ONYX-015 selectivity and the p14ARF pathway

Delivery systems for enhancing oncolytic adenoviruses efficacy

Oncolytic adenovirus (OAds) has long been considered a promising biotherapeutic agent against various types of cancer owing to selectively replicate in and lyse cancer cells, while remaining dormant in healthy cells. In the last years, multiple (pre)clinical studies using genetic engineering technologies enhanced OAds anti-tumor effects in a broad range of cancers. However, poor targeting delivery, tropism toward healthy tissues, low-level expression of Ad receptors on tumor cells, and pre-existing neutralizing antibodies are major hurdles for systemic administration of OAds. Different vehicles have been developed for addressing these obstacles, such as stem cells, nanoparticles (NPs) and shielding polymers, extracellular vesicles (EVs), hydrogels, and microparticles (MPs). These carriers can enhance the therapeutic efficacy of OVs through enhancing transfection, circulatory longevity, cellular interactions, specific targeting, and immune responses against cancer. In this paper, we reviewed adenovirus structure and biology, different types of OAds, and the efficacy of different carriers in systemic administration of OAds.

Oncolytic Adenovirus-A Nova for Gene-Targeted Oncolytic Viral Therapy in HCC

Hepatocellular carcinoma (HCC) is one of the most frequent cancers worldwide, particularly in China. Despite the development of HCC treatment strategies, the survival rate remains unpleasant. Gene-targeted oncolytic viral therapy (GTOVT) is an emerging treatment modality-a kind of cancer-targeted therapy-which creates viral vectors armed with anti-cancer genes. The adenovirus is a promising agent for GAOVT due to its many advantages. In spite of the oncolytic adenovirus itself, the host immune response is the determining factor for the anti-cancer efficacy. In this review, we have summarized recent developments in oncolytic adenovirus engineering and the development of novel therapeutic genes utilized in HCC treatment. Furthermore, the diversified roles the immune response plays in oncolytic adenovirus therapy and recent attempts to modulate immune responses to enhance the anti-cancer efficacy of oncolytic adenovirus have been discussed.

Going viral: a review of replication-selective oncolytic adenoviruses

Oncolytic viruses have had a tumultuous course, from the initial anecdotal reports of patients having antineoplastic effects after natural viral infections a century ago to the development of current cutting-edge therapies in clinical trials. Adenoviruses have long been the workhorse of virotherapy, and we review both the scientific and the not-so-scientific forces that have shaped the development of these therapeutics from wild-type viral pathogens, turning an old foe into a new friend. After a brief review of the mechanics of viral replication and how it has been modified to engineer tumor selectivity, we give particular attention to ONYX-015, the forerunner of virotherapy with extensive clinical testing that pioneered the field. The findings from those as well as other oncolytic trials have shaped how we now view these viruses, which our immune system has evolved to vigorously attack, as promising immunotherapy agents.

Oncolytic Immunotherapy for Treatment of Cancer

Immunotherapy entails the treatment of disease by modulation of the immune system. As detailed in the previous chapters, the different modes of achieving immune modulation are many, including the use of small/large molecules, cellular therapy, and radiation. Oncolytic viruses that can specifically attack, replicate within, and destroy tumors represent one of the most promising classes of agents for cancer immunotherapy (recently termed as oncolytic immunotherapy). The notion of oncolytic immunotherapy is considered as the way in which virus-induced tumor cell death (known as immunogenic cancer cell death (ICD)) allows the immune system to recognize tumor cells and provide long-lasting antitumor immunity. Both immune responses toward the virus and ICD together contribute toward successful antitumor efficacy. What is now becoming increasingly clear is that monotherapies, through any of the modalities detailed in this book, are neither sufficient in eradicating tumors nor in providing long-lasting antitumor immune responses and that combination therapies may deliver enhanced efficacy. After the rise of the genetic engineering era, it has been possible to engineer viruses to harbor combination-like characteristics to enhance their potency in cancer immunotherapy. This chapter provides a historical background on oncolytic virotherapy and its future application in cancer immunotherapy, especially as a combination therapy with other treatment modalities.

