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B T Hill

Publications and source records attributed to B T Hill.

At least 19 recordsLinked to original sources
PubMed1992

Over-expression of P-glycoprotein and glutathione S-transferase pi in MCF-7 cells selected for vincristine resistance in vitro.

This study has provided evidence that exposure of the wild-type MCF-7 human breast carcinoma cell line to the mutagen ethyl methane sulphonate (EMS), followed by selection in vincristine (VCR), resulted in a stably-resistant subline, designated VCREMS, which expressed an approximately 14-fold level of resistance to VCR. This VCREMS subline showed cross-resistance (3-fold) to adriamycin (ADR) and to etoposide (3-fold), but not to cisplatin. The addition of a non-toxic concentration of verapamil (6.6 microM) significantly enhanced VCR cytotoxicity only in the resistant subline. This resistance was associated with over-expression of P-glycoprotein (Pgp), but without a concomitant increase in Pgp mRNA or gene amplification. In addition, activities of total glutathione S-transferases (GST) and glutathione peroxidase were elevated in this resistant subline, with over-expression of the GST-pi isozyme and its associated mRNA being identified, without gene amplification. This VCR-selected resistant MCF-7 cell line therefore provides another example of a breast carcinoma subline in which there is co-ordinate over-expression of both Pgp and GST-pi, without attributing a causal relationship to either event, and extends the range of anti-tumour drugs known to elicit modifications in glutathione metabolism.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1992

Characterization of a cisplatin-resistant human ovarian carcinoma cell line expressing cross-resistance to 5-fluorouracil but collateral sensitivity to methotrexate.

In vitro exposure of the TR170 ovarian carcinoma cell line to six intermittent 24-h treatments with a 90% inhibitory concentration of cisplatin (CDDP) (0.15 micrograms/ml; 0.5 microM) resulted in a 2-fold stably resistant subline designated TR170/CP+ (B.T. Hill et al., Int. J. Cancer, 39: 219-225, 1987). Resistance to CDDP in these CP+ cells has now been associated with reduced uptake of 195mCDDP (2-fold; P less than 0.01) and decreased removal of specific Pt-DNA adducts, quantitated immunochemically, indicative of an apparent increased tolerance of CDDP-induced DNA damage. Specifically these resistant cells appeared deficient in removal of the major cis-Pt-(NH3)2d(pGpG) adduct and the difunctional cis-Pt(NH3)2d(GMP)2 lesion, showed less efficiency in removing cis-Pt(NH3)2d(pApG) adducts, but proved as proficient as the parental cell line in removing DNA-DNA interstrand cross-links. Activities of DNA polymerase-alpha and -beta were comparable in both lines, and no significant alterations in glutathione metabolism were identified. Response to acute X-irradiation was not modified in these TR170/CP+ cells, but they showed marked (10-fold) cross-resistance to 5-fluorouracil and, unusually, proved collaterally sensitive (12-fold) to methotrexate. Resistance to 5-fluorouracil was associated with significantly increased thymidylate synthase activity (P less than 0.01), but this was not reflected in altered gene expression, while increased sensitivity to methotrexate was accompanied by increased drug uptake but by unaltered activity and expression of dihydrofolate reductase. These results indicate that exposure to CDDP can result in numerous alterations, both intracellularly and at the cellular membrane, reflected in significant changes in the tumor cells' responses to the cytotoxic effects of a range of antitumor drugs. The clinical relevance of these observations remains to be established.

Antineoplastic Agents↗
PubMed1992

Mechanisms associated with the expression of cisplatin resistance in a human ovarian tumor cell line following exposure to fractionated X-irradiation in vitro.

