Targeting multiple signal pathways by chemopreventive agents for cancer prevention and therapy

In recent years, growing interest has been focused on the field of cancer prevention. Cancer prevention by chemopreventive agents offers significant promise for reducing the incidence and mortality of cancer. Chemopreventive agents may exert their effects either by blocking or metabolizing carcinogens or by inhibiting tumor cell growth. Another important benefit of chemopreventive agents is their nontoxic nature. Therefore, chemopreventive agents have recently been used for cancer treatment in combination with chemotherapeutics or radiotherapy, uncovering a novel strategy for cancer therapy. This strategy opens a new avenue from cancer prevention to cancer treatment. In vitro and in vivo studies have demonstrated that chemopreventive agents could enhance the antitumor activity of chemotherapeutics, improving the treatment outcome. Growing evidence has shown that chemopreventive agents potentiate the efficacy of chemotherapy and radiotherapy through the regulation of multiple signaling pathways, including Akt, NF-κB, c-Myc, cyclooxygenase-2, apoptosis, and others, suggesting a multitargeted nature of chemopreventive agents. However, further in-depth mechanistic studies, in vivo animal experiments, and clinical trials are needed to investigate the effects of chemopreventive agents in combination treatment of cancer with conventional cancer therapies. More potent natural and synthetic chemopreventive agents are also needed to improve the efficacy of mechanism-based and targeted therapeutic strategies against cancer, which are likely to make a significant impact on saving lives. Here, we have briefly reviewed the role of chemopreventive agents in cancer prevention, but most importantly, we have reviewed how they could be useful for cancer therapy in combination with conventional therapies.     

Combining angiogenesis inhibition and radiotherapy: A double-edged sword

A large number of patients that undergo radiotherapy develop local failure. To improve the efficacy of treatment, there is an increasing interest in combining radiotherapy with novel targeted therapies. Inhibiting the growth of new tumor blood vessels, i.e. tumor angiogenesis, is such a targeted therapy. Growing tumors induce angiogenesis to ensure an adequate delivery of oxygen and nutrients and several angiostatic drugs have been approved for the treatment of cancer patients. Both pre-clinical and clinical studies have shown that radiotherapy can influence tumor angiogenesis and that angiogenesis inhibition can potentiate the effect of radiotherapy. Therefore, the combination of angiogenesis inhibition and radiotherapy holds a promising future in cancer treatment. However, the radiosensitizing effects of angiogenesis inhibition are transient and recent findings indicate that the effects of irradiation on angiogenesis depend on the dose and treatment schedule. This raises questions regarding the scheduling of both treatment modalities in order to achieve the optimal treatment efficacy with minimal toxicity. In this review the opportunities and pitfalls of combining angiostatic agents with radiotherapy are discussed. The lessons learned from (pre)clinical studies are summarized with an emphasis on scheduling and dosing of the combination therapy. Finally, the opportunities of ongoing clinical studies are discussed and opportunities to improve the combination of angiostatic drugs with radiotherapy are presented.     

Sulfoglycolipids as candidate antiangiogenic radiosensitizers

Angiogenesis is considered an essential process for the growth of solid tumors and, accordingly, angiogenesis has been a focus of attention for cancer therapy. Although various antiangiogenic agents have been developed, adverse effects and limitations associated with antitumor therapies have recently become apparent. To overcome these problems, combining such agents with chemotherapy or radiotherapy is now strongly recommended in clinical practice. Provided such combination treatment, from the onset of therapy, different strategies in developing antiangiogenic agents should be used to enhance any combinatory effects and reduce adverse effects. By applying the concept of radiosensitizers, a new class of antiangiogenic treatments should now be possible. We recently developed sulfoglycolipids that possess such properties. In this review, we discuss the properties of antiangiogenic radiosensitizers and their potential usefulness.     

