Positron emission tomography of herpes simplex virus 1 oncolysis

Enhancing the Antitumor Efficacy of Oncolytic Adenovirus Through Sonodynamic Therapy-Augmented Virus Replication

The therapeutic efficacy of oncolytic adenoviruses (OAs) relies on efficient viral transduction and replication. However, the limited expression of coxsackie-adenovirus receptors in many tumors, along with the intracellular antiviral signaling, poses significant obstacles to OA infection and oncolysis. Here, we present sonosensitizer-armed OAs (saOAs) that potentiate the antitumor efficacy of oncolytic virotherapy through sonodynamic therapy-augmented virus replication. The saOAs could not only efficiently infect tumor cells via transferrin receptor-mediated endocytosis but also exhibit enhanced viral replication and tumor oncolysis under ultrasound irradiation. We revealed that the sonosensitizer loaded on the viruses induced the generation of ROS within tumor cells, which triggered JNK-mediated autophagy, ultimately leading to the enhanced viral replication. In mouse models of malignant melanoma, the combination of saOAs and sonodynamic therapy elicited a robust antitumor immune response, resulting in significant inhibition of melanoma growth and improved host survival. This work highlights the potential of sonodynamic therapy in enhancing the effectiveness of OAs and provides a promising platform for fully exploiting the antitumor efficacy of oncolytic virotherapy.

Oncolytic HSV1 targets different growth phases of breast cancer leptomeningeal metastases

Leptomeningeal metastasis is a fatal complication of breast cancer which results when cancer cells seed in the meninges. Currently there is no cure, limiting survival to less than four months. Treatment options are palliative. We studied a replication conditional Herpes simplex virus 1 (HSV1) in this regard and present the therapeutic efficacy of oncolytic HSV1 on different stages of breast cancer leptomeningeal metastases growth, namely the lag, intermediate, and exponential phases. These phases characterized in a murine model represent the early, intermediate, and late stages of leptomeningeal disease in patients. In this model, virus was introduced into the ventricular system by stereotactic surgery, the same path cancer cells were introduced to create leptomeningeal metastases. Tumor growth was measured with Gd-MRI and virus replication was assessed by FHBG-PET and Fluc bioluminescence. Imaging results were correlated with H&E and HSV-TK immunohistochemical staining. A remarkable growth inhibition was observed when the lag phase was targeted which was associated with multiple virus replication cycles. The onset of debilitating symptoms was delayed, and survival was lengthened by nearly 2 weeks. A growth inhibition similar to the lag phase was observed when the intermediate phase was targeted, associated with robust virus replication. The regression of existing tumor led to a reversal of neurological symptoms, extending survival by nearly one week. A modest response was observed when the lag phase was targeted lengthening survival by 3 days. Oncolytic HSV1 presents a novel treatment option for breast cancer leptomeningeal metastases with potential for targeting different disease stages where virus replication and tumor response can be monitored with molecular imaging techniques that are in the clinic.

Quantitative imaging of apoptosis following oncolytic virotherapy by magnetic resonance fingerprinting aided by deep learning

Non-invasive imaging methods for detecting intratumoural viral spread and host responses to oncolytic virotherapy are either slow, lack specificity or require the use of radioactive or metal-based contrast agents. Here we show that in mice with glioblastoma multiforme, the early apoptotic responses to oncolytic virotherapy (characterized by decreased cytosolic pH and reduced protein synthesis) can be rapidly detected via chemical-exchange-saturation-transfer magnetic resonance fingerprinting (CEST-MRF) aided by deep learning. By leveraging a deep neural network trained with simulated magnetic resonance fingerprints, CEST-MRF can generate quantitative maps of intratumoural pH and of protein and lipid concentrations by selectively labelling the exchangeable amide protons of endogenous proteins and the exchangeable macromolecule protons of lipids, without requiring exogenous contrast agents. We also show that in a healthy volunteer, CEST-MRF yielded molecular parameters that are in good agreement with values from the literature. Deep-learning-aided CEST-MRF may also be amenable to the characterization of host responses to other cancer therapies and to the detection of cardiac and neurological pathologies.

Noninvasive Imaging for Patients with COVID-19 and Acute Chest Pain

Acute chest pain is a common presentation in patients with COVID-19. Although noninvasive cardiac imaging modalities continue to be important cornerstones of management, the pandemic has brought forth difficult and unprecedented challenges in the provision of timely care while ensuring the safety of patients and providers. Clinical practice has adapted to these challenges, with several recommendations and societal guidelines emerging on the appropriate use of imaging modalities. In this review, we summarize the current evidence base on the use of noninvasive cardiac imaging modalities in COVID-19 patients with acute chest pain, with a focus on acute coronary syndromes.

