Regulatory Considerations in the Approval of Rezafungin (REZZAYO) for the Treatment of Candidemia and Invasive Candidiasis in Adults.

On March 22, 2023, the FDA approved rezafungin (REZZAYO) for the treatment of candidemia and invasive candidiasis in adults with limited or no alternative treatment options. Rezafungin is an echinocandin that supports weekly dosing, enabling outpatient parenteral treatment that potentially avoids the need for a central venous catheter. Approval of rezafungin was based on a single adequate and well-controlled phase 3 study designed with a Day 30 all-cause mortality primary endpoint and 20% noninferiority margin, which demonstrated that rezafungin is noninferior to the comparator echinocandin. Nonclinical studies of rezafungin in non-human primates identified a neurotoxicity safety signal; however, rezafungin's safety profile in the completed clinical studies was similar to other FDA-approved echinocandins. Here we describe the rationale for this approval and important considerations during the review process for a flexible development program intended to expedite the availability of antimicrobial therapies to treat serious infections in patients with limited treatment options.

FDA, CDC, and NIH Co-sponsored Public Workshop Summary-Development Considerations of Antimicrobial Drugs for the Treatment of Gonorrhea.

There is an unmet need for developing drugs for the treatment of gonorrhea, due to rapidly evolving resistance of Neisseria gonorrhoeae against antimicrobial drugs used for empiric therapy, an increase in globally reported multidrug resistant cases, and the limited available therapeutic options. Furthermore, few drugs are under development. Development of antimicrobials is hampered by challenges in clinical trial design, limitations of available diagnostics, changes in and varying standards of care, lack of robust animal models, and clinically relevant pharmacodynamic targets. On April 23, 2021, the U.S. Food and Drug Administration; Centers for Disease Control and Prevention; and National Institute of Allergy and Infectious Diseases, National Institutes of Health co-sponsored a workshop with stakeholders from academia, industry, and regulatory agencies to discuss the challenges and strategies, including potential collaborations and incentives, to facilitate the development of drugs for the treatment of gonorrhea. This article provides a summary of the workshop.

Food and Drug Administration Public Workshop Summary-Development Considerations of Antifungal Drugs to Address Unmet Medical Need.

Pressing challenges in the treatment of invasive fungal infections (IFIs) include emerging and rare pathogens, resistant/refractory infections, and antifungal armamentarium limited by toxicity, drug-drug interactions, and lack of oral formulations. Development of new antifungal drugs is hampered by the limitations of the available diagnostics, clinical trial endpoints, prolonged trial duration, difficulties in patient recruitment, including subpopulations (eg, pediatrics), and heterogeneity of the IFIs. On 4 August 2020, the US Food and Drug Administration convened a workshop that included IFI experts from academia, industry, and other government agencies to discuss the IFI landscape, unmet need, and potential strategies to facilitate the development of antifungal drugs for treatment and prophylaxis. This article summarizes the key topics presented and discussed during the workshop, such as incentives and research support for drug developers, nonclinical development, clinical trial design challenges, lessons learned from industry, and potential collaborations to facilitate antifungal drug development.

FDA Public Workshop Summary-Addressing Challenges in Inhaled Antifungal Drug Development.

Allergic bronchopulmonary aspergillosis and invasive fungal diseases represent distinct infectious entities that cause significant morbidity and mortality. Currently, administered inhaled antifungal therapies are unapproved, have suboptimal efficacy, and are associated with considerable adverse reactions. The emergence of resistant pathogens is also a growing concern. Inhaled antifungal development programs are challenged by inadequate nonclinical infection models, highly heterogenous patient populations, low prevalence rates of fungal diseases, difficulties defining clinical trial enrollment criteria, and lack of robust clinical trial endpoints. On September 25, 2020, the US Food and Drug Administration (FDA) convened a workshop with experts in pulmonary medicine and infectious diseases from academia, industry, and other governmental agencies. Key discussion topics included regulatory incentives to facilitate development of inhaled antifungal drugs and combination inhalational devices, limitations of existing nonclinical models and clinical trial designs, patient perspectives, and industry insights.

