Challenges of applying multicellular tumor spheroids in preclinical phase

Abstract

The three-dimensional (3D) multicellular tumor spheroids (MCTs) model is becoming an essential tool in cancer research as it expresses an intermediate complexity between 2D monolayer models and in vivo solid tumors. MCTs closely resemble in vivo solid tumors in many aspects, such as the heterogeneous architecture, internal gradients of signaling factors, nutrients, and oxygenation. MCTs have growth kinetics similar to those of in vivo tumors, and the cells in spheroid mimic the physical interaction of the tumors, such as cell-to-cell and cell-to-extracellular matrix interactions. These similarities provide great potential for studying the biological properties of tumors and a promising platform for drug screening and therapeutic efficacy evaluation. However, MCTs are not well adopted as preclinical tools for studying tumor behavior and therapeutic efficacy up to now. In this review, we addressed the challenges with MCTs application and discussed various efforts to overcome the challenges.

The Ultrastructural Analysis of Human Colorectal Cancer Stem Cell-Derived Spheroids and Their Mouse Xenograft Shows That the Same Cells Types Have Different Ratios

“…SEM observation of the outer surface of our spheroids showed some samples having blebs and short microvilli, as observed by [ 17 ], and some others having a smooth surface, according to [ 20 ]. As assessed in [ 29 ], important morphological parameters to characterize spheroid growth and response to treatments are their size and circularity. Even if the production of a homogeneous spheroids population is still challenging, the spheroids population we analyzed resulted in having the shape descriptor circularity near to 1, the value of a perfect circle and similarly-sized elements in which diameters had a very low standard deviation.…”

Amphiphilic Poly(N-vinylpyrrolidone) Nanoparticles Conjugated with DR5-Specific Antitumor Cytokine DR5-B for Targeted Delivery to Cancer Cells

“…As well known, tumor spheroids are considered as a more relevant model for anticancer drug discovery compared to monolayer cultures [ 51 ], particularly for studying the antitumor activity of nanomedicines [ 52 , 53 ]. Due to their 3D structure, the tumor spheroids can mimic heterogeneity and microenvironment of small avascular solid tumors in vivo, including specific gene expression, cell-to-cell and cell-to extracellular matrix interactions, growth kinetics, metabolic rates and resistance to chemotherapy [ 54 ]. As a result, this 3D in vitro model allows us to get more complete information on cytotoxic effects, being an intermediate stage between 2D in vitro model (monolayer culture) and testing in animals.…”

In Vitro Magnetic Techniques for Investigating Cancer Progression

“…'Spheroids' generally refer to cells taken from a 2D monoculture, where they were initially expanded, and cultured in suspended media. This suspension drives the aggregation of the free-floating cells into sphere-like clusters dominated by cell-cell attachments, such as N-cadherin and E-cadherin interactions [96,97]. Traditional techniques for spheroid formation include the hanging drop and liquid overlay methods, as well as the use of spinner flasks.…”

“…However, there are several challenges to culturing spheroids with these techniques that have greatly limited the use of spheroids for accurate, translatable research in cancer. Namely, spheroids formed with these methods tend to lack uniformity and reproducibility with respect to aggregate geometry and packing density [94,97]. This is especially concerning for applications such as high-throughput drug screening, where the mass transport rates of the chemotherapeutics may vary between wells such that an accurate comparison of drug sensitivity is not achievable [98].…”