Isolation of more potent oncolytic paramyxovirus by bioselection

Fast Track Adaptation of Oncolytic Coxsackie B3 Virus to Resistant Colorectal Cancer Cells - a Method to Personalize Virotherapy

BACKGROUND

The efficacy of oncolytic viruses (OV) in cancer treatment depends on their ability to successfully infect and destroy tumor cells. However, patients' tumors vary, and in the case of individual insensitivity to an OV, therapeutic efficacy is limited. Here, we present a protocol for rapid generation of tumor cell-specific adapted oncolytic coxsackievirus B3 (CVB3) with enhanced oncolytic potential and a satisfactory safety profile. This is achieved by combining directed viral evolution (DVE) with genetic modification of the viral genome and the use of a microRNA-dependent regulatory tool.

METHODS

The oncolytic CVB3 variant PD-H was adapted to the refractory colorectal carcinoma cell line Colo320 through serial passaging. XTT assays and virus plaque assays were used to determine virus cytotoxicity and virus replication in vitro. Recombinant PD-H variants were generated through virus mutagenesis. Apoptosis was detected by Western blots, Caspase 3/7 assays, and DAPI staining. The therapeutic efficacy and safety of the adapted recombinant OV PD-SK-375TS were assessed in vivo using a subcutaneous Colo320 xenograft mouse model.

RESULTS

PD-H was adapted to the colorectal cancer cell line Colo320 within 10 passages. Sequencing of passage 10 virus P-10 revealed a heterogenous virus population with five nucleotide mutations resulting in amino acid substitutions. The genotypically homogeneous OV PD-SK was generated by inserting the five detected mutations of P-10 into the genome of PD-H. PD-SK showed significantly stronger replication and cytotoxicity than PD-H in Colo320 cells, but not in other colorectal carcinoma cell lines. Increase of apoptosis induction was detected as key mechanisms of Colo320 cell-specific adaptation of PD-SK. For in vivo safety PD-SK was engineered with target sites of the miR-375 (miR-375TS) to exclude virus replication in normal tissues. PD-SK-375TS, unlike the PD-H-375TS not adapted homolog suppressed the growth of subcutaneous Colo320 tumors in nude mice without causing any side effects.

CONCLUSION

Taken together, here we present an optimized protocol for the rapid generation of tumor cell-specific adapted oncolytic CVB3 based on the oncolytic CVB3 strain PD-H. The protocol is promising for the generation of personalized OV for tumor therapy and has the potential to be applied to other OV.

Senecavirus A as an Oncolytic Virus: Prospects, Challenges and Development Directions

Oncolytic viruses have the capacity to selectively kill infected tumor cells and trigger protective immunity. As such, oncolytic virotherapy has become a promising immunotherapy strategy against cancer. A variety of viruses from different families have been proven to have oncolytic potential. Senecavirus A (SVA) was the first picornavirus to be tested in humans for its oncolytic potential and was shown to penetrate solid tumors through the vascular system. SVA displays several properties that make it a suitable model, such as its inability to integrate into human genome DNA and the absence of any viral-encoded oncogenes. In addition, genetic engineering of SVA based on the manipulation of infectious clones facilitates the development of recombinant viruses with improved therapeutic indexes to satisfy the criteria of safety and efficacy regulations. This review summarizes the current knowledge and strategies of genetic engineering for SVA, and addresses the current challenges and future directions of SVA as an oncolytic agent.

Experimental virus evolution in cancer cell monolayers, spheroids, and tissue explants

Viral laboratory evolution has been used for different applications, such as modeling viral emergence, drug-resistance prediction, and therapeutic virus optimization. However, these studies have been mainly performed in cell monolayers, a highly simplified environment, raising concerns about their applicability and relevance. To address this, we compared the evolution of a model virus in monolayers, spheroids, and tissue explants. We performed this analysis in the context of cancer virotherapy by performing serial transfers of an oncolytic vesicular stomatitis virus (VSV-Δ51) in 4T1 mouse mammary tumor cells. We found that VSV-Δ51 gained fitness in each of these three culture systems, and that adaptation to the more complex environments (spheroids or explants) correlated with increased fitness in monolayers. Most evolved lines improved their ability to suppress β-interferon secretion compared to the VSV-Δ51 founder, suggesting that the selective pressure exerted by antiviral innate immunity was important in the three systems. However, system-specific patterns were also found. First, viruses evolved in monolayers remained more oncoselective that those evolved in spheroids, since the latter showed concomitant adaptation to non-tumoral mouse cells. Second, deep sequencing indicated that viral populations evolved in monolayers or explants tended to be more genetically diverse than those evolved in spheroids. Finally, we found highly variable outcomes among independent evolutionary lines propagated in explants. We conclude that experimental evolution in monolayers tends to be more reproducible than in spheroids or explants, and better preserves oncoselectivity. Our results also suggest that monolayers capture at least some relevant selective pressures present in more complex systems.

