Peter G. Shields

Circulating Tumor Cells: A Useful Predictor of Treatment Efficacy in Metastatic Breast Cancer

PURPOSE Five or more circulating tumor cells (CTCs) per 7.5 mL of blood predicts for poorer progression-free survival (PFS) in patients with metastatic breast cancer (MBC). We conducted a prospective study to demonstrate that CTC results correlate strongly with radiographic disease progression at the time of and in advance of imaging. PATIENTS AND METHODS Serial CTC levels were obtained in patients starting a new treatment regimen for progressive, radiographically measurable MBC. Peripheral blood was collected for CTC enumeration at baseline and at 3- to 4-week intervals. Clinical outcomes were based on radiographic studies performed in 9- to 12-week intervals. RESULTS Sixty-eight patients were evaluable for the CTC-imaging correlations, and 74 patients were evaluable for the PFS analysis. Median follow-up was 13.3 months. A statistically significant correlation was demonstrated between CTC levels and radiographic disease progression in patients receiving chemotherapy or endocrine therapy. This correlation applied to CTC results obtained at the time of imaging (odds ratio [OR], 6.3), 3 to 5 weeks before imaging (OR, 3.1), and 7 to 9 weeks before imaging (OR, 4.9). Results from analyses stratified by type of therapy remained statistically significant. Shorter PFS was observed for patients with five or more CTCs at 3 to 5 weeks and at 7 to 9 weeks after the start of treatment. CONCLUSION We provide, to our knowledge, the first evidence of a strong correlation between CTC results and radiographic disease progression in patients receiving chemotherapy or endocrine therapy for MBC. These findings support the role of CTC enumeration as an adjunct to standard methods of monitoring disease status in MBC.

Smoking, alcoholism and genetic polymorphisms alter CYP2B6 levels in human brain.

CYP2B6 metabolizes drugs such as nicotine and bupropion, and many toxins and carcinogens. Nicotine induces CYP2B1 in rat brain and in humans polymorphic variation in CYP2B6 affects smoking cessation rates. The aim of this study was to compare CYP2B6 expression in brains of human smokers and non-smokers and alcoholics and non-alcoholics (n=26). CYP2B6 expression was brain region-specific, and was observed in both neurons and astrocytes. CYP2B6 levels were higher in brains of smokers and alcoholics, particularly in cerebellar Purkinje cells and hippocampal pyramidal neurons, cells known to be damaged in alcoholics. Significantly more (p<0.05) CYP2B6 protein was seen in four brain regions of smoking alcoholics compared to non-smoking non-alcoholics: hippocampus (5.8-fold), caudate nucleus (3.3-fold), putamen (3.0-fold) and cerebellar hemisphere (1.6-fold). The genetic variant C1459T (R487C) has been associated with reduced hepatic enzyme levels, stability and activity. Preliminary genotyping of this small sample (n=24) suggested that individuals with the CC genotype had higher brain CYP2B6 than those with the CT or TT genotype. Higher brain CYP2B6 activity in smokers and alcoholics may cause altered sensitivity to centrally acting drugs, increased susceptibility to neurotoxins and carcinogenic xenobiotics and contribute to central tolerance to nicotine.

Mitochondrial DNA Content: Its Genetic Heritability and Association With Renal Cell Carcinoma

BACKGROUND The extent to which mitochondrial DNA (mtDNA) content (also termed mtDNA copy number) in normal human cells is influenced by genetic factors has yet to be established. In addition, whether inherited variation of mtDNA content in normal cells contributes to cancer susceptibility remains unclear. Renal cell carcinoma accounts for 85% of all renal cancers. No studies have investigated the association between mtDNA content and the risk of renal cell carcinoma. METHODS We first used a classic twin study design to estimate the genetic contribution to the determination of mtDNA content. mtDNA content was measured by quantitative real-time polymerase chain reaction in peripheral blood lymphocytes from 250 monozygotic twins, 92 dizygotic twins, and 33 siblings (ie, individual siblings of a pair of twins). We used biometric genetic modeling to estimate heritability of mtDNA content. We then used a case-control study with 260 case patients with renal cell carcinoma and 281 matched control subjects and multivariable logistic regression analysis to examine the association between mtDNA content in peripheral blood lymphocytes and the risk of renal cell carcinoma. All statistical tests were two-sided. RESULTS The heritability (ie, proportion of phenotypic variation in a population that is attributable to genetic variation among individuals) of mtDNA content was 65% (95% confidence interval [CI] = 50% to 72%; P < .001). Case patients with renal cell carcinoma had a statistically significantly lower mtDNA content (1.18 copies) than control subjects (1.29 copies) (difference = 0.11, 95% CI = 0.03 to 0.17; P = .006). Low mtDNA content (ie, less than the median in control subjects) was associated with a statistically significantly increased risk of renal cell carcinoma, compared with high content (odds ratio = 1.53, 95% CI = 1.07 to 2.19). In a trend analysis, a statistically significant dose-response relationship was detected between lower mtDNA content and increasing risk of renal cell carcinoma (P for trend <.001). CONCLUSIONS mtDNA content appears to have high heritability. Low mtDNA content appears to be associated with increased risk of renal cell carcinoma.

