Adenovirus varieties have been explored extensively as a viral vector for gene therapy and also as an oncolytic virus. [1]
Of the many different viruses being explored for oncolytic potential, an adenovirus was the first to be approved by a regulatory agency, the genetically modified H101 strain. It gained regulatory approval in 2005 from China's State Food and Drug Administration (SFDA) for the treatment of head and neck cancer. [2] [3]
Adenoviruses have so far been through three generations of development. [4] Some of the strategies for modification of adenoviruses are described below.
For adenovirus replication to occur, the host cell must be induced into S phase by viral proteins interfering with cell cycle proteins. The adenoviral E1A gene is responsible for inactivation of several proteins, including retinoblastoma, allowing entry into S-phase. The adenovirus E1B55kDa gene cooperates with another adenoviral product, E4ORF6, to inactivate p53, thus preventing apoptosis. It was initially proposed that an adenovirus mutant lacking the E1B55kDa gene, dl1520 (ONYX-015), could replicate selectively in p53 deficient cells.[ citation needed ]
A conditionally replicative adenovirus (CRAd) with a 24 base pair deletion in the retinoblastoma-binding domain of the E1A protein (Ad5- Δ24E3), is unable to silence retinoblastoma, and therefore unable to induce S-phase in host cells. [5] This restricts Ad5-Δ24E3 to replication only in proliferating cells, such as tumour cells.[ citation needed ]
The most commonly used group of adenoviruses is serotype 5 (Ad5), whose binding to host cells is initiated by interactions between the cellular coxsackie virus and adenovirus receptor (CAR), and the knob domain of the adenovirus coat protein trimer. CAR is necessary for adenovirus infection. [6] Although expressed widely in epithelial cells, CAR expression in tumours is extremely variable, leading to resistance to Ad5 infection. [6] Retargeting of Ad5 from CAR, to another receptor that is ubiquitously expressed on cancer cells, may overcome this resistance. [6]
Tissue/cell-type | Enriched miRNA | Use of the MRE | References |
---|---|---|---|
Liver | miR-122 | Prevent liver toxicity, hepatotoxicity | [11] |
Muscle | miR-133, miR-206 | Prevent muscle inflammation, myositis | [12] |
Pancreas | miR-148a | Promote pancreatic tumor targeting | [13] |
Prostate | miR-143, miR-145 | Promote prostate tumor targeting | [14] |
Neuron | miR-124 | Promote astrocyte targeting | [15] |
Arming with Transgenes
To enhance the efficacy, therapeutic transgenes are integrated into oncolytic adenovirus [16]
Immunostimulatory genes Like interferon α (IFNα), [17] tumor necrosis factor alpha (TNFα), [18] and interleukin 12 (IL-12) [19] have been integrated into oncolytic adenovirus to enhance immune response inside the tumor microenvironment. When these molecules selectively expressed in tumor cells, oncolytic adenoviruses promote immune responses against tumor and minimize systemic side effects [20]
Oncolytic adenoviruses have been genetically modified with transgene encoding for granulocyte-macrophage colony-stimulating factor (GM-CSF) to enhance tumor antigens presentation by antigen-presenting cells (APCs). This approach aims to improve recognition of tumor by T-cell and subsequent immune responses, [21] [22]
Oncolytic adenoviruses have been genetically engineered to express checkpoint inhibitors (CTLA-4, anti-PD-L1 antibodies) to release brake of T-cell activity, [23] [24] and to express costimulatory molecules (CD40L, 4-1BBL) to augment T-cell activation and proliferation, [25] [26]
H101 and the very similar Onyx-015 have been engineered to remove a viral defense mechanism that interacts with a normal human gene p53 , which is very frequently dysregulated in cancer cells. [3] Despite the promises of early in vivo lab work, these viruses do not specifically infect cancer cells, but they still kill cancer cells preferentially. [3] While overall survival rates are not known, short-term response rates are approximately doubled for H101 plus chemotherapy when compared to chemotherapy alone. [3] It appears to work best when injected directly into a tumour, and when any resulting fever is not suppressed. [3] Systemic therapy (such as through infusion through an intravenous line) is desirable for treating metastatic disease. [27] It is now marketed under the brand name Oncorine. [28]
