Combined hedgehog and epidermal growth factor receptor (EGFR) inhibition in a direct patient tumor model (DPTM) of head and neck squamous cell cancer (HNSCC).

Abstract

5558 Background: A DPTM of HNSCC was established to optimally test novel therapies and the role of cancer stem cells (CSC) in relapses after therapy. This study examines the role of the Hedgehog pathway (HhP) in HNSCC and the effect of the smoothened (SMO) inhibitor IPI-926 alone and combined with the EGFR inhibitor cetuximab (Cet). Methods: Mouse models generated from implanted HNSCC surgical cases were optimized for a combination of factors (e.g. mouse strain, tumor location) yielding the most similar tumor to the parental cancer using morphologic, stroma invasion and gene expression analysis. Results: Tumor fragments from 25 cases were implanted with a 65% engraftment rate. An unbiased gene analysis comparing pathways enriched in 42 HNSCC and 14 head and neck normal tissues showed enrichment for the HhP in the cancers. IHC staining for the ligand sonic hedgehog (SHH) of a tissue array of 60 HNSCC and 20 normal tissues indicated that 65% were positive (++) or very positive (+++) and only 35% of the cancers were negative or faint (+), while 78% of normal tissues were negative for SHH. Samples from 3 DPTM and 3 cell line-derived xenografts were positive for SHH. Four DPTMs were treated in vivo with Cet, IPI-926, and the combination. IPI-926 had activity (T/C <40%) in two cases, and both Cet and the combination induced regressions in three. Whereas in all cases Cet-treated tumors re-grew 4-8 weeks post-therapy, combination- treated mice were relapse-free 3 months post-therapy. To test if Cet leads to CSC accumulation, putative CSC markers were measured by flow cytometry. CD24/44 and CD24/ALDH cells accumulated in Cet-treated tumors but decreased in combination-treated tumors. Implanted CD24/44 and CD24/ALDH positive cells generated tumors at a higher rate than negative cells despite a 100-fold cell dilution. These subgroups expressed SMO and GLI1 genes 200-fold and 700-fold higher than negative cells, respectively. Conclusions: The HhP is activated in HNSCC, with over-expression seen in the CSC subpopulation, where data suggests autologous signaling. When combined with Cet, HhP inhibition with IPI-926 diminishes CSC and prevents tumor relapse in a DPTM of HNSCC. Author Disclosure Employment or Leadership Position Consultant or Advisory Role Stock Ownership Honoraria Research Funding Expert Testimony Other Remuneration Infinity Infinity