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G H Mickisch

Publications and source records attributed to G H Mickisch.

At least 37 records · Page 2Linked to original sources
PubMed1995

Gene therapy on renal-cell carcinoma: magic bullet or tragic insanity?

Correction of the aberrant genetic code as a means of rational therapy has been a challenge since the first discoveries of an abnormal genetic link to expression of certain disorders. Our growing understanding of the molecular basis of cancer has also led us into a new era in cancer therapy. The possibility of gene therapy represents one of the biggest potential returns on the investment in molecular biology research over the past several years. As a massive gene therapy attack mounts against many forms of malignancy employing various techniques, strategies, and concepts, there appears to be reason to be optimistic, with expectations thus far decidedly outweighing results. Scientists and clinicians have joined together to target directly the molecular basis of tumorigenesis through the restoration of tumor-suppressor gene function or inhibition of oncogene expression. In addition, scientists mapping the human genome have supplied us with a number of genes that can be used to destroy cancer cells selectively [e.g., the herpes simplex-thymidine kinase (HS-tk) gene], induce a potent antitumor immune response (e.g., interleukin 2), and afford protection to normal tissues from the toxic effects of standard chemotherapy [e.g., multidrug resistance gene type 1 (mdr 1)]. These new anticancer tools provide new opportunities for more specific tumor cell destruction in vivo without the common regional and systemic side effects related to conventional forms of chemotherapy, immunotherapy, radiation, and surgery. Hence, over the next 5-10 years, gene therapy is likely to become a realistic treatment option for certain cancers.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenoviridae↗
PubMed1995

Dexverapamil to modulate vinblastine resistance in metastatic renal cell carcinoma.

Multidrug resistance (MDR) in a variety of human tumours such as renal cell carcinoma (RCC) is thought to be caused by expression of the MDR1 gene and may be reversed by applying modern chemosensitisers such as dexverapamil, which inhibit the MDR1 gene product P-glycoprotein. This preliminary report gives information on a clinical study complying with good clinical practice regulations in patients with advanced RCC. The final evaluation is pending. Vinblastine, if anything the most effective chemotherapeutic agent (5-day continuous regimen), was combined with oral dexverapamil (6 times per day) as a chemosensitiser and dexamethasone to increase dexverapamil tolerance. All patients had histologically proven RCC, which was metastatic and progressive at study entry. The statistical design featured a pre-study regimen of two cycles of vinblastine alone followed by evaluation. If no response was documented, with all patients thus serving as their own control, dexverapamil and dexamethasone were added for three cycles of combination therapy. Having obtained institutional permission from the ethical review committee, we enrolled patients of whom 25 qualified for the combined-treatment arm; 13 patients finished the study, 5 patients failed to complete all treatment cycles (1 because of treatment-related toxicity, 3 for personal reasons, not related to treatment, 1 for tumour-related reasons) and 7 patients were at too early a stage for evaluation. Altogether, 61% of all patients tolerated a dose of dexverapamil of at least 2400 mg/day with peak serum levels reaching, in some cases, approximately 8 microM (the sum of dexverapamil plus nordexverapamil levels). WHO grade 3 and 4 toxicities were mainly myelosuppression (5/18). The combination of 1.4 mg m-2 day-1 vinblastine plus dexverapamil was generally felt to be safe and well tolerated. One partial response and 7 stable diseases were noted in this heavily pretreated study population. Four-hourly administration of dexverapamil in combination with dexamethasone plus escalation to the individually tolerated doses have permitted increases in serum levels of dexverapamil.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1995

[Molecular therapeutic control and gene therapy approaches].

The past decade has seen the successful application of genetic techniques to the investigation of the most important phenotypes of cancer cells; for example, the identification of particular molecules on the surface of cancer cells makes it possible to target these antigens and destroy them selectively via immunotoxins. At present, gene therapy is not a new treatment modality in most instances, but rather a new technology facilitating further exploration of preexisting treatment strategies, such as immunotherapy or chemotherapy, owing to the indirect approaches of contemporary clinical application. It can be anticipated that gene transfer technology will have a considerable impact on the way certain urological anticancer strategies are pursued in the future.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed1994

From laboratory expertise to clinical practice: multidrug-resistance-based gene therapy becomes available for urologists.