FDA Public Workshop Summary-Coccidioidomycosis (Valley Fever): Considerations for Development of Antifungal Drugs.

Coccidioidomycosis is a fungal disease endemic to the southwestern United States, Mexico, and Central and South America. Prevalence rates are increasing steadily, and new endemic areas of Coccidioides are emerging. Standard treatment is often administered for months to decades, and intolerance to medications and treatment failures are common. No new treatments for coccidioidomycosis have been approved in the United States in nearly 40 years. On 5 August 2020, the US Food and Drug Administration convened experts in coccidioidomycosis from academia, industry, patient groups, and other government agencies to discuss the disease landscape and strategies to facilitate product development for treatment of coccidioidomycosis. This article summarizes the key topics concerning drug development for coccidioidomycosis presented by speakers and panelists during the workshop, such as unmet need, trial designs, endpoints, incentives, research and development support, and collaborations to facilitate antifungal drug development.

Identification of clinically used drugs that activate pregnane X receptors.

The pregnane X receptor (PXR) binds xenobiotics and regulates the expression of several drug-metabolizing enzymes and transporters. Human PXR (hPXR) activation and CYP3A4 induction can be involved in drug-drug interactions, resulting in reduced efficacy or increased toxicity. However, there are known species-specific differences with regard to PXR activation that should be taken into account when animal PXR data are extrapolated to humans. We profiled 2816 clinically used drugs from the National Institutes of Health Chemical Genomics Center Pharmaceutical Collection for their ability to activate hPXR and rat PXR (rPXR) at the cellular level, induce human CYP3A4 at the cellular level, and bind human PXR at the protein level. From 6 to 11% of drugs were identified as active across the four assays, which included assay-specific and pan-active compounds. The lowest concordance was observed between the hPXR and rPXR assays, and many compounds active in both assays nonetheless demonstrated significant potency differences between species. Analysis based on clustering potency values demonstrated the greatest activity correlation between the hPXR activation and CYP3A4 induction assays. Structure-activity relationship analysis identified chemical scaffolds that were pan-active (e.g., dihydropyridine calcium channel blockers) and others that were uniquely active in individual assays (e.g., steroids and fatty acids). These results provide important information on PXR activation by clinically used drugs, highlight the species specificity of PXR activation by xenobiotics, and provide a means of prioritizing compounds for follow-up studies and optimization efforts.

Whole-genome approach implicates CD44 in cellular resistance to carboplatin.

Carboplatin is a chemotherapeutic agent used in the management of many cancers, yet treatment is limited by resistance and toxicities. To achieve a better understanding of the genetic contribution to carboplatin resistance or toxicities, lymphoblastoid cell lines from 34 large Centre d'Etude du Polymorphisme Humain pedigrees were utilised to evaluate interindividual variation in carboplatin cytotoxicity. Significant heritability, ranging from 0.17-0.36 (p = 1 x 10(-7) to 9 x 10(-4)), was found for cell growth inhibition following 72-hour treatment at each carboplatin concentration (10, 20, 40 and 80 microM) and IC(50) (concentration for 50 per cent cell growth inhibition). Linkage analysis revealed 11 regions with logarithm of odds (LOD) scores greater than 1.5. The highest LOD score on chromosome 11 (LOD = 3.36, p = 4.2 x 10(-5)) encompasses 65 genes within the 1 LOD confidence interval for the carboplatin IC 50 . We further analysed the IC(50) phenotype with a linkage-directed association analysis using 71 unrelated HapMap and Perlegen cell lines and identified 18 single nucleotide polymorphisms within eight genes that were significantly associated with the carboplatin IC(50) (p < 3.6 x 10(-5); false discovery rate <5 per cent). Next, we performed linear regression on the baseline expression and carboplatin IC(50) values of the eight associated genes, which identified the most significant correlation between CD44 expression and IC(50) (r(2)= 0.20; p = 6 x 10(-4)). The quantitative real-time polymerase chain reaction further confirmed a statistically significant difference in CD44 expression levels between carboplatin-resistant and -sensitive cell lines (p = 5.9 x 10(-3)). Knockdown of CD44 expression through small interfering RNA resulted in increased cellular sensitivity to carboplatin (p < 0.01). Our whole-genome approach using molecular experiments identified CD44 as being important in conferring cellular resistance to carboplatin.

