Biomedical subjects

S B Howell

Publications and source records attributed to S B Howell.

At least 55 records · Page 3Linked to original sources

PubMed1998

The effect of different chemotherapeutic agents on the enrichment of DNA mismatch repair-deficient tumour cells.

Loss of DNA mismatch repair is a common finding in hereditary non-polyposis colon cancer as well as in many types of sporadic human tumours. We compared the effect of loss of DNA mismatch repair on drug sensitivity as measured by a clonogenic assay with its effect on the ability of the same drug to enrich for mismatch repair-deficient cells in a proliferating tumour cell population. Mixed populations containing 50% DNA mismatch repair-deficient cells constitutively expressing green fluorescent protein and 50% mismatch repair-proficient cells were exposed to different chemotherapeutic agents. 6-Thioguanine, to which DNA mismatch repair-deficient cells are known to be resistant, was included as a control. The results in the cytotoxicity assays and in the enrichment experiments were concordant. Treatment with either carboplatin, cisplatin, doxorubicin, etoposide or 6-thioguanine resulted in enrichment for mismatch repair-deficient cells, and clonogenic assays demonstrated resistance to these agents, which varied from 1.3- to 4.8-fold. Treatment with melphalan, paclitaxel, perfosfamide or tamoxifen failed to enrich for mismatch repair-deficient cells, and no change in sensitivity to these agents was detected in the clonogenic assays. These results identify the topoisomerase II inhibitors etoposide and doxorubicin as additional agents for which loss of DNA mismatch repair causes drug resistance. The concordance of the results from the two assay systems validates the enrichment assay as a rapid and reliable method for screening for the effect of loss of DNA mismatch repair on sensitivity to additional drugs.

Adenocarcinoma↗

PubMed1998

Prediction-based threading of the hMSH2 DNA mismatch repair protein.

Mutations in the genes whose products participate in DNA mismatch repair underlie the increased risk of cancer in families with hereditary nonpolyposis colon carcinoma. Mutations in hMSH2 account for approximately 50% of the mutations found in these families. We sought to predict the 3-dimensional structure of hMSH2 by identifying structural homologues using prediction-based threading and by computer modeling using information from these putative structurally related proteins. Prediction-based threading identified three candidate structural homologues: glycogen phosphorylase (gpb), a 70 kDa soluble lytic transglycosylase, and ribonucleotide reductase protein R1. An independent approach utilizing a potential-based threading program also identified gpb as a structural homologue. The models based on the structures of these proteins suggest that the ATP binding domain and helix-turn-helix domain are exposed on the outside of the protein. All known bacterial MutS and hMSH2 mutations appear to be clustered in similar vicinities in the theoretical models of hMSH2; the major site is within the ATP binding domain and near the carboxyl-terminal end, whereas a smaller number map to the region coding for exon 5 and the amino-terminal domain. All point mutations also appear to affect amino acids that are exposed on the outside surface of the protein.

Bacterial Proteins↗

PubMed1998

Observations on control of N2 and N3 neck disease in squamous cell carcinoma of the head and neck by intra-arterial chemoradiation.

Patients with head and neck squamous cell cancer with N2 and N3 neck disease have a poor prognosis and are at risk to fail regionally despite combined surgery and radiation. Twenty-two patients with N2 and N3 neck disease (and T3-4 primaries) were treated with intra-arterial, high-dose cisplatin (CDDP), 150 mg/m2 per week for 4 weeks, and concurrent radiation. All patients were followed for at least 2 years or until death from any cause. Twenty patients had a complete response at the primary site. Two of the 20 with a complete response later had a neck recurrence and died. Five patients with palpable nodes after treatment underwent fine-needle aspiration (FNA), one of which was positive and two suggestive of cancer. Six neck dissections were performed in this group, only two of which had positive nodes. This chemoradiation protocol may offer reasonable control of N2 and N3 neck disease in advanced head and neck squamous cell cancer. Neck dissection appeared to be necessary in only those patients with nodes 8 weeks after treatment in whom FNA was positive or suggestive of cancer. Because of the relatively small size of this series, additional accrual and monitoring of such patients is planned.

