Molecular engineering of matrix-targeted retroviral vectors incorporating a surveillance function inherent in von Willebrand factor

A Phase I-II Study Using Rexin-G Tumor-Targeted Retrovector Encoding a Dominant-Negative Cyclin G1 Inhibitor for Advanced Pancreatic Cancer

Rexin-G is a replication-incompetent retroviral vector displaying a cryptic SIG-binding peptide for targeting abnormal Signature (SIG) proteins in tumors and encoding a dominant-negative human cyclin G1 construct. Herein we report on the safety and antitumor activity of escalating doses of Rexin-G in gemcitabine-refractory pancreatic adenocarcinoma, with one 10-year survivor. For the safety analysis (n = 20), treatment-related grade 1 adverse events included fatigue (n = 6), chills (n = 2), and headache (n = 1), with no organ damage and no DLT. No patient tested positive for vector-neutralizing antibodies, antibodies to gp70, replication-competent retrovirus (RCR), or vector integration into genomic DNA of peripheral blood lymphocytes (PBLs). For the efficacy analysis (n = 15), one patient achieved a complete response (CR), two patients had a partial response (PR), and 12 had stable disease (SD). Median progression-free survival (PFS) was 2.7, 4.0, and 5.6 months at doses 0–I, II, and III, respectively. Median overall survival (OS) and 1-year OS rate at dose 0–I were 4.3 months and 0%, and at dose II–III they were 9.2 months and 33.3%. To date, one patient is still alive with no evidence of cancer 10 years after the start of Rexin-G treatment. Taken together, these data suggest that Rexin-G, the first targeted gene delivery system, is uniquely safe and exhibits significant antitumor activity, for which the FDA granted fast-track designation.

Cell cycle checkpoint control: The cyclin G1/Mdm2/p53 axis emerges as a strategic target for broad-spectrum cancer gene therapy - A review of molecular mechanisms for oncologists

Basic research in genetics, biochemistry and cell biology has identified the executive enzymes and protein kinase activities that regulate the cell division cycle of all eukaryotic organisms, thereby elucidating the importance of site-specific protein phosphorylation events that govern cell cycle progression. Research in cancer genomics and virology has provided meaningful links to mammalian checkpoint control elements with the characterization of growth-promoting proto-oncogenes encoding c-Myc, Mdm2, cyclins A, D1 and G1, and opposing tumor suppressor proteins, such as p53, pRb, p16^INK4A and p21^WAF1, which are commonly dysregulated in cancer. While progress has been made in identifying numerous enzymes and molecular interactions associated with cell cycle checkpoint control, the marked complexity, particularly the functional redundancy, of these cell cycle control enzymes in mammalian systems, presents a major challenge in discerning an optimal locus for therapeutic intervention in the clinical management of cancer. Recent advances in genetic engineering, functional genomics and clinical oncology converged in identifying cyclin G1 (CCNG1 gene) as a pivotal component of a commanding cyclin G1/Mdm2/p53 axis and a strategic locus for re-establishing cell cycle control by means of therapeutic gene transfer. The purpose of the present study is to provide a focused review of cycle checkpoint control as a practicum for clinical oncologists with an interest in applied molecular medicine. The aim is to present a unifying model that: i) clarifies the function of cyclin G1 in establishing proliferative competence, overriding p53 checkpoints and advancing cell cycle progression; ii) is supported by studies of inhibitory microRNAs linking CCNG1 expression to the mechanisms of carcinogenesis and viral subversion; and iii) provides a mechanistic basis for understanding the broad-spectrum anticancer activity and single-agent efficacy observed with dominant-negative cyclin G1, whose cytocidal mechanism of action triggers programmed cell death. Clinically, the utility of companion diagnostics for cyclin G1 pathways is anticipated in the staging, prognosis and treatment of cancers, including the potential for rational combinatorial therapies.

