Newcastle Disease Virus as an Anti-Cancer Therapy

 

Abdul Rahman Omar,^* Aini Ideris, Abdul Manaf Ali,^* Fauziah Othman,^*,** Khatijah Yusoff,^*,*** Jafri Malin Abdullah,^**** Haryati Shila Mohamad Wali, Madihah Zawawi,^* and Narayani Meyyappan^**

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Abstracts

Newcastle disease virus (NDV) is one of the most economically important avian virus which affects the poultry industry worldwide. Although NDV is being very actively studied in Malaysia, there are still no studies on its potential as an anticancer agent, a new approach to treating cancer known as virotherapy. Currently, a collaborative research is being undertaken between Universiti Putra Malaysia (UPM), Universiti Sains Malaysia (USM) and Majlis Kanser Nasional (MAKNA) in characterising various local NDV isolates as anticancer agent. This paper describes an overview of the research that have been carried out worldwide in the use of NDV for cancer treatment and also some of our findings in characterising local NDVs with oncolytic properties.

Keywords: Newcastle disease virus, anticancer agent, apoptosis

Intro

Cancer is one of the major killers in human in the world including Malaysia. It can affect any organ(s) of the body regardless of age, gender, race/ethnic background, diet, and the environment. The most predominant cancer affecting males in Malaysia are cancer of the lung, nasopharynx, mouth, stomach and liver, while amongst females, the most prevalent cancers, are cancer of the breast, cervix, lung and stomach (3). The conventional approach to the treatment of cancer is cytotoxic chemotherapy, either alone or in combination with surgery and radiotherapy. Another approach, known as immunotherapy is through the use of immunomodulatory factors such as cytokines and interferons. Viruses with inherent oncolytic activities have been used in the past as potential cancer therapeutics. Lately, the application of virus as virotherapy for cancer has been revived among the scientific community (40). This paper describes an overview on the application of NDV as an alternative approach to treat cancer in human.

Virotheraphy in Cancer Medicines

It has been known for more than 70 years that some viruses such as adenovirus, herpes simplex virus (HSV), reovirus, rabies virus, poliovirus, measles virus, vesicular stomatitis virus, hepatitis A virus and NDV have the ability to destroy cancer cells. These viruses are either used without any genetic manipulation or undergo genetic engineering for increasing selectivity in animal models and human clinical trials (24, 32, 40, 50). NDV has been classified together with other viruses such as reovirus and parvovirus as viruses with inherent oncolytic effects, meanwhile, viruses such as HSV and adenovirus are examples of those that have been manipulated to enhance their cytolytic properties as anti-cancer agents (Table 1). These viruses were manipulated in such a way that they are attenuated in normal cells without altering their ability to lyse tumour cells. In some of the modifications, the engineered viruses were targeted to very specific cancer cells (24).

Oncolytic Newcastle Diseases Virus

Among the first intentional use of NDV to treat cancer in humans was documented in the early 1950’s where NDV and adenovirus were injected directly into uterine carcinoma which underwent partial necrosis and sloughing followed by regrowth (8). In another report, NDV was also shown to be oncolytic on Ehrlich ascites carcinoma (19). However, all of these trials were stopped because early oncolytic effects were lost with regrowth of the tumours when the patients produced virus neutralising antibodies. Similar results were also produced after the use of other oncolytic viruses such as mumps virus and influenza virus (1). Nevertheless, systemic administration of mumps virus for the therapy of human cancer in Japan caused partial tumour remission despite the production of virus-neutralising antibodies (6, 43). Similar results were also obtained with repeated systemic administration of NDV for the therapy of cancer in Hungary (14). It was then postulated that perhaps these oncolytic viruses lose their effects on the cancer cells because of humoral antiviral immunity of the host, whereas when an incompletely replicating or non-cytolytic virus establishes a persistent relationship with a tumour, antiviral immune components such as antibodies and activated T cells attack and eliminate tumour cells expressing viral antigen (50).

The oncolytic properties of NDV have been studied both in mouse models (Table 2) and in human clinical trials (Table 3). In both instances, favorable results from partial to complete regression of tumours were obtained for various types of tumours including those in the advanced stages that were not responsive to standard therapy. The ability of NDV to successfully infect and destroy cancer cells seemed to be dependent on many factors (50).

The use of NDV as non-viral oncolysate based treatment has been reported in Hungary (14). In that study, patients with advanced tumour received repeated administrations of high dose inhalation, ingestion, injection or enema of the attenuated NDV strain (MTH68/H) derived from Hertfordshire strain showed significant regressions of varying degrees. The use of high doses of live NDV has also been shown to be effective against non-responsive grade IV glioblastoma (11). However, not all NDV strains are able to induce direct oncolysis. For example, the most oncolytic NDV strain was Cassel’s 73T whilst the NDV strain Ulster (which exhibits abortive replication in normal cells) induces host immunity towards tumour cells expressing the NDV antigen (50). It has been shown that the former NDV strain selectively replicates in tumour cells as compared to normal cells and new virions produced by infected tumour cells are non-infectious (49). They also indicated that the strain Ulster which infected various cancer cells gave least favorable trends in the induction of clinically evaluated antitumour responses. This finding lead to the postulation that x-ray irradiated viral infected tumour cells were more immunogenic than the viral oncolysates. However, it appeared that this effect was strain dependent. For example, the vaccine strains Roakin and B1 suppressed cellular DNA synthesis in Daudi Burkitt’s lymphoma cells leading to cell death (53), but treatment on the same cells using strain 73T did not damage the cells (57).

