Posted July 29, 2014
Michael Spinella, Ph.D., Dartmouth College
Testicular germ cell tumors (TGCTs) are the most common cancer among young men between the ages of 15 and 35 and the most common carcinoma among men in active duty military service. Approximately 80% of patients with this type of testicular cancer can be cured with current therapies. These therapies, however, are very toxic, resulting in substantial long-term side effects that greatly impact quality of life for many decades.
Dr. Michael Spinella has demonstrated that pluripotent embryonal carcinoma (EC) cells, the stem cells of some TGCTs, are especially susceptible to an epigenetic therapy that targets DNA methylation using a drug called 5-aza, which is approved for the treatment of a form of preleukemia. He found that EC cells can be killed with doses of 5-aza that are 1,000-fold lower than doses needed to kill other types of cancer cells. He also observed that EC cells have abnormally high levels of an enzyme called DNMT3B and hypothesized that this enzyme is responsible for the sensitivity of EC cells to 5-aza. With funding from a Fiscal Year 2009 Investigator-Initiated Research Award, Dr. Spinella sought to characterize the role of DNMT3B in the hypersensitivity of EC cells to 5-aza.
In a series of cell culture experiments, Dr. Spinella demonstrated that 5-aza treatment results in decreased viability of EC cells due to apoptosis and increased amounts of DNA damage. Importantly, 5-aza treatment led to the death of EC cells that were resistant to commonly used chemotherapy drugs. He observed that knockdown of DNM3TB levels in EC cells resulted in attenuated cell death following 5-aza treatment, but not a reduction in the extent of DNA damage. These findings suggest that high levels of DNMT3B do not mediate the extent of DNA damage in response to 5-aza, but rather may influence how cells respond to the DNA damage. Dr. Spinella demonstrated that 5-aza led to the demethylation, or "turning on," of tumor suppressor genes in EC cells. Microarray studies revealed that treatment with 5-aza induced repression of pluripotency ("stem cell") genes and induction of genes in the apoptosis pathway in EC cells, and these changes were dependent on high DNMT3B expression. Further, he confirmed that DNMT3B is overexpressed in human EC samples.
Based on the work supported by the PRMRP, Dr. Spinella concluded that the 5-aza hypersensitivity in EC cells is due to a combination of DNA damage, DNA demethylation, and alterations in gene expression. He believes that low-dose DNA methylation inhibitor therapy will be able to treat testicular cancer patients who would otherwise die from their disease and provide a less toxic therapy to all testicular cancer patients. Dr. Spinella and his team are currently involved in preclinical animal and human tissue studies to take the necessary steps to test this new therapy in testicular cancer patients. Importantly, he notes that there are also plans for Phase I and Phase II clinical trials of these drugs in testicular cancer patients who have failed all other available therapy.
Biswal BK, Beyrouthy MJ, Hever-Jardine MP, et al. 2012. Acute hypersensitivity of pluripotent testicular cancer-derived emrbyonal carcinoma to low-dose 5-aza deoxycytidine is associated with global DNA damage-associated p53 activation, anti-pluripotency and DNA demethylation. PLoS One 7(12):e53003.