Population differences in platinum toxicity as a means to identify novel genetic susceptibility variants

Review of genetic and pharmacogenetic differences in cytotoxic and targeted therapies for pancreatic cancer in African Americans

Pancreatic ductal adenocarcinoma (PDAC) is currently the third leading cause of cancer mortality and the incidence is projected to increase by 2030. Despite recent advances in its treatment, African Americans have a 50-60% higher incidence and 30% higher mortality rate when compared to European Americans possibly resulting from differences in socioeconomic status, access to healthcare, and genetics. Genetics plays a role in cancer predisposition, response to cancer therapeutics (pharmacogenetics), and in tumor behavior, making some genes targets for oncologic therapeutics. We hypothesize that the germline genetic differences in predisposition, drug response, and targeted therapies also impact PDAC disparities. To demonstrate the impact of genetics and pharmacogenetics on PDAC disparities, a review of the literature was performed using PubMed with variations of the following keywords: pharmacogenetics, pancreatic cancer, race, ethnicity, African, Black, toxicity, and the FDA-approved drug names: Fluoropyrimidines, Topoisomerase inhibitors, Gemcitabine, Nab-Paclitaxel, Platinum agents, Pembrolizumab, PARP-inhibitors, and NTRK fusion inhibitors. Our findings suggest that the genetic profiles of African Americans may contribute to disparities related to FDA approved chemotherapeutic response for patients with PDAC. We recommend a strong focus on improving genetic testing and participation in biobank sample donations for African Americans. In this way, we can improve our current understanding of genes that influence drug response for patients with PDAC.

Extending the lymphoblastoid cell line model for drug combination pharmacogenomics

Combination drug therapies have become an integral part of precision oncology, and while evidence of clinical effectiveness continues to grow, the underlying mechanisms supporting synergy are poorly understood. Immortalized human lymphoblastoid cell lines (LCLs) have been proven as a particularly useful, scalable and low-cost model in pharmacogenetics research, and are suitable for elucidating the molecular mechanisms of synergistic combination therapies. In this review, we cover the advantages of LCLs in synergy pharmacogenomics and consider recent studies providing initial evidence of the utility of LCLs in synergy research. We also discuss several opportunities for LCL-based systems to address gaps in the research through the expansion of testing regimens, assessment of new drug classes and higher-order combinations, and utilization of integrated omics technologies.

Current Insights into Interethnic Variability in Testicular Cancers: Population Pharmacogenetics, Clinical Trials, Genetic Basis of Chemotherapy- Induced Toxicities and Molecular Signal Transduction

Testicular cancer is an aggressive malignancy with a rising incidence rate across the globe. Testicular germ cell tumors are the most commonly diagnosed cancers, and surgical removal of the testes is often a radical necessity along with chemotherapy and radiotherapy. While seminomas are receptive to radiotherapy as well as chemotherapy, non-seminomatous germ cell tumors respond to chemotherapy only. Due to the singular nature of testicular cancers with associated orchiectomy and mortality, it is important to study the molecular basis and genetic underpinnings of this group of cancers across male populations globally. In this review, we shed light on the population pharmacogenetics of testicular cancer, pediatric and adult tumors, current clinical trials, genetic determinants of chemotherapy-induced toxicity in testicular cancer, as well as the molecular signal transduction pathways operating in this malignancy. Taken together, our discussions will help in enhancing our understanding of genetic factors in testicular carcinogenesis and chemotherapy-induced toxicity, augment our knowledge of this aggressive cancer at the cellular and molecular level, as well as improve precision medicine approaches to combat this disease.

Time course and clinical characterization of cisplatin-induced ototoxicity after treatment for nasopharyngeal carcinoma in a South East Asian population

BACKGROUND

The purpose of this study was to characterize the clinical course of hearing loss in patients with nasopharyngeal carcinoma (NPC) and the clinical factors affecting its severity.

METHODS

The time course of hearing loss in patients with NPC was assessed using threshold shift from baseline and Common Terminology Criteria for Adverse Events (CTCAE) grade.

