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Biomedical subjects

M Citron

Publications and source records attributed to M Citron.

At least 55 records · Page 3Linked to original sources
PubMed1995

Combination chemotherapy for metastatic or recurrent carcinoma of the breast--a randomized phase III trial comparing CAF versus VATH versus VATH alternating with CMFVP: Cancer and Leukemia Group B Study 8281.

PURPOSE: We sought to compare three doxorubicin-based therapies for metastatic breast cancer for response frequency, time to treatment failure (TTF), and survival. MATERIALS AND METHODS: Women with metastatic breast cancer who had measurable disease, required laboratory tests, had received no prior chemotherapy for metastases, had a Cancer and Leukemia Group B (CALGB) performance status < or = 2, and provided informed consent were eligible. Treatment included the following: arm I--cyclophosphamide, doxorubicin, and fluorouracil (CAF); arm II--vinblastine, doxorubicin, thiotepa, and halotestin (VATH); and arm III--VATH alternating with cyclophosphamide, methotrexate, fluorouracil, vincristine, and prednisone (CMFVP) on cycles 3, 5, 7, 9, etc. Doses were modified for toxicities. Standard CALGB response and toxicity criteria were used. RESULTS: Between August 1982 and February 1987, 497 women were entered and 491 were treated on study. Pretreatment characteristics were well balanced and the median follow-up duration was 79 months. There were no significant differences in response (complete [CR] plus partial [PR]) at 50% on arm I, 57% on arm II, and 51% on arm III. The median TTFs were 8, 8, and 9 months, respectively, in favor of arm III when compared with arm I (P = .028). The median survival times for treatment arms I, II, and III were 15, 17, and 17 months, respectively. After multivariate regression analyses, only estrogen receptors (ER), performance status, and number of metastatic sites influenced TTF and survival. Leukopenia was the most common grade 3 or 4 toxicity, occurring in 90%, 80%, and 92% of patients per arm, respectively. Lethal toxicities were seen in four, five, and six women, respectively. Overall, there were more grade > or = 3 toxicities on arm II than I, and most occurred on arm III (P = .02). CONCLUSION: The VATH regimen appears similarly effective to the CAF regimen as initial therapy. Alternating CMFVP with VATH did not improve response rate or survival. After accounting for other variables, treatment arm was not related to outcome. New therapeutic regimens are still needed.

Adult↗
PubMed1995

O6-methylguanine-DNA methyltransferase in human brain tumors detected by activity assay and monoclonal antibodies.

O6-methylguanine-DNA methyltransferase (MGMT) activity was measured in 68 tissue samples taken from brain. A wide range in activity among samples was observed, with all nonmalignant samples showing transferase activity (Mer+) but approximately 15% of WHO grade II low-grade astrocytomas and WHO grade IV glioblastoma multiformes lacking activity (Mer-). On average, astrocytomas and glioblastomas showed less transferase activity than either nonmalignant tissue or meningiomas. Monoclonal antibodies specific for MGMT showed both cytoplasmic and nuclear staining of Mer+ brain tumor cells in culture but no staining of Mer- cells in culture. In pathology specimens from anaplastic astrocytomas, glioblastoma multiformes, and meningiomas, antibody staining revealed both cytoplasmic and nuclear MGMT, while one sample showed little or no MGMT-specific staining. These results help explain why nitrosoureas have been among the most successful agents in treatment of brain tumors and indicate the subcellular localization for the repair activity, which may be relevant to nitrosourea resistance.

Antibodies, Monoclonal↗
PubMed1995

beta-Amyloid, protein processing and Alzheimer's disease.

Alzheimer's disease (AD) is a neurodegenerative disorder resulting in the deposition of amyloid beta-peptide (A beta) in senile plaques in cerebral and limbic corteces and the walls of meningeal and cerebral blood vessels. A beta is a proteolytic break-down product of a membrane bound precursor, the beta-amyloid precursor protein (beta APP). Conventional secretory processing of beta APP prevents A beta formation. An additional processing pathway of beta APP involving endosomal/lysosomal targeting is described. Within isolated lysosomes amygloidogenic fragments are found which might serve as precursors for A beta production. From such precursors A beta might be proteolytically processed. Indeed, secreted A beta was identified in the media of cultured cells. A beta is also secreted in vivo and can be detected in human plasma and cerebral spinal fluid. These findings provide a cellular system to analyze the molecular mechanism and the biological regulation of A beta generation. Furthermore, the effect of inherited mutations within the beta APP gene in some cases of familial AD can now be analyzed in such tissue culture cells transfected with the mutant cDNA constructs. A model will be presented proposing that A beta generation might occur during reinternalization of the full-length molecule.

