Drug resistance in cancer: a perspective.

Drug resistance remains the thorniest obstacle in developing improved systemic therapies for disseminated cancer. The combination of genetic instability together with the great molecular heterogeneity that are displayed by malignant cells makes constructing effective, rational treatment programs difficult in the extreme. However, new insights into the action of antitumor agents at the molecular level plus greater understanding of the relationship of drug resistant states to the fundamental abnormalities that generate malignancy point the way to producing therapies that are more specific and therapeutically effective. However, a non-trival problem is the drug development system itself which is currently poorly set up to yield patient specific drug programs in a timely fashion.

Eradication of human non-Hodgkin's lymphoma in SCID mice by BCL-2 antisense oligonucleotides combined with low-dose cyclophosphamide.

Cancers overexpressing Bcl-2 protein, which prevents programmed cell death (apoptosis), are less sensitive to stresses that produce cellular damage, including chemotherapy. If the level of Bcl-2 protein can be reduced sufficiently using antisense oligonucleotides (ASOs) targeting the gene message, then cytotoxic agents may be rendered more effective in eliminating disease and increasing cure rate. Preclinical studies in SCID mice bearing Bcl-2 overexpressing systemic human B-cell lymphoma (DoHH2) were undertaken to support development of a clinical trial. These data confirm that a combination of an ASO (5 mg/kg) targeting bcl-2 and a low dose of cyclophosphamide (35 mg/kg) was an effective strategy, leading to the eradication of the DoHH2 cells in vivo and cure of the animals. When mice deficient in natural killer cell activity were treated with an ASO, similar results were observed, suggesting that ASO stimulation of the host immune system was not a significant factor in elimination of lymphoma cells. These studies indicate that therapeutic strategies involving the use of an ASO targeting bcl-2 in combination with a cytotoxic agent may improve clinical outcomes.

The use of conventional salvage chemotherapy before dose-intensive cytotoxic therapy and autologous transplantation for aggressive-histology lymphoma: a case for re-evaluation.

The use of CSCT to judge suitability for DIT and AHSCT in patients with aggressive-histology lymphoma who recur after primary chemotherapy is a widespread practice that excludes many NHL patients from this potentially curative therapy. Surprisingly, little direct evidence exists to suggest that CSCT used in this way is a useful strategy. On the other hand, it is clear that many of these patients undergoing DIT and AHSCT will not be cured using any currently available strategy or technique, and a method to identify such patients would be most helpful. CSCT may or may not be the best way to do so. This is an important question, but currently there are insufficient data to give us a definitive answer. Clinical trials are needed to resolve the issue. If the utility of CSCT is not validated, it should be abandoned. If it is validated, however, we may begin to address ways in which CSCT may be given more effectively.

Toxicity studies in thymidine kinase-deficient herpes simplex virus therapy for malignant astrocytoma.

Previous studies have shown that genetically engineered thymidine kinase (tk)-defective herpes simplex virus type 1 (HSV-1) can effectively and selectively destroy gliomas in animal models. The consequences of viral infection and tumor regression must be characterized before this therapy can be applied in human trials. To study the potential for long-term toxicity, immunocompetent rats harboring 9L gliosarcomas were injected intratumorally with a tk-defective HSV-1, KOS-SB, at titers that previously have been demonstrated to cause tumor regression. In animals surviving 3 months or longer following viral treatment, there was no evidence of persistent infection or inflammation in peritumoral brain tissue or in remote systemic organs studied with routine histological and immunocytochemical analyses. Polymerase chain reaction using primers specific for HSV-1 detected HSV-1 DNA in peritumoral tissue only in animals sacrificed within 3 months of viral injection. There was no evidence of HSV-1 DNA in systemic tissues at any time after treatment. We conclude that stereotactic intratumoral injection of tk-deficient HSV can be attempted for the treatment of brain tumors without risk of systemic infection or significant toxicity to normal brain or remote proliferating tissues.

Modelling the process of drug resistance.

Modelling the process of drug resistance can provide insight into such issues as the difference between intrinsic and acquired drug resistance. Other important biological questions such as whether resistance arises through selective or inducible events can also be addressed by reference to appropriate models. If drug resistant cells are produced by some type of inducible up regulation step then this has a number of qualifications for cancer chemotherapy. Selection theories of drug resistance imply that certain sequences of drugs will be superior to others something which can be tested by experiment.

Gas-chromatographic analysis of busulfan for therapeutic drug monitoring.

The development and validation of a gas chromatographic assay method for determination of total and free busulfan concentrations in human plasma for pharmacokinetic studies is reported. 1,6-Bis(methanesulfonyloxy)hexane, the internal standard, and a potential metabolite, 3-hydroxysulfolane, were synthesized. Plasma and plasma ultrafiltrate samples containing busulfan and internal standard were extracted with ethyl acetate and derivatized with 2,3,5,6-tetrafluorothiophenol prior to gas chromatographic determination. The 63Ni electron-capture detector provided a limit of detection of 0.0600 microgram/ml with a limit of quantitation of 0.100 microgram/ml busulfan in biological samples. Calibration curves were linear from 0.100 to 3.00 micrograms/ml in plasma (500 microliters) and 0.100 to 2.00 micrograms/ml in plasma ultrafiltrate (100 microliters). Extraction and derivatization yields ranged from 78.4% to 89.6% and 56.0% to 71.3%, respectively. Specificity of this assay for busulfan in the presence of its potential metabolites was demonstrated. Also, plasma samples containing co-administered drugs gave no response under these conditions. Clinical samples obtained following administration of a 1 mg/kg oral busulfan dose demonstrate the applicability of this method to analysis of total and free plasma concentrations.