Evolving Role of Oncolytic Virotherapy: Challenges and Prospects in Clinical Practice

Selective oncotropism and cytolytic activity against tumors have made certain viruses subject to investigation as novel treatment modalities. However, monotherapy with oncolytic viruses (OVs) has shown limited success and modest clinical benefit. The capacity to genetically engineer OVs makes them a desirable platform to design complementary treatment modalities to overcome the existing treatment options' shortcomings. In recent years, our knowledge of interactions of the tumors with the immune system has expanded profoundly. There is a growing body of literature supporting immunomodulatory roles for OVs. The concept of bioengineering these platforms to induce the desired immune response and complement the current immunotherapeutic modalities to make immune-resistant tumors responsive to immunotherapy is under investigation in preclinical and early clinical trials. This review provides an overview of attempts to optimize oncolytic virotherapy as essential components of the multimodality anticancer therapeutic approach and discusses the challenges in translation to clinical practice.

Nuclear Medicine in Times of COVID-19: How Radiopharmaceuticals Could Help to Fight the Current and Future Pandemics

The emergence and global spread of COVID-19, an infectious disease caused by the novel coronavirus SARS-CoV-2, has resulted in a continuing pandemic threat to global health. Nuclear medicine techniques can be used for functional imaging of (patho)physiological processes at the cellular or molecular level and for treatment approaches based on targeted delivery of therapeutic radionuclides. Ongoing development of radiolabeling methods has significantly improved the accessibility of radiopharmaceuticals for in vivo molecular imaging or targeted radionuclide therapy, but their use for biosafety threats such as SARS-CoV-2 is restricted by the contagious nature of these agents. Here, we highlight several potential uses of nuclear medicine in the context of SARS-CoV-2 and COVID-19, many of which could also be performed in laboratories without dedicated containment measures. In addition, we provide a broad overview of experimental or repurposed SARS-CoV-2-targeting drugs and describe how radiolabeled analogs of these compounds could facilitate antiviral drug development and translation to the clinic, reduce the incidence of late-stage failures and possibly provide the basis for radionuclide-based treatment strategies. Based on the continuing threat by emerging coronaviruses and other pathogens, it is anticipated that these applications of nuclear medicine will become a more important part of future antiviral drug development and treatment.

E. coli nitroreductase NfsA is a reporter gene for non-invasive PET imaging in cancer gene therapy applications

The use of reporter genes to non-invasively image molecular processes inside cells has significant translational potential, particularly in the context of systemically administered gene therapy vectors and adoptively administered cells such as immune or stem cell based therapies. Bacterial nitroreductase enzymes possess ideal properties for reporter gene imaging applications, being of non-human origin and possessing the ability to metabolize a range of clinically relevant nitro(hetero)cyclic substrates. Methods: A library of eleven Escherichia coli nitroreductase candidates were screened for the ability to efficiently metabolize 2-nitroimidazole based positron emission tomography (PET) probes originally developed as radiotracers for hypoxic cell imaging. Several complementary methods were utilized to detect formation of cell-entrapped metabolites, including various in vitro and in vivo models to establish the capacity of the 2-nitroimidazole PET agent EF5 to quantify expression of a nitroreductase candidate. Proof-of-principle PET imaging studies were successfully conducted using ¹⁸F-HX4. Results: Recombinant enzyme kinetics, bacterial SOS reporter assays, anti-proliferative assays and flow cytometry approaches collectively identified the major oxygen-insensitive nitroreductase NfsA from E. coli (NfsA_Ec) as the most promising nitroreductase reporter gene. Cells expressing NfsA_Ec were demonstrably labelled with the imaging agent EF5 in a manner that was quantitatively superior to hypoxia, in monolayers (2D), multicellular layers (3D), and in human tumor xenograft models. EF5 retention correlated with NfsA_Ec positive cell density over a range of EF5 concentrations in 3D in vitro models and in xenografts in vivo and was predictive of in vivo anti-tumor activity of the cytotoxic prodrug PR-104. Following PET imaging with ¹⁸F-HX4, a significantly higher tumor-to-blood ratio was observed in two xenograft models for NfsA_Ec expressing tumors compared to the parental tumors thereof, providing verification of this reporter gene imaging approach. Conclusion: This study establishes that the bacterial nitroreductase NfsA_Ec can be utilized as an imaging capable reporter gene, with the ability to metabolize and trap 2-nitroimidazole PET imaging agents for non-invasive imaging of gene expression.

Virotherapy: Current Trends and Future Prospects for Treatment of Colon and Rectal Malignancies

Colorectal cancer (CRC) is one of the most common malignancies. In recent decades, early diagnosis and conventional therapies have resulted in a significant reduction in mortality. However, late stage metastatic disease still has very limited effective treatment options. There is a growing interest in using viruses to help target therapies to tumour sites. In recent years the evolution of immunotherapy has emphasised the importance of directing the immune system to eliminate tumour cells; we aim to give a state-of-the-art over-view of the diverse viruses that have been investigated as potential oncolytic agents for the treatment of CRC.