Interactions between cisplatin (CDDP) and irradiation are of potential significance for the combined modality treatment of cancer. Previous data have indicated that following in vitro exposure to X-irradiation certain tumour cells expressed resistance to CDDP. To identify parameters associated with this CDDP resistance, the human ovarian carcinoma cell line SK-OV-3/P was pre-exposed to fractionated X-irradiation (total dose: 50 Gy) in vitro. The resultant subline (SK-OV-3/DKR-10) proved 2-fold resistant to CDDP, but not to acute X-irradiation. Consistent with unaltered dihydrofolate reductase and thymidylate synthase activities, SK-OV-3/DXR-10 cells were neither cross-resistant to methotrexate nor to 5-fluorouracil. Verapamil (6.6 microM) significantly (P less than 0.05) enhanced CDDP-induced cytotoxicity in the resistant DXR-10 subline, but not in the parental cells. Total glutathione levels were significantly (P less than 0.01) lower in the resistant subline and BSO pretreatment failed to influence cytotoxicity, whilst related enzyme activities were not consistently modified in the SK-OV-3/DXR-10 cells. Resistance in these cells was associated with significantly decreased cisplatin uptake (P less than 0.002). Immediately following drug exposure the total platination level of the DNA, quantitated immunochemically, was higher (P less than 0.05) in the resistant subline indicative of increased tolerance to DNA damage. After an 18 h post-treatment incubation the parental cell line appeared proficient in the removal of the intrastrand adduct Pt-AG, but deficient in removing the major adduct Pt-GG and the difunctional Pt-(GMP)2 lesion, whilst the DXR-10 resistant subline appeared proficient in removal of all four Pt-DNA adducts. DNA polymerases alpha and beta activities, however, were comparable in both cell lines. These data implicate both enhanced repair and increased tolerance of DNA damage as mechanisms of resistance to CDDP resulting from in vitro exposure of a human ovarian carcinoma cell line to fractionated X-irradiation.

Biological Transport↗
PubMed1992

Expression of resistance to etoposide and vincristine in vitro and in vivo after X-irradiation of ovarian tumor cells.

Two human ovarian carcinoma cell lines (JA-T/P and SK-OV-3/P) were exposed to 10 fractions of 5 Gy X-irradiation in vitro. Surviving populations generated sublines designated DXR-10 which expressed significant resistance to etoposide (VP-16) and vincristine (VCR), but not to adriamycin (ADR) or acute X-irradiation, as judged by clonogenic assays. JA-T/P and JA-T/DXR-10 tumor cells were xenografted into nude mice and treated with a single dose of VCR (1.8 mg/kg), VP-16 (24.5 mg/kg) or ADR (10.0 mg/kg) and 48 h later the surviving clonogenic cells in each tumor were quantitated. Significantly fewer colonies grew from the JA-T/P xenografts treated with either VCR or VP-16, as opposed to the JA-T/DXR-10 tumors, whilst comparable colony numbers were recorded after ADR treatment. These data suggest that the resistant phenotype following exposure to fractionated X-irradiation in vitro is also expressed in vivo.

Animals↗
PubMed1992

Expression of collateral sensitivity to cisplatin, methotrexate, and fluorouracil in a human ovarian carcinoma cell line following exposure to fractionated x-irradiation in vitro.

Examples of collateral sensitivity, even in experimental tumor systems, remain few. Preliminary data from this laboratory indicated that certain tumor cells expressed increased sensitivity to cisplatin after exposure in vitro to x-irradiation. To further clarify whether the type of fractionated radiation procedure used clinically can induce hypersensitivities to certain antitumor drugs we have pre-exposed the human ovarian carcinoma cell line JA-T/P derived from a tumor from an untreated patient to fractionated x-irradiation (total dose 50 Gy) in vitro. The resultant subline JA-T/DXR-10 expressed collateral sensitivity to cisplatin (CDDP), methotrexate (MTX) and fluorouracil (5-FU), but not to acute x-irradiation. Hypersensitivity to CDDP was associated with decreased activity of DNA polymerase beta (3.5-fold, P less than .01), but unaltered glutathione metabolism. Pre-incubation with cyclosporin A or with 3-aminobenzamide significantly enhanced (twofold, P less than .01) CDDP-induced cytotoxicity in JA-T/P cells, but not in the DXR-10 subline. Consistent with MTX hypersensitivity dihydrofolate reductase activity was significantly decreased (2.9-fold, P less than .01). Despite collateral sensitivity to 5-FU, however, thymidylate synthase activity was increased (twofold, P less than .05) suggesting alternative mechanisms for 5-FU-induced cytotoxicity in these JA-T/DXR-10 cells. These data demonstrate that DNA repair and associated reduced folate metabolism can be modified not only by drugs but also by fractionated x-irradiation.

