Advancement of PI3 Kinase Inhibitor Combination Therapies for PI3K-Aberrant Chordoma

Objectives  Targeted inhibitors of the PI3 kinase (PI3K) pathway have shown promising but incomplete antitumor activity in preclinical chordoma models. The aim of this study is to advance methodology for a high-throughput drug screen using chordoma models to identify new combination therapies for chordoma. Study Design  Present work is an in vitro study. Setting  The study conducted at an academic research laboratory. Materials and Methods  An in vitro study on automated high-throughput screening of chordoma cells was performed using a library of 1,406 drugs as both mono- and combination therapies with PI3K inhibitors. Combination indices were determined for dual therapies and synergistic outliers were identified as potential therapeutic agents. T (brachyury) siRNA knockdown in combination with PI3K pathway inhibition was also assessed. Results  Fifty-nine combination therapies were identified as having potential therapeutic efficacy. Effective combinations included PI3K inhibitors with GSK1838705A (ALK/IGF-1R inhibitor), LY2874455 (VEGFR/FGFR inhibitor), El1 (selective Ezh2 inhibitor), and (-)-p-bromotetramisole oxalate (alkaline phosphatase inhibitor). The top ranking targets identified included ALK, PDGFR, VEGFR, aurora kinase, and BCL-2. T (brachyury) inhibition produced significant reduction in cell viability and growth; however PI3K inhibition in combination with T (brachyury) knockdown did not result in further reduction in growth and viability in vitro. Conclusion  High throughput with in vitro combination screening is feasible with chordoma cells and allows for rapid identification of synergistic dual-therapies. Potential combination therapies and targetable pathways were identified. T (brachyury) knockdown produced significant reduction in cell viability, but did not show additional benefit with PI3K pathway inhibition in this model. Further in vitro and in vivo validation of these therapeutic combinations is warranted.

Abstract PO-006: Single cell transcriptomic analysis of primary head and neck cancer stem cells

Despite advances in treatment modalities for head and neck squamous cell carcinoma (HNSCC) survival rates remain unchanged. Tumor heterogeneity within HNSCC as well as within the tumor microenvironment (TME) has been shown to be a major driver of treatment failure and poor outcomes. A key component of the TME and a potential key to deciphering tumor heterogeneity are cancer stem cells. While numerous studies have demonstrated the tumorigenicity and malignant potential of these cells, few studies have investigated their expression profiles. The aim of this study is to leverage single cell technology to investigate the expression profile of primary HNSCC cancer stem cells. We performed single cell sequencing of five primary HPV-negative head and neck cancers and two HNSCC cell lines that were presorted into the CSC (CD44high/ALDH+) and non-CSC (CD44low/ALDH-) phenotype. We are able to characterize an expression profile of the CSC TME niche and a novel CSC expression profile (DCN, C110rf96, KLF4, MEG3 and NR4A1) relative to non-CSC. We confirm this CSC profile is conserved across all five primary tumors. Together these data provide some of the first insights into CSC transcriptome, further define the CSC-TME niche, and identify conserved targets within HNSCC CSC as a means to decipher the challenges inherent to tumor heterogeneity.

Citation Format: Molly E. Heft Neal, Stephanie The, John Henry J. Owen, Clifford Chang, Mark E.P. Prince, Arvind Rao, Steven B. Chinn. Single cell transcriptomic analysis of primary head and neck cancer stem cells [abstract]. In: Proceedings of the AACR Virtual Special Conference on Tumor Heterogeneity: From Single Cells to Clinical Impact; 2020 Sep 17-18. Philadelphia (PA): AACR; Cancer Res 2020;80(21 Suppl):Abstract nr PO-006.