Treatment of metastatic renal cancer with capsid-modified oncolytic adenoviruses

Renal cancer is a common and deadly disease that lacks curative treatments when metastatic. Here, we have used oncolytic adenoviruses, a promising developmental approach whose safety has recently been validated in clinical trials. Although preliminary clinical efficacy data exist for selected tumor types, potency has generally been less than impressive. One important reason may be that expression of the primary receptor, coxsackie-adenovirus receptor, is often low on many or most advanced tumors, although not evaluated in detail with renal cancer. Here, we tested if fluorescence-assisted cell sorting could be used to predict efficacy of a panel of infectivity-enhanced capsid-modified marker gene expressing adenoviruses in renal cancer cell lines, clinical specimens, and subcutaneous and orthotopic murine models of peritoneally metastatic renal cell cancer. The respective selectively oncolytic adenoviruses were tested for killing of tumor cells in these models, and biodistribution after locoregional delivery was evaluated. In vivo replication was analyzed with noninvasive imaging. Ad5/3-Delta24, Ad5-Delta24RGD, and Ad5.pK7-Delta24 significantly increased survival of mice compared with mock or wild-type virus and 50% of Ad5/3-Delta24 treated mice were alive at 320 days. Because renal tumors are often highly vascularized, we investigated if results could be further improved by adding bevacizumab, a humanized antivascular endothelial growth factor antibody. The combination was well tolerated but did not improve survival, suggesting that the agents may be best used in sequence instead of together. These results set the stage for clinical testing of oncolytic adenoviruses for treatment of metastatic renal cancer currently lacking other treatment options.     

A demand for next-generation oncolytic adenoviruses

Oncolytic viruses are a class of novel therapeutic agents used for the treatment of cancer that have the unique property of tumor-dependent self-perpetuation. Initial clinical trials have demonstrated that these agents are very safe and well tolerated. However, to date they have failed to demonstrate therapeutic benefit as monotherapies and as a consequence, next-generation oncolytic adenoviruses are now needed. This review discusses the approaches to deriving next-generation oncolytic adenoviruses together with potential preclinical test systems that might better predict their clinical outcome. Many of these approaches and test systems may be applicable to other viral systems being developed as oncolytic agents.     

Cotton rat tumor model for the evaluation of oncolytic adenoviruses

Oncolytic human adenovirus (Ad) vectors exert their antitumor effect by replicating in and lysing tumor cells. These vectors are commonly evaluated in immunodeficient mice bearing human tumor xenografts. However, this model suffers because the mice are immunodeficient and are not permissive for human Ads. We have developed a cotton rat model to test the selectivity, immunogenicity, and efficacy of oncolytic Ad vectors. The cotton rat is a rodent species that is semipermissive for human Ads. We show that the cotton cancer rat cell line LCRT supports the replication of human Ad in tissue culture and that the cells are destroyed on virus replication. When injected subcutaneously, LCRT cells formed tumors in immunocompetent cotton rats, and the growth of these tumors was delayed by the injection of an oncolytic Ad vector. Replication of the Ad vector in the tumor was demonstrated by sampling tumor tissue and isolating infectious virus particles at various times after intratumoral injection of the virus. We propose that the cotton rat can be used as an animal model to evaluate oncolytic Ad vectors.     

Mesenchymal progenitor cells as cellular vehicles for delivery of oncolytic adenoviruses

