No abstract

Increased glucose uptake and accumulation of lactate, even under normoxic conditions (i.e., aerobic glycolysis or the Warburg Effect), is a common feature of cancer cells. This phenomenon clearly indicates that lactate is not a surrogate of tumor hypoxia. Tumor lactate can predict for metastases and overall survival of patients, as shown by several studies of different entities. Metastasis of tumors is promoted by lactateinduced secretion of hyaluronan by tumor-associated fibroblasts that create a milieu favorable for migration. Lactate itself has been found to induce the migration of cells and cell clusters. Furthermore, radioresistance has been positively correlated with lactate concentrations, suggesting an antioxidative capacity of lactate. Findings on interactions of tumor metabolites with immune cells indicate a contribution of lactate to the immune escape. Furthermore, lactate bridges the gap between high lactate levels in wound healing, chronic inflammation, and cancer development. Tumor cells ensure sufficient oxygen and nutrient supply for proliferation through lactate-induced secretion of VEGF, resulting in the formation of new vessels. In summary, accumulation of lactate in solid tumors is a pivotal and early event in the development of malignancies. The determination of lactate should enter further clinical trials to confirm its relevance in cancer biology. Cancer Res; 71(22); 6921-5. Ó2011 AACR.

The aim of the present study was to assess the feasibility of a 3D tumor cell culture model, that is, multicellular tumor spheroids (MCTSs) as an adequate model for micrometastases and therefore as a pharmacological model for efficacy testing of trifunctional therapeutic antibodies. Unlike conventional monolayer cultures, spheroids allow researchers to study parameters, such as 3D cell shape, 3D cell arrangement and microenvironment, and penetration efficiency of defense cells that may largely influence the efficacy of antibody treatment in vivo. The authors established a long-term coculture of human MCTSs with peripheral blood mononuclear cells (PBMCs) to test the anticancer effect of the trifunctional, bispecific antibody catumaxomab (anti-EpCAM x anti-CD3) or similar therapeutic molecules. The test system is accessible to various analytical methods and thus allows for characterizing multiple parameters, which can help elucidate the mode of action of immunotherapeutic anticancer treatment. For example, the novel approach enables precise, reproducible volume growth analysis of MCTSs under immunotherapeutic treatments. For evaluation of changes within individual spheroids, cryosections can be stained (e.g., for proliferating or apoptotic cells as well as infiltrating PBMCs). Molecular PCR-based assays or flow cytometric analyses allow for discrimination between different cell types, particularly leukocyte subtypes. Furthermore, MCTSs can be disaggregated to form standard monolayers for cell viability or plating efficiency experiments. For these reasons, the MCTS model is a powerful tool to analyze drug efficacy with various endpoints under highly reproducible, standardized conditions.

Multicellular tumor spheroids (MCTS) are routinely employed as three-dimensional in vitro models to study tumor biology. Cultivation of MCTS in spinner flasks provides better growing conditions, especially with regard to the availability of nutrients and oxygen, when compared with microtiter plates. The main endpoint of drug response experiments is spheroid size. It is common practice to analyze spheroid size manually with a microscope and an ocular micrometer. This requires removal of some spheroids from the flask, which entails major limitations such as loss of MCTS and the risk of contamination. With this new approach, the authors present an efficient and highly reproducible method to analyze the size of complete MCTS populations in culture containers with transparent, flat bottoms. MCTS sediments are digitally scanned and spheroid volumes are calculated by computerized image analysis. The equipment includes regular office hardware (personal computer, flatbed scanner) and software (Adobe Photoshop, Microsoft Excel, ImageJ). The accuracy and precision of the method were tested using industrial precision steel beads with known diameter. In summary, in comparison with other methods, this approach provides benefits in terms of semiautomation, noninvasiveness, and low costs.

After Warburg stated his hypothesis on tumor cell metabolism about 80 years ago, the field of carbohydrate metabolism of cancer cells and solid tumors is experiencing a boom for the past few years. Numerous studies have been focused on the characteristics of cancer metabolism and its accessibility to novel therapeutic interventions. Malignant transformation is associated with an increase in glycolytic flux, mainly caused by an upregulation of numerous glycolysis-related genes in the majority of human cancers. As a consequence of these alterations, tumor cells are producing lactate at higher levels compared to non-malignant tissue, even in the presence of oxygen, a phenomenon termed "aerobic glycolysis" or "Warburg effect". A correlation between alterations in glycolytic pathways and therapy resistance in tumors is partially due to radical scavenger properties of specific metabolites which may decrease therapy-induced radical formation. Glycolytic activity and glycolysis-linked metabolic milieu are often variable between individual tumors resulting in variations in treatment response and aggressiveness. The peculiarities of tumor cell metabolism can be utilized for cancer diagnostics, such as metabolic imaging techniques and metabolic tumor markers. An emerging field of research is the manipulation of tumor cell metabolism for therapeutic purposes; respective studies include approaches of glycolysis inhibition or forcing mitochondrial respiration, respectively, based on biochemical and molecular principles. Up to now, such approach could eliminate tumors in patients without side effects when applied as single drug. Nevertheless, several agents that manipulate tumor metabolism may become a supportive therapy in combination with established cancer treatments.