Adolescent↗

PubMed1998

Sensitivity to cisplatin and platinum-containing compounds of Schizosaccharomyces pombe rad mutants.

The role of genes that affect response to radiation in determining sensitivity to platinum-containing compounds was studied using a panel of 23 strains of the yeast Schizosaccharomyces pombe. The radiation-hypersensitive mutants all had the same genetic background and most of them contained mutations that disabled either cell cycle checkpoints or DNA repair. The tested platinum compounds included cisplatin and two complexes containing diaminocyclohexane (oxaliplatin and tetraplatin), two ammine/cyclohexylamine complexes with different orientation of the leaving groups (JM216 and JM335) and a multinuclear platinum complex (BBR 3464). The cytotoxic effect of the selected platinum complexes was evaluated by using a microtiter growth inhibition assay with a 48 hr exposure to drug. The mutants fell into three groups with respect to sensitivity to cisplatin: four mutants (rad2, -7, -11, -15) exhibited minimal change in sensitivity; fifteen mutants (rad4-6, -8-10, -12-14, -16-17, -19-21, and -22) were 5.1-21.7-fold hypersensitive; only rad1 and -3 mutants, defective in checkpoints, and rad18, defective in repair, displayed a marked hypersensitivity. None of the mutants demonstrated appreciable change in sensitivity to JM216 presumably as a consequence of a lack of resistance of the wild-type strain, whereas a moderate increase in sensitivity to JM335 was observed for most of the mutants, and hypersensitivity to BBR3464 was observed only in rad1 and -3. No relevant changes in sensitivity to tetraplatin were observed. Most of the mutants, with the exception of rad2, -7, and -15, were hypersensitive to oxaliplatin. These findings demonstrate that specific mutations have disparate effects on the profile of sensitivity to different members of the same class of cytotoxic agents, which provides genetic evidence that different mechanisms are involved in differential cytotoxicity induced by Pt compounds. The results also demonstrate the utility of such a panel of mutants, constructed on the same genetic background, for detecting specific cellular response; presumably, this reflects the recognition or processing of specific DNA adducts. In conclusion, because the rad1 and rad3 gene products are determinants of cellular response to a large number of platinum-containing compounds, the present results support a critical role of genes involved in cell cycle control in cellular sensitivity to these agents.

Cell Cycle↗

PubMed1998

Immunohistochemical analysis of the distribution of the human ATPase (hASNA-I) in normal tissues and its overexpression in breast adenomas and carcinomas.

Human ATPase (hASNA-I) is a novel human gene recently cloned on the basis of homology to the arsA gene of bacteria. Its protein product is an ATPase that is free in the cytoplasm and bound in the perinuclear area and nucleolus in human cells. We prepared the hASNA-I-specific 5G8 monoclonal antibody and used it to investigate the expression of hASNA-I in normal human tissues and breast cancers. hASNA-I was detected immunohistochemically only in the epithelial cells of the liver, kidney, and stomach wall, in the adrenal medulla, in the islet cells of the pancreas, in the red pulp of the spleen, and in cardiac and skeletal muscle. No staining was observed in the uterus, testis, lung, thyroid, cerebellum, and large intestine. Although no staining was also observed in normal breast tissue, all four cases of breast fibroadenomas and all 15 cases of either primary or metastatic breast carcinoma demonstrated increased staining. No embryological or functional common denominator is readily apparent. However, the increased expression in malignant breast cells is of particular interest with respect to the use of this antibody for screening of cytological specimens.

Adenoma↗

PubMed1998

The role of DNA mismatch repair in drug resistance.

