Robust envelope exchange platform for oncolytic measles virus.

The use of oncolytic viruses (OV) to precisely target and eliminate tumors ('virotherapy') is a rapidly evolving therapeutic approach to treating cancer. A major obstacle in virotherapy, especially for systemic administration, is the host's immune response towards the OV. In the case of measles virus (MeV), most individuals have been immunized against this agent leading to pre-existing neutralizing antibodies that can impair OV delivery to the tumor. These antibodies predominantly target the hemagglutinin (H) and fusion (F) envelope glycoproteins displayed at the particle's surface. Here, we introduce a novel and versatile pseudotyping platform for rapid envelope exchange of oncolytic MeV that allows for engineering of chimeric viruses invulnerable to pre-existing anti-MeV antibodies. Using this system, we have successfully exchanged the MeV F and H proteins with the glycoprotein G of vesicular stomatitis virus (VSV) and the surface proteins of Newcastle disease virus (NDV) or canine distemper virus (CDV), all of which are not endemic in the general human population. While the MeV-VSV and MeV-NDV pseudotypes were non-functional, the MeV-CDV pseudotype was successfully propagated to high-titer virus stocks. This study describes the successful generation of a robust envelope exchange platform for oncolytic MeV while also highlighting its intricate pseudotyping tolerance.

MicroRNA-mediated multi-tissue detargeting of oncolytic measles virus.

Precise oncotropism is required for successful systemic administration of next-generation oncolytic measles viruses (MVs). We have previously established a system for efficient post-entry targeting by insertion of synthetic microRNA target sites (miRTS) into the MV genome, thereby repressing replication in the presence of cognate microRNAs. Thus, differential expression of microRNAs, as frequently observed in normal compared with malignant tissues, can be exploited to increase vector specificity and safety. Here we report the combination of miRTS for different microRNAs in a single vector to detarget pivotal organs at risk during systemic administration (liver, brain, gastrointestinal tract). Accordingly, miRTS for miR-122, miR-7 and miR-148a that are enriched in these tissues were inserted to create multi-tissue-detargeted MV (MV-EGFP(mtd)). Replication of MV-EGFP(mtd) is repressed in cell lines as well as in non-transformed primary human hepatocytes and liver slices expressing cognate microRNAs. Oncolytic potency of MV-EGFP(mtd) is retained in a model of pancreatic cancer in vitro and in vivo. This work is a proof-of-concept that favorable expression profiles of multiple microRNAs can be exploited concomitantly to reshape the tropism of MV without compromising oncolytic efficacy. This strategy can be adapted to different vectors and cancer entities for safe and efficient high-dose systemic administration in clinical trials.

Chemovirotherapy for head and neck squamous cell carcinoma with EGFR-targeted and CD/UPRT-armed oncolytic measles virus.

First-line treatment of recurrent and/or refractory head and neck squamous cell carcinoma (HNSCC) is based on platinum, 5-fluorouracil (5-FU) and the monoclonal antiEGFR antibody cetuximab. However, in most cases this chemoimmunotherapy does not cure the disease, and more than 50% of HNSCC patients are dying because of local recurrence of the tumors. In the majority of cases, HNSCC overexpress the epidermal growth factor receptor (EGFR), and its presence is associated with a poor outcome. In this study, we engineered an EGFR-targeted oncolytic measles virus (MV), armed with the bifunctional enzyme cytosine deaminase/uracil phosphoribosyltransferase (CD/UPRT). CD/UPRT converts 5-fluorocytosine (5-FC) into the chemotherapeutic 5-FU, a mainstay of HNSCC chemotherapy. This virus efficiently replicates in and lyses primary HNSCC cells in vitro. Arming with CD/UPRT mediates efficient prodrug activation with high bystander killing of non-infected tumor cells. In mice bearing primary HNSCC xenografts, intratumoral administration of MV-antiEGFR resulted in statistically significant tumor growth delay and prolongation of survival. Importantly, combination with 5-FC is superior to virus-only treatment leading to significant tumor growth inhibition. Thus, chemovirotherapy with EGFR-targeted and CD/UPRT-armed MV is highly efficacious in preclinical settings with direct translational implications for a planned Phase I clinical trial of MV for locoregional treatment of HNSCC.

Armed and targeted measles virus for chemovirotherapy of pancreatic cancer.

No curative therapy is currently available for locally advanced or metastatic pancreatic cancer. Therefore, new therapeutic approaches must be considered. Measles virus (MV) vaccine strains have shown promising oncolytic activity against a variety of tumor entities. For specific therapy of pancreatic cancer, we generated a fully retargeted MV that enters cells exclusively through the prostate stem cell antigen (PSCA). Besides a high-membrane frequency on prostate cancer cells, this antigen is expressed on pancreatic adenocarcinoma, but not on non-neoplastic tissue. PSCA expression levels differ within heterogeneous tumor bulks and between human pancreatic cell lines, and we could show specific infection of pancreatic adenocarcinoma cell lines with both high- and low-level PSCA expression. Furthermore, we generated a fully retargeted and armed MV-PNP-anti-PSCA to express the prodrug convertase purine nucleoside phosphorylase (PNP). PNP, which activates the prodrug fludarabine effectively, enhanced the oncolytic efficacy of the virus on infected and bystander cells. Beneficial therapeutic effects were shown in a pancreatic cancer xenograft model. Moreover, in the treatment of gemcitabine-resistant pancreatic adenocarcinoma cells, no cross-resistance to both MV oncolysis and activated prodrug was detected.