Rexin-G®, a tumor-targeted retrovector for malignant peripheral nerve sheath tumor: A case report

Soft tissue sarcoma is a rare neoplasm of mesenchymal origin, accounting for only ~1% of all adult cancers and consisting of 75 histological subtypes. In the present report, the unique case of a 14 year-old female with metastatic malignant peripheral nerve sheath tumor (formerly, malignant melanotic schwannoma) of the parotid gland, who experienced a durable response and sustained tumor control with Rexin-G^®, a tumor-targeted retroviral expression vector encoding an anti-cyclin G1 construct, is described. Post-parotidectomy, and prior to the administration of Rexin-G^®, the patient received various chemotherapy regimens, including doxorubicin, ifosfamide, temozolomide, sorafenib, and an immunological therapy with interleukin-2, which only resulted in the further progression of lung metastases. The patient subsequently participated in a Phase 1/2 gene therapy study, during which she received intravenous Rexin-G^® as monotherapy for two years with minimal drug-associated adverse events. Currently, the patient has no evidence of active disease 9 years after commencing the Rexin-G^® treatment, and with no additional anti-cancer therapy. In conclusion, Rexin-G^® may be a viable therapeutic option for malignant peripheral nerve sheath tumors, and should be further investigated in prospective histology-specific clinical trials for this type, and possibly other types, of chemotherapy-resistant sarcoma.

Nanopharmaceuticals (part 1): products on the market

In 2000, the National Institute of Health launched the National Nanotechnology Initiative to support, coordinate, and advance research and development of nanoscale projects. The impact of this new program on health-science related research and development became quickly visible. Broad governmental financial support advanced the start of new, and the deepening of already existing, interdisciplinary research. The anticipated merger of nanoscience with medicine quickly instigated the conceptualization of nanomedicine. The adoption of nanoscience terminology by pharmaceutical scientists resulted in the advent of nanopharmaceuticals. The term "nano" became tantamount to "cutting-edge" and was quickly embraced by the pharmaceutical science community. Colloidal drug delivery systems reemerged as nanodrug delivery systems; colloidal gold became a suspension of nano gold particles. In this review, we first review nanoscience related definitions applied to pharmaceuticals, we then discuss all 43 currently approved drug formulations which are publicized as nanopharmaceuticals, and finally we analyze clinical aspects of selected drug formulations.

Immunotherapeutic and oncolytic viral therapeutic strategies in pancreatic cancer

Pancreatic adenocarcinoma is an aggressive disease with dismal outcomes despite recent advances using combination chemotherapeutic regimens. The lack of an adequate immune response to malignant cells has been identified as a factor associated with tumor aggressiveness and refractoriness to systemic treatment. Preclinical and early clinical studies have identified numerous immunotherapeutic and oncolytic viral therapeutic strategies aimed towards amplifying the immune reaction to pancreatic cancer and have established encouraging results. Promising antitumor efficacy has been observed both in vitro and in vivo with many of these approaches. These novel applications have also led to improved understanding of the process of pancreatic tumor growth and invasion, knowledge of the tumor microenvironment and have pioneered further investigations of similar therapies. Here we review both immunotherapeutic and oncolytic viral therapeutic strategies in pancreatic cancer.

Ligand-targeted particulate nanomedicines undergoing clinical evaluation: current status

Since the introduction of Doxil® on the market nearly 20years ago, a number of nanomedicines have become part of treatment regimens in the clinic. With the exception of antibody-drug conjugates, these nanomedicines are all devoid of targeting ligands and rely solely on their physicochemical properties and the (patho)physiological processes in the body for their biodistribution and targeting capability. At the same time, many preclinical studies have reported on nanomedicines exposing targeting ligands, or ligand-targeted nanomedicines, yet none of these have been approved at this moment. In the present review, we provide a concise overview of 13 ligand-targeted particulate nanomedicines (ligand-targeted PNMs) that have progressed into clinical trials. The progress of each ligand-targeted PNM is discussed based on available (pre)clinical data. Main conclusions of these analyses are that (a) ligand-targeted PNMs have proven to be safe and efficacious in preclinical models; (b) the vast majority of ligand-targeted PNMs is generated for the treatment of cancer; (c) contribution of targeting ligands to the PNM efficacy is not unambiguously proven; and (d) targeting ligands do not cause localization of the PNM within the target tissue, but rather provide benefits in terms of target cell internalization and target tissue retention once the PNM has arrived at the target site. Increased understanding of the in vivo fate and interactions of the ligand-targeted PNMs with proteins and cells in the human body is mandatory to rationally advance the clinical translation of ligand-targeted PNMs. Future perspectives for ligand-targeted PNM approaches include the delivery of drugs that are unable or inefficient in passing cellular membranes, treatment of drug resistant tumors, targeting of the tumor blood supply, the generation of targeted vaccines and nanomedicines that are able to cross the blood-brain barrier.