Alzheimer Disease↗
PubMed1994

Excessive production of amyloid beta-protein by peripheral cells of symptomatic and presymptomatic patients carrying the Swedish familial Alzheimer disease mutation.

The 39- to 43-amino acid amyloid beta-protein (A beta), which is progressively deposited in cerebral plaques and blood vessels in Alzheimer disease (AD), is secreted by cultured human cells during normal metabolism. In studies of cell lines transfected with beta-amyloid precursor protein (beta APP) cDNAs, the beta APP mutation K670N/M671L found in a Swedish familial AD (FAD) pedigree has previously been shown to cause a marked augmentation of A beta secretion. Here, we have conducted blinded analyses of beta APP metabolism in primary skin fibroblasts from affected members of the Swedish FAD pedigree and their unaffected siblings or spouses. These fibroblasts continuously secrete a homogenous population of A beta molecules starting at Asp-1 (D672 of beta APP). We found a consistent and significant approximately 3-fold elevation of A beta release from all biopsied skin fibroblasts bearing the FAD mutation. No significant alterations of other metabolic derivatives of beta APP were detected. The elevated A beta levels were found in cells from both patients with clinical AD and presymptomatic subjects. Thus, A beta overproduction in this FAD pedigree is not a secondary event but is consistent with a causal role in the development of the disease. Increased A beta secretion can begin many years prior to onset of symptoms, even in peripheral tissues, indicating that it does not require preexisting neural abnormalities.

Alzheimer Disease↗
PubMed1994

O6-methylguanine-DNA methyltransferase in ovarian malignancy and its correlation with postoperative response to chemotherapy.

O6-Methylguanine-DNA methyltransferase (MGMT) in human neoplastic tissues has been associated with tumor resistance to alkylating agents. The purposes of this study are to assay MGMT activity in ovarian cancers and to correlate MGMT titers with chemotherapy response to cisplatin and cyclophosphamide in patients with ovarian cancer. MGMT levels were determined by a biochemical assay of tumor tissues from 20 patients with ovarian malignancy. The clinical stages of the patients studied were 4 in Stage I, 2 in Stage II, 12 in Stage III, and 2 in Stage IV. The mean MGMT activity was 34 +/- 9 fmole methyls transferred/mg protein. Among 13 patients with tumor MGMT levels more than 10 fmole/mg protein, 10 (77%) of them were resistant to postoperative combination chemotherapy. In the remaining 7 patients with low MGMT titer of less than 10 fmole/mg protein, a majority (71%) had a complete response (P < 0.10). These preliminary results indicate that ovarian cancer has detectable MGMT activity, and this activity is possibly correlated with treatment failure to a postoperative cisplatin regimen.

Adult↗
PubMed1994

Second-site suppressors of the bacteriophage P1 virs mutant reveal the interdependence of the c4, icd, and ant genes in the P1 immI operon.

The immI operon of phage P1 contains the genes c4, icd, and ant, which are transcribed in that order from the same constitutive promoter, P51b. The gene c4 encodes an antisense RNA which inhibits the synthesis of an antirepressor by acting on a target ant mRNA. Interaction depends on the complementarity of two pairs of short sequences encompassing virs+ and the ribosome-binding site involved in ant expression. Accordingly, in a P1 virs mutant phage, antirepressor is synthesized constitutively. We have isolated lysogen-proficient, second-site suppressors of P1 virs in order to evaluate the interdependence of the immI-specific genes. From a total of 17 suppressors analyzed, 15 were found to be located in the icd gene. They were identified as frameshift mutations, containing base insertions or deletions in tandem repeats of a single base pair. One suppressor was identified as a P51b promoter-down mutation; the second site of another suppressor was found to be located in the c4 gene. Furthermore, it was shown that virs cannot be suppressed by ant (icd+) suppressors. The results confirm the model that the immI operon is transcribed as a unit, that the icd and ant genes are translationally coupled, and that the constitutive synthesis of Icd protein alone is lethal to the bacterial cell. The existence of a c4 suppressor of virs, whose effect is not yet known, points to a still more complex regulation of antirepressor synthesis than was anticipated from the model.

Bacteriophage P1↗
PubMed1994

O6-methylguanine-DNA methyltransferase in normal and malignant tissue of the breast.

