Assay Development and Screening
Advanced In Vitro Cell Culture Systems
Historically, cancer drug leads are identified in high throughput screening (HTS) growth inhibition assays performed in tumor cell line panels maintained and assayed in 2 dimensional cultures. However, the overall probability for success in oncology clinical trials is a dismal 3.4%. To improve clinical development success rates for solid tumors, more physiologically relevant in vitro 3-dimensional models are being deployed in lead generation to identify better cancer drug candidates. Multicellular tumor spheroids (MCTSs) resemble avascular tumor nodules, micro-metastases, or the intervascular regions of large solid tumors with respect to morphology, volume growth kinetics, and form diverse microenvironments due to gradients of nutrient distribution and oxygen concentration. Head and neck cancers (HNC) are the 8th leading cause of cancer worldwide and in 2019 it’s projected that 53,000 people in the USA will develop oral cavity or pharynx cancer and 10,860 will die of these cancers. Seven drugs are approved for HNC therapy, but only 10-25% of patients respond to single agent therapy, and 5-year survival and/or cure rates have not improved. Although pembrolizumab (Keytruda®) was well tolerated in patients with recurrent or metastatic HNC and produced clinically relevant antitumor activity, only 16% patients responded to treatment. The low response rates and limited efficacy of HNC drugs underscores the need to discover new and effective therapies. We have developed methods to characterize HNC MCTS morphologies, viability and growth phenotypes and to conduct cancer drug HTS. In a total of 95 pairwise cancer drug x HNC cell line experiments only 35.8% of MCTS cultures exhibited a concentration dependent growth inhibitory response using metabolic viability reagents, and only 24.4% produced ≥50% reduction in Calcein AM live cell staining. In contrast, 67.8% increased ethidium homodimer dead cell staining by ≥50% and 89.5% altered ≥1 morphological feature; size, shape/perimeter or density/compactness. These data demonstrate that multiple analysis methods are required to accurately assess the impact of cancer drugs on HNC MCTS cultures and to maximize the value of these physiologically relevant tumor cultures.