Opportunities for Education in Heart Failure Pharmacotherapy Demonstrated by a Survey of Clinicians.

Aim We conducted a survey of practitioners' knowledge of the clinical application of the major drug classes in HF, with reference to the European Society of Cardiology guidelines. The aim was to identify areas for practice development through education, which may improve HF morbidity and mortality. Methods We distributed a 14 item questionnaire assessing doctors knowledge of indications and contraindications for the major HF drug classes. Results Total number of responses was 127: Intern (N=21), SHO (N=64), Registrar (N=12), SpR (N=14), Consultant (N=4), GP (N=2). Consultants and GPs were excluded from analysis due to underrepresentation. Median years of practice was 4. Indications were correctly identified in a mean of 78% of responses overall. Of participants who felt comfortable with initiation and up-titration of beta blockers (N=84), only 31% (N=26) correctly identified an optimal target heart rate of less than 70 beats per minute. Forty-five percent (N=50) identified serum potassium and creatinine concentrations generally considered safe as contraindications to the initiation of MRA. Twenty-five percent of respondents (N=28) were unaware of a specialist HF service that catered to their institution, and how to refer to it, but 99% (N=110) felt that their practice would benefit from further education on HF pharmacotherapy. Conclusion Results of this survey suggest a need, and indeed a demand, for further education for clinicians in order to reduce mortality, morbidity, and hospital readmission in HF, as well as their attendant costs.

Persisting Symptomatic Severe Secondary Mitral Regurgitation in Heart Failure Patients.

Aims We aimed to assess the rate of persisting severe symptomatic secondary mitral regurgitation (MR) in a newly diagnosed heart failure (HF) population following optimisation of guideline directed medical therapy (GDMT), cardiac resynchronisation therapy (CRT) and revascularisation. Methods We assessed all new patients referred to our hospital group's HF clinics. We retrospectively reviewed these patients at HF clinic enrolment, HF programme completion, as well as most recent follow up. Results Of the 242 new patients referred to our HF clinics, there were 10 patients (4.1%) who had either persisting symptomatic severe secondary MR at HF programme completion, or had undergone mitral valve surgery. There were no percutaneous mitral valve repairs at the time of these patients' referrals. The rates of ACE/ARB/ARNI, BB and MRA use were 87.8%, 94.1%, and 49.8% in those with mid ranged, or reduced ejection fraction. The rates of ICD and CRT therapy were 15.1% and 4.4% at follow up. Patients with severe MR had higher time adjusted rates of death or hospitalization for heart failure. Conclusion In a well-treated newly diagnosed HF population, repeat assessment at HF programme completion suggests 4.1% of patients have a persisting indication for percutaneous mitral valve repair based on persisting severe symptomatic secondary MR.

FDA Approval Summary: Atezolizumab or Pembrolizumab for the Treatment of Patients with Advanced Urothelial Carcinoma Ineligible for Cisplatin-Containing Chemotherapy.

The U.S. Food and Drug Administration (FDA) granted accelerated approval to atezolizumab and pembrolizumab in April and May 2017, respectively, for the treatment of patients with locally advanced or metastatic urothelial carcinoma who are not eligible for cisplatin-containing chemotherapy. These approvals were based on efficacy and safety data demonstrated in the two single-arm trials, IMvigor210 (atezolizumab) and KEYNOTE-052 (pembrolizumab). The primary endpoint, confirmed objective response rate, was 23.5% (95% confidence interval [CI]: 16.2%-32.2%) in patients receiving atezolizumab and 28.6% (95% CI: 24.1%-33.5%) in patients receiving pembrolizumab. The median duration of response was not reached in either study and responses were seen regardless of PD-L1 status. The safety profiles of both drugs were generally consistent with approved agents targeting PD-1/PD-L1. Two ongoing trials (IMvigor130 and KEYNOTE-361) are verifying benefit of these drugs. Based on concerning preliminary reports from these trials, FDA revised the indications for both agents in cisplatin-ineligible patients. Both drugs are now indicated for patients not eligible for any platinum-containing chemotherapy or not eligible for cisplatin-containing chemotherapy and whose tumors/infiltrating immune cells express a high level of PD-L1. The indications for atezolizumab and pembrolizumab in patients who have received prior platinum-based therapy have not been changed. This article summarizes the FDA thought process and data supporting the accelerated approval of both agents and the subsequent revision of the indications. IMPLICATIONS FOR PRACTICE: The accelerated approvals of atezolizumab and pembrolizumab for cisplatin-ineligible patients with advanced urothelial carcinoma represent the first approved therapies for this patient population. These approvals were based on single-arm trials demonstrating reasonable objective response rates and favorable durations of response with an acceptable toxicity profile compared with available non-cisplatin-containing chemotherapy regimens. However, based on concerning preliminary reports from two ongoing phase III trials, the FDA revised the indication for both agents in cisplatin-ineligible patients. Both are now indicated either for patients not eligible for any platinum-containing chemotherapy or not eligible for cisplatin-containing chemotherapy and whose tumors have high expression of PD-L1.