RESULTS

In the chemoradiotherapy (CRT) groups, the threshold shift was significantly higher from 3 months at 4 kHz (P = 2.30 × 10^-9 , concurrent CRT only) but not within 2 years posttreatment in the radiotherapy (RT) group. The CRT groups had worse CTCAE grades than the RT group (percentage of latest CTCAE grade ≥1: 64.9% vs 29.0%, respectively). Cumulative cisplatin dose and cochlear RT dose significantly affects threshold shifts, especially at high frequencies.

CONCLUSION

Although cisplatin led to high frequency hearing impairment from about 3 months posttreatment, RT conferred no significant hearing impairment in the first 2 years.

Clinical Evaluation of Cisplatin Sensitivity of Germline Polymorphisms in Neoadjuvant Chemotherapy for Urothelial Cancer

BACKGROUND

Level 1 evidence has demonstrated increased overall survival with cisplatin-based neoadjuvant chemotherapy for patients with muscle-invasive urothelial cancer. Usage remains low, however, in part because neoadjuvant chemotherapy will not be effective for every patient. To identify the patients most likely to benefit, we evaluated germline pharmacogenomic markers for association with neoadjuvant chemotherapy sensitivity in 2 large cohorts of patients with urothelial cancer.

PATIENTS AND METHODS

Patients receiving neoadjuvant cisplatin-based chemotherapy for muscle-invasive urothelial cancer were eligible. Nine germline single nucleotide polymorphisms (SNPs) potentially conferring platinum sensitivity were tested for an association with a complete pathologic response to neoadjuvant chemotherapy (pT0) or elimination of muscle-invasive cancer (<pT2).

RESULTS

The data from 205 patients were analyzed-59 patients were included in the discovery set and 146 in an independent replication cohort-from 3 institutions. The stage pT0 (26%) and < pT2 (50%) rates were consistent across the discovery and replication populations. Using a multivariate recessive genetic model, rs244898 in RARS (odds ratio, 6.8; 95% confidence interval, 1.8-28.9; P = .006) and rs7937567 in GALNTL4 (odds ratio, 4.8; 95% confidence interval, 1.1-22.6; P = .04) were associated with pT0 in the discovery set. Despite these large effects, neither were associated with achievement of pT0 in the replication set. A third SNP, rs10964552, was associated with stage < pT2 in the discovery set but also failed to replicate.

CONCLUSION

Germline SNPs previously associated with platinum sensitivity were not associated with the neoadjuvant chemotherapy response in a large replication cohort of patients with urothelial cancer. These results emphasize the need for replication when evaluating pharmacogenomic markers and demonstrate that multi-institutional efforts are feasible and will be necessary to achieve advances in urothelial cancer pharmacogenomics.

In vitro human cell line models to predict clinical response to anticancer drugs

In vitro human cell line models have been widely used for cancer pharmacogenomic studies to predict clinical response, to help generate pharmacogenomic hypothesis for further testing, and to help identify novel mechanisms associated with variation in drug response. Among cell line model systems, immortalized cell lines such as Epstein-Barr virus (EBV)-transformed lymphoblastoid cell lines (LCLs) have been used most often to test the effect of germline genetic variation on drug efficacy and toxicity. Another model, especially in cancer research, uses cancer cell lines such as the NCI-60 panel. These models have been used mainly to determine the effect of somatic alterations on response to anticancer therapy. Even though these cell line model systems are very useful for initial screening, results from integrated analyses of multiple omics data and drug response phenotypes using cell line model systems still need to be confirmed by functional validation and mechanistic studies, as well as validation studies using clinical samples. Future models might include the use of patient-specific inducible pluripotent stem cells and the incorporation of 3D culture which could further optimize in vitro cell line models to improve their predictive validity.

