Phase I/II Study of Volasertib (BI 6727), An Intravenous Polo-Like Kinase (Plk) Inhibitor, in Patients with Acute Myeloid Leukemia (AML): Updated Results of the Dose Finding Phase I Part for Volasertib in Combination with Low-Dose Cytarabine (LD-Ara-C) and As Monotherapy in Relapsed/Refractory AML

The prognosis of patients (pts) with relapsed or refractory (rel/ref) AML who are considered unlikely to benefit from or tolerate intensive salvage treatment is unfavorable and novel treatment strategies are needed. Repeated cycles of LD-Ara-C are a therapeutic option for palliative treatment; however, the outlook for these pts remains unsatisfactory.

Plks are critical in cellular division and mitotic progression and Plk1 is overexpressed in many cancers including AML. Volasertib is a first in class, selective and potent cell cycle kinase inhibitor that induces mitotic arrest and apoptosis by targeting Plk. In phase I/II trials in pts with solid tumors, volasertib demonstrated a favorable safety profile and encouraging antitumor activity. Here, we present updated results from the phase I part of an ongoing phase I/II study of volasertib in combination with LD-Ara-C or as monotherapy in AML pts considered ineligible for intensive salvage treatment.

This study follows a two-stage design. The phase I part, reported here, investigates the maximum tolerated dose (MTD) of volasertib as a 1-hr intravenous infusion on days 1 and 15 Q4W as monotherapy or in combination with fixed dose LD-Ara-C 20 mg bid subcutaneously on days 1–10 Q4W in pts with rel/ref AML. Dose escalation follows a 3+3 design with de-escalation. Blood samples for pharmacokinetic (PK) analyses were taken in cycles 1 and 2 and concentrations of volasertib and LD-Ara-C were determined.

In the monotherapy arm, increasing volasertib doses (150, 200, 350, 400, 450 mg) were evaluated in 29 pts (median age: 71 yrs [range 26–84]). Drug-related adverse events (AEs) were reported in 8 pts (27.6 %). Most frequent drug-related AEs (>5%) were anemia in 3 pts (10.3%), and thrombocytopenia, epistaxis, and nausea in 2 pts each (6.9%). Grade 3/4 drug-related AEs included thrombocytopenia (2 cases), anemia, diarrhea, mucositis, neutropenia, and pneumonia (1 case each); there was 1 fatal (grade 5) drug-related AE (fungal pneumonia). Of the drug-related AEs, the following were dose-limiting toxicities (DLTs) per protocol: grade 4 pneumonia and fatal fungal pneumonia (n=1, at 150 mg), and grade 3 mucositis (n=1, at 400 mg). Monotherapy dose escalation is ongoing; pts have received volasertib doses of 500 mg without having reached the MTD. Preliminary best response data indicated minor antileukemic activity at low doses (150 and 200 mg); with 4/13 pts achieving no change as best response, mostly of short duration (median number of cycles initiated: 1 [range 1–5]). At higher monotherapy doses (≥350 mg), antileukemic activity was observed with 4/16 pts achieving a complete remission with incomplete blood count recovery (CRi) and 5/16 having temporarily stable blood values as best response.

In the combination arm, volasertib doses of 150–400 mg were investigated. The MTD for volasertib in combination with LD-Ara-C was 350 mg (Bug et al ASH 2010). Seven out of 32 pts treated with volasertib + LD-Ara-C achieved a complete remission (CR or CRi). In responding patients, a median number of 6 treatment cycles was initiated (range 3–13) and a preliminary analysis revealed a median overall survival of 551 days (range 165–595).

PK analysis showed that volasertib is a moderate clearance drug with multi-compartmental PK behavior with a large volume of distribution (>4000 L) and a long terminal half-life (∼111 hrs). No drug interaction after co-administration of LD-Ara-C was observed.

The phase I part of the study determined the MTD of volasertib in combination with LD-Ara-C to be 350 mg; the MTD of volasertib monotherapy has not yet been determined. Volasertib was well tolerated in this heavily pretreated AML pt population at doses above the recommended phase II volasertib dose used in pts with solid tumors. Most of the reported higher grade drug-related AEs were due to the myelosuppressive effect of volasertib. Preliminary results from the phase I trial show antileukemic activity of volasertib as monotherapy and in combination with LD-Ara-C. These results indicate Plk to be a potential new target for AML treatment and warrant proceeding with further clinical investigation of volasertib in AML pts.

Bug:Novartis Pharma GmbH: Consultancy, Honoraria; Celgene GmbH: Consultancy, Honoraria. Off Label Use: Volasertib is an investigational agent. Müller-Tidow:Boehringer Ingelheim: Research Funding. Krug:Boehringer Ingelheim: Research Funding. Voss:Boehringer Ingelheim: Employment. Taube:Boehringer Ingelheim: Employment. Fritsch:Boehringer Ingelheim: Employment. Garin-Chesa:Boehringer Ingelheim: Employment. Ottmann:Boehringer Ingelheim: Consultancy. Döhner:Celgene, Clavis: Membership on an entity's Board of Directors or advisory committees.