Oncolytic Replication of E1b-Deleted Adenoviruses

Various viruses have been studied and developed for oncolytic virotherapies. In virotherapy, a relatively small amount of viruses used in an intratumoral injection preferentially replicate in and lyse cancer cells, leading to the release of amplified viral particles that spread the infection to the surrounding tumor cells and reduce the tumor mass. Adenoviruses (Ads) are most commonly used for oncolytic virotherapy due to their infection efficacy, high titer production, safety, easy genetic modification, and well-studied replication characteristics. Ads with deletion of E1b55K preferentially replicate in and destroy cancer cells and have been used in multiple clinical trials. H101, one of the E1b55K-deleted Ads, has been used for the treatment of late-stage cancers as the first approved virotherapy agent. However, the mechanism of selective replication of E1b-deleted Ads in cancer cells is still not well characterized. This review will focus on three potential molecular mechanisms of oncolytic replication of E1b55K-deleted Ads. These mechanisms are based upon the functions of the viral E1B55K protein that are associated with p53 inhibition, late viral mRNA export, and cell cycle disruption.

Bacteriophage-derived vectors for targeted cancer gene therapy

Cancer gene therapy expanded and reached its pinnacle in research in the last decade. Both viral and non-viral vectors have entered clinical trials, and significant successes have been achieved. However, a systemic administration of a vector, illustrating safe, efficient, and targeted gene delivery to solid tumors has proven to be a major challenge. In this review, we summarize the current progress and challenges in the targeted gene therapy of cancer. Moreover, we highlight the recent developments of bacteriophage-derived vectors and their contributions in targeting cancer with therapeutic genes following systemic administration.

Synthetic immunosurveillance systems: nanodevices to monitor physiological events

The field of nanotechnology has recently seen vast advancements in its applications for therapeutic strategy. This technological revolution has led way to nanomedicine, which spurred the development of clever drug delivery designs and ingenious nanovehicles for the monitoring of cellular events in vivo. The clinical implementations of this technology are innumerable and have demonstrated utility as diagnostic tools and fortifying machineries for the mammalian immune system. Recently engineered viral vectors and multi-subunit packaging RNAs have verified stable enough for long-term existence in the physiological environment and therefore reveal unique potential as artificial immunosurveillance devices. Physiological and pathological events recorded by nanodevices could help develop "biocatalogs" of patients' infection history, frequency of disease, and much more. In this article, we introduce a novel design concept for a multilayer synthetic immune network parallel to the natural immune system; an artificial network of continuously patrolling nanodevices incorporated in the blood and lymphatic systems, and adapted for molecular event recording, anomaly detection, drug delivery, and gene silencing. We also aim to discuss the approaches and advances recently reported in nanomedicine, especially as it pertains to promising viral and RNA-based nanovehicles and their prospective applications for the development of a synthetic immunosurveillance system (SIS). Alternative suggestions and limitations of these technologies are also discussed.

2-aminopurine enhances the oncolytic activity of an E1b-deleted adenovirus in hepatocellular carcinoma cells

Adenoviruses with deletions of viral genes have been extensively studied as potential cancer therapeutics. Although a high degree of cancer selectivity has been demonstrated with these conditionally replicating adenoviruses, low levels of virus replication can be detected in normal cells. Furthermore, these mutations were also found to reduce the activity of the replicating viruses in certain cancer cells. Recent studies have shown that co-administration of chemotherapeutic drugs may increase the activity of these viruses without affecting their specificity. We constructed an adenovirus with deletions of both the E1b and the VA-RNA genes and found that replication of this virus was selective for human hepatocellular carcinoma (HCC) cell lines when compared to normal cell lines. Furthermore, we show that 2-aminopurine (2′AP) treatment selectively enhanced virus replication and virus-mediated death of HCC cells. 2′AP did not compensate for the loss of VA-RNA activities, but rather the loss of an E1b-55K activity, such as the DNA damage response, suggesting that co-administration of 2′AP derivatives that block host DNA damage response, may increase the oncolytic activity of AdΔE1bΔVA without reducing its selectivity for HCC cells.

Oncolytic viruses in the treatment of cancer: a review of current strategies

Oncolytic viruses are live, replication-competent viruses that replicate selectively in tumor cells leading to the destruction of the tumor cells. Tumor-selective replicating viruses offer appealing advantages over conventional cancer therapy and are promising a new approach for the treatment of human cancer. The development of virotherapeutics is based on several strategies. Virotherapy is not a new concept, but recent technical advances in the genetic modification of oncolytic viruses have improved their tumor specificity, leading to the development of new weapons for the war against cancer. Clinical trials with oncolytic viruses demonstrate the safety and feasibility of an effective virotherapeutic approach. Strategies to overcome potential obstacles and challenges to virotherapy are currently being explored. Systemic administrations of oncolytic viruses will successfully extend novel treatment against a range of tumors. Combination therapy has shown some encouraging antitumor responses by eliciting strong immunity against established cancer.