FDA Approval Summary: Nivolumab in Advanced Renal Cell Carcinoma After Anti-Angiogenic Therapy and Exploratory Predictive Biomarker Analysis.

On November 23, 2015, the U.S. Food and Drug Administration approved nivolumab (OPDIVO, Bristol-Myers Squibb Company) for patients with advanced renal cell carcinoma (RCC) who have received prior anti-angiogenic therapy. The approval was based on efficacy and safety data demonstrated in an open-label, randomized study of 821 patients with advanced RCC who progressed after at least one anti-angiogenic therapy. Patients were randomized to nivolumab or everolimus and followed for disease progression. The primary end point was overall survival. Subsequent therapies, including everolimus for patients who developed progressive disease on the nivolumab arm, were allowed, but no cross-over was permitted. The median overall survival was 25.0 months on the nivolumab arm and 19.6 months on everolimus arm (hazard ratio: 0.73; 95% confidence interval: 0.60-0.89). The confirmed response rates were 21.5% versus 3.9%; median durations of response were 23.0 versus 13.7 months, and median times to response were 3.0 versus 3.7 months in the nivolumab and everolimus arms, respectively. A statistically significant improvement in progression-free survival was not observed in this trial. The safety profile of nivolumab in renal cell cancer was similar to that in other disease settings. However, the incidence of immune-mediated nephritis appeared to be higher in patients with RCC. The Oncologist 2017;22:311-317 IMPLICATIONS FOR PRACTICE: The overall benefit/risk profile demonstrated in trial CA209025 supported the approval of nivolumab as an additional treatment option for patients with advanced renal cell carcinoma after anti-angiogenic therapy. The use of nivolumab in patients who had received vascular endothelial growth factor-targeted therapy resulted in a 5.4 month improvement in median overall survival compared with the everolimus arm. This difference is statistically significant and clinically meaningful.

FDA Approval Summary: Atezolizumab for the Treatment of Patients with Progressive Advanced Urothelial Carcinoma after Platinum-Containing Chemotherapy.

Until recently in the United States, no products were approved for second-line treatment of advanced urothelial carcinoma. On May 18, 2016, the U.S. Food and Drug Administration approved atezolizumab for the treatment of patients with locally advanced or metastatic urothelial carcinoma whose disease progressed during or following platinum-containing chemotherapy or within 12 months of neoadjuvant or adjuvant treatment with platinum-containing chemotherapy. Atezolizumab is a programmed death-ligand 1 (PD-L1) blocking antibody and represents the first approved product directed against PD-L1. This accelerated approval was based on results of a single-arm trial in 310 patients with locally advanced or metastatic urothelial carcinoma who had disease progression after prior platinum-containing chemotherapy. Patients received atezolizumab 1,200 mg intravenously every 3 weeks until disease progression or unacceptable toxicity. Key efficacy measures were objective response rate (ORR), as assessed by Independent Review per RECIST 1.1, and duration of response (DoR). With a median follow-up of 14.4 months, confirmed ORR was 14.8% (95% CI: 11.1, 19.3) in all treated patients. Median DoR was not reached and response durations ranged from 2.1+ to 13.8+ months. Of the 46 responders, 37 patients had an ongoing response for ≥ 6 months. The most common adverse reactions (≥20%) were fatigue, decreased appetite, nausea, urinary tract infection, pyrexia, and constipation. Infection and immune-related adverse events also occurred, including pneumonitis, hepatitis, colitis, endocrine disorders, and rashes. Overall, the benefit-risk assessment was favorable to support accelerated approval. The observed clinical benefits need to be verified in confirmatory trial(s). IMPLICATIONS FOR PRACTICE: This accelerated approval of atezolizumab for second-line use in advanced urothelial carcinoma provides patients with an effective, novel treatment option for the management of their disease. This represents the first immunotherapy approved in this disease setting.

