Concepts in use of high-dose methotrexate therapy

In cancer chemotherapy, routine monitoring of drug concentrations has been practical only for methotrexate (MTX). The primary setting for pharmacokinetic monitoring of MTX is its use in high doses (HDMTX) for adjuvant therapy of osteosarcoma, for single-agent treatment of intracranial lymphomas, and in combination therapy of childhood leukemia as well as adult and pediatric non-Hodgkin lymphomas. Typically, HDMTX is infused in doses of 3-15 g/m2 over a period of 6-24 h. Precautions must be taken to ensure a high urine flow and an alkaline urine pH, so as to prevent precipitation of MTX in urine. Patients with decreased renal function, advanced in age, and taking nonsteroidal anti-inflammatory drugs or nephrotoxic agents are at increased risk of developing renal dysfunction during MTX infusion, thus being placed at high risk for toxicity. At the end of HDMTX infusion, and periodically thereafter for 24-48 h, drug concentrations are measured to assure that the disappearance rate of MTX from plasma is occurring at a normal rate. Also, at the end of HDMTX infusion, the patient is given leucovorin (5-formyl-tetrahydrofolic acid; LV), which replenishes intracellular stores of reduced folate and attenuates the toxicity secondary to HDMTX. In the presence of inappropriately high concentrations of MTX, routine doses of LV will be ineffective; the dose of LV required must be increased in proportion to the MTX concentration it faces in plasma. In practice, routine monitoring of plasma MTX concentrations allows early detection of abnormal clearance, as well as institution of early and effective countermeasures, including the use of increased and prolonged LV rescue.

Phase I and pharmacokinetic study of the multidrug resistance modulator dexverapamil with EPOCH chemotherapy

PURPOSE

Dexverapamil is a competitive inhibitor of the P-glycoprotein (Pgp) efflux pump, a potent mechanism of multidrug resistance (mdr-1) in vitro. We performed a phase I study to determine the maximum-tolerated dose (MTD) and pharmacokinetics of dexverapamil with etoposide, prednisone, vincristine, cyclophosphamide, and doxorubicin (EPOCH) chemotherapy.

PATIENTS AND METHODS

Eligible patients had relapsed or refractory lymphoma or sarcoma. Patients initially received EPOCH alone, and those with stable or progressive disease were crossed-over to received dexverapamil on subsequent cycles of EPOCH. Dexverapamil was administered orally for 6 days and escalated over eight dose levels ranging from 240 to 1,200 mg/m2/d. Pharmacokinetics of dexverapamil and its active metabolite, nor-dexverapamil, were obtained in most patients. In seven patients, pharmacokinetics of doxorubicin, doxorubicinol, and etoposide were determined on paired cycles of EPOCH with or without dexverapamil.

RESULTS

Sixty-five patients received 130 cycles of dexverapamil/EPOCH chemotherapy. The MTD of dexverapamil was 150 mg/m2 every 4 hours (900 mg/m2/d), and hypotension was the principal dose-limiting toxicity. The dexverapamil area under the curve (AUC) increased proportionally with dexverapamil dose, but significant interpatient variation occurred. At the MTD, the median plasma average concentrations of dexverapamil and nor-dexverapamil were 1.2 and 1.4 mumol/L, respectively. Dexverapamil did not affect the steady-state concentration (Css) of etoposide, but increased the Css of doxorubicin and doxorubicinol nearly twofold. The absolute neutrophil and platelet nadirs were significantly lower on the dexverapamil cycles compared with cycles of EPOCH alone, but other chemotherapy-related toxicities did not change.

CONCLUSION

The phase II recommended dose of dexverapamil with EPOCH is 150 mg/m2 every 4 hours. This dose was well tolerated on an outpatient basis and achieved plasma concentrations of dexverapamil and nor-dexverapamil within the effective range for Pgp inhibition in vitro. Although dexverapamil increased the hematopoietic toxicity of EPOCH, it was mild, readily reversible, and offset by EPOCH dose reductions. Dexverapamil should be considered for further study.

