Tissue inhibitor of metalloproteinases-2 improves antitumor efficacy of a replicating adenovirus in vivo

Clinical studies of replicating adenoviruses for the treatment of cancer have demonstrated their safety but have yielded disappointing results, indicating the need for new strategies to improve their efficacy. We hypothesized that the efficacy of a replicating adenovirus could be improved by expression of tissue inhibitor of metalloproteinases-2 (TIMP-2), a 21-kDa unglycosylated secretory protein. TIMP-2 specifically inhibits the active forms of a number of matrix metalloproteinases (MMPs) that play a role in the degradation of basement membranes and the extracellular matrix and are therefore involved in the control of the growth, invasion and metastasis of tumor cells, as well as angiogenesis. In addition, TIMP-2 can abrogate tumor growth and angiogenesis by a variety of mechanisms independent of MMP inhibition. In this study, we demonstrate that expression of TIMP-2 enhanced the antitumor efficacy of a replicating adenovirus in vivo, by reducing both tumor growth and angiogenesis.

An adenovirus vector with a chimeric fiber incorporating stabilized single chain antibody achieves targeted gene delivery

Adenovirus (Ad) vectors are of utility for many therapeutic applications. Strategies have been developed to alter adenoviral tropism to achieve a cell-specific gene delivery capacity employing fiber modifications allowing genetic incorporation of targeting motifs. In this regard, single chain antibodies (scFv) represent potentially useful agents to achieve targeted gene transfer. However, the distinct biosynthetic pathways that scFv and Ad capsid proteins are normally routed through have thus far been problematic with respect to scFv incorporation into the Ad capsid. Utilization of stable scFv, which also maintain correct folding and thus functionality under intracellular reducing conditions, could overcome this restriction. We genetically incorporated a stable scFv into a de-knobbed, fibritin-foldon trimerized Ad fiber and demonstrated selective targeting to the cognate epitope expressed on the membrane surface of cells. We have shown that the scFv employed in this study retains functionality and that stabilizing the targeting molecule, per se, is critical to allow retention of antigen recognition in the adenovirus capsid-incorporated context.

An adenovirus serotype 5 vector with fibers derived from ovine atadenovirus demonstrates CAR-independent tropism and unique biodistribution in mice

Many clinically important tissues are refractory to adenovirus (Ad) infection due to negligible levels of the primary Ad5 receptor the coxsackie and adenovirus receptor CAR. Thus, development of novel CAR-independent Ad vectors should lead to therapeutic gain. Ovine atadenovirus type 7, the prototype member of genus Atadenovirus, efficiently transduces CAR-deficient human cells in vitro, and systemic administration of OAdV is not associated with liver sequestration in mice. The penton base of OAdV7 does not contain an RGD motif, implicating the long-shafted fiber molecule as a major structural dictate of OAdV tropism. We hypothesized that replacement of the Ad5 fiber with the OAdV7 fiber would result in an Ad5 vector with CAR-independent tropism in vitro and liver "detargeting" in vivo. An Ad5 vector displaying the OAdV7 fiber was constructed (Ad5Luc1-OvF) and displayed CAR-independent, enhanced transduction of CAR-deficient human cells. When administered systemically to C57BL/6 mice, Ad5Luc1-OvF reporter gene expression was reduced by 80% in the liver compared to Ad5 and exhibited 50-fold higher gene expression in the kidney than the control vector. To our knowledge, this is the first report of a fiber-pseudotyped Ad vector that simultaneously displays decreased liver uptake and a distinct organ tropism in vivo. This vector may have future utility in murine models of renal disease.

Generation and selection of targeted adenoviruses embodying optimized vector properties

The utility of adenovirus serotype 5 (Ad5)-based vectors for gene therapy applications would be improved by cell-specific targeting. However, strategies to redirect Ad5 vectors to alternate cellular receptors via replacement of the capsid fiber protein have often resulted in structurally unstable vectors. In view of this, we hypothesized that the selection of modified adenoviruses during their rescue and propagation would be a straightforward approach that guarantees the generation of functional, targeted vectors. Based on our first generation fiber-fibritin molecule, several new chimeric fibers containing variable amounts of fibritin and the Ad5 fiber shaft were analyzed via a new scheme for Ad vector selection. Our selected chimera, composed of the entire Ad5 fiber shaft fused to the 12th coiled-coil segment of fibritin, is capable of efficient capsid incorporation and ligand display. Moreover, transduction by the resultant vector is independent of the expression of the native Ad5 receptor. The incorporation of the Fc-binding domain of Staphylococcus aureus protein A at the carboxy terminus of this chimeric fiber facilitates targeting of the vector to a variety of cellular receptors by means of coupling with monoclonal antibodies. In addition, we have concluded that Ad5 vectors incorporating individual targeting ligands require individual optimization of the fiber-fibritin chimera, which may be accomplished by selecting the optimal fiber-fibritin variant at the stage of rescue of the virus in cells of interest, as described herein.

