Novel Pineal Germinoma Model Demonstrates Sensitivity to MTOR Inhibition

Germinomas are the most common pineal region tumor. Epidemiologically most patients with pineal germinomas are below the age of 20 and males. Patients generally present with symptoms of headache, nausea, and visual disturbances. Although radiation is a mainstay of treatment, long-term impacts on the central nervous system can be profound. These include both behavioral and cognitive deficits. Previous work has linked somatic mutations in the AKT/mTOR pathway to a subset of intracranial germ cell tumors. Our goal here was to determine whether targeted inhibition of the mTOR pathway was effective in pineal germinomas. Ultimately, we aim to determine whether mTOR inhibition is a feasible treatment method for decreasing the radiation doses needed without decreasing treatment efficacy.

We describe the case of a 19-year-old male with two months of impaired balance and back pain. He began to have visual disturbance s along with altered mentation and was thus taken for an MRI. A heterogeneously enhancing 4.4 cm pineal region mass was discovered.

Pathologic examination showed large epithelioid cells with strongly positive Oct-4 and c-Kit staining.

The patient underwent biopsy with subtotal resection through a supracerebellar infratentorial approach. We generated ex-vivo organotypic slice cultures from the surgically resected specimen. Briefly, the surgical specimen was kept in ice-cold artificial CSF solution and then cut to a thickness of 300–500 μm. These sections were then cultured over a semipermeable membrane insert in a serum free media (DMEM/F12 + N2 supplement). This ex-vivo method allows for study of the intact tumor microenvironment. Furthermore, drug perturbations of tumor tissue can be directly studied. At baseline, the ex-vivo sections demonstrated strong Oct-4 and c-Kit staining; this recapitulated the molecular phenotype observed in-vivo. Moreover, these sections were strongly phospho-S6 positive. Treatment with AZD8055 led to an inhibition of the phospho-S6 staining. Furthermore, this inhibition occurred in a dose-dependent manner and was pronounced at low doses of AZD8055 treatment, with complete inhibition occurring at a dose of 50nM.

From the primary sample, we also dissociated the tumor cells to form a primary cell line. This primary cell line was used for in-vitro assays to determine the efficacy of AZD8055 treatment on cell viability. To determine cell viability an ATP-luminescence assay was used. This cell line showed a clear dose dependent effect of AZD8055 treatment. Importantly, the cells had a robust response to even low doses of AZD8055 highlighting the potential therapeutic benefit that may be achieved in combination of AZD8055 and radiation

Fig. 4

Given the strong clinical relevance of mTOR inhibitory chemotherapeutics, this is an area that warrants further research. Taken together, we show that AZD8055 treatment has a profound molecular effect and can even impact cell survival and proliferation. Future studies examining the interaction between mTOR inhibition and standard of care radiation are warranted.

No conflict of interest has been declared by the author(s).