Library screening and receptor-directed targeting of gammaretroviral vectors

Gene- and cell-based therapies hold great potential for the advancement of the personalized medicine movement. Gene therapy vectors have made dramatic leaps forward since their inception. Retroviral-based vectors were the first to gain clinical attention and still offer the best hope for the long-term correction of many disorders. The fear of nonspecific transduction makes targeting a necessary feature for most clinical applications. However, this remains a difficult feature to optimize, with specificity often coming at the expense of efficiency. The aim of this article is to discuss the various methods employed to retarget retroviral entry. Our focus will lie on the modification of gammaretroviral envelope proteins with an in-depth discussion of the creation and screening of envelope libraries.

Current advances in retroviral gene therapy

There have been major changes since the incidents of leukemia development in X-SCID patients after the treatments using retroviral gene therapy. Due to the risk of oncogenesis caused by retroviral insertional activation of host genes, most of the efforts focused on the lentiviral therapies. However, a relative clonal dominance was detected in a patient with β-thalassemia Major, two years after the subject received genetically modified hematopoietic stem cells using lentiviral vectors. This disappointing result of the recent clinical trial using lentiviral vector tells us that the current and most advanced vector systems does not have enough safety. In this review, various safety features that have been tried for the retroviral gene therapy are introduced and the possible new ways of improvements are discussed. Additional feature of chromatin insulators, co-transduction of a suicidal gene under the control of an inducible promoter, conditional expression of the transgene only in appropriate target cells, targeted transduction, cell type-specific expression, targeted local administration, splitting of the viral genome, and site specific insertion of retroviral vector are discussed here.

Assessment of the evolution of cancer treatment therapies

Cancer therapy has been characterized throughout history by ups and downs, not only due to the ineffectiveness of treatments and side effects, but also by hope and the reality of complete remission and cure in many cases. Within the therapeutic arsenal, alongside surgery in the case of solid tumors, are the antitumor drugs and radiation that have been the treatment of choice in some instances. In recent years, immunotherapy has become an important therapeutic alternative, and is now the first choice in many cases. Nanotechnology has recently arrived on the scene, offering nanostructures as new therapeutic alternatives for controlled drug delivery, for combining imaging and treatment, applying hyperthermia, and providing directed target therapy, among others. These therapies can be applied either alone or in combination with other components (antibodies, peptides, folic acid, etc.). In addition, gene therapy is also offering promising new methods for treatment. Here, we present a review of the evolution of cancer treatments, starting with chemotherapy, surgery, radiation and immunotherapy, and moving on to the most promising cutting-edge therapies (gene therapy and nanomedicine). We offer an historical point of view that covers the arrival of these therapies to clinical practice and the market, and the promises and challenges they present.

Rexin-G, a targeted genetic medicine for cancer

IMPORTANCE OF THE FIELD

Rexin-G, a tumor-targeted retrovector bearing a cytocidal cyclin G1 construct, is the first targeted gene therapy vector to gain fast track designation and orphan drug priorities for multiple cancer indications in the US.

AREAS COVERED IN THIS REVIEW

This review describes the major milestones in the clinical development of Rexin-G: from the molecular cloning and characterization of the human cyclin G1 proto-oncogene in 1994, to the design of the first knockout constructs and genetic engineering of the targeted delivery system from 1995 to 1997, through the initial proofs-of-concept, molecular pharmacology and toxicology studies of Rexin-G in preclinical cancer models from 1997 to 2001, to the pioneering clinical studies in humans from 2002 to 2004, which--together with the advancements in bioprocess development of high-potency clinical grade vectors circa 2005 - 2006--led to the accelerated approval of Rexin-G for all solid tumors by the Philippine FDA in 2007 and the rapid progression of clinical studies from 2007 to 2009 to the cusp of pivotal Phase III trials in the US.

WHAT THE READER WILL GAIN

In recording the development of Rexin-G as a novel form of targeted biological therapy, this review also highlights important aspects of vector design engineering which served to overcome the physiological barriers to gene delivery as it addresses the key regulatory issues involved in the development of a targeted gene therapy product.

