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P Frost

Publications and source records attributed to P Frost.

At least 73 records · Page 4Linked to original sources
PubMed1993

2'-deoxy-5-azacytidine increases binding of cisplatin to DNA by a mechanism independent of DNA hypomethylation.

The chemotherapeutic agents 2'-deoxy-5-azacytidine (DAC) and cisplatin (cDDP) have been shown in vitro to be synergystic in their cytotoxicity toward human tumour cells. We have investigated possible molecular mechanisms underlying this synergy using the plasmid pSVE3 in vitro and after transfection into CMT3 cells. Increased binding of cDDP to DAC-substituted DNA generated in vivo was confirmed by flameless atomic absorption spectrophotometry (FAAS). The plasmid used in these experiments was unmethylated suggesting that DAC was effective in enhancing cDDP binding to DNA without acting as a hypomethylating agent, but by directly changing the topology of DNA. The role of DNA methylation in cDDP binding was studied using methylated and unmethylated plasmid incubated in vitro with cDDP. Restriction analyses and FAAS measurement of bound platinum indicated that methylated DNA bound more cDDP than unmethylated DNA. In addition, in vivo studies confirmed the in vitro observations since replication of methylated plasmid was inhibited to a greater extent than unmethylated plasmid.

Azacitidine↗
PubMed1992

[UV cured acrylates--potent contact allergens in the occupational environment].

Allergic contact dermatitis is still an important disease in occupational medicine. Acrylic compounds are known to be potent contact sensitizers causing allergic eczema after occupational exposure. To illustrate the problem and the need for preventive arrangements the authors present an unusual clustering of allergic contact dermatitis in three technicians who produced hearing aids using ultraviolet cured akrylate compounds. All three technicians developed eczema on their fingers few months after introduction of the new acrylate compounds in the production. Skin patch testing with the products confirmed that sensitization.

Adult↗
PubMed1992

The use of molecular genetic markers to demonstrate the effect of organ environment on clonal dominance in a human renal-cell carcinoma grown in nude mice.

Transduction of the SN12C human renal-cell carcinoma line with the neoR gene produces a genetically "tagged" cell population within which individual clones can be identified if they dominate the tumor during its growth in vivo. We used this technique to determine whether the clones that dominate the primary local tumor and its metastases are the same or different when the tumor is growing in different organ sites in nude mice. The results show that clonal dominance is influenced by the organ environment in which the primary tumor grows, i.e., distinct clones dominated in the kidney, colon and subcutaneous sites. In addition, tumors grown in the orthotopic site (kidney) were all populated by the same dominant clones, and each distant visceral metastasis retained the same clonality. SN12C neoR-cells grown in an epithelial, ectopic site (colon) produced tumors with uniquely different dominant clones, and their visceral metastases retained the dominant pattern expressed by the parent tumor from which they were derived. In contrast, SN12C tumors growing subcutaneously showed a random pattern of clonal dominance in both their primary and metastatic sites. Parallel cytogenetic analyses could not demonstrate these patterns. We conclude that the organ environment significantly influences clonal dominance of human renal carcinoma and that tumor injection into orthotopic sites may produce a more reproducible selection of dominant clones.

Animals↗
PubMed1992

Synergistic cytotoxicity with 2'-deoxy-5-azacytidine and topotecan in vitro and in vivo.

Synergy, when it can be convincingly established, is an effective strategy for the development of novel drug combinations. We have evaluated the interaction between 2'-deoxy-5-azacytidine (DAC) and 9-dimethylaminomethyl-10-hydroxycamptothecin (topotecan) based on our hypothesis that DAC, through DNA hypomethylation, might increase the transcription of topoisomerase I (topo I) leading to increased sensitivity to topotecan. Five human tumor cell lines, A375 melanoma, DX-3 melanoma, DMS4C non-small cell lung carcinoma, UP-1 unknown primary adenocarcinoma, SN12C renal carcinoma, and the murine CT-26 tumor cell line, were studied. Drug interactions were assessed using the multiple drug effect analysis of Chou and Talalay (Chors, T-C, and Talalay, P. Adv. Enzyme Regul., 22:27-54, 1984.). A synergistic interaction was documented in four human cell lines and the murine CT-26 line. An antagonistic interaction was observed with the SN12C cell line. The toxicology and efficacy of this combination were analyzed using CT-26 in BALB/c mice. Various treatment schedules were studied, including: single doses of each agent; single sequential combination treatments where DAC was administered followed by topotecan 24 h later; and multiple sequential treatments where DAC and topotecan were administered on days 1, 2, 8, and 9. Efficacy studies showed that the single sequential combination of DAC (50 mg/kg) and topotecan (10 mg/kg) resulted in tumor growth delay as compared to single doses of DAC (50 mg/kg) or topotecan (10 mg/kg). When the multiple sequential combination schedule was used, the antitumor effect was more pronounced. In that experiment 50% of the control animals had tumors of 20 mm by day 28. For animals receiving a single sequential treatment with DAC and topotecan, the median time until the mean tumor size reached 20 mm was 38 days, and for the group with multiple sequential combination treatments the time was 51 days. Studies of the mechanism of the interaction showed that the activity of topotecan versus each cell line correlated with the topo I activity in nuclear extracts However, there was no correlation between topo I levels and synergy and no reproducible increase in topo I activity following exposure to DAC. Thus, while the exact mechanism of the interaction remains unclear, DAC can be effectively combined with topotecan to enhance antitumor activity.

