Phase II study of topotecan (NSC 609 699) in patients with recurrent or metastatic soft tissue sarcoma

BACKGROUND

New drugs are needed for treatment of unresectable or metastatic soft tissue sarcoma. Topotecan, a semisynthetic derivative of the alkaloid, camptothecin, exerts its cytotoxic effect through inhibition of topoisomerase I.

PATIENTS AND METHODS

Thirty-two adult patients with locally advanced or metastatic soft tissue sarcoma entered this phase II study of topotecan, administered at 1.5 mg/m2/day IV x 5 days every 3 weeks. All had measurable disease and none had received previous chemotherapy.

RESULTS

There were 3 partial responses (10.3%; 95% CI 2.2-27.4%) in 29 evaluable patients. Grade 3 or 4 neutropenia occurred in 25 patients, and there was a 17% incidence of infection/neutropenic fever leading to one toxic death.

CONCLUSIONS

Topotecan, in this dose and schedule, has low activity in adult soft tissue sarcoma.

Role of leucovorin dosing and administration schedule

Leucovorin (LV) is commonly administered in association with 5-fluorouracil (5-FU) to enhance its cytotoxic effects. In this paper, the cellular and clinical pharmacology of 5-FU potentiation by LV are reviewed, and the dosing and administration schedules are discussed in relation to reported clinical trials. In vitro experimental data suggest that prolonged cellular exposures to relatively low LV concentrations simultaneously with prolonged 5-FU administration are the optimal conditions to enhance 5-FU efficacy. Clinical studies of 5-FU/LV in metastatic colorectal carcinoma have established that 5-day bolus 5-FU with low-dose bolus LV injections yield therapeutic benefits equivalent to those obtained with intravenous bolus schedules using higher doses of LV. It remains to be determined, however, if bolus administration schedules are the optimal clinical treatment regimens. Infusional 5-FU/LV regimens appear to be a strategy worthy of further clinical investigation.

Identification and characterization of human mitochondrial methenyltetrahydrofolate synthetase activity

We present evidence for the presence of the folate metabolism enzyme methenyltetrahydrofolate synthetase (MTHFS) in mitochondria. MTHFS activity was identified in the matrix of mitochondria purified from human liver biopsies. Mitochondrial and cytoplasmic MTHFS specific activities are similar, 85% of the total cellular MTHFS activity is in the cytoplasm and both native enzymes have similar molecular weights (approximately 25 kDa). Studies using purified mitochondrial MTHFS from CA46 human Burkitt lymphoma cells reveal that mitochondrial MTHFS behaves kinetically like the cytoplasmic enzyme with Km values of 4.7, 0.8 and 22 microM respectively for (6R,S)-5-formyltetrahydrofolate monoglutamate, (6S)-5-formyltetrahydrofolate pentaglutamate and ATP. This finding adds to previous observations that various folate-dependent enzymes reside in the mitochondria of eucaryotic cells. Intracellular tetrahydrofolate metabolism is highly compartmentalized and mitochondrial MTHFS activity is necessary for the entry of mitochondrial 5-formyltetrahydrofolate into the mitochondrial folate pool.

Leucovorin rescue of human cancer and bone marrow cells following edatrexate or methotrexate

We have examined the cytotoxic activities of edatrexate (EDX) and methotrexate (MTX) and their reversal by leucovorin in nine human cancer cell lines and in human bone marrow CFU-GM cells. EDX was 3.7- to 123-fold more toxic than MTX against the cancer cell lines and 25-fold against the bone marrow cells. Lower EDX concentrates generally were needed to inhibit cancer cell growth relative to bone marrow cells, however, whereas bone marrow and cancer cell growth were more often susceptible to the same MTX concentrations. The new antifolate was metabolized to long-chain polyglutamates to a greater extent than MTX in seven cell lines. Leucovorin at 0.2 microM rescued two breast cancer and two non-small cell lung cancer cell lines to a lesser extent following EDX than MTX, but significant rescue was observed in two head and neck cancer cell lines that formed large amounts of polyglutamates. These cell lines also accumulated reduced folates to a greater extent than the other cell lines following leucovorin exposure. Leucovorin rescued bone marrow cells following MTX but only partially following the highest EDX concentrations. EDX may enjoy a better therapeutic index than MTX against some cancer cell lines relative to bone marrow precursor cells, especially after leucovorin rescue.

Docetaxel in advanced renal carcinoma. A phase II trial of the National Cancer Institute of Canada Clinical Trials Group

BACKGROUND

Most patients diagnosed with renal carcinoma developed metastatic disease at some time during their course, with available therapy inducing response in only a small proportion of patients. Docetaxel (Taxotere, RP56976) a semi-synthetic analogue of paclitaxel with a broad range of in vitro antitumor activity, was evaluated in a phase II study.