TAKE HOME MESSAGE

Progressive clinical development of Rexin-G demonstrates the potential safety and efficacy of targeted genetic medicine, while validating the design engineering of the molecular biotechnology platform.

Advanced phase I/II studies of targeted gene delivery in vivo: intravenous Rexin-G for gemcitabine-resistant metastatic pancreatic cancer

Rexin-G, a nonreplicative pathology-targeted retroviral vector bearing a cytocidal cyclin G1 construct, was tested in a phase I/II study for gemcitabine-resistant pancreatic cancer. The patients received escalating doses of Rexin-G intravenously from 1 × 10¹¹ colony-forming units (cfu) 2–3× a week (dose 0–1) to 2 × 10¹¹ cfu 3× a week (dose 2) for 4 weeks. Treatment was continued if there was less than or equal to grade 1 toxicity. No dose-limiting toxicity (DLT) was observed, and no vector DNA integration, replication-competent retrovirus (RCR), or vector-neutralizing antibodies were noted. In nine evaluable patients, 3/3 patients had stable disease (SD) at dose 0–1. At dose 2, 1/6 patients had a partial response (PR) and 5/6 patients had SD. Median progression-free survival (PFS) was 3 months at dose 0–1, and >7.65 months at dose 2. Median overall survival (OS) was 4.3 months at dose 0–1, and 9.2 months at dose 2. One-year survival was 0% at dose 0–1 compared to 28.6% at dose 2, suggesting a dose–response relationship between OS and Rexin-G dosage. Taken together, these data indicate that (i) Rexin-G is safe and well tolerated, and (ii) Rexin-G may help control tumor growth, and may possibly prolong survival in gemcitabine-resistant pancreatic cancer, thus, earning US Food and Drug Administration's (FDA) fast-track designation as second-line treatment for pancreatic cancer.

Not gene therapy, but genetic surgery-the right strategy to attack cancer

In this review, I will suggest to divide all the approaches united now under common term "gene therapy" into two broad strategies of which the first one uses the methodology of targeted therapy with all its characteristics, but with genes in the role of agents targeted at a certain molecular component(s) presumably crucial for cancer maintenance. In contrast, the techniques of the other strategy are aimed at the destruction of tumors as a whole using the features shared by all cancers, for example relatively fast mitotic cell division or active angiogenesis. While the first strategy is "true" gene therapy, the second one is more like genetic surgery when a surgeon just cuts off a tumor with his scalpel and has no interest in knowing delicate mechanisms of cancer emergence and progression. I will try to substantiate the idea that the last strategy is the only right one, and its simplicity is paradoxically adequate to the super-complexity of tumors that originates from general complexity of cell regulation, strongly disturbed in tumor cells, and especially from the complexity of tumors as evolving cell populations, affecting also their ecological niche formed by neighboring normal cells and tissues. An analysis of the most widely used for such a "surgery" suicide gene/prodrug combinations will be presented in some more details.

Phase I/II and phase II studies of targeted gene delivery in vivo: intravenous Rexin-G for chemotherapy-resistant sarcoma and osteosarcoma

Rexin-G, a pathotropic nanoparticle bearing a cytocidal cyclin G1 construct was tested in a phase I/II study for chemotherapy-resistant sarcomas and a phase II study for chemotherapy-resistant osteosarcoma. Twenty sarcoma patients and 22 osteosarcoma patients received escalating doses of Rexin-G intravenously from 8 x 10(11) to 24 x 10(11) colony forming units (cfu)/cycle. Treatment was continued if there was <or= grade 1 toxicity. No dose-limiting toxicity (DLT) was observed, and no vector DNA integration, replication-competent retrovirus (RCR) or vector-neutralizing antibodies were noted. In the phase I/II study, 3/6 patients had stable disease (SD) at the lowest dose; median progression-free survival (PFS) was 1.2 months, and overall survival (OS), 3.3 months. At higher doses, 10/14 patients had SD; median PFS was 3.7 months and median OS, 7.8 months. In this phase I/II study, a dose-response relationship with Rexin-G dosage was observed for progression-free and OS times (P = 0.02 and 0.005, respectively). In the phase II study, 10/17 evaluable patients had SD, median PFS was >or=3 months and median OS, 6.9 months. These studies suggest that Rexin-G is safe, may help control tumor growth, and may possibly improve survival in chemotherapy-resistant sarcoma and osteosarcoma.

