A Phase 1 Clinical-Pharmacodynamic Study of the Farnesyltransferase Inhibitor Tipifarnib in Combination with the Proteasome Inhibitor Bortezomib in Advanced Acute Leukemias.

Combination therapy utilizing 2 novel agents with independent mechanisms of action and non-overlapping toxicities may be useful in the setting of advanced cancers. Tipifarnib (T) is an orally bioavailable farnesyltranferase inhibitor with documented single-agent activity in acute myeloid leukemia (AML). Bortezomib (B) is a broad inhibitor of proteasomal function, approved for treatment in multiple myeloma and mantle cell lymphoma. Preclinical studies indicated synergistic activity between these 2 agents for eliciting apoptosis within leukemia and myeloma cell lines and ex-vivo cells adhered to fibronectin. In this phase I combination trial, we studied the effect of combined effect of T plus B in patients with advanced acute leukemias.

Objectives: The primary endpoint was toxicity assessment. Secondary endpoints included effect of combined therapy on signaling intermediates, including p-AKT, Bim, Bax, and NF-kB, as well as effects on farnesyltransferase (FT) and the proteasome activity.

Eligibility: Patients with AML, ALL, or CML-BC who had received < 3 cycles of prior therapy were eligible.

Methods: Patients received T on days 1–14 and B on days 1, 4, 8, and 11. Cycles were repeated every 21 days. Dose escalation occurred using cohorts of 3–6 patients. The starting dose was T: 300 mg/m² and B: 1.0 mg/m² Bone marrow aspirate was obtained at baseline, day 8, and between day 15 and the start of the next cycle. Measurement of signaling intermediates were performed in Ficoll-enriched leukemic marrow blasts using Western Blot (p-AKT, Bax, Bim) and ELISA (NF-kB). FT and proteasomal activity were directly measured within peripheral blood mononuclear cells (PBMC) using previously described methods.

Results: To date, 27 patients have been enrolled at 3 centers. Four patients were ineligible after screening, and 23 patients have been treated. Median age was 69 years (range 48–84) Diagnosis: AML=25, ALL=1, MDS=1. Accrual to the 4^th and final dosing cohort has occurred, without maximum tolerated dose being reached at the 4^th and final planned dosing cohort (T: 600 mg/m² and B: 1.3 mg/m²). Six patients received ≥ 2 cycles of treatment. Dose-limiting toxicities to date have included: nausea/diarrhea (1 patient), sensory neuropathy (1 patient), and fatigue (1 patient). Common drug-related (> 10%) non dose-limiting toxicities included: infection/febrile neutropenia, diarrhea, nausea, vomiting, sensory neuropathy, and fatigue, most of which were grade 1 or 2. FTase inhibition within peripheral blood mononuclear cells (PBMC) was measured serially in 8 patients to date, with a median of 70% inhibition by day 8, and with 5 out of 6 evaluable patients having sustained inhibition at day 22. Proteasome function within PBMCs was reduced by a median of 44.3% in 7 patient samples pre-infusion and 1 hour post-infusion on day 8. Proteasome activity within PBMCs at day 22 was decreased from baseline in 5 out of 7 patient samples tested. Compared to baseline, NF-kB binding activity within leukemic blasts at day 8 was decreased by a median of 39% at in 10 out of 14 paired samples. No significant change in expression of p-AKT, Bax, or Bim, as measured by Western Blot, was detected at day 8. Two patients achieved clinical response; 1 patient had a complete response and another patient had complete response with incomplete count recovery. Four others had stable disease following cycle 1.

Conclusion: combined therapy with T + B was well tolerated and demonstrated inhibition of several relevant target signals within leukemic blasts and PBMCs. In addition, clinical activity was seen in 2 patients to date. Accrual to the trial is ongoing and updated clinical and pharmacodynamic data will be presented.