Syncytia Formation in Oncolytic Virotherapy

Oncolytic virotherapy uses replication-competent virus as a means of treating cancer. Whereas this field has shown great promise as a viable treatment method, the limited spread of these viruses throughout the tumor microenvironment remains a major challenge. To overcome this issue, researchers have begun looking at syncytia formation as a novel method of increasing viral spread. Several naturally occurring fusogenic viruses have been shown to possess strong oncolytic potential and have since been studied to gain insight into how this process benefits oncolytic virotherapy. Whereas these naturally fusogenic viruses have been beneficial, there are still challenges associated with their regular use. Because of this, engineered/recombinant fusogenic viruses have also been created that enhance nonfusogenic oncolytic viruses with the beneficial property of syncytia formation. The purpose of this review is to examine the existing body of literature on syncytia formation in oncolytics and offer direction for potential future studies.

Directed evolution as a tool for the selection of oncolytic RNA viruses with desired phenotypes

Viruses have some characteristics in common with cell-based life. They can evolve and adapt to environmental conditions. Directed evolution can be used by researchers to produce viral strains with desirable phenotypes. Through bioselection, improved strains of oncolytic viruses can be obtained that have better safety profiles, increased specificity for malignant cells, and more efficient spread among tumor cells. It is also possible to select strains capable of killing a broader spectrum of cancer cell variants, so as to achieve a higher frequency of therapeutic responses. This review describes and analyses virus adaptation studies performed with members of four RNA virus families that are used for viral oncolysis: reoviruses, paramyxoviruses, enteroviruses, and rhabdoviruses.

Three-dimensional tumor cell cultures employed in virotherapy research

Oncolytic virotherapy constitutes an upcoming alternative treatment option for a broad spectrum of cancer entities. However, despite great research efforts, there is still only a single US Food and Drug Administration/European Medicines Agency-approved oncolytic virus available for clinical use. One reason for that is the gap between promising preclinical data and limited clinical success. Since oncolytic viruses are biological agents, they might require more realistic in vitro tumor models than common monolayer tumor cell cultures to provide meaningful predictive preclinical evaluation results. For more realistic invitro tumor models, three-dimensional tumor cell-culture systems can be employed in preclinical virotherapy research. This review provides an overview of spheroid and hydrogel tumor cell cultures, organotypic tumor-tissue slices, organotypic raft cultures, and tumor organoids utilized in the context of oncolytic virotherapy. Furthermore, we also discuss advantages, disadvantages, techniques, and difficulties of these three-dimensional tumor cell-culture systems when applied specifically in virotherapy research.

Newcastle Disease Virus Establishes Persistent Infection in Tumor Cells In Vitro: Contribution of the Cleavage Site of Fusion Protein and Second Sialic Acid Binding Site of Hemagglutinin-Neuraminidase

