Abnormal vascularization of malignant tumors is associated with the development of microregions of heterogeneous cells and environments. Experimental models such as multicell spheroids and a variety of new techniques are being used to determine the characteristics of these microregions and to study the interactions of the cells and microenvironments. The special cellular microecology of tumors influences responsiveness to therapeutic agents and has implications for future directions in cancer research.

http://science.sciencemag.org/content/sci/240/4849/177.full.pdf

Cell and environment interactions in tumor microregions: the multicell spheroid model

Molecules involved in the antigen receptor-dependent regulation of early T cell activation genes were investigated with the use of functional sequences of the T cell activation-specific enhancer of interleukin-2 (IL-2). One of these sequences forms a protein complex, NFAT-1, specifically with nuclear extracts of activated T cells. This complex appeared 10 to 25 minutes before the activation of the IL-2 gene. Studies with inhibitors of protein synthesis indicated that the time of synthesis of the activator of the IL-2 gene in Jurkat T cells corresponds to the time of appearance of NFAT-1. NFAT-1, or a very similar protein, bound functional sequences of the long terminal repeat (LTR) of the human immunodeficiency virus type 1; the LTR of this virus is known to be stimulated during early T cell activation. The binding site for this complex activated a linked promoter after transfection into antigen receptor-activated T cells but not other cell types. These characteristics suggest that NFAT-1 transmits signals initiated at the T cell antigen receptor.

https://science.sciencemag.org/content/sci/241/4862/202.full.pdf

Identification of a putative regulator of early T cell activation genes

Drug development is a lengthy and costly process that proceeds through several stages from target identification to lead discovery and optimization, preclinical validation and clinical trials culminating in approval for clinical use. An important step in this process is high-throughput screening (HTS) of small compound libraries for lead identification. Currently, the majority of cell-based HTS is being carried out on cultured cells propagated in two-dimensions (2D) on plastic surfaces optimized for tissue culture. At the same time, compelling evidence suggests that cells cultured in these non-physiological conditions are not representative of cells residing in the complex microenvironment of a tissue. This discrepancy is thought to be a significant contributor to the high failure rate in drug discovery, where only a low percentage of drugs investigated ever make it through the gamut of testing and approval to the market. Thus, three-dimensional (3D) cell culture technologies that more closely resemble in vivo cell environments are now being pursued with intensity as they are expected to accommodate better precision in drug discovery. Here we will review common approaches to 3D culture, discuss the significance of 3D cultures in drug resistance and drug repositioning and address some of the challenges of applying 3D cell cultures to high-throughput drug discovery.

/pdf/three-dimensional-in-vitro-cell-culture-models-in-drug-4juso4njdm.pdf

Three-Dimensional in Vitro Cell Culture Models in Drug Discovery and Drug Repositioning.

Spherical cancer models in tumor biology.

https://link.springer.com/content/pdf/10.1016/j.bulm.2003.11.002.pdf

A history of the study of solid tumour growth: the contribution of mathematical modelling.

(1970). A Multi-component Radiation Survival Curve Using an in Vitro Tumour Model. International Journal of Radiation Biology and Related Studies in Physics, Chemistry and Medicine: Vol. 18, No. 5, pp. 491-495.

A Multi-component Radiation Survival Curve Using an in Vitro Tumour Model

Medium calcium ions were essential to the development of the lymphocyte transformation response induced by PHA. Magnesium ions could not substitute for calcium ions. Calcium exerted its influence during the induction phase of the process before DNA synthesis began since its removal after the response had fully developed did not alter subsequent levels of nucleic acid synthesis. The early development of RNA synthesis was prevented by low calcium levels indicating that calcium either directly influenced the initiation of this process or some prior event(s).

Requirement for calcium ions in lymphocyte transformation stimulated by phytohemagglutinin

SummaryRadiation-resistant, hypoxic cells have been demonstrated in an in vitro tumour model by reoxygenation, specific chemical sensitization, and autoradiography experiments Enhanced cell-killing was found when spheroids were given two large fractions of radiation The development of central necrosis was also found to correlate with oxygen deprivation and was only slightly affected by deficiencies in other metabolites These results suggest that multicelluar spheroids provide a useful in vitro model for tumour therapy

Hypoxic Cells in an in Vitro Tumour Model

Radiosensitization by Nifuroxime of the Hypoxic Cells in an in Vitro Tumour Model

Cells which were grown and irradiated as multicell spheroids were found to exhibit time-dependent fluctuations in sensitivity to further irradiation These variations in radiosensitivity iosld be attributed to repair of sublethal radiation damage and to irradiation-induced reoxygenation; the relative influence of each process depended on the magnitude of the initial radiation exposure and the time between fractions Repair of sublethal radiation damage was predominant after small radiation doses Despite repair and cellular repopulation between successive exposures, therapy-like regimens produced complete reoxygenation after several days Single radiation exposures large enough to kill virtually all oxygenated cells resulted in an immediate, but transient sensitization of the surviving hypoxic cells, presumably resulting from a transient, irradiation-induced inhibition of the respiration of the aerobic cells of the spheroid Thus, in the in vitro tumor system, post-irradiation reoxygenation can be achieved by both inhibition of cellular respiration and/or by cell killing

Robert M. Sutherland

Papers

A Multi-component Radiation Survival Curve Using an in Vitro Tumour Model

Requirement for calcium ions in lymphocyte transformation stimulated by phytohemagglutinin

Hypoxic Cells in an in Vitro Tumour Model

Radiosensitization by Nifuroxime of the Hypoxic Cells in an in Vitro Tumour Model

Repair and reoxygenation following irradiation of an in vitro tumor model.