Paclitaxel and Its Evolving Role in the Management of Ovarian Cancer

Paclitaxel, a class of taxane with microtubule stabilising ability, has remained with platinum based therapy, the standard care for primary ovarian cancer management. A deeper understanding of the immunological basis and other potential mechanisms of action together with new dosing schedules and/or routes of administration may potentiate its clinical benefit. Newer forms of taxanes, with better safety profiles and higher intratumoural cytotoxicity, have yet to demonstrate clinical superiority over the parent compound.

Paclitaxel and Its Evolving Role in the Management of Ovarian Cancer

Paclitaxel, a class of taxane with microtubule stabilising ability, has remained with platinum based therapy, the standard care for primary ovarian cancer management. A deeper understanding of the immunological basis and other potential mechanisms of action together with new dosing schedules and/or routes of administration may potentiate its clinical benefit. Newer forms of taxanes, with better safety profiles and higher intratumoural cytotoxicity, have yet to demonstrate clinical superiority over the parent compound.

Paclitaxel and Its Evolving Role in the Management of Ovarian Cancer

Paclitaxel, a class of taxane with microtubule stabilising ability, has remained with platinum based therapy, the standard care for primary ovarian cancer management. A deeper understanding of the immunological basis and other potential mechanisms of action together with new dosing schedules and/or routes of administration may potentiate its clinical benefit. Newer forms of taxanes, with better safety profiles and higher intratumoural cytotoxicity, have yet to demonstrate clinical superiority over the parent compound.

Population-based in vitro hazard and concentration-response assessment of chemicals: the 1000 genomes high-throughput screening study

BACKGROUND

Understanding of human variation in toxicity to environmental chemicals remains limited, so human health risk assessments still largely rely on a generic 10-fold factor (10½ each for toxicokinetics and toxicodynamics) to account for sensitive individuals or subpopulations.

OBJECTIVES

We tested a hypothesis that population-wide in vitro cytotoxicity screening can rapidly inform both the magnitude of and molecular causes for interindividual toxicodynamic variability.

METHODS

We used 1,086 lymphoblastoid cell lines from the 1000 Genomes Project, representing nine populations from five continents, to assess variation in cytotoxic response to 179 chemicals. Analysis included assessments of population variation and heritability, and genome-wide association mapping, with attention to phenotypic relevance to human exposures.

RESULTS

For about half the tested compounds, cytotoxic response in the 1% most "sensitive" individual occurred at concentrations within a factor of 10½ (i.e., approximately 3) of that in the median individual; however, for some compounds, this factor was > 10. Genetic mapping suggested important roles for variation in membrane and transmembrane genes, with a number of chemicals showing association with SNP rs13120371 in the solute carrier SLC7A11, previously implicated in chemoresistance.

CONCLUSIONS

This experimental approach fills critical gaps unaddressed by recent large-scale toxicity testing programs, providing quantitative, experimentally based estimates of human toxicodynamic variability, and also testable hypotheses about mechanisms contributing to interindividual variation.

Genetic Variants of the MDM2 Gene Are Predictive of Treatment-Related Toxicities and Overall Survival in Patients With Advanced NSCLC

INTRODUCTION

Platinum agents can cause the formation of DNA adducts and induce apoptosis to eliminate tumor cells. The aim of the present study was to investigate the influence of genetic variants of MDM2 on chemotherapy-related toxicities and clinical outcomes in patients with advanced non-small-cell lung cancer (NSCLC).

MATERIALS AND METHODS

We recruited 663 patients with advanced NSCLC who had been treated with first-line platinum-based chemotherapy. Five tagging single nucleotide polymorphisms (SNPs) in MDM2 were genotyped in these patients. The associations of these SNPs with clinical toxicities and outcomes were evaluated using logistic regression and Cox regression analyses.