A model of breast cancer meningeal metastases: characterization with in vivo molecular imaging

Meningeal metastasis is a fatal complication of breast cancer which affects 8-15% of patients who experience severe neurological complications of cranial nerves, cerebrum, and spinal cord. Survival once diagnosed is less than 4 months. Currently there is no cure. Aggressive multimodal radiation, intra-CSF, or systemic chemotherapy is palliative. Investigation of urgently needed new treatment modalities is hindered by the lack of suitable animal models to effectively study tumor growth kinetics. We present a model of meningeal metastases where tumor growth and associated neurological symptoms have been characterized over 3 weeks by sequential molecular imaging, tumor growth kinetics, and histopathology. Meningeal metastases were induced by stereotaxic injection of human breast cancer cells (MDA-MB-231-Rluc) into the lateral ventricle. Tumor identified by Gd-MRI and Rluc-bioluminescence depict growth in 3 phases, namely lag, exponential, and plateau phase. Invasive tumor growth was highlighted by changes in contrast distribution in the meninges, ventricle and brain compartments over time where moderate contrast uptake in the early growth phase gave rise to a heavy tumor burden in the base of the brain in the latter phases. Tumor growth was accompanied with debilitating neurological symptoms and change in body mass. Tumor was confirmed by ex vivo histology. The reliability of the model to study novel therapeutics was confirmed by oncolytic virus delivered into the lateral ventricle showed potential for treatment. This effective and reliable model resembles human disease progression and is ideally suited to investigate novel treatments.

Molecular Imaging of Smoke-Induced Changes in Nuclear Factor-Kappa B Expression in Murine Tissues Including the Lung

Many inflammatory responses are mediated by activation of the transcription factor, nuclear factor-kappa B (NF-κB), and a wide variety of human diseases involve abnormal regulation of its expression. In this investigation, we evaluated the effect of smoke inhalation injury on NF-κB expression in lung using two strains of NF-κB reporter mice. Groups of reporter mice with viral thymidine kinase (TK) or "fire fly" luciferase (Luc) genes under control by the NF-κB promoter (TK/NF-κB mice and Luc/NF-κB mice) were subjected to nonlethal smoke inhalation injury. Sham-treated animals served as controls. Twenty-four hours (each animal was injected intravenously with either 9-(4-18F-fluoro-3-[hydroxymethyl]butyl)guanine (FHBG) (~ 1.0 mCi) or luciferin (1.0 mg). One hour later, the TK/NF-κB mice were studied by micro-positron emission tomography (µ-PET) imaging using a Concord P4 µ-PET camera, and the Luc/NF-κB mice were studied by bioluminescence imaging with a charge-coupled device camera. The µ-PET data demonstrated that smoke injury produced massive increases in NF-κB expression (FHBG-standardized uptake value: 3.1 vs 0.0) 24 hours after smoke inhalation, which was reduced 48 hours after smoke inhalation, but still significantly different than the control. Qualitative analysis of the bioluminescence data revealed a remarkably similar effect of burn NF-κB luciferase expression in vivo. Biodistribution studies of FHBG uptake and luciferase activity in lung tissue demonstrated a similar increase 24 hours after injury, which was reduced 48 hours later, but still significantly higher than the sham. The present data with these models providing longitudinal imaging data on the same mouse may prove useful in the examination of the factors producing lung injury by smoke inhalation, as well as the treatment(s) for the damage produced with and without burn injury.

Genetically Engineered Vaccinia Viruses As Agents for Cancer Treatment, Imaging, and Transgene Delivery

Despite advances in technology, the formidable challenge of treating cancer, especially if advanced, still remains with no significant improvement in survival rates, even with the most common forms of cancer. Oncolytic viral therapies have shown great promise for the treatment of various cancers, with the possible advantages of stronger treatment efficacy compared to conventional therapy due to higher tumor selectivity, and less toxicity. They are able to preferentially and selectively propagate in cancer cells, consequently destroying tumor tissue mainly via cell lysis, while leaving non-cancerous tissues unharmed. Several wild-type and genetically engineered vaccinia virus (VACV) strains have been tested in both preclinical and clinical trials with promising results. Greater understanding and advancements in molecular biology have enabled the generation of genetically engineered oncolytic viruses for safer and more efficacious treatment, including arming VACVs with cytokines and immunostimulatory molecules, anti-angiogenic agents, and enzyme prodrug therapy, in addition to combining VACVs with conventional external and systemic radiotherapy, chemotherapy, immunotherapy, and other virus strains. Furthermore, novel oncolytic vaccinia virus strains have been generated that express reporter genes for the tracking and imaging of viral therapy and monitoring of therapeutic response. Further study is needed to unlock VACVs’ full potential as part of the future of cancer therapy.

Advancing Clostridia to Clinical Trial: Past Lessons and Recent Progress

Most solid cancers contain regions of necrotic tissue. The extent of necrosis is associated with poor survival, most likely because it reflects aggressive tumour outgrowth and inflammation. Intravenously injected spores of anaerobic bacteria from the genus Clostridium infiltrate and selectively germinate in these necrotic regions, providing cancer-specific colonisation. The specificity of this system was first demonstrated over 60 years ago and evidence of colonisation has been confirmed in multiple tumour models. The use of "armed" clostridia, such as in Clostridium Directed Enzyme Prodrug Therapy (CDEPT), may help to overcome some of the described deficiencies of using wild-type clostridia for treatment of cancer, such as tumour regrowth from a well-vascularised outer rim of viable cells. Successful preclinical evaluation of a transferable gene that metabolises both clinical stage positron emission tomography (PET) imaging agents (for whole body vector visualisation) as well as chemotherapy prodrugs (for conditional enhancement of efficacy) would be a valuable early step towards the prospect of "armed" clostridia entering clinical evaluation. The ability to target the immunosuppressive hypoxic tumour microenvironment using CDEPT may offer potential for synergy with recently developed immunotherapy strategies. Ultimately, clostridia may be most efficacious when combined with conventional therapies, such as radiotherapy, that sterilise viable aerobic tumour cells.

