Fredika A. Robertson, Ph.D., executive director for clinical research services at Virginia Commonwealth University’s Center for Clinical and Translational Research, described the development of a tumor spheroid system for small compound screening. This system was developed using tumor cells isolated from the pleural fluid of breast cancer patients.
“These freshly isolated metastatic tumor cells spontaneously form 3D multilayered tumor spheroids, and have several advantages over 2D monolayer cultures for screening,” Dr. Robertson pointed out. These advantages include the enrichment in the 3D spheroids of cancer stem cells or tumor-initiating cells expressing markers such as CD44+, ALDH-1+, and CD133, as well as the recapitulation by the spheroids of the necrotic center that exists in tumors beyond 1–2 mm in size.
“We found that our 3D tumor spheroid system mimics activation of multiple cellular signaling pathways, allowing us to identify the activation of specific signaling pathways in breast metastasis,” said Dr. Robertson. With her group, Dr. Robertson showed that the receptor tyrosine kinase anaplastic lymphoma kinase (ALK) is activated in preclinical models of inflammatory breast cancer, where it signals through a variety of downstream pathways, including JAK1/STAT3, AKT, and mTOR.
“We found that the ALK inhibitor, Crizotinib [Xalkori®, Pfizer] effectively eradicates the 3D tumor spheroids from patients with ALK+ tumors,” Dr. Robertson pointed out. “This is an example of how the identification of the biological signaling pathways that are activated in our patient-derived 3D tumor spheroid systems directly led to clinical trials using this targeted therapeutic.”
Tumor spheroids were also the subject of a presentation by Jason Ekert, Ph.D., senior research scientist at Janssen Research and Development. Dr. Ekert described efforts to develop a tumor model that more faithfully recapitulated the role of cancer signaling pathways in patient tumors.
Pathways involving the transmembrane receptor kinases epidermal growth factor receptor (EGFR) and cMET are involved in the transduction of growth factor signals to the cell, and are thought be active in a large number of lung tumors.
“We were interested in better understanding the differences between 2D monolayer and 3D spheroid lung tumor cultures in the context of the EGFR-cMET cancer biology pathway,” explained Dr. Ekert. “Our flow cytometry data told us that EGFR and cMET expression was reduced in spheroid cultures compared to monolayer cultures, and that basal phosphorylation of EGFR and cMET was higher in spheroid cultures.”
Dr. Ekert suggests that such subtle microenvironment-induced changes in lung tumor cell physiology add a level of complexity to cell-based assays that may be more representative of the in vivo tumor microenvironment, thereby improving the predictive capability of screening assays. He went on to highlight the ability of the 3D system to discriminate between different EGFR and cMET mutants that inhibited cell migration and proliferation.