In addition to irradiated infected xenograft tumour cells, autologous tumour cell vaccine (ATV) have also been used by several researchers. In one study, Bohle et al. (7) demonstrated favorable results using ATV comprising a dose of 1 × 10⁷ human colorectal tumour cells together with 32 hemagglutination unit (HAU) of non-irradiated NDV given intracutaneously to patients. Recently, a study in China indicated that patients who have received ATV and NDV vaccine strain La Sota IV have significant regression of advanced tumours of the digestive tract compared to the controlled group (26).

The oncolytic properties of NDV have also been studied in animal models by xenotransplanting tumour cells onto athymic and nude mice. It was found that the most oncolytic strain 73T completely destroyed human neuroblastoma or fibrosarcoma tumours xenotransplanted in athymic mice following intra-tumoural route of the virus (Table 2) (27, 28). Similarly, the oncolytic effects of 73T were also shown in other tumour cells such as bladder carcinoma, Wilm’s tumour, osteosarcoma and cervical carcinoma (39). In addition, direct administration of 73T either through intra-tumoural and intra-peritoneal routes showed complete regression of various advanced tumours including neuroblastoma in nude mice model (Table 2) (35). It was found that only live virus showed better results than inactivated virus, and the oncolytic virus itself might provide additional benefits (10, 39). However,these results were strain dependent. A study by Schirrmacher et al. (48) on effects of NDV strains to colon carcinoma showed that the non-lytic strain Ulster displayed stronger antitumour activity than the lytic 73T. On the other hand, intra-tumoural injection of NDV on human melanoma was found to be more effective when using lytic strain Italien compared to the non-lytic strain Ulster.

It can be concluded from the above studies that replication competency is necessary for maximal effects and multiple NDV doses are more effective than a single dose. It seems that depending on the NDV strains, intra- or peritumoural application is more effective than systemic application for various tumours in mice model. Compared to other viruses with inherent oncolytic properties, NDV therapy is safer, non-neurotropic with very minimal side effects. The only side effects that have been reported were low-grade fever, vomiting and fatigue (50). Nevertheless, the clinical usefulness of NDV need to be carefully evaluated since any cancer treatment depends on its antitumour potency and its therapeutic index between cancerous and normal cells. Additionally, it has been known that most of the therapies that are currently available for metastatic solid tumours are not effective in one or both of these areas.

Oncolytic NDV induced apoptosis

Apoptosis which is an energy-dependent process of cell suicide is also known as programmed cell death. It is a natural response of the cells when exposed to a variety of stimuli. Apoptotic cells have a characteristic morphology and show distinct biochemical processes that can be detected using transmission electron microscope and expression of apoptotic gene markers, respectively (29). A number of viruses have been shown to cause apoptosis in cells during infection (33). In general, the mechanisms associated with virus-induced apoptosis are associated with one or more of the host regulatory genes that function as an oncogene and/or tumour suppressor factor. Examples of such genes are CD95/FasR/APO-1, bcl-2, c-myc, p53, Rb, p21WAF1 and ICE/ced-3 (40, 52). The importance of these genes in NDV-induced apoptosis of cancer cells is, however, not known. It has been shown that strain MTH-68/H was found to be cytotoxic on rat phaeochromocytoma (PC12) cells (17) causing internucleosomal DNA fragmentation, the most characteristic feature of apoptosis. The role of the anti-apoptotic protein,c-ras in tumour cells has been implied since mutation(s) in the protein promoted reovirus replication leading to oncolysis (12, 13). However, such evidence has never been demonstrated for NDV induced oncolysis although it is known that certain tumour cells such as fibrosarcoma and neuroblastoma which were susceptible to oncolysis by 73T NDV had certain forms of ras mutation (27, 28).

Conclusions

The relationship of NDV with tumours may be extremely variable. Depending on the tumour cells, NDV may exhibit their oncolytic activities either directly or indirectly. In the former pathway, viruses such as 73T affect the physiology of the infected cells whilst infection through the latter pathway (by strain Ulster) initiates immunity of the host upon the virus and virus-infected cells. In addition, NDV has been tested in the form of live virus or in the form of autologous or allogenic tumour vaccines. In both cases, it initiated weak tumour antigens, breaking tolerance towards tumour and generate immune responses against tumour antigens. The upregulation of TRAIL in activated PMBC by HN protein indicated that TNF-induced apoptosis may be an important mechanism in oncolytic NDV-induced apoptosis. The relationship between the activation of oncogenes and/or loss of tumour suppressor genes that are commonly found in malignant human tumour and susceptibility to NDV oncolysis remains to be determined. Once the identification of such gene(s) and the sequence of immunological reactions that accompanies oncolysis or tumour rejection become known, it will be possible to construct genetically engineered NDV strains that are safer with improved oncolytic effects on cancer cells.