Molecular imaging of oncolytic viral therapy

Oncolytic viruses have made their mark on the cancer world as a potential therapeutic option, with the possible advantages of reduced side effects and strengthened treatment efficacy due to higher tumor selectivity. Results have been so promising, that oncolytic viral treatments have now been approved for clinical trials in several countries. However, clinical studies may benefit from the ability to noninvasively and serially identify sites of viral targeting via molecular imaging in order to provide safety, efficacy, and toxicity information. Furthermore, molecular imaging of oncolytic viral therapy may provide a more sensitive and specific diagnostic technique to detect tumor origin and, more importantly, presence of metastases. Several strategies have been investigated for molecular imaging of viral replication broadly categorized into optical and deep tissue imaging, utilizing several reporter genes encoding for fluorescence proteins, conditional enzymes, and membrane protein and transporters. Various imaging methods facilitate molecular imaging, including computer tomography, magnetic resonance imaging, positron emission tomography, single photon emission CT, gamma-scintigraphy, and photoacoustic imaging. In addition, several molecular probes are used for medical imaging, which act as targeting moieties or signaling agents. This review will explore the preclinical and clinical use of in vivo molecular imaging of replication-competent oncolytic viral therapy.

Molecular imaging with bioluminescence and PET reveals viral oncolysis kinetics and tumor viability

Viral oncolysis, the destruction of cancer cells by replicating virus, is an experimental cancer therapy that continues to be explored. The treatment paradigm for this therapy involves successive waves of lytic replication in cancer cells. At present, monitoring viral titer at sites of replication requires biopsy. However, repeat serial biopsies are not practically feasible for temporal monitoring of viral replication and tumor response in patients. Molecular imaging provides a noninvasive method to identify intracellular viral gene expression in real time. We imaged viral oncolysis and tumor response to oncolysis sequentially with bioluminescence and positron emission tomography (PET), revealing the kinetics of both processes in tumor xenografts. We demonstrate that virus replication cycles can be identified as successive waves of reporter expression that occur ∼2 days after the initial viral tumor infection peak. These waves correspond to virions that are released following a replication cycle. The viral and cellular kinetics were imaged with Fluc and Rluc bioluminescence reporters plus two 18F-labeled PET reporters FHBG [9-(4-18F-fluoro-3-[hydroxymethyl] butyl) guanine] and FLT (18F-3'-deoxy-3-'fluorothymidine), respectively. Correlative immunohistochemistry on tumor xenograft sections confirmed in vivo results. Our findings show how PET can be used to identify virus replication cycles and for real-time measurements of intratumoral replicating virus levels. This noninvasive imaging approach has potential utility for monitoring viral oncolysis therapy in patients.

Rational development of radiopharmaceuticals for HIV-1

The global battle against HIV-1 would benefit from a sensitive and specific radiopharmaceutical to localize HIV-infected cells. Ideally, this probe would be able to identify latently infected host cells containing replication competent HIV sequences. Clinical and research applications would include assessment of reservoirs, informing clinical management by facilitating assessment of burden of infection in different compartments, monitoring disease progression and monitoring response to therapy. A "rational" development approach could facilitate efficient identification of an appropriate targeted radiopharmaceutical. Rational development starts with understanding characteristics of the disease that can be effectively targeted and then engineering radiopharmaceuticals to hone in on an appropriate target, which in the case of HIV-1 (HIV) might be an HIV-specific product on or in the host cell, a differentially expressed gene product, an integrated DNA sequence specific enzymatic activity, part of the inflammatory response, or a combination of these. This is different from the current approach that starts with a radiopharmaceutical for a target associated with a disease, mostly from autopsy studies, without a strong rationale for the potential to impact patient care. At present, no targeted therapies are available for HIV latency, although a number of approaches are under study. Here we discuss requirements for a radiopharmaceutical useful in strategies targeting persistently infected cells. The radiopharmaceutical for HIV should be developed based on HIV biology, studied in an animal model and then in humans, and ultimately used in clinical and research settings.

A vaccinia virus encoding the human sodium iodide symporter facilitates long-term image monitoring of virotherapy and targeted radiotherapy of pancreatic cancer

To assess therapeutic response and potential toxicity of oncolytic virotherapy, a noninvasive, deep-tissue imaging modality is needed. This study aimed to assess the feasibility, parameters, and determining factors of serial imaging and long-term monitoring of virotherapy and the therapeutic response of pancreatic cancer xenografts treated with a vaccinia virus carrying the human sodium iodide symporter GLV-1h153.