U.S. Food and Drug Administration Approval Summary: Enzalutamide for the Treatment of Patients With Chemotherapy-Naïve Metastatic Castration-Resistant Prostate Cancer.

The U.S. Food and Drug Administration approved enzalutamide for the treatment of patients with chemotherapy-naïve metastatic castration-resistant prostate cancer (mCRPC). At the prespecified interim analysis, a statistically significant improvement in overall survival was demonstrated for patients in the enzalutamide arm compared with patients in the placebo arm. The overall benefit-risk profile supports the expanded indication for enzalutamide. On September 10, 2014, the U.S. Food and Drug Administration approved enzalutamide for the treatment of patients with chemotherapy-naïve metastatic castration-resistant prostate cancer (mCRPC). Enzalutamide was initially approved in 2012 for use in patients with mCRPC who had previously received docetaxel. The current approval was based on the results of a randomized, placebo-controlled, double-blind trial conducted in 1,717 asymptomatic or minimally symptomatic patients with chemotherapy-naïve mCRPC. Patients were assigned to receive either enzalutamide 160 mg or placebo orally once daily. The coprimary endpoints were overall survival (OS) and radiographic progression-free survival (rPFS), which was assessed by independent central radiology review. At the prespecified interim analysis, a statistically significant improvement in OS was demonstrated for patients in the enzalutamide arm compared with patients in the placebo arm (hazard ratio [HR], 0.71; 95% confidence interval [CI], 0.60-0.84). The median OS was 32.4 and 30.2 months in the enzalutamide and placebo arms, respectively. A statistically significant prolongation of rPFS was observed in patients in the enzalutamide arm (HR, 0.17; 95% CI, 0.14-0.21). In addition, the time to initiation of cytotoxic chemotherapy was prolonged in the enzalutamide arm (HR, 0.35; 95% CI, 0.30-0.40), with median times of 28.0 and 10.8 months in the enzalutamide and placebo arms, respectively. The safety profile was similar to that previously reported for enzalutamide. Adverse reactions of interest included seizure, hypertension, and falls. Enzalutamide should be discontinued if a seizure occurs during treatment. The overall benefit-risk profile supports the expanded indication for enzalutamide.

A survey of patients' attitudes to clinical research.

Every year hundreds of patients voluntarily participate in clinical trials across Ireland. However, little research has been done as to how patients find the experience. This survey was conducted in an attempt to ascertain clinical trial participants' views on their experience of participating in a clinical trial and to see and how clinical trial participation can be improved. One hundred and sixty-six clinical trial participants who had recently completed a global phase IV cardiovascular endpoint clinical trial were sent a 3-page questionnaire. Ninety-one (91%) respondents found the experience of participating in a clinical trial a good one with 85 (84.16%) respondents saying they would recommend participating in a clinical trial to a friend or relative and eighty-five (87.63%) respondents feeling they received better healthcare because they had participated in a clinical trial.

Association of central obesity with early Carotid intima-media thickening is independent of that from other risk factors.