Active targeting of RGD-conjugated bioreducible polymer for delivery of oncolytic adenovirus expressing shRNA against IL-8 mRNA

Even though oncolytic adenovirus (Ad) has been highlighted in the field of cancer gene therapy, transductional targeting and immune privilege still remain difficult challenges. The recent reports have noted the increasing tendency of adenoviral surface shielding with polymer to overcome the limits of its practical application. We previously reported the potential of the biodegradable polymer, poly(CBA-DAH) (CD) as a promising candidate for efficient gene delivery. To endow the selective-targeting moiety of tumor vasculature to CD, cRGDfC well-known as a ligand for cell-surface integrins on tumor endothelium was conjugated to CD using hetero-bifunctional cross-linker SM (PEG)(n). The cytopathic effects of oncolytic Ad coated with the polymers were much more enhanced dose-dependently when compared with that of naked Ad in cancer cells selectively. Above all, the most potent oncolytic effect was assessed with the treatment of Ad/CD-PEG(500)-RGD in all cancer cells. The enhanced cytopathic effect of Ad/RGD-conjugated polymer was specifically inhibited by blocking antibodies to integrins, but not by blocking antibody to CAR. HT1080 cells treated with Ad/CD-PEG(500)-RGD showed strong induction of apoptosis and suppression of IL-8 and VEGF expression as well. These results suggest that RGD-conjugated bioreducible polymer might be used to deliver oncolytic Ad safely and efficiently for tumor therapy.

Targeted genetic and viral therapy for advanced head and neck cancers

Head and neck cancers usually present with advanced disease and novel therapies are urgently needed. Genetic therapy aims at restoring malfunctioned tumor suppressor gene(s) or introducing proapoptotic genes. Oncolytic virotherapeutics induce multiple cycles of cancer-specific virus replication, followed by oncolysis, virus spreading and infection of adjacent cancer cells. Oncolytic viruses can also be armed to express therapeutic transgene(s). Recent advances in preclinical and clinical studies are revealing the potential of both therapeutic classes for advanced head and neck cancers, including the approval of two products (Gendicine and H101) by a governmental agency. This review summarizes the available clinical data to date and discusses the challenges and future directions.

[Advances on mutant p53 research]

Inactivation of tumor suppressor gene is a key event in carcinogenesis. p53 is one of the most important tumor suppressor genes in the genome, and its mutations are found in approximately 50% of human cancers. p53 mutation is also the main cause for human Li-Fraumeni syndrome. The vast majority of p53 mutations are missense mutations, and the corresponding mutant p53 proteins not only lose wild-type p53 tumor suppressor activities, but also gain new oncogenic properties favoring cancer development. Here, we mainly discussed the structural and functional alterations of mutant p53, the molecular mechanisms underlying gain of oncogenic functions, and the strategies and explorations of suppressing mutant p53 activities.

Lysis of Dysplastic but not Normal Oral Keratinocytes and Tissue-Engineered Epithelia with Conditionally Replicating Adenoviruses

There is no effective medical treatment for oral precancer, and surgery to remove these lesions is imprecise because abnormal mucosa extends beyond the visible lesion. Development of vectors for tumor-selective viral replication has been a significant advance, and viral lysis is well suited to destruction of oral precancerous mucosa. To facilitate evaluation of new treatments, we engineered dysplastic oral epithelium using keratinocytes isolated from dysplastic lesions. We show that these model systems recapitulate the key characteristics of the clinical lesions closely, and that topical delivery of the conditionally replicating adenovirus (CRAd) dl922-947 can lyse tissue-engineered epithelia that show mild, moderate, or severe dysplasia, but normal oral epithelia are very resistant to this treatment. The lytic effect is determined by various factors, including the grade and proliferation index of the dysplastic epithelia. The presence of suprabasal cycling cells, expression of the coxsackie adenovirus receptor (CAR), the transcription cofactor p300, and other aberrations that affect the regulation of the cell cycle or apoptosis and promote viral replication may also be important. The ability of dl922-947 to destroy engineered oral dysplasia was significantly greater than that observed using wild-type adenovirus, d/1520, or viruses modified to bypass cell entry dependent on the presence of CAR. Evidence of infection in clinical dysplastic lesions was also shown ex vivo using tissue explants. We conclude that dl922-947 may provide an efficient molecular cytotoxic to dissolve oral dysplastic lesions.

