Gene therapy of cancer: Mechanisms of ``bystander effect'' killing in cells expressing the herpes simplex virus-thymidine kinase gene and its potential clinical applications

At the fore-front of cancer research, gene therapy offers the potential to either promote cell death or alter the behavior of tumor-cells. One example makes use of a toxic phenotype generated by the prodrug metabolizing gene, thymidine kinase (HSVtk) from the Herpes Simplex Virus. This gene confers selective toxicity to a relatively nontoxic prodrug, ganciclovir (GCV). Tumor cells transduced with the HSVtk gene are sensitive to 1-50 $\mu$M GCV; normal tissue is insensitive up to 150-250 $\mu$M GCV. Utilizing these different sensitivities, it is possible to selectively ablate tumor cells expressing this gene. Interestingly, if a HSVtk$\sp+$ expressing population is mixed with a HSVtk$\sp-$ population at high density, all the cells are killed after GCV administration. This phenomenon for killing all neighboring cells is termed the "bystander effect", which is well documented in HSVtk$\sp-$ GCV systems, though its exact mechanism of action is unclear.^ Using the mouse colon carcinoma cell line CT26, data are presented supporting possible mechanisms of "bystander effect" killing of neighboring CT26-tk$\sp-$cells. A major requirement for bystander killing is the prodrug GCV: as dead or dying CT26tk$\sp+$ cells have no toxic effect on neighboring cells in its absence. In vitro, it appears the bystander effect is due to transfer of toxic GCV-metabolites, through verapamil sensitive intracellular-junctions. Additionally, possible transfer of the HSVtk enzyme to bystander cells after GCV addition, may play a role in bystander killing. A nude mouse model suggests that in a 50/50 (tk$\sp+$/tk$\sp-$) mixture of CT26 cells the bystander eradication of tumors does not involve an immune component. Additionally in a possible clinical application, the "bystander effect" can be directly exploited to eradicate preexisting CT26 colon carcinomas in mice by intratumoral implantation of viable or lethally irradiated CT26tk$\sp+$ cells and subsequent GCV administration. Lastly, an application of this toxic phenotype gene to a clinical marking protocol utilizing a recombinant adenoviral vector carrying the bifunctional protein GAL-TEK to eradicate spontaneously-arisen or vaccine-induced fibrosarcomas in cats is demonstrated. ^

Strange bedfellows: The ethics and politics of medical futility in Texas

Background: Futile medical treatments are interventions that are not associated with a benefit to the patient. The definition and concept of medical futility are controversial. The Texas Advance Directives Act (TADA) was passed in 1999 to address medically inappropriate interventions by allowing providers to withdraw inappropriate interventions against a surrogate decision maker's wishes following a review, attempt to transfer the patient, and 10-day waiting period. The original legislation was a negotiated compromise by players across the political spectrum. However, in recent years there has been increasing controversy regarding TADA and attempts to alter its applicability in Texas. ^ Purpose: The purpose of this project was to apply Paul Sabatier's advocacy coalition framework (ACF) to gain understanding into the historical, ethical, and political basis of the initial compromise, and determine the sources of conflict that have led to increased opposition to TADA. ^ Methods: Using the ACF model, key actors within the medical futility policy debate in Texas were aggregated into coalitions based on shared beliefs. A narrative summary based analysis identified the core elements of the policy subsystem, as well as the constraints and resources of the subsystem actors. Externalities that promoted adjustments to coalition beliefs and tactics used by coalition participants were analyzed. Data sources included review of the published literature regarding medical futility, as well as analysis of published newspaper accounts and editorials regarding the medical futility issue in Texas, legislative testimony, and review of weblogs and online commentaries dealing with the issue. ^ Results: Primary coalition participants in developing compromise legislation in 1999 were the Providers and Vitalists, with Autonomists gaining a prominent role starting in 2006. Internal factors associated with the breakdown of consensus included changes to the makeup of the governing coalition and changes in individual case information available to the Vitalist coalition. Externalities related to the intertwining of the Sun Hudson case and the Terri Schiavo case generated negative publicity for the TADA from progressive and conservative viewpoints. Dissemination of information in various venues regarding contentious cases was associated with more polarization of viewpoints, and realignment of coalition alliances. ^ Conclusions: The ACF provided an outline for the initial compromise over the creation of the Texas Advance Directives Act as well as the eventual loss of consensus. The debate between the Provider, Vitalist, and Autonomist coalitions has been affected by internal policy evolution, changes in the governing coalition, and important externalities. The debate over medical futility in Texas has had much broader implications in the dispute over Health Care Reform.^