Identification of genomic regions contributing to etoposide-induced cytotoxicity.

Etoposide is routinely used in combination-based chemotherapy for testicular cancer and small-cell lung cancer; however, myelosuppression, therapy-related leukemia and neurotoxicity limit its utility. To determine the genetic contribution to cellular sensitivity to etoposide, we evaluated cell growth inhibition in Centre d' Etude du Polymorphisme Humain lymphoblastoid cell lines from 24 multi-generational pedigrees (321 samples) following treatment with 0.02-2.5 microM etoposide for 72 h. Heritability analysis showed that genetic variation contributes significantly to the cytotoxic phenotypes (h (2) = 0.17-0.25, P = 4.9 x 10(-5)-7.3 x 10(-3)). Whole genome linkage scans uncovered 8 regions with peak LOD scores ranging from 1.57 to 2.55, with the most significant signals being found on chromosome 5 (LOD = 2.55) and chromosome 6 (LOD = 2.52). Linkage-directed association was performed on a subset of HapMap samples within the pedigrees to find 22 SNPs significantly associated with etoposide cytotoxicity at one or more treatment concentrations. UVRAG, a DNA repair gene, SEMA5A, SLC7A6 and PRMT7 are implicated from these unbiased studies. Our findings suggest that susceptibility to etoposide-induced cytotoxicity is heritable and using an integrated genomics approach we identified both genomic regions and SNPs associated with the cytotoxic phenotypes.

Identification of pregnane X receptor ligands using time-resolved fluorescence resonance energy transfer and quantitative high-throughput screening.

The human pregnane X nuclear receptor (PXR) is a xenobiotic-regulated receptor that is activated by a range of diverse chemicals, including antibiotics, antifungals, glucocorticoids, and herbal extracts. PXR has been characterized as an important receptor in the metabolism of xenobiotics due to induction of cytochrome P450 isozymes and activation by a large number of prescribed medications. Developing methodologies that can efficiently detect PXR ligands will be clinically beneficial to avoid potential drug-drug interactions. To facilitate the identification of PXR ligands, a time-resolved fluorescence resonance energy transfer (TR-FRET) assay was miniaturized to a 1,536-well microtiter plate format to employ quantitative high-throughput screening (qHTS). The optimized 1,536-well TR-FRET assay showed Z'-factors of >or=0.5. Seven- to 15-point concentration-response curves (CRCs) were generated for 8,280 compounds using both terbium and fluorescein emission data, resulting in the generation of 241,664 data points. The qHTS method allowed us to retrospectively examine single concentration screening datasets to assess the sensitivity and selectivity of the PXR assay at different compound screening concentrations. Furthermore, nonspecific assay artifacts such as concentration-based quenching of the terbium signal and compound fluorescence were identified through the examination of CRCs for specific emission channels. The CRC information was also used to define chemotypes associated with PXR ligands. This study demonstrates the feasibility of profiling thousands of compounds against PXR using the TR-FRET assay in a high-throughput format.

Mapping genes that contribute to daunorubicin-induced cytotoxicity.