Onyx-015 (originally named Ad2/5 dl1520 [29] [30] ) is an experimental oncolytic virus created by genetically engineering an adenovirus. [29] [31] It has been trialed as a possible treatment for cancer. The E1B-55kDa gene has been deleted allowing the virus to selectively replicate in and lyse p53-deficient cancer cells. [32]
Traditional research has focussed on species C Adenovirus serotype 5 (Ad5) for creating oncolytic vaccines for the potential use as cancer treatment. However, recent data suggests that it may not be the best virus serotype for deriving all oncolytic agents for treating human malignancies. [33] For example, oncolytic vaccines based on the Ad5 serotype have relatively poor clinical efficacy as monotherapies. [34] [35] [36] [37] The need for increased potency (infectivity and lytic activity) has led to an expanded search involving a larger number of less well studied adenovirus serotypes.[ citation needed ]
One non-species C oncolytic adenovirus currently in development is ColoAd1. It was created using a process of “directed evolution”. This involves the creation of new viral variants or serotypes specifically directed against tumour cells via rounds of directed selection using large populations of randomly generated recombinant precursor viruses. The increased biodiversity produced by the initial homologous recombination step provides a large random pool of viral candidates which can then be passed through a series of selection steps designed to lead towards a pre-specified outcome (e.g. higher tumor specific activity) without requiring any previous knowledge of the resultant viral mechanisms that are responsible for that outcome. [38] One particular application of this approach produced ColoAd1, which is a novel Ad11p/Ad3 chimeric Group B oncolytic virus with specificity for human colon cancer and a broad spectrum of anti-cancer activity in common solid tumours. [38] The therapeutic efficacy of ColoAd1 is currently being evaluated in three ongoing clinical trials (see the EU Clinical Trials Register for further details). ColoAd1 potency can be further enhanced via the use of therapeutic transgenes, which can be introduced into the ColoAd1 genome without compromising the selectivity or activity of the virus. Recent studies with ColoAd1 have shown a unique mechanism of cell death similar to Oncosis with expression of inflammatory cell death markers and cell membrane blistering and have highlighted mechanisms by which ColoAd1 alters host cell metabolism to facilitate replication. [39] [40]
Tumours form in cells when mutations in genes involved in cell cycle control and apoptosis accumulate over time. [41] Most tumours studied, have defects in the p53 tumor suppressor pathway. [42] p53 is a transcription factor that plays a role in apoptosis, cell cycle and DNA repair. It blocks cell progression in response to cellular stress or DNA damage. Many viruses replicate by altering the cell cycle and exploiting the same pathways that are altered in cancer cells. [43] E1B proteins produced by adenoviruses protect the infected cell by binding to and degrading the p53 transcription factors, [44] preventing it from targeting the cell for apoptosis. This allows the virus to replicate, package its genome, lyse the cell and spread to new cells.[ citation needed ]
This gave rise to the idea that an altered adenovirus could be used to target and eliminate cancer cells. Onyx-015 is an adenovirus that was developed in 1987 with the function of the E1B gene knocked out, [45] meaning cells infected with Onyx-015 are incapable of blocking p53's function. If Onyx-015 infects a normal cell, with a functioning p53 gene, it will be prevented from multiplying by the action of the p53 transcription factor. However, if Onyx-015 infects a p53 deficient cell it should be able to survive and replicate, resulting in selective destruction of cancer cells.
There are as of 2023 several ongoing and finished clinical trial testing oncolytic adenoviruses. [46] [47] [48]
ColoAd1 from PsiOxus Therapeutics has entered Phase I/II clinical study with its oncolytic vaccine. Phase I of the trial recruited patients with metastatic solid tumors and showed evidence for virus replication within tumour sites after intravenous delivery. The second phase of the ColoAd1 study will involve the comparison of intra-tumoural versus intravenous injection to examine viral replication, viral spread, tumour necrosis and anti-tumoural immune responses (see the EU Clinical Trials Register for further details).
