Role of Adipose Cells in Tumor Microenvironment - The Mechanobiology of Obesity and Related Diseases - page 277

testing [ 151 ]. Over the past decade, efforts have been made toward designing
three-dimensional (3D) cell culture models replicating the structure, physiology,
and function of tumors seen in vivo. 3D culture systems mimicking the tumor
microenvironment are expected to be more appropriate in drug screens, as they
could simulate endogenous tissue structure and organization. Appropriately
designed 3D models may allow to recreate composition, structure, and mechanical
forces of ECM and, therefore, simulate concentration gradients of signaling
molecules and therapeutic agents within tumors.
In recent years, a number of 3D cell culture techniques have been developed to
recreate complex tissue organization [ 152 ]. While some tissues are capable of
forming organoids spontaneously [ 153 ], others require scaffolds in order for the
cells to integrate in an organotypic manner. Most efforts have focused on bio-
polymer scaffolds with Matrigel or other ECM-based platforms [ 154 ]. Sponge
scaffolds have also been introduced [ 155 ], and to generate substantial tissue
amounts, agitation-based bioreactors have been implemented [ 156 ]. Microfluidics
setups in the context of perfusion simulating vasculature have also been designed,
however, they are cumbersome and have other shortcomings, such as the current
inability to retain key cell types. To this day, 3D culture cancer models in which all
cellular components, namely epithelial, endothelial, mesenchymal/stromal and
hematopoietic, are assembled in a manner resembling tumor organization have not
been reported. Dominance of certain cell populations at the expense of other key
populations being lost in conventional culture settings has been the major technical
challenge.
An advance in tissue culture, allowing to maintain all cell populations of
interest, has come with the development of the 3D levitation system based on
magnetic nanoparticles [ 157 ]. This technology is based on the cellular uptake and
membrane adhesion of magnetic Nanoshuttle (NS) and subsequent magnetic
levitation and concentration of the magnetized cells. A unique feature of the
magnetic levitation approach is the expedited timeline of 3D spheroid formation
driven by magnetic field without the loss of cell populations (some which do not
engage in other systems). While simpler approaches to spheroid culture in agitated
medium and/or low-adherence have been reported for many cell types [ 158 ], the
rationale behind using magnetic levitation is to enforce retention of distinct cell
types composing a complex tissue, many of which tend to get lost in conventional
culture settings. The levitation method assures cell-cell interaction between dif-
ferent cell types by magnetically guiding cells together. Another advantage of this
system is the dependence of intercellular contacts on endogenously synthesized
ECM molecules rather than on artificial substrates serving as a foundation of other
3D culture designs.
Recently, we developed a 3D tissue culture system based on magnetic levitation
to model WAT [ 159 ]. We showed that preadipocytes remain viable in spherical
organoids termed ''adipospheres'' for a long period of time, while in 2D culture
they lose adherence and die after reaching confluence. Upon adipogenesis
induction, cells in adipospheres efficiently formed large lipid droplets typical of
white adipocytes in vivo. Adiposphere-based co-culture of 3T3-L1 preadipocytes