Cisplatin↗
PubMed1991

Anomalous relationship between cisplatin sensitivity and the formation and removal of platinum-DNA adducts in two human ovarian carcinoma cell lines in vitro.

Two human ovarian tumor cell lines (SK-OV-3 and TR175), established from patients previously treated with alkylating agents, but not with cisplatin, expressed greater than 23-fold differences in cisplatin sensitivities in vitro. Cisplatin resistance in SK-OV-3 cells appeared to be associated with increased levels of glutathione and activities of glutathione reductase and glutathione peroxidase, with reduced catalase activity. No significant modification of drug uptake was noted and there was only marginally lower (16%) total platination of DNA, measured immunochemically, in these cells compared with the more sensitive TR175 cell line. SK-OV-3 cells, however, showed a significantly lower overall ability to remove drug-induced DNA damage, with an apparent inability to remove either the major DNA-DNA intrastrand cross-links in the sequence pGpG or the adducts cis-Pt(NH3)2d(GMP)2, although by alkaline elution repair of DNA-DNA interstrand cross-links was demonstrated. Significantly more of these interstrand cross-links were induced in these resistant cells. These data provide evidence for the involvement of altered glutathione metabolism and increased tolerance of certain types of drug-induced DNA damage as factors associated with the resistance phenotype of SK-OV-3 cells. Paradoxically, however, although the highly cisplatin-sensitive TR175 cells had lower glutathione levels this was not reflected in significantly higher total platination of DNA, and these cells appeared to be proficient in removing all the major platinum-DNA adducts quantitated in this study. Mechanisms responsible for this relative sensitivity to cisplatin remain to be identified.

Buthionine Sulfoximine↗
PubMed1991

A lack of detectable modification of topoisomerase II activity in a series of human tumor cell lines expressing only low levels of etoposide resistance.

Etoposide (VP-16) resistance is expressed following in vitro exposure of HN-1 and MCF-7 human tumor cells to the drug itself or to fractionated X irradiation. VP-16-selected sublines prove cross-resistant to Adriamycin, amsacrine and actinomycin D, whilst X-ray-pretreated sublines show cross-resistance to only actinomycin D. These differential responses, in the HN-1 series, are not associated with significant differences in amounts of immunoreactive topoisomerase (topo) II, altered topo-II catalytic activity of nuclear extracts or changes in susceptibility of the topo II to VP-16- or amsacrine-induced DNA-protein cross-link formation. Therefore significant modifications in topo II appear not to be implicated in VP-16 resistance in these HN-1 sublines.

Amsacrine↗
PubMed1991

Lack of significant modulation of the formation and removal of platinum-DNA adducts by aphidicolin glycinate in two logarithmically-growing ovarian tumour cell lines in vitro.

Two recently established human ovarian carcinoma cell lines (JA-T and TR175) have been used to study the effects of aphidicolin glycinate (APG), a specific competitive inhibitor of DNA polymerase alpha (Ikegani et al. (1978) Nature, 275, 458-460), on the formation and removal of four platinum-DNA adducts. Logarithmically-growing cells were exposed to cis-diamminedichloroplatinum (II) (cisplatin) (10 micrograms, 33.4 microM) in the presence or absence of APG (5 or 50 micrograms/ml, 11.6 or 116 microM). Platinum-DNA adducts were quantitated using a competitive ELISA technique. No differences were observed between the initial levels of total DNA platination and of specific DNA adducts formed in the presence or absence of APG in either cell line. Following 18 h posttreatment incubation both lines showed some ability to remove each of the three main platinum-DNA lesions (Pt-GMP, Pt-AG and Pt-GG). However, the levels of these specific DNA adducts decreased over this time period, by similar rates with or without APG addition. It was also shown that the APG concentrations used had minimal inhibitory effects alone on growth or DNA synthesis during this 18 h posttreatment incubation period. Furthermore its addition did not significantly modify cisplatin-induced cytotoxicity, as judged by inhibition of growth or DNA synthesis over this time period. We therefore conclude that under these experimental conditions APG does not modulate 'repair' of cisplatin-induced DNA damage in logarithmically-growing cultures of these two apparently 'repair-proficient' human ovarian tumour cell lines.