Efficacy of weekly cisplatin-based chemotherapy in recurrent and metastatic head and neck cancer.

After disease recurrence or dissemination, patients who had been treated previously with radiation with or without surgery for cancer of the head and neck were given either cisplatin (16 patients), cisplatin/etoposide (15 patients), or cisplatin/etoposide/5-fluorouracil (5-FU) (19 patients) in an ambulatory care clinic. Intravenous (i.v.) cisplatin 25 mg/m2 was given weekly, while etoposide was given i.v. (80 mg/m2) on day 1 and orally (160 mg/m2) on day 2 of every odd-numbered week. In the three-drug regimen, 5-FU 500 mg/m2 i.v. was given every even-numbered week. Patients in all three groups received daily oral prednisone to decrease myelosuppression and oral co-trimoxazole and ketoconazole to prevent infection. The supportive drugs were given to all groups to keep these variables constant. As expected, myelosuppression did not occur in the cisplatin group, while the rates of severe neutropenia (less than 1.0 x 10(9)/L) in the two- and three-drug groups were 26% and 74%, respectively. The incidence of infection requiring hospitalization was low (2.5%). The response rate (complete plus partial) was lowest in the cisplatin group (6%) and higher in the cisplatin/etoposide (47%) and cisplatin/etoposide/5-FU (53%) groups. Because of the low response rate and the short time to progression (5 weeks) in the cisplatin group, 9 of these 16 patients were treated subsequently with cisplatin/etoposide. Time to progression and response duration were similar in the cisplatin/etoposide and cisplatin/etoposide/5-FU groups--12 and 14 weeks, and 12 and 9 weeks, respectively. Median survival times of the cisplatin and cisplatin/etoposide/5-FU groups were 36 and 34 weeks, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Treatment of recurrent and metastatic head and neck cancer with cisplatin/etoposide/bleomycin.

Cisplatin/etoposide/bleomycin (DEB) was given as an outpatient regimen in a novel weekly schedule to 27 patients with recurrent and/or widely metastatic cancer of the head and neck region. Six of these patients also received mitomycin (DEB/M) when their disease failed to respond after at least three weekly DEB doses. All but three patients had been treated previously with radiotherapy directed to the primary site and regional nodal disease; four had also received chemotherapy with cisplatin or carboplatin. Before treatment with DEB, 19 patients had distant metastases. Of an intended 12 doses per patient, a mean of 8.2 was achieved. Myelosuppression was the major toxicity, with neutropenia in 45% of patients and significant anemia in 26%. The overall response rate to DEB in 27 patients was 59%, increasing to 70% after the addition of mitomycin. There were two complete and 17 partial responses. The median duration of response was 12 weeks and median survival was 6 months, with 20% of patients surviving 1 year. We conclude that the relatively short survival time together with the significant toxicity of the DEB/M regimen does not warrant its routine use in clinical practice. However, this regimen, or one patterned on it, should be evaluated in combination with radiotherapy as the initial treatment for selected patients with previously untreated head and neck cancer.

Genetic and kinetic factors in the drug resistance of micrometastatic disease.

Of all of the potential scenarios described above the last is perhaps the most pessimistic or at least the one which will require the greatest advances in understanding and modulating tumor cell behaviour. If this type of phenomenon is indeed the basis of treatment failure in stage II breast cancer then it will be difficult to demonstrate this directly by any of the techniques currently available. If consistent application of the strategies dictated by other treatment failure scenarios fail to yield progressively improving results then one might have to infer this more pessimistic situation indirectly. This carries with it the implication that ultimate and truly satisfactory control of micro-metastatic breast cancer will have to await further fundamental discoveries involving the growth parameters and properties of tumor cells during the time when they exist as small isolated colonies.

New information on drug resistance: implications for the adjuvant treatment of breast cancer.

We would suggest on the basis of our analysis that drug resistance still appears to represent a plausible explanation for drug treatment failure in adjuvant breast chemotherapy. It may not be the only factor, but, if present, clearly has to be circumvented if treatment results are to be improved. Since it seems most unlikely that a new wonder drug for breast cancer will emerge in the next few years, then it is to our existing armamentarium of antineoplastic agents that we will have to turn for improved therapeutic results. Fundamental questions will need to be asked about what indeed are the most appropriate agents to be used in combination chemotherapy protocols for this disease and what are the optimal dose ratios. Our own institutional experience in a number of areas has suggested that many chemotherapeutic protocols that are widely used represent significant underdosing and that achieving optimal results requires pushing therapeutic agents closer to the reasonable limits of tolerance. Enhanced techniques for patient support during programs of more intensive chemotherapy are now available, and it has also been our experience that patients tolerate briefer, intensive programs of chemotherapy better than they do protracted, less intensive protocols. The role of new drug combinations that incorporate synergistic or significant biochemical modulation effects (i.e., platinum-etoposide, 5-fluorouracil-leucovorin) need to be examined in the context of the management of breast cancer. We appear to have reached something of a plateau with existing protocols and approaches, and it is time to move ahead.

Mathematical models to predict behaviour of tumours?

Mathematical modeling is an important tool in science that allows the investigator to examine phenomena that are not easily studied by direct experiment. The growth of neoplasms and their response to treatment are processes that appear particularly well suited for study by this approach. The ready availability of inexpensive powerful microcomputers and sophisticated software makes this research avenue open to all experimental and clinical oncologists.

Impact of dose-intense chemotherapy on the development of permanent drug resistance.

Using a somatic mutation theory for drug resistance, dose intense regimens are shown to be superior in increasing the likelihood of no doubly resistant cells and in curing the tumor. Consideration of this model suggests that dose intensity of early chemotherapy cycles should be calculated separately and correlated with treatment outcome.