Personalized in vitro cancer modeling - fantasy or reality?

Abstract

With greater technological advancements and understanding of pathophysiology, "personalized medicine" has become a more realistic goal. In the field of cancer, personalized medicine is the ultimate objective, as each cancer is unique and each tumor is heterogeneous. For many decades, researchers have relied upon studying the histopathology of tumors in the hope that it would provide clues to understanding the pathophysiology of cancer. Current preclinical research relies heavily upon two-dimensional culture models. However, these models have had limited success in recreating the complex interactions between cancer cells and the stroma environment in vivo. Thus, there is increasing impetus to shift to three-dimensional models, which more accurately reflect this phenomenon. With a more accurate in vitro tumor model, drug sensitivity can be tested to determine the best treatment option based on the tumor characteristics. Many methods have been developed to create tumor models or "tumoroids," each with its advantages and limitations. One significant problem faced is the replication of angiogenesis that is characteristic of tumors in vivo. Nonetheless, if three-dimensional models could be standardized and implemented as a preclinical research tool for therapeutic testing, we would be taking a step towards making personalized cancer medicine a reality.

Figure 1

Summary of 3D tumor models. There are seven main methods: 1) Cancer models created by cellular spheroid technique can be formed by five main methods: rotary cell culture system , microarray , hanging drop plate technique , , hanging drop array , or collagen-implanted spheroids . 2) Organotypic explant culture involves dissecting organs into slices, which are subsequently cultured on a semiporous membrane or embedded in a collagen matrix, and grown in an air–liquid growth medium interface . 3) Polarized epithelial cell culture is an approach in which cells are grown on a porous membrane, forming polarized monolayers . 4) Gyratory and spinner flasks are used to culture cells in suspension; the fluid movement aids transport of both nutrients and waste, facilitating growth of the spheroid . 5) Microcarrier beads made from various materials, including dextran, gelatine, glycosaminoglycans, and other porous polymers, can be used to create these tumoroids by acting as a support structure for culture of cell lines that are anchorage dependent . 6) Artificial skin can also be used as a 3D culture model. It is made up of three main layers: the fibroblast and a biodegradable fibre mesh layer, which together form the dermis, and keratinocytes, which form the epidermis . Fibroblasts are first cultured in vitro and seeded onto the fiber mesh layer. Keratinocytes are then added to the dermal tissue to form the epidermis . 7) Artificial cancer masses are created by seeding cancer cells onto a collagen hydrogel. Plastic compression is then applied to enhance cell and matrix density , .

Figure 2

Figure illustrates some of the fundamental milestones which must be met before in vitro models can accurately recreate the tumor microenvironment.

Figure 3

Illustration of the complex concentric architecture typically observed in tumoroids. Concentration gradients of nutrients and metabolites typically establish three distinct zones in the tumoroid: an outer proliferative zone, a middle quiescent zone, and an inner apoptotic/necrotic core. Proximity to vasculature ensures that there is an abundance of oxygen and glucose peripherally, along with the efficient removal of waste products, permitting high levels of cell proliferation. Centrally, low levels oxygen lead to anaerobic respiration, a buildup of toxic metabolites such as CO₂ and lactate, and subsequent cell apoptosis.