Antibiotics, Antineoplastic↗
PubMed1990

An evaluation of the role of glutathione and its associated enzymes in the expression of differential sensitivities to antitumour agents shown by a range of human tumour cell lines.

Glutathione and its associated enzyme activities have been quantitated in a series of human tumour continuous cell lines expressing a range of in vitro sensitivities to certain antitumour agents. Fourteen different parental lines and 15 various drug- and X-ray-selected resistant sublines have been studied. Quantitative relationships between total glutathione levels and related enzyme activities and sensitivities to six clinically-useful antitumour drugs or X-rays, as judged by colony forming assays, have been determined by linear regression analysis. A positive correlation has been identified between glutathione levels and sensitivities to cisplatin. Adriamycin, or to X-rays. In addition, positive correlations were noted between cisplatin sensitivities and glutathione peroxidase and reductase activities and for Adriamycin responses with respect to glutathione peroxidase activity, using cumene hydroperoxide as substrate. However, no positive correlations were noted for glutathione levels or these enzyme activities with differential methotrexate, etoposide, vincristine or 5-fluorouracil cytotoxicities. Furthermore, no direct relationship was apparent between total glutathione S-transferase activities and any of these drug or X-ray sensitivities in this series of cell lines. These data appear to provide further evidence linking altered glutathione metabolism with differential cytotoxicities of certain clinically-useful antitumour agents.

Antineoplastic Agents↗
PubMed1990

Overexpression of P-glycoprotein in mammalian tumor cell lines after fractionated X irradiation in vitro.

We observed that in vitro exposure of mammalian tumor cells to fractionated x irradiation results in the expression of drug resistance. The cause of this resistance was investigated in a series of Chinese hamster ovary cell lines that had survived exposure to multiple lethal doses of radiation. These cell lines had increased levels of P-glycoprotein (Pgp), the multidrug-resistance-associated membrane glycoprotein. Consistent with the classic multidrug resistance phenotype, they exhibited cross-resistance to multiple drugs, as well as sensitivity to reversal of vincristine resistance by verapamil. However, the cell lines showed no change in their sensitivity to x rays. Pgp overexpression occurred in these cells, despite a lack of Pgp gene amplification or of significant alteration in Pgp messenger RNA levels. Although the cause of increased Pgp levels is not yet known, these data suggest a biological basis for the clinical problem of drug resistance that can occur in previously irradiated tumors.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1990

Cytogenetic analysis of a cell line established from a Krukenberg tumor.

Cytogenetic analysis was performed on a cell line, designated KS1, derived from a Krukenberg tumor. A modal chromosome number of 60-65 chromosomes was present, as were several clonal chromosome rearrangements involving, among others, chromosomes 2, 3, 6, 9, 11, 12, and 22. Ten to 30 double minutes were present in most cells.

Cell Line↗
PubMed1990

Differential expression of drug resistance following in vitro exposure of human tumour cell lines to fractionated X-irradiation.

We have established that drug resistance can be expressed following in vitro exposure of tumour cells not only to antitumor drugs but also to fractionated X-irradiation. These data therefore suggest a biological basis for the clinical problem of drug resistance that can occur in patients with previously irradiated tumors. These observations, if confirmed, have clinical implications for the combined modality approach and need to be considered when attempting to identify resistant tumour cells in clinical specimens with the aim of monitoring or identifying effective drug regimens.

ATP Binding Cassette Transporter, Subfamily B, Mem↗