AIM: We investigated whether anthropometric measurements or metabolic risk factors correlated more with vascular changes associated with obesity. METHODS: One hundred never smoking subjects (71 women, 29 men) without vascular events, with blood pressure (BP) <140/90 mm Hg, LDL cholesterol <4 mmol/l, glucose <6.2 mmol/l participated. Anthropometric measurements (body mass index (BMI), waist/hip ratio (WHR), waist circumference (WC) and Waist/height ratio WHTR) and metabolic risk factors (glucose, insulin, lipid and uric acid levels plus BP) were assessed. Subjects underwent vascular measurements (Carotid intima-media thickness (IMT) using duplex ultrasonography, vascular stiffness assessment (Augmentation Index) by applanation tonometry and brachial artery reactivity tests). RESULTS: Risk factors were in the 'normal distribution'. BMI, WHR, WC, WHTR correlated significantly with triglyceride, HDL, LDL, insulin, glucose, uric acid and systolic BP levels (P<0.001). IMT correlated with WHTR, BMI, WC, Glucose (P<0.001), Homoeostasis Model Assessment (HOMA) and cholesterol levels (P<0.05). Only Age, WHTR or BMI were significant correlates of IMT in a multivariate analysis (P<0.01) including WHTR or BMI, with age, sex, systolic BP, HDLc and HOMA. Augmentation Index correlated with age (P<0.0001), WHTR and WC (P<0.0005) but with age only in a multivariate analysis. Brachial reactivity did not correlate with any anthropometric or metabolic parameters. Anthropometric cutoff points, (BMI > or =25, WC > or =102 cm men, > or =88 cm women, WHR > or =0.9 men, > or =0.8 women and WHTR > or =0.5 men and women) significantly differentiated normal from abnormal metabolic and vascular measurements. The WHTR ratio > or =0.5 was as reliable as the BMI cutoff > or =25 in determining metabolic and vascular abnormalities. BMI and WHTR were strongly associated with 89% agreement (P<0.0001). CONCLUSION: These results demonstrated that in 'healthy individuals', anthropometric parameters and metabolic risk factors correlated with each other, but anthropometric parameters were the only significant correlates of carotid IMT. A waist/height ratio > or =0.5 predicts both early vascular and metabolic changes. These data support a risk factor independent vasculotrophic effect of obesity.

Dyslipidemia therapy update: the importance of full lipid profile assessment.

Lipid guidelines typically focus on total cholesterol +/- low-density lipoprotein cholesterol levels with less emphasis on high-density lipoprotein cholesterol (HDL-C) or triglyceride assessment, thus potentially underestimating cardiovascular (CV) risk and the need for lifestyle or treatment optimization. In this article, we highlight how reliance on isolated total cholesterol assessment may miss prognostically relevant lipid abnormalities; we describe from the European Systematic COronary Risk Evaluation (SCORE) data set how incorporation of HDL-C may improve estimation of CV risk; and, finally, we critically evaluate the evidence base surrounding triglycerides and CV risk.

Analysis of the Association Between Adverse Events and Outcome in Patients Receiving a Programmed Death Protein 1 or Programmed Death Ligand 1 Antibody.

PURPOSE: To assess the relationship among tumor response rate, overall survival, and the development of related adverse events of special interest (AESIs) or related immune-mediated adverse events (imAEs) in patients with urothelial cancer treated with anti-programmed death protein 1 or ligand 1 (anti-PD-1/L1) antibodies. PATIENTS AND METHODS: We examined seven trials in 1,747 patients with metastatic or locally advanced urothelial cancer that led to approval of an anti-PD-1/L1 antibody. Five trials enrolled patients who had received prior platinum-based therapy, and two enrolled patients who were cisplatin ineligible. The data sets were searched for AESIs, related AESIs, imAEs, and related imAEs. The relationship to study drug was determined by the investigator. ImAEs were defined as AESIs treated with topical or systemic corticosteroids. RESULTS: In these exploratory analyses, a related AESI was reported in 64% of responding patients and in 34% of patients who did not respond to the anti-PD-1/L1 antibody, whereas a related imAE occurred in 28% and 12% of patients who did and did not respond to study drug, respectively. In a responder analysis, an increase in overall survival was seen in patients with related AESIs compared with those with no related AESIs (hazard ratio, 0.45; 95% CI, 0.39 to 0.52). Fifty-seven percent of responding patients with a related AESI reported the AESI before documentation of response. CONCLUSION: Patients who responded to treatment with an anti-PD-1/L1 antibody were more likely to report a related AESI or related imAE. This relationship did not seem to be due to the increased duration of exposure in responding patients. Systemic corticosteroid use did not appear to affect the duration of response.

Kinds and spectrum of mutations induced by 1-nitrosopyrene adducts during plasmid replication in human cells.