METHODS

Pancreatic cancer xenografts (PANC-1) in nude mice were treated systemically or intratumorally with GLV-1h153 and serially imaged using (124)I PET at 1, 2, 3, and 5 wk after viral injection. Signal intensity was compared with tumor therapeutic response and optical imaging, and tumors were histologically analyzed for morphology and the presence of virus. Autoradiography was performed using technetium-pertechnetate and γ-scintigraphy to assess determining factors for radiouptake in tumors. Finally, the enhanced therapeutic effect of combination therapy with GLV-1h153 and systemic radioiodine was assessed.

RESULTS

GLV-1h153 successfully facilitated serial long-term imaging of virotherapy, with PET signal intensity correlating to tumor response. GLV-1h153 colonization of tumors mediated radioiodine uptake at potentially therapeutic doses. Successful radiouptake required the presence of virus, adequate blood flow, and viable tissue, whereas loss of signal intensity was linked to tumor death and necrosis. Finally, combining systemically administered GLV-1h153 and (131)I led to enhanced tumor kill when compared with virus or (131)I alone (P < 0.01).

CONCLUSION

GLV-1h153 is a promising oncolytic agent for the treatment, long-term imaging, and monitoring of therapeutic response in a xenograft model of pancreatic cancer. GLV-1h153 provided insight into tumor biologic activity and facilitated enhanced tumor kill when combined with systemic targeted radiotherapy. These results warrant further investigation into parameters and potential synergistic effects of combination therapy.

Imaging characteristics, tissue distribution, and spread of a novel oncolytic vaccinia virus carrying the human sodium iodide symporter

Introduction

Oncolytic viruses show promise for treating cancer. However, to assess therapy and potential toxicity, a noninvasive imaging modality is needed. This study aims to determine the in vivo biodistribution, and imaging and timing characteristics of a vaccinia virus, GLV-1h153, encoding the human sodium iodide symporter (hNIS.

Methods

GLV-1h153 was modified from GLV-1h68 to encode the hNIS gene. Timing of cellular uptake of radioiodide ¹³¹I in human pancreatic carcinoma cells PANC-1 was assessed using radiouptake assays. Viral biodistribution was determined in nude mice bearing PANC-1 xenografts, and infection in tumors confirmed histologically and optically via Green Fluorescent Protein (GFP) and bioluminescence. Timing characteristics of enhanced radiouptake in xenografts were assessed via ¹²⁴I-positron emission tomography (PET). Detection of systemic administration of virus was investigated with both ¹²⁴I-PET and 99m-technecium gamma-scintigraphy.

Results

GLV-1h153 successfully facilitated time-dependent intracellular uptake of ¹³¹I in PANC-1 cells with a maximum uptake at 24 hours postinfection (P<0.05). In vivo, biodistribution profiles revealed persistence of virus in tumors 5 weeks postinjection at 10⁹ plaque-forming unit (PFU)/gm tissue, with the virus mainly cleared from all other major organs. Tumor infection by GLV-1h153 was confirmed via optical imaging and histology. GLV-1h153 facilitated imaging virus replication in tumors via PET even at 8 hours post radiotracer injection, with a mean %ID/gm of 3.82±0.46 (P<0.05) 2 days after intratumoral administration of virus, confirmed via tissue radiouptake assays. One week post systemic administration, GLV-1h153-infected tumors were detected via ¹²⁴I-PET and 99m-technecium-scintigraphy.

Conclusion

GLV-1h153 is a promising oncolytic agent against pancreatic cancer with a promising biosafety profile. GLV-1h153 facilitated time-dependent hNIS-specific radiouptake in pancreatic cancer cells, facilitating detection by PET with both intratumoral and systemic administration. Therefore, GLV-1h153 is a promising candidate for the noninvasive imaging of virotherapy and warrants further study into longterm monitoring of virotherapy and potential radiocombination therapies with this treatment and imaging modality.

Combination of pet imaging with viral vectors for identification of cancer metastases

There are three main ways for dissemination of solid tumors: direct invasion, lymphatic spread and hematogenic spread. The presence of metastases is the most significant factor in predicting prognosis and therefore evidence of metastases will influence decision-making regarding treatment. Conventional imaging techniques are limited in the evaluation and localization of metastases due to their restricted ability to identify subcentimeter neoplastic disease. Hence, there is a need for an effective noninvasive modality that can accurately identify occult metastases in cancer patients. One such method is the combination of positron emission tomography (PET) with vectors designed for delivery of reporter genes into target cells. Vectors expressing the herpes simplex virus-1 thymidine kinase (HSV1-tk) reporter system have recently been shown to allow localization of micrometastases in animal models of cancer using non invasive imaging. Combination of HSV1-tk and PET imaging is based on the virtues of vectors which can carry and selectively express the HSV1-tk reporter gene in a variety of cancer cells but not in normal tissue. A radioactive tracer which is applied systemically is phosphorylated by the HSV1-tk enzyme, and as a consequence, the tracer accumulates in proportion to the level of HSV1-tk expression which can be imaged by PET. In this paper we review the recent developments in molecular imaging of micrometastases using replication-competent viral or nonviral vectors carrying the HSV1-tk gene using PET imaging. These diagnostic paradigms introduce an advantageous new concept in noninvasive molecular imaging with the potential benefits for improving patient care by providing guidance for therapy to patients with risk for metastases.