METHODS

Eligibility criteria included histologically proven metastatic or advanced, bidimensionally measurable disease, no prior chemotherapy, immunotherapy, or hormonal therapy, adequate hematologic (neutrophils > or = 2.0 x 10(9)/L, platelets > or = 100 x 10(9)/L) and biochemical (serum creatinine and bilirubin < or = 1.5 x normal, transaminases < or = 3 x normal) parameters, WHO performance status of at least 2, and a life expectancy of > 12 weeks. Docetaxel was administered in a dose of 100 mg/m2 as a 1 hour intravenous infusion every 3 weeks. The first 2 patients entered onto the study were not premedicated for hypersensitivity reactions; subsequent patients received dexamethasone 10 mg and diphenhydramine 50 mg i.v. 30 minutes prior to docetaxel.

RESULTS

Twenty patients were entered onto the study, with 2 considered inevaluable for response. Sixty cycles of therapy were administered, with only 2 cycles delivered at a dose of 55 mg/m2 or less. No objective responses were seen; 1 patient demonstrated a mixed response. Neutropenia was significant, with 42/60 cycles developing grade 3/4 granulocytopenia. Fifty-five percent of patients demonstrated hypersensitivity reactions despite the premedication regimen employed, higher than that of the phase I studies which established the dose and schedule used in this trial.

CONCLUSIONS

1) Docetaxel is an ineffective agent in advanced renal carcinoma. 2) The high rate of hypersensitivity reactions suggests the need for more intensive premedication and/or slower infusion times at this dose level.

The importance of dose scheduling with mitoxantrone, 5-fluorouracil and leucovorin in metastatic breast cancer

We have studied a mitoxantrone, 5-fluorouracil (5-FU) and leucovorin chemotherapy regimen in metastatic breast cancer. 8 patients received mitoxantrone 10 mg/m2 on day 1, leucovorin 200 mg/m2 and 5-FU 300 mg/m2 on days 1-5 by intravenous bolus every 28 days in a pilot study. Grades 3-4 granulocytopenia followed 55% of the courses, with 2 patients admitted for febrile neutropenia. Only a 29% objective response rate was seen in a subsequent phase II trial using reduced mitoxantrone doses. Comparison with other trials suggested that 5-day bolus 5-FU administration adversely affects the combination's therapeutic index.

Phase I pharmacokinetic study of DUP-937, a new anthrapyrazole

DUP-937 is a new anthrapyrazole intercalator that inhibits DNA synthesis. A phase I trial was conducted in which DUP-937 was given in an intravenous bolus weekly for 3 weeks. Cycles were repeated every 5 weeks. Twenty men and 13 women with median ECOG performance status of 1 completed 74 cycles. The starting dose was 0.55 mg/m2/week and doses were escalated to 16 mg/m2/week. Non-hematological toxicity was generally mild or moderate and consisted mainly of gastro-intestinal effects, fatigue, alopecia and local reactions. Grade 3 neutropenia was first documented at 7.36 mg/m2 and became more common at higher dose levels. Three of four patients had > or = grade 3 neutropenia at the 16 mg/m2 dose level. Thrombocytopenia was minimal. The dose-limiting toxicity was neutropenia and the maximum tolerated dose was 16 mg/m2 weekly for 3 weeks. Mean area under the curve (AUC) values increased with dose. Linear pharmacokinetics were observed as total body clearance (CLtb), half-life (t1/2) and volume of distribution (Vss) did not change with increasing doses. One partial remission in a patient with prostate carcinoma was documented.

Factors that influence the therapeutic activity of 5-fluorouracil [6RS]leucovorin combinations in colon adenocarcinoma xenografts