An important component of high-dose chemotherapy/autologous bone marrow support regimens for adjuvant treatment of breast cancer is carmustine. Preclinical studies have shown that the level of the DNA repair protein O6-methylguanine-DNA methyltransferase is correlated with the resistance of cultured human tumor cells to this drug, but little is known about transferase levels of breast tissue in vivo. We measured the DNA repair activity in 80 tissue samples from 65 patients, including normal, abnormal, benign, and malignant specimens. Wide interindividual variations was observed and average transferase levels were similar in normal and benign tissue. However, transferase levels were significantly elevated in stage I-IV disease. In addition, the frequency of samples with no detectable transferase was greatly reduced in this malignant group, and transferase was positively correlated with the presence of positive nodes, a marker for disease progression. In contrast, transferase levels were not correlated with age or estrogen receptor status, and the levels in normal tissue did not vary between patients with benign or malignant disease. These results suggest that this DNA repair activity may be increased in breast cancer relative to normal tissue and encourage further study of the predictive value of transferase measurements in high-dose chemotherapy/autologous bone marrow transplant for breast cancer.

Adult↗
PubMed1993

Activation of protein kinase C inhibits cellular production of the amyloid beta-protein.

The 39-43-amino acid amyloid beta-protein (A beta), which is progressively deposited in cerebral plaques and blood vessels in Alzheimer's disease (AD), is released by cultured human cells during normal metabolism. Here we show that agents which activate protein kinase C or otherwise enhance protein phosphorylation caused a substantial decrease in A beta production in vitro. Protein kinase C activation also markedly decreased A beta release from cells that express mutant forms of the beta-amyloid precursor protein genetically linked to familial AD. Inhibition of A beta secretion could also be effected by direct stimulation of m1 muscarinic acetylcholine receptors with carbachol. These results demonstrate that activation of the protein kinase C signal transduction pathways down-regulates the generation of the amyloidogenic A beta peptide. Pharmacologic agents that activate this system, including a variety of first messengers, could potentially slow the development or growth of some A beta plaques during the early stages of AD.

Amino Acid Sequence↗
PubMed1992

Mutation of the beta-amyloid precursor protein in familial Alzheimer's disease increases beta-protein production.

Progressive cerebral deposition of the 39-43-amino-acid amyloid beta-protein (A beta) is an invariant feature of Alzheimer's disease which precedes symptoms of dementia by years or decades. The only specific molecular defects that cause Alzheimer's disease which have been identified so far are missense mutations in the gene encoding the beta-amyloid precursor protein (beta-APP) in certain families with an autosomal dominant form of the disease (familial Alzheimer's disease, or FAD). These mutations are located within or immediately flanking the A beta region of beta-APP, but the mechanism by which they cause the pathological phenotype of early and accelerated A beta deposition is unknown. Here we report that cultured cells which express a beta-APP complementary DNA bearing a double mutation (Lys to Asn at residue 595 plus Met to Leu at position 596) found in a Swedish FAD family produce approximately 6-8-fold more A beta than cells expressing normal beta-APP. The Met 596 to Leu mutation is principally responsible for the increase. These data establish a direct link between a FAD genotype and the clinicopathological phenotype. Further, they confirm the relevance of the continuous A beta production by cultured cells for elucidating the fundamental mechanism of Alzheimer's disease.

Alzheimer Disease↗
PubMed1992

Greenfield filter instead of heparin as primary treatment for deep venous thrombosis or pulmonary embolism in patients with cancer.

BACKGROUND AND METHOD: During the last 5 years, the authors placed Greenfield filters as primary therapy in 41 patients with cancer with deep venous thrombosis (DVT) and/or pulmonary embolism (PE) instead of administering heparin. RESULTS: There were no operative deaths. Complications included erythema of the incision in one patient, recurrent PE in one patient, and chronic filter prong penetration of the inferior vena caval wall in one patient. Follow-up was complete for 90% (37 of 41) of the patients. Forty-six percent of the patients died of their cancer early in the study. In follow-up, leg swelling improved completely or partially in 74.5% of patients and was unchanged in 22% of patients. The condition of one patient worsened secondary to recurrent DVT. The patients with improved symptoms also had improved functional ability, whereas those whose condition did not change were mostly bedridden, many with end-stage advanced metastatic disease. CONCLUSIONS: These results indicate that Greenfield filter insertion is safe and effective as primary therapy in patients with cancer with DVT and/or PE.

Adult↗
PubMed1992

Pyrimidine dimer removal enhanced by DNA repair liposomes reduces the incidence of UV skin cancer in mice.