Positron emission tomography reporter genes and reporter probes: gene and cell therapy applications

Positron emission tomography (PET) imaging reporter genes (IRGs) and PET reporter probes (PRPs) are amongst the most valuable tools for gene and cell therapy. PET IRGs/PRPs can be used to non-invasively monitor all aspects of the kinetics of therapeutic transgenes and cells in all types of living mammals. This technology is generalizable and can allow long-term kinetics monitoring. In gene therapy, PET IRGs/PRPs can be used for whole-body imaging of therapeutic transgene expression, monitoring variations in the magnitude of transgene expression over time. In cell or cellular gene therapy, PET IRGs/PRPs can be used for whole-body monitoring of therapeutic cell locations, quantity at all locations, survival and proliferation over time and also possibly changes in characteristics or function over time. In this review, we have classified PET IRGs/PRPs into two groups based on the source from which they were derived: human or non-human. This classification addresses the important concern of potential immunogenicity in humans, which is important for expansion of PET IRG imaging in clinical trials. We have then discussed the application of this technology in gene/cell therapy and described its use in these fields, including a summary of using PET IRGs/PRPs in gene and cell therapy clinical trials. This review concludes with a discussion of the future direction of PET IRGs/PRPs and recommends cell and gene therapists collaborate with molecular imaging experts early in their investigations to choose a PET IRG/PRP system suitable for progression into clinical trials.

Theranostic potential of oncolytic vaccinia virus

Biological cancer therapies, such as oncolytic, or replication-selective viruses have advantages over traditional therapeutics as they can employ multiple different mechanisms to target and destroy cancers (including direct cell lysis, immune activation and vascular collapse). This has led to their rapid recent clinical development. However this also makes their pre-clinical and clinical study complex, as many parameters may affect their therapeutic potential and so defining reason for treatment failure or approaches that might enhance their therapeutic activity can be complicated. The ability to non-invasively image viral gene expression in vivo both in pre-clinical models and during clinical testing will considerably enhance the speed of oncolytic virus development as well as increasing the level and type of useful data produced from these studies. Further, subsequent to future clinical approval, imaging of reporter gene expression might be used to evaluate the likelihood of response to oncolytic viral therapy prior to changes in tumor burden. Here different reporter genes used in conjunction with oncolytic viral therapy are described, along with the imaging modalities used to measure their expression, while their applications both in pre-clinical and clinical testing are discussed. Possible future applications for reporter gene expression from oncolytic viruses in the phenotyping of tumors and the personalizing of treatment regimens are also discussed.

Angiogenesis inhibition using an oncolytic herpes simplex virus expressing endostatin in a murine lung cancer model

Herpes-mediated viral oncolysis alone is not sufficient to completely eradicate tumors. In this study we used a replication conditional, endostatin-expressing herpes simplex virus-1 mutant (HSV-Endo) in a murine lung cancer model. We hypothesized that the anti-angiogenic action of endostatin would improve upon the oncolytic effect of HSV-1. HSV-Endo was evaluated in a pulmonary metastases and orthotopic flank model, where there was significantly less tumor burden and reduced microvessel density compared to a control virus. Endostatin expression appears to improve the anti-tumor effect of HSV-1 in a lung cancer model.

Oncolytic herpes simplex virus expressing yeast cytosine deaminase: relationship between viral replication, transgene expression, prodrug bioactivation

Yeast cytosine deaminase (yCD) is a well-characterized prodrug/enzyme system that converts 5-fluorocytosine (5-FC) to 5-fluorouracil (5-FU), and has been combined with oncolytic viruses. However, in vivo studies of the interactions between 5-FC bioactivation and viral replication have not been previously reported, nor have the kinetics of transgene expression and the pharmacokinetics of 5-FC and 5-FU. We constructed a replication-conditional HSV-1 expressing yCD and examined cytotoxicity when 5-FC was initiated at different times after viral infection, and observed that earlier 5-FC administration led to greater cytotoxicity than later 5-FC administration in vitro and in vivo. Twelve days of 5-FC administration was superior to 6 days in animal models, but dosing beyond 12 days did not further enhance efficacy. Consistent with the dosing schedule results, both viral genomic DNA copy number and viral titers were observed to peak on Day 3 after viral injection and gradually decrease thereafter. The virus is replication-conditional and was detected in tumors for as long as 2 weeks after viral injection. The maximum relative extent of yCD conversion of 5-FC to 5-FU in tumors was observed on Day 6 after viral injection and it decreased progressively thereafter. The observation that 5-FU generation within tumors did not lead to appreciable levels of systemic 5-FU (<10 ng/ml) is important and has not been previously reported. The approaches used in these studies of the relationship between the viral replication kinetics, transgene expression, prodrug administration and anti-tumor efficacy are useful in the design of clinical trials of armed, oncolytic viruses.