Adenocarcinoma↗
PubMed1992

Identification of ras oncogene mutations in the stool of patients with curable colorectal tumors.

Colorectal (CR) tumors are usually curable if detected before metastasis. Because genetic alterations are associated with the development of these tumors, mutant genes may be found in the stool of individuals with CR neoplasms. The stools of nine patients whose tumors contained mutations of K-ras were analyzed. In eight of the nine cases, the ras mutations were detectable in DNA purified from the stool. These patients included those with benign and malignant neoplasms from proximal and distal colonic epithelium. Thus, colorectal tumors can be detected by a noninvasive method based on the molecular pathogenesis of the disease.

Adult↗
PubMed1992

Clonal origin of bladder cancer.

BACKGROUND: Patients with cancer of the urinary bladder often present with metachronous tumors, appearing at different times and at different sites in the bladder. This observation has been attributed to a "field defect" in the bladder that allows the independent transformation of epithelial cells at a number of sites. We tested this hypothesis using molecular genetic techniques. METHODS: We examined 13 tumors from cystectomy specimens from four women, using a method that analyzes the pattern of X-chromosome inactivation to determine whether the tumors were derived from the same precursor cell. In addition, we analyzed allelic loss on autosomes to determine whether different tumors had the same genetic alterations. The alterations evaluated included the loss of chromosome 9q sequences (commonly found in superficial bladder tumors) and the loss of 17p and 18q sequences (usually found only in advanced tumors). RESULTS: For each patient studied, all the tumors had inactivation of the same X chromosome, whereas normal bladder mucosa cells had random patterns of inactivation. Moreover, each tumor that could be evaluated from a given patient had lost the same allele on chromosome 9q, suggesting that the loss of this allele preceded the spread of neoplastic cells elsewhere in the bladder. The losses of chromosome 17p and 18q alleles, which are late events in tumor progression, were not common to different tumors from the same patient. CONCLUSIONS: A number of bladder tumors can arise from the uncontrolled spread of a single transformed cell. These tumors can then grow independently with variable subsequent genetic alterations.

Alleles↗
PubMed1992

Studies on the mechanism of the synergistic interaction between 2'-deoxy-5-azacytidine and cisplatin.

2'-Deoxy-5-azacytidine (5-aza-CdR) and cisplatin interact to produce synergistic cytotoxicity against many human tumor cell lines. Preliminary experiments designed to explore the mechanism of this synergy suggested a poor correlation between synergy and the degree of genomic hypomethylation measured following exposure to 5-aza-CdR. Subsequent studies using plasmid DNA suggested that rather than DNA hypomethylation, incorporation of 5-aza-CdR into DNA mediated increased cisplatin binding to DNA and could therefore be essential to the synergistic interaction between these two agents. In this series of experiments, we evaluated the degree of synergy with cisplatin produced against two human melanoma cell lines by two additional antimetabolites that were chosen on the basis of their biochemical properties. In addition, we investigated the synergy between 5-aza-CdR and cisplatin in parental and 5-aza-CdR-resistant murine cell lines, which differed in their sensitivity to 5-aza-CdR and DNA methylation status but incorporated similar amounts of 5-aza-CdR into DNA when exposed to this antimetabolite. In the studies testing additional antimetabolites, cytosine arabinoside, which is incorporated into DNA but does not hypomethylate it, produced synergy with cisplatin that was similar or superior to that obtained using 5-aza-CdR. With 3-deaza-adenosine, which is not incorporated into DNA but produces DNA hypomethylation through inhibition of S-adenosylhomocysteine hydrolase, a primarily antagonistic interaction was observed in the two cell lines studied. In the 5-aza-CdR-sensitive and -resistant cell lines, a very similar synergistic interaction was documented for 5-aza-CdR and cisplatin despite the significant difference observed in DNA methylation levels. Taken as a whole, these data suggest that DNA hypomethylation was not critical to the synergistic cytotoxicity produced by 5-aza-CdR and cisplatin. This finding suggests additional strategies that could further modulate this interaction.