Novel Nicotine Delivery Systems and Public Health: The Rise of the E-Cigarette

Inhalation of smoke from burning tobacco remains the most deadly risky behavior in the United States. For years, corporations have sought alternative methods to administer nicotine to the brain without the harms of combustion while retaining the immediate rewarding aspects of cigarettes that make them so profitable, pleasurable, and addictive. The latest attempt at reduced harm products is a heterogeneous collection of battery-driven inhalers termed by the World Health Organization (WHO) as electronic nicotine delivery systems (ENDS)1 or more popularly as electronic cigarettes or e-cigarettes. These devices pose significant challenges to the public health community because their distribution and use has become widespread in the United States while simultaneously evading most regulatory structures. Ultimately, these devices force a close consideration of how the health and regulatory system evaluates claims of safety and harm reduction in a dynamic, consumer driven environment to ensure the broad protection of public health.

Effects of dopamine transporter and receptor polymorphisms on smoking cessation in a bupropion clinical trial.

This study examined the role of dopaminergic genes in prospective smoking cessation and response to bupropion treatment in a placebo-controlled clinical trial. Smokers of European ancestry (N=418) provided blood samples for genetic analysis and received either bupropion or placebo (10 weeks) plus counseling. Assessments included the dopamine D2 receptor (DRD2) genotype, dopamine transporter (SLC6A3) genotype, demographic factors, and nicotine dependence. Smoking status was verified at the end of treatment (EOT) and at 6-month follow-up. The results provided evidence for a significant DRD2 * SLC6A3 interaction effect on prolonged smoking abstinence and time to relapse at EOT, independent of treatment condition. Such effects were no longer significant at 6-month follow-up, however. These results provide the first evidence from a prospective clinical trial that genes that alter dopamine function may influence smoking cessation and relapse during the treatment phase.

Reduced nicotine content cigarettes: effects on toxicant exposure, dependence and cessation

AIMS To examine the effects of reduced nicotine cigarettes on smoking behavior, toxicant exposure, dependence and abstinence. DESIGN Randomized, parallel arm, semi-blinded study. Setting University of Minnesota Tobacco Use Research Center. INTERVENTIONS Six weeks of: (i) 0.05 mg nicotine yield cigarettes; (ii) 0.3 mg nicotine yield cigarettes; or (iii) 4 mg nicotine lozenge; 6 weeks of follow-up. Measurements Compensatory smoking behavior, biomarkers of exposure, tobacco dependence, tobacco withdrawal and abstinence rate. FINDINGS Unlike the 0.3 mg cigarettes, 0.05 mg cigarettes were not associated with compensatory smoking behaviors. Furthermore, the 0.05 mg cigarettes and nicotine lozenge were associated with reduced carcinogen exposure, nicotine dependence and product withdrawal scores. The 0.05 mg cigarette was associated with greater relief of withdrawal from usual brand cigarettes than the nicotine lozenge. The 0.05 mg cigarette led to a significantly higher rate of cessation than the 0.3 mg cigarette and a similar rate as nicotine lozenge. CONCLUSION The 0.05 mg nicotine yield cigarettes may be a tobacco product that can facilitate cessation; however, future research is clearly needed to support these preliminary findings.

Toward Personalized Therapy for Smoking Cessation: A Randomized Placebo-controlled Trial of Bupropion

We examined whether a pretreatment phenotypic marker of nicotine metabolism rate (NMR) predicts successful smoking cessation with bupropion. Smokers (N = 414) were tested for pretreatment NMR, based on the ratio of 3′‐hydroxycotinine/cotinine derived during smoking, before entering a placebo‐controlled randomized trial of bupropion plus counseling. At the end of the 10‐week treatment phase, slow metabolizers (1st NMR quartile) had equivalent quit rates with placebo or bupropion (32%). Fast metabolizers (4th NMR quartile) had low quit rates with placebo (10%), and these were enhanced significantly by bupropion (34%). Smokers in the 2nd quartile (placebo: 25%, bupropion: 30%) and the 3rd quartile (placebo: 20%, bupropion: 30%) did not benefit significantly from bupropion. At the 6‐month follow‐up, the relationship between the NMR and quitting remained similar, but was no longer statistically significant. A pretreatment assessment of NMR may identify smokers who are most and least likely to benefit from treatment with bupropion for smoking cessation.