RESULTS

Two SNPs (rs1470383 and rs1690924) showed significant associations with chemotherapy-related toxicities (ie, overall, hematologic, and gastrointestinal toxicity). Compared with the wild genotype AA carriers, patients with the GG genotype of rs1470383 had an increased risk of overall toxicity (odds ratio [OR], 3.28; 95% confidence interval [CI], 1.34-8.02; P = .009) and hematologic toxicity (OR, 4.10; 95% CI, 1.73-9.71; P = .001). Likewise, patients with the AG genotype of rs1690924 showed more sensitivity to gastrointestinal toxicity than did those with the wild-type homozygote GG (OR, 2.32; 95% CI, 1.30-4.14; P = .004). Stratified survival analysis revealed significant associations between rs1470383 genotypes and overall survival in patients without overall or hematologic toxicity (P = .007 and P = .0009, respectively).

CONCLUSION

The results of our study suggest that SNPs in MDM2 might be used to predict the toxicities of platinum-based chemotherapy and overall survival in patients with advanced NSCLC. Additional validations of the association are warranted.

Dose-dense paclitaxel in advanced ovarian cancer

Carboplatin and paclitaxel, delivered on a 3-weekly basis, is the historical standard for the management of advanced epithelial ovarian cancers (EOC). Increased dose intensity, the inclusion of additional active cytotoxic agents and lengthening treatment duration have failed to improve the outcomes seen with standard doses of carboplatin and paclitaxel in the treatment of EOC. Dose-dense (i.e. weekly) delivery of paclitaxel may exploit anticancer mechanisms such as anti-angiogenesis and the induction of apoptosis. Tumour regrowth may be more effectively impaired by the dose-dense delivery of paclitaxel. Non-randomised studies of dose-dense chemotherapy in EOC have been promising, particularly in heavily pretreated and platinum-resistant disease, with reported response rates as high as 60%. Dose-dense paclitaxel also seems to be well tolerated. These observations led to a number of comparative trials of dose-dense paclitaxel chemotherapy, three have been reported and four are ongoing. This review explores the rationale behind dose-dense delivery of paclitaxel and evaluates the results of completed phase III trials.

Highlights from the first symposium on upper tract urothelial carcinoma

OBJECTIVES

Upper tract urothelial carcinoma (UTUC) is a rare disease in Western countries and garners little focused attention in urologic and oncologic circles. We report highlights from the first symposium on UTUC.

METHODS

All participants were asked to provide a summary of their presentation to be included as part of these proceedings. Submitted summaries were synthesized into this document. All contributors reviewed and provided input on the final draft.

RESULTS

Five highlights are included in this report, including landmark research that not only reveals the likely cause of Balkan endemic nephropathy and associated UTUC but also links it directly to UTUC in Taiwan. Because of the ubiquitous use of Aristolochia plants in these herbal remedies, a public health problem of considerable magnitude is anticipated in Asian countries. Gene expression signatures reveal some differential expression in bladder carcinoma, such as CLCA2 and GABRE. Few urinary markers have proven utility for the diagnosis and follow-up of UTUC, and no tissue or blood-based markers are currently undergoing clinical application. Novel endoscopic therapies provide some hope of improving tissue sampling, diagnosis, and kidney-sparing therapeutics, but the greatest potential lies in improving clinical (preoperative) risk stratification, which is critically limited in this disease. Biomarkers, currently untested, hold promise in identifying patients most likely to benefit from perioperative chemotherapy and at high risk from cisplatin-induced nephrotoxicity.

CONCLUSIONS

Despite its rarity in the West, UTUC is reaching potentially epidemic proportions in the East because of exposure to carcinogenic herbal remedies. Critical trials are needed to improve our understanding and treatment of UTUC. Because of the broad range of comorbid conditions in patients suffering from this disease, it is the consensus of the participants that future clinical trials should be practical in design and applicable to a broad range of patients, diverging from the current dogma of narrow patient selection criteria in clinical trials. Practical designs would maximize accrual for a still uncommon disease, and their findings would be applicable to a larger proportion of patients than current narrowly selected designs.

