Modeling adaptive drug resistance of colorectal cancer and therapeutic interventions with tumor spheroids

Abstract

Drug resistance is a major barrier against successful treatments of cancer patients. Various intrinsic mechanisms and adaptive responses of tumor cells to cancer drugs often lead to failure of treatments and tumor relapse. Understanding mechanisms of cancer drug resistance is critical to develop effective treatments with sustained anti-tumor effects. Three-dimensional cultures of cancer cells known as spheroids present a biologically relevant model of avascular tumors and have been increasingly incorporated in tumor biology and cancer drug discovery studies. In this review, we discuss several recent studies from our group that utilized colorectal tumor spheroids to investigate responses of cancer cells to cytotoxic and molecularly targeted drugs and uncover mechanisms of drug resistance. We highlight our findings from both short-term, one-time treatments and long-term, cyclic treatments of tumor spheroids and discuss mechanisms of adaptation of cancer cells to the treatments. Guided by mechanisms of resistance, we demonstrate the feasibility of designing specific drug combinations to effectively block growth and resistance of cancer cells in spheroid cultures. Finally, we conclude with our perspectives on the utility of three-dimensional tumor models and their shortcomings and advantages for phenotypic and mechanistic studies of cancer drug resistance.

Therapeutic Targeting of Cancer Stem Cells Prevents Resistance of Colorectal Cancer Cells to MEK Inhibition

“…54,55 Over the past several years, we have developed tumor spheroid models of colorectal cancers for mechanistic studies of drug resistance and to test and identify effective treatment strategies. 56 Here, we leveraged our established 3D tumor spheroid model in a cyclic treatment regimen to demonstrate that colorectal cancer cells develop adaptive resistance to single-agent inhibition of MEK through feedback signaling and gain of stemness. We found that a combination treatment approach targeting MEK and CSCs effectively blocks adaptive resistance of cancer cells by suppressing tumor stemness.…”

“…Spheroid and organoid cultures of cancer cells have been leveraged to study mechanisms of drug resistance in different cancers. − For example, a 3D model of colorectal cancer composed of cells derived from a primary tumor reproduced resistance to 5-FU treatment in the animal model, and an organoid culture model developed under an air-liquid interface contained CSCs and exhibited resistance to anticancer drugs. , Over the past several years, we have developed tumor spheroid models of colorectal cancers for mechanistic studies of drug resistance and to test and identify effective treatment strategies . Here, we leveraged our established 3D tumor spheroid model in a cyclic treatment regimen to demonstrate that colorectal cancer cells develop adaptive resistance to single-agent inhibition of MEK through feedback signaling and gain of stemness.…”

EMMPRIN promotes spheroid organization and metastatic formation: comparison between monolayers and spheroids of CT26 colon carcinoma cells

“…In this study, we demonstrate that EMMPRIN is an important participant in the formation of spheroids as a spatial organization of tumor cells, and that this organization and the expression of high levels of EMMPRIN promote cellular properties that enhance their ability to metastasize. Spheroids have emerged as a useful tool that more closely simulates the in vivo organization of solid tumors in comparison to the standard in vitro culturing approach of monolayers, and provide a better in vitro platform to study the enhanced metastatic properties of tumor cells ( 19 ). We emphasize that in our study the cells seeded as monolayers or spheroids were not stimulated in any other way, allowing us to assess the effects of the spatial organization alone.…”

“…The spherical structure creates gradients of oxygen and nutrients that generate heterogeneity in the rate of proliferation and metabolism of the spheroid cells, and in their expression of genes ( 16 , 17 ). Although these 3D structures are only an intermediate model of the tissue and do not fully model the intricate interactions between cells and their neighboring cells or the tissue-specific extracellular matrix (ECM) components ( 18 ), spheroids have become a relevant in vitro model to study the development of resistance to chemotherapeutic treatment ( 19 ) and a high throughput screening platform for drugs ( 20 ). However, other than E-cadherin and integrins, the proteins mediating the cell-cell interactions that form the spheroid structure are still not well characterized ( 21 ).…”

Inhibiting BRAF/EGFR/MEK suppresses cancer stemness and drug resistance of primary colorectal cancer cells

“…Our previous studies used spheroid cultures of cancer cell lines in cyclic treatments to establish the feasibility of investigating mechanisms of drug resistance and testing the efficacy of different drug combinations [ 16 ]. Using primary cancer cells is critical to facilitate translational potential of this approach.…”