Modulation of multidrug resistance by dexverapamil in EPOCH-refractory lymphomas

We conducted a controlled trial of dexverapamil, an inhibitor of Pgp, in 45 Hodgkin's (HD) and 154 Non-Hodgkin's (NHL) lymphomas refractory to EPOCH chemotherapy. A total of 154 patients initially received EPOCH alone and (4.2%) with stable disease over two cycles or progressive disease "crossed over" to receive dexverapamil with EPOCH. Dexverapamil was escalated 8 dose levels, from 240 to 1200 mg/m2 per day. When possible, serial biopsies were obtained to measure MDR-1 expression by quantitative polymerase chain reaction. Median age was 44 years, 67% had stage IV disease, and median (range) prior regimens were 2 (1-12) in NHL and 1 (1-4) in HD. The maximum tolerated dose of dexverapamil was 900 mg/m2/day, and median plasma average concentrations of dexverapamil and nor-dexverapamil were 1.2 and 1.4 microM, respectively. There were 3 complete and 2 partial responses (12%) and 5 minor responses in NHL, and 2 of 10 HD patients achieved partial responses. MDR-1 was measured in 44 biopsies from 19 patients. Pre-therapy, MDR-1 was low (median 2.5 U) but increased (median 12.2 U) at cross-over. Among 6 patients with MDR-1 > 15, 3 responded to dexverapamil whereas only 1/8 patients with MDR-1 < 15 responded. EPOCH and dexverapamil were well tolerated. This study suggests that MDR-1 plays a role in clinical drug resistance of lymphomas, but also suggests that non-MDR-1 mechanisms are present in such patients. Earlier intervention with dexverapamil may be more effective and warrants further study.

Phase II study of paclitaxel in relapsed non-Hodgkin's lymphomas

PURPOSE

To assess the efficacy and toxicity of paclitaxel administered as a 96-hour infusion to patients with relapsed non-Hodgkin's lymphomas (NHLs).

PATIENTS AND METHODS

Eligible patients had relapsed NHL and measurable disease and were considered incurable. Paclitaxel was infused at a dose of 140 mg/m2 every 3 weeks. Premedications to prevent paclitaxel hypersensitivity reactions were not administered and no patients received corticosteroids. Expression of the multidrug resistance (mdr-1) gene was determined in tumor from 17 patients by mRNA quantitative polymerase chain reaction (PCR).

RESULTS

Thirty-one patients received a total of 99 cycles of paclitaxel. Two patients were not assessable for response. The median age was 50 years, 71% had stage IV disease, and intermediate/high-grade histology was present in 65% of patients. Patients had received a median of three prior chemotherapy regimens, and 68% of patients had responded to the previous chemotherapy (chemotherapy-sensitive). Of 29 assessable patients, five (17%) achieved a partial response (PR). With a median potential follow-up time of 17 months, the median event-free and overall survival durations were 1.6 and 7.5 months, respectively. No correlation was found between response to paclitaxel and extent of prior treatment or response. The mdr-1 gene was easily detectable in 14 of 17 tumor biopsies, but was low in all but one sample. The most serious toxicity was grade 4 neutropenia, which occurred during 14% of cycles.

CONCLUSION

Paclitaxel was well tolerated, but had a low response rate in patients with relapsed NHLs. There was no clear association between response to paclitaxel and extent of our response to prior treatment. Most patients had chemotherapy-sensitive disease, which suggests that the low response rate to paclitaxel was probably not due to general chemotherapy resistance. Paclitaxel provided good palliation in a minority of patients and is a reasonable agent to consider for use in patients who have failed to respond to standard chemotherapy.

The role of thymidylate synthase expression in prognosis and outcome of adjuvant chemotherapy in patients with rectal cancer

PURPOSE

We assessed the prognostic importance of the level of thymidylate synthase (TS) expression in patients with primary rectal cancer and whether, for Dukes' B and C cancer patients, the benefit of chemotherapy was associated with TS expression.

PATIENTS AND METHODS

The level of TS expression in the primary rectal cancers of 294 of 801 patients enrolled on protocol R-01 of the National Surgical Adjuvant Breast and Bowel Project (NSABP) was immunohistochemically assessed with the monoclonal antibody TS 106.

RESULTS

Forty-nine percent of patients whose tumors had low TS levels (n = 91) were disease free at 5 years compared with 27% of patients with high levels of TS (n = 203; P < .01). Moreover, 60% of patients with low TS levels were alive after 5 years compared with 40% of patients with high TS levels (P < .01). The level of TS protein was significantly associated with Dukes' stage (P < .01); patients with a more advanced Dukes' stage had a significantly higher level of TS. The level of TS expression remained prognostic for both disease-free survival (P < .01) and survival (P < .05) independent of Dukes' stage and other pathologic characteristics evaluated. Thirty-eight percent and 54% of patients with high TS levels (n = 71) were disease free and alive, respectively, after 5 years when treated with chemotherapy, compared with 17% and 31%, respectively, of similar patients when treated with surgery alone (n = 64) (P < .01). No difference was noted in disease-free survival (P = .46) or survival (P = .43) in patients with low TS levels.