Loss of DNA mismatch repair (MMR) has been observed in a variety of human cancers. In addition to predisposing to oncogenesis, loss of MMR activity is of concern with respect to the use of chemotherapeutic agents to treat established tumors. Loss of MMR results in drug resistance directly by impairing the ability of the cell to detect DNA damage and activate apoptosis and indirectly by increasing the mutation rate throughout the genome. The MMR proteins are involved in mediating the activation of cell cycle checkpoints and apoptosis in response to DNA damage. MMR-deficient cells have been reported to be resistant to the methylating agents procarbazine and temozolomide, the alkylating agent busulfan, the platinum-containing drugs cisplatin and carboplatin, the antimetabolite 6-thioguanine, and the topoisomerase II inhibitors etoposide and doxorubicin. In the case of cisplatin, busulfan, temozolomide, and procarbazine, the degree of resistance has been shown to be sufficient to produce a large difference in clinical responsiveness in vivo in tumor model systems. The available preclinical data suggest that tumors that contain a significant fraction of cells deficient in MMR will demonstrate reduced responsiveness to specific drugs. The challenge now is to assess the clinical significance of the presence of deficient cells in tumors and to discover drugs that retain activity against MMR-deficient cells.

Alkylating Agents↗

PubMed1998

An organ-preserving selective arterial chemotherapy strategy for head and neck cancer.

PURPOSE: Squamous cancer of the upper aerodigestive tract is a disheartening disease. Despite our best efforts, the long-term survival rate remains only 15% to 40%, and surgical cures often decrease the quality of life owing to the loss of swallowing and speech organs. A better understanding of tumor dynamics and the discovery that thiosulfate can neutralize cisplatin led us to develop a treatment plan that combines a rapid superselective high-dose intraarterial delivery of cisplatin (CDDP), simultaneous intravenous infusion of its antagonist, thiosulfate, and radiation therapy. METHODS: Patients with advanced head and neck squamous cancer were entered into the protocol after a multidisciplinary evaluation that included CT or MR imaging. Forty-two patients constituted the first cohort. After baseline angiography, an arterial acceptance test determined the maximum infusion rate that the tumor's nutrient artery would accept. CDDP was then infused at that rate, usually within 3 to 5 minutes, while the antagonist thiosulfate was given intravenously. In the second cohort of 85 patients with stage 3 or 4 previously untreated and unresectable disease, local radiation was added to the treatment plan. The radiation dose (180-200 cGy/d x 35) was delivered regionally on the basis of the known radiosensitizing effect of CDDP. RESULTS: Cohort 1 allowed us to develop the infusion technique and to establish a dose quantity and delivery frequency. When 150 mg/m2 was administered weekly for 4 weeks, no severe toxicity was found. In cohort 2, 72 (92%) of the remaining 78 patients had complete disappearance of their tumor. Seventeen severe toxic events were associated with 323 femoral catheterizations. One patient died of pulmonary embolus, precluding follow-up evaluation. Six patients had neurologic sequelae, three with transient and three with permanent strokes. CONCLUSION: Rapid superselective chemotherapy with CDDP combined with a circulatory systemic antagonist allowed delivery of an antitumoral drug directly into the lesion while protecting the kidneys and bone marrow from the agent's systemic effects. Use of a dose regimen of 150 mg CDDP/m2 per week for 4 weeks resulted in the disappearance of a large percentage of advanced squamous cancers.

Antineoplastic Agents↗

PubMed1997

Loss of DNA mismatch repair: effects on the rate of mutation to drug resistance.