Natural and genetically modified oncolytic viruses have been systematically tested as anticancer therapeutics. Among this group, conditionally replicative adenoviruses have been developed for a broad range of tumors with a rapid transition to clinical settings. Unfortunately, clinical trials have shown limited antitumor efficacy partly due to insufficient viral delivery to tumor sites. We investigated the possibility of using mesenchymal progenitor cells (MPC) as virus carriers based on the documented tumor-homing abilities of this cell population. We confirmed preferential tumor homing of MPCs in an animal model of ovarian carcinoma and evaluated the capacity of MPCs to be loaded with oncolytic adenoviruses. We showed that MPCs were efficiently infected with an adenovirus genetically modified for coxsackie and adenovirus receptor-independent infection (Ad5/3), which replicated in the cell carriers. MPCs loaded with Ad5/3 caused total cell killing when cocultured with a cancer cell line. In an animal model of ovarian cancer, MPC-based delivery of the Ad5/3 increased the survival of tumor-bearing mice compared with direct viral injection. Further, tumor imaging confirmed a decrease in tumor burden in animals treated with oncolytic virus delivered by MPC carriers compared with the direct injection of the adenovirus. These data show that MPCs can serve as intermediate carriers for replicative adenoviruses and suggest that the natural homing properties of specific cell types can be used for targeted delivery of these virions.     

Deletion of VAI and VAII RNA genes in the design of oncolytic adenoviruses

Deletion of viral functions that can be complemented by the specific phenotype of tumor cells is a common strategy to design oncolytic viruses. For example, enhanced mRNA cytoplasmic export in tumor cells phenocopies the adenovirus E1B-55K function and renders mutants of this protein tumor selective. Also, an activated RB pathway complements specific E1A functions that can be deleted to produce oncolytic viruses. In this paper we demonstrate that an adenoviral mutant deleted in virus-associated I (VAI) and VAII RNAs (Ad-VAdel) has oncotropism characterized by 100-fold replication deficiency compared with wild-type adenovirus in normal cells and an unaffected ability to replicate and kill different types of tumor cells. This mutant also displays active antitumoral activity in vivo. In contrast, this oncotropism is less evident in a mutant expressing an inactive form of VAI (Adsub719) because VAII RNA expression is upregulated. The mRNA translation promoted by VA RNA genes can be phenocopied in tumor cells with the activation of signal transduction pathways, such as the Ras pathway.     

In vivo and in vitro distribution of type 5 and fiber-modified oncolytic adenoviruses in human blood compartments

Abstract

Background. Successful tumor targeting of systemically administered oncolytic adenoviruses may be hindered by interactions with blood components.

Materials and methods. Blood distribution of oncolytic adenoviruses featuring type 5 adenovirus fiber, 5/3 capsid chimerism, or RGD-4C in the fiber knob was investigated in vitro and in patients with refractory solid tumors.

Results. Virus titers and prevalence in serum of patients increased over the first post-treatment week, suggesting replication. Detection of low virus loads was more sensitive in blood clots than in serum, although viral levels > 500 viral particles/mL did not differ significantly between both sample types. While adenovirus bound to erythrocytes, platelets, granulocytes, and peripheral blood mononuclear cells in vitro, the virus was mainly detectable in erythrocytes and granulocytes in cancer patients. Taken together with a temporary post-treatment decrease in thrombocyte counts, platelet activation by adenovirus and subsequent clearance seem likely to occur in humans. Fiber modifications had limited observed effect on virus distribution in blood cell compartments. Neutrophils, monocytes and cytotoxic T lymphocytes were the major leukocyte subpopulations interacting with adenoviruses.

Conclusion. Serum and blood clots are relevant to estimate oncolytic adenovirus replication. Insight into viral interactions with blood cells may contribute to the development of new strategies for tumor delivery.     

High-dose VitC plus oncolytic adenoviruses enhance immunogenic tumor cell death and reprogram tumor immune microenvironment

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Vaccinia virus and oncolytic virotherapy of cancer

Vaccinia viruses possess many of the key attributes necessary for an ideal viral backbone for use in oncolytic virotherapy. These include a short lifecycle, with rapid cell-to-cell spread. strong lytic ability, a large cloning capacity and well-defined molecular biology. In addition, although capable of replicating in human cells, they are not considered a natural health problem and are especially well characterized. having been delivered to millions of individuals during the campaign to eradicate smallpox. A variety of tumor-targeting mutations have been described in several different vaccinia strains and the expression of a variety of different transgenes has been studied. Early clinical results using either vaccine strains or genetically modified vaccinia strains have demonstrated antitumor effects. Future prospects for the development of these viruses will be discussed.