Newcastle disease virus (NDV) is an oncolytic virus being developed for the treatment of cancer. Following infection of a human ovarian cancer cell line (OVCAR3) with a recombinant low-pathogenic NDV, persistent infection was established in a subset of tumor cells. Persistently infected (PI) cells exhibited resistance to superinfection with NDV and established an antiviral state, as demonstrated by upregulation of interferon and interferon-induced genes such as myxoma resistance gene 1 (Mx1) and retinoic acid-inducing gene-I (RIG-I). Viruses released from PI cells induced higher cell-to-cell fusion than the parental virus following infection in two tumor cell lines tested, HT1080 and HeLa, and remained attenuated in chickens. Two mutations, one in the fusion (F) protein cleavage site, F117S (F_117S), and another in hemagglutinin-neuraminidase (HN), G169R (HN_169R), located in the second sialic acid binding region, were responsible for the hyperfusogenic phenotype. F_117S improves F protein cleavage efficiency, facilitating cell-to-cell fusion, while HN_169R possesses a multifaceted role in contributing to higher fusion, reduced receptor binding, and lower neuraminidase activity, which together result in increased fusion and reduced viral replication. Thus, establishment of persistent infection in vitro involves viral genetic changes that facilitate efficient viral spread from cell to cell as a potential mechanism to escape host antiviral responses. The results of our study also demonstrate a critical role in the viral life cycle for the second receptor binding region of the HN protein, which is conserved in several paramyxoviruses.IMPORTANCE Oncolytic Newcastle disease virus (NDV) could establish persistent infection in a tumor cell line, resulting in a steady antiviral state reflected by constitutively expressed interferon. Viruses isolated from persistently infected cells are highly fusogenic, and this phenotype has been mapped to two mutations, one each in the fusion (F) and hemagglutinin-neuraminidase (HN) proteins. The F_117S mutation in the F protein cleavage site improved F protein cleavage efficiency while the HN_169R mutation located at the second receptor binding site of the HN protein contributed to a complex phenotype consisting of a modest increase in fusion and cell killing, lower neuraminidase activity, and reduced viral growth. This study highlights the intricate nature of these two mutations in the glycoproteins of NDV in the establishment of persistent infection. The data also shed light on the critical balance between the F and HN proteins required for efficient NDV infection and their role in avian pathogenicity.

Development of an Oncolytic Adenovirus with Enhanced Spread Ability through Repeated UV Irradiation and Cancer Selection

Oncolytic adenoviruses (Ads) have been shown to be safe and have great potential for the treatment of solid tumors. However, the therapeutic efficacy of Ads is antagonized by limited spread within solid tumors. To develop Ads with enhanced spread, viral particles of an E1-wildtype Ad5 dl309 was repeatedly treated with UV type C irradiation and selected for the efficient replication and release from cancer cells. After 72 cycles of treatment and cancer selection, AdUV was isolated. This vector has displayed many favorable characteristics for oncolytic therapy. AdUV was shown to lyse cancer cells more effectively than both E1-deleted and E1-wildtype Ads. This enhanced cancer cell lysis appeared to be related to increased AdUV replication in and release from infected cancer cells. AdUV-treated A549 cells displayed greater expression of the autophagy marker LC3-II during oncolysis and formed larger viral plaques upon cancer cell monolayers, indicating increased virus spread among cancer cells. This study indicates the potential of this approach of irradiation of entire viral particles for the development of oncolytic viruses with designated therapeutic properties.

Negative contrast Cerenkov luminescence imaging of blood vessels in a tumor mouse model using [68Ga]gallium chloride

Background

Cerenkov luminescence imaging (CLI) is an emerging imaging technique where visible light emitted from injected beta-emitting radionuclides is detected with an optical imaging device. CLI research has mostly been focused on positive contrast imaging for ascertaining the distribution of the radiotracer in a way similar to other nuclear medicine techniques. Rather than using the conventional technique of measuring radiotracer distribution, we present a new approach of negative contrast imaging, where blood vessel attenuation of Cerenkov light emitted by [⁶⁸Ga]GaCl₃ is used to image vasculature.

Methods

BALB/c nude mice were injected subcutaneously in the right flank with HT-1080 fibrosarcoma cells 14 to 21 days prior to imaging. On the imaging day, [⁶⁸Ga]GaCl₃ was injected and the mice were imaged from 45 to 90 min after injection using an IVIS Spectrum in vivo imaging system. The mice were imaged one at a time, and manual focus was used to bring the skin into focus. The smallest view with pixel size around 83 μm was used to achieve a sufficiently high image resolution for blood vessel imaging.

Results

The blood vessels in the tumor were clearly visible, attenuating 7% to 18% of the light. Non-tumor side blood vessels had significantly reduced attenuation of 2% to 4%. The difference between the attenuation of light of tumor vessels (10% ± 4%) and the non-tumor vessels (3% ± 1%) was significant. Moreover, a necrotic core confirmed by histology was clearly visible in one of the tumors with a 21% reduction in radiance.

Conclusions

The negative contrast CLI technique is capable of imaging vasculature using [⁶⁸Ga]GaCl₃. Since blood vessels smaller than 50 μm in diameter could be imaged, CLI is able to image structures that conventional nuclear medicine techniques cannot. Thus, the negative contrast imaging technique shows the feasibility of using CLI to perform angiography on superficial blood vessels, demonstrating an advantage over conventional nuclear medicine techniques.