Daunorubicin is an anthracycline antibiotic agent used in the treatment of hematopoietic malignancies. Toxicities associated with this agent include myelosuppression and cardiotoxicity; however, the genes or genetic determinants that contribute to these toxicities are unknown. We present an unbiased genome-wide approach that incorporates heritability, whole-genome linkage analysis, and linkage-directed association to uncover genetic variants contributing to the sensitivity to daunorubicin-induced cytotoxicity. Cell growth inhibition in 324 Centre d' Etude du Polymorphisme Humain lymphoblastoid cell lines (24 pedigrees) was evaluated following treatment with daunorubicin for 72 h. Heritability analysis showed a significant genetic component contributing to the cytotoxic phenotypes (h2 = 0.18-0.63 at 0.0125, 0.025, 0.05, 0.1, 0.2, and 1.0 mumol/L daunorubicin and at the IC50, the dose required to inhibit 50% cell growth). Whole-genome linkage scans at all drug concentrations and IC50 uncovered 11 regions with moderate peak LOD scores (> 1.5), including 4q28.2 to 4q32.3 with a maximum LOD score of 3.18. The quantitative transmission disequilibrium tests were done using 31,312 high-frequency single-nucleotide polymorphisms (SNP) located in the 1 LOD confidence interval of these 11 regions. Thirty genes were identified as significantly associated with daunorubicin-induced cytotoxicity (P < or = 2.0 x 10(-4), false discovery rate < or = 0.1). Pathway and functional gene ontology analysis showed that these genes were overrepresented in the phosphatidylinositol signaling system, axon guidance pathway, and GPI-anchored proteins family. Our findings suggest that a proportion of susceptibility to daunorubicin-induced cytotoxicity may be controlled by genetic determinants and that analysis using linkage-directed association studies with dense SNP markers can be used to identify the genetic variants contributing to cytotoxicity.

Effect of population and gender on chemotherapeutic agent-induced cytotoxicity.

Large interindividual variance is observed in both response and toxicity associated with chemotherapy. Our goal is to identify factors that contribute to chemotherapy-induced toxicity. To this end, we used EBV-transformed B-lymphoblastoid HapMap cell lines derived from 30 Yoruban trios (African descent) and 30 Centre d' Etude du Polymorphisme Humain (CEPH) trios (European descent) to evaluate population- and gender-specific differences in cytotoxicity of carboplatin, cisplatin, daunorubicin, and etoposide using a high-throughput, short-term cytotoxicity assay. The IC(50) was compared for population- and gender-specific differences for the four drugs. We observed large interindividual variance in IC(50) values for carboplatin, cisplatin, daunorubicin, and etoposide for both Yoruban and CEPH populations (range from 8- to 433-fold). Statistically significant differences in carboplatin and daunorubicin IC(50) were shown when comparing Yoruban cell lines (n = 89) to CEPH cell lines (n = 87; P = 0.002 and P = 0.029, respectively). This population difference in treatment induced cytotoxicity was not seen for either cisplatin or etoposide. In the Yoruban population, cell lines derived from females were less sensitive to platinating agents than males [median carboplatin IC(50), 29.1 versus 24.6 micromol/L (P = 0.012); median cisplatin IC(50), 7.0 versus 6.0 micromol/L (P = 0.020) in female and male, respectively]. This difference was not observed in the CEPH population. These results show that population and gender may affect risk for toxicities associated with certain chemotherapeutic agents.

Cell-Based Assay for Identifying the Modulators of Antioxidant Response Element Signaling Pathway.

The antioxidant response element (ARE) signaling pathway plays an important role in the amelioration of cellular oxidative stress. Thus, assays that detect this pathway can be useful for identifying chemicals that induce or inhibit oxidative stress signaling. The focus of this chapter is to describe a cell-based ARE assay in a quantitative high-throughput screening (qHTS) format to test a large collection of compounds that induce nuclear factor erythroid 2-related factor (Nrf2)/ARE signaling. The assay is described through cell handling, assay preparation, and instrument usage.

Use of CEPH and non-CEPH lymphoblast cell lines in pharmacogenetic studies.