CYP1A1 T3801 C polymorphism and lung cancer: A pooled analysis of 2,451 cases and 3,358 controls

CYP1A1 is involved in the metabolism of benzopyrene, a suspected lung carcinogen; it is therefore conceivable that genetically determined variations in its activity modify individual susceptibility to lung cancer. The role of the CYP1A1 MspI polymorphism in lung cancer has been widely studied but has not been fully clarified. We have included 2,451 cases and 3,358 controls in a pooled analysis of 22 case‐control studies on CYP1A1 and lung cancer risk. We found a clear association between the CYP1A1 homozygous MspI restriction fragment length polymorphism (RFLP) and lung cancer risk in Caucasians (age‐ and gender‐adjusted odds ratio = 2.36; 95% confidence interval 1.16–4.81); other associations were weaker or not statistically significant. The association with the homozygous variant was equally strong for squamous cell carcinomas and adenocarcinomas among Caucasians. We analyzed the risk by duration of smoking: for Caucasian subjects with the MspI RFLP combined variants (homozygotes plus heterozygotes), the increase in the risk of lung cancer was steeper than among the individuals with the homozygous reference allele. Our analysis suggests that Caucasians with homozygous variant CYP1A1 polymorphism have a higher risk of lung cancer. The data were more consistent among Caucasians, with a strong association between the homozygous variant in both squamous cell carcinomas and adenocarcinomas, and a stronger association in men than in women. The analyses were more inconsistent and failed to reach statistical significance in Asians. This observation might be due to design specificities or unknown effect modifiers in the Asian studies.

Catechol-O-Methyltransferase (COMT) Gene Variants Predict Response to Bupropion Therapy for Tobacco Dependence

BACKGROUND Although bupropion is efficacious for smoking cessation, only a minority of smokers are able to quit. Pharmacogenetic research may improve treatment outcomes through discovery of DNA sequences predictive of successful pharmacotherapy for subgroups of smokers. We investigated variants in the catechol-O-methyltransferase (COMT) gene in a smoking cessation trial of bupropion. METHODS A double-blind, placebo-controlled, 10-week trial of bupropion and counseling (with a 6-month follow-up period) was conducted at two university-based smoking cessation research programs. Abstinence was biochemically verified at the end of treatment and at 6 months after the target quit date. RESULTS At the end of the treatment phase, statistically significant interaction effects indicated that COMT haplotypes of two SNPs (rs737865 and rs165599) predicted the efficacy of bupropion compared with placebo. This interaction effect was attenuated at 6-month follow-up. CONCLUSIONS COMT haplotypes at rs737865 and rs165599 may predict a favorable outcome for bupropion treatment for smoking cessation. European-American smokers with a G allele at both SNPs may not benefit from bupropion treatment. Small numbers of some COMT haplotypes limit interpretation of response. If study findings are confirmed in additional large studies, COMT genotyping could be applied to identify likely responders to bupropion treatment for smoking cessation.

Mutagen Sensitivity Has High Heritability: Evidence from a Twin Study

Despite numerous studies showing that mutagen sensitivity is a cancer predisposition factor, the heritability of mutagen sensitivity has not been clearly established. In this report, we used a classic twin study design to examine the role of genetic and environmental factors on the mutagen sensitivity phenotype. Mutagen sensitivity was measured in peripheral blood lymphocytes from 460 individuals [148 pairs of monozygotic (MZ) twins, 57 pairs of dizygotic (DZ) twins, and 50 siblings]. The intraclass correlation coefficients were all significantly higher in MZ twins than in dizygotes (DZ pairs and MZ-sibling pairs combined) for sensitivity to four different mutagen challenges. Applying biometric genetic modeling, we calculated a genetic heritability of 40.7%, 48.0%, 62.5%, and 58.8% for bleomycin, benzo[a]pyrene diol epoxide, gamma-radiation, and 4-nitroquinoline-1-oxide sensitivity, respectively. This study provides the strongest and most direct evidence that mutagen sensitivity is highly heritable, thereby validating the use of mutagen sensitivity as a cancer susceptibility factor.