Abstract
Simple SummaryTesticular germ cell tumors (TGCTs) are the most common solid malignancy in young men. Fortunately, these tumors are highly curable with conventional genotoxic chemotherapy. However, because these chemotherapeutics have significant short- and long-term side effects, less toxic treatment options are desired. We report that thioridazine, an FDA-approved antipsychotic, differentiates embryonal carcinoma (EC) cells, the cancer stem cells of many malignant TGCTs, and suppresses their tumor propagating activity. Additionally, thioridazine treatment of mice with EC-containing neoplasms extends survival relative to untreated control mice. These findings identify thioridazine as a promising alternative or adjuvant to chemotherapy for the treatment of TGCTs.Testicular germ cell tumors (TGCTs) are exceptionally sensitive to genotoxic chemotherapy, resulting in a high cure rate for the young men presenting with these malignancies. However, this treatment is associated with significant toxicity, and a subset of malignant TGCTs demonstrate chemoresistance. Mixed nonseminomas often contain pluripotent embryonal carcinoma (EC) cells, the cancer stem cells (CSCs) of these tumors. We hypothesized that differentiation therapy, a treatment strategy which aims to induce differentiation of tumor-propagating CSCs to slow tumor growth, could effectively treat mixed nonseminomas without significant toxicity. The FDA-approved antipsychotic thioridazine and the agricultural antibiotic salinomycin are two drugs previously found to selectively target CSCs, and here we report that these agents differentiate EC cells in vitro and greatly reduce their tumorigenic potential in vivo. Using a novel transformed induced pluripotent stem cell allograft model and a human xenograft model, we show that thioridazine extends the survival of tumor-bearing mice and can reduce the number of pluripotent EC cells within tumors. These results suggest that thioridazine could be repurposed as an alternative TGCT treatment that avoids the toxicity of conventional chemotherapeutics.
Highlights
Testicular germ cell tumors (TGCTs) comprise nearly 95% of all testicular cancers [1]
Quantitative polymerase chain reaction (PCR) analysis revealed a dramatic reduction in the expression of Pou5f1 and an additional pluripotency marker, L1td1, after thioridazineor salinomycin-mediated differentiation, with thioridazine treatment causing the greater reduction in pluripotency gene expression in most cases (Supplementary Figure S1A)
Western blot analysis shows that with the exception of EC14, the murine embryonal carcinoma (EC) cells expressed OCT4 protein at levels similar to the human EC cell lines NTERA-2 cl.D1 (NT2D1) and NCCIT, and that thioridazine- or salinomycin-differentiated cells displayed a reduction in OCT4 levels to a similar or even greater extent than NT2D1 cells differentiated with hexamethylene bisacetamide (HMBA), a known inducer of NT2D1 differentiation [44] (Figure 1C)
Summary
Testicular germ cell tumors (TGCTs) comprise nearly 95% of all testicular cancers [1]. The most common TGCTs arise from a precursor lesion known as germ cell neoplasia in situ (GCNIS) [2]. GCNIS-related TGCTs are described as either seminomas (~40% of TGCTs) or nonseminomas (~60%), with this distinction being critical for making treatment decisions [2,3]. The majority of TGCTs exhibit an exceptional sensitivity to conventional genotoxic chemotherapy, contributing to an overall five-year survival rate of nearly 95% [6,7,8]. Contemporary treatment regimens yield a high cure rate, some TGCT patients succumb to cisplatin-resistant or relapsing metastatic disease. Between 15% and 20% of these patients will relapse following first-line chemotherapy, only half of which can be rescued by salvage efforts [11]
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