Insertion of the human sodium iodide symporter to facilitate deep tissue imaging does not alter oncolytic or replication capability of a novel vaccinia virus

INTRODUCTION

Oncolytic viruses show promise for treating cancer. However, to assess therapeutic efficacy and potential toxicity, a noninvasive imaging modality is needed. This study aimed to determine if insertion of the human sodium iodide symporter (hNIS) cDNA as a marker for non-invasive imaging of virotherapy alters the replication and oncolytic capability of a novel vaccinia virus, GLV-1h153.

METHODS

GLV-1h153 was modified from parental vaccinia virus GLV-1h68 to carry hNIS via homologous recombination. GLV-1h153 was tested against human pancreatic cancer cell line PANC-1 for replication via viral plaque assays and flow cytometry. Expression and transportation of hNIS in infected cells was evaluated using Westernblot and immunofluorescence. Intracellular uptake of radioiodide was assessed using radiouptake assays. Viral cytotoxicity and tumor regression of treated PANC-1tumor xenografts in nude mice was also determined. Finally, tumor radiouptake in xenografts was assessed via positron emission tomography (PET) utilizing carrier-free 124I radiotracer.

RESULTS

GLV-1h153 infected, replicated within, and killed PANC-1 cells as efficiently as GLV-1h68. GLV-1h153 provided dose-dependent levels of hNIS expression in infected cells. Immunofluorescence detected transport of the protein to the cell membrane prior to cell lysis, enhancing hNIS-specific radiouptake (P < 0.001). In vivo, GLV-1h153 was as safe and effective as GLV-1h68 in regressing pancreatic cancer xenografts (P < 0.001). Finally, intratumoral injection of GLV-1h153 facilitated imaging of virus replication in tumors via 124I-PET.

CONCLUSION

Insertion of the hNIS gene does not hinder replication or oncolytic capability of GLV-1h153, rendering this novel virus a promising new candidate for the noninvasive imaging and tracking of oncolytic viral therapy.

Radiolabeled antiviral drugs and antibodies as virus-specific imaging probes

A number of small-molecule drugs inhibit viral replication by binding directly to virion structural proteins or to the active site of a viral enzyme, or are chemically modified by a viral enzyme before inhibiting a downstream process. Similarly, antibodies used to prevent or treat viral infections attach to epitopes on virions or on viral proteins expressed on the surface of infected cells. Such drugs and antibodies can therefore be thought of as probes for the detection of viral infections, suggesting that they might be used as radiolabeled tracers to visualize sites of viral replication by single-photon emission computed tomography (SPECT) or positron emission tomography (PET) imaging. A current example of this approach is the PET imaging of herpes simplex virus infections, in which the viral thymidine kinase phosphorylates radiolabeled thymidine analogues, trapping them within infected cells. One of many possible future applications might be the use of a radiolabeled hepatitis C protease inhibitor to image infection in animals or humans and provide a quantitative measure of viral burden. This article reviews the basic features of radionuclide imaging and the characteristics of ideal tracer molecules, and discusses how antiviral drugs and antibodies could be evaluated for their suitability as virus-specific imaging probes. The use of labeled drugs as low-dose tracers would provide an alternative application for compounds that have failed to advance to clinical use because of insufficient in vivo potency, an unsuitable pharmacokinetic profile or hepato- or nephrotoxicity.

Comparison of intravenous versus intraperitoneal administration of oncolytic herpes simplex virus 1 for peritoneal carcinomatosis in mice

hrR3 is an oncolytic herpes simplex virus 1 (HSV-1) mutant that replicates preferentially in tumors compared with normal tissues. Portal venous administration of hrR3 in mice bearing diffuse colorectal carcinoma liver metastases significantly reduces tumor burden and prolongs animal survival. In this study, we compared survival benefit and biodistribution of hrR3 following intravenous (i.v.) administration versus intraperitoneal (i.p.) administration in immunocompetent mice bearing colon carcinoma peritoneal metastases. Mice bearing peritoneal metastases received 1 x 10(8) plaque-forming units hrR3 or mock-infected media every other day for three doses and were randomized to have the viruses administered by either an i.p. or i.v. route. Biodistribution was assessed by PCR amplification of HSV-1-specific sequences from tumor and normal tissues including the small bowel, liver, spleen, kidney, lung, heart and brain. LD(50) for i.p. administration was compared with the LD(50) for i.v. administration. In subsequent experiments, animals were monitored for survival. The frequency of HSV-1 detection in peritoneal tumors was similar in mice randomized to either i.p. or i.v. administration. However, i.p. administration resulted in a more restricted systemic biodistribution, with a reduced frequency of virus detected in the kidney, lung and heart. The LD(50) associated with i.p. administration was higher than that with i.v. administration. Tumor burden was more effectively reduced with i.p. compared with i.v. administration. Median survival following i.p. administration was approximately twice that observed with i.v. administration. I.p. administration of an HSV-1 oncolytic mutant is associated with a more restricted biodistribution, less toxicity and greater efficacy against peritoneal metastases compared with i.v. administration.

