Melanoma - Breast Cancer - Thyroid Cancer - Prostate Cancer
In microgravity, cells grow in 3D in suspension and form aggregates that represent better the cells in human body due to lack of sedimentation and reduced fluid shear. Likewise, 3D aggregates of cancer cells are considered to represent a simple tumor model by mimicking small metastasis and areas of solid tumors in vivo1.The reason behind is that in 3D cultures grown in microgravity, due to lack of nutrition transportation, the presence of small necrosis areas is observed in the middle of spheroids. This area mimics the metastatic tumor regions by showing low metabolic activity and increased drug resistance2. Additionally, multicellular spheroids are not as complicated as real tumors, which make them a convenient model for research purposes1. Therefore, studying factors that alter the behavior of cancer cells in microgravity potentially leads to identification of novel cancer targets and can help scientists to find new anticancer therapeutic strategies.
Another advantage microgravity offers is that in 3D environment, some signaling pathways have an important or even exclusive role, which is not the case in 2D monolayer cultures3. Since this is essential for drug screening process, tumor progression and chemoresistance can be further studied in microgravity. This approach can potentially reduce the numbers of animal for testing and increase the efficiency of drug candidate evaluation4. Moreover, this approach would be also an interest for pharmaceutical companies since the cost of drug development increases exponentially at the stage of in vivo tumor models and even more when entering clinical trial4.
So far, several research groups studied various cancer types in microgravity such as melanoma, breast cancer, thyroid cancer and prostate cancer.
MelanomaPrevious research by Taga et al investigated the effect of microgravity on melanoma cells in simulated microgravity. The findings showed that microgravity altered the melanoma characteristics and increased the invasiveness of the tumor even though the overall tumor growth was decreased5. This research is a possible indicator of microgravity environment is supporting the selection of tumorigenic cells with higher survival capability.
Moreover, microgravity allows growing co-cultures of cancer cells and stromal cells to further investigate the roles of environmental factors that have an impact on the cancer development and progress6. For example; a study performed by Marrero et al, generated multicellular tumor spheroids size of 1 cm that consist of melanoma and keratinocytes7. The model they have developed can be used for understanding how tumor cells react in the presence of environmental stimuli. For this experiment, lacking of immune cells can provide a simple environment but in further research, adding immune cells to the culture would help to study cancer immunotheraphy.
Breast CancerA research performed on human breast cancer cells by Qian et al, studied the effects of simulated microgravity. In this study, human breast cancer cells were incubated in a clinostat for 24, 48 and 72 hours. The results indicated that cell proliferation, invasiveness and migration ability decreased, whereas cell apoptosis increased8. More recently, Kopp et al indicated that the formation of multicellular spheroids of MCF-7 breast cancer cells occurred in simulated microgravity and after five days glandular structures were visible. The breast cancer cells seem to be affected by microgravity quickly since the cells induced several adaptive mechanisms even after one day in microgravity9. Moreover, in the study IL8 gene expression level was elevated earlier in the process, further research would be helpful to understand whether IL8 has a role in forming multicellular tumor spheroids and in tumor progression9.
Thyroid CancerA recent research about thyroid cancer performed by Kopp et al, showed that in simulated microgravity, the cells formed larger and numerous multicellular spheroids than cells grown in monolayer cultures. Authors discussed that the difference in morphological appearance can be sourced from alterations of the enzyme levels, which are associated with cytoskeletal proteins and inflammatory cytokines10. In this regard, IL-8 and osteopontin were identified as possible factors since they were expressed differently in microgravity and they are involved in regulating the cytoskeletal dynamics10. Moreover, striking differences between normal and malignant cells were observed in the expression of genes such as neutrophil gelatinase-associated lipocalin (NGAL), vascular endothelial growth factor (VEGFA), osteopontin (OPN), interleulin-6 (IL6) and interleukin-17 (IL17)10. These genes have roles in angiogenesis process and their expression decreased in microgravity.
Additionally, different microgravity simulation models can induce similar or different effects depending on the cell type. Previous research performed by Warnke et al, compared the behavior of two different microgravity simulation machines: a clinostat and a random positioning machine. The results indicated that caveolin-1 (CAV1), connective tissue growth (CTGF) and vascular endothelial growth factor (VEGF) genes are equally expressed in both conditions11. For this study, two different microgravity platforms showed the same effect on gene expression. Moreover, findings also suggested that these genes were involved in the process of spheroid formation since they were found to be expressed similarly in two different microgravity simulation environments11. Thus, microgravity can be used as a comparative approach to search for gravity-sensitive genes and proteins.