Many human tumors such as bladder carcinoma that are initially responsive to chemotherapy eventually fail to respond to treatment. For most drugs, dose escalation that may be required for a cure cannot be achieved because sensitive tissues such as bone marrow limit cytotoxic therapy. Approaches to prevent or circumvent myelosuppression are therefore a high priority of research on dose intensification protocols. One such strategy is to protect bone marrow cells by virtue of expression of the multidrug-resistance (MDR1) gene encoding for P-glycoprotein. In our first set of experiments, we transplanted bone marrow cells derived from transgenic mice that constitutively express MDR1 to lethally irradiated recipients (n = 36). From 6 weeks to 10 months after the transplant, all animals contained MDR1 DNA in spleen and bone marrow specimens as indicated by Southern-blot analysis and expressed MDR1 RNA in bone marrow samples as detected by slot-blot analysis. In addition, these animals were resistant to the myelosuppressive effect of doxorubicin, daunomycin, taxol, vinblastine, vincristine, etoposide, and actinomycin D, whereas control animals that were reconstituted with normal bone marrow reacted with a significant decrease in their white blood counts. In a second set of experiments, we retrovirally transfected a construct consisting of a murine long-terminal repeat (LTR) promoter and the human MDR1 gene into CD34-positive bone marrow stem cells from rhesus monkeys using the same technique as in the ongoing clinical ADA gene-therapy protocol. Upon transplantation, high-level and long-lasting expression of the human MDR1 gene was observed in recipient monkeys.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Chemoresistance of renal cell carcinoma: 1986-1994.

Multidrug resistance (MDR) in a variety of human tumors such as renal cell carcinoma (RCC) is thought to be caused by expression of the mdr1 gene and may be reversed by applying chemosensitizers such as Dexverapamil that inhibit the mdr1 gene product P-glycoprotein. On the basis of our preclinical analysis, we initiated a clinical (GCP) study with vinblastine (VBL), the most effective--if at all--chemotherapeutic agent; dexverapamil; and dexamethasone in patients with RCC. All patients had histologically proven RCC that was metastatic and progressive at study entry. The statistical design featured a preliminary study of two cycles of VBL alone followed by tumor evaluation. If no response was documented, with all patients thus serving as their own control, dexverapamil and dexamethasone were added for a minimum of three cycles of combination therapy. Having obtained institutional permission by the ethical review committee (MEC 124, 106-1993/12), we enrolled 24 patients on this protocol starting on May 3, 1993. In the preliminary study, 1 complete response (CR) was achieved with VBL alone, and myelotoxicity led to an adequate dose reduction from 2 mg/m2 VBL per day given as a 5-day continuous infusion (days 1-5) in 6/10 yet evaluable patients to 1.4 mg/m2 per day. In 8/11 yet evaluable patients, dexverapamil doses reached > or = 3000 mg/day by 7-day oral uptake (days 0-6, supported by 20 mg dexamethasone given twice daily), which is significantly higher than those previously reported. The combination of VBL given at 1.4 mg/m2 per day plus, dexverapamil given at 3000 mg per day was felt to be safe and well tolerated. Nine patients were yet evaluable for response. One partial response and three minor responses were noted in this heavily pretreated study population. It appears that this innovative approach may have some activity in RCC and may eventually lead to a rational treatment modality. Careful evaluation in ongoing studies is warranted.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1993

Pseudomonas exotoxin conjugated to monoclonal antibody MRK16 specifically kills multidrug resistant cells in cultured renal carcinomas and in MDR-transgenic mice.

Using renal carcinoma and prostate carcinoma cell lines, we investigated the concept of targeting and killing multidrug resistant cells in urogenital cancers. Renal carcinoma lines HTB44, 45, 46, and 47 expressed a relatively low, but detectable level of multidrug resistance (MDR)1 mRNA as indicated by Northern blot analysis, whereas prostate lines LNCaP and DU145 were found to be MDR1-negative. Anti-P-glycoprotein monoclonal antibody MRK16 was conjugated to Pseudomonas exotoxin (PE) by a stable thioether bond. Treatment with MRK16-PE resulted in a dose-dependent killing of multidrug resistant renal carcinoma cells, while non-MDR expressing prostate carcinoma cells were not affected. Addition of excess MRK16 blocked the effect of MRK16-PE. Furthermore, MOPC-PE, a non-MDR associated monoclonal antibody control conjugate, did not target and kill multidrug resistant renal carcinoma cells. Having established that MRK16-PE was active against and specific for multidrug resistant cells in culture, we also tested bioactivity in MDR-transgenic mice, whose bone marrow cells express the human MDR1 gene at a level approximately equal to that found in many human cancers. Again, MRK16-PE killed multidrug resistant bone marrow cells with high efficiency in an intact animal, and killing was blocked by unconjugated MRK16.

ADP Ribose Transferases↗
PubMed1992

Monoclonal antibody MRK16 reverses the multidrug resistance of multidrug-resistant transgenic mice.