1-Nitropyrene has been shown in bacterial assays to be the principal mutagenic agent in diesel emission particulates. It has also been shown to be mutagenic in human fibroblasts and carcinogenic in animals. To investigate the kinds of mutations induced by this carcinogen and compare them with those induced by a structurally related carcinogen, (+/-)-7 beta,8 alpha-dihydroxy-9 alpha,10 alpha-epoxy-7,8,9,10-tetra-hydrobenzo [a]pyrene (BPDE) (J.-L. Yang, V. M. Maher, and J. J. McCormick, Proc. Natl. Acad. Sci. USA 84:3787-3791, 1987), we treated a shuttle vector with tritiated 1-nitrosopyrene (1-NOP), a carcinogenic mutagenic intermediate metabolite of 1-nitropyrene which forms the same DNA adduct as the parent compound, and introduced the plasmids into a human embryonic kidney cell line, 293, for DNA replication to take place. The treated plasmid, pZ189, carrying a bacterial suppressor tRNA target gene, supF, was allowed 48 h to replicate in the human cells. Progeny plasmids were then rescued, purified, and introduced into bacteria carrying an amber mutation in the beta-galactosidase gene in order to detect those carrying mutations in the supF gene. The frequency of mutants increased in direct proportion to the number of DNA-1-NOP adducts formed per plasmid. At the highest level of adduct formation tested, the frequency of supF mutants was 26 times higher than the background frequency of 1.4 X 10(-4). DNA sequencing of 60 unequivocally independent mutant derived from 1-NOP-treated plasmids indicated that 80% contained a single base substitution, 5% had two base substitutions, 4% had small insertions or deletions (1 or 2 base pairs), and 11% showed a deletion or insertion of 4 or more base pairs. Sequence data from 25 supF mutants derived from untreated plasmids showed that 64% contained deletions of 4 or more base pairs. The majority (83%) of the base substitution in mutants from 1-NOP-treated plasmids were transversions, with 73% of these being G . C --> T . A. This is very similar to what we found previously in this system, using BPDE, but each carcinogen produced its own spectrum of mutations. Of the five hot spots for base substitution mutations produced in the supF gene with 1-NOP, two were the same as seen with BPDE-treated plasmids. However, the three other hot spots were cold spots for BPDE-treated plasmids. Conversely, four of the other five hot spots seen with BPDE-treated plasmids were cold spots for 1-NOP-treated plasmids. Comparison of the two carcinogens for the frequency of supF mutants induced per DNA adduct showed that 1-NOP-induced adducts were 3.8 times less than BPDE adducts. However, the 293 cell excised 1-NOP-induced adducts faster than BPDE adducts.

Effect of nucleotide excision repair in human cells on intrachromosomal homologous recombination induced by UV and 1-nitrosopyrene.

To study the role of nucleotide excision repair in the induction of intrachromosomal homologous recombination in mammalian cells, we introduced a plasmid containing a substrate for recombination into three human cell lines that differ in their repair capacity and compared the frequency of recombination induced by UV radiation and by 1-nitrosopyrene. One strain had a normal capacity for nucleotide excision repair, the second exhibited an intermediate rate of repair, and the third, derived from a patient with xeroderma pigmentosum, had no ability to repair UV- or 1-nitrosopyrene-induced DNA damage. The endogenous thymidine kinase genes in these cell strains had been inactivated, and the cells contained an integrated copy of a plasmid carrying duplicated copies of the herpes simplex virus type 1 thymidine kinase (Htk) gene, each inactivated by an 8-base-pair XhoI site inserted at a unique site. A functional tk gene can only be generated by a productive recombination event between the two Htk genes. In all three stains, UV and 1-nitrosopyrene induced dose-dependent increases in the frequency of recombinants. However, the doses required to cause a specific increase in recombination in the repair-deficient strains were 10 to 30 times lower than the dose required for the cell strain with a normal capacity for repair. These results strongly suggest that unexcised DNA lesions, rather than excision repair per se, stimulate intrachromosomal homologous recombination. Southern blot analysis of DNA from representative recombinants indicated that in all cases one of the two Htk genes had become wild type (XhoI resistant). The majority (90%) retained the Htk duplication, consistent with nonreciprocal transfer of genetic information (gene conversion).

Site-specific excision repair of 1-nitrosopyrene-induced DNA adducts at the nucleotide level in the HPRT gene of human fibroblasts: effect of adduct conformation on the pattern of site-specific repair.