Immunotherapeutic applications of CpG oligodeoxynucleotide TLR9 agonists

Toll-like receptor 9 (TLR9) agonists have demonstrated substantial potential as vaccine adjuvants, and as mono- or combination therapies for the treatment of cancer and infectious and allergic diseases. Commonly referred to as CpG oligodeoxynucleotides (ODN), TLR9 agonists directly induce the activation and maturation of plasmacytoid dendritic cells and enhance differentiation of B cells into antibody-secreting plasma cells. Preclinical and early clinical data support the use of TLR9 agonists as vaccine adjuvants, where they can enhance both the humoral and cellular responses to diverse antigens. In mouse tumor models TLR9 agonists have shown activity not only as monotherapy, but also in combination with multiple other therapies including vaccines, antibodies, cellular therapies, other immunotherapies, antiangiogenic agents, radiotherapy, cryotherapy, and some chemotherapies. Phase I and II clinical trials have indicated that these agents have antitumor activity as single agents and enhance the development of antitumor T-cell responses when used as therapeutic vaccine adjuvants. CpG ODN have shown benefit in multiple rodent and primate models of asthma and other allergic diseases, with encouraging results in some early human clinical trials. Although their potential clinical contributions are enormous, the safety and efficacy of these TLR9 agonists in humans remain to be determined.     

Biological agents versus chemotherapy in the treatment of colorectal cancer

Biological agents are commonly incorporated as an adjunct to cytotoxic chemotherapy in the treatment of patients with advanced colorectal cancer. In contrast to cytotoxic chemotherapy, biological agents have minimal single agent activity and are largely considered to be cytostatic. Recent data supports the use of either combination regimens with chemotherapy and/or biological therapy. Interest in combining biological agents of co-existing molecular pathways is the most recent strategic approach. However, with the advent of these novel therapies, questions have arisen regarding appropriate clinical indication and potential treatment-related toxicities. The role of biological agents in the treatment of colorectal cancer and their role in contrast to cytotoxic chemotherapy will be explored.     

Continuing pursuit for ideal systemic anticancer radiotherapeutics

Cancer is one of the major causes of death for non-transmissible chronic diseases worldwide. Conventional treatments including surgery, chemotherapy and external beam radiotherapy are generally far from curative. Complementary therapies are attempted for achieving more successful treatment response. Systemic targeted radiotherapy (STR) is a radiotherapeutic modality based on systemic administration of radioactive agents for selectively delivering high doses of energy to destroy cancer cells. For this purpose, diverse tumour-target specific agents including monoclonal antibodies (MoAb), MoAb fragments and peptides have been tested and some of them have already got FDA approval for clinical use. However, MoAbs and their tailored analogues have shown non-homogeneous tumour distribution, limited diffusion, insufficient intratumoral accumulation and retention, unwanted uptake in normal tissues and scarcity of identified cancer antigens for generating new MoAbs. Similarly, peptides have also exhibited retention in normal organs, lacks of favourable membrane permeability or drug cell internalization and short-term residence in cancer cells. Recently, a new category of target-specific agent with strong affinity for necrosis has emerged as an excellent option for developing targeted radiotherapeutic agents to be used after necrosis-inducing treatments (NITs). The combination of their high, specific and long-term accumulation and retention at necrotic sites with the crossfire effect of ionizing particle-emitters allows irradiating adjacent residual viable tumour cells during a prolonged period of time. It may considerably enhance the therapeutic response and open a new horizon for improved cancer treatability or curability.     

Biological agents versus chemotherapy in the treatment of colorectal cancer

Biological agents are commonly incorporated as an adjunct to cytotoxic chemotherapy in the treatment of patients with advanced colorectal cancer. In contrast to cytotoxic chemotherapy, biological agents have minimal single agent activity and are largely considered to be cytostatic. Recent data supports the use of either combination regimens with chemotherapy and/or biological therapy. Interest in combining biological agents of co-existing molecular pathways is the most recent strategic approach. However, with the advent of these novel therapies, questions have arisen regarding appropriate clinical indication and potential treatment-related toxicities. The role of biological agents in the treatment of colorectal cancer and their role in contrast to cytotoxic chemotherapy will be explored.     

Danusertib, an aurora kinase inhibitor

INTRODUCTION: Drugs that interfere with the normal progression of mitosis belong to the most successful cytotoxic agents currently used for anticancer treatment. Aurora kinases are serine/threonine kinases that function as key regulators of mitosis and are frequently overexpressed in human cancers. The use of several small molecule aurora kinase inhibitors as potential anticancer therapeutic is being investigated. Danusertib (formerly PHA-739358) is a small ATP competitive molecule that inhibits aurora A, B and C kinases. Interestingly, danusertib also inhibits several receptor tyrosine kinases such as Abl, Ret, FGFR-1 and TrkA. These tyrosine kinases are involved in the pathogenesis of a variety of malignancies and the observed multi-target inhibition may increase the antitumor activity resulting in extending the indication. Danusertib was one of the first aurora kinase inhibitors to enter the clinic and has been studied in Phase I and II trials. AREAS COVERED: This review provides an updated summary of preclinical and clinical experience with danusertib up to July 2011. EXPERT OPINION: Future studies with danusertib should focus on the possibility of combining this agent with other targeted anticancer agents, chemotherapy or radiotherapy. As a single agent, danusertib may show more promise in the treatment of leukemias than in solid tumors.     