Animals↗
PubMed1992

Short term benefits of post-operative oral dietary supplements in surgical patients.

The present study was undertaken to investigate the short term clinical efficacy of oral dietary supplements administered post-operatively to patients undergoing predetermined moderate to severe gastrointestinal surgery. Trial end points for comparison included effects of oral dietary supplements on nutritional intake, nutritional status and incidence of serious complications. 54 patients who were scheduled to undergo predetermined moderate to major gastrointestinal surgical procedures entered the study. They were randomly assigned to receive a normal ward diet post-operatively or the same diet supplemented ad libitum by an oral nutritional sip feed. The study period was defined as commencing from the day patients were adjudged to be capable of ingesting 'free fluids' to the day of hospital discharge. 40 patients (20 in each group) completed the study. The mean daily energy intake (KCal/day) assessed from 7 day food diaries was significantly higher in the treatment group (1833 +/- SEM 99) than in the control group (1108 +/- 56, p < 0.0001). This increase occurred not only as a consequence of energy intake from the oral dietary supplements (470 +/- 30) but also because more energy was consumed from the ward diet by the treatment than the control patients (1353 +/- 92 vs 1108 +/- 56, p < 0.02). The mean daily protein intake g/day in the treatment group (66.0 +/- 3.4) was also greater than in the control group (52.9 +/- 29 p < 0.0001). This difference was due solely to the intake in protein from the oral dietary supplements (15.7 +/- 1.0), protein intake from the ward diet being similar in the treatment (50.1 +/- 3.2) and control (52.9 +/- 29) groups. Patients in the treatment group maintained their pre-operative weight where as control patients had lostsignificant amount of their pre-operative weight by study day 3 (4.5 +/- 12 kg and by discharge (4.7 +/- 1.2 kg, p < 0.02). Pre-operative muscle function as evidenced by grip strength dynamometry decreased to a greater extent in the control than treatment group patients by study day 3 (14.6 +/- 2.2 KPa vs 2.8 +/- 2.4 < 0.03) and by discharge (10.4 +/- 3.1 KPa vs 0.10 +/- 1.9 p < 0.03). The incidence of serious infections (pneumonia, wound infection) was significantly higher in the control group (10) than in the treatment group (3, p < 0.02). It is concluded that the prescription of oral dietary supplements on an ad libitum basis to post-operative patients undergoing moderate to major gastrointestinal surgery results in clinically significant short term benefits.

Journal Article↗
PubMed1991

Cytogenetic heterogeneity of genetically marked and metastatically competent "dominant" tumor cell clones.

Examination of tumors usually shows them to consist of phenotypically and clonally heterogeneous cell subpopulations. On the other hand, previous studies from our laboratory have provided compelling evidence for the rapid evolution, or overgrowth, of single "dominant" clones during the course of primary tumor growth. Thus in one such study, syngeneic CBA mice were injected with a mixture of 50-100 different genetically tagged clones of a mouse mammary carcinoma called SP1. The vast majority of these clones were non-metastatic. The different clones were tagged by random integrations of foreign DNA using calcium phosphate-mediated transfection of the plasmid pSV2neo, the resultant primary tumors were found to consist of a single dominant clone, called B5, which was also shown to be metastatically competent. The detection of single dominant clones such as B5 in primary tumors can be reconciled with the concept of tumor cell heterogeneity if it could be shown that the dominant clone was in fact heterogeneous for other genetic or phenotypic markers, i.e., was homogeneous only for the plasmid-based genetic marker used for its detection. To study this question, we examined the karyotypes of several sublines of B5, two derived from a primary advanced tumor and one from a spontaneous lung metastasis. We indeed found evidence to support the existence of marked cellular heterogeneity within and between the three sublines examined. Thus, while all three retained common cytogenetic markers, each also expressed unique markers. Moreover, karyotypic heterogeneity within a given subline was observed. Thus the concept of clonal dominance of primary tumors by metastatically competent cell subpopulations is not incompatible with the concept of the cellular heterogeneity of tumors. The implications of the results are discussed.

Adenocarcinoma↗
PubMed1991

Identification of p53 gene mutations in bladder cancers and urine samples.