UV exposure has been linked to skin cancer in humans by epidemiology and the rare genetic disease xeroderma pigmentosum. However, UV produces multiple photoproducts in DNA, and their relative contribution is uncertain. An enzyme which specifically repairs cyclobutane pyrimidine dimers in DNA, T4 endonuclease V, was encapsulated in liposomes for topical delivery into mouse and human skin. In both species, liposomes applied after UV exposure localized in the epidermis and stimulated the removal of cyclobutane pyrimidine dimers. UV-irradiated mice treated with these liposomes had a dose-dependent decrease in the incidence of squamous cell carcinoma compared to controls. The results demonstrate that unrepaired cyclobutane pyrimidine dimers in DNA are a direct cause of cancer in mammalian skin.

Animals↗
PubMed1992

The c4 repressor of bacteriophage P1 is a processed 77 base antisense RNA.

The c4 repressors of the temperate bacteriophages P1 and P7 inhibit antirepressor synthesis and are essential for establishment and maintenance of lysogeny. Using in vivo complementation tests we have previously shown that c4 is an antisense RNA acting on a target, ant mRNA, which is transcribed from the same promoter. Here we identify the c4 repressor molecule of P1 as a 77 +/- 1 base RNA by mapping its termini and show that the c4 RNA in P7 lysogens has the same or a similar size. P1 c4 RNA is encoded in a region shown to be sufficient for c4 complementation. It covers exactly the 74 bases previously suggested to fold into a stem-loop secondary structure essential for c4 function. Furthermore, we demonstrate that the 5' end of c4 RNA is generated by processing. Thus, c4 is the first example of an antisense RNA to be processed. A possible mechanism of processing is discussed.

Base Sequence↗
PubMed1992

Detection of messenger RNA from O6-methylguanine-DNA methyltransferase gene MGMT in human normal and tumor tissues.

BACKGROUND: The level of the DNA repair protein O6-methylguanine-DNA methyltransferase is an important determinant of the response of tumor cells in culture to alkylating nitrosoureas. In these cells, the abundance of messenger RNA (mRNA) is directly correlated with repair activity. PURPOSE: Our purpose was to compare transferase mRNA levels with the repair activity in primary human tumors. METHODS: Human transferase mRNA was measured in tissue samples from brain tumors, normal lung, lung tumors, ovarian tumors, and normal human liver by use of an RNA protection assay with an antisense probe prepared from the cloned gene. RESULTS: Normal and tumor tissue samples from the same patient had similar transferase activity levels, but transferase expression varied widely among tissue samples from different patients. Brain and lung samples, on average, had transferase mRNA levels closer to those in liver samples than their transferase activity levels. In two cases, tissue samples which were transferase deficient by the activity assays were found to lack transferase mRNA. CONCLUSIONS: Deficiencies in transferase activity are due to reduced or absent mRNA transcription or processing. In brain and lung, there may be post-transcriptional control of mRNA expression. The wide interindividual variation in transferase expression is also seen at the transcription level. IMPLICATIONS: These are among the first measures of transferase mRNA expression in primary human tissue. More samples should be examined to extend these observations.

Brain Neoplasms↗
PubMed1992

Transcriptional control via translational repression by c4 antisense RNA of bacteriophages P1 and P7.

The c4 repressors of bacteriophages P1 and P7 are antisense RNAs that inhibit antirepressor synthesis. This antisense inhibition is unusual in that the c4 repressor and the repressed genes orfx and ant are cotranscribed in that order from the same promoter, and c4 RNA is processed from a precursor RNA. Here, we show that c4 RNA directly represses translation of orfx, a small open reading frame, to which ant is translationally coupled. This translational repression blocks ant transcription via a rho-dependent terminator. Thus, c4 RNA controls expression of the ant gene by a novel indirect mechanism combining translational repression, translational coupling, and rho-dependent termination.

Bacteriophages↗
PubMed1991

O6-methylguanine-DNA methyltransferase in human normal and tumor tissue from brain, lung, and ovary.

The resistance of human tumor strains in culture to cell killing by alkylating nitrosoureas is correlated with their levels of the DNA repair activity O6-methylguanine-DNA methyltransferase. Strains with the Mer- phenotype have no activity and are extremely sensitive. However, the relationship between the sensitivity of human tumors in vivo and transferase levels is not known, and even the existence of Mer- human tumors in vivo has been questioned. In this study 73 human tumor and normal tissue samples from brain, lung, and ovary were assayed for transferase levels and methylpurine glycosylase activity. For each organ, transferase levels varied over 100-fold, and Mer- tumors were detected in each group. There was no correlation between transferase and glycosylase levels, indicating that the absence of transferase in some tumor samples was not an artifact due to necrosis or inactivation of enzymes in the extract.

Bacterial Proteins↗