Measurement of PSMA Expression in Vivo in Recurrent Meningiomas by PET Imaging: a Preliminary Study to a Therapeutic Trial Using Radioligand Therapy (RLT)

Overview

Meningioma is the most common intracerebral tumor in adults. Conventional treatment includes surgery and external beam radiation therapy. However, when multiple surgeries and radiation therapy sessions fail to control tumor progression, no standard treatment is adopted. Therefore, refractory multi-recurrent meningiomas remain an unmet medical need and warrant the search for new therapies. In this respect, radioligand therapy (RLT) with LUTATHERA is used in the context of early compassionate access. RLT is based on the combination of a vector molecule directed specifically at a target (here the somatostatin receptors), with a radioactive isotope emitting particles destroying the targeted cells, and possibly their neighbors (here Lutetium 177). This treatment is indicated only if positron emission tomography (PET) imaging of somatostatin receptors is positive, excluding patients. In terms of efficacy, this treatment allows disease control in recurrences for low grade (grade 1) but has an insufficient effect in most aggressive meningiomas (grade 2, 3). RLT targeting the prostate specific membrane antigen (PSMA) prolongs the survival of patients with metastatic prostate cancer that significantly expresses PSMA, presenting a tumor signal higher than the hepatic signal in PET with PSMA ligands. PSMA is a transmembrane receptor, overexpressed in tumor cells and endothelial cells of neovascularization of various solid tumors. Initial results in immunohistochemistry (IHC) suggest that PSMA is expressed by neovascularization of meningiomas in a manner correlated with grades and recurrence. This is partly explained by the highly vascular nature of these lesions and has been iconographed by clinical cases in PSMA PET confirming in vivo an overexpression of PSMA. This overexpression of PSMA within meningiomas could offer a therapeutic alternative in RLT in patients where Lutathera is not suitable. However, there is no systematic study of the frequency and intensity of PSMA expression by PSMA ligand PET in recurrent meningiomas. The aim of the study is to evaluate the frequency of significant in vivo PSMA expression in recurrent meningiomas via PSMA ligand PET. We consider that at least 50% of recurrent meningiomas should have a significant level of PSMA expression in PSMA ligand PET to justify a therapeutic RLT trial targeting PSMA. In addition, as an exploratory study, in the subgroup of operated patients, an IHC analysis will be performed to explore the association between the PET signal and PSMA expression and confirm the specificity of the signal.