CONCLUSION

The expression of TS is an important independent prognosticator of disease-free survival and survival in patients with rectal cancer. Adjuvant fluorouracil (5-FU)-based chemotherapy demonstrated significant improvement in disease-free and overall survival for patients with high TS levels. Prospective studies measuring TS levels will be needed to understand further the role of TS as a prognosticator of survival and chemotherapeutic benefit.

Biological basis for cancer treatment

The new knowledge of the regulation of cell growth and the genetic and biochemical changes that lead to malignancy have created many new opportunities for cancer drug discovery. These new targets include oncogenes, growth factors and their receptors, signal transduction pathways, and cell differentiation signals. Attempts to identify new therapies based on these targets can complement traditional drug discovery efforts that rely on high-volume screening of candidate natural products and synthetic chemicals against human tumor cell lines and against defined molecular reactions. Through modern computer-based data analysis, drug screening data can be used to establish mechanism of drug action of new agents; these analyses shed light on patterns of cross-resistance of new compounds and their interactions with defined molecular targets as well as allow selection of chemically and biologically unique agents as candidates for clinical development.

Decreased expression of the human folate receptor mediates transport-defective methotrexate resistance in KB cells

The human membrane-associated folate binding protein, or folate receptor (hFR), is a necessary component of folate and methotrexate (MTX) transport in some cell lines. To investigate the role of hFR in acquired MTX resistance in human cells, we characterized nine MTX-resistant clones selected from human nasopharyngeal epidermoid carcinoma (KB) cells (cells which transport folates/anti-folates via the hFR) cultured in media containing low folate concentrations. Compared with wild type KB cells, the level of resistance of the clones ranges from 2- to 80-fold higher and the resistant phenotypes of the clones are characterized as follows. 1) DHFR levels are increased (3-13-fold) in four of nine clones; 2) MTX polyglutamation is not detectably different; 3) the extents of MTX efflux are similar; 4) initial rates of MTX efflux are similar except for two clones which exhibit slightly faster efflux rates (approximately 2-fold); and 5) the Vmax for specific MTX and 5-methyltetrahydrofolate transport are decreased (2-18-fold) in all mutants. The Kt values for MTX transport of each mutant are similar to the Kt of KB cells. These results indicate that all nine MTX-resistant clones exhibit defective MTX transport and that four clones also have increased DHFR levels. Based on folic acid binding assays, the hFR is reduced by 1.8-24-fold in these clones relative to KB cell hFR expression. Western, Northern, and Southern analyses are consistent with decreased hFR expression in these clones rather than mutations, resulting in alterations in the size or ligand binding affinities of the hFR. The decrement in hFR expression correlates closely with the degree of reduction in MTX transport Vmax for each clone. Since folate and MTX influx proceed via hFR in KB cells and in these mutants, the correlation (R2 = 0.90) between hFR expression and the MTX transport Vmax of each clone indicates that hFR expression is an important determinant of acquired MTX resistance in this human tumor cell line. These studies demonstrate that defective transport (manifested by decreased Vmax) resulting from decreased expression of the hFR is frequent in KB cells cultured under these conditions and suggest that modulation of hFR may be relevant to MTX cytotoxicity or resistance in tissues or cells expressing functionally significant levels of hFR.

Age does not influence taxol dose intensity in recurrent carcinoma of the ovary

BACKGROUND

In the treatment of advanced-stage ovarian cancer, it is common practice to treat elderly patients in a less aggressive fashion than young patients. This approach is based on the notion that age is associated with poor patient tolerance to aggressive chemotherapy. Relatively little data exist to support this contention. The most exciting new chemotherapy agent to be developed in the last 10 years is taxol, a diterpeniod derivative of the Northwestern yew Taxus brevifolia.

METHODS

The ability to administer dose-intensive taxol to adult patients with recurrent ovarian cancer was assessed retrospectively, and the question was asked whether the administered dose intensity of taxol was unfavorably influenced by age. Forty-eight patients with recurrent ovarian carcinoma received taxol at an initial dose of 250 mg/m2 every 3 weeks. Age in this cohort ranged from 26 to 74 years, with a median of 55. Twenty-nine percent (14 of 48) of the patients treated were 61 years of age or greater. Criteria for administration of taxol included a creatinine clearance of > 45 ml/minute, minimal abnormalities in liver function tests, good performance status, and the absence of substantial comorbid disease.

