Search PubMed⌕ Search

Biomedical subjects

Martin L Smith

Publications and source records attributed to Martin L Smith.

At least 19 recordsLinked to original sources
PubMed2007

Manipulation of base excision repair to sensitize ovarian cancer cells to alkylating agent temozolomide.

PURPOSE: To improve the treatment of women with ovarian cancer, we are investigating the modulation of a prominent DNA-damaging agent, temozolomide, by manipulating the DNA base excision repair (BER) pathway via BER inhibitor, methoxyamine, and overexpression of N-methylpurine DNA glycosylase (MPG). EXPERIMENTAL DESIGN: Enhancement of temozolomide via methoxyamine and MPG overexpression was analyzed using in vitro assays, including 3-(4-5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium salt (MTS) assay, apoptosis via Annexin staining, and Western blotting for H2AX phosphorylation to quantitate DNA damage. RESULTS: Our data show that we can effectively modulate the activity of the chemotherapeutic agent, temozolomide, via modulator methoxyamine, in three ovarian cancer cell lines, SKOV-3x, Ovcar-3, and IGROV-1. This enhancement of temozolomide-induced cytotoxicity is not dependent on p53 status as we transfected an ovarian cancer cell line with a dominant-negative p53-expressing plasmid (IGROV-1mp53) and obtained similar results. Our results show that MPG-overexpressing IGROV-1 and IGROV-1mp53 cells are significantly more sensitive to the clinical chemotherapeutic temozolomide in combination with methoxyamine as assayed by cytotoxicity, apoptosis, and levels of DNA damage than either agent alone. CONCLUSIONS: These studies show that although clinical trials in ovarian cancer to determine temozolomide single-agent efficacy are in development, through manipulation of the BER pathway, an increase in response to temozolomide is achieved. The combination of temozolomide plus methoxyamine has potential for second-line therapy for patients who have failed standard platinum plus paclitaxel chemotherapy.

Antineoplastic Agents, Alkylating↗
PubMed2006

Impact of a palliative care service on in-hospital mortality in a comprehensive cancer center.

BACKGROUND: Palliative care services provide symptom control and psychosocial support for dying patients and their families. These services are not available in many cancer centers and tertiary hospitals. The purpose of this study was to review the impact of a palliative care program, established in 1999, on overall in-hospital mortality. METHODS: We reviewed the M. D. Anderson Cancer Center computerized database to determine the total number of deaths and discharges and the place of death for each fiscal year from 1999 to 2004. The median length of stay for patients who died in different locations within the hospital was calculated. Annual palliative care consultations for patients who subsequently died in the hospital were retrieved. The annual mortality rate for the cancer center was calculated. RESULTS: The overall in-hospital mortality rates were 3.6, 3.7, 3.6, 3.5, 3.6, and 3.7% of all discharges for the period 1999-2004 respectively (p > 0.2). The number of deaths in the medical intensive care unit (MICU) dropped from 252 in 671 (38%) in 1999 to 213 in 764 (28%) in 2004 (p < 0.0001). Involvement of the palliative care service in the care of patients dying in the hospital grew from 8 in 583 (1%) in 1999 to 264 in 764 (35%) in 2004 (p < 0.0001). The median length of hospital stay (MLOS) for patients who subsequently died in-hospital was significantly longer than that for patients who were discharged alive. CONCLUSIONS: Increased involvement by the palliative care service in the care of decedent patients was associated with a decreased MICU mortality and no change in overall hospital mortality rate or inpatient length of hospital stay.

Cancer Care Facilities↗
PubMed2005

Phosphorylation of human p53 at serine 46 determines promoter selection and whether apoptosis is attenuated or amplified.