Using multidrug-resistant (MDR)-transgenic mice, whose bone marrow cells express the human MDR1 gene at a level approximately equal to that found in many human cancers, we determined the efficacy of human-specific anti-P-glycoprotein monoclonal antibody MRK16 in overcoming multidrug resistance in an intact animal. MRK16 alone (2 mg) did not significantly affect the WBC counts of the MDR-transgenic mice, but MRK16, as well as the F(ab')2 fragments of MRK16, led to a dose-dependent circumvention of bone marrow resistance against daunomycin, doxorubicin, vincristine, vinblastine, etoposide, and taxol. This sensitizing effect could not be enhanced by combining MRK16 with low molecular weight chemosensitizing agents such as verapamil, quinine, quinidine, or cyclosporin A. We also investigated the concept of specifically targeting and killing multidrug-resistant cells by using MRK16 coupled to Pseudomonas exotoxin (PE). MRK16-PE resulted in a dose-dependent killing of bone marrow cells in MDR-transgenic mice, whereas no bone marrow toxicity was observed in normal control mice. Administration of excess MRK16 prior to injection of MRK16-PE successfully blocked the effect of MRK16-PE. MOPC-PE, a non-MDR-related control monoclonal antibody conjugate, did not target and kill multidrug-resistant bone marrow cells in MDR-transgenic mice. Thus, these immunological approaches to reversing multidrug resistance appear to be both specific and effective.

Alkaloids↗
PubMed1992

Transplantation of bone marrow cells from transgenic mice expressing the human MDR1 gene results in long-term protection against the myelosuppressive effect of chemotherapy in mice.

Many human cancers that are initially responsive to chemotherapy eventually fail to respond to treatment. For some drugs, dose escalation that may be required for a cure cannot be achieved because sensitive tissues such as bone marrow (BM) limit cytotoxic therapy. Approaches to prevent or circumvent BM toxicity are therefore a high priority of research on dose escalation protocols. In this study, we have transplanted BM cells from transgenic mice that constitutively express physiologic amounts of a functional human multidrug resistance (MDR1) cDNA to lethally irradiated C57BL/6 x SJL F1 mice (n = 36). From 6 weeks to 10 months after the transplant, all animals contained MDR1 DNA in spleen and BM specimens as indicated by Southern blot analysis, and expressed MDR1 messenger RNA in BM samples as detected by slot blot analysis. In addition, these animals were resistant to the myelosuppressive effect of doxorubicin, daunomycin, taxol, vinblastine, vincristine, etoposide, and actinomycin D, whereas control animals that were reconstituted with normal BM were drug sensitive. Finally, the chemoprotection afforded by the MDR1 gene could readily be reversed by adding chemosensitizers such as cyclosporin A and R-verapamil to chemotherapy. Hence, it appears that BM cells expressing the human MDR1 gene maintain this function after transplantation to host animals for a minimum of 10 months, and confer multidrug resistance to these BM recipients. This selective advantage conferred by expression of the MDR1 cDNA suggests a strategy for the use of MDR1 gene therapy in cancer chemotherapy and for the introduction of otherwise nonselectable genes into BM.

Animals↗
PubMed1991

Chemotherapy and chemosensitization of transgenic mice which express the human multidrug resistance gene in bone marrow: efficacy, potency, and toxicity.

A common form of multidrug resistance in human cancer results from expression of the MDR1 gene which encodes a plasma membrane energy-dependent multidrug efflux pump. We have engineered transgenic mice which express this multidrug transporter in their bone marrow cells and demonstrated that peripheral WBC of these animals provide a rapid and reliable system for assessing the bioactivity of agents that reverse multidrug resistance. Immunocytochemical analysis of bone marrow smears suggests that the activation of the MDR1 transgene has probably occurred at a very early stage of bone marrow differentiation since most bone marrow cells express the transporter. Expression of this transgene in bone marrow produces about 10-fold resistance to leukopenia induced by taxol compared to normal bone marrow. Chemosensitization of MDR1 mice to daunomycin and taxol, measured by a fall in WBC, is detectable at a dose as low as 0.01 mg/kg R-verapamil. A dose of 0.5 mg/kg R-verapamil reduces the WBC by nearly 50%. Chemosensitization of MDR-transgenic mice with 5 mg/kg R-verapamil, which is highly effective in reversing MDR and readily tolerated by mice, necessitates a reduction of the maximum tolerated dose of most chemotherapeutic agents by only 20%. In addition, detailed histopathological examination shows that treatment of mice with chemotherapeutic drugs and R-verapamil does not change the organ-related toxicity pattern but only moderately accentuates inherent toxic side effects of the chemotherapeutic agents. We conclude that MDR1-transgenic mice represent a valid model for evaluating efficacy, potency, and toxicity associated with chemotherapy and chemosensitization of multidrug-resistant cells in animals.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1991

Transgenic mice that express the human multidrug-resistance gene in bone marrow enable a rapid identification of agents that reverse drug resistance.