First Trimester Screening and its Impact on Uptake of Diagnostic Testing

Introduction: First Trimester Screening (FTS) combines maternal age with fetal nuchal translucency (NT) and maternal analytes to identify pregnancies at an increased risk for Down syndrome and trisomy 18. Though the accuracy of this screening is high, it cannot replace the conclusive accuracy of prenatal diagnostic testing (PDT). Since FTS has been available, a decrease in the number of women who pursue PDT has been observed. This study sought to determine if there has been a significant change in the amount of PDT performed in our clinics, if the type of FTS result affects the patient’s decision regarding PDT, and what the patient’s intentions are regarding PDT. Material and Methods: A database review was performed for the two years prior and the two years after the January 2007 American College of Obstetricians and Gynecologists (ACOG) guidelines regarding FTS were issued. We compared the number of women who were AMA and the number of women who were AMA and had PDT between those time periods. We also determined the number of positive and negative FTS results, and determined how many of those patients had PDT. Finally, we surveyed our patients and referring physicians to determine: what the patient understands about FTS, what the patient’s intentions are regarding FTS, and how physicians present the option of FTS to their patients. Results: We determined that there was a 19.6% decrease in the amount of PDT performed when we compared the two time periods at our three specified clinics. Many of our patients were against having PDT prior to their genetic counseling session, but after they received genetic counseling, 76% of our population became open to the possibility of having PDT. Conclusion: Similar to previous studies, we determined that there has been a significant decrease in the number of PDT procedures performed at our clinics, which coincides with the release of the January 2007 ACOG statement regarding FTS. While our patients regarded FTS as a way to gain early information about their pregnancy in a non-invasive manner, they also stated they would use their results as a way to aid in their decision regarding PDT.

The physician's perception of medical error and its application to the development of an educational training tool.

It is becoming clear that if we are to impact the rate of medical errors it will have to be done at the practicing physician level. The purpose of this project was to survey the attitude of physicians in Alabama concerning their perception of medical error, and to obtain their thoughts and desires for medical education in the area of medical errors. The information will be used in the development of a physician education program.

Physical Activity in Latino Children: Research and Its Implications

Childhood obesity affects children across all ages and genders. However, Latino children and adolescents are at an increased risk, with one out of three Latino children (ages 2-19) being classified as overweight. Physical inactivity is deemed a major factor contributing to the energy imbalance that leads to excess adiposity. The aims of this study are twofold: 1) to present relevant research regarding Latino children’s physical patterns, influences on their physical activity, and interventions designed to promote physical activity and fitness in this population; and 2) to discuss implications derived from this research to help health educators, practitioners, and policy makers increase awareness, and to motivate and enable Latino children to adopt an active lifestyle. Research reveals that Latino children and adolescents are consistently less active than their white counterparts. Latino girls are, in particular, at an increased risk for inactivity. Few studies have investigated the factors that contribute to low levels of physical activity among Latino children. Moreover, few physical activity interventions have involved Latino children. Some of our recent research studies have filled some gaps, including providing information on what physical activities Latino children like, what they intend to do, what they are actually doing, and where and when they do physical activity. Based on our research and review of related literature, we made specific physical activity recommendations for researchers, practitioners, and policy makers. These individual points should be applied and integrated within a broad framework and used in combinations to develop multi-component, coordinated approaches to enhancing physical activity among Latino youth.