The therapeutic activity of FUra alone or combined with [6RS]LV doses ranging from 50 to 1,000 mg/m2 was examined in eight colon adenocarcinoma xenografts, of which five were established from adult neoplasms (HxELC2, HxGC3, HxVRC5, HxHC1, and HxGC3/c1TK-c3 selected for TK deficiency) and three were derived from adolescent tumors (HxSJC3A, HxSJC3B, and HxSJC2). The growth-inhibitory effects of FUra were potentiated by higher doses of [6RS]LV (500-1,000 mg/m2) in three lines (HxGC3/c1TK-c3, HxSJC3A, and HxSJC3B) and by a low dose of [6RS]LV in only one tumor (HxVRC5). Expansion of pools of CH2-H4PteGlun+H4PteGlun (greater than or equal to 2.4-fold) in response to higher doses of [6RS]LV was obtained in all lines except HxHC1. Metabolism of [6RS]LV was high in HxVRC5, with high levels of 5-CH3-H4PteGlu being detected, but not in HxHC1, in which levels of 5-CH3-H4PteGlu and CH = H4PteGlu+10-CHO-H4PteGlu remained relatively low. In the adolescent tumors, levels of CH = H4PteGlu+10-CHO-H4PteGlu were consistently higher than those of 5-CH3-H4PteGlu following [6RS]LV administration, and in HxSJC3A, in which pools of CH2-H4PteGlun+H4PteGlun were significantly expanded, 5-CH3-H4PteGlu concentrations were lower than those observed in the other two lines. The sensitivity of tumors to FUra +/- [6RS]LV and the characteristics of [6S]LV metabolism did not correlate with the activity of CH = H4PteGlu synthetase, the enzyme responsible for the initial cellular metabolism of [6S]LV to CH = H4PteGlu. Thus, no single metabolic phenotype correlated with the [6RS]LV-induced expansion of CH2-H4PteGlun+H4PteGlun pools. Potentiation of the therapeutic efficacy of FUra by [6RS]LV was observed in HxGC3/c1TK-c3 xenografts but not in parent HxGC3 tumors, demonstrating the influence of dThd salvage capability in the response to FUra-[6RS]LV combinations. Plasma dThd concentrations in CBA/CaJ mice were high (1.1 microM). The present data therefore demonstrate the importance of (1) higher doses of [6RS]LV, (2) expansion of pools of CH2-H4PteGlun+H4PteGlun, and (3) dThd salvage capability in potentiation of the therapeutic efficacy of FUra in colon adenocarcinoma xenografts. The plasma levels of FUra achieved in mice are presented.

Lack of interference by the unnatural isomer of 5-formyltetrahydrofolate with the effects of the natural isomer in leucovorin preparations

Leucovorin, a mixture of the natural (6S) and unnatural (6R) diastereomers of 5-formyltetrahydrofolate, is administered clinically to enhance the antitumor activity of 5-fluorouracil. Because the 6R isomer persists at high concentrations in plasma for prolonged periods after iv leucovorin administration (J Clin Oncol 4:685-696, 1986), we have examined it to ascertain whether the 6R isomer could interfere with the cellular effects of the 6S isomer. The 6R compound had a poorer uptake into human CCRF-CEM lymphoblastic cells than the 6S compound, but the 6R compound could competitively inhibit the uptake of the natural isomer as determined in defined buffers. However, the 6R compound failed to interfere with cell growth support and enhancement of 5-fluorouracil cytotoxicity by the 6S isomer in CCRF-CEM cells in tissue culture experiments at concentrations up to 1 mM. Thus, the unnatural isomer of 5-formyltetrahydrofolate present in leucovorin preparations seems unlikely to have clinically relevant consequences.

Methenyltetrahydrofolate synthetase prevents the inhibition of phosphoribosyl 5-aminoimidazole 4-carboxamide ribonucleotide formyltransferase by 5-formyltetrahydrofolate polyglutamates

Methenyltetrahydrofolate synthetase (EC 6.3.3.2) catalyzes the irreversible ATP and Mg2+-dependent transformation of 5-formyltetrahydrofolate (N5-HCO-H4-pteroylglutamic acid (PteGlu] to 5,10-methenyltetrahydrofolate. The physiological function of this reaction remains unknown even though it is potentially involved in the intracellular metabolism of the large doses of N5-HCO-H4-PteGlu (leucovorin) administered to cancer patients. We have tried to elucidate methenyltetrahydrofolate synthetase's physiological role by examining the consequences of its inhibition in MCF-7 human breast cancer cells by the folate analog 5-formyltetrahydrohomofolate (fTHHF), a potent competitive inhibitor with a Ki of 1.4 microM. fTHHF inhibited MCF-7 cell growth with an IC50 of 2.0 microM during 72-h exposures, and this effect was fully reversible by hypoxanthine but not thymidine, indicating specific inhibition of de novo purine synthesis. A correlation was observed between increases in intracellular N5-HCO-H4-PteGlu concentrations following fTHHF and cell growth inhibition. De novo purine synthesis was inhibited at the second folate-dependent enzyme, phosphoribosyl aminoimidazole-carboxamide formyltransferase (AICAR transferase; EC 2.1.2.3), as determined by aminoimidazole carboxamide rescue and azaserine inhibition studies. N5-HCO-H4-PteGlu pentaglutamate was a potent inhibitor of purified MCF-7 cell AICAR transferase with a Ki of 3.0 microM while the monoglutamate was not an inhibitor up to 10 microM and fTHHF was only weakly inhibitory with a Ki of 16 microM. These findings suggest that methenyltetrahydrofolate synthetase activity is needed to prevent de novo purine synthesis inhibition by N5-HCO-H4-PteGlu polyglutamates.

