5T4-Targeted Therapy Ablates Cancer Stem Cells and Prevents Recurrence of Head and Neck Squamous Cell Carcinoma

Purpose: Locoregional recurrence is a frequent treatment outcome for patients with advanced head and neck squamous cell carcinoma (HNSCC). Emerging evidence suggests that tumor recurrence is mediated by a small subpopulation of uniquely tumorigenic cells, that is, cancer stem cells (CSC), that are resistant to conventional chemotherapy, endowed with self-renewal and multipotency. Experimental Design: Here, we evaluated the efficacy of MEDI0641, a novel antibody-drug conjugate targeted to 5T4 and carrying a DNA-damaging payload (pyrrolobenzodiazepine) in preclinical models of HNSCC. Results: Analysis of a tissue microarray containing 77 HNSCC with follow-up of up to 12 years revealed that patients with 5T4(high) tumors displayed lower overall survival than those with 5T4(low) tumors (P = 0.038). 5T4 is more highly expressed in head and neck CSC (ALDH(high)CD44(high)) than in control cells (non-CSC). Treatment with MEDI0641 caused a significant reduction in the CSC fraction in HNSCC cells (UM-SCC-11B, UM-SCC-22B) in vitro. Notably, a single intravenous dose of 1 mg/kg MEDI0641 caused long-lasting tumor regression in three patient-derived xenograft (PDX) models of HNSCC. MEDI0641 ablated CSC in the PDX-SCC-M0 model, reduced it by five-fold in the PDX-SCC-M1, and two-fold in the PDX-SCC-M11 model. Importantly, mice (n = 12) treated with neoadjuvant, single administration of MEDI0641 prior to surgical tumor removal showed no recurrence for more than 200 days, whereas the control group had 7 recurrences (in 12 mice; P = 0.0047). Conclusions: Collectively, these findings demonstrate that an anti-5T4 antibody-drug conjugate reduces the fraction of CSCs and prevents local recurrence and suggest a novel therapeutic approach for patients with HNSCC. (C) 2016 AACR.