Utility of a herpes oncolytic virus for the detection of neural invasion by cancer

Prostate, pancreatic, and head and neck carcinomas have a high propensity to invade nerves. Surgical resection is a treatment modality for these patients, but it may incur significant deficits. The development of an imaging method able to detect neural invasion (NI) by cancer cells may guide surgical resection and facilitate preservation of normal nerves. We describe an imaging method for the detection of NI using a herpes simplex virus, NV1066, carrying tyrosine kinase and enhanced green fluorescent protein (eGFP). Infection of pancreatic (MiaPaCa2), prostate (PC3 and DU145), and adenoid cystic carcinoma (ACC3) cell lines with NV1066 induced a high expression of eGFP in vitro. An in vivo murine model of NI was established by implanting tumors into the sciatic nerves of nude mice. Nerves were then injected with NV1066, and infection was confirmed by polymerase chain reaction. Positron emission tomography with [(18)F]-2'-fluoro-2'-deoxyarabinofuranosyl-5-ethyluracil performed showed significantly higher uptake in NI than in control animals. Intraoperative fluorescent stereoscopic imaging revealed eGFP signal in NI treated with NV1066. These findings show that NV1066 may be an imaging method to enhance the detection of nerves infiltrated by cancer cells. This method may improve the diagnosis and treatment of patients with neurotrophic cancers by reducing injury to normal nerves and facilitating identification of infiltrated nerves requiring resection.

Dual-modality in vivo monitoring of subventricular zone stem cell migration and metabolism

Rat subventricular zone (SVZ) stem cells were labeled with superparamagnetic iron oxide particles (SPIO) to follow their fate and migratory potential with magnetic resonance imaging (MRI) and positron emission tomography (PET). Labeled cells were transplanted into either the right rostral migratory stream (RMS) or striatum of normal adult Sprague-Dawley rats and serially followed for 3 months. Minimal migration of the cells implanted into the striatum was observed after 3 weeks whereas SVZ cells implanted into the RMS migrated toward the olfactory bulb at 1 week post-transplantation. PET studies of glucose metabolism using (18)F-FDG demonstrated enhanced glucose utilization in the striatum of transplanted animals. PET studies conducted 3 months after transplantation showed elevated accumulation of (11)C-raclopride (dopamine receptor type 2) and (11)C-CFT (dopamine transporter) binding in the striatal grafts. Implanted SVZ cells did not induce significant inflammation as identified by PET using (11)C-PK11195, a ligand detecting activated microglia. Histological analysis identified viable SPIO-labeled cells (some of which were nestin-positive) 7 weeks post-transplantation, suggesting a prolonged presence of undifferentiated neural stem cells within transplants. In addition, double immunostaining for neuronal and astrocytic markers (NeuN and GFAP) indicated that differentiation into neuronal and astrocytic phenotypes also occurred. Thus, combining MRI and PET enables monitoring of cell migration and metabolism non-invasively in vivo for extended periods of time.

Systemic delivery of (gamma1)34.5-deleted herpes simplex virus-1 selectively targets and treats distant human xenograft tumors that express high MEK activity

Deltagamma(1)34.5 mutant herpes simplex type 1 viruses are under active clinical investigation as oncolytic therapy for cancer. Mitogen-activated protein kinase/extracellular signal-regulated kinase kinase (MEK) activity has been shown to suppress protein kinase R and thereby confer oncolytic susceptibility to some human tumors by R3616, a virus deleted for both copies of gamma(1)34.5. We report that systemic delivery of R3616 can selectively target and destroy human xenograft tumors that overexpress MEK activity compared with tumors that express lower MEK activity. These results suggest systemic delivery of R3616 may be effective in the treatment of some human tumors.

Tumor genotype determines susceptibility to oncolytic herpes simplex virus mutants: strategies for clinical application

Oncolytic Herpes simplex virus -1 (HSV-1) mutants based on deletion of the γ134.5 gene are promising therapies for cancer. Δγ134.5 mutant replication and cytolysis is tumor cell type specific and severely attenuated in normal tissues. The basis for attenuation lies in the activation of the protein kinase R (PKR)-mediated host cellular defense pathway, which inhibits protein synthesis in infected cells. Tumor cells which overexpress MAPK kinase (MEK) activity support robust replication of Δγ134.5 mutants via MEK-mediated inhibition of PKR, resulting in tumor oncolysis. Systemic delivery of γ134.5 mutants may allow selective targeting and destruction of metastases from a broad range of solid human tumors that overexpress MEK. Barriers to systemic HSV-1 oncolytic therapy include innate immunity, adaptive immunity and hepatic adsorption. Immunomodulating agents may overcome innate immunity to HSV-1-based vectors. Preclinical data combined with the pervasiveness of HSV-1 despite widespread immunity suggest that preexisting immunity may not eliminate oncolytic efficacy. In the future, biopsy-determined tumor MEK status may select patients for Δγ134.5 oncolytic therapy.