Studies showing that different types of DNA adducts are repaired in human cells at different rates suggest that DNA adduct conformation is the major determinant of the rate of nucleotide excision repair. However, recent studies of repair of cyclobutane pyrimidine dimers or benzo[a]pyrene diol epoxide (BPDE)-induced adducts at the nucleotide level in DNA of normal human fibroblasts indicate that the rate of repair of the same adduct at different nucleotide positions can vary up to 10-fold, suggesting an important role for local DNA conformation. To see if site-specific DNA repair is a common phenomenon for bulky DNA adducts, we determined the rate of repair of 1-nitrosopyrene (1-NOP)-induced adducts in exon 3 of the hypoxanthine phosphoribosyltransferase gene at the nucleotide level using ligation-mediated PCR. To distinguish between the contributions of adduct conformation and local DNA conformation to the rate of repair, we compared the results obtained with 1-NOP with those we obtained previously using BPDE. The principal DNA adduct formed by either agent involves guanine. We found that rates of repair of 1-NOP-induced adducts also varied significantly at the nucleotide level, but the pattern of site-specific repair differed from that of BPDE-induced adducts at the same guanine positions in the same region of DNA. The average rate of excision repair of 1-NOP adducts in exon 3 was two to three times faster than that of BPDE adducts, but at particular nucleotides the rate was slower or faster than that of BPDE adducts or, in some cases, equal to that of BPDE adducts. These results indicate that the contribution of the local DNA conformation to the rate of repair at a particular nucleotide position depends upon the specific DNA adduct involved. However, the data also indicate that the conformation of the DNA adduct is not the only factor contributing to the rate of repair at different nucleotide positions. Instead, the rate of repair at a particular nucleotide position depends on the interaction between the specific adduct conformation and the local DNA conformation at that nucleotide.

Kinds of mutations formed when a shuttle vector containing adducts of benzo[a]pyrene-7,8-diol-9,10-epoxide replicates in COS7 cells.

We have investigated the kinds of mutations induced when a shuttle vector containing covalently bound residues of the (+/-)-7 beta,8 alpha-dihydroxy-9 alpha,10 alpha-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (BPDE) replicates in the monkey kidney cell line COS7. The target for detecting mutations was the 200-base pair gene for a tyrosine suppressor tRNA (supF), inserted at the EcoRI site in shuttle vector p3AC (Sarkar et al., Mol. Cell. Biol. 4:2227-2230, 1984). When introduced by transformation, a functioning supF gene in progeny plasmid recovered from COS7 cells allows suppression of a lacZ amber mutation in the indicator Escherichia coli host. Treatment of p3AC with BPDE caused a linear increase in the number of BPDE residues bound per plasmid. Untreated plasmids and plasmids containing 6.6 BPDE residues were transfected into COS7 cells, and the progeny were assayed for mutations in the supF gene. The frequency of mutants generated during replication of the BPDE-treated plasmids was not higher than that from untreated plasmids, but the two populations differed markedly in the kinds of mutations they contained. Gel electrophoresis analysis of the size alterations of 77 mutant plasmids obtained with untreated DNA and 45 obtained with BPDE-treated DNA showed that the majority of the mutant progeny of untreated plasmids exhibited gross alterations, principally large deletions. In contrast, the majority of the mutants generated during replication of the BPDE-treated plasmids contained only minor alterations, principally point mutations. Sequence analysis of progeny of untreated plasmids containing putative point mutations showed insertions and deletions of bases and a broad spectrum of base substitutions; in those from BPDE-treated plasmids, all base substitutions involved guanosine . cystosine pairs.

Carcinogens can induce homologous recombination between duplicated chromosomal sequences in mouse L cells.