A long-term goal of pharmacogenomic research is the design of individualized therapy based on the genomic sequence of the patient in order to maximize response and minimize adverse drug reactions. Identifying genetic variants that predict drug response is challenging because drug responses reflect not only properties intrinsic to the target cell, but also host metabolic factors. One model that is currently being employed to study genotype-phenotype correlations involves the use of lymphoblastoid cell lines (LCLs). These cell lines have been used to identify genetic variation that influences response or susceptibility to cancer, radiation, transport, cytotoxicity, and variation in global gene expression. LCLs, particularly those derived from large pedigrees, are a valuable resource for identifying candidate genes and have potential for studies of many relevant phenotypes. This paper highlights studies that have utilized Centre d' Etude du Polymorphisme Humain (CEPH) and non-CEPH cell lines derived from humans for pharmacogenetic studies, and the advantages and disadvantages associated with this approach.

Factors associated with the treatment of latent tuberculosis infection among health-care workers at a midwestern teaching hospital.

STUDY OBJECTIVE: To assess factors associated with initiating therapy and compliance with treatment for latent tuberculosis infection among health-care workers with positive tuberculin skin test results. DESIGN: Prospective cohort study. SETTING: An urban midwestern teaching hospital in St. Louis, MO. STUDY POPULATION: Health-care workers with positive tuberculin skin test results. MEASUREMENTS: (1) Rates of initiating therapy for latent tuberculosis infection among all health-care workers with positive tuberculin skin test results, and (2) compliance rates with therapy for latent tuberculosis infection among health-care workers with recent tuberculin skin test conversion. RESULTS: A total of 440 tuberculin skin test-positive health-care workers were evaluated from January 1, 1994, to May 1, 2000. Of those evaluated, 1 health-care worker had presumed active tuberculosis, 1 had no record of being evaluated, 1 had missing records, and 33 were not recommended isoniazid therapy, leaving 404 workers for analysis. Overall, 396 of 404 health-care workers (98%) with positive tuberculin skin test results initiated isoniazid therapy. In univariate analysis, bacille Calmette-Guérin (BCG) vaccination (p = 0.02) and foreign birth (p = 0.03) were significantly associated with not initiating isoniazid therapy. Compliance data were available for 388 of 404 health-care workers (96%). Of these, 318 of 388 health-care workers (82%) were compliant with 6 months of therapy. BCG vaccination (odds ratio [OR], 3.5; 95% confidence interval [CI], 1.8 to 7.1) and symptoms while receiving therapy (OR, 4.5; 95% CI, 2.0 to 10.1) were significantly associated with noncompliance in multivariate analysis. Among new converters, Asian race (p = 0.006), foreign birth (p = 0.01), BCG vaccination (p = 0.006), and symptoms while receiving therapy (p < 0.001) were significantly associated with noncompliance in univariate analysis. CONCLUSION: This hospital had a high rate of initiating isoniazid therapy for tuberculosis infection among their health-care workers, and a high rate of compliance with therapy. These rates of initiation and completion of isoniazid therapy were much higher than those previously reported in the literature. This may be largely due to a focused program, which includes active follow-up of health-care workers with positive tuberculin skin test results, consisting of physician counseling and monthly phone consultations by nurses, along with free services and medications provided on-site.

Assessment of compound hepatotoxicity using human plateable cryopreserved hepatocytes in a 1536-well-plate format.

