ROLE OF GSH METABOLISM IN MEDIATING STROMAL-LEUKEMIA INTERACTION AND PROMOTING CELL SURVIVAL AND DRUG RESISTANCE IN CHRONIC LYMPHOCYTIC LEUKEMIA

Chronic lymphocytic leukemia (CLL) is the most common adult leukemia in the western countries. The interaction between CLL cells and the bone marrow stromal environment is thought to play a major role in promoting the leukemia cell survival and drug resistance. My dissertation works proved a novel biochemical mechanism by which the bone marrow stromal cells exert a profound influence on the redox status of primary CLL cells and enhance their ability to sustain oxidative stress and drug treatment. Fresh leukemia cells isolated from the peripheral blood of CLL patients exhibited two major redox alterations when they were cultured alone: a significant decrease in cellular glutathione (GSH) and an increase in basal ROS levels. However, when cultured in the presence of bone marrow stromal cells, CLL cells restored their redox balance with an increased synthesis of GSH, a decrease in spontaneous apoptosis, and an improved cell survival. Further study showed that CLL cells were under intrinsic ROS stress and highly dependent on GSH for survival, and that the bone marrow stromal cells promoted GSH synthesis in CLL cells through a novel biochemical mechanism. Cysteine is a limiting substrate for GSH synthesis and is chemically unstable. Cells normally obtain cysteine by uptaking the more stable and abundant precursor cystine from the tissue environment and convert it to cysteine intracellularly. I showed that CLL cells had limited ability to take up extracellular cystine for GSH synthesis due to their low expression of the transporter Xc-, but had normal ability to uptake cysteine. In the co-culture system, the bone marrow stromal cells effectively took up cystine and reduced it to cysteine for secretion into the tissue microenvironment to be taken up by CLL cells for GSH synthesis. The elevated GSH in CLL cells in the presence of bone marrow stromal cells significantly protected the leukemia cells from stress-induced apoptosis, and rendered them resistant to standard therapeutic agents such as fludarabine and oxaliplatin. Importantly, disabling of this protective mechanism by depletion of cellular GSH using a pharmacological approach potently sensitized CLL cells to drug treatment, and effectively enhanced the cytotoxic action of fludarabine and oxaliplatin against CLL in the presence of stromal cells. This study reveals a key biochemical mechanism of leukemia-stromal cells interaction, and identifies a new therapeutic strategy to overcome drug resistance in vivo.

Generalized resistance resources of informal caregivers: A study of demands for care, competing demands, perception of burden and cognitive stress

This study examines the relationship among psychological resources (generalized resistance resources), care demands (demands for care, competing demands, perception of burden) and cognitive stress in a selected population of primary family caregivers. The study utilizes Antonovsky's Salutogenic Model of Health, specifically the concept of generalized resistance resources (GRRs), to analyze the relative effect of these resources on mediating cognitive stress, controlling for other care demands. The study is based on a sample of 784 eligible caregivers who (1) were relatives, (2) had the main responsibility for care, defined as a primary caregiver, and (3) provided a scaled stress score for the amount of overall care given to the care recipient (family member). The sample was drawn from the 1982 National Long-Term Care Survey (NLTCS) of individuals who assisted a given NLTCS sample person with ADL limitations.^ The study tests the following hypotheses: (a) There will be a negative relationship between generalized resistance resources (GRRs) and cognitive stress controlling for care demands (demands for care, competing demands, and perceptions of burden); (b) of the specific GRRs (material, cognitive, social, cultural-environmental) the social domain will represent the most significant factor predicting a decrease in cognitive stress; and (c) the social domain will be more significant for the female than the male primary family caregiver in decreasing cognitive stress.^ The study found that GRRs had a statistically significant mediating effect on cognitive stress, but the GRRs were a less significant predictor of stress than perception of burden and demands for care. Thus, although the analysis supported the underlying hypothesis, the specific hypothesis regarding GRRs' greater significance in buffering cognitive stress was not supported. Second, the results did not demonstrate the statistical significance or differences among the GRR domains. The hypothesis that the social GRR domain was most significant in mediating stress of family caregivers was not supported. Finally, the results confirmed that there are differences in the importance of social support help in mediating stress based on gender. It was found that gender and social support help were related to cognitive stress and gender had a statistically significant interaction effect with social support help. Implications for clinical practice, public health policy, and research are discussed. ^

PHENOTYPIC ASSOCIATION OF GENE AMPLIFICATION WITH MULTIPLE DRUG RESISTANCE IN VINCRISTINE RESISTANT CHINESE HAMSTER OVARY CELLS

