MicroRNA-sensitive oncolytic measles virus for chemovirotherapy of pancreatic cancer

Advanced pancreatic cancer is characterized by few treatment options and poor outcomes. Oncolytic virotherapy and chemotherapy involve complementary pharmacodynamics and could synergize to improve therapeutic efficacy. Likewise, multimodality treatment may cause additional toxicity, and new agents have to be safe. Balancing both aims, we generated an oncolytic measles virus for 5-fluorouracil-based chemovirotherapy of pancreatic cancer with enhanced tumor specificity through microRNA-regulated vector tropism. The resulting vector encodes a bacterial prodrug convertase, cytosine deaminase-uracil phosphoribosyl transferase, and carries synthetic miR-148a target sites in the viral F gene. Combination of the armed and targeted virus with 5-fluorocytosine, a prodrug of 5-fluorouracil, resulted in cytotoxicity toward both infected and bystander pancreatic cancer cells. In pancreatic cancer xenografts, a single intratumoral injection of the virus induced robust in vivo expression of prodrug convertase. Based on intratumoral transgene expression kinetics, we devised a chemovirotherapy regimen to assess treatment efficacy. Concerted multimodality treatment with intratumoral virus and systemic prodrug administration delayed tumor growth and prolonged survival of xenograft-bearing mice. Our results demonstrate that 5-fluorouracil-based chemovirotherapy with microRNA-sensitive measles virus is an effective strategy against pancreatic cancer at a favorable therapeutic index that warrants future clinical translation.

Sequencing of serially passaged measles virus affirms its genomic stability and reveals a nonrandom distribution of consensus mutations

Oncolytic virotherapy is an emerging treatment option for numerous cancers, with several virus families currently being evaluated in clinical trials. More specifically, vaccine-strain measles virus has arisen as a promising candidate for the treatment of different tumour types in several early clinical trials. Replicating viruses, and especially RNA viruses without proofreading polymerases, can rapidly adapt to varying environments by selecting quasispecies with advantageous genetic mutations. Subsequently, these genetic alterations could potentially weaken the safety profile of virotherapy. In this study, we demonstrate that, following an extended period of virus replication in producer or cancer cell lines, the quasispecies consensus sequence of vaccine strain-derived measles virus accrues a remarkably small number of mutations throughout the nonsegmented negative-stranded RNA genome. Interestingly, we detected a nonrandom distribution of genetic alterations within the genome, with an overall decreasing frequency of mutations from the 3' genome start to its 5' end. Comparing the serially passaged viruses to the parental virus on producer cells, we found that the acquired consensus mutations did not drastically change viral replication kinetics or cytolytic potency. Collectively, our data corroborate the genomic stability and excellent safety profile of oncolytic measles virus, thus supporting its continued development and clinical translation as a promising viro-immunotherapeutic.

Enhanced Control of Oncolytic Measles Virus Using MicroRNA Target Sites

Measles viruses derived from the live-attenuated Edmonton-B vaccine lineage are currently investigated as novel anti-cancer therapeutics. In this context, tumor specificity and oncolytic potency are key determinants of the therapeutic index. Here, we describe a systematic and comprehensive analysis of a recently developed post-entry targeting strategy based on the incorporation of microRNA target sites (miRTS) into the measles virus genome. We have established viruses with target sites for different microRNA species in the 3′ untranslated regions of either the N, F, H, or L genes and generated viruses harboring microRNA target sites in multiple genes. We report critical importance of target-site positioning with proximal genomic positions effecting maximum vector control. No relevant additional effect of six versus three miRTS copies for the same microRNA species in terms of regulatory efficiency was observed. Moreover, we demonstrate that, depending on the microRNA species, viral mRNAs containing microRNA target sites are directly cleaved and/or translationally repressed in presence of cognate microRNAs. In conclusion, we report highly efficient control of measles virus replication with various miRTS positions for development of safe and efficient cancer virotherapy and provide insights into the mechanisms underlying microRNA-mediated vector control.

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.

Molecular principles of cancer invasion and metastasis (review)

The main threat and the reason for most cancer deaths are not the primary neoplasias, but secondary tumors, the metastases. Drastic phenotypic and biochemical changes occur during the metamorphosis of a normal tissue cell into an invasive cancer cell. These alterations concern various areas such as growth factor signaling, cell-cell adhesion, gene expression, motility or cell shape. Cancer cells of epithelial origin can even shed their typical qualities and characteristics and adopt a mesenchymal-like phenotype. This is often referred to as an epithelial-mesenchymal transition. Various oncogenes, tumor suppressor genes and metastasis suppressor genes are known to affect the invasiveness and the metastatic potential of tumor cells. Cells of the innate and adaptive immunity, adjacent stroma cells as well as chemokines and their receptors also play a vital role in the spread of cancer cells. Furthermore, the micro-environment, vascularization and the supply with special cytokines affect the above-mentioned changes. Finally, some researchers claim that tumors consist of two types of cells - transit amplifying cells and cancer stem cells. Only the latter are thought to be able to proliferate indefinitely and thus they might be the cells that successfully spread and initially build most of the clinically relevant metastases. This review article describes some of the molecular principles which underlie those changes as well as covers some aspects of current research.