Therapeutic targeting of EGFR in malignant gliomas

Importance of the field: Despite the improved prognosis for many cancer patients, the survival of those with malignant gliomas (MGs) remains dismal. Even with aggressive intervention, including surgery, chemotherapy and radiotherapy, the overall 2-year survival rate is only 25% in the most optimistic series, and 5-year survival rates are consistently in the low single digits. Therefore, it is evident that novel therapeutic paradigms are necessary to overcome the inherent limitations of conventional treatments. EGFR gene overexpression can be found in 40 – 50% of patients with MGs, whereas its expression is very low in normal brain. Therapeutic targeting of EGFR has indicated clinical success in the treatment of MGs.

Areas covered in this review: The purpose of this review is to discuss the current status of several EGFR-targeted therapies in MGs patients and address the efficacy of these drugs as monotherapy or in combination with other drugs and/or treatments. We also emphasize the lessons learned and the future perspectives in the development of EGFR-targeted therapies for MGs.

What the reader will gain: A more comprehensive understanding of the molecular, structural and biological characteristics of EGFR and the mechanisms of action of EGFR-targeted antagonists will most likely contribute to the successful use of strategies of EGFR-targeted therapy in the clinic.

Take home message: Therapeutic targeting of EGFR include anti-EGFR mAbs, small-molecule EGFR tyrosine kinase inhibitors, peptide vaccination therapy and other therapeutic strategies. Each EGFR antagonist has its own advantages and limitations in terms of BBB crossing, ease of delivery, combination therapies and potential toxicity. Therefore, a multiple approach combining different agents that target EGFR signaling at multiple levels seems to have potential as future therapeutics for MGs, once the technical and safety issues unique to each of the approaches are overcome.     

Bugs and drugs: oncolytic virotherapy in combination with chemotherapy

Single agent therapies are rarely successful in treating cancer, particularly at metastatic or end stages, and survival rates with monotherapies alone are generally poor. The combination of multiple therapies to treat cancer has already driven significant improvements in the standard of care treatments for many types of cancers. The first combination treatments exploited for cancer therapy involved the use of several cytotoxic chemotherapy agents. Later, with the development of more targeted agents, the use of novel, less toxic drugs, in combination with the more classic cytotoxic drugs has proven advantageous for certain cancer types. Recently, the combination of oncolytic virotherapy with chemotherapy has shown that the use of these two therapies with very distinct anti-tumor mechanisms may also lead to synergistic interactions that ultimately result in increased therapeutic effects not achievable by either therapy alone. The mechanisms of synergy between oncolytic viruses (OVs) and chemotherapeutic agents are just starting to be elucidated. It is evident, however, that the success of these OV-drug combinations depends greatly on the particular OV, the drug(s) selected, and the cancer type targeted. This review summarizes the different OV-drug combinations investigated to date, including the use of second generation armed OVs, which have been studied with the specific purpose of generating synergistic interactions with particular chemotherapy agents. The known mechanisms of synergy between these OV-drug combinations are also summarized. The importance of further investigating these mechanisms of synergy will be critical in order to maximize the therapeutic efficacy of OV-drug combination therapies in the future.     

Synthetic and application perspectives of azapodophyllotoxins: alternative scaffolds of podophyllotoxin