BACKGROUND: The loss of the ability of cells to repair mismatches in double-stranded DNA is a common finding in human tumors. This defect results in genomic instability and in increased resistance to several of the drugs used in cancer chemotherapy. The human colon cancer cell line HCT116 is deficient in DNA mismatch repair (MMR) because of a genetic defect in the hMLH1 gene, which is located on chromosome 3. In this study, we investigated whether MMR-deficient HCT116+chr2 cells (i.e., HCT116 cells into which chromosome 2 has been transferred [as a control]) have a higher rate of mutation to resistance to commonly used chemotherapeutic agents (i.e., cisplatin, doxorubicin, paclitaxel [Taxol], and etoposide) than MMR-proficient HCT116+chr3 cells (i.e., HCT116 cells into which chromosome 3 has been transferred to provide a wild-type copy of the hMLH1 gene). METHODS: Spontaneous mutation rates were calculated from measurements of the mutant fractions of cells before and after their expansion through a known number of generations (also known as the technique of maximum likelihood estimation). Aliquots of 500000 cells were expanded in culture over a period of 2 weeks, and the mutant fractions were determined both before and after expansion of secondary cultures (each also with an initial 500000 cells) in drug concentrations that produced survival fractions of 0.0002%. RESULTS: Mutation rates in MMR-proficient and MMR-deficient cells did not differ on exposure to cisplatin, doxorubicin, or paclitaxel; however, the relative mutation rate was 2.4-fold higher in MMR-deficient cells exposed to etoposide (P=.002). CONCLUSION: These results suggest that genes involved in the control of cellular sensitivity to etoposide are targets for mutation when the loss of MMR destabilizes the genome. Tumors containing large fractions of MMR-deficient cells may demonstrate more rapid emergence of clinical resistance to etoposide.

Adaptor Proteins, Signal Transducing↗

PubMed1997

Differential induction of c-Jun NH2-terminal kinase and c-Abl kinase in DNA mismatch repair-proficient and -deficient cells exposed to cisplatin.

The c-Abl nonreceptor tyrosine kinase and the c-Jun NH2-terminal kinase (JNK/stress-activated protein kinase) are activated during the injury response to the DNA-damaging agent cisplatin. Loss of DNA mismatch repair activity results in resistance to cisplatin in human cancer cells, suggesting that the mismatch repair proteins function as a detector for cisplatin DNA adducts. To identify signaling pathways activated by this detector, we investigated the effect of the loss of DNA mismatch repair function on the ability of cisplatin to activate the JNK and c-Abl kinases. The results demonstrate that cisplatin activates JNK kinase 3.8 +/- 0.2-fold more efficiently in DNA mismatch repair-proficient than repair-deficient cells, and that activation of c-Abl is completely absent in the DNA mismatch repair-deficient cells. Furthermore, the results show that cisplatin-induced activation of JNK occurs through a stress-activated protein kinase/extracellular signal-regulated kinase kinase 1-independent mechanism. We conclude that activation of JNK and c-Abl by cisplatin is in part dependent upon the integrity of DNA mismatch repair function, suggesting that these kinases are part of the signal transduction pathway activated when mismatch repair proteins recognize cisplatin adducts in DNA.

Adenocarcinoma↗

PubMed1997

Synergy between tamoxifen and cisplatin in human melanoma cells is dependent on the presence of antiestrogen-binding sites.

We have demonstrated previously that cisplatin (DDP) and tamoxifen (TAM) act synergistically to kill human melanoma T-289 cells, and that the observed synergy is lost in the 3-fold TAM-resistant subline, 289/TAM6. We have identified the intracellular antiestrogen-binding sites (AEBSs), defined by their ability to bind antiestrogens while having no affinity for estrogen, as a possible mediator of this synergy. We report here that [3H]TAM binds to AEBSs, as defined by the ability of N,N-diethyl-2-[4-(phenylmethyl)phenoxy]ethanamine-HCl, an AEBS-specific ligand, to compete with [3H]TAM binding. Furthermore, we have characterized the number of binding sites and their affinity for [3H]TAM by Scatchard analysis in whole-cell lysates, microsomal fractions, and nuclear fractions of both cell lines by competing [3H]TAM binding with increasing concentrations of unlabeled TAM. These data demonstrate that the loss of a high-affinity AEBS from the nuclear fraction of the 289/TAM6 cell line correlates with the loss of synergy between DDP and TAM in these cells. This implicates AEBSs as a critical component of the mechanism that mediates the synergistic interaction of DDP and TAM in human melanoma cells.