Patents for the therapeutic use of ONYX-015 are held by ONYX Pharmaceuticals [49] [50] and it was used in combination with the standard chemotherapeutic agents cisplatin and 5-fluorouracil to combat head and neck tumours. [51] Onyx-015 has been extensively tested in clinical trials, with the data indicating that it is safe and selective for cancer. [52] However, limited therapeutic effect has been demonstrated following injection and systemic spread of the virus was not detected. [53] ONYX-015 when combined with chemotherapy, however, proved reasonably effective in a proportion of cases. During these trials a plethora of reports emerged challenging the underlying p53-selectivity, with some reports showing that in some cancers with a wild-type p53 ONYX-015 actually did better than in their mutant p53 counterparts. These reports slowed the advancement through Phase III trials in the US, however recently China licensed ONYX-015 for therapeutic use as H101. [54] Further development of Onyx-015 was abandoned in the early 2000s, the exclusive rights being licensed to the Chinese company, Shanghai Sunway Biotech. On November 17, 2005, the Chinese State Food and Drug Administration approved H101, an oncolytic adenovirus similar to Onyx-015 (E1B-55K/E3B-deleted), for use in combination with chemotherapy for the treatment of late-stage refractory nasopharyngeal cancer. [55] [56] Outside of China, the push to the clinic for ONYX-015 has been largely been discontinued for financial reasons and until a real mechanism can be found. [57]
A tumor suppressor gene (TSG), or anti-oncogene, is a gene that regulates a cell during cell division and replication. If the cell grows uncontrollably, it will result in cancer. When a tumor suppressor gene is mutated, it results in a loss or reduction in its function. In combination with other genetic mutations, this could allow the cell to grow abnormally. The loss of function for these genes may be even more significant in the development of human cancers, compared to the activation of oncogenes.
Adenoviruses are medium-sized, nonenveloped viruses with an icosahedral nucleocapsid containing a double-stranded DNA genome. Their name derives from their initial isolation from human adenoids in 1953.
An oncovirus or oncogenic virus is a virus that can cause cancer. This term originated from studies of acutely transforming retroviruses in the 1950–60s, when the term oncornaviruses was used to denote their RNA virus origin. With the letters RNA removed, it now refers to any virus with a DNA or RNA genome causing cancer and is synonymous with tumor virus or cancer virus. The vast majority of human and animal viruses do not cause cancer, probably because of longstanding co-evolution between the virus and its host. Oncoviruses have been important not only in epidemiology, but also in investigations of cell cycle control mechanisms such as the retinoblastoma protein.
An oncolytic virus is a virus that preferentially infects and kills cancer cells. As the infected cancer cells are destroyed by oncolysis, they release new infectious virus particles or virions to help destroy the remaining tumour. Oncolytic viruses are thought not only to cause direct destruction of the tumour cells, but also to stimulate host anti-tumour immune system responses. Oncolytic viruses also have the ability to affect the tumor micro-environment in multiple ways.
Virotherapy is a treatment using biotechnology to convert viruses into therapeutic agents by reprogramming viruses to treat diseases. There are three main branches of virotherapy: anti-cancer oncolytic viruses, viral vectors for gene therapy and viral immunotherapy. These branches use three different types of treatment methods: gene overexpression, gene knockout, and suicide gene delivery. Gene overexpression adds genetic sequences that compensate for low to zero levels of needed gene expression. Gene knockout uses RNA methods to silence or reduce expression of disease-causing genes. Suicide gene delivery introduces genetic sequences that induce an apoptotic response in cells, usually to kill cancerous growths. In a slightly different context, virotherapy can also refer more broadly to the use of viruses to treat certain medical conditions by killing pathogens.
p73 is a protein related to the p53 tumor protein. Because of its structural resemblance to p53, it has also been considered a tumor suppressor. It is involved in cell cycle regulation, and induction of apoptosis. Like p53, p73 is characterized by the presence of different isoforms of the protein. This is explained by splice variants, and an alternative promoter in the DNA sequence.