Lymphoblastoid cell lines models of drug response: successes and lessons from this pharmacogenomic model

A new standard for medicine is emerging that aims to improve individual drug responses through studying associations with genetic variations. This field, pharmacogenomics, is undergoing a rapid expansion due to a variety of technological advancements that are enabling higher throughput with reductions in cost. Here we review the advantages, limitations, and opportunities for using lymphoblastoid cell lines (LCL) as a model system for human pharmacogenomic studies. There are a wide range of publicly available resources with genome-wide data available for LCLs from both related and unrelated populations, removing the cost of genotyping the data for drug response studies. Furthermore, in contrast to human clinical trials or in vivo model systems, with high-throughput in vitro screening technologies, pharmacogenomics studies can easily be scaled to accommodate large sample sizes. An important component to leveraging genome-wide data in LCL models is association mapping. Several methods are discussed herein, and include multivariate concentration response modeling, issues with multiple testing, and successful examples of the 'triangle model' to identify candidate variants. Once candidate gene variants have been determined, their biological roles can be elucidated using pathway analyses and functionally confirmed using siRNA knockdown experiments. The wealth of genomics data being produced using related and unrelated populations is creating many exciting opportunities leading to new insights into the genetic contribution and heritability of drug response.

EPS8 inhibition increases cisplatin sensitivity in lung cancer cells

Cisplatin, a commonly used chemotherapeutic, is associated with ototoxicity, renal toxicity and neurotoxicity, thus identifying means to increase the therapeutic index of cisplatin may allow for improved outcomes. A SNP (rs4343077) within EPS8, discovered through a genome wide association study of cisplatin-induced cytotoxicity and apoptosis in lymphoblastoid cell lines (LCLs), provided impetus to further study this gene. The purpose of this work was to evaluate the role of EPS8 in cellular susceptibility to cisplatin in cancerous and non-cancerous cells. We used EPS8 RNA interference to determine the effect of decreased EPS8 expression on LCL and A549 lung cancer cell sensitivity to cisplatin. EPS8 knockdown in LCLs resulted in a 7.9% increase in cisplatin-induced survival (P = 1.98 × 10(-7)) and an 8.7% decrease in apoptosis (P = 0.004) compared to control. In contrast, reduced EPS8 expression in lung cancer cells resulted in a 20.6% decrease in cisplatin-induced survival (P = 5.08 × 10(-5)). We then investigated an EPS8 inhibitor, mithramycin A, as a potential agent to increase the therapeutic index of cisplatin. Mithramycin A decreased EPS8 expression in LCLs resulting in decreased cellular sensitivity to cisplatin as evidenced by lower caspase 3/7 activation following cisplatin treatment (42.7% ± 6.8% relative to control P = 0.0002). In 5 non-small-cell lung carcinoma (NSCLC) cell lines, mithramycin A also resulted in decreased EPS8 expression. Adding mithramycin to 4 NSCLC cell lines and a bladder cancer cell line, resulted in increased sensitivity to cisplatin that was significantly more pronounced in tumor cell lines than in LCL lines (p<0.0001). An EGFR mutant NSCLC cell line (H1975) showed no significant change in sensitivity to cisplatin with the addition of mithramycin treatment. Therefore, an inhibitor of EPS8, such as mithramycin A, could improve cisplatin treatment by increasing sensitivity of tumor relative to normal cells.

Germline single nucleotide polymorphisms associated with response of urothelial carcinoma to platinum-based therapy: the role of the host

BACKGROUND

Variations in urothelial carcinoma (UC) response to platinum chemotherapy are common and frequently attributed to genetic and epigenetic variations of somatic DNA. We hypothesized that variations in germline DNA may contribute to UC chemosensitivity.

PATIENTS AND METHODS

DNA from 210 UC patients treated with platinum-based chemotherapy was genotyped for 80 single nucleotide polymorphisms (SNPs). Logistic regression was used to examine the association between SNPs and response, and a multivariable predictive model was created. Significant SNPs were combined to form a SNP score predicting response. Eleven UC cell lines were genotyped as validation.