Resistance of tumors to pharmacologic agents poses a significant problem in the treatment of human malignancies. This study overviews the scope of clinical resistance and focuses upon current research attempts toward investigation of the phenomenon of multidrug resistance (MDR).^ The objective of this investigation was to determine whether gene amplification had a role in the development of the MDR phenotype in Chinese hamster ovary cells (CHO) primarily selected for resistance to vincristine (VCR). A DNA fragment, previously shown to be amplified in two independently derived Chinese hamster cell lines exhibiting the MDR phenotype, was also amplified in VCR hamster lines. Sequences flanking this fragment were shown to contain coding information for a 4.3 kb transcript overproduced in VCR cells. These sequences were not enriched in double minute DNA preparations isolated from VCR cells. There was an approximately forty-fold increase in both the level of gene amplification and transcript overproduction in the VCR cell lines, independent of the level of primary resistance. This DNA amplification and overproduction of the 4.3 kb transcript was also demonstrated in CHO cells independently selected for resistance to Adriamycin and vinblastine.^ All the DNA sequences of two hamster cDNA clones containing 785 and 932 base pair inserts showed direct homology to the published mouse mdr sequences (about 90%). This sequence conservation held for only portions of the gene when the human mdr1 sequences were compared with those from either the mouse or hamster.^ Somatic cell hybrids, constructed between VCR CHO cells and sensitive murine cells, were used to determine whether there was a functional relationship between the chromosome bearing the amplified sequences and the MDR phenotype. Concordant segregation between vincristine resistance, the MDR phenotype, the presence of MDR-associated amplified sequences, overexpression of the mRNA encoded by these sequences, overexpression of the mRNA encoded by these sequences, and CHO chromosome Z1 was consistent with the hypothesis that there is an amplified gene on chromosome Z1 of the VCR CHO cells which is responsible for MDR in these cells. ^

Molecular alterations in nucleotide excision repair genes in malignant glioma and their relevance to malignant progression and drug resistance

Recently, it has become apparent that DNA repair mechanisms are involved in the malignant progression and resistance to therapy of gliomas. Many investigators have shown that increased levels of O6-methyl guanine DNA alkyltransferase, a DNA monoalkyl adduct repair enzyme, are correlated with resistance of malignant glioma cell lines to nitrosourea-based chemotherapy. Three important DNA excision repair genes ERCC1 (excision repair cross complementation group 1), ERCC2 (excision repair cross complementation group 2), and ERCC6 (excision repair cross complementation group 6) have been studied in human tumors. Gene copy number variation of ERCC1 and ERCC2 has been observed in primary glioma tissues. A number of reports describing a relationship between ERCC1 gene alterations and resistance to anti-cancer drugs have been also described. The levels of ERCC1 gene expression, however, have not been correlated with drug resistance in gliomas. The expression of ERCC6 gene transcribes has been shown to vary with tissue types and to be highest in the brain. There have been no comprehensive studies so far, however, of ERCC6 gene expression and molecular alterations in malignant glioma. This project examined the ERCC1 expression levels and correlated them with cisplatin resistance in malignant glioma cell lines. We also examined the molecular alterations of ERCC6 gene in primary glioma tissues and cells and analyzed whether these alterations are related to tumor progression and chemotherapy resistance. Our results indicate the presence of mutations and/or deletions in exons II and V of the ERCC6 gene, and these alterations are more frequent in exon II. Furthermore, the mutations and/or deletions in exon II were shown to be associated with increased malignant grade of gliomas. The results on the Levels of ERCC1 gene transcripts showed that expression levels correlate with cisplatin resistance. The increase in ERCC1 mRNA induced by cisplatin could be down-regulated by cyclosporin A and herbimycin A. The results of this study are likely to provide useful information for clinical treatment of human gliomas. ^

The transcription factor nuclear factor kappa B (NFkappaB) maintains TRAIL resistance in human pancreatic cancer cells

