Malignant pleural mesothelioma (MPM) is a therapy-resistant cancer characterised by strong anti-apoptotic signalling. Mesenchymal stromal cells (MSCs) engineered to deliver soluble TRAIL (MSC-sTRAIL) represent a promising strategy for selectively inducing tumour cell apoptosis. We demonstrated that pharmacological priming enhances the activity of MSC-sTRAIL in aggressive, treatment-resistant tumours. This study investigated whether pharmacological priming could enhance the activity of MSC-sTRAIL in models of MPM.

The activity of MSC-sTRAIL was evaluated using a multi-level experimental strategy involving 2D MPM cell lines (MSTO-211H, NCI-H2452, NCI-H28 and ZL-34), 3D tumour sphere (TMS) models, patient-derived primary cultures and MSTO-211H xenografts. The cytotoxicity of sTRAIL was assessed alone or in combination with bortezomib, venetoclax or gedatolisib. Antitumour efficacy was validated using in vivo xenograft models.

Several MPM cell lines were assessed in 2D culture to evaluate their sensitivity to sTRAIL produced by engineered MSCs. MSTO cells were the most sensitive, H2452 and ZL32 the most resistant, and H28 displayed an intermediate level of resistance. MSTO-211H cells had a TRAIL receptor profile permissive to apoptosis (high DR4/DR5 and low decoy receptors). In 3D, MSC-sTRAIL induced effector-to-target–dependent toxicity and significantly impacted tumour growth in xenografts. Despite the reduction of tumour volume observed in vivo, we investigated whether a combinatorial approach with chemotherapeutic agents could enhance the antitumour activity of MSC-sTRAIL in TRAIL-sensitive and -resistant cell lines, as has been previously demonstrated in other solid malignancies. Bortezomib, venetoclax and gedatolisib were tested in combination with MSC-sTRAIL in 2D models, demonstrating bortezomib markedly enhanced sTRAIL-induced toxicity and restored sensitivity in TRAIL-resistant 3D TMS. TMS displayed stem-like features and increased expression of anti-apoptotic mediators, which were downregulated following bortezomib treatment. In vivo, bortezomib pre-treatment followed by MSC-sTRAIL reduced tumour burden and was associated with stromal remodelling and increased collagen deposition. In addition, bortezomib priming demonstrated significant efficacy in overcoming TRAIL resistance mechanisms across six patient-derived primary MPM samples, showing that the combinatorial approach reduced the average cell viability of primary MPM by 15-fold compared to treatment with TRAIL alone.

These data support proteasome-mediated priming as a promising strategy to enhance TRAIL-based therapies in resistant tumors.

The study was supported by Project ‘‘Dipartimenti Eccellenti MIUR 2017 e 2022’’ and Associazione Angela Serra.