Podophyllotoxin (1) has been known to possess anti-tumor activity and is still considered an important lead for research and development of antineoplastic agents. Derivatives of podophyllotoxin, namely etoposide (2), etopophos (3) and teniposide (4) have been developed and are currently used in clinic for the treatment of a variety of malignancies. These agents are also used in combination therapies with other drugs. Due to the drug resistance developed by cancer cells as well as side effects associated with the use of these agents in clinic, the search for new effective anticancer analogues of podophyllotoxin remains an intense area of research. The structural complexity of podophyllotoxin, arising from the presence of four stereogenic carbons in ring C has restricted most of the structural activity relationship (SAR) studied by derivatization of the parent natural product rather than by de novo multi-step chemical synthesis. These issues provide strong impetus to a search for analogues of 1 with simplified structures, which can be accessible via short synthetic sequences from simple starting materials. Even if such initial compounds might have diminished cytotoxic potencies compared with the parent cyclolignan, the ease of preparation of carefully designed libraries of analogues would lead to more informative SAR studies and expeditious structure optimization. In this regard, during the last two decades considerable efforts have been made to synthesize aza- analogs of podophyllotoxin, i. e. aza-podophyllotoxins, with hetero atoms at different positions of the podophyllotoxin skeleton, while keeping the basic podophyllotoxin structure. Recently, there have been significant efforts towards the convenient synthesis of aza-analogs of 1. The use of multicomponent reactions (MCRs) and the synergies of ultrasound and microwave irradiations have increased the synthetic speed and variety of azapodophyllotoxins which are and will be available to be tested against a diverse population of carcinomas and other diseases. It has been reported that several aza-podophyllotoxins retain a great fraction of the cytotoxicity associated with the parent lignan. This review focuses on the strategies towards synthesis of various aza-podophyllotoxin analogues and their biological activities.     

Prospect of combination of anti-PD-1/PD-L1 therapy and other therapeutics for treatment of lung cancer

Lung cancer is the leading cause of cancer death worldwide, mainly because it has no obvious symptoms at the early stage and it is usually diagnosed at the advanced stage. Surgery and chemotherapy are the main common treatment options for lung cancer patients. During the past 25 years, great progress has been made in the treatment of lung cancer. Novel materials such as nanoparticles have shown therapeutic potential for lung cancer as they can selectively enter tumor cells due to their small size and surface modifiability. However,the prognosis of patients with lung cancer is still unsatisfactory. Targeted immunotherapy has shown potential for the treatment of lung cancer. The anti-tumor immunotherapy has been widely concerned as immune escape plays an important role in the occurrence and development of tumors. In particular, agents targeting PD-1/PD-L1 have been widely studied and some anti-PD-1/PD-L1 agents have been approved for the treatment of lung cancer by FDA since they have shown significant anti-tumor activity in lung cancer patients. Nevertheless, not all patients response to this therapy and the immune-related adverse events have emerged. The immune-related adverse events mainly involve the gut, skin, endocrine glands, liver,lung and other tissues. With the development of this field, combination therapy has been regarded as a promising strategy to improve the safety and efficacy of antiPD-1/PD-L1 therapy. Studies have shown that the radiotherapy, chemotherapy, oncolytic virus, antiangiogenic agents and indoleamine 2,3-dioxygenase(IDO) inhibitors may improve the efficacy and reduce the incidence of adverse events of anti-PD-1/PD-L1 therapy. Radiotherapy can not only kill tumor cells, but also stimulate the immune system by releasing tumor antigens. Chemotherapy may induce the tumor-specific adaptive immune response.Oncolytic virotherapy, which is a form of immunotherapy,can kill tumors directly and induce the host immune response to tumour cells. Angiogenic factors have immunosuppressive effect, thus the antiangiogenic drugs may improve anti-tumor activity of anti-PD-1/PD-L1 agents in the treatment of lung cancer. Researches on IDO inhibitors in combined with other therapies are active and this combination may have good safety. In this review, we summarized the mechanisms and advantages of the combination therapy based on anti-PD-1/PD-L1 therapy,providing basis for its further clinical application.     

Taxanes for advanced non-small cell lung cancer

The emergence of novel chemotherapeutic agents with promising anticancer activity in non-small cell lung cancer (NSCLC) during the 1990s has led to an expanded role for chemotherapy in the management of this disease. The taxanes (paclitaxel and docetaxel) are novel microtubule stabilising agents, and have become an integral part of several commonly-used chemotherapy regimens in NSCLC. Taxanes inhibit the growth of lung cancer cell lines, exhibit synergistic interaction with other chemotherapy agents and enhance the efficacy of radiation in vitro. When used in low doses (metronomic dosing), they have important antiangiogenic properties. Several Phase II and III clinical trials have established the efficacy of the taxanes, as single agents and when used in combination with a platinum compound, in the treatment of advanced NSCLC. The use of a taxane in combination with a platinum compound has become an acceptable standard for patients with advanced or metastatic NSCLC. In addition to its efficacy in the first-line therapy of NSCLC, docetaxel is also the FDA-approved second-line agent for recurrent or relapsed NSCLC in the US. Several ongoing trials are comparing the efficacy of combining molecularly targeted agents with taxane-based regimens for the treatment of advanced NSCLC.     