A phase I study of trimetrexate, an analog of methotrexate, administered monthly in the form of nine consecutive daily bolus injections

Trimetrexate glucuronate (TMTX) is a methotrexate (MTX) analog that is active against transport-deficient MTX-resistant tumor cells. We performed a phase I study of TMTX administered by daily bolus for 9 consecutive days since this schedule is one of the most active in experimental murine tumor models. The drug was administered in this fashion every 4 weeks for at least two cycles. Fifteen patients with refractory metastatic cancers were studied and all had received prior chemotherapy. The dose-limiting toxicity was a rapidly reversible thrombocytopenia first seen at a daily dose of 4.0 mg/m2 which occurred 7 days after the end of TMTX administration. There was great inter- and intrapatient variability in the platelet nadirs observed in the six patients treated at 4.0 mg/m2. One patient died of massive hemoptysis during a platelet nadir at that dose level. Granulocyte counts never dropped below 1500/mm3. Only one patient had significant non-hematological toxicity: a radiation recall skin toxicity along with a self-limited maculopapular rash. One patient with melanoma and lung metastases treated at 4.0 mg/m2 had a partial response. TMTX plasma levels were measured by HPLC every 3 days prior to daily dosing in patients receiving 4 mg/m2 to determine whether drug accumulation occurred during this prolonged administration schedule. Nadir drug levels varied from less than 0.02 to 0.35 microM and did not seem to increase during the 9-day schedule in individual patients. By comparison with other phase I trials, the hematologic toxicity of TMTX seems to be schedule-dependent, with less drug being tolerated and more severe thrombocytopenia observed with more protracted treatment protocols. A firm phase II starting dose for daily bolus X 9 schedules is difficult to recommend in view of the variable toxicity observed in the patients treated at 4.0 mg/m2 daily, who, in addition, had all been extensively pretreated. A reasonable starting dose might be 3.0 mg/m2 daily with built-in dosage increases or decreases.

Human liver methenyltetrahydrofolate synthetase: improved purification and increased affinity for folate polyglutamate substrates

Methenyltetrahydrofolate synthetase (5-formyltetrahydrofolate cyclodehydrase (cyclo-ligase) (ADP-forming) EC 6.3.3.2) catalyzes the ATP- and Mg2+-dependent transformation of 5-formyltetrahydrofolate (leucovorin) to 5,10-methenyltetrahydrofolate. The enzyme has been purified 49,000-fold from human liver by a two-column procedure with Blue Sepharose followed by folinate-Sepharose chromatography. It appears as a single band both on SDS-polyacrylamide gel electrophoresis (Mr 27,000) and on isoelectric focusing (pI = 7.0) and is monomeric, with a molecular weight of 27,000 on gel filtration. Initial-velocity studies suggest that the enzyme catalyzes a sequential mechanism and at 30 degrees C and pH 6.0 the turnover number is 1000 min-1. The enzyme has a higher affinity for its pentaglutamate substrate (Km = 0.6 microM) than for the monoglutamate (Km = 2 microM). The antifolate methotrexate has no inhibitory effect at concentrations up to 350 microM, while methotrexate pentaglutamate is a competitive inhibitor with a Ki = 15 microM. Similarly, dihydrofolate monoglutamate is a weak inhibitor with a Ki = 50 microM, while the pentaglutamate is a potent competitive inhibitor with a Ki of 3.8 microM. Thus, dihydrofolate and methotrexate pentaglutamates could regulate enzyme activity and help explain why leucovorin fails to rescue cells from high concentrations of methotrexate.

5-Fluorouracil-metronidazole combination therapy in metastatic colorectal cancer. Clinical, pharmacokinetic and in vitro cytotoxicity studies

We have investigated the role of metronidazole (MND) combined with 5-fluorouracil (5-FU) in the treatment of metastatic colorectal cancer. MND (750 mg/m2) was administered i.v. 1 h before 5-FU (600 mg/m2) i.v., daily for 5 consecutive days. Treatment was repeated every 4 weeks until disease progression or prohibitive toxicity occurred. Of the 27 patients entered in the study, 4 (15%) had an objective complete or partial response lasting an average of 7 months. 5-FU toxicity was greatly enhanced by the administration of MND, however, 74% of patients having granulocytopenia (less than 1500/microliter). We investigated the possible mechanisms underlying this enhanced 5-FU toxicity by examining whether MND modified 5-FU pharmacokinetics or whether the two drugs had a synergistic effect in vitro against the HCT-8 colon cancer cell line. While the in vitro studies failed to reveal any synergism between 5-FU and MND, pharmacokinetic evaluation revealed that 5-FU clearance was significantly reduced (26.9%, P less than 0.001) by prior MND administration. MND reduces 5-FU's therapeutic index in the treatment of colorectal cancer by impairing its clearance, which leads to increased toxicity without enhanced therapeutic efficacy.

