Safety, Pharmacokinetics, and Efficacy of BP-100-1.01 (Liposomal Grb-2 Antisense Oligonucleotide) in Patients with Refractory or Relapsed Acute Myeloid Leukemia (AML), Philadelphia Chromosome Positive Chronic Myelogenous Leukemia (CML), Acute Lymphoblastic Leukemia (ALL), and Myelodysplastic Syndrome (MDS)

Background: Essential to cancer cell signaling, the growth receptor bound protein-2 (Grb-2) is evolutionarily conserved and utilized by oncogenic tyrosine kinases including Bcr-Abl to activate Ras, ERK, and AKT. BP-100-1.01is a neutrally-charged, liposome-incorporated antisense designed to inhibit Grb-2 expression.

Aim: To define the safety, maximum tolerated dose (MTD), optimal biologically active dose, pharmacokinetics and anti-leukemia activity of BP-100-1.01 in patients (pts) with hematologic malignancies.

Methods: This is a standard 3+3 phase I dose-finding study in pts with relapsed or refractory acute myeloid leukemia (AML), chronic myeloid leukemia in blast phase (CML-BP), acute lymphoblastic leukemia (ALL) and myelodysplastic syndrome (MDS). The starting dose was 5 mg/m² twice weekly, IV over 2-3 hours for 28 days. Dose escalation proceeded through 5, 10, 20, 40, 60, and 90 mg/m².Uponcompletion of single agent phase 1, combination of cytarabine 20 mg SubQ BID x 10 days + 60 mg/m² of BP-100-1.01 was studied (Cohort 1B). Flow cytometric analysis was performed on peripheral blood samples from cohorts 3, 4, 5, 6 and 1B collected at baseline, on day 15 and at end-of-treatment (EOT). Fluorescent-labeled antibodies specific for Grb-2 or phosphorylated Erk (pErk) were utilized to determine Grb-2 protein levels and pErk levels in CD33-expressing cells.

Results: A total of33 pts were included (13 in Cohort 1, 6 in Cohort 2, 3 each in Cohorts 3, 4, 5, and 4 in cohort 6). One patient has been treated in cohort 1B. The median age was 64 yrs (range, 32-89) and diagnoses were AML (n=24), CML-BP (n=5) and MDS (n=4). The median number of prior therapies was 4 (range, 1- 8). Of 33 pts, 21 were evaluable and 11 failed completion of a full 28-Day cycle due to disease progression (with no toxicity) and were replaced, per protocol. Only one pt (treated at 5 mg/m²) experienced dose limiting toxicity (DLT), grade 3 mucositis and hand-foot syndrome, while receiving concurrent hydroxyurea for proliferative CML-BP. The patient had a previous history of hydroxyurea-induced mucositis. Being the first patient to receive BP-100-1.01, these toxicities were considered possibly related to BP-100-1.01. The cohort was expanded to a total of 6 pts. No other DLTs have been noted in any pt. Among 21 evaluable pts, 11 experienced at least a 50% reduction in peripheral or bone marrow blasts from baseline. Additionally 2 pts with improvement in leukemia cutis lesions received 1 cycle each. Furthermore, 6 pts demonstrated transient improvement (n=3) and/or stable disease (n=3). Among the 21 evaluable pts, a median of 1 cycle was administered (1-5): Four pts received 2 cycles, 3 pts received 5 cycles, and all others received 1 cycle. Notably one pt (treated at 5 mg/m²)with CML-BP showed a significant reduction in blasts from 81% to 5%. Due to leptomeningeal disease progression therapy was discontinued before a full cycle. The 1^st patient treated in cohort 1B achieved CR after 1 cycle. The patient did not experience any DLTs, but came off study due to failure to thrive in the context of dementia.

The levels of Grb-2 and pErk proteins were indicated by their respective median fluorescent signals and are shown in the table. Median fluorescent signals of Grb-2 and pErk on days 15 and EOT were compared to baseline. On day 15 Grb-2 levels decreased by >25% in 7 out of 12 samples tested, and pErk levels by >25% in 6 out of 12 samples. The average decrease in Grb-2 levels was 61% (range: 47 to 85%) and in pErk levels 52% (range: 28 to 82%). On the last measured sample (EOT or day 22), BP-100-1.01 decreased >25% Grb-2 levels in 11 out of 13 samples, and >25% pErk levels in 7 out of 13 samples. The average decrease in Grb-2 levels was 49% (range: 28 to 91%) and in pErk levels was 52% (range: 27 to 91%).

Conclusions: BP-100-1.01, at dose range 5 mg/m² to 90 mg/m² is well tolerated with no MTD yet identified. There is suggestion of Grb-2 target protein down-regulation, and possible anti-leukemia activity.