Population genetics of VNTR loci and their applications in evolutionary studies

Variable number of tandem repeats (VNTR) are genetic loci at which short sequence motifs are found repeated different numbers of times among chromosomes. To explore the potential utility of VNTR loci in evolutionary studies, I have conducted a series of studies to address the following questions: (1) What are the population genetic properties of these loci? (2) What are the mutational mechanisms of repeat number change at these loci? (3) Can DNA profiles be used to measure the relatedness between a pair of individuals? (4) Can DNA fingerprint be used to measure the relatedness between populations in evolutionary studies? (5) Can microsatellite and short tandem repeat (STR) loci which mutate stepwisely be used in evolutionary analyses?^ A large number of VNTR loci typed in many populations were studied by means of statistical methods developed recently. The results of this work indicate that there is no significant departure from Hardy-Weinberg expectation (HWE) at VNTR loci in most of the human populations examined, and the departure from HWE in some VNTR loci are not solely caused by the presence of population sub-structure.^ A statistical procedure is developed to investigate the mutational mechanisms of VNTR loci by studying the allele frequency distributions of these loci. Comparisons of frequency distribution data on several hundreds VNTR loci with the predictions of two mutation models demonstrated that there are differences among VNTR loci grouped by repeat unit sizes.^ By extending the ITO method, I derived the distribution of the number of shared bands between individuals with any kinship relationship. A maximum likelihood estimation procedure is proposed to estimate the relatedness between individuals from the observed number of shared bands between them.^ It was believed that classical measures of genetic distance are not applicable to analysis of DNA fingerprints which reveal many minisatellite loci simultaneously in the genome, because the information regarding underlying alleles and loci is not available. I proposed a new measure of genetic distance based on band sharing between individuals that is applicable to DNA fingerprint data.^ To address the concern that microsatellite and STR loci may not be useful for evolutionary studies because of the convergent nature of their mutation mechanisms, by a theoretical study as well as by computer simulation, I conclude that the possible bias caused by the convergent mutations can be corrected, and a novel measure of genetic distance that makes the correction is suggested. In summary, I conclude that hypervariable VNTR loci are useful in evolutionary studies of closely related populations or species, especially in the study of human evolution and the history of geographic dispersal of Homo sapiens. (Abstract shortened by UMI.) ^

Revisiting health literacy and its impact on patient-physician communication

Objective. To review professional literature on health literacy and its impact on patient-physician communication, to describe significant literature on this issue, and to summarize implications of the findings from this literature. Design. Update of a review of literature. Data sources: MEDLINE. Review Methods. Articles dealing with the impact of health literacy on patient-physician communication were selected. The articles addressed at least one of four criteria on the subject: prevalence of the problem; effect of health literacy on patient-physician communication; association of health literacy to health outcomes; and interventions to enhance communication with patients exhibiting limited health literacy. Results. Approximately 623 articles were selected for review; 87 were fully reviewed and found to be relevant to the issue; and 25 articles were cited. Conclusion. Limited health literacy is extremely widespread throughout the U.S., particularly among specific populations. Providers must be aware that patients often process health care decision making differently from their own familiar procedures and that by taking the steps to make medical language and health information simpler and the time to confirm patient understanding, health outcomes of limited health literacy populations will improve. ^

Objective assessment of the built environment and its relationship to physical activity and obesity

The role of physical activity in the promotion of individual and population health has been well documented in research and policy publications. Significant research activities have produced compelling evidence for the support of the positive association between physical activity and improved health. Despite the knowledge about these public health benefits of physical activity, over half of US adults do not engage in physical activity at levels consistent with public health recommendations. Just as physical inactivity is of significant public health concern in the US, the prevalence of obesity (and its attendant co-morbidities) is also increasing among US adults.^ Research suggests racial and ethnic disparities relevant to physical inactivity and obesity in the US. Various studies have shown more favorable outcomes among non-Hispanic whites when compared to other minority groups as far as physical activity and obesity are concerned. The health disparity issue is especially important because Mexican-Americans who are the fastest growing segment of the US population are disproportionately affected by physical inactivity and obesity by a significant margin (when compared to non-Hispanic whites), so addressing the physical inactivity and obesity issues in this group is of significant public health concern. ^ Although the evidence for health benefits of physical activity is substantial, various research questions remain on the potential motivators for engaging in physical activity. One area of emerging interest is the potential role that the built environment may play in facilitating or inhibiting physical activity.^ In this study, based on an ongoing research project of the Department of Epidemiology at the University of Texas M. D. Anderson Cancer Center, we examined the built environment, measured objectively through the use of geographical information systems (GIS), and its association with physical activity and obesity among a cohort of Mexican- Americans living in Harris County, Texas. The overall study hypothesis was that residing in dense and highly connected neighborhoods with mixed land-use is associated with residents’ increased participation in physical activity and lowered prevalence of obesity. We completed the following specific aims: (1) to generate a land-use profile of the study area and create a “walkability index” measure for each block group within the study area; (2) to compare the level of engagement in physical activity between study participants that reside in high walkability index block groups and those from low walkability block groups; (3) to compare the prevalence of obesity between study participants that reside in high walkability index block groups and those from low walkability block groups. ^ We successfully created the walkability index as a form of objective measure of the built environment for portions of Harris County, Texas. We used a variety of spatial and non-spatial dataset to generate the so called walkability index. We are not aware of previous scholastic work of this kind (construction of walkability index) in the Houston area. Our findings from the assessment of relationships among walkability index, physical activity and obesity suggest the following, that: (1) that attempts to convert people to being walkers through health promotion activities may be much easier in high-walkability neighborhoods, and very hard in low-walkability neighborhoods. Therefore, health promotion activities to get people to be active may require supportive environment, walkable in this case, and may not succeed otherwise; and (2) Overall, among individuals with less education, those in the high walkability index areas may be less obese (extreme) than those in the low walkability area. To the extent that this association can be substantiated, we – public health practitioners, urban designers, and policy experts – we may need to start thinking about ways to “retrofit” existing urban forms to conform to more walkable neighborhoods. Also, in this population especially, there may be the need to focus special attention on those with lower educational attainment.^

