The Oncolytic Adenovirus XVir-N-31, in Combination with the Blockade of the PD-1/PD-L1 Axis, Conveys Abscopal Effects in a Humanized Glioblastoma Mouse Model.

Glioblastoma (GBM) is an obligatory lethal brain tumor with a median survival, even with the best standard of care therapy, of less than 20 months. In light of this fact, the evaluation of new GBM treatment approaches such as oncolytic virotherapy (OVT) is urgently needed. Based on our preliminary preclinical data, the YB-1 dependent oncolytic adenovirus (OAV) XVir-N-31 represents a promising therapeutic agent to treat, in particular, therapy resistant GBM. Preclinical studies have shown that XVir-N-31 prolonged the survival of GBM bearing mice. Now using an immunohumanized mouse model, we examined the immunostimulatory effects of XVir-N-31 in comparison to the wildtype adenovirus (Ad-WT). Additionally, we combined OVT with the inhibition of immune checkpoint proteins by using XVir-N-31 in combination with nivolumab, or by using a derivate of XVir-N-31 that expresses a PD-L1 neutralizing antibody. Although in vitro cell killing was higher for Ad-WT, XVir-N-31 induced a much stronger immunogenic cell death that was further elevated by blocking PD-1 or PD-L1. In vivo, an intratumoral injection of XVir-N-31 increased tumor infiltrating lymphocytes (TILs) and NK cells significantly more than Ad-WT not only in the virus-injected tumors, but also in the untreated tumors growing in the contralateral hemisphere. This suggests that for an effective treatment of GBM, immune activating properties by OAVs seem to be of greater importance than their oncolytic capacity. Furthermore, the addition of immune checkpoint inhibition (ICI) to OVT further induced lymphocyte infiltration. Consequently, a significant reduction in contralateral non-virus-injected tumors was only visible if OVT was combined with ICI. This strongly indicates that for an effective eradication of GBM cells that cannot be directly targeted by an intratumoral OV injection, additional ICI therapy is required.

Carboxypeptidase E transmits its anti-migratory function in glioma cells via transcriptional regulation of cell architecture and motility regulating factors.

Glioblastoma (GBM), the most frequent and aggressive malignant primary brain tumor, is characterized by a highly invasive growth. In our previous study we showed that overexpression of Carboxypeptidase E (CPE) mitigated glioma cell migration. In the present study we aimed at deciphering the regulatory mechanisms of the secreted form of CPE (sCPE). By transcriptome analysis and inhibition of signaling pathways involved in the regulation of cell growth and motility, we discovered that overexpression of sCPE was accompanied by differential regulation of mRNAs connected to the motility-associated networks, among others FAK, PAK, Cdc42, integrin, STAT3 as well as TGF-ß. Especially SLUG was downregulated in sCPE-overexpressing glioma cells, paralleled by reduced expression of matrix-metalloproteinases (MMP) and, in consequence, by decreased cell migration. Expression of SLUG was regulated by ERK since inhibition of ERK reverted sCPE-mediated SLUG downregulation and enhanced cell motility. In a mouse glioma model, overexpression of sCPE significantly prolonged survival. Our results implicate a novel role for sCPE that mainly affects the expression of motility-associated genes via several signal pathways.