Regulation of dihydrofolate reductase in human breast cancer cells and in mutant hamster cells transfected with a human dihydrofolate reductase minigene

The regulation of dihydrofolate reductase (DHFR) gene expression was studied in gene-amplified, estrogen-responsive human breast cancer cells (MTX MCF-7). Previous studies have shown that estrogen increases, whereas tamoxifen decreases the rate of DHFR enzyme synthesis resulting in corresponding changes in the level of this enzyme. DHFR levels also increase following incubation with methotrexate (MTX), an effect which is dependent on both the concentration of extracellular drug and the duration of exposure and which occurs at concentrations that are insufficient to inhibit cell growth. MTX, like estrogen and tamoxifen, has no apparent effect on the rate of DHFR enzyme degradation. The increase in DHFR in response to MTX is additive with that of estrogen and is not prevented by tamoxifen. Whereas hormone-mediated changes in DHFR are associated with changes in the level of DHFR mRNA, there is no apparent change in DHFR mRNA concentrations in cells exposed to MTX. The regulation of DHFR enzyme levels was also studied in gene-deleted Chinese hamster ovary cells which were transfected with a functional human DHFR minigene constructed from human DHFR genomic and cDNA sequences. Incubation with MTX increases DHFR levels in Chinese hamster ovary cells transfected with the human DHFR minigene but has no effect in cells transfected with a DHFR minigene which uses a viral promotor and polyadenylation signal. Thus, the human DHFR minigene contains sequences other than the protein coding region which effect the regulation of this gene by MTX.

Sensitive analysis of asparagine and glutamine in physiological fluids and cells by precolumn derivatization with phenylisothiocyanate and reversed-phase high-performance liquid chromatography

The analytical methodologies for the determination of free amino acids in plasma, serum, erythrocytes and leukemic cells are described. Deproteinization of the sample by methanol or organic acids is followed by derivatization with phenylisothiocyanate to form stable phenylthiocarbamylamino acid derivatives. The derivatives are separated by reversed-phase high-performance liquid chromatography in 80 min using a 5-microns C18 column (250 X 4 mm I.D.) and monitored by ultraviolet detection at 254 nm. Twenty physiological amino acids are resolved and quantified in plasma and erythrocyte samples. The resolution and sensitivity of the analytical method permitted unequivocal quantification of very low asparagine and glutamine levels in leukemic cells and growth media following treatment with asparaginase and glutaminase enzymes despite the presence of high aspartic and glutamic acid levels.

Determinants of the sensitivity of human small-cell lung cancer cell lines to methotrexate

We have characterized the determinants of methotrexate (MTX) responsiveness in eight patient-derived cell lines of small-cell lung cancer (SCLC). Clonogenic survival was correlated with factors known to affect sensitivity to drug. NCI-H209 and NCI-H128 were most drug sensitive, with drug concentrations required to inhibit clonogenic survival by 50% with less than 0.1 microM MTX. Six cell lines (NCI-H187, NCI-H345, NCI-H60, NCI-H524, NCI-H146, and NCI-N417D) were relatively drug resistant. In all cell lines studied, higher molecular weight MTX-polyglutamates (MTX-PGs) with 3-5 glutamyl moieties (MTX-Glu3 through MTX-Glu5) were selectively retained. Relative resistance to low (1.0 microM) drug concentrations appeared to be largely due to decreased intracellular metabolism of MTX. Five of the six resistant lines were able to synthesize polyglutamates at higher (10 microM) drug concentrations, although one resistant cell line (NCI-N417D) did not synthesize higher molecular weight MTX-PGs, even after exposure to 10 microM drug. Two cell lines with resistance to 10 microM MTX (NCI-H146 and NCI-H524) synthesized and retained higher molecular weight MTX-PGs in excess of binding capacity after exposure to 10 microM drug. However, the specific activity of thymidylate synthase in these cell lines was low. MTX sensitivity in patient-derived cell lines of SCLC requires the ability of cells to accumulate and retain intracellular drug in the form of polyglutamate metabolites in excess of dihydrofolate reductase, as well as a high basal level of consumption of reduced folates in the synthesis of thymidylate.