Create, raise, kill

Ksenia Perfilieva, "Elements", according to the article "3D bioprinting of the tumor microenvironment: recent achievements" (Timofeeva et al., Journal of General Biology, 2021).

3D printing allows you to create living objects with the desired characteristics with the desired cellular composition. Such models of living tissues (organs) open the way to the study of interactions between cellular elements and the intercellular environment in conditions close to functioning in a living organism. It is known that the tumor microenvironment has a significant impact on the rate of its development, as well as on the ability to resist antitumor agents. The article discusses methods for creating and researching 3D models of various variants of the tumor microenvironment and the tumor cells themselves.

Creating life in a test tube is a long–standing dream of a person – has not yet been realized, but the opportunity to make in a Petri dish the necessary "spare parts" for a person to replace those that have fallen into disrepair, perhaps, is becoming a reality. Officially, the technology of creating three-dimensional models of living cellular tissues and organs, in which the viability and functions of cells are preserved, was first patented in the USA in 2006 (although people were already familiar with the more advanced technology of printing a living person by DNA sequence thanks to talented creators of virtual reality.

Luc Besson did not miss so much in 1997 (!), creating a cinematic 3D bioprinter for printing the ideal person (a frame from the film "The Fifth Element").

3D-bioprinting, yesterday's fantasy, is now a real biomedical technology that allows you to create not only relatively simple and homogeneous living objects – tissues with a small set of different cell types, but even whole organs with vessels (Fig. 1). The object is literally printed ready-made, i.e. it does not take a long time to grow it as in classical cell culture, although the functioning of such an object implies its further development. Inks (biochernils) are a special medium with living cells, which provides a given mechanical strength and is able to maintain the viability of cells.

Fig. 1. (A – C) Suspension medium used as a technological means for three-dimensional bioprinting of the human heart and an example of 3D bioprinting, a miniature human heart made of cardiomyocytes, endothelial cells and extracellular human matrix. (D) A 3D-printed heart extracted from the medium, then perfused with red and blue dyes to demonstrate the hollow chambers inside the structure even contains several vessels. The scale size is 1 mm. See details here.

You can use several types of biochernils, combining them into a heterogeneous object. There are three main methods of various modifications of 3D bioprinting, i.e. printing: inkjet, laser and extrusion-based printing (Fig. 2), but other methods are also being developed. A variety of printing methods are able to control the structure of the resulting "living objects" at the nano level, up to individual cells. Thus, there is a unique opportunity to connect living tissue elements in any combinations and study their interactions in close to native conditions.

Fig. 2. The main methods of 3D bioprinting: 1 – jet, 2 – extrusion, 3 – laser (illustration from the article under discussion).

One of the important current and already working areas of application of 3D bioprinting technologies is the study of the effect of cosmetic and medicinal products on living tissues, not only without involving living organisms in tests, but directly on human tissues. In the article under discussion, the authors presented an overview of the creation and study of microenvironment models of human malignant tumors recreated on the basis of 3D bioprinting. The cellular environment of the tumor (angiogenic vascular, infiltrating immune, endothelial, stromal cells) and the extracellular matrix (matrix proteins, signaling molecules, growth factors, etc.) are a heterogeneous environment (tumor microenvironment), the properties of which can promote or inhibit tumor growth. Multifactorial processes are complicated by the presence of individual characteristics in the course of the disease in different people. Studying the interactions between all elements of a living object on 3D models will help to find approaches for the individual treatment of malignant tumors, since each patient's tumor is unique due to individual (including genetic) human characteristics. One of the amazing advantages of 3D bioprinting is the possibility of integration into the models of blood networks, which are extremely important in the processes of tumor formation, since they provide the intensity of oxygen and nutrient delivery. To date, it has been possible to create viable 3D models for several types of cancer: breast (breast cancer), skin, lung, liver, ovaries, cervix, colorectal, glioblastoma. Creating models is almost a creative process. Biochernils are not standardized today, in fact, the cellular material used for bioprinting should also be unique.

For example, one of the models based on a bone matrix and a hydrogel was created to study the interaction of breast cancer cells and mesenchymal stem cells (Fig.3). It was shown that in this "two-component" system, the growth of the number of tumor cells is accelerated and the proliferation (division) of mesenchymal cells is simultaneously reduced. 

3. Mesenchymal stem cells (MSCs) are multipotent cells that can divide and differentiate into various cell types, including osteoblasts, chondrocytes, myocytes, adipocytes, and possibly other cell types.

In another experiment, a 3D model using a culture of breast cancer cells and stem cells derived from adipose tissue, the effects of an antitumor agent (doxorubicin) were investigated. The 3D model was a disk with tumor cells in the center and adipose tissue cells at the edges. In the experiment, the thickness of the layer with fat cells was varied. It was shown that an increase in this layer led to an increase in the resistance of tumor cells to an antitumor drug. Attempts to create heterogeneous 3D models with different types of cells (tumor, fibroblasts, mesenchymal stem cells, fat cells, etc.) were successful.

In general, all experiments demonstrated greater resistance of tumor cells in 3D models compared to classical cultures (2D models). The main prospects for the development of research are expected, obviously, in several directions: the selection and creation of biochernils with specified properties, as well as their standardization for subsequent use in experiments; obtaining heterogeneous cellular material for creating various 3D tumor models, the actual study of processes in multicomponent tumor models and the effects of drugs on them.

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