Teacher support and encouragement in the classroom and its impact on childhood obesity

Objectives. Obesity is a growing problem in the United States among children. Great efforts are being made to target this problem, both at home and at school. While parents and peers have proven an effective means of distributing information, the well of the influence of teacher encouragement of health behaviors remains untapped. The purpose of this study is to assess the association of teacher encouragement with diet and physical activity behaviors and obesity in a sample of eighth grade students in central Texas. ^ Methods. In the spring of 2011, the Coordinated Approach to Child Health (CATCH) study distributed teacher surveys to each of the teachers in the schools on the grant. In addition to questions concerning the implementation of CATCH, this survey employed social support questions to gauge the prevalence of teacher encouragement of health behaviors in the classroom. During the same time frame, eighth graders in these same schools completed student surveys which assessed dietary and physical activity knowledge and behaviors and demographics and participated in objective measures of student height and weight. A cross-sectional secondary data analysis was conducted in order to compare self-reported teacher encouragement to student behaviors and several student obesity measures on a by school basis. ^ Results. 1150 teachers and 2582 students from 29 of the 30 measurement schools returned completed surveys. No statistically significant relationship was found between the six teacher encouragement measures and their corresponding student reported health behaviors, nor was one found the mean support per school and child percent overweight. A menial positive relationship was found between the mean support per school and child BMI z-scores, BMI, and percent obese (p = 0.035, 0.003 and 0.003, respectively); however, these relationships were not in the predicted direction. ^ Conclusion. While the findings of this investigation show primarily null results, motivating questions as to the impact to teacher encouragement on middle school student's health remain. It is possible that in order to draw more effective conclusions, more comprehensive studies are warranted which specifically target these relationships.^

Weight-for-age percentile and its association to community acquired methicillin resistant Staphylococcus aureus among pediatric patients in Houston, TX

BACKGROUND: Weight has been implicated as a risk factor for symptomatic community-acquired methicillin resistant Staphylococcus Aureus (CA-MRSA). Information from Texas Children's Hospital (TCH) in Houston, TX was used to implement a case-control study to assess weight-for-age percentile (WFA), race and seasonal exposure as risk factors. ^ METHODS: A retrospective chart review to collect data from TCH was conducted covering the time period January 1st, 2008 to May 31st, 2011. Cases were confirmed and identified by the infectious disease department and were matched on a 1:1 ratio to controls that were seen by the emergency department for non-infected fractures from June 1st, 2008 to May 31st, 2011. Data abstraction was performed using TCH's electronic medical records (EMR) system (EPIC ®). ^ RESULTS: Of 702 CA-MRSA identified cases, ages 9 to 16.99, 564 (80.3%) had the variable `weight' present in their EMR, were not duplicates and not determined to be outliers. Cases were randomly matched to a pool of available controls (n=1864) according to age and gender, yielding 539 1:1 matched pairs (95.5% case matching success) with a total study sample size, N=1078. Case median age was 13.38 years with the majority being White (66.05%) and male (59.4%). Adjusted conditional logistic regression analysis of the matched pairs identified the following risk factors to presenting with CA-MRSA infection among pediatric patients, ages 9 to 16.99 years: a) Individual weight in the highest (75th-99.9th) WFA quartile (OR=1.36; 95% confidence interval [CI]=1.06-1.74; P= 0.016), b) Infection during summer months (OR: 1.69; 95% CI=1.2-2.38; P= 0.003), c) patients of African American race/ethnicity (OR= 1.48; 95% CI=1.13-1.95; P= 0.004). ^ CONCLUSIONS: Pediatric patients, 9 to 16.99 years of age, in the highest WFA quartile (75th-99.9th), or of African-American race had an associated increased risk of presenting with CA-MRSA infection. Furthermore, children in this population were at a higher risk of contracting CA-MRSA infection during the summer season.^