RESULTS

Six SNPs were significantly associated with 101 complete or partial responses (48%). Four SNPs retained independence association and were incorporated into a response prediction model. Each additional risk allele was associated with a nearly 50% decrease in odds of response [odds ratio (OR) = 0.51, 95% confidence interval 0.39-0.65, P = 1.05 × 10(-7)). The bootstrap-adjusted area under the curves of this model was greater than clinical prognostic factors alone (0.78 versus 0.64). The SNP score showed a positive trend with chemosensitivity in cell lines (P = 0.115).

CONCLUSIONS

Genetic variants associated with response of UC to platinum-based therapy were identified in germline DNA. A model using these genetic variants may predict response to chemotherapy better than clinical factors alone.

Update on first-line treatment of advanced ovarian carcinoma

Despite the high response rate to first-line treatment of advanced ovarian cancer, the vast majority of patients relapse. Maximal debulking surgery and chemotherapy with a platinum doublet have remained the standard of care for many years and new approaches are imperative. Recent clinical trials have given grounds for hope. Neoadjuvant chemotherapy, intraperitoneal delivery, and dose-dense strategies have all shown promising results, as has the targeting of angiogenesis. A greater understanding of the molecular landscape of ovarian cancer is helping to identify new treatment options. In this review, we will highlight the key trials and recent progress in these areas.

Functional consequences of PRPF39 on distant genes and cisplatin sensitivity

Variation in gene expression has been found to be important in disease susceptibility and pharmacogenomics. Local and distant expression quantitative trait loci (eQTLs) have been identified via genome-wide association study (GWAS); yet the functional analysis of these variants has been challenging. The aim of this study was to unravel the functional consequence of a gene with a local SNP with evidence for local and distant regulatory roles in cellular sensitivity to cisplatin, one of the most widely used chemotherapeutic drugs. To this end, we measured cellular susceptibility to cisplatin in 176 HapMap lymphoblastoid cell lines derived from Yoruba individuals from Ibadan, Nigeria. The 276 cytotoxicity-associated SNPs at the suggestive threshold of P ≤ 0.0001 were significantly enriched for eQTLs. Of these SNPs, we found one intronic SNP, rs17115814, that had a significant relationship with the expression level of its host gene, PRPF39 (P= 0.0007), and a significant correlation with the expression of over 100 distant transcripts (P ≤ 0.0001). Successful knockdown of PRPF39 expression using siRNA resulted in a significant increase in cisplatin resistance. We then measured the expression of 61 downstream targets after PRPF39 knockdown and found 53 gene targets had significant (P ≤ 0.05) expression changes. Included in the list of genes that significantly changed after PRPF39 knockdown were MAP3K4 and TFPD2, two important signaling genes previously shown to be relevant in cisplatin response. Thus, modulation of a local target gene identified through a GWAS was followed by a downstream cascade of gene expression changes resulting in greater resistance to cisplatin.

Lymphoblastoid cell lines in pharmacogenomic discovery and clinical translation

The ability to predict how an individual patient will respond to a particular treatment is the ambitious goal of personalized medicine. The genetic make up of an individual has been shown to play a role in drug response. For pharmacogenomic studies, human lymphoblastoid cell lines (LCLs) comprise a useful model system for identifying genetic variants associated with pharmacologic phenotypes. The availability of extensive genotype data for many panels of LCLs derived from individuals of diverse ancestry allows for the study of genetic variants contributing to interethnic and interindividual variation in susceptibility to drugs. Many genome-wide association studies for drug-induced phenotypes have been performed in LCLs, often incorporating gene-expression data. LCLs are also being used in follow-up studies to clinical findings to determine how an associated variant functions to affect phenotype. This review describes the most recent pharmacogenomic findings made in LCLs, including the translation of some findings to clinical cohorts.