The ability of a series of DNA-damaging agents to induce homologous intrachromosomal recombination between duplicated genes in the chromosome of mouse cells was investigated. The target cells were the thymidine kinase-deficient mouse L-cell strain 333M, which contains a single integrated copy of a plasmid with two herpes simplex virus thymidine kinase (Htk) genes, each containing an 8-base-pair XhoI linker inserted at a unique site. Expression of a functional Htk enzyme requires a productive recombinational event between the two nonfunctional genes. The spontaneous rate of recombination in this strain is 3 per 10(6) cells per generation. The agents tested represent physical carcinogens (UV and ionizing radiation), a simple alkylating agent (N-methyl-N'-nitro-N-nitrosoguanidine), an alkylating cross-linking agent (mitomycin C), and a reactive metabolite of a polycyclic aromatic hydrocarbon ((+/-)-7 beta,8 alpha-dihydroxy-9 alpha,10 alpha-epoxy-7,8,9,10- tetrahydrobenzo[a]pyrene [BPDE] ). The background frequency of tk+ recombinants in the untreated population averaged 18 X 10(-6) +/- 5 X 10(-6). Ionizing radiation had little or no effect on recombination; exposure to mitomycin C, N-methyl-N'-nitro-N-nitrosoguanidine, BPDE, or UV, at doses that lowered the survival to between 90 and 10% of the control, caused a dose-dependent increase in frequency of recombinants, reaching 50 X 10(-6) to 100 X 10(-6). No tk+ cells could be generated with a control cell line that contained only one mutant copy of the Htk gene. Molecular hybridization analysis showed that 85 to 90% of the tk+ recombinants retained the Htk gene duplication, consistent with nonreciprocal transfer of wild-type genetic information, gene conversion. In the rest, only a single copy of the Htk gene remained, reflecting a single reciprocal exchange within a chromatid or a single unequal exchange between sister chromatids. Each recombinant tested contained an XhoI-resistant (wild-type) Htk gene.

Evidence from mutation spectra that the UV hypermutability of xeroderma pigmentosum variant cells reflects abnormal, error-prone replication on a template containing photoproducts.

Xeroderma pigmentosum (XP) variant patients are genetically predisposed to sunlight-induced skin cancer. Fibroblasts derived from these patients are extremely sensitive to the mutagenic effect of UV radiation and are abnormally slow in replicating DNA containing UV-induced photoproducts. However, unlike cells from the majority of XP patients, XP variant cells have a normal or nearly normal rate of nucleotide excision repair of such damage. To determine whether their UV hypermutability reflected a slower rate of excision of photoproducts specifically during early S phase when the target gene for mutations, i.e., the hypoxanthine (guanine) phosphoribosyltransferase gene (HPRT), is replicated, we synchronized diploid populations of normal and XP variant fibroblasts, irradiated them in early S phase, and compared the rate of loss of cyclobutane pyrimidine dimers and 6-4 pyrimidine-pyrimidones from DNA during S phase. There was no difference. Both removed 94% of the 6-4 pyrimidine-pyrimidones within 8 h and 40% of the dimers within 11 h. There was also no difference between the two cell lines in the rate of repair during G1 phase. To determine whether the hypermutability resulted from abnormal error-prone replication of DNA containing photoproducts, we determined the spectra of mutations induced in the coding region of the HPRT gene of XP variant cells irradiated in early S and G1 phases and compared with those found in normal cells. The majority of the mutations in both types of cells were base substitutions, but the two types of cells differed significantly from each other in the kinds of substitutions, but the two types differed significantly from each other in the kinds of substitutions observed either in mutants from S phase (P < 0.01) or from G1 phase (P = 0.03). In the variant cells, the substitutions were mainly transversions (58% in S, 73% in G1). In the normal cells irradiated in S, the majority of the substitutions were G.C --> A.T, and most involved CC photoproducts in the transcribed strand. In the variant cells irradiated in S, substitutions involving cytosine in the transcribed strand were G.C --> T.A transversions exclusively. G.C --> A.T transitions made up a much smaller fraction of the substitutions than in normal cells (P < 0.02), and all of them involved photoproducts located in the nontranscribed strand. The data strongly suggest that XP variant cells are much less likely than normal cells to incorporate either dAMP or dGMP opposite the pyrimidines involved in photoproducts. This would account for their significantly higher frequency of mutants and might explain their abnormal delay in replicating a UV-damaged template.

Abnormal, error-prone bypass of photoproducts by xeroderma pigmentosum variant cell extracts results in extreme strand bias for the kinds of mutations induced by UV light.