The development of preclinical models for the rapid testing of agents that circumvent multidrug resistance in cancer is a high priority of research on drug resistance. A common form of multidrug resistance in human cancer results from expression of the MDR1 gene, which encodes a Mr 170,000 glycoprotein that functions as a plasma membrane energy-dependent multidrug efflux pump. We have engineered transgenic mice that express this multidrug transporter in their bone marrow and demonstrated that these animals are resistant to leukopenia by a panel of anticancer drugs including anthracyclines, vinca alkaloids, etoposide, taxol, and actinomycin D. Differential leukocyte counts indicate that both neutrophils and lymphocytes are protected. Drugs such as cisplatin, methotrexate, and 5-fluorouracil, which are not handled by the multidrug transporter, produce bone marrow suppression in both normal and transgenic mice. The resistance conferred by the MDR1 gene can be circumvented in a dose-dependent manner by simultaneous administration of agents previously shown to be inhibitors of the multidrug transporter in vitro, including verapamil isomers, quinidine, and quinine. Verapamil and quinine, both at levels suitable for human trials that produced only partial sensitization of the MDR1-transgenic mice, were fully sensitizing when used in combination. We conclude that MDR1-transgenic mice provide a rapid and reliable system to determine the bioactivity of agents that reverse multidrug resistance in animals.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1991

Multidrug resistant transgenic mice as a novel pharmacologic tool.

Multidrug resistance resulting from expression of an energy-dependent drug efflux pump encoded by the human MDR1 gene is a major impediment to effective cancer therapy. Pharmacologic intervention aimed at inhibiting this multidrug transporter should improve existing chemotherapy of human cancer, but drug development has been delayed by the difficulty and expense of developing valid animal models. Using recombinant DNA technology, a transgenic mouse has been engineered whose bone marrow is protected from the toxic effects of chemotherapy by expression of the MDR1 gene. This animal system allows the rapid screening of drugs which inhibit the multidrug transporter and heralds a new era of using transgenic animals for pharmacologic screening.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1991

New potent verapamil derivatives that reverse multidrug resistance in human renal carcinoma cells and in transgenic mice expressing the human MDR1 gene.

Multidrug resistance in human renal cell carcinoma is mainly caused by expression of the MDR1 gene and is characterized by a broad spectrum cross resistance to many natural product chemotherapeutic agents. This resistance can be overcome by applying chemosensitizers which inhibit the function of the MDR1 gene product P-glycoprotein. The development of new reversing agents with fewer side effects and a higher potency in modifying resistance is a high priority of research on drug resistance. We have evaluated four new verapamil derivatives on 21 primary human renal cell carcinomas in vitro, and also tested them in an MDR-transgenic mice model. These mice express the human MDR1 gene in their bone marrow cells and measurement of their white blood counts provides a simple, rapid and reliable system to screen for the potency of MDR-reversing agents in vivo. We demonstrate here that all four drugs are effective in reversing multidrug resistance in primary cultures of human renal cell carcinomas when used in combination with vinblastine chemotherapy, and to a lesser extent with doxorubicin or daunomycin chemotherapy. Our in vivo data indicate that two of these reversing agents display low toxicity at high concentrations and are more effective at low, clinically achievable concentrations, than the other two drugs and R-verapamil. These results make the two new drugs attractive candidates to be taken into clinical trials.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1991

Circumvention of multidrug resistance mediated by P-170 glycoprotein using calcium antagonists in primary human renal cell carcinoma.

In experimental cell lines and in some human tumors, calcium antagonists reversed multidrug resistance mediated by P-170 glycoprotein in vitro. So far, clinical trials have not been very rewarding as intrinsic cardiovascular activities of these compounds impeded sufficient dosage. Renal cell carcinomas are considered to be good models for the evaluation of this new therapeutic concept. In 35 primary human renal cell carcinomas, the potency of 7 different calcium antagonists in combination with vinblastine monotherapy was examined in a tetrazolium-based microculture assay (MTT test) in order to circumvent chemoresistance. Concomitantly, P-170 glycoprotein expression was traced immunohistochemically using moab C 219. Substances derived from piperazine (flunarizine) showed only minor effects in this respect. The calcium antagonists of the papaverine type such as verapamil etc. revealed the strongest reversal of chemoresistance. Derivatives of benzothiazepine (diltiazem) or of dihydropyridine (nifedipine etc.) acted similarly and reached about 70% of the verapamil activity. All calcium antagonists lead to a significant enhancement of vinblastine cytotoxicity. An obvious link of P-170 glycoprotein to vinblastine chemoresistance was demonstrated. This particular resistance characteristic was detected in 19 of 27 resistant cases, but in none of the tumors displaying a chemoresponse. In particular, the new stereoisomer R-verapamil, which showed strong reversal of chemoresistance but which exerts 10 times lower cardiovascular side effects than racemic verapamil, seems to be suitable for further evaluation with regard to the clinical application.

ATP Binding Cassette Transporter, Subfamily B, Mem↗