Binding, Competitive↗

PubMed1997

In vitro and in vivo resistance to cisplatin in cells that have lost DNA mismatch repair.

In vitro studies have shown that loss of DNA mismatch repair due to lack of either hMSH2 or hMLH1 activity results in low-level resistance to cisplatin but not to oxaliplatin, an analogue that produces a different type of DNA adduct. No information is currently available on whether this low-level resistance is sufficient to result in enrichment of mismatch repair-deficient cells during drug exposure in vitro or to account for clinical failure of treatment in vivo. Mixed populations of cells containing a minority of DNA mismatch repair-deficient cells constitutively expressing green fluorescence protein were exposed repeatedly in vitro to cisplatin and oxaliplatin. Treatment with cisplatin resulted in a gradual enrichment for DNA mismatch repair-deficient cells, whereas treatment with oxaliplatin did not. MSH2-/- and MSH2+/+ embryonic stem cells were established as xenografts in athymic nude mice. Animals were treated 48 h after tumor implantation with a single LD10 dose of either cisplatin or oxaliplatin. MSH2-/- tumors were significantly less responsive to cisplatin than MSH2+/+ tumors, whereas there was no difference in sensitivity to oxaliplatin. These results demonstrate that the degree of cisplatin resistance conferred by loss of DNA mismatch repair is sufficient to produce both enrichment of mismatch repair-deficient cells during treatment in vitro and a large difference in clinical responsiveness in vivo. The results identify loss of DNA mismatch repair as a mechanism of resistance to cisplatin but not oxaliplatin.

Adenocarcinoma↗

PubMed1997

A phase I and pharmacokinetic study of high dose tamoxifen and weekly cisplatin in patients with metastatic melanoma.

BACKGROUND: The authors have previously demonstrated that tamoxifen (TAM) is synergistic with cisplatin (DDP) in patients with metastatic melanoma. In vitro studies have demonstrated that TAM/DDP synergy is dependent on a TAM effect that is currently under investigation. In an attempt to improve the complete response rate of this regimen, the authors initiated a Phase I trial to determine the maximum tolerated dose (MTD) of TAM that could be safely administered with weekly DDP. METHODS: TAM was started on Day 1 at a dose of 80 mg/day and was increased by 40 mg to the MTD in groups of 3 patients. DDP (80 mg/m2) was begun on Day 2 and repeated weekly for a total of 3 weeks. During Week 4, the patients were not treated with DDP but instead evaluated for response. If disease stabilization or regression was documented, the patients received a second 3-week cycle of DDP and were then reevaluated for response. Patients with progressive disease were removed from the study. RESULTS: In 25 consecutive patients, the overall response rate was 20%. No responses were observed in patients treated with TAM at a dose of <240 mg/day. Among 13 patients treated at or above this dose, there were 2 complete responses, 3 partial responses, 2 mixed responses, and 6 patients with progressive disease. The overall response rate for patients treated with 240 mg of TAM or higher was 38.5%. Dose-limiting toxicity, which occurred at a TAM dose of 280 mg/day, was primarily hematologic and gastrointestinal in nature. There was one toxic death (due to septic neutropenia) at this dose. There were no episodes of thrombosis. CONCLUSIONS: A TAM dose of 240 mg/day is the recommended Phase II dose. Based on the 38.5% overall response rate at this dose, the authors have initiated a Phase II study.

Adult↗

PubMed1997

Molecular mechanisms controlling sensitivity to toxic metal ions in yeast.