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL/Apo2L) is a member of the TNF family of cytokines that induces apoptosis in a variety of tumor cells while sparing normal cells. However, many human cancer cell lines display resistance to TRAIL-induced apoptosis and the mechanisms contributing to resistance remain controversial. Previous studies have demonstrated that the dimeric transcription factor Nuclear Factor kappa B (NFκB) is constitutively active in a majority of human pancreatic cancer cell lines and primary tumors, and although its role in tumor progression remains unclear it has been suggested that NFκB contributes to TRAIL resistance. Based on this, I examined the effects of NFκB inhibitors on TRAIL sensitivity in a panel of nine pancreatic cancer cell lines. I show here that inhibitors of NFκB, including two inhibitors of the proteasome (bortezomib (Velcade™, PS-341) and NPI-0052), a small molecule inhibitor of IKK (PS1145), and a novel synthetic diterpene NIK inhibitor (NPI-1342) reverse TRAIL resistance in pancreatic cancer cell lines. Further analysis revealed that the expression of the anti-apoptosic proteins BclXL and XIAP was significantly decreased following exposure to these inhibitors alone and in combination with TRAIL. Additionally, treatment with NPI0052 and TRAIL significantly reduced tumor burden relative to the control tumors in an L3.6pl orthotopic pancreatic xenograft model. This was associated with a significant decrease in proliferation and an increase in caspase 3 and 8 cleavage. Combination therapy employing PS1145 or NPI-1342 in combination with TRAIL also resulted in a significant reduction in tumor burden compared to either agent alone in a Panc1 orthotopic xenograft model. My studies show that combination therapy with inhibitors of NFκB alone and TRAIL is effective in pre-clinical models of pancreatic cancer and suggests that the approach should be evaluated in patients. ^

Trends in anti-tuberculosis drug resistance from 2003--2007 at Pham Ngoc Thach tuberculosis and lung disease hospital, Ho Chi Minh City, Vietnam

Vietnam is one of the countries with the highest prevalence and incidence of tuberculosis (TB) in the world (1). Although Vietnam has had many successes in TB control, it still faces the challenge of drug resistant and multidrug-resistant tuberculosis (MDR-TB). MDR-TB appears to be relatively stable, but data on MDR-TB continues to be scarce and routine testing of all isolates for drug susceptibility is not performed under Vietnam's National Tuberculosis Program (6). Pham Ngoc Thach Hospital (PNT), the leading tuberculosis and lung disease hospital in Ho Chi Minh City, serves as a reference hospital and laboratory for both Ho Chi Minh City and the Southern Vietnam region. This study is an unmatched, nested case-control study consisting of a secondary analysis of a previously created dataset composed of drug susceptibility and basic demographic data from a cohort of patients diagnosed with tuberculosis at PNT from 2003 through 2007 in order to calculate the prevalence of resistance among acid-fast bacilli smear-positive patients. The susceptibility records for the years 2003-2004 were not representative of the entire population, but over the years 2005-2007 the investigator found a decrease in resistance to all primary TB drugs on which records were available, as well as MDR-TB. Overall, females showed a higher proportion of resistance to TB drugs than males, and females had a greater likelihood of presenting with MDR-TB than males (OR=1.77). Persons 35-54 had greater likelihood of having MDR-TB than younger and older age groups. Among the population with HIV data, HIV-positivity was associated with greater likelihood of MDR-TB (OR=1.70, 95% CI=0.97-3.11). This study shows that rates of TB drug resistance are high, but declining, in one of Vietnam's largest TB hospitals, and that females and HIV-positive individuals are possible high-risk groups in this population.^

PROSTATE CANCER STEM CELLS: DRUG TOLERANCE, EXPERIMENTAL RECONSTITUTION AND CASTRATION RESISTANCE

Prostate cancer (PCa) is one of the leading malignancies affecting men in the Western world. Although tremendous effort has been made towards understanding PCa development and developing clinical treatments in the past decades, the exact mechanisms of PCa are still not clearly understood. Emerging evidence has postulated that a population of stem cell-like cells inside a tumor, termed ‘cancer stem cells (CSCs)’, may be the cells responsible for tumor initiation, progression, recurrence, metastasis and therapy resistance. Like CSC studies in other cancer types, it has been reported that PCa also contains CSCs. However, there remain several unresolved questions that need to be clarified. First, the relationship between prostate CSCs (PCSCs) and therapy resistance (chemo- and radio-) is not known. Herein, we have found that not all CSCs are drug-tolerant, and not all drug-tolerant cells are CSCs. Second, whether primary human PCa (HPCa) actually contain PCSCs remains unclear, due to the well-known fact that we have yet to establish a reliable assay system that can reproducibly and faithfully reconstitute tumor regeneration from single HPCa cells. Herein, after utilizing more than 114 HPCa samples we have provided evidence that immortalized bone marrow-derived stromal cells (Hs5) can help dissociated HPCa cells generate undifferentiated tumors in immunodeficient NOD/SCID-IL2Rγ-/- mice, and the undifferentiated PCa cells seem to have a survival advantage to generate tumors. Third, the evolution of PCa from androgen dependent to the lethally castration resistant (CRPC) stage remains enigmatic, and the cells responsible for CRPC development have not been identified. Herein, we have found a putative cell population, ALDH+CD44+α2β1+ PCa cells that may represent a cell-of-origin for CRPC. Taken together, our work has improved our understanding of PCSC properties, possibly highlighting a potential therapeutic target for CRPC.