Taxanes for advanced non-small cell lung cancer

The emergence of novel chemotherapeutic agents with promising anticancer activity in non-small cell lung cancer (NSCLC) during the 1990s has led to an expanded role for chemotherapy in the management of this disease. The taxanes (paclitaxel and docetaxel) are novel microtubule stabilising agents, and have become an integral part of several commonly-used chemotherapy regimens in NSCLC. Taxanes inhibit the growth of lung cancer cell lines, exhibit synergistic interaction with other chemotherapy agents and enhance the efficacy of radiation in vitro. When used in low doses (metronomic dosing), they have important antiangiogenic properties. Several Phase II and III clinical trials have established the efficacy of the taxanes, as single agents and when used in combination with a platinum compound, in the treatment of advanced NSCLC. The use of a taxane in combination with a platinum compound has become an acceptable standard for patients with advanced or metastatic NSCLC. In addition to its efficacy in the first-line therapy of NSCLC, docetaxel is also the FDA-approved second-line agent for recurrent or relapsed NSCLC in the US. Several ongoing trials are comparing the efficacy of combining molecularly targeted agents with taxane-based regimens for the treatment of advanced NSCLC.     

An overview of immunomodulatory intervention in rheumatoid arthritis

In recent years there has been exceptional progress in the development of immunomodulatory interventions for the treatment of rheumatoid arthritis (RA). Part of the impetus for the creation of novel therapies for RA has come from a growing appreciation of the substantial morbidity and mortality that this chronic, progressive disease causes for affected patients. In addition, there has been the realization that currently available therapeutics are suboptimal as regards both their efficacy and tolerability. The development of newer therapies has been facilitated by two factors; a greater understanding of the immunopathogenesis of RA and progress in biotechnology that has allowed the creation of specific inhibitors and other agents. Myriad studies performed by investigators throughout the world have helped delineate the immunologic basis of RA. It appears that various components of the immune system are involved in the initiation and propagation of this systemic inflammatory disease. T-cells, and in particular activated CD4(+) 'memory' T-cells, serve a central role in orchestrating the immune response that underlies rheumatoid inflammation. Other cells, including monocytes, fibroblasts, B-cells, dendritic cells, mast cells and neutrophils also contribute significantly to various aspects of disease. Adhesion molecules mediate many intercellular interactions, thus contributing to activities such as the accrual of cells within the synovium and the activation of cells. Cytokines, small peptides that exert numerous inflammatory activities and cause many of the signs and symptoms of RA, play a crucial role. Indeed, RA may be considered a disorder of 'cytokine dysregulation' in that the activity of proinflammatory cytokines such as TNF-alpha and IL-1 is enhanced, and overwhelms the effects of antiinflammatory factors. Finally, a host of other inflammatory mediators are involved in the disease process. Thus, many components of the immune response may be attractive therapeutic targets for immunomodulatory intervention in RA. Advances in biotechnology have permitted the creation of specific inhibitors of distinct components of the immune system. Monoclonal antibodies (MAbs) have been created to target various cell surface molecules and cytokines. At first, most MAbs were murine in origin, which can present problems as regards immunogenicity. More recently, progress in molecular biologic techniques has allowed the synthesis of hybrid antibodies that are partly human. Such techniques have also allowed the creation of cytokine receptors coupled to immunoglobulin molecules, and other constructs. These agents can be modified to provide optimal characteristics in terms of half-life, immunogenicity and specificity, and this is an exciting area of new development. Progress has also been made in molecular-based agents that directly modify the genes or gene products for specific targets. To date, a number of trials assessing novel immunomodulatory therapies have been undertaken. In some cases, such as with inhibitors of TNF-alpha, the results have been dramatic and exciting. Further development and refinement may allow the introduction of these agents into the clinic in the foreseeable future, and will provide an important area for further research. In other cases, for example with therapies targeting CD4(+) molecules, the results have not been as promising as was hoped. Nevertheless, critical analysis of the results of these studies has provided insights into the pathogenesis of RA which may prove quite valuable for future trials. A number of agents are being studied actively at the present time, and it is hoped that they too may generate novel therapies for, and a greater understanding of, this difficult disease. The future for immunomodulatory intervention in RA looks very promising. Greater understanding of the intricacies of the immune response that underlie this disease should continue to yield viable, specific targets for novel therapies. Advances in biopharmaceuticals should generate treatments that maximize efficacy while minimizing toxicity. This should allow the clinician truly to modify the disease and achieve tangible improvements in the lives of RA patients.     

An update on drug combinations for treatment of myeloma

Multiple myeloma is the second most common haematological malignancy. It is becoming increasingly manageable with conventional and high-dose chemotherapy but there remains a critical need to develop both new drugs and combinations to improve long-term outcomes. Novel biological therapies that specifically target myeloma cells and/or their microenvironmental interactions are being developed that are highly effective, both as single agents and as combinations. Chief among these new agents are the proteasome inhibitor, bortezomib, and the immunomodulatory agents, thalidomide and lenalidomide. These drugs show improved single agent activity that is enhanced in combination. However, many drugs that are being developed in this setting may only have limited single agent activity, but combination use with these and other agents represents a very exciting way of targeting important pathogenic pathways crucial in myeloma development. This represents a challenge for both drug development and clinical trial evaluation, which has the potential to revolutionise the clinical management of myeloma and a paradigm for drug development in other diseases.     

Developmental antiangiogenic agents for the treatment of Non-Small Cell Lung Cancer (NSCLC)

Standard therapy for advanced or metastatic non-small cell lung cancer (NSCLC) has primarily consisted of traditional cytotoxic chemotherapy, although use of targeted therapies has been approved in specific settings. Antiangiogenic agents represent a promising therapeutic strategy for treatment of advanced NSCLC. Bevacizumab is currently approved when given in combination with first-line platinum-based therapy in selected patients with nonsquamous NSCLC. Bevacizumab may also provide benefit in other clinical settings, as a part of a combination or maintenance strategy. Other antiangiogenic agents under development, including multi-targeted kinase inhibitors (MTKIs) and antibody-based agents, have exhibited mixed results in the NSCLC population. Published efficacy and safety data from clinical trials for antiangiogenic agents are reviewed, with an emphasis on novel agents and novel settings for established agents. Identification of biomarkers associated with improved efficacy may help select patients likely to receive the most benefit from these agents and may improve outcomes through development of personalized therapeutic strategies.     

Combining cytotoxic and immune-mediated gene therapy to treat brain tumors

Glioblastoma (GBM) is a type of intracranial brain tumor, for which there is no cure. In spite of advances in surgery, chemotherapy and radiotherapy, patients die within a year of diagnosis. Therefore, there is a critical need to develop novel therapeutic approaches for this disease. Gene therapy, which is the use of genes or other nucleic acids as drugs, is a powerful new treatment strategy which can be developed to treat GBM. Several treatment modalities are amenable for gene therapy implementation, e.g. conditional cytotoxic approaches, targeted delivery of toxins into the tumor mass, immune stimulatory strategies, and these will all be the focus of this review. Both conditional cytotoxicity and targeted toxin mediated tumor death, are aimed at eliminating an established tumor mass and preventing further growth. Tumors employ several defensive strategies that suppress and inhibit anti-tumor immune responses. A better understanding of the mechanisms involved in eliciting anti-tumor immune responses has identified promising targets for immunotherapy. Immunotherapy is designed to aid the immune system to recognize and destroy tumor cells in order to eliminate the tumor burden. Also, immune-therapeutic strategies have the added advantage that an activated immune system has the capability of recognizing tumor cells at distant sites from the primary tumor, therefore targeting metastasis distant from the primary tumor locale. Pre-clinical models and clinical trials have demonstrated that in spite of their location within the central nervous system (CNS), a tissue described as 'immune privileged', brain tumors can be effectively targeted by the activated immune system following various immunotherapeutic strategies. This review will highlight recent advances in brain tumor immunotherapy, with particular emphasis on advances made using gene therapy strategies, as well as reviewing other novel therapies that can be used in combination with immunotherapy. Another important aspect of implementing gene therapy in the clinical arena is to be able to image the targeting of the therapeutics to the tumors, treatment effectiveness and progression of disease. We have therefore reviewed the most exciting non-invasive, in vivo imaging techniques which can be used in combination with gene therapy to monitor therapeutic efficacy over time.