The capacity of DNA damaging agents to induce apoptosis is regulated by target gene induction by p53. We found that p53 targeted MDM2 in cells in which DNA repair was occurring, but persistent DNA damage induced by chemotherapy led p53 to selectively target PTEN. High dose chemotherapy induced the phosphorylation of p53 on serine 46, whereas low dose chemotherapy did not. A nonphosphorylatable serine 46 to alanine p53 mutant (S46A) targeted the MDM2 promoter in preference to that for PTEN. A serine 46 to aspartate mutant (S46D, a phosphorylation mimic) targeted PTEN in preference to MDM2. These observations show that phosphorylation of serine 46 in p53 is sufficient for it to induce the PTEN (phosphatase and tensin homolog deleted on chromosome ten) tumor suppressor protein in preference to MDM2. S46A induced significantly less cell death than the S46D in cells. The phosphorylation-induced change of p53 promoter targeting suppresses the induction of MDM2 and the formation of the autoregulatory feedback loop. Induction of PTEN by p53 followed by expression of PTEN inhibits AKT-induced translocation of MDM2 into the nucleus and sustains p53 function. The protection of p53 from MDM2 by PTEN and the damage-induced activation of PTEN by phosphorylated p53 leads to the formation of an apoptotic amplification cycle in which p53 and PTEN coordinately increase cellular apoptosis.

Antineoplastic Agents↗
PubMed2005

Lack of prognostic importance of reverse-transcriptase polymerase chain reaction detection of circulating messenger RNA in patients with melanoma.

BACKGROUND: Molecular serologic markers for detecting early melanoma metastases have been described. The objective of this study was to determine whether reverse-transcriptase polymerase chain reaction detection of circulating tyrosinase messenger RNA (mRNA) can identify the presence of subclinical metastases and predict subsequent clinical recurrence in surgically treated melanoma patients who are at significant risk for relapse. METHODS: Preoperative peripheral blood samples of disease-free melanoma patients, disease stage ranging from I to IV, were analyzed for the presence of tyrosinase mRNA by semiquantitative reverse-transcriptase polymerase chain reaction as a putative marker for circulating melanoma cells. Multivariate analysis was performed to evaluate the prognostic value of tyrosinase mRNA in the blood and in the correlating pathologic stage of disease with recurrence and survival. RESULTS: The study group consisted of 96 patients. The mean age was 54 years (range, 24 to 83 years). The mean Breslow thickness was 3 mm (range, 0.9 to 21 mm). Circulating melanoma cells were detected in 66 patients (69 percent). Blood polymerase chain reaction positivity by American Joint Committee on Cancer stage was as follows: stage I, 19 of 28 patients (68 percent); stage II, 17 of 25 patients (68 percent); stage III, 28 of 41 patients (68 percent); and stage IV, two of two patients (100 percent). Tyrosinase detection was not associated with stage of disease (p = 0.77). At a median follow-up of 30 months, disease recurred in 21 patients (22 percent), and 15 patients (16 percent) died. Disease stage of the patients correlated with recurrence (p < 0.0001) and death (p < 0.0001). The finding of mRNA tyrosinase in peripheral blood samples was not associated with recurrence (p = 0.1) or death (p = 0.77). CONCLUSIONS: The use of polymerase chain reaction to detect circulating tyrosinase mRNA in peripheral blood does not correlate with traditional prognostic indicators in patients with cutaneous melanoma and does not appear to be an effective prognostic tool.

Adult↗
PubMed2005

A radiation-induced acute apoptosis involving TP53 and BAX precedes the delayed apoptosis and neoplastic transformation of CGL1 human hybrid cells.

Exposing CGL1 (HeLa x fibroblast) hybrid cells to 7 Gy of X rays results in the onset of a delayed apoptosis in the progeny of the cells 10 to 12 cell divisions postirradiation that correlates with the emergence of neoplastically transformed foci. The delayed apoptosis begins around day 8 postirradiation and lasts for 11 days. We now demonstrate that the delayed apoptosis is also characterized by the appearance of approximately 50-kb apoptotic DNA fragments and caspase 3 activation postirradiation. In addition, we confirm that stabilization of TP53 and transactivation of pro-apoptosis BAX also occurs during the delayed apoptosis and show that anti-apoptosis BCL-X(L) is down-regulated. To test whether the delayed apoptosis was due to a nonfunctional acute TP53 damage response in CGL1 cells, studies of acute apoptosis were completed. After irradiation, CGL1 cells underwent an acute wave of apoptosis that involves TP53 stabilization, transactivation of BAX gene expression, and a rapid caspase activation that ends by 96 h postirradiation. In addition, the acute onset of apoptosis correlates with transactivation of a standard wild-type TP53-responsive reporter (pG13-CAT) in CGL1 cells after radiation exposure. We propose that the onset of the delayed apoptosis is not the result of a nonfunctional acute TP53 damage response pathway but rather is a consequence of X-ray-induced genomic instability arising in the distant progeny of the irradiated cells.

