Real-world benefit of nivolumab in a Canadian non-small-cell lung cancer cohort

Background

Nivolumab was the first immuno-oncology agent available for the treatment of lung cancer in Canada. In the present study, we evaluated the real-world benefit of nivolumab in Canadian patients with lung cancer.

Methods

Patients included in the cohort were identified from a registry of patients treated through expanded access to nivolumab before and after Health Canada approval. Demographics were collected from the application forms. Outcome data for the duration of treatment and survival were collected retrospectively.

Results

In contrast to the randomized clinical trial populations, our study cohort included patients who were older (median age: 66 years; range: 36-92 years) and who had an Eastern Cooperative Oncology Group performance status of 2 (8.9%). Despite the poorer-prognosis cohort, median overall survival was 12.0 months, which is comparable to the survival demonstrated in the randomized phase iii trials of nivolumab in lung cancer. Median time to treatment discontinuation was 3.45 months and was similar for all patient subgroups, including poorer-prognosis groups such as those with a performance status of 2, those 75 years of age and older, and those with brain metastases.

Conclusions

Nivolumab given in a real-world clinical setting was associated with results similar to those reported in the phase iii clinical trial setting.

A phase I trial of AEG35156 (XIAP antisense) administered as a continuous intravenous infusion in patients with advanced tumors

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Background: The X-linked inhibitor of apoptosis (XIAP) is a potent anti-apoptotic protein. AEG35156 is a synthetic 2nd generation antisense oligonucleotide to human XIAP that enhances cancer cell apoptosis preclinically as a single agent and in combination with chemotherapeutics. Methods: The primary objective was to establish the maximum tolerated dose (MTD) of AEG35156 given as a 7-day continuous infusion every 3 weeks. Other objectives were to determine AEG35156 pharmacokinetics, XIAP inhibition in peripheral blood mononuclear cells and in tumour cells where feasible and document anti-tumour activity. Results: Sixteen adult patients have completed at least one 7-day infusion. Two dose-limiting toxicities (DLT) were observed in five patients treated at 160 mg/m2/day: grade 3 thrombocytopenia for more than 7 days and grade 3 ALT and AST elevation. Seven patients have been treated at 125 mg/m2/day with one DLT of grade 3 transaminase elevation. An approximately 50% decrease in XIAP mRNA was seen in peripheral blood leucocytes three days after the start of infusions at 160mg/m2/day. One patient with small lymphocytic non-Hodgkin’s lymphoma had marked but short lived decreases in peripheral lymphoblasts during AEG35156 administration closely associated with XIAP mRNA knockdown. One patient with breast cancer had an unconfirmed partial response. The trial has now been amended to also determine the MTD of a 3-day continuous infusion every 3 weeks. Three patients have been treated with 3-day infusions at 160mg/m2/day every 3 weeks with no significant toxicities observed and patients are currently being accrued at 213mg/m2/day. Conclusions: AEG35156 can be safely delivered by continuous infusion and preliminary evidence of XIAP mRNA knockdown and antitumour activity has been observed.

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Phase II Study of Troxacitabine (BCH-4556) in Patients with Advanced Non-Small-Cell Lung Cancer

Troxacitabine. a promising new L-nucleoside, inhibits DNA polymerase and leads to complete DNA chain termination. The National Cancer Institute of Canada Clinical Trials Group (NCIC-CTG) conducted a phase II study to assess the efficacy and toxicity of troxacitabine in untreated patients with advanced non-small-cell lung cancer (NSCLC). Previously untreated patients were eligible if they had inoperable stage IIIB or IV NSCLC, ECOG PS < or = 2, adequate hematology and biochemistry, and at least one bidimensionally measurable lesion. Patients with prior malignancy or brain metastases were excluded. Troxacitabine (10 mg/m(2)) was administered intravenously over 30 minutes every 3 weeks. Between June 1999 and May 2000, 17 eligible patients received treatment. Patient characteristics included: median age 64 years; female 41%; stage IV (94%); PS 0 (12%), 1 (59%), and 2 (29 %), 3 or more disease sites (59%). In 17 patients, there were 8 stable disease, 9 disease progression, and no objective responses. Median duration of stable disease was 3.6 months (range = 2.0-7.1). A total of 56 cycles were administered (median = 3), and 88% of patients received 90% or more of the planned dose intensity. The majority (82%) of patients experienced skin rash. Hematologic and biochemical toxicities, grade 3/4 (%) were: granulocytopenia (41), anemia (12), thrombocytopenia (6), and hyperglycemia (6). Troxacitabine appears to have little activity in NSCLC in the dose and schedule tested.