RhoA and cytoskeletal disruption mediate reduced osteoblastogenesis and enhanced adipogenesis of human mesenchymal stem cells in modeled microgravity

Spaceflight, aging, and disuse lead to reduced BMD. This study shows that overexpression of constitutively active RhoA restores actin cytoskeletal arrangement, enhances the osteoblastic phenotype, and suppresses the adipocytic phenotype of human mesenchymal stem cells cultured in modeled microgravity.

INTRODUCTION

Reduced BMD during spaceflight is partly caused by reduced bone formation. However, mechanisms responsible for this bone loss remain unclear. We have previously shown reduced osteoblastogenesis and enhanced adipogenesis of human mesenchymal stem cells (hMSCs) cultured in modeled microgravity (MMG). The small GTPase, RhoA, regulates actin stress fiber formation and has been implicated in the lineage commitment of hMSCs. We examined the effects of MMG on actin cytoskeletal organization and RhoA activity and the ability of constitutively active RhoA to reverse these effects.

MATERIALS AND METHODS

hMSCs were seeded onto plastic microcarrier beads at a density of 10(6) and allowed to form aggregates in DMEM containing 10% FBS for 7 days. Aggregates were incubated in DMEM containing 2% FBS for 6 h with or without an adenoviral vector containing constitutively active RhoA at a multiplicity of infection (moi) of 500 and allowed to recover in 10% FBS for 24 h. Cells were transferred to the rotary cell culture system to model microgravity or to be maintained at normal gravity for 7 days in DMEM, 10% FBS, 10 nM dexamethasone, 10 mM beta-glycerol phosphate, and 50 muM ascorbic acid 2-phosphate.

RESULTS

F-actin stress fibers are disrupted in hMSCs within 3 h of initiation of MMG and are completely absent by 7 days, whereas monomeric G-actin is increased. Because of the association of G-actin with lipid droplets in fat cells, the observed 310% increase in intracellular lipid accumulation in hMSCs cultured in MMG was not unexpected. Consistent with these changes in cellular morphology, 7 days of MMG significantly reduces RhoA activity and subsequent phosphorylation of cofilin by 88+/-2% and 77+/-9%, respectively. Importantly, introduction of an adenoviral construct expressing constitutively active RhoA reverses the elimination of stress fibers, significantly increases osteoblastic gene expression of type I collagen, alkaline phosphatase, and runt-related transcription factor 2, and suppresses adipocytic gene expression of leptin and glucose transporter 4 in hMSCs cultured in MMG.

CONCLUSION

Suppression of RhoA activity during MMG represents a novel mechanism for reduced osteoblastogenesis and enhanced adipogenesis of hMSCs.

Complex mosaicism is a novel approach to infectivity enhancement of adenovirus type 5-based vectors

The use of adenovirus type 5 (Ad5) for cancer therapy is limited by deficiency of its primary cell attachment receptor, coxsackie and adenovirus receptor (CAR), on cancer cells. Ad5 retargeting to alternate receptors through fiber genetic modification can be used to circumvent CAR dependence of its tropism, and thereby achieve infectivity enhancement. Here we propose and test a novel "complex mosaicism" approach for fiber modification, which combines serotype chimerism with peptide ligand(s) incorporation in a single-fiber molecule. We incorporated integrin-binding peptide RGD-4C in the HI-loop, at the carboxy (C)-terminus, or both locales of the Ad3 knob, in the context of Ad5/3 chimera fiber in order to retarget simultaneously the Ad vector to integrins and Ad3 receptors. The infectivity enhancement of the fiber modifications was assessed in various cancer cell lines as cancer-targeting models. Replication-defective complex mosaic Ad-luc vectors bearing chimeric fiber (F.5/3), with or without C-terminal RGD-modification of Ad3 knob, demonstrated up to 55-fold gene transfer increase in bladder cancer cell lines. Although this augmentation was primarily due to Ad3 receptor targeting, some contribution of RGD-mediated integrin-targeting was also observed, suggesting that complex mosaic modification can function in a dual-receptor targeting via a single Ad3 fiber knob.

Prospective study of serological conversion as a risk factor for development of leprosy among household contacts

Although the prevalence of leprosy has declined over the years, there is no evidence that incidence rates are falling. A method of early detection of those people prone to develop the most infectious form of leprosy would contribute to breaking the chain of transmission. Prophylactic treatment of serologically identified high-risk contacts of incident patients should be an operationally feasible approach for routine control programs. In addition, classification of high-risk household contacts will allow control program resources to be more focused. In this prospective study, we examined the ability of serology used for the detection of antibodies to phenolic glycolipid I of Mycobacterium leprae to identify those household contacts of multibacillary leprosy patients who had the highest risk of developing leprosy. After the start of multidrug therapy for the index case, a new case of leprosy developed in one in seven of the 178 households studied. In households where new cases appeared, the seropositivity rates were significantly higher (P < 0.001) than those in households without new cases. Seropositive household contacts had a significