ABSTRACT
Cirmtuzumab is a humanized monoclonal antibody (mAb) that targets ROR1, an oncoembryonic orphan receptor for Wnt5a found on cancer stem cells (CSCs). Aberrant expression of ROR1 is seen in many malignancies and has been linked to Rho-GTPase activation and cancer stem cell self-renewal. For patients with chronic lymphocytic leukemia (CLL), self-renewing, neoplastic B cells express ROR1 in 95% of cases. High-level leukemia cell expression of ROR1 is associated with an unfavorable prognosis. We conducted a phase 1 study involving 26 patients with progressive, relapsed, or refractory CLL. Patients received four biweekly infusions, with doses ranging from 0.015 to 20 mg/kg. Cirmtuzumab had a long plasma half-life and did not have dose-limiting toxicity. Inhibition of ROR1 signaling was observed, including decreased activation of RhoA and HS1. Transcriptome analyses showed that therapy inhibited CLL stemness gene expression signatures in vivo. Cirmtuzumab is safe and effective at inhibiting tumor cell ROR1 signaling in patients with CLL.
Subject(s)
Antibodies, Monoclonal, Humanized/metabolism , Leukemia, Lymphocytic, Chronic, B-Cell/drug therapy , Receptor Tyrosine Kinase-like Orphan Receptors/antagonists & inhibitors , Signal Transduction/drug effects , Antibodies, Monoclonal, Humanized/administration & dosage , Antibodies, Monoclonal, Humanized/chemistry , Antibodies, Monoclonal, Humanized/pharmacology , Antibodies, Monoclonal, Humanized/therapeutic use , Dose-Response Relationship, Drug , Drug Tolerance , Humans , Infusions, Intravenous , Leukemia, Lymphocytic, Chronic, B-Cell/metabolism , Leukemia, Lymphocytic, Chronic, B-Cell/pathology , Receptor Tyrosine Kinase-like Orphan Receptors/genetics , Receptor Tyrosine Kinase-like Orphan Receptors/metabolism , Signal Transduction/genetics , Structure-Activity RelationshipABSTRACT
We examined the sera of six patients before and after i.v. infusions of autologous chronic lymphocytic leukemia (CLL) cells transduced ex vivo with an adenovirus encoding CD154 (Ad-CD154). Five patients made high-titer antibodies against adenovirus and three made IgG reactive with a leukemia-associated surface antigen, which we identified as ROR1. Anti-ROR1 antibodies were not detected in the sera of untreated patients. We generated anti-ROR1 mAbs and found they reacted specifically with the CLL cells of all patients, but not with nonleukemic leukocytes, a wide variety of normal adult tissues, or blood mononuclear cells, including CD5(+) B cells of healthy adults. ROR1 could bind Wnt5a, which induced activation of NF-kappaB when coexpressed with ROR1 in HEK293 cells and enhanced the survival of CLL cells in vitro, an effect that could be neutralized by posttreatment anti-ROR1 antisera. We conclude that patients with CLL can break immune tolerance to ROR1, which is an oncofetal surface antigen and survival-signaling receptor in this neoplastic disease.