Phase II study of troxacitabine in chemotherapy-naïve patients with advanced cancer of the pancreas

BACKGROUND

Troxacitabine (Troxatyl) is a novel L-enantiomer nucleoside analog with activity in pancreatic cancer xenograft models.

PATIENTS AND METHODS

Troxacitabine 1.5 mg/m(2) was administered by 30-min infusions daily x5 every 4 weeks to 54 patients with advanced pancreatic cancer. Patients were evaluated for objective tumor response, time to tumor progression (TTP), changes in tumor marker CA 19-9, survival, safety, pain, analgesic consumption, Karnofsky performance status and weight change.

RESULTS

Median TTP was 3.5 months (95% CI 2.0-3.8), median survival 5.6 months (95% CI 4.9-7.4), and the 1 year survival rate 19%. Best responses were stable disease in 24 patients with eight patients having stable disease for at least 6 months (15%). A 50% or greater decrease in CA 19-9 was seen in seven of 44 assessed patients (16%). Grade 3 and 4 neutropenia were observed in 37% and 30% of patients with one episode of febrile neutropenia. The most common drug-related non-hematological toxic effects reported were cutaneous, with 22% and 6% of patients reporting grade 2 and 3 skin rash, respectively and 4% grade 2 hand-foot syndrome.

CONCLUSION

Troxacitabine administered by a bolus daily x5 monthly regimen has modest activity in advanced pancreatic adenocarcinoma.

Phase II study of troxacitabine (BCH-4556) in patients with advanced and/or metastatic renal cell carcinoma: a trial of the National Cancer Institute of Canada-Clinical Trials Group

PURPOSE

A multi-institution phase II study was undertaken by National Cancer Institute of Canada-Clinical Trials Group to evaluate the efficacy and toxicity of intravenous troxacitabine (Troxatyl; Shire Pharmaceuticals Plc, Laval, Quebec, Canada), in patients with renal cell carcinoma.

PATIENTS AND METHODS

Between June 1999 and March 2000, 35 patients (24 male) with a mean age of 60 years who had advanced and/or metastatic disease were treated with troxacitabine given as an intravenous infusion over 30 minutes at a dose of 10 mg/m2 intravenously, once every 3 weeks.

RESULTS

Of the 33 of 35 patients evaluable for response, there were two confirmed partial responses, 21 patients had stable disease (median duration, 4.4 months), and 10 patients had progressive disease. Eight patients remained stable for more than 6 months, of whom six remain free of progression. The most common drug-related nonhematologic toxicities observed were skin rash (77.1%), hand-foot syndrome (68.6%), alopecia (51.4%), fatigue (51.4%), and nausea (57.1%). Out of a total of 145 cycles of treatment, 98 were given without steroid premedication, whereas 47 cycles were given with steroid premedication. Without premedication, skin rash occurred in 37% of cycles compared with 26% when steroids were given prophylactically.

CONCLUSION

Troxacitabine given at a dose of 10 mg/m2 once every 3 weeks was well tolerated in patients with metastatic renal cell cancer, with common toxicities being a moderate to severe granulocytopenia and skin rash. Steroid premedication may reduce the frequency and severity of the skin rash. Our current study suggests that the nucleoside analog troxacitabine may have modest activity against renal cell carcinoma; however, larger studies are required to confirm this.

The palliative benefit of irinotecan in 5-fluorouracil-refractory colorectal cancer: its prospective evaluation by a Multicenter Canadian Trial

Most patients with colorectal cancer (CRC) who have failed initial 5-fluorouracil (5-FU) chemotherapy have worsening of disease-related symptoms (DRS) and quality of life (QOL). Irinotecan has a reported response rate of 10%-20% in such patients. The aim of this phase II trial was to prospectively determine the palliative benefit of irinotecan utilizing DRS as primary endpoints of response. Patients had advanced CRC refractory to 5-FU with at least 1 DRS defined as (1) Karnofsky performance status (KPS) 60%-80%, (2) baseline analgesic use > or = 10 mg morphine/day (or equivalent), or (3) disease-related pain score > 1 cm on a 10-cm linear analogue self-assessment (LASA) scale. Patients received irinotecan 125 mg/m2 weekly for 4 weeks on an every-6-weeks schedule. The primary endpoint was palliative response defined as > or = 50% decrease in pain score or analgesic usage, or 10% increase in KPS, from baseline for 4 weeks. QOL was assessed by the European Organization for Research and Treatment of Cancer Quality-of-Life Questionnaire Core 30 (EORTC QLQ-C30) version 2 instrument. A total of 65 patients were entered onto the study. Median baseline parameters were KPS 70%, analgesic score 11 mg/day, and pain score 2.4 cm. A palliative response was achieved in 27 patients (42%), improvement in pain score predominated. LASA and EORTC QLQ-C30 instruments showed parallel changes in DRS. The radiological response rate was 11% (complete responses and partial responses, n = 46); 23 patients achieved stable disease. Median overall survival was 7.2 months. Irinotecan provides a rate of palliative benefit higher than the radiological response rate. Patients-oriented palliative endpoints can be useful in assessing the benefit of agents in early-phase clinical trials.

Mechanisms of uptake and resistance to troxacitabine, a novel deoxycytidine nucleoside analogue, in human leukemic and solid tumor cell lines

Troxacitabine (Troxatyl; BCH-4556; (-)-2'-deoxy-3'-oxacytidine), a deoxycytidine analogue with an unusual dioxolane structure and nonnatural L-configuration, has potent antitumor activity in animal models and is in clinical trials against human malignancies. The current work was undertaken to identify potential biochemical mechanisms of resistance to troxacitabine and to determine whether there are differences in resistance mechanisms between troxacitabine, gemcitabine, and cytarabine in human leukemic and solid tumor cell lines. The CCRF-CEM leukemia cell line was highly sensitive to the antiproliferative effects of troxacitabine, gemcitabine, and cytarabine with inhibition of proliferation by 50% observed at 160, 20, and 10 nM, respectively, whereas a deoxycytidine kinase (dCK)-deficient variant (CEM/dCK(-)) was resistant to all three drugs. In contrast, a nucleoside transport-deficient variant (CEM/ARAC8C) exhibited high levels of resistance to cytarabine (1150-fold) and gemcitabine (432-fold) but only minimal resistance to troxacitabine (7-fold). Analysis of troxacitabine transportability by the five molecularly characterized human nucleoside transporters [human equilibrative nucleoside transporters 1 and 2, human concentrative nucleoside transporter (hCNT) 1, hCNT2, and hCNT3] revealed that short- and long-term uptake of 10-30 microM [(3)H]troxacitabine was low and unaffected by the presence of either nucleoside transport inhibitors or high concentrations of nonradioactive troxacitabine. These results, which suggested that the major route of cellular uptake of troxacitabine was passive diffusion, demonstrated that deficiencies in nucleoside transport were unlikely to impart resistance to troxacitabine. A troxacitabine-resistant prostate cancer subline (DU145(R); 6300-fold) that exhibited reduced uptake of troxacitabine was cross-resistant to both gemcitabine (350-fold) and cytarabine (300-fold). dCK activity toward deoxycytidine in DU145(R) cell lysates was <20% of that in DU145 cell lysates, and no activity was detected toward troxacitabine. Sequence analysis of cDNAs encoding dCK revealed a mutation of a highly conserved amino acid (Trp(92)-->Leu) in DU145(R) dCK, providing a possible explanation for the reduced phosphorylation of troxacitabine in DU145(R) lysates. Reduced deamination of deoxycytidine was also observed in DU145(R) relative to DU145 cells, and this may have contributed to the overall resistance phenotype. These results, which demonstrated a different resistance profile for troxacitabine, gemcitabine, and cytarabine, suggest that troxacitabine may have an advantage over gemcitabine and cytarabine in human malignancies that lack or have low nucleoside transport activities.

Troxacitabine, a novel dioxolane nucleoside analog, has activity in patients with advanced leukemia

PURPOSE

To investigate the toxicity profile, activity, and pharmacokinetics of a novel L-nucleoside analog, troxacitabine (BCH-4556), in patients with advanced leukemia.

PATIENTS AND METHODS

Patients with refractory or relapsed acute myeloid (AML) or lymphocytic (ALL) leukemia, myelodysplastic syndromes (MDS), or chronic myelogenous leukemia in blastic phase (CML-BP). Troxacitabine was given as an intravenous infusion over 30 minutes daily for 5 days. The starting dose was 0.72 mg/m(2)/d (3.6 mg/m(2)/course). Courses were given every 3 to 4 weeks according to toxicity and antileukemic efficacy. The dose was escalated by 50% until grade 2 toxicity was observed, and then by 30% to 35% until the dose-limiting toxicity (DLT) was defined.

RESULTS

Forty-two patients (AML: 31 patients; MDS: six patients [five MDS + one CMML]; ALL: four patients; CML-BP: one patient) were treated. Median age was 61 years (range, 23 to 79 years), and 29 patients were males. Stomatitis and hand-foot syndrome were the DLTs. The MTD was defined as 8 mg/m(2)/d. The pharmacokinetic behavior of troxacitabine is linear over the dose range of 0.72 to 10.0 m/m(2). Approximately 69% of troxacitabine was excreted as unchanged drug in the urine. Marrow hypoplasia occurred between days 14 and 28 in 73% of AML patients. Three complete remissions and one partial remission were observed in 30 assessable AML patients. One MDS patient achieved a hematologic improvement. A patient with CML-BP achieved a return to chronic phase disease.

CONCLUSION

Troxacitabine has a unique metabolic and pharmacokinetic profile and significant antileukemic activity. DLTs were stomatitis and hand-foot syndrome. Troxacitabine merits further study in hematologic malignancies.

The new dioxolane, (-)-2'-deoxy-3'-oxacytidine (BCH-4556, troxacitabine), has activity against pancreatic human tumor xenografts

There is a great need for new therapeutic agents for patients with advanced pancreatic cancer. The new dioxolane analogue troxacitabine was evaluated in two human pancreatic cancer xenograft models. The models used included the Panc-01 and MiaPaCa pancreatic cancer cell lines. Whereas there is certainly no absolute evidence that either of the in vivo models is predictive for clinical activity, there is at least some evidence that they may be helpful in selecting agents for clinical trials in patients with pancreatic cancer. Troxacitabine was administered i.v. to the animals at doses of 10 and 25 mg/kg on a daily x 5 regimen. Gemcitabine was used as a positive control. The end points for the study included tumor growth inhibition (TGI), final weight, and the number of partial and complete tumor responses in the animals. Troxacitabine was highly active against the Panc-01 model (n = 8), with TGI levels of 88.5% and 84.3% at the 10 and 25 mg/kg doses, respectively. The mean final tumor weights for animals given troxacitabine were also significantly smaller (P < 0.001) compared with vehicle controls. At the 10 mg/kg dose, there were three partial tumor shrinkages and one complete tumor shrinkage, whereas at the 25 mg/kg dose, there were three partial tumor shrinkages. Troxacitabine had less activity against the MiaPaCa model (n = 10) and, by traditional response criteria, would be considered inactive, with TGIs of 4% and 22.7% at the 10 and 25 mg/kg dose level, respectively. Of note is that in comparison with gemcitabine, troxacitabine was more efficacious against Panc-01 and was equally active against MiaPaCa. These in vivo results are encouraging and support the prospect of performing Phase II and perhaps Phase III trials with troxacitabine in patients with advanced pancreatic cancer.

Phase II study of first-line LY231514 (multi-targeted antifolate) in patients with locally advanced or metastatic colorectal cancer: an NCIC Clinical Trials Group study

BACKGROUND

Metastatic colon cancer is difficult to treat with treatment being palliative and with little effect on survival. This trial has evaluated the effects of LY231514 (Multitargeted antifolate (MTA)) given to previously untreated patients with recurrent or metastatic colorectal carcinoma.

PATIENTS AND METHODS

All patients were required to have a histological diagnosis of colorectal adenocarcinoma with measurable disease and no prior chemotherapy for metastatic disease. Patients had to have had performance status of 0-2, pretreatment absolute granulocyte count of > or = 1.5 x 10(9)/l and a platelet count of > or = 150 x 10(9)l. Patients received MTA at a dose of 600 mg/m2 by 10 minute infusion on day 1 repeated every 21 days. After the first 9 patients, this dose was reduced down to 500 mg/m2 every 21 days because of toxicity. Doses of MTA were modified depending on nadir counts.

RESULTS

Thirty-two eligible patients were enrolled and twenty-nine were evaluable for response. Three patients did not have repeat radiological testing to determine response because they went off study after only one cycle of treatment due to toxicity. In the 29 evaluable patients, there was 1 complete response, 4 partial responses and 14 patients with stable disease. Response rate was 17.2% (95% confidence intervals: 5.8%-35.8%). All responses occurred in the patients receiving a starting dose of MTA 500 mg/m2. Median time to progression for all eligible patients was 3.3 months. The most common toxicities experienced were mild to moderate fever, lethargy, anorexia, nausea, vomiting, stomatitis, abdominal pain, diarrhea, and skin rash. There was one death due to sepsis.

CONCLUSION

Single-agent MTA at 500 mg/m2 given every three weeks has modest activity in metastatic colorectal carcinoma.

5-Formyltetrahydrofolate regulates homocysteine remethylation in human neuroblastoma

The metabolic role of 5-formyltetrahydrofolate is not known; however, it is an inhibitor of several folate-dependent enzymes including serine hydroxymethyltransferase. Methenyltetrahydrofolate synthetase (MTHFS) is the only enzyme known to metabolize 5-formyltetrahydrofolate and catalyzes the conversion of 5-formyltetrahydrofolate to 5,10-methenyltetrahydrofolate. In order to address the function of 5-formyltetrahydrofolate in mammalian cells, intracellular 5-formyltetrahydrofolate levels were depleted in human 5Y neuroblastoma by overexpressing the human cDNA encoding MTHFS (5YMTHFS cells). When cultured with 2 mM exogenous glycine, the intracellular serine and glycine concentrations in 5YMTHFS cells are elevated approximately 3-fold relative to 5Y cells; 5YMTHFS cells do not contain measurable levels of free methionine and display a 30-40% decrease in cell proliferation rates compared with 5Y cells. Medium supplemented with pharmacological levels of exogenous folinate or methionine ameliorated the glycine induced growth inhibition. Analysis of the folate derivatives demonstrated that 5-methyltetrahydrofolate accounts for 30% of total cellular folate in 5Y cells when cultured with 5 mM exogenous glycine. 5YMTHFS cells do not contain detectable levels of 5-methyltetrahydrofolate under the same culture conditions. These results suggest that 5-formyltetrahydrofolate inhibits serine hydroxymethyltransferase activity in vivo and that serine synthesis and homocysteine remethylation compete for one-carbon units in the cytoplasm.

Mitoxantrone, 5-fluorouracil, and high dose leucovorin (NFL) versus intravenous cyclophosphamide, methotrexate, and 5-fluorouracil (CMF) in first-line chemotherapy for patients with metastatic breast carcinoma: a randomized phase II trial

BACKGROUND

Previous Phase II studies using the combination of mitoxantrone, 5-fluorouracil, and high dose leucovorin (NFL) in the treatment of metastatic breast carcinoma have shown this regimen to be active and well tolerated. In this randomized Phase II study, the authors compared the NFL regimen with a standard CMF regimen in the first-line therapy of patients with metastatic breast carcinoma.

METHODS

One hundred twenty-eight women receiving their first chemotherapy for metastatic breast carcinoma were entered into this randomized study. Sixty-four patients were treated with NFL: mitoxantrone 12 mg/m2 IV on Day 1; leucovorin 300 mg IV over 30-60 minutes on Days 1, 2, and 3, immediately preceding administration of 5-fluorouracil; and 5-fluorouracil 350 mg/m2 IV bolus on Days 1, 2, and 3. Sixty-four patients received CMF: cyclophosphamide 600 mg/m2 IV on Day 1; methotrexate 40 mg/m2 IV on Day 1; and 5-fluorouracil 600 mg/m2 IV on Day 1. Both regimens were repeated at 21-day intervals; responding patients received at least 8 courses.

RESULTS

Patients treated with NFL had a higher response rate than patients treated with the CMF regimen (45% vs. 26%, respectively; P = 0.021). Median duration of response was 9 months with NFL and 6 months with CMF (P = 0.10); 11 patients had long responses (>12 months) with NFL versus 4 patients with CMF (P = 0.06). Median survival was similar for both groups. Both regimens were well tolerated, with infrequent Grade 3 or 4 toxicities.

CONCLUSIONS

NFL is an active, well-tolerated regimen for the treatment of metastatic breast carcinoma; it produced a higher response rate than the CMF regimen used in this study. Although more intense CMF regimens or regimens containing doxorubicin would likely increase the response rate, they would almost certainly do so with the consequence of greater toxicity as compared with NFL. NFL is an excellent initial palliative treatment option for elderly patients or patients who have exhibited poor tolerance for other chemotherapy regimens.

Confocal microscopy visualization of antifolate uptake by the reduced folate carrier in human leukaemic cells

Confocal microscopy was used to visualize the intracellular uptake of the fluorescent methotrexate analogue, fluorescein-MTX (F-MTX), in human leukaemic cell lines and leukaemic blasts. Cytosolic labelling of wild-type K562 human erythroleukaemia cells was detected during 3-60 min incubations with F-MTX (1 microM) and was completely inhibited by co-exposure to either methotrexate or the thymidylate synthase inhibitor, ZD1694. There was no significant intracellular F-MTX accumulation over this period in a K562 subline (K500E) with a documented defect (approximately 10% of wild type) in membrane transport by the reduced folate carrier (RFC). F-MTX uptake was re-established in K500E cells transfected with a cDNA to human RFC, establishing a role for RFC in the cellular uptake of this compound. High levels of intracellular labelling were detected in all cell lines after prolonged (24 h) F-MTX incubations, however F-MTX accumulation at this time was not inhibited by ZD1694. F-MTX uptake by RFC was also detected in leukaemic blasts from children with acute lymphoblastic leukaemia and could be blocked with ZD1694. In leukaemic blasts with a documented defect in MTX uptake, F-MTX accumulation was abolished in almost all the cells. These results display the power of confocal microscopy for directly visualizing RFC-mediated anti-folate uptake. Over short intervals, F-MTX uptake is mediated by RFC, however, RFC-independent processes predominate during long drug exposures. Direct assay by confocal microscopy may be better suited than other indirect methods (i.e. flow cytometry) for detecting low levels of RFC transport in leukaemic blasts from patients undergoing chemotherapy with methotrexate.

Functional aspects of membrane folate receptors in human breast cancer cells with transport-related resistance to methotrexate

Two methotrexate (MTX)-resistant human breast-cancer cell lines with impaired transport via the reduced folate carrier (RFC), one established in vitro (MTX(R)-ZR-75-1) and another inherently resistant (MDA-231), were adapted to grow in medium containing 2 nM folic acid. This induced the expression of previously undetectable membrane folate receptors (MFR) to levels of 8.2 and 2.3 pmol/10(7) cells, respectively. Polymerase chain reaction (PCR) quantitation revealed that MFR messenger-RNA levels of the isoform first described in human nasopharyngeal carcinoma KB cells (MFR-alpha) were increased in low-folate-adapted MTX(R)-ZR-75-1 cells, whereas placental transcripts (MFR-beta) coincided with MFR-alpha expression in low-folate (LF)-adapted MDA-231 cells. These cell lines were used to study the role of MFR in the uptake and growth-inhibitory effects of five different antifolates with varying affinities for MFR: N10-propargyl-5, 8-dideazafolic acid (CB3717) > 5,10-dideazatetra-hydrofolic acid (DDATHF) > N-5-[N-(3,4-dihydro-2-methyl-4-oxoquinazolin-6-methyl) -N-methyl-amino]-2-theonyl}-glutamic acid (ZD1694) >> MTX > edatrexate (EDX). Expression of MFR only slightly decreased the resistant phenotype for MTX, EDX, and ZD1694, suggesting that these drugs are not transported intracellularly to cytotoxic concentrations at these levels of MFR expression. On the other hand, both cell lines became from at least 180- to 400-fold more sensitive to growth inhibition by CB3717 and DDATHF, which may be correlated with their high affinity for MFR. These sensitivity/resistance profiles were largely similar following cell culture in medium containing 1 nM L-leucovorin, a folate with an affinity for MFR 10-fold lower than that of folic acid, the one exception being the increased sensitivity for ZD1694 seen in the LF-adapted cells with the highest level of MFR expression (MTX(R)-ZR-75-1). These results illustrate that the efficacy of MFR in mediating antifolate transport and cytotoxicity depends on their affinity for the folate antagonist, their degree of expression, and the levels of competing folates.

Biochemical and molecular studies of human methenyltetrahydrofolate synthetase

5-FormylH4folate is administered clinically under the name Leucovorin in association with the antineoplastic agent 5-fluorouracil (5-FU) to enhance the cytotoxic effects of 5-FU. The combination has been shown to be superior to 5-FU alone in the treatment of patients with metastatic colorectal carcinoma. Methenyltetrahydrofolate synthetase (MTHFS) catalyzes the transformation of 5-formyl-tetrahydrofolate to methenylH4folate, which is the obligatory initial metabolic step prior to the intracellular conversion of 5-formylH4folate to other reduced folates and the increase in intracellular folate pools required for 5-FU potentiation. In the following paper, we will summarize results of biochemical and molecular studies of human MTHFS.

Cloning and characterization of the human 5,10-methenyltetrahydrofolate synthetase-encoding cDNA

Methenyltetrahydrofolate synthetase (MTHFS) catalyses the obligatory initial metabolic step in the intracellular conversion of 5-formyltetrahydrofolate to other reduced folates. We have isolated and sequenced a human MTHFS cDNA which is 872-bp long and codes for a 203-amino-acid protein of 23,229 Da. Escherichia coli BL21(DE3), transfected with pET11c plasmids containing an open reading frame encoding MTHFS, showed a 100-fold increase in MTHFS activity in bacterial extracts after IPTG induction. Northern blot studies of human tissues determined that the MTHFS mRNA was expressed preferentially in the liver and Southern blot analysis of human genomic DNA suggested the presence of a single-copy gene.

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.