The development of gene therapy: from monogenic recessive disorders to complex diseases such as cancer

During the last 4 decades, gene therapy has moved from preclinical to clinical studies for many diseases ranging from monogenic recessive disorders such as hemophilia to more complex diseases such as cancer, cardiovascular disorders, and human immunodeficiency virus (HIV). To date, more than 1,340 gene therapy clinical trials have been completed, are ongoing, or have been approved in 28 countries, using more than 100 genes. Most of those clinical trials (66.5%) were aimed at the treatment of cancer. Early hype, failures, and tragic events have now largely been replaced by the necessary stepwise progress needed to realize clinical benefits. We now understand better the strengths and weaknesses of various gene transfer vectors; this facilitates the choice of appropriate vectors for individual diseases. Continuous advances in our understanding of tumor biology have allowed the development of elegant, more efficient, and less toxic treatment strategies. In this introductory chapter, we review the history of gene therapy since the early 1960s and present in detail two major recurring themes in gene therapy: (1) the development of vector and delivery systems and (2) the design of strategies to fight or cure particular diseases. The field of cancer gene therapy experienced an "awkward adolescence." Although this field has certainly not yet reached maturity, it still holds the potential of alleviating the suffering of many individuals with cancer.

Phase I trial of a pathotropic retroviral vector expressing a cytocidal cyclin G1 construct (Rexin-G) in patients with advanced pancreatic cancer

Rexin-G is a pathotropic retroviral vector displaying a von Willebrand factor-targeting motif and expressing a dominant negative cyclin G1 gene. We undertook a phase I trial of intravenous (i.v.) administration of Rexin-G in patients with gemcitabine refractory, metastatic pancreatic adenocarcinoma. Twelve patients were treated. Dose escalation was performed from a dose of 1 x 10(11) colony forming units (CFU) per cycle to 6 x 10(11) CFU per cycle. The treatment was well tolerated. One dose-limiting toxicity (DLT) at dose level 2 (1.5 x 10(11) CFU per cycle) was observed, consisting of grade 3 transaminitis. There was no detection of replication-competent virus in patients' peripheral blood mononuclear cells (PBMCs) or viral integration in DNA obtained from PBMCs, and no development of neutralizing antibodies. No evidence of antitumor activity was observed. The best objective response was progressive disease in 11 of the 12 study patients, while 1 patient showed radiographically stable disease with clinical deterioration and increase in the CA19.9 tumor marker. Median time to progression was 32 days. The median duration of survival of the study patients was 3.5 months from treatment initiation. Rexin-G is well tolerated in doses up to 6 x 10(11) CFU in patients with recurrent pancreatic cancer, but there was no evidence of clinical antitumor activity.

Targeted gene-delivery strategies for angiostatic cancer treatment

Gene therapy is one of the promising strategies in cancer treatment. Recent studies identified molecular targets on angiogenically activated endothelial cells that can be used to deliver gene-transfer vehicles to the tumor site specifically. Furthermore, non-viral vehicles are emerging as an alternative for traditional viral gene-therapy approaches. Here, we describe how viral and non-viral gene-transfer vehicles have been and can be modified to target tumor endothelial cells for anti-angiogenesis gene therapy. Improving the specificity and safety of existing gene-therapy vehicles will make angiogenesis-targeted cancer gene therapy a valuable tool in the clinical setting.

Advanced targeting strategies for murine retroviral and adeno-associated viral vectors

Targeted gene delivery involves broadening viral tropism to infect previously nonpermissive cells, replacing viral tropism to infect a target cell exclusively, or stealthing the vector against nonspecific interactions with host cells and proteins. These approaches offer the potential advantages of enhanced therapeutic effects, reduced side effects, lowered dosages, and enhanced therapeutic economics. This review will discuss a variety of targeting strategies, both genetic and nongenetic, for re-engineering the tropism of two representative enveloped and nonenveloped viruses, murine retrovirus and adeno-associated virus. Basic advances in understanding the structural biology and virology of the parent viruses have aided rational design efforts to engineer novel properties into the viral attachment proteins. Furthermore, even in the absence of basic, mechanistic knowledge of viral function, high-throughput library and directed evolution approaches can yield significant improvements in vector function. These two complementary strategies offer the potential to gain enhanced molecular control over vector properties and overcome challenges in generating high titer, stealthy, retargeted vectors.