Apoptosis↗
PubMed2003

Imbalancing the DNA base excision repair pathway in the mitochondria; targeting and overexpressing N-methylpurine DNA glycosylase in mitochondria leads to enhanced cell killing.

The DNA base excision repair (BER) pathway is responsible for the repair of alkylation and oxidative DNA damage. The short-patch BER pathway, beginning with the simple glycosylase N-methylpurine DNA glycosylase (MPG), is responsible for the removal of damaged bases such as 3-methyladenine and 1,N(6)-ethenoadenine from the DNA after alkylation or oxidative DNA damage. The resulting apurinic site is further processed by the other members in the pathway, resulting in the insertion of the correct nucleotide. If apurinic sites accumulate, they are mutagenic and cytotoxic to the cell. To evaluate its efficacy in sensitizing breast cancer cells to chemotherapy, MPG has been overexpressed in the breast cancer cell line, MDA-MB231. With MPG overexpression, an increase in DNA damage and increased cytotoxicity to methyl methanesulfonate as well as increased apoptosis levels was observed in these cells. Because mitochondrial DNA has been shown to be more sensitive to DNA damage than nuclear DNA, a construct containing mitochondrial-targeted MPG using the human manganese superoxide dismutase mitochondrial-targeting sequence was made. Overexpression of the mitochondrially targeted MPG dramatically increased the breast cancer cells' sensitivity to methyl methanesulfonate. In conclusion, we believe that the increase in sensitivity to DNA damage by overexpression of nuclear MPG is because of an imbalance in the BER pathway, and an even greater increase in cell sensitivity is observed when mitochondrial DNA is targeted.

Annexin A5↗
PubMed2002

Selenomethionine regulation of p53 by a ref1-dependent redox mechanism.

The cancer chemopreventive properties of selenium compounds are well documented, yet little is known of the mechanism(s) by which these agents inhibit carcinogenesis. We show that selenium in the form of selenomethionine (SeMet) can activate the p53 tumor suppressor protein by a redox mechanism that requires the redox factor Ref1. Assays to measure direct reduction/oxidation of p53 showed a SeMet-dependent response that was blocked by a dominant-negative Ref1. By using a peptide containing only p53 cysteine residues 275 and 277, we demonstrate the importance of these residues in the SeMet-induced response. SeMet induced sequence-specific DNA binding and transactivation by p53. Finally, cellular responses to SeMet were determined in mouse embryo fibroblasts wild-type or null for p53 genes. The evidence suggests that the DNA repair branch of the p53 pathway was activated. The central relevance of DNA repair to cancer prevention is discussed.

Animals↗
PubMed2002

Selenomethionine induction of DNA repair response in human fibroblasts.

Selenium compounds have a long history in chemoprevention of mammary and colon cancers in rodent models. Selenium compounds are in current clinical trials, having shown promise in prevention of prostate and other human cancers. In human tissues, it has been estimated that each cell sustains approximately 10 000 potentially mutagenic (if not repaired) lesions per day due to endogenous DNA damage. Almost no studies have addressed the potential for selenium compounds to induce DNA repair, a potential mechanism for their cancer-preventive actions. We show that selenium in the form of selenomethionine induces a DNA repair response in normal human fibroblasts in vitro, and protects cells from DNA damage. We show a possible mechanism for the inducible DNA repair response, in which enhanced repair complex formation was observed in selenomethionine-treated cells.

Blotting, Western↗
PubMed2002

Implication of p53 in base excision DNA repair: in vivo evidence.

The tumor suppressor p53 plays an important role in response to DNA damage, including DNA repair. One DNA repair pathway, nucleotide excision repair (NER), has been well-documented to be regulated by p53. It seemed probable that p53 may affect other DNA repair pathways. We employed matched isogenic pairs of cell lines, wild-type or p53-deficient, to investigate this question using methyl methanesulfonate (MMS), a base-damaging agent. Alkylation damage induced by MMS is repaired exclusively by the base excision repair (BER) pathway. Cells carrying mutant or no p53 genes exhibited slow BER of MMS-induced DNA damage, and exhibited MMS-sensitivity. One contributing factor is the abundance of DNA polymerase beta (beta-pol), an enzyme required for BER, which was almost absent in p53 mutant and p53-null cells. Our findings demonstrate an in vivo requirement for p53 in regulating the base excision repair response, a novel finding of great potential importance in understanding the DNA repair branch of the p53 pathway.