What happens in real microgravity is still an area to explore for many cell types. Human thyroid cancer cells were flown to space during the Shenzhou-8 Space mission. Compared to simulated microgravity controls, 3D multicellular spheroids were bigger in size ranged from 5 to 10 mm. Moreover, gene expression of connective tissue growth factor (CTGF) and epidermal growth factor (EGF) was upregulated in both simulated microgravity and space samples compared to normal gravity samples12. The authors suggested that the bigger spheroids could be helpful to reveal the vascular mimicry of the tumors and to promote understanding of the escape mechanisms of tumors.
Prostate CancerHuman prostate carcinoma cells were also studied in real microgravity by the research conducted by Chung and colleagues on the Space Shuttle STS-107. The experiment showed that when LNCaP human prostate carcinoma cells were co-cultured with osteoblasts, they formed golf-ball sized organoids in less than one week2. On Earth, the 3D cultures seem to reach a limited size of 3-5mm only, as the authors discussed2. In another Space Shuttle experiment, scientists managed to develop a microencapsulation technology. Later this technology was used on Earth to encapsulate cancer drug, which turned out to be a successful tumor treatment on a xenograft of prostate cancer model2.
All in all, microgravity offers a whole new platform to understand the role of gravity in cancer cell progress. The suspension-based 3D cancer cell culture aggregates formed in microgravity with increased growth and possibility to be co-cultured by other cell types are useful tools to understand the molecular mechanisms behind it and to improve treatment options on Earth.
1. Grimm, D., Wehland, M., Pietsch, J., Aleshcheva, G., Wise, P., van Loon, J., ... & Bauer, J. (2014) Growing tissues in real and simulated microgravity: new methods for tissue engineering. Tissue Engineering Part B: Reviews, 20(6), 555-566.
2. Becker, J. L., & Souza, G. R. (2013) Using space-based investigations to inform cancer research on Earth. Nature Reviews Cancer, 13(5), 315-327.
3. Hirschhaeuser, F., Menne, H., Dittfeld, C., West, J., Mueller-Klieser, W., & Kunz-Schughart, L. A. (2010) Multicellular tumor spheroids: an underestimated tool is catching up again. Journal of biotechnology, 148(1), 3-15.
4. Hammond, T., Allen, P., & Birdsall, H. (2016) Is There a Space-Based Technology Solution to Problems with Preclinical Drug Toxicity Testing?. Pharmaceutical research, 1-7.
5. Taga, M., Yamauchi, K., Odle, J., Furian, L., Sundaresan, A., Ramesh, G. T., ... & Kulkarni, A. D. (2006) Melanoma growth and tumorigenicity in models of microgravity. Aviation, space, and environmental medicine, 77(11), 1113-1116.
6. Wang, R., Chu, G. C. Y., Zhau, H. E., & Chung, L. W. (2016) Using a Spaceflight Three-Dimensional Microenvironment to Probe Cancer–Stromal Interactions. In Effect of Spaceflight and Spaceflight Analogue Culture on Human and Microbial Cells (pp. 131-150). Springer New York.
7. Marrero, B., Messina, J. L., & Heller, R. (2009) Generation of a tumor spheroid in a microgravity environment as a 3D model of melanoma. In Vitro Cellular & Developmental Biology-Animal, 45(9), 523-534
8. Qian, A., Zhang, W., Xie, L., Weng, Y., Yang, P., Wang, Z., ... & Shang, P. (2008) Simulated weightlessness alters biological characteristics of human breast cancer cell line MCF-7. Acta Astronautica, 63(7), 947-958.
9. Kopp, S., Slumstrup, L., Corydon, T. J., Sahana, J., Aleshcheva, G., Islam, T., ... & Grimm, D. (2016) Identifications of novel mechanisms in breast cancer cells involving duct-like multicellular spheroid formation after exposure to the Random Positioning Machine. Scientific reports, 6.
10. Kopp, S., Warnke, E., Wehland, M., Aleshcheva, G., Magnusson, N. E., Hemmersbach, R., ... & Grimm, D. (2015) Mechanisms of three-dimensional growth of thyroid cells during long-term simulated microgravity. Scientific reports, 5.
11. Warnke, E., Pietsch, J., Wehland, M., Bauer, J., Infanger, M., Görög, M., ... & Grimm, D. (2014) Spheroid formation of human thyroid cancer cells under simulated microgravity: a possible role of CTGF and CAV1. Cell Communication and Signaling, 12(1), 1.