Phase II-I-II study of two different doses and schedules of pralatrexate, a high-affinity substrate for the reduced folate carrier, in patients with relapsed or refractory lymphoma reveals marked activity in T-cell malignancies.

PURPOSE: To determine the maximum-tolerated dose (MTD) and efficacy of pralatrexate in patients with lymphoma. PATIENTS AND METHODS: Pralatrexate, initially given at a dose of 135 mg/m(2) on an every-other-week basis, was associated with stomatitis. A redesigned, weekly phase I/II study established an MTD of 30 mg/m(2) weekly for six weeks every 7 weeks. Patients were required to have relapsed/refractory disease, an absolute neutrophil greater than 1,000/microL, and a platelet count greater than 50,000/microL for the first dose of any cycle. RESULTS: The every-other-week, phase II experience was associated with an increased risk of stomatitis and hematologic toxicity. On a weekly schedule, the MTD was 30 mg/m(2) weekly for 6 weeks every 7 weeks. This schedule modification resulted in a 50% reduction in the major hematologic toxicities and abrogation of the grades 3 to 4 stomatitis. Stomatitis was associated with elevated homocysteine and methylmalonic acid, which were reduced by folate and vitamin B12 supplementation. Of 48 assessable patients, the overall response rate was 31% (26% by intention to treat), including 17% who experienced complete remission (CR). When analyzed by lineage, the overall response rates were 10% and 54% in patients with B- and T-cell lymphomas, respectively. All eight patients who experienced CR had T-cell lymphoma, and four of the six patients with a partial remission were positron emission tomography negative. The duration of responses ranged from 3 to 26 months. CONCLUSION: Pralatrexate has significant single-agent activity in patients with relapsed/refractory T-cell lymphoma.

Pralatrexate, a novel class of antifol with high affinity for the reduced folate carrier-type 1, produces marked complete and durable remissions in a diversity of chemotherapy refractory cases of T-cell lymphoma.

T-cell lymphomas (TCLs) are characterised by poor responses to therapy with brief durations of remissions. An early phase study of pralatrexate has demonstrated dramatic activity in patients with relapsed/refractory disease. Of the first 20 lymphoma patients treated, 16 had B-cell lymphoma and four had refractory aggressive TCL. All four patients with TCL achieved a complete remission. Patients with B-cell lymphoma achieved stable disease at best. For each TCL patient, the response was more durable than their best response with chemotherapy. This early experience is the first to document this unique activity of pralatrexate in TCL.

The schedule-dependent effects of the novel antifolate pralatrexate and gemcitabine are superior to methotrexate and cytarabine in models of human non-Hodgkin's lymphoma.

PURPOSE: Methotrexate is known to synergize with cytarabine [1-beta-D-arabinofuranosylcytosine (ara-C)] in a schedule-dependent manner. The purpose of this article is to compare and contrast the activity of pralatrexate (10-propargyl-10-deazaminopterin)/gemcitabine to the standard combination of methotrexate/ara-C and to determine if schedule dependency of this combination is important in lymphoma. EXPERIMENT DESIGN: Cytotoxicity assays using the standard trypan blue exclusion assay were used to explore the in vitro activity of pralatrexate and gemcitabine against a panel of lymphoma cell lines. Both severe combined imunodeficient beige and irradiated nonobese diabetic/severe combined imunodeficient mouse xenograft models were used to compare and contrast the in vivo activity of these combinations as a function of schedule. In addition, apoptosis assays were conducted. RESULTS: Compared with methotrexate-containing combinations, pralatrexate plus gemcitabine combinations displayed improved therapeutic activity with some schedule dependency. The combination of pralatrexate and gemcitabine was superior to any methotrexate and ara-C combination in inducing apoptosis and in activating caspase-3. In vivo, the best therapeutic effects were obtained with the sequence of pralatrexate --> gemcitabine. Complete remissions were only appreciated in animals receiving pralatrexate followed by gemcitabine. CONCLUSIONS: These data show that the combination of pralatrexate followed by gemcitabine was superior to methotrexate/ara-C in vitro and in vivo, and was far more potent in inducing apoptosis in a large B-cell lymphoma. These data provide strong rationale for further study of this combination in lymphomas where methotrexate and ara-C are used.

Pulsatile administration of the epidermal growth factor receptor inhibitor gefitinib is significantly more effective than continuous dosing for sensitizing tumors to paclitaxel.

PURPOSE: Gefitinib is an inhibitor of the epidermal growth factor receptor (EGFR) tyrosine kinase. Continuous inhibition of EGFR signaling is thought necessary for optimal inhibition of tumor cell proliferation. We hypothesized that continuous gefitinib may antagonize the effects of cytotoxics that inhibit tumor cells in other phases of the cell cycle. Furthermore, we hypothesized that intermittent dosing would allow for dose escalation and greater inhibition of EGFR-dependent antiapoptotic pathways. EXPERIMENTAL DESIGN: To test these assertions, we compared combinations of paclitaxel and gefitinib using either intermittent or continuous dosing schedules in mice. RESULTS: We found that when used in combination with paclitaxel, pulsatile gefitinib was significantly superior to continuous dosing. When gefitinib was administered for one or two consecutive days before paclitaxel, much higher doses could be given safely. Two days of gefitinib treatment before paclitaxel was most effective, causing significantly greater mean tumor regression and a higher percentage of complete responses than other schedules. CONCLUSIONS: The results suggest that the dose and schedule of an EGFR inhibitor required to effectively inhibit proliferation may differ from that required to stimulate apoptosis or to induce other effects. The former may require continuous EGFR inhibition to maintain cell cycle arrest, whereas sensitization to apoptosis may be optimally induced by profound but temporary inhibition of survival pathways. Our data suggest that the effects of receptor inhibition vary as a function of dose and schedule and that continuous administration of tyrosine kinase inhibitors may not be the best schedule with which to combine such agents with taxanes.

Maitake beta-glucan MD-fraction enhances bone marrow colony formation and reduces doxorubicin toxicity in vitro.

Previous studies have indicated that MD-fraction (MDF), in which the active component is beta 1,6-glucan with beta 1,3-branches, has anti-tumor activity as an oral agent and acts as an immune adjuvant. Since some other beta glucans appear to promote mobilization of hematopoietic stem cells, the effects of a beta glucan extract from the Maitake mushroom "MD-fraction" on hematopoietic stem cells were examined in a colony forming assay. Here we report for the first time that MDF has a dose response effect on mouse bone marrow cells (BMC) hematopoiesis in vitro. Using the Colony Forming Unit (CFU) assay to detect formation of granulocyte-macrophage (CFU-GM) colonies, and the XTT cytotoxicitiy assay to measure BMC viability, the data showed that the addition of MDF significantly enhanced the development of CFU-GM in a dose range of 50-100 microg/ml (p<0.004). The mechanism of action included significant increase of nonadherent BMC viability, which was observed at MDF doses of 12.5-100 microg/ml (p<0.005). In the presence of Doxorubicin (DOX), MDF promoted BMC viability and protected CFU-GM from DOX induced toxicity. In addition, MDF treatment promoted the recovery of CFU-GM colony formation after BMC were pretreated with DOX. These studies provided the first evidence that MDF acts directly in a dose dependent manner on hematopoietic BMC and enhances BMC growth and differentiation into colony forming cells.