Activated ALK by mutation or amplification is a validated therapeutic target in patients with high-risk neuroblastoma, and tyrosine kinase inhibitors are being developed to abrogate ALK signaling (Bresler et al. 2014). Native ALK is expressed on the surface of the majority of neuroblastoma tumors, but not on normal tissue, giving it properties of a tumor antigen. We hypothesized that ALK-targeted antibodies may be useful in neuroblastoma as a single-agent therapy or in combination with small-molecule ALK inhibitors – especially where mutations reduce kinase inhibitor sensitivity. In this work, an anti-ALK monoclonal antibody (anti-ALK2) was conjugated to a cytotoxic agent (ALK2-ADC) and its anti-tumor activity was investigated in a panel of neuroblastoma cell lines (n=10) harboring wild-type and mutant ALK. Cell surface ALK was quantified using flow cytometry and revealed differential antigen expression. Using in vitro growth inhibition assays, there was evidence for a dose-dependent cytotoxicity to neuroblastoma cells at subnanomolar concentrations that correlated with cell surface ALK expression and was independent of the underlying mutation status. In order to evaluate the therapeutic potential of ALK2-ADC in vivo, mice bearing Felix-patient-derived xenograft tumors, containing the third most common ALK mutation (R1245C), were used to demonstrate that ALK2-ADC led to significant reduction in tumor growth compared to unconjugated antibody and a control ADC (p<0.0001). Although ALK2-ADC binds to mouse ALK as well as human ALK, doses up to 10 mg/kg in the rodent model appeared to be well tolerated with no overt toxicity noted. Additional in vivo studies are ongoing to assess the anti-tumor potential of the ADC in a broader range of ALK-expressing neuroblastomas. Thus, targeting human ALK-expressing with an antibody-drug conjugate demonstrated favorable efficacy and tolerability supporting future development of this approach as a novel therapy for neuroblastoma patients.
Author Disclosure Information: R. Sano, K. Krytska, C. Larmour and Y.P. Mosse: None. G.F.Ligon; J.S. Lillquist, Diego Alvarado and G. McMahon: Kolltan Pharmaceuticals. U. Cucchi; P. Orsini, S. Rizzi: Nerviano