Inhibition of the PI3K/Akt pathway as a therapeutic strategy for pediatric-type diffuse high-grade gliomas

Abstract

[eng] This thesis aims to contribute to the field of therapy development in pHGG. These deadly cancers infiltrate structures such as the brainstem, cerebellum, thalamus and spinal cord, rendering surgery unfeasible. All pharmacological approaches for patients with pHGG have failed in clinical trials, partly because the BBB remains intact, impeding CNS drug distribution, and partly because we have not evaluated the right medicines. The RTK-PI3K-MAPK axis is altered in more than 60% of the pHGG. Activating mutations and amplifications of the PI3K/Akt pathway are shared by 40% of DIPG. These tumorigenic alterations are likely actionable with novel small molecule medicines, provided that such medicines cross the BBB. In this thesis work, I hypothesized that the inhibition of the PI3K/Akt pathway is a therapeutic strategy for human pHGG xenografts in mice bearing mutations in the gene PIK3CA. To address my hypothesis, the main objectives of my thesis were: i. To establish preclinical pHGG models covering most of the subclasses of the disease, and to compare the methods of paraffin tissue analysis, liquid biopsy of CSF and mouse weight monitoring to assess tumor burden in mice with orthotopic pHGG xenografts. I will develop ddPCR methods to quantify allele frequencies of human genes H3F3A K27M, H3F3A G34R and ACVR1 R206H in mouse samples. I will use the developed methods to evaluate the preclinical activity of potential therapeutic candidates, including ACVR1 inhibitors, ONC201, trametinib and taselisib in DIPG xenografts. ii. To characterize the PI3K/Akt/mTOR pathway in preclinical pHGG models and in patients diagnosed with DIPG. In preclinical models, I will use next generation sequencing (NGS) technology to detect the alterations in the PI3K/Akt pathway. I will measure RNA and protein expression related to the activation of the pathway. In samples from patients diagnosed with pHGG, I will analyse markers of the pathway using immunoassays. iii. To test the efficacy and CNS drug distribution of the PI3K/Akt pathway inhibitors ipatasertib and inavolisib in pHGG xenografts. I will evaluate the pharmacodynamic profile of both candidate drugs in DIPG models in vitro. I will measure their preclinical efficacy, selectivity for the tumor and distribution in the blood, CSF and brain in mice bearing DIPG intracranial xenografts with conserved BBB.