Assessing progesterone receptor modulation in glioblastoma: from in vitro and animal model to a human pilot protocol.

BACKGROUND: Gliomas, including glioblastomas (GB) and high-grade astrocytomas (HGA), are the most common brain tumors in adults, with poor survival rates around 15 months. Hormonal factors, particularly progesterone receptor (PR) activation, promote tumor growth. Current treatment involves surgery, radiotherapy and chemotherapy (temozolomide), but survival rates remain low. Repurposing mifepristone (MF), a contraceptive drug, shows promise for GB treatment, warranting further study. METHODS: PR expression in U87, U251 and C6 cell lines were assessed using immunofluorescence and Western Blot. PR isoforms were quantified by densitometry. Progesterone (P4) and 5α-dihydroprogesterone (5α-DHP) synthesis were evaluated using LC/MS. MF's effect on cell viability was determined by IC(50) and IC(20) values. Its impact on non-tumoral cells and 3D glioma sphere formation was also analyzed. The effects of in situ administration of MF were assessed in vivo using a rat model with C6 glioma implants. Clinical outcomes were evaluated in GB patients receiving MF alongside standard treatment. RESULTS: PR was predominantly nuclear in all cell lines, with U87 showing the highest PR-B isoform levels. Only U251 synthesized 5α-DHP significantly. MF reduced viability in U251, U87 and C6 cells without affecting non-tumoral cells. Sphere formation efficiency decreased with MF treatment. In rats, MF reduced tumor volume dose-dependently. Clinically, MF improved patient survival from 165 to 588days and enhanced quality of life without severe adverse effects. CONCLUSION: MF effectively reduces GB cell viability, sphere formation efficacy and tumor volume. These findings support further investigation of MF as a therapeutic strategy in GB treatment. PRÉCIS (CONDENSED ABSTRACT): Our research highlights the critical role PR in GB progression using in vitro and in vivo models. MF, a PR modulator, effectively reduced cell viability and sphere formation in cellular assays and significantly decreased tumor volume in an in vivo study. The pilot trial demonstrated the pharmacological safety of using MF as an adjuvant in GB treatment. Patients treated with MF showed a significant increase in survival, with an 80% survival rate at 1 year compared to 0% in those who were treated with the standard treatment.