Efficient Retroviral Vector Targeting of Carcinoembryonic Antigen-Positive Tumors

Many gene therapy approaches require specific, efficient gene delivery to cells in vivo. To target colorectal tumors we fused a single-chain variable fragment (scFv) directed against carcinoembryonic antigen (CEA) to the amphotropic murine leukemia virus envelope. A proline-rich hinge and matrix metalloprotease (MMP) cleavage site linked the two proteins. Following attachment to CEA, MMP cleavage of the envelope at the cell surface removed the scFv and proline-rich hinge, allowing transduction. This allowed selective targeting of CEA-positive cells in vivo after injection of producer cells at the site of the tumor, with up to 10% of cells within a CEA-positive tumor xenograft becoming transduced. Intraperitoneal injection of amphotropic producer cells resulted in transduction of cells in spleen, liver, and kidney, which was not detected when CEA-targeted producer cells were used. These results demonstrate the feasibility of using targeted retroviral vectors for in vivo gene delivery to tumors. Furthermore, the lack of transduction of host cells eliminates the risk of insertional mutagenesis leading to transformation of host hematopoietic cells.

Targeting retroviral and lentiviral vectors

Retroviral vectors capable of efficient in vivo gene delivery to specific target cell types or to specific locations of disease pathology would greatly facilitate many gene therapy applications. The surface glycoproteins of membrane-enveloped viruses stand among the choice candidates to control the target cell receptor recognition and host range of retroviral vectors onto which they are incorporated. This can be achieved in many ways, such as the exchange of glycoprotein by pseudotyping, their biochemical modifications, their conjugation with virus-cell bridging agents or their structural modifications. Understanding the fundamental properties of the viral glycoproteins and the molecular mechanism of virus entry into cells has been instrumental in the functional alteration of their tropism. Here we briefly review the current state of our understanding of the structure and function of viral envelope glycoproteins and we discuss the emerging targeting strategies based on retroviral and lentiviral vector systems.

Cancer gene therapy

Cancer gene therapy is the transfer of genetic material to the cells of an individual with the goal of eradicating cancer cells, both in the primary tumor and metastases. Cancer gene therapy strategies exploit our expanding knowledge of the genetic basis of cancer, thereby allowing rationally targeted interventions at the molecular level. The successful implementation of cancer gene therapy in the clinic awaits the development of vectors capable of specific and efficient gene delivery to cancer cells. The first clinical applications of cancer gene therapy are likely to be in combination with conventional therapies, such as radiotherapy and immunotherapy.

Establishment of a nude mouse model of hepatic metastasis for evaluation of targeted retroviral gene delivery

BACKGROUND AND OBJECTIVES

The goal of this study was to establish a reproducible nude mouse model of liver metastasis and investigate the potential of deploying targeted injectable retroviral vectors for metastatic gastrointestinal cancer.

METHODS

Human cancer cells were injected into the portal vein via an indwelling catheter. The animals were sacrificed at specified time intervals, and the number of tumor nodules was counted in histologic sections of harvested livers. A group of animals received either an extracellular matrix-targeted or a nontargeted retroviral vector bearing a beta-galactosidase gene by portal vein infusion.

RESULTS

The number of tumor nodules increased progressively over time at </=50 days post-infusion (r = 0.81; P < 0.0001). Transduction of tumor nodules was observed in the animals that received a matrix-targeted, but not a nontargeted, vector.

CONCLUSIONS

We have established a reproducible nude mouse model of liver metastasis, and demonstrated the feasibility of gene delivery to metastatic tumor nodules in vivo by portal vein infusions of a matrix-targeted retroviral vector.

Post-intervention vessel remodeling

By-pass surgery and percutaneous transluminal (coronary) angioplasty, PT(C)A, are standard techniques for the treatment of vascular occlusions. Their usefulness is limited by by-pass graft failure and restenosis occurring after the procedures. Twenty percent of patients treated with PTCA/PTA need a new revascularization procedure within 6 months, despite a successful procedure. Stents are used to prevent restenosis in selected lesions, but in-stent restenosis also remains an important clinical problem. In this review we discuss progress of gene therapy for the treatment of post-PT(C)A restenosis, in-stent restenosis and by-pass graft stenosis over the last 2 years (2000-2002).