Mutant p53 proteins: between loss and gain of function

Cancer might result from both the aberrant activation of genes, whose physiological tuning is essential for the life of a normal cell, and the inactivation of tumor suppressor genes, whose main job is to preserve the integrity of cell genome. Among the latter, p53 is considered a key tumor suppressor gene that is inactivated mainly by missense mutations in half of human cancers. It is becoming increasingly clear that the resulting mutant p53 proteins gain oncogenic properties favoring the insurgence, the maintenance, and the spreading of malignant tumors. In this review, we mainly discuss the molecular mechanisms underlying gain of function of human tumor-derived p53 mutants, their impact on the chemoresistance and the prognosis of human tumors, with a special focus on head and neck cancers, and the perspectives of treating tumors through the manipulation of mutant p53 proteins.

Minimal hepatic toxicity of Onyx-015: spatial restriction of coxsackie-adenoviral receptor in normal liver

We administered an adenoviral vector, Onyx-015, into the hepatic artery of patients with metastatic colorectal cancer involving the liver. Thirty-five patients enrolled in this multi-institutional phase I/II trial received up to eight arterial infusions of up to 2 × 10¹² viral particles. Hepatic toxicity was the primary dose-limiting toxicity observed in preclinical models. However, nearly 200 infusions of this adenoviral vector were administered directly into the hepatic artery without significant toxicity. Therefore, we undertook this analysis to determine the impact of repeated adenoviral exposure on hepatic function. Seventeen patients were treated at our institution, providing a detailed data set on the changes in hepatic function following repeated exposure to adenovirus. No changes in hepatic function occurred with the first treatment of Onyx-015 among these patients. Transient increases in transaminase levels occurred in one patient starting with the second infusion and transient increases in bilirubin was observed in two patients starting with the fifth treatment. These changes occurred too early to be explained by viral-mediated lysis of hepatocytes. In addition, viremia was observed starting 3–5 days after the viral infusion in half of the patient, but was not associated with hepatic toxicity. To further understand the basis for the minimal hepatic toxicity of adenoviral vectors, we evaluated the replication of adenovirus in primary hepatocytes and tumor cells in culture and the expression of the coxsackie-adenoviral receptor (CAR) in normal liver and colon cancer metastatic to the liver. We found that adenovirus replicates poorly in primary hepatocytes but replicates efficiently in tumors including tumors derived from hepatocytes. In addition, we found that CAR is localized at junctions between hepatocytes and is inaccessible to hepatic blood flow. CAR is not expressed on tumor vasculature but is expressed on tumor cells. Spatial restriction of CAR to the intercellular space in normal liver and diminished replication of adenovirus in hepatocytes may explain the minimal toxicity observed following repeated hepatic artery infusions with Onyx-015.

Effects of Onyx-015 among metastatic colorectal cancer patients that have failed prior treatment with 5-FU/leucovorin

Despite recent improvements in the treatment of metastatic colorectal cancer, few patients are cured and the response rates to second-line treatments are poor. Onyx-015, an oncolytic virus, was administered to patients with metastatic colorectal cancer by hepatic artery infusion. No dose-limiting toxicities were observed in the phase I/II studies. Onyx-015 can kill tumor cells by mechanisms that are distinct from chemotherapeutic agents and may therefore have activity among patients who have failed first-line chemotherapy. The 24 patients included in this analysis had failed first-line therapy with 5-FU/leucovorin, 79% of the patients failed two or more regimens and 58% had failed treatment with Irinotecan. Despite the extensive prior therapy, the median survival of these patients was 10.7 months, 46% were alive at 1 year and two patients (8%) had partial responses. In all, 11 patients (46%) had stable disease at the completion of the four planned viral treatments (3 months). The median survival of this group of patients was 19 months, suggesting that stable disease may be an important predictor of benefit with oncolytic viruses. Eight of the 11 patients with stable disease at 3 months demonstrated a unique radiographic pattern of transient enlargement of tumor masses (10-48%) after the initial infusions of Onyx-015, followed by radiographic evidence of extensive tumor necrosis and regression. The initial enlargement and subsequent tumor necrosis resulted in a prolonged time to achieve objective tumor regression. In addition, the transient enlargement of the tumor masses may have resulted in premature removal of responding patients. Treatment of eight patients was stopped prior to completion of the planned four treatments due to presumed progression as defined by standard radiographic criteria (>25% increase in tumor size). Functional imaging, such as positron emission tomography (PET) scans, may help distinguish clinical responses from progressive disease following treatment with oncolytic viruses. Onyx-015 may benefit patients with refractory colorectal cancer and additional studies that include PET scans to assess clinical response are warranted.

Liposomal enhancement of the antitumor activity of conditionally replication-competent adenoviral plasmids

Many human tumors have a functional deficiency in p53. Numerous studies have taken advantage of this phenomenon to use a conditionally replication-competent adenovirus (Ad dl1520) that will grow in and lyse tumor cells while sparing normal tissues. However, success has been limited, in part due to difficulties in reaching a sufficiently high proportion of tumor cells. Preexisting or developing immune responses directed toward viral proteins further decrease the efficacy of the approach. We have developed a liposome-encapsulated conditionally replication-competent plasmid based on the dl1520 virus. Like the parent virus, this plasmid generates infectious particles following transfection of p53-defective, but not p53-wild-type tumor cells, but unlike the parent virus it is able to infect CAR-negative tumor cells. The antitumor efficacy of this infectious plasmid was demonstrated in mice with xenografted human tumors, in which it was active after both local and intravenous administration for subcutaneous tumors and following intravenous administration for disseminated malignancy. Activity was retained systemically, even in the presence of neutralizing antibody. Such liposomally encapsulated conditionally replication-competent plasmids may complement the use of conventional viral particles, particularly in settings in which liver uptake of adenoviral vector is undesirable or there are problematic inhibitory effects from humoral immune responses.

Tumor-specific intravenous gene delivery using oncolytic adenoviruses

In this report, we describe a vector system that specifically delivers transgene products to tumors following intravenous (i.v.) administration. The Escherichia coli cytosine deaminase (CD) gene was placed in the E3B region of the tumor-selective, replication-competent adenovirus ONYX-411, under the control of endogenous viral late gene regulatory elements. Thus, CD expression was directly coupled to the tumor-selective replication of the viral vector. In vitro, CD was expressed efficiently in various human cancer cell lines tested but not in cultured normal human cells, including human hepatocytes. Following i.v. administration into nude mice carrying human tumor xenografts, robust CD activity was detected only in tumors but not in liver or other normal tissues. Levels of CD activity in the tumors increased progressively following i.v. virus administration, correlating closely with virus replication in vivo. Subsequent administration of 5-fluorocytosine (5-FC) demonstrated a trend to improve the antitumor efficacy of these viruses in a mouse xenograft model, presumably due to the intratumoral conversion of 5-FC to the chemotherapeutic drug 5-fluorouracil. We show that the combination of a highly selective oncolytic virus, ONYX-411, with the strategic use of the viral E3B region for transgene insertion provides a powerful platform that allows for tumor-specific, persistent and robust transgene expression after i.v. administration. This technology provides an opportunity to enhance greatly both safety and efficacy of cancer gene therapy.

Oncolytic viruses for the treatment of cancer: current strategies and clinical trials

Tumor-selective replicating viruses offer appealing advantages over conventional cancer therapy and are a promising new approach for the treatment of human cancer. The development of virotherapeutics is based on several strategies that each provides a different foundation for tumor-selective targeting and replication. Results emerging from clinical trials with oncolytic viruses demonstrate the safety and feasibility of a virotherapeutic approach and provide early indications of efficacy. Strategies to overcome potential obstacles and challenges to virotherapy are currently being explored and are discussed here. Importantly, the successful development of systemic administration of oncolytic viruses will extend the range of tumors that can be treated using this novel treatment modality.

Future directions: oncolytic viruses

Oncolytic viruses offer a promising new modality for cancer treatment. The strategy of this therapy is to develop viruses capable of selectively infecting and replicating in malignant tumor cells. Oncolytic viruses can spread and destroy malignant tumors without deleterious effects in normal tissues. These viruses are genetically engineered based on both the biology of replicating viruses and the major genetic defects in human cancer cells, so that they can replicate in cancer cells but not in normal cells. The key to the development of such viruses is the identification of viral genes, the deletion or modification of which enables tumor-specific cell destruction. Several clinical trials have demonstrated the safety of oncolytic viruses as cancer therapy and have also shown some encouraging results. Much evidence suggests that oncolytic viral therapy works in synergy with standard cancer therapies. In this review, we will focus on the oncolytic viruses that may be beneficial to patients with lung cancer in the near future.

