Pralatrexate Is Active in Cutaneous T-Cell Lymphoma (CTCL): Results of a Multicenter, Dose-Finding Trial.
Authors: Horwitz Steven M. , Duvic Madeleine , Kim Youn , Zain Jasmine M , Lechowicz Mary Jo , Myskowski Patricia , Fruchtman Steven , O'Connor Owen A 
Published: October 2019

Abstract
Abstract 919

Background:
Pralatrexate enters cancer cells via the reduced folate carrier-1 (RFC-1) and is efficiently polyglutamated by folylpolyglutamyl synthetase (FPGS), leading to high intracellular retention. In a Phase 1/2 study of patients with hematologic malignancies, pralatrexate demonstrated activity in aggressive T-cell lymphoma with a maximum tolerated dose (MTD) of 30 mg/m2 once weekly for 6 of 7 weeks. The generally indolent course of CTCL may be better treated at lower doses in a maintenance fashion if a lower incidence and severity of adverse events can be achieved while preserving activity. PDX-010 is an open-label, single-agent, multicenter, Phase 1 dose-reduction trial in patients with relapsed or refractory CTCL. The primary objective is to identify an optimal dose and schedule of pralatrexate for these patients.

Methods:
Eligibility included mycosis fungoides (MF), Sézary syndrome (SS), and primary cutaneous anaplastic large cell lymphoma (ALCL); with disease progression after at least 1 prior systemic therapy. The pralatrexate dose and schedule started at 30 mg/m2 by IV push on 3 of 4 weeks and subsequent cohorts received reduced doses (20, 15, 10 mg/m2) and/or schedules (3/4 or 2/3 weeks) of pralatrexate based on tolerability. All patients received supplementation with vitamin B12 1 mg intramuscularly every 8-10 weeks and folic acid 1 mg orally once daily. As we sought a well tolerated regimen the definition of DLTs to trigger dose reduction included toxicities such as grade ≥ 3 neutropenia, grade ≥ 2 thrombocytopenia, febrile neutropenia, grade ≥ 2 mucositis/stomatitis, and any toxicity leading to dose omission or reduction in cycle 1. If DLT occurred and a response was seen, the following cohort was opened at the next lower dose or next less frequent schedule. Response was evaluated by modified severity-weighted adjustment tool (SWAT) every 2 cycles for 6 months and then every 4 cycles. For patients with lymph node involvement, scans were completed at baseline and upon clinical response or end of treatment, whichever occurred first.

Results:
Thirty-one patients received pralatrexate, with 18 (58%) men and median age of 57 yrs (range, 30-81). Patients had received a median of 6 prior therapies (range, 1-25). Cohorts at the following doses/schedules were enrolled: 30 mg/m2 x 3/4 weeks (n=2), 20 mg/m2 x 3/4 weeks (n=3), 20 mg/m2 x 2/3 weeks (n=7), 15 mg/m2 x 3/4 weeks (n=6), 15 mg/m2 x 2/3 weeks (n=3), and 10 mg/m2 x 3/4 weeks (n=10). Patients received pralatrexate for a median of 72 days (range, 7-491+); 4 patients received >10 cycles of treatment. The most common treatment-related adverse events (all grades) were mucositis (18 patients [58%]), nausea (14 patients [45%]), fatigue (14 patients [45%]), pyrexia (7 patients [23%]), vomiting (6 patients [19%]), anemia (6 patients [19%]), and edema (5 patients [16%]). Grade 3-4 treatment-related toxicities in >1 patient each were mucositis (4 patients [13%]) and anemia (2 patients [6%]). Mucositis was dose limiting (≥ grade 2) in 8 patients (26%). A total of 11 responses were observed, including 2 complete responses and 9 partial responses. In the 18 patients who received pralatrexate at a dose intensity of 15 mg/m2 x 3/4 weeks or greater, the objective response rate was 56% (10/18 patients). This appeared to be the threshold dose for substantial activity in CTCL, below which the incidence of responses decreased in this dose de-escalation trial.

Conclusion:
Pralatrexate shows impressive activity in the treatment of relapsed CTCL. The optimal dose and schedule that provided activity with tolerability for CTCL was determined to be pralatrexate 15 mg/m2 weekly on 3 of 4 weeks. This cohort is being expanded to better assess efficacy and durability.

Disclosures:
Horwitz: Allos Therapeutics, Inc: Consultancy, Research Funding. Duvic:Allos Therapeutics, Inc.: Research Funding. Lechowicz:Allos Therapeutics, Inc.: Consultancy. Fruchtman:Allos Therapeutics, Inc.: Employment.