacogenomic testing in their practice also may be unfamiliar with the concepts and principles underlying this rapidly evolving discipline. Consequently, the purpose of this review is to provide the clinical pharmacologist with a primer on the principles and molecular mechanisms underlying pharmacogenomics. In addition, the methods currently being used to discover novel pharmacogenomic biomarkers and then apply these to clinical practice will be described.

Risk-based and diagnostics-linked personalized medicine for cancer

Personalized medicine is gaining momentum in healthcare by allowing physicians to determine an individual’s predisposition to different diseases and to better diagnose and treat those diseases. Personalized medicine is frequently described as the right drug for the right patient at the right time; that is, a physician will prescribe treatment based on the individual characteristics of each patient such that the patient is likely to respond to a particular treatment with minimal adverse events. The heterogeneity of cancer makes the implementation of personalized medicine a necessity.