Targeting an Oncolytic Influenza A Virus to Tumor Tissue by Elastase

Abstract

Oncolytic viruses are currently established as a novel type of immunotherapy. The challenge is to safely target oncolytic viruses to tumors. Previously, we have generated influenza A viruses (IAVs) containing deletions in the viral interferon antagonist. Those deletions have attenuated the virus in normal tissue but allowed replication in tumor cells. IAV entry is mediated by hemagglutinin (HA), which needs to be activated by a serine protease, for example, through trypsin. To further target the IAV to tumors, we have changed the trypsin cleavage site to an elastase cleavage site. We chose this cleavage site because elastase is expressed in the tumor microenvironment. Moreover, the exchange of the cleavage site previously has been shown to attenuate viral growth in lungs. Newly generated elastase-activated influenza viruses (AE viruses) grew to similar titers in tumor cells as the trypsin-activated counterparts (AT viruses). Intratumoral injection of AE viruses into syngeneic B16f1 melanoma-derived tumors in mice reduced tumor growth similar to AT viruses and had a better therapeutic effect in heterologous human PANC-1-derived tumors. Therefore, the introduction of the attenuation marker “elastase cleavage site” in viral HA allows for safe, effective oncolytic virus therapy.

A recombinant influenza virus with a CTLA4‐specific scFv inhibits tumor growth in a mouse model

“…Moreover, we found that rFlu‐CTLA4 had better oncolytic efficacy than delNS1 in vivo and in vitro (data not shown here). In addition, entry into tumor cells is mediated by hemagglutinin, which needs to be activated by a serine protease, such as trypsin (Kuznetsova et al, 2017). Herein, we speculated that the use of trypsin for the generation of enhanced viral titers in the HepG2 cell line could affect the in vivo oncolytic activity of the virus.…”

“…Influenza virus is a member of the family Orthomyxoviridae and is considered a promising oncolytic agent (Hock et al, 2017; Kasloff et al, 2014; Kuznetsova et al, 2017; Masemann et al, 2018; Pizzuto et al, 2016). Recently, Hamilton et al's (2018) group reported that a recombinant influenza virus expressing a single‐chain antibody antagonizing the immune checkpoint molecule CTLA4 (IAV‐CTLA4) could delay tumor growth in a mouse melanoma model.…”

Development and application of reverse genetic technology for the influenza virus

“…First, the virus can proliferate in the cell and lyse the tumor cells. The virus particles released after cell lysis can infect other cells again until all the tumor cells are killed [ 85 , 94 , 95 ]. Second, influenza viruses express proteins that are cytotoxic to tumor cells during the cell replication cycle, and they also stimulate the body to produce tumor cell-specific and non-specific immune responses [ 96 ].…”

“…Antitumor research on influenza virus has made great progress in recent years with the development of reverse genetic technology. First, in terms of tumor immunotherapy, multiple recombinant influenza viruses expressing tumor necrosis factor and interleukin family members have been established, and they have good therapeutic effects on tumor models [95,[98][99][100].…”

Trial Watch: Oncolytic viro-immunotherapy of hematologic and solid tumors

“…70,71 Oncotropism can be natural or, more frequently, genetically acquired/restricted. Genetic engineering procedures implemented so far to OVs consisted of 1) modifying the OV attachment protein to redirect or strengthen its binding to a tumor-associated receptor, [72][73][74][75][76][77][78][79][80][81] 2) inserting cis-regulatory elements in the OV genome to guarantee a transcriptional and/or post-transcriptional control of its expression/replication in target rather than off-target tissues, 61,[82][83][84][85][86][87][88][89][90][91][92][93][94][95][96] and/or 3) abolishing the activity of virulence factors in charge of hacking proliferation, survival and/or antiviral machineries of the host cell. 41,92,[96][97][98][99][100][101][102][103][104][105] The latter strategy has been extensively applied in the development of most OVs currently evaluated into the clinic.…”