Phase I Trial of the Base – Excision Repair Blocker Methoxyamine (TRC-102) Combined with Fludarabine in Relapsed/Refractory Chronic Lymphocytic Leukemia (CLL) and Lymphoid Malignancies

Background: Methoxyamine (TRC-102) is a first in class inhibitor of base excision repair (BER). It covalently binds to the DNA abasic site generated by DNA-glycosylase-mediated removal of incorporated fludarabine. In vitro and animal studies demonstrated that methoxyamine augments the cytotoxicity of fludarabine against CLL cells but not normal bone marrow cells. We conducted a phase I trial to determine the maximum tolerated dose and dose limiting toxicities (DLT) of methoxyamine combined with fludarabine.

Methods: Eligible patients were older than 18 years of age and had relapsed /refractory lymphoid malignancies (CLL, Lymphoma, Multiple Myeloma). Fludarabine 25mg/m² was given intravenously daily for 5 days; methoxyamine was given intravenously on day 2 of cycle 1 and day 1 of subsequent cycles, at doses of 15, 30, 60, 90 and 120mg/m² in a 3+3 dose escalation design. Treatment cycles were repeated every 28 days. DNA damage was assessed with the Comet Tail Length in the single cell Comet electrophoresis assay; for pharmacokinetic analysis, serum methoxyamine concentrations were measured using electrospray-ionization mass spectrometry.

Results: 19 patients were enrolled in the trial; median age was 64 (range 45 – 82) years. The diagnoses included CLL (n = 10), non-Hodgkin lymphoma (NHL) (n = 7), and plasma cell myeloma (PCM) (n = 2). Median number of prior therapies was 3 (range 1 to 5). Among patients with CLL, 8/10 had received prior fludarabine therapy.

No DLTs have been observed. The median number of treatment cycles administered was 3 (range 1 – 6). Grade 3 – 4 hematologic adverse events (AE) were common [neutropenia (63.1%); lymphopenia (68.4%); anemia (42.1%); thrombocytopenia (26.3%)]. Non-hematologic grade 3 – 4 events included 3 cases of pneumonia (15.8%) and one case of hyperuricemia (5.2%). Grade 1 – 2 events included fatigue (84.2%), nausea (68.4%), hypocalcemia (57.9%), anorexia (52.6%) and constipation (47.4%).

Seven patients developed progressive disease (NHL = 4, PCM = 2, CLL = 1). Partial response was observed in 2 CLL patients and one case of follicular lymphoma, while 9 subjects had stable disease (CLL = 7; NHL = 2). After a median follow up of 13 months, overall survival was 75% (95% CI, 45% - 90%). Median time to next treatment among responding patients was 12 months (range 3.8 – 30.4 months).

Among CLL patients, the median decrease in absolute lymphocyte count (ALC) after the first week of treatment was 90% (95% CI, 78% - 98%) and 8/10 CLL patients had normal or low lymphocyte counts. The decrease in ALC correlated directly with DNA damage measured by Comet assay 24 hours after methoxyamine infusion (Pearson Correlation 0.9162; R² 0.8995; p = 0.001).

The serum half-life of methoxyamine was not affected by dosing or fludarabine co-administration. Median half-life was 41.26 hours (95% CI, 35.77 – 49.50h).

Conclusions: The combination of methoxyamine and fludarabine was well tolerated, with no dose limiting toxicities observed. The combination has activity in low-grade lymphoma as well as CLL patients who relapsed after fludarabine – containing regimens. DNA damage measurements with the Comet assay correlate with disease response in CLL patients.

Fludarabine remains an important component in the treatment of lymphoid malignancies. The combination with methoxyamine has the potential of increasing its activity with limited additional toxicity. Future studies are planned investigating the efficacy of fludarabine and methoxyamine combined with targeted agents for treatment of lymphoid malignancies.