A Phase I Study Of KB004, a Novel Non-Fucosylated humaneered® Antibody, Targeted Against The Receptor Tyrosine Kinase EphA3, In Advanced Hematologic Malignancies

EphA3 is involved in cell positioning in fetal development. In the adult it is an oncofetal antigen re-expressed in hematologic malignancies (blood and bone marrow, leukemic stem cells) and solid tumors (tumor stem cells, neovasculature and stroma) and may be prognostic. KB004 is a humaneered® high affinity antibody targeted against EphA3 with 3 putative mechanisms of action: direct induction of apoptosis in tumor cells, activation of ADCC and disruption of tumor vasculature by induction of endothelial cell rounding and subsequent blood vessel infarction. Herein, we describe results of an ongoing, phase 1 dose-escalation study of KB004 in adult patients with advanced hematologic cancers.

1) primary: to determine safety and MTD for KB004 in patients with hematologic malignancies refractory to or unfit for chemotherapy; 2) secondary: to examine PK profile, immunogenicity, and clinical activity of KB004. Exploratory objectives include evaluation of EphA3 expression on tumor, stromal, and endothelial cells.

This is a multicenter phase 1 study. Key eligibility criteria include: 1) relapsed or refractory hematologic malignancy 2) ECOG PS 0-1; 3) adequate end-organ function. Additional eligibility criteria amended later to protect against hemorrhagic events, included platelets ≥ 10,000/uL (untransfused) and normal coagulation times. A standard 3 + 3 escalation study design (amended to allow up to 6 pts. per cohort in the absence of a DLT) was utilized. KB004 was administered as a 1 or 2 hr infusion on days 1, 8, and 15 of each 21-day cycle, at incremental doses of 20, 40, 70, 100, 140, 190, 250 mg and thereafter 33% increments up to a planned maximum of 700 mg. At 70 mg and above infusion reaction (IR) prophylaxis included an H1 blocker, H2 blocker, acetaminophen and IV steroids. Peripheral blood and bone marrow biopsy specimens for PK analysis and EphA3 expression, respectively, were collected during cycle 1.

To date, 37 patients (AML 32, MDS 2, lymphoma 1, myelofibrosis 2) received KB004; 20 mg: 9 pts, 40 mg: 3pts, 70 mg: 8 pts, 100 mg: 7pts, 140 mg: 5pts, 190 mg 5pts. At 70 mg, two patients had intracranial hemorrhages 5 and 18 days after last KB004 dose in the context of thrombocytopenia and hyperleukocytosis. A causal relationship to KB004 could not be excluded. One occurred in course 1 and was considered a DLT. KB004 blood levels were near the limit of quantitation at 48 and 96 hours. Following the change to entry criteria no further episodes of serious bleeding or other DLTs or significant changes in soluble clotting factors have been observed.

Overall KB004 is well tolerated. The most common toxicity was mild to moderate transient IRs in 28 (76%) patients characterized by chills, elevated temperature, fever, rigors, back pain, nausea, vomiting, hypotension, hypertension, transient hypoxia (in 2 cases). Fourteen % of infusions were slowed due to an adverse event, two (1.2%) were prematurely discontinued but no patient discontinued KB004 secondary to an IR. No other significant KB004-related toxicity has been observed. KB004 Cmax at all dose levels was above the predicted effective concentration (1 ug/ml) and was approximately dose proportional. However at dose levels below 190 mg sustained exposure to cover the entire interval between doses was not achieved.

One CRp was observed at the 20mg dose level in a 78 yr-old patient with relapsed AML, who remains on study and in sustained remission for over a year. Serial bone marrow biopsies with KB004 treatment show decreased reticulin and collagen fibrosis. A > 50% reduction in marrow blast percentage was seen in 14% of AML patients, and 59% had overall stable disease beyond 1 cycle.

Bone marrow biopsies positive for EphA3 expression with a cut-off of 10% of nucleated cells were obtained in 75% of AML patients. EphA3 was expressed in at least 30% of nucleated cells in the baseline sample of the patient with an ongoing CRp.

KB004 is a novel agent targeted against EphA3 that is well tolerated with evidence of clinical activity. It is anticipated that 190 mg given over 2 hours will provide sufficient plasma exposure to achieve sustained efficacy over the interval between doses. The study is ongoing. Additional PK, PD, and clinical data will be presented.

Durrant:KaloBios: Research Funding. Yarranton:KaloBios: Employment, Equity Ownership; Glaxo: Equity Ownership; EnGen: Equity Ownership, Science Advisor, Science Advisor Other; StemLine Therapeutics: Equity Ownership. Walling:KaloBios: Consultancy; Corcept Therapeutics: Consultancy; Prothena: Consultancy; New Gen Therapeutics: Consultancy; Valent Technologies: Consultancy; LBC Pharmaceuticals: Consultancy; Amgen: Equity Ownership; BioMarin: Equity Ownership; Crown BioScience: Membership on an entity’s Board of Directors or advisory committees.