Contamination of the environment has made toxic metal ions a major health issue. The use of yeasts as model systems for the identification of molecular mechanisms that control sensitivity to these agents is particularly attractive because of the ease of genetic manipulation and the availability of the complete Saccharomyces cerevisiae genomic sequence. This paper reviews information on those genes and mechanisms that have been identified in both the budding yeast S. cerevisiae and the fission yeast Schizosaccharomyces pombe as being capable of modulating sensitivity to important toxic metals. The factors that influence sensitivity to toxic metal ions include cellular thiols (glutathione, phytochelatins, labile sulfide, and metallothioneins) and the products of genes directly and indirectly involved in the transport or sequestration of the metal ion. A complete understanding of the molecular basis of sensitivity to toxic metal ions in lower organisms is expected to provide useful insights in the metal ion detoxification pathways and diseases related to these pathways in humans.

Cadmium↗

PubMed1997

Digitonin enhances the efficacy of carboplatin in liver tumour after intra-arterial administration.

Platinum-containing drugs enter the cell slowly and have a poor tissue penetration. Increasing the permeability of the cell membrane might increase the intracellular drug concentration. Digitonin, a detergent that increases cell permeability by binding to cholesterol molecules in the cell membrane, can increase cisplatin accumulation and reduce tumour growth in vitro. The aim of this study was to determine whether digitonin could increase the efficacy of carboplatin (CBDCA) in vivo. In LH rats, a hepatoma was implanted in the liver. At 7 days after implantation, digitonin (or saline in the control group) was infused via the hepatic artery and, 10 min later, CBDCA was injected. Biopsies from the tumour and liver parenchyma were obtained after 1 h. The concentration of platinum measured in the liver tumours was higher in the digitonin group than in the control groups. In the liver parenchyma the concentrations were of the same magnitude. Measured with the 133Xe-clearance technique, digitonin did not alter the tumour blood flow. Digitonin enhanced the tumour-growth-retarding effect of CBDCA given intra-arterially at 5 mg/kg but not at 25 mg/kg. No increase in toxicity was observed for digitonin given together with CBDCA at 5 mg/kg. Systemic administration of CBDCA was not influenced by digitonin. These findings demonstrate that pretreatment with digitonin increases the tumour uptake of CBDCA and potentiates the cytotoxic effect of CBDCA.

Animals↗

PubMed1997

Expression of the DNA mismatch repair proteins hMLH1 and hPMS2 in normal human tissues.

hMLH1 and hPMS2 are part of the DNA mismatch repair complex. Mutations in these genes have been linked to hereditary non-polyposis colon cancer; they also occur in a variety of sporadic cancers. Western blot analysis and immunohistochemistry demonstrated that hMLH1 and hPMS2 are widely expressed nuclear proteins with a distribution pattern very similar to that previously described for hMSH2. These observations showing similar localization of hMLH1 and hPMS2 with hMSH2 are consistent with the biochemical function of these proteins in DNA mismatch repair.

Adaptor Proteins, Signal Transducing↗

PubMed1997

Role of determinants of cadmium sensitivity in the tolerance of Schizosaccharomyces pombe to cisplatin.

The genetic mechanisms underlying cisplatin (DDP) resistance in yeast were investigated by examining the cytotoxicity of DDP to Schizosaccharomyces pombe mutants that were either hypersensitive or resistant to Cd. Despite reports that have linked glutathione (GSH) to DDP resistance in human cancer cells, we found that a mutant of S. pombe that was hypersensitive to Cd by virtue of a 15-fold reduction in GSH level and lack of phytochelatin production was as tolerant as the wild-type strain to DDP. A mutant that harbored a mutation in hmt1, the gene encoding an ATP-binding cassette-type transporter for vacuolar sequestration of a phytochelatin/Cd complex, exhibited only mild hypersensitivity to DDP even though it was 100-fold more sensitive to Cd. Overexpression of hmt1 in wild-type or mutant cells conferred tolerance to Cd but failed to do the same for DDP. However, a strain that produced 6-fold more sulfide than wild-type cells was found to be 6-fold more resistant to DDP and twice as resistant to Cd; an association between DDP resistance and sulfide production was observed in three other strains that were examined, and overproduction of sulfide was accompanied by reduced platination of DNA. These results indicate that GSH and the GSH-derived phytochelatin peptides do not play critical roles in determining sensitivity to DDP in S. pombe but rather identify increased production of sulfide as a possible new mechanism of DDP resistance that may also be relevant to human cells.