Gene therapy for restenosis: current status

Atherosclerosis is a major cause of morbidity and mortality in Western world. Vascular occlusion caused by atherosclerosis usually requires invasive treatment, such as surgical bypass or angioplasty. However, bypass graft failure and restenosis limit the usefulness of these procedures, with 20% of patients needing a new revascularisation procedure within 6 months of angioplasty. Numerous pharmacological agents have been investigated for the prevention of restenosis but none has shown undisputed efficacy in clinical medicine. Gene transfer offers a novel approach to the treatment of restenosis because of easy accessibility of vessels and already existing gene delivery methods. It can be used to overexpress therapeutically important proteins locally without high systemic toxicity, and the therapeutic effect can be targeted to a particular pathophysiological event. Promising results have been obtained from many pre-clinical experiments using therapeutic genes or oligonucleotides to prevent restenosis. Early clinical trials have shown that plasmid- and adenovirus-mediated vascular gene transfers can be conducted safely and are well tolerated. Ex vivo gene therapy with E2F-decoy succeeded in reducing graft occlusion rate after surgical bypass in a randomised, double-blind clinical trial. In the future, further development of gene delivery methods and vectors is needed to improve the efficacy and safety of gene therapy. Also, better knowledge of vascular biology at the molecular level is needed to find optimal strategies and gene combinations to treat restenosis. Provided that these difficulties can be solved, gene therapy offers an enormous potential for clinical medicine in the future.

Cells as vehicles for cancer gene therapy: the missing link between targeted vectors and systemic delivery?

Systemic administration of currently manufactured viral stocks has not so far achieved sufficient circulating titers to allow therapeutic targeting of metastatic disease. This is due to low initial viral titers, immune inactivation, nonspecific adhesion, and loss of particles. One way to exploit the elegant molecular manipulations that have been made to increase vector targeting is to protect these vectors until they reach the local sites of tumor growth. Various cell types home preferentially to tumors and can be loaded with the constructs required to produce targeted vectors. Here we discuss the potential of using such cell carriers to chaperone precious vectors directly to the tumors. The vectors can incorporate mechanisms to achieve tumor site-inducible expression, along with tumor cell-specific expression of the therapeutic gene and/or replicating viral genomes that would be released at the tumor. In this way, the great advances that have so far been made with the engineering of vector tropisms might be genuinely exploited and converted into clinical benefit.

Envelope-targeted retrovirus vectors transduce melanoma xenografts but not spleen or liver

Many cancer gene therapy applications would benefit from the development of targeted vectors that could deliver genes in vivo. We have previously achieved efficient in vitro targeting of retrovirus vectors to melanoma cells by fusion of a single chain antibody recognizing the high-molecular-weight melanoma-associated antigen (HMWMAA), followed by a blocking peptide and a matrix metalloprotease cleavage site, to the amino terminus of the murine leukemia virus amphotropic strain envelope. Here we report that up to 3% of cells within an HMWMAA-positive tumor xenograft were infected following a single injection of targeted vector into the tumor and up to 10% of tumor cells became infected when they were co-injected with viral producer cells. No infected cells were detected after delivery of targeted vectors to HMWMAA-negative tumor xenografts. Intraperitoneal injection of amphotropic vectors or producer cells resulted in transduction in spleen and liver, which was not detected when targeted vectors or producer cells were used. Our results demonstrate the feasibility of using targeted retroviral vectors for in vivo gene delivery to tumors and highlight the safety benefits of targeted vectors that do not infect other host tissues.

Retargeting gene delivery using surface-engineered retroviral vector particles

Retroviral vectors with the capacity to deliver transgenes to specific tissues are expected to be of great value for various gene transfer applications in vivo. Initial attempts to modify vector host-range by the insertion of ligands on their surface glycoproteins have frequently failed, essentially owing to the impairment of the fusogenicity of the vector particles bound to the targeted cell-surface molecules. Several strategies aimed to recover the fusogenic activity of surface-engineered vector particles have recently been explored and have given rise to novel concepts in the field.