An attenuated adenovirus, ONYX-015, as mouthwash therapy for premalignant oral dysplasia

PURPOSE

Dysplastic lesions of the oral epithelium are known precursors of oral cancer. A significant proportion of oral dysplastic lesions have functional defects in p53 response pathways. The ONYX-015 adenovirus is selectively cytotoxic to cells carrying defects in p53-dependent signaling pathways. The current study sought to establish the feasibility and activity of ONYX-015 administered topically as a mouthwash to patients with clinically apparent and histologically dysplastic lesions of the oral mucosa.

PATIENTS AND METHODS

A total of 22 patients (19 assessable patients) were enrolled onto the study. ONYX-015 was administered on three different schedules to consecutive cohorts. Biopsies of the involved mucosa were performed to evaluate histologic response and changes in expression of putative markers of malignant potential, including p53, cyclin D1, and Ki-67. Serology was performed to measure antiadenoviral titers.

RESULTS

Histologic resolution of dysplasia was seen in seven (37%) of 19 patients, and the grade of dysplasia improved in one additional patient. The majority of responses were transient. No toxicity greater than grade 2 (febrile episode in one patient) was observed. Only one of seven patients demonstrated an increase in circulating antiadenoviral antibody titer while on therapy. Although responding and resistant lesions had similar mean p53 staining at baseline, histologic response correlated with a decrease in p53 positivity over time. Significant changes in cyclin D1 or Ki-67 were not observed. Viral replication was confirmed in two of three lesions examined.

CONCLUSION

This novel approach to cancer prevention is tolerable, feasible, and has demonstrable activity.

Replicative oncolytic adenoviruses in multimodal cancer regimens

The use of replication-competent viruses that have a cytolytic cycle has emerged as a viable strategy (oncolytic virotherapy) to specifically kill tumor cells and the field has advanced to the point of clinical trials. A theoretical advantage of replicative oncolytic viruses is that their numbers should increase via viral replication within infected tumor cells and resulting viral progeny can then infect additional cells within the tumor mass. The life cycle of a virus involves multiple interactions between viral and cellular proteins/genes, which maximize the ability of the virus to infect and replicate within cells. Understanding such interactions has led to the design of numerous genetically engineered adenovirus (Ad) vectors that selectively kill tumor cells while sparing normal cells. These viruses have also been modified to function as therapeutic gene delivery vehicles, thus augmenting their anticancer capacity. In addition, the oncolytic mode of tumor killing differs from that of standard anticancer therapies, providing the possibility for synergistic interactions with other therapies in a multimodal antitumor approach. In this review, we describe the oncolytic Ad vectors tested in preclinical and clinical models and their use in combination with chemo-, radio-, and gene therapies.

Oncolytic viruses for treatment of malignant brain tumours

Wild type viruses have been known for decades for their capability to destroy malignant tumour cells upon infection and intracellular replication. Genetic engineering of such viruses was, however, only recently done in an attempt to improve their utility as biological anticancer agents. Wild type or recombinant viruses able to selectively destroy tumour cells while sparing normal tissue are known as oncolytic viruses. Most oncolytic viruses currently investigated in clinical trials are derived from adenovirus (AV) or herpes simplex virus type I (HSVI). More than 300 patients with solid tumours were now treated in clinical trials with oncolytic viruses, and in most cases virus was administered directly into the tumour mass. About 10% of the above patients had recurrent malignant glioma. Total intratumoral doses of up to 2 x 10(12) virus particles were well tolerated, and in general no severe side effects resulted from the clinical use of oncolytic AV and HSVI, either in the brain or in the rest of the body. Encouraging anti-tumoral activity was demonstrated in some types of tumours treated locally with oncolytic viruses, and systemic chemotherapy was found to potentiate the anti-tumour effect of virus mediated oncolysis. In malignant glioma, standard gene therapy approaches employing non-replicating virus vectors failed to demonstrate significant benefit in clinical studies. Therapy with oncolytic viruses seems to hold more promise in early clinical trials than gene therapy with non-replicating virus vectors. However, further major advancements in virus designs, application modalities, and understanding of the interactions of the host's immune system with the virus are clearly needed before oncolytic virus therapy of malignant brain tumours can be introduced to clinical practice.