Hepatotoxicity is a major concern for both drug development and toxicological evaluation of environmental chemicals. The assessment of compound-induced hepatotoxicity has traditionally relied on in vivo testing; however, it is being replaced by human in vitro models due to an emphasis on the reduction of animal testing and species-specific differences. Since most cell lines and hybridomas lack the full complement of enzymes at physiological levels found in the liver, primary hepatocytes are the gold standard to study liver toxicities in vitro due to the retention of most of their in vivo activities. Here, we optimized a cell viability assay using plateable cryopreserved human hepatocytes in a 1536-well-plate format. The assay was validated by deriving inhibitory concentration at 50% values for 12 known compounds, including tamoxifen, staurosporine, and phenylmercuric acetate, with regard to hepatotoxicity and general cytotoxicity using multiple hepatocyte donors. The assay performed well, and the cytotoxicity of these compounds was confirmed in comparison to HepG2 cells. This is the first study to report the reliability of using plateable cryopreserved human hepatocytes for cytotoxicity studies in a 1536-well-plate format. These results suggest that plateable cryopreserved human hepatocytes can be scaled up for screening a large compound library and may be amenable to other hepatocytic assays such as metabolic or drug safety studies.

Profiling environmental chemicals for activity in the antioxidant response element signaling pathway using a high throughput screening approach.

BACKGROUND: Oxidative stress has been implicated in the pathogenesis of a variety of diseases ranging from cancer to neurodegeneration, highlighting the need to identify chemicals that can induce this effect. The antioxidant response element (ARE) signaling pathway plays an important role in the amelioration of oxidative stress. Thus, assays that detect the up-regulation of this pathway could be useful for identifying chemicals that induce oxidative stress. OBJECTIVES: We used cell-based reporter methods and informatics tools to efficiently screen a large collection of environmental chemicals and identify compounds that induce oxidative stress. METHODS: We utilized two cell-based ARE assay reporters, ß-lactamase and luciferase, to screen a U.S. National Toxicology Program 1,408-compound library (NTP 1408, which contains 1,340 unique compounds) for their ability to induce oxidative stress in HepG2 cells using quantitative high throughput screening (qHTS). RESULTS: Roughly 3% (34 of 1,340) of the unique compounds demonstrated activity across both cell-based assays. Based on biological activity and structure-activity relationship profiles, we selected 50 compounds for retesting in the two ARE assays and in an additional follow-up assay that employed a mutated ARE linked to ß-lactamase. Using this strategy, we identified 30 compounds that demonstrated activity in the ARE-bla and ARE-luc assays and were able to determine structural features conferring compound activity across assays. CONCLUSIONS: Our results support the robustness of using two different cell-based approaches for identifying compounds that induce ARE signaling. Together, these methods are useful for prioritizing chemicals for further in-depth mechanism-based toxicity testing.

The future of toxicity testing: a focus on in vitro methods using a quantitative high-throughput screening platform.

The US Tox21 collaborative program represents a paradigm shift in toxicity testing of chemical compounds from traditional in vivo tests to less expensive and higher throughput in vitro methods to prioritize compounds for further study, identify mechanisms of action and ultimately develop predictive models for adverse health effects in humans. The NIH Chemical Genomics Center (NCGC) is an integral component of the Tox21 collaboration owing to its quantitative high-throughput screening (qHTS) paradigm, in which titration-based screening is used to profile hundreds of thousands of compounds per week. Here, we describe the Tox21 collaboration, qHTS-based compound testing and the various Tox21 screening assays that have been validated and tested at the NCGC to date.

Identification of known drugs that act as inhibitors of NF-kappaB signaling and their mechanism of action.

Nuclear factor-kappa B (NF-kappaB) is a transcription factor that plays a critical role across many cellular processes including embryonic and neuronal development, cell proliferation, apoptosis, and immune responses to infection and inflammation. Dysregulation of NF-kappaB signaling is associated with inflammatory diseases and certain cancers. Constitutive activation of NF-kappaB signaling has been found in some types of tumors including breast, colon, prostate, skin and lymphoid, hence therapeutic blockade of NF-kappaB signaling in cancer cells provides an attractive strategy for the development of anticancer drugs. To identify small molecule inhibitors of NF-kappaB signaling, we screened approximately 2800 clinically approved drugs and bioactive compounds from the NIH Chemical Genomics Center Pharmaceutical Collection (NPC) in a NF-kappaB mediated beta-lactamase reporter gene assay. Each compound was tested at fifteen different concentrations in a quantitative high throughput screening format. We identified nineteen drugs that inhibited NF-kappaB signaling, with potencies as low as 20 nM. Many of these drugs, including emetine, fluorosalan, sunitinib malate, bithionol, narasin, tribromsalan, and lestaurtinib, inhibited NF-kappaB signaling via inhibition of IkappaBalpha phosphorylation. Others, such as ectinascidin 743, chromomycin A3 and bortezomib utilized other mechanisms. Furthermore, many of these drugs induced caspase 3/7 activity and had an inhibitory effect on cervical cancer cell growth. Our results indicate that many currently approved pharmaceuticals have previously unappreciated effects on NF-kappaB signaling, which may contribute to anticancer therapeutic effects. Comprehensive profiling of approved drugs provides insight into their molecular mechanisms, thus providing a basis for drug repurposing.