Organ distribution of gene expression after intravenous infusion of targeted and untargeted lentiviral vectors

Lentiviral vectors represent an attractive technology platform from which to develop a targetable injectable gene delivery system for transduction of specific cell populations in vivo, irrespective of their cell cycle status. Targeted HIV-1-based lentiviral vectors were generated by pseudotyping them with chimeric murine leukemia virus (MLV) envelope glycoproteins displaying N-terminal targeting polypeptides. Vectors displaying an EGF polypeptide were fully infectious on EGF receptor-negative cells, but were inactive on cells with abundant EGF receptors (inverse targeting). Receptor-mediated inactivation of gene transfer was overcome by competing the EGF receptors on the target cells with soluble EGF or by removing the displayed EGF domain from the surface of the vector particles by factor Xa cleavage of a specific protease substrate engineered into its tethering linker (protease targeting). Intravenous infusion of nontargeted HIV-1 vectors led to maximal luciferase activity in liver and spleen with moderate or minimal activity in heart, skeletal muscle, lung, brain, kidney, ovaries and bone marrow. In contrast, intravenous EGF-displaying vectors were expressed maximally in spleen with very low level luciferase expression detectable in liver (EGF-receptor rich). Liver transduction by the EGF-displaying vector was restored by pretreating the animals with soluble EGF suggesting that these vectors are inversely targeted to spleen.

Lesion-targeted injectable vectors for vascular restenosis

Pathologic lesions caused by catheter-based revascularization procedures for occlusive artery disease include disruption of the endothelium, exposure of extracellular matrix (ECM) proteins, and proliferation of vascular smooth muscle cells, which lead to neointima formation and restenosis. We have developed matrix-collagen-targeted retroviral vectors that are able to accumulate at sites of vascular injury (Hall et al., Hum. Gene Ther. 1997;8:2183-2192; Hall et al., Hum. Gene Ther. 2000;11:983-993). The primary tissue-targeting motif, adapted from the physiological surveillance sequence found in von Willebrand factor, served to localize and concentrate the vector within vascular lesions. In the present study, we evaluated the efficiency of this vector-targeting system in rats with nonligated balloon-injured carotid arteries. Both intraarterial (by retrograde femoral artery catheterization) and intravenous (via femoral vein) injection of a matrix-targeted vector enhanced transduction of neointimal cells ( approximately 20%) at severely denuded areas when compared with the nontargeted vector (<1%). Further, intraarterial instillation of a matrix-targeted, but not a nontargeted, vector bearing an antisense cyclin G1 construct inhibited neointima lesion formation in the injured carotid arteries. Taken together, these data indicate that strategic targeting of retroviral vectors to vascular lesions would have therapeutic potential in the management of vascular restenosis and many other disorders of uncontrolled proliferation where endothelial disruption, ECM remodeling, and collagen deposition form the nexus for preferential vector localization and concentration in vivo.

Systemic administration of a matrix-targeted retroviral vector is efficacious for cancer gene therapy in mice

Targeting cytocidal vectors to tumors and associated vasculature in vivo is a long-standing goal of human gene therapy. In the present study, we demonstrated that intravenous infusion of a matrix (i.e., collagen)-targeted retroviral vector provided efficacious gene delivery of a cytocidal mutant cyclin G1 construct (designated Mx-dnG1) in human cancer xenografts in nude mice. A nontargeted CAE-dnG1 vector (p = 0.014), a control matrix-targeted vector bearing a marker gene (Mx-nBg; p = 0.004), and PBS served as controls (p = 0.001). Enhanced vector penetration and transduction of tumor nodules (35.7 +/- 1.4%, mean +/- SD) correlated with therapeutic efficacy without associated toxicity. Kaplan-Meier survival studies were conducted in mice treated with PBS placebo, the nontargeted CAE-dnG1 vector, and the matrix-targeted Mx-dnG1 vector. Using the Tarone log-rank test, the overall p value for comparing all three groups simultaneously was 0.003, with a trend that was significant to a level of 0.004, indicating that the probability of long-term control of tumor growth was significantly greater with the matrix-targeted Mx-dnG1 vector than with the nontargeted CAE-dnG1 vector or PBS placebo. The present study demonstrates that a matrix-targeted retroviral vector deployed by peripheral vein injection (1) accumulated in angiogenic tumor vasculature within 1 hr, (2) transduced tumor cells with high-level efficiency, and (3) enhanced therapeutic gene delivery and long-term efficacy without eliciting appreciable toxicity.