Animals↗
PubMed2002

Sensitivity of p53-deficient cells to oxaliplatin and thio-TEPA (N, N', N" triethylenethiophosphoramide).

P53 is known as a determinant of cellular responses to DNA damage, including apoptosis, cell cycle arrest, and DNA repair. Its role is most easily understood in the context of Burkitt lymphoma and other apoptosis-prone cell types. A number of epithelial cancer cell types, by contrast, exhibit a higher threshold for apoptosis induction in response to DNA damage. In fact, p53 mediates DNA repair and protective responses in the latter cell types, in some cases p53-deficient cells being more sensitive to DNA damage, antithetical to the situation in Burkitt lymphoma and other apoptosis-prone cell types. Ultraviolet light, cisplatin, and nitrogen mustards produce damage that is repaired by a p53-regulated pathway. Here, we explore the sensitivity of the platinum compound oxaliplatin and thio-TEPA (N, N', N", triethylenethiophosphoramide), a cancer chemotherapeutic agent that produces largely base damage, in p53-defective cells. This work demonstrates that the contribution of p53 temporally correlates with DNA repair pathways to produce a resistant phenotype, while the p53-defective cells are more sensitive to certain DNA-damaging chemotherapeutic agents.

Antineoplastic Agents↗
PubMed2002

p53 regulation of DNA excision repair pathways.

The regulation of DNA excision repair pathways by p53 and its downstream genes is an emerging body of literature, largely distinct and separable from the more-studied cell cycle arrest and apoptosis responses regulated by p53. Regulation of nucleotide excision repair of UV-damage by p53 and its downstream genes Gadd45 and p48XPE has been well-documented, but much remains to be done in elucidating mechanisms. Moreover, p53 also participates in base excision repair of hydrogen peroxide-induced damage, still at an early stage of investigation. In human cancers carrying inactivating mutations in p53, especially those wherein p53 mutation occurs early, accelerated mutagenesis by exogenous and endogenous DNA damage is predicted. At the same time, the excision repair pathways could provide a useful target for DNA-damaging chemotherapeutics against p53-defective cancers, having decreased ability to repair chemotherapeutic damage. To our knowledge, this is the first review to address this emerging field.

Animals↗
PubMed2002

National practices regarding payment to research subjects for participating in pediatric research.

OBJECTIVE: Payment to subjects for participation in research is reportedly common, but no published data documents the nature of this practice. Institutional review boards (IRBs) are responsible for ensuring both the safety and voluntary participation of research subjects, yet guidance from federal and expert pediatric sources regarding appropriate payment approaches is conflicting. Ethical issues of payment for participation of adult versus pediatric research subjects may differ. This empirical study sought to examine current payment practices for participation in pediatric research as reported by IRBs. DESIGN: An 18-question survey regarding payment practices for participation in pediatric research was sent to IRB chairs at member institutions of the National Association of Children's Hospitals and Related Institutions, and to a systematic random sample of IRB chairs listed with the Office for Protection From Research Risks. Descriptive, nonparametric, and qualitative analyses were used to describe institution types, payment practices, and correlations among responses. RESULTS: Data from 128 institutions that conduct pediatric research revealed that payment for participation in pediatric research was allowed by 66% of responding institutions, and practices varied widely among institutions. Most responding IRBs that allowed payment required disclosure of payment before enrollment (during the consent process), following federal guidelines more closely than American Academy of Pediatrics guidelines. An IRB's perception of potential benefits or harms of a study correlated with the amount of payment approved. CONCLUSIONS: IRBs must balance the need to recruit pediatric research subjects against the risk of undue influence during the recruitment process. Federal guidelines and expert pediatric opinion differ in recommendations regarding payment; responding IRBs appeared to follow federal guidelines more closely than guidelines proposed by the American Academy of Pediatrics.

Child↗