Oncolytic adenovirus
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]
Engineering of oncolytic adenovirus
Adenoviruses have so far been through three generations of development.[4] Some of the strategies for modification of adenoviruses are described below.
Attenuation
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]
Targeting
The most commonly used group of adenoviruses is
- Adapter molecules
- Bi-specific adapter molecules can be administered along with the virus to redirect viral coat protein tropism. These molecules are fusion proteins that are made up of an antibody raised against the knob domain of the adenovirus coat protein, fused to a natural ligand for a cell-surface receptor.[7] The use of adapter molecules has been shown to increase viral transduction. However, adapters add complexity to the system, and the effect of adapter molecule binding on the stability of the virus is uncertain.[citation needed]
- Coat-protein modification
- This method involves genetically modifying the fiber knob domain of the viral coat protein to alter its specificity. Short oesophageal adenocarcinoma.[8][9] When combined with a form of non-transductional targeting, these viruses proved to be effective and selective therapeutic agents for Oesophageal Adenocarcinoma.[citation needed]
- Transcriptional targeting
- This approach takes advantage of deregulated promoter to drive and control the expression of adenoviral genes. For instance, oesophageal adenocarcinoma by placing the early genes under the control of a Cox-2 promoter (adenoviruses have two early genes, E1A and E1B, that are essential for replication).[9] When combined with transductional targeting, AdCox2Lluc showed potential for treatment of Oesophageal Adenocarcinoma. Cox-2 is also a possible tumour-specific promoter candidate for other cancer types, including ovarian cancer.[citation needed]
- A suitable tumour-specific promoter for prostate cancer is prostate-specific antigen (PSA), whose expression is greatly elevated in prostate cancer. CN706 is a CRAd with a PSA tumour-specific promoter driving expression of the adenoviral E1A gene, required for viral replication. The CN706 titre is significantly greater in PSA-positive cells.[10]
- Post-Transcriptional detargeting
- Another layer of regulation that has emerged to control adenoviral replication is the use of microRNAs (miRNA) artificial target sites or miRNA response elements (MREs). Differential expression of miRNAs between healthy tissues and tumors permit to engineer oncolytic viruses in order to have their ability to replicate impaired in those tissues of interest while allowing its replication in the tumor cells.
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]
- stimulation of immune response
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]
- Enhancement of Ag presentation
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]
- Targeting costimulatory and Immune Checkpoints on T-cells
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]
Examples
Oncorine (H101)
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 (dl1520)
Onyx-015 (originally named Ad2/5 dl1520
Directed Evolution
Traditional research has focussed on species C Adenovirus serotype 5 (Ad5) for creating
ColoAd1
One non-species C oncolytic
Background
This gave rise to the idea that an altered adenovirus could be used to target and eliminate cancer cells.
Clinical trials
There are as of 2023 several ongoing and finished clinical trial testing oncolytic adenoviruses.[46][47][48]
ONYX-015 (dl1520)/H101
Patents for the therapeutic use of
See also
References
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