Although bladder cancers are very common, little is known about their molecular pathogenesis. In this study, invasive bladder cancers were evaluated for the presence of gene mutations in the p53 suppressor gene. Of 18 tumors evaluated, 11 (61 percent) were found to have genetic alterations of p53. The alterations included ten point mutations resulting in single amino acid substitutions, and one 24-base pair deletion. In all but one case, the mutations were associated with chromosome 17p allelic deletions, leaving the cells with only mutant forms of the p53 gene products. Through the use of the polymerase chain reaction and oligomer-specific hybridization, p53 mutations were identified in 1 to 7 percent of the cells within the urine sediment of each of three patients tested. The p53 mutations are the first genetic alterations demonstrated to occur in a high proportion of primary invasive bladder cancers. Detection of such mutations ex vivo has clinical implications for monitoring individuals whose tumor cells are shed extracorporeally.

Alleles↗
PubMed1991

Reduced tumorigenicity of murine tumor cells secreting gamma-interferon is due to nonspecific host responses and is unrelated to class I major histocompatibility complex expression.

Spontaneous SP1 murine adenocarcinoma cells transfected with the murine gamma-interferon (IFN-gamma) gene expressed IFN-gamma (SP1/IFN-gamma) failed to grow in syngeneic hosts and grew in nude mice. The rejection of SP1/IFN-gamma cells was related to the amount of IFN-gamma produced and appeared to be mediated primarily by nonspecific cellular mechanisms, although some role for T-cells in the afferent arm of this response is possible. SP1 cells are H2-Kk negative but express class I antigens when producing IFN-gamma. However, class I major histocompatibility complex (MHC) expression, while likely necessary, was insufficient in itself to prevent tumor growth since secretion of greater than 64 units/ml IFN-gamma was needed to inhibit tumorigenicity while only 8 units/ml IFN-gamma could induce class I antigens. Similar results were obtained with the murine colon carcinoma CT-26, a tumor that constitutively expresses class I MHC antigens, further supporting the contention that class I MHC expression is not essential for the rejection response induced by IFN-gamma. The failure of SP1/IFN-gamma cells to protect against a challenge with parent SP1 cells argues that factors other than IFN-gamma production or class I MHC expression are needed to induce a protective response against weakly or nonimmunogenic tumor cells.

Adenocarcinoma↗
PubMed1991

Prolonged continuous acyclovir treatment of normal adults with frequently recurring genital herpes simplex virus infection. The Acyclovir Study Group.

In this 3-year study of suppressive acyclovir for recurrent genital herpes, patients with more than six recurrences per year were randomized initially to 400 mg of acyclovir or placebo orally two times per day, with recurrences treated with 200 mg of acyclovir five times per day for 5 days. In the second year of the study, all patients received acyclovir as a daily suppressive or intermittent acute therapy; in the third year, all received daily acyclovir. Among 525 patients completing 3 study years, 289 received 3 years of suppressive therapy and 236 received 1 year of acute therapy followed by 2 years of suppressive therapy. Of those who completed the third year, 61% were recurrence free that year; 25% of the suppressive therapy-only group were recurrence free for all 3 years. The annual recurrence rate dropped from more than 12 recurrences per year at baseline to 1.0 (suppressive therapy) and 1.4 (acute and suppressive therapy) recurrences during the third year. No significant toxic effects were detected. Daily suppressive acyclovir therapy was effective and well tolerated.

Acyclovir↗
PubMed1991

Immunogenicity of a non-class I MHC expressing murine tumor transfected with the influenza virus hemagglutinin or murine interleukin-2 genes.

The transfection of murine SP1 tumor cells with the hemagglutinin (HA) gene of influenza virus results, after fluorescent-activated cell sorting (FACS), in the selection of high-HA-expressing cell lines called H4A and H4B. Both lines fail to grow in syngeneic animals at doses that result in 100% tumor take of non-transfected tumor cells. Both grow in immunosuppressed mice. SP1 and H4A or H4B cells express few class I major histocompatibility complex (MHC) antigens but do express class II IAk antigens. H4A or H4B cells engender a cytotoxic T lymphocyte (CTL) response but cannot protect against a challenge with SP1 cells. This CTL response is inhibited by anti-CD4 but not anti-CD8 antibodies. Using FACS, we were able to select a population (called H5AK5) with high class-I MHC antigen expression. Like H4A and H4B, H5AK5 cells fail to grow in syngeneic animals but do grow in immunosuppressed mice. However, unlike H4A or H4B, H5AK5 can induce protection against a challenge with 1 x 10(5) SP1 cells. These studies indicate that the immunogenicity of HA-transfected SP1 cells may correlate with the cell-surface expression of class II MHC antigens. However, HA-expressing SP1 cells seem able to induce a protective response against a parent SP1 cell challenge only if they also express class I MHC antigens. This view is supported by the observations that SP1 cells expressing murine interleukin-2 do not express class I MHC antigens, fail to grow in syngeneic animals, do grow in immunosuppressed mice but do not protect against a challenge with parental SP1 cells.

Animals↗