The Werner's syndrome 4330T>C (Cys1367Arg) gene variant does not affect the in vitro cytotoxicity of topoisomerase inhibitors and platinum compounds.

PURPOSE: Werner's syndrome (WS) is a recessive disorder of premature onset of processes associated with aging. Defective DNA repair has been reported after exposure of cells isolated from WS patients to DNA-damaging agents. The germline 4330T>C (Cys1367Arg) variant in the WS gene (WRN) has been associated with protection from age-related diseases, suggesting it has a functional role. We studied whether the 4330T>C variant confers altered drug sensitivity in vitro. METHODS: 4330T>C was genotyped in 372 human lymphoblastoid cell lines (LCLs) from unrelated healthy Caucasian individuals using a TaqMan-based method. The study was powered to detect the effect of the 4330T>C genotypes after exposure to camptothecin (based upon preliminary data). The effect of the 4330T>C variant on the cytotoxicity of etoposide, carboplatin, cisplatin and daunorubicin was also tested. WRN expression in 57 LCLs was measured by microarray. RESULTS: No significant difference between the IC50 of the cells was observed among genotypes (P = 0.46) after exposure to camptothecin. No association was also observed for etoposide, carboplatin, cisplatin, and daunorubicin (ANOVA, P > 0.05). WRN expression also did not vary across genotypes (ANOVA, P = 0.37). CONCLUSION: These results suggest that this nonsynonymous variant has relatively normal function at the cellular level.

Susceptibility loci involved in cisplatin-induced cytotoxicity and apoptosis.

OBJECTIVES: Cisplatin is a widely used chemotherapeutic agent; however, nephrotoxicity and neuropathy are obstacles for drug efficacy. Little is known about the genes or genetic variants contributing to the risk of developing these toxicities or chemotherapeutic response. Thus, we have applied a cell-based model to identify and characterize previously unknown genes that may be involved in cellular susceptibility to cisplatin. METHODS: Lymphoblastoid cell lines from 27 large Centre d'Etude du Polymorphisme Humain pedigrees were used to elucidate the genetic contribution to cisplatin-induced cytotoxicity. Phenotype was defined as cell growth inhibition following exposure of cell lines to increasing concentrations of cisplatin for 48 h. RESULTS: Significant heritability, ranging from 0.32 to 0.43 (P<10), was found for the cytotoxic effects of each concentration (1, 2.5, 5, 10, and 20 micromol/l) and IC50, the concentration required for 50% cell growth inhibition. Linkage analysis revealed 11 genomic regions on six chromosomes with logarithm of odds (LOD) scores above 1.5 for cytotoxic phenotypes. The highest LOD score was found on chromosome 4q21.3-q35.2 (LOD=2.65, P=2.4x10(-4)) for 5 micromol/l cisplatin. Quantitative transmission disequilibrium tests were performed using 191973 nonredundant single nucleotide polymorphisms (SNPs) located in the 1 LOD confidence interval of these 11 regions. Twenty SNPs, with 10 SNPs located in five genes, were significantly associated with cisplatin-induced cytotoxicity (P