Xeroderma pigmentosum (XP) is a rare genetic disease characterized by a greatly increased susceptibility to sunlight-induced skin cancer. Cells from the majority of patients are defective in nucleotide excision repair. However, cells from one set of patients, XP variants, exhibit normal repair but are abnormally slow in replicating DNA containing UV photoproducts. The frequency of UV radiation-induced mutations in the XP variant cells is significantly higher than that in normal human cells. Furthermore, the kinds of UV-induced mutations differ very significantly from normal. Instead of transitions, mainly C-->T, 30% of the base substitutions consist of C-->A transversions, all arising from photoproducts located in one strand. Mutations involving cytosine in the other strand are almost all C-->T transitions. Forty-five percent of the substitutions involve thymine, and the majority are transversions. To test the hypothesis that the UV hypermutability and the abnormal spectrum of mutations result from abnormal bypass of photoproducts in DNA, we compared extracts from XP variant cells with those from HeLa cells and a fibroblast cell strain, MSU-1.2, for the ability to replicate a UV-irradiated form I M13 phage. The M13 template contains a simian virus 40 origin of replication located directly to the left or to the right of the target gene, lacZalpha, so that the template for the leading and lagging strands of DNA replication is defined. Reduction of replication to approximately 37% of the control value required only 1 photoproduct per template for XP variant cell extracts, but approximately 2.2 photoproducts for HeLa or MSU-1.2 cell extracts. The frequency of mutants induced was four times higher with XP variant cell extracts than with HeLa or MSU-1.2 cell extracts. With XP variant cell extracts, the proportion of C-->A transversions reached as high as 43% with either M13 template and arose from photoproducts located in the template for leading-strand synthesis; with HeLa or MSU-1.2 cell extracts, this value was only 5%, and these arose from photoproducts in either strand. With the XP variant extracts, 26% of the substitutions involved thymine, and virtually all were T-->A transversions. Sequence analysis of the coding region of the catalytic subunit of DNA polymerase delta in XP variant cell lines revealed two polymorphisms, but these do not account for the reduced bypass fidelity. Our data indicate that the UV hypermutability of XP variant cells results from reduced bypass fidelity and that unlike for normal cells, bypass of photoproducts involving cytosine in the template for the leading strand differs significantly from that of photoproducts in the lagging strand.

Cell cycle-dependent strand bias for UV-induced mutations in the transcribed strand of excision repair-proficient human fibroblasts but not in repair-deficient cells.

To study the effect of nucleotide excision repair on the spectrum of mutations induced in diploid human fibroblasts by UV light (wavelength, 254 nm), we synchronized repair-proficient cells and irradiated them when the HPRT gene was about to be replicated (early S phase) so that there would be no time for repair in that gene before replication, or in G1 phase 6 h prior to S, and determined the kinds and location of mutations in that gene. As a control, we also compared the spectra of mutations induced in synchronized populations of xeroderma pigmentosum cells (XP12BE cells, which are unable to excise UV-induced DNA damage). Among the 84 mutants sequenced, base substitutions predominated. Of the XP mutants from S or G1 and the repair-proficient mutants from S, approximately 62% were G.C----A.T. In the repair-proficient mutants from G1, 47% were. In mutants from the repair-proficient cells irradiated in S, 71% (10 of 14) of the premutagenic lesions were located in the transcribed strand; with mutants from such cells irradiated in G1, only 20% (3 of 15) were. In contrast, there was no statistically significant difference in the fraction of premutagenic lesions located in the transcribed strand of the XP12BE cells; approximately 75% (24 of 32) of the premutagenic lesions were located in that strand, i.e., 15 of 19 (79%) in the S-phase cells and 9 of 13 (69%) in the G1-phase cells. The switch in strand bias supports preferential nucleotide excision repair of UV-induced damage in the transcribed strand of the HPRT gene.

Association of time-varying clearance of nivolumab with disease dynamics and its implications on exposure response analysis.

Nivolumab is a human monoclonal antibody that blocks the interaction between PD-1 programmed death-1 (PD-1) and its ligands, PD-L1 and PD-L2. Nivolumab demonstrated efficacy in clinical trials for various types of cancer. A time-varying clearance was identified for nivolumab. We show that the change of clearance over time is associated with the post-treatment effects: clearance decreases when disease status improves. This interaction between posttreatment effects and drug exposure may lead to a biased steep estimate of the exposure-response (E-R) relationship for efficacy. Under this scenario, simulations were performed to develop a proposed methodology to assess the causal effect of drug exposure upon clinical response. Data from nivolumab trials were subsequently used to verify the proposed methodology for E-R analysis. The results showed that E-R analysis results based on pharmacokinetic (PK) metrics derived from the first dose are more consistent with the true E-R or dose-response relationship than the steady-state PK metrics.