Oncolytic viruses

Although the cytotoxic effects of viruses are usually viewed in terms of pathogenicity, it is possible to harness this activity for therapeutic purposes. Viral genomes are highly versatile, and can be modified to direct their cytotoxicity towards cancer cells. These viruses are known as oncolytic viruses. How are viruses engineered to become tumour specific, and can they be used to safely treat cancer in humans?

Defects in G1-S cell cycle control in head and neck cancer: a review

Tumors gradually develop as a result of a multistep acquisition of genetic alterations and ultimately emerge as selfish, intruding and metastatic cells. The genetic defects associated with the process of tumor progression affect control of proliferation, programmed cell death, cell aging, angiogenesis, escape from immune control and metastasis. Fundamental cancer research over the last thirty years has revealed a multitude of genetic alterations which specify more or less separate steps in tumor development and which are collectively responsible for the process of tumor progression. The genes affected play in normal cells a crucial role in control over cell duplication and the interaction between cells, and between cells and their direct surrounding. This is illustrated on control during the G1/S phase of the cell cycle by its ultimate regulators: cyclins and cyclin dependent kinases. These proteins not only control the transition through the G1/S phase of the cell cycle, but also serve as mediators of the interaction between cells, and between cells and their surrounding. Defaults in the regulation of these proteins are associated with tumor progression, and, therefore, serve as targets for therapy. Defaults in those genes are found in various tumor types, although some of those prevail in particular tumor types. In this review emphasis is given to the defaults that occur in head and neck cancer.

Molecular therapies for colorectal cancer metastatic to the liver

Colorectal cancers are the fourth most commonly diagnosed cancers and will account for over 56,000 deaths in the United States in 2002. A majority of patients with advanced colorectal cancer develop liver metastases during the course of their disease. Treatment of colorectal cancer metastatic to the liver by surgery or chemotherapy is limited and most patients succumb to their disease. Therefore, a broad spectrum of novel treatments, including innovative molecular therapies such as gene and immunotherapy or replication-competent viral therapy, is under preclinical investigation and several clinical trials are in progress. Here we review molecular therapies for colorectal cancer metastatic to the liver.

Toward a new generation of conditionally replicating adenoviruses: pairing tumor selectivity with maximal oncolysis

Conditionally replicating adenoviruses (CRADs) represent a promising new platform for the treatment of cancer. CRADs have been demonstrated to kill tumor cells when other therapies fail, indicating that their antitumor properties are complementary to, and distinct from, those of standard treatments such as chemotherapy and radiation. In clinic trials CRADs have shown encouraging results, demonstrating mild side effects when administered at high doses and via different routes, including intratumorally, intraperitoneally, and intravenously. Tumor-selective replication has been detected, although as a single agent the efficacy appears to be limited. Interestingly, combined treatment with radiation or chemotherapy has been found to enhance CRAD efficacy considerably. To date, the molecular mechanisms underlying adenovirus-mediated oncolysis, and the way in which chemotherapy enhances oncolysis, are not well understood. A fuller knowledge of these processes will open up new strategies to improve the cell-killing potential of CRADs. Here, we discuss several possibilities that may lead to CRADs with enhanced oncolytic activity. These approaches include strategies to functionally couple tumor targeting and optimal oncolytic activity, and ways to further increase tumor cell disruption at later stages of infection to facilitate the spreading of virus throughout the tumor mass. In addition, improved methods to evaluate the efficacy of these agents in animal models, and in the clinic, will be required to systematically test and optimize CRAD efficacy, also taking into account the influence of tumor characteristics and the administration route.

A tumor host range selection procedure identifies p150(sal2) as a target of polyoma virus large T antigen

Cancer cells may undergo loss or alterations in functions that certain viruses normally target to promote virus replication. Virus mutants that have lost the targeting function(s) should be able to grow in such cancer cells but not in normal cells. A "tumor host range" (t-hr) selection procedure has been devised and applied to polyoma virus based on this rationale. Studies of one t-hr mutant have led to the identification of the mSal2 gene product (p150(sal2)) as a binding partner of the large T antigen. mSal2 encodes a multizinc finger protein and putative transcription factor homologous to the Drosophila homeotic gene Spalt. The t-hr mutant encodes an altered large T protein that fails to interact with p150(sal2) and is defective in replication and tumor induction in newborn mice.