Dose-dense therapy is of benefit in primary treatment of ovarian cancer: contra

Several studies in the past have tried to improve the prognosis of ovarian cancer by increasing the dose intensity of platinum. Only 2 out of 12 randomized studies showed survival benefit at the cost of significant long-term toxicity. Dose-dense induction therapy with combined weekly paclitaxel (at a dose of 90 mg/m(2)) and weekly carboplatin [at an area under the curve (AUC) of 4 mg·ml/min] followed by 3-weekly paclitaxel/carboplatin was very effective in platinum-resistant patients (response 58%, progression-free survival 10 months). In first-line, however, no survival benefit was found with the same dose-dense weekly paclitaxel/carboplatin regimen over standard-dosed 3-weekly paclitaxel/carboplatin in a randomized study. Very recently, the Japanese Gynecologic Oncology Group (JGOG) study no. 3016, randomizing patients in first-line between dose-dense weekly paclitaxel 80 mg/m(2) plus 3-weekly carboplatin AUC 6 and 3-weekly paclitaxel/carboplatin, showed a significant increase in progression-free survival (median 28 versus 17.2 months in the control arm; hazard ratio for progression, 0.71; 95% confidence interval, 0.58-0.88; P=0.0015). The 3-year overall survival was 72% versus 65% (P=0.03), respectively. The hematologic toxicity was substantial in both arms and substantially higher than observed with the weekly paclitaxel/carboplatin induction regimen. Many patients had treatment delays, dose reductions and stopped treatment prematurely. The JGOG 3016 study is the only dose-dense study with such a significant survival benefit. It is also the only dose-intensity study performed in Asian patients. Genotypes and phenotypes are thought to represent important determinants of drug efficacy in ovarian cancer. Therefore, confirmatory studies with this JGOG regimen together with translational research are needed in both Caucasian and Asian patients.

Identification of novel germline polymorphisms governing capecitabine sensitivity

BACKGROUND

Capecitabine, an oral 5-fluorouracil (5-FU) prodrug, is widely used in the treatment of breast, colorectal, and gastric cancers. To guide the selection of patients with potentially the greatest benefit of experiencing antitumor efficacy, or, alternatively, of developing toxicities, identifying genomic predictors of capecitabine sensitivity could permit its more informed use.

METHODS

The objective of this study was to perform capecitabine sensitivity genome-wide association studies (GWAS) using 503 well genotyped human cell lines from individuals representing multiple different world populations. A meta-analysis that included all ethnic populations then enabled the identification of novel germline determinants (single nucleotide polymorphisms [SNPs]) of capecitabine susceptibility.

RESULTS

First, an intrapopulation GWAS of Caucasian individuals identified reference SNP 4702484 (rs4702484) (within adenylate cyclase 2 [ADCY2]) at a level reaching genome-wide significance (P = 5.2 × 10(-8) ). This SNP is located upstream of the 5 methyltetrahydrofolate-homocysteine methyltransferase reductase (MTRR) gene, and it is known that the enzyme for MTRR is involved in the methionine-folate biosynthesis and metabolism pathway, which is the primary target of 5-FU-related compounds, although the authors were unable to identify a direct relation between rs4702484 and MTRR expression in a tested subset of cells. In the meta-analysis, 4 SNPs comprised the top hits, which, again, included rs4702484 and 3 additional SNPs (rs8101143, rs576523, and rs361433) that approached genome-wide significance (P values from 1.9 × 10(-7) to 8.8 × 10(-7) ). The meta-analysis also identified 1 missense variant (rs11722476; serine to asparagine) within switch/sucrose nonfermentable-related, matrix-associated, actin-dependent regulator of chromatin (SMARCAD1), a novel gene for association with capecitabine/5-FU susceptibility.

CONCLUSIONS

Toward the goal of individualizing cancer chemotherapy, the current study identified novel SNPs and genes associated with capecitabine sensitivity that are potentially informative and testable in any patient regardless of ethnicity.