Viral vectors are modified viruses designed to deliver genetic material into cells. This process can be performed inside an organism or in cell culture. Viral vectors have widespread applications in basic research, agriculture, and medicine.
Adenovirus E1B protein usually refers to one of two proteins transcribed from the E1B gene of the adenovirus: a 55kDa protein and a 19kDa protein. These two proteins are needed to block apoptosis in adenovirus-infected cells. E1B proteins work to prevent apoptosis that is induced by the small adenovirus E1A protein, which stabilizes p53, a tumor suppressor.
JX-594 is an oncolytic virus is designed to target and destroy cancer cells. It is also known as Pexa-Vec, INN pexastimogene devacirepvec) and was constructed in Dr. Edmund Lattime's lab at Thomas Jefferson University, tested in clinical trials on melanoma patients, and licensed and further developed by SillaJen.
Gene therapy utilizes the delivery of DNA into cells, which can be accomplished by several methods, summarized below. The two major classes of methods are those that use recombinant viruses and those that use naked DNA or DNA complexes.
Anticancer genes have a special ability to target and kill cancer cells without harming healthy ones. They do this through processes like programmed cell death, known as apoptosis, and other mechanisms like necrosis and autophagy. In the late 1990s, researchers discovered these genes while studying cancer cells. Sometimes, mutations or changes in these genes can occur, which might lead to cancer. These changes can include small alterations in the DNA sequence or larger rearrangements that affect the gene's function. When these anticancer genes are lost or altered, it can disrupt their ability to control cell growth, potentially leading to the development of cancer.
Jennerex Biotherapeutics, Inc. was an American private biopharmaceutical company that developed the oncolytic viruses JX-594 and JX-929 among others. By creating oncolytic viruses that can (1) kill tumor cells directly through lysis, (2) activate the immune system by delivering genes that encode immunostimulants and by overcoming tumor cell-induced immunological tolerance, and (3) reduce tumor nutrient supply through the destruction of blood vessels, Jennerex aimed to create a novel approach to treating and possibly curing cancer.
Adenovirus early region 1A (E1A) is a gene expressed during adenovirus replication to produce a variety of E1A proteins. It is expressed during the early phase of the viral life span.
Adenovirus genomes are linear, non-segmented double-stranded (ds) DNA molecules that are typically 26-46 Kbp long, containing 23-46 protein-coding genes. The example used for the following description is Human adenovirus E, a mastadenovirus with a 36 Kbp genome containing 38 protein-coding genes. While the precise number and identity of genes varies among adenoviruses, the basic principles of genome organization and the functions of most of the genes described in this article are shared among all adenoviruses.
Many variants of herpes simplex virus have been considered for viral therapy of cancer; the early development of these was thoroughly reviewed in the journal Cancer Gene Therapy in 2002. This page describes the most notable variants—those tested in clinical trials: G207, HSV1716, NV1020 and Talimogene laherparepvec. These attenuated versions are constructed by deleting viral genes required for infecting or replicating inside normal cells but not cancer cells, such as ICP34.5, ICP6/UL39, and ICP47.
Lentiviral vectors in gene therapy is a method by which genes can be inserted, modified, or deleted in organisms using lentiviruses.
Maurice Green was an American virologist. He was regarded as a pioneer in the study of animal viruses, in particular their role in cancer. Green founded the Institute of Molecular Virology at St. Louis University School of Medicine in the late 1950s, and later served as its chairman.
David H. Kirn is an American entrepreneur-innovator, physician-scientist, CEO and professor. He is co-founder and CEO of 4D Molecular Therapeutics (4DMT), a biotechnology company designing and developing adeno-associated virus gene therapy vectors.
Enadenotucirev is an investigational oncolytic virus that is in clinical trials for various cancers.
Akseli Hemminki July 27, 1973 (Helsinki) is a Finnish specialist in Oncology and Radiotherapy, Professor of Oncology and founder of two biotechnology companies.