Cyclical Treatment of Colorectal Tumor Spheroids Induces Resistance to MEK Inhibitors

Abstract

Adaptive drug resistance is a major obstacle to successful treatment of colorectal cancers. Physiologic tumor models of drug resistance are crucial to understand mechanisms of treatment failure and improve therapy by developing new therapeutics and treatment strategies. Using our aqueous two-phase system microtechnology, we developed colorectal tumor spheroids and periodically treated them with sub-lethal concentrations of three Mitogen Activated Kinase inhibitors (MEKi) used in clinical trials. We used long-term, periodic treatment and recovery of spheroids to mimic cycles of clinical chemotherapy and implemented a growth rate metric to quantitatively assess efficacy of the MEKi during treatment. Our results showed that efficacy of the MEKi significantly reduced with increased treatment cycles. Using a comprehensive molecular analysis, we established that resistance of colorectal tumor spheroids to the MEKi developed through activation of the PI3K/AKT/mTOR pathway. We also showed that other potential feedback mechanisms, such as STAT3 activation or amplified B-RAF, did not account for resistance to the MEKi. We combined each of the three MEKi with a PI3K/mTOR inhibitor and showed that the combination treatments synergistically blocked resistance to the MEKi. Importantly, and unlike the individual inhibitors, we demonstrated that synergistic concentrations of combinations of MEK and PI3K/mTOR inhibitors effectively inhibited growth of colorectal tumor spheroids in long-term treatments. This proof-of-concept study to model treatment-induced drug resistance of cancer cells using 3D cultures offers a unique approach to identify underlying molecular mechanisms and develop effective treatments.

Overactivation of Akt Contributes to MEK Inhibitor Primary and Acquired Resistance in Colorectal Cancer Cells

“…Primary colorectal cancers frequently harbor somatic mutation of KRAS (~40%), BRAF (~10-15%) and PIK3CA (~10-20%) [6][7][8][9]. These mutations induce activation of the Raf/mitogen activated protein kinase kinase (MEK)/extracellular signal regulated kinase (ERK) and phosphoinositol-3 kinase (PI3K)/Akt pathways which contribute to resistance to chemotherapy and anti-EGFR treatments [3][4][5].…”

Toxicity of Combinations of Kinase Pathway Inhibitors to Normal Human Cells in a Three-Dimensional Culture

“…While heterogeneity of cells within a tumor is a major cause of drug resistance and tumor relapse, cancer cells can also develop adaptive responses to the treatment such as activation of compensatory survival pathways and overactivation of the target. 13 To overcome resistance to single-agent chemotherapy, combination therapies that involve simultaneous use of two drugs have been pursued. 4,14 This approach has proved effective in blocking drug resistance and improving outcomes.…”

Curcumin Down-Regulates CD44 Marker Expresion and Inhibits the Growth of Tumorsphere in 3D Culture Condition of Gastric Cancer Cell line MKN45

“…Có thể nói rằng, nuôi cấy các tumorsphere hay còn gọi là các spheroid là một mô hình vượt trội so với nuôi cấy 2D trong việc nghiên cứu phát triển thuốc [21]. Thakuri và cộng sự đã chỉ rằng, việc xử lý các tumorsphere của ung thư đại tràng bởi chất ức chế MEK phối hợp với các chất ức chế con đường tín hiệu ung thư đã làm giảm khả năng kháng lại các chất ức chế MEK [22].…”