Antineoplastic Agents↗

PubMed1997

Comparative genomic hybridization analysis of chromosomal changes occurring during development of acquired resistance to cisplatin in human ovarian carcinoma cells.

The genetic changes underlying the development of resistance to the platinum-containing drugs are poorly defined. We analyzed six resistant cell lines using comparative genomic hybridization (CGH) in order to screen and identify possible genetic changes in common. We compared parental 2008 and A2780 human ovarian cancer cells to sublines selected for resistance to cisplatin (DDP) (2008/C8, 2008/C13*5.25, 2008/A, A2780/CP); we also compared 2008 cells to sublines selected for resistance to antimonite (2008/H) and arsenite (2008/I) which demonstrated cross-resistance to DDP. DNA samples from the resistant cell lines were hybridized against DNA from the parental cells rather than from normal human cells to permit detection of only those changes associated with the development of resistance. The DNA sequence copy number changes were surprisingly numerous in the DDP, antimony, and arsenite-resistant variants of the 2008 cell line and most of the chromosomes were affected. On the other hand, in the A2780/CP subline only a few changes were found and these were limited to just four chromosomes. The most common findings among the DDP-resistant cell lines were gains of material from chromosomes or chromosome arms 2q (5 out of 6 lines), 4 (4/6), 6q (5/6), and 8q (4/6). Deletions were observed on chromosomes or chromosome arms 2p (4/6), X (4/6), 7p (5/6), 11p (4/6), and 13 (4/6). The most frequently involved chromosomal regions, affected in the majority of cell lines, were: gain of 2q14.1-q33, 4p15.2-p13, 4q22-q25, 4q31.1-q34, 6q13-q16, 8q12-q21.2, and loss of Xp22.2-q21, 7p21-p14, 11cen-p14 in sublines of 2008, and loss of 2pter-p22 and 13q21 in sublines of 2008 and A2780. The results suggest that the acquired resistance and cross-resistance to DDP in these cell lines was associated with substantial genomic instability, quite unlike the changes observed in association with the development of resistance to drugs participating in the multidrug resistance phenotype.

Chromosome Aberrations↗

PubMed1997

Resistance to cytotoxic drugs in DNA mismatch repair-deficient cells.

Loss of DNA mismatch repair is a common finding in many types of sporadic human cancers as well as in tumors arising in patients with hereditary nonpolyposis colon cancer. The effect of the loss of DNA mismatch repair activity on sensitivity to a panel of commonly used chemotherapeutic agents was tested using one pair of cell lines proficient or deficient in mismatch repair due to loss of hMSH2 function and another due to loss of hMLH1 function. 6-Thioguanine and N-methyl-N'-nitro-N-nitrosoguanidine, to which these cells are known to be resistant, were included in the panel as controls. The results were concordant in both pairs of cells. Loss of either hMSH2 or hMLH1 function was associated with low level resistance to cisplatin, carboplatin, and etoposide, but there was no resistance to melphalan, perfosfamide, 5-fluorouracil, doxorubicin, or paclitaxel. The results are consistent with the concept that the DNA mismatch repair proteins function as a detector for adducts produced by 6-thioguanine, N-methyl-N'-nitro-N-nitrosoguanidine, cisplatin, and carboplatin but not for melphalan and perfosfamide. They also suggest that these proteins play a role in detecting the DNA damage produced by the binding of etoposide to topoisomerase II and propagating signals that contribute to activation of apoptosis.

Adaptor Proteins, Signal Transducing↗