Genome-wide meta-analysis identifies variants associated with platinating agent susceptibility across populations

Platinating agents are used in the treatment of many cancers, yet they can induce toxicities and resistance that limit their utility. Using previously published and additional world population panels of diverse ancestry totaling 608 lymphoblastoid cell lines (LCLs), we performed meta-analyses of over 3 million SNPs for both carboplatin- and cisplatin-induced cytotoxicity. The most significant SNP in the carboplatin meta-analysis is located in an intron of NBAS (p = 5.1 × 10⁻⁷). The most significant SNP in the cisplatin meta-analysis is upstream of KRT16P2 (p = 5.8 × 10⁻⁷). We also show that cisplatin-susceptibility SNPs are enriched for carboplatin-susceptibility SNPs. Most of the variants that associate with platinum-induced cytotoxicity are polymorphic across multiple world populations; therefore, they could be tested in follow-up studies in diverse clinical populations. Seven genes previously implicated in platinating agent response, including BCL2, GSTM1, GSTT1, ERCC2, and ERCC6 were also implicated in our meta-analyses.

Germline polymorphisms discovered via a cell-based, genome-wide approach predict platinum response in head and neck cancers

Identifying patients prior to treatment who are more likely to benefit from chemotherapeutic agents or more likely to experience adverse events is an aim of personalized medicine. Pharmacogenomics offers a potential means of achieving this goal through the discovery of predictive germline genetic biomarkers. When applied particularly to the treatment of head and neck cancers, such information could offer significant benefit to patients as a means of potentially reducing morbidity associated with platinum-based chemotherapy. We developed a genome-wide, cell-based approach to identify single nucleotide polymorphisms (SNPs) associated with platinum susceptibility and then evaluated these SNPs as predictors for response and toxicity in head and neck cancer patients treated with platinum-based therapy as part of a phase II clinical trial. Sixty head and neck cancer patients were evaluated. Of 45 genome-wide SNPs examined, we found that 2 SNPs, rs6870861 (P=0.004; false discovery rate [FDR] <0.05) and rs2551038 (P=0.005; FDR <0.05), were associated significantly with overall response to carboplatin-based induction chemotherapy when incorporated into a model along with total carboplatin exposure. Interestingly, these 2 SNPs are associated strongly with the baseline expression of >20 genes (all P ≤10(-4)), and that 2 genes (SLC22A5 and SLCO4C1) are important organic cation/anion transporters known to affect platinum uptake and clearance. Several other SNPs were associated nominally with carboplatin-related hematologic toxicities. These findings demonstrate importantly that a genome-wide, cell-based model can identify novel germline genetic biomarkers of platinum susceptibility, which are replicable in a clinical setting with treated cancer patients and seem clinically meaningful for potentially enabling future personalization of care in such patients.

Comprehensive evaluation of the contribution of X chromosome genes to platinum sensitivity

Using a genome-wide gene expression data set generated from Affymetrix GeneChip Human Exon 1.0ST array, we comprehensively surveyed the role of 322 X chromosome gene expression traits on cellular sensitivity to cisplatin and carboplatin. We identified 31 and 17 X chromosome genes whose expression levels are significantly correlated (after multiple testing correction) with sensitivity to carboplatin and cisplatin, respectively, in the combined HapMap CEU (Utah residents with ancestry from northern and western Europe) and YRI (Yoruba in Ibahan, Nigeria) populations (false discovery rate, FDR < 0.05). Of those, 14 overlap for both cisplatin and carboplatin. Using an independent gene expression quantification method, the Illumina Sentrix Human-6 Expression BeadChip, measured on the same HapMap cell lines, we found that 4 and 2 of these genes are significantly associated with carboplatin and cisplatin sensitivity, respectively, in both analyses. Two genes, CTPS2 and DLG3, were identified by both genome-wide gene expression analyses as correlated with cellular sensitivity to both platinating agents. The expression of DLG3 gene was also found to correlate with cellular sensitivity to platinating agents in NCI-60 cancer cell lines. In addition, we evaluated whether the expression of X chromosome genes contributed to the observed differences in sensitivity to the platinums between CEU and YRI-derived cell lines. Of the 34 distinct genes significantly correlated with either carboplatin or cisplatin sensitivity, 14 are differentially expressed (defined as P < 0.05) between CEU and YRI. Thus, sex chromosome genes play a role in cellular sensitivity to platinating agents and differences in the expression level of these genes are an important source of variation that should be included in comprehensive pharmacogenomic studies.