RESULTS

Elderly patients in this cohort (age > 60 years) did not differ from younger patients with respect to administered dose intensity, number of cycles of therapy administered, or the occurrence of serious or mild toxicities.

Recent National Cancer Institute lymphoma trials of etoposide-containing combination chemotherapy

Short-course prednisone/doxorubicin/cyclophospha- mide/etoposide-cytarabine/bleomycin/vincristine/methotrexate (ProMACE-CytaBOM) contains the same drugs as standard ProMACE-CytaBOM but is delivered weekly for 16 weeks rather than 2 weeks out of 3 for 18 weeks. This results in a significant increase in dose intensity, ranging from 27% to 65% for all drugs. A total of 46 patients have been treated with short-course ProMACE-CytaBOM. The overall complete response rate of 91% and relapse rate of 17% compares favorably with results obtained using standard ProMACE-CytaBOM (86% and 27%, respectively). Toxicity was slightly greater with short-course therapy, but in general the regimen was well tolerated. Further dose intensification is possible in eligible patients by dose escalating myelotoxic drugs. A second strategy for augmenting the dose intensity is to deliver the drugs by continuous intravenous infusion. Infusional chemotherapy with doxorubicin/etoposide/vincristine/oral prednisone/bolus cyclophosphamide (EPOCH) results in significant antitumor activity in heavily pretreated patients with chemotherapy-resistant Hodgkin's disease and non-Hodgkin's lymphomas. Complete responses or partial responses were seen in 91% of 21 evaluable patients.

The National Cancer Institute: cancer drug discovery and development program

The discovery and development of novel therapeutic products for the treatment of malignancy is vitally important to those physicians responsible for the management of cancer patients. A description of the ongoing efforts at the National Cancer Institute (NCI) is intended to provide insight into those complex processes necessary to accomplish this mission. An update on the NCI's revised cancer screen is accompanied by a brief summary of those new agents scheduled to be entered into clinical investigation in the near future. The tremendous potential advantages and challenges associated with the use of a molecular approach to cancer drug design are discussed. Despite the differences of opinion that may exist regarding the optimal strategies for accomplishing the mission, there is no disagreement regarding the importance of the effort to find effective new therapies for cancer patients.

Production and characterization of monoclonal antibodies that localize human thymidylate synthase in the cytoplasm of human cells and tissue

Thymidylate synthase (TS; EC 2.1.1.45) is an important cellular enzyme that converts dUMP to dTMP, which is essential for DNA biosynthesis. In addition, TS is an important cellular target for the fluoropyrimidine cytotoxic drugs that are widely used in the treatment of solid tumors. We have generated five monoclonal antibodies against human TS using a recombinant human TS enzyme. These antibodies react specifically with human TS and display negligible cross-reactivity with other cellular proteins found in human cells. Binding affinity studies demonstrate that all antibodies form a tight interaction with recombinant human TS enzyme (Kd range = 0.3-11.0 nM). All antibodies display reactivity on enzyme-linked immunosorbent assay and immunoprecipitation. On Western blot analysis each detects a protein of approximately 36 kDa molecular mass under denaturing conditions. In addition to their reactivity on immunoprecipitation and Western analysis, two of the antibodies, TS 106 and TS 109, are reactive on immunohistochemical staining of human colon carcinoma cell lines and tissue, producing a granular cytoplasmic staining pattern. Specificity for TS is demonstrated by the lack of staining with preimmune IgG and the disappearance of the signal when the antibodies are preabsorbed with recombinant human TS enzyme. Quantitation of TS by Western blot analysis and biochemical FdUMP binding assay in 5-fluorouracil-resistant colon carcinoma cell lines (NCI H630R10, NCI H630R1) and a sensitive colon carcinoma cell line (NCI H630) revealed a 36- and 6-fold increase in TS in the resistant cell line as measured by the biochemical assay compared to a 39- and 10.6-fold increase as measured by densitometric analysis of the Western blot. These comparative studies of immunohistochemical, Western, and biochemical analyses reveal that the immunological detection of TS in human colon cell lines is a sensitive and quantitative assay. Thus the ability of these antibodies to detect TS in human cancer cells and tissue may allow measurement of TS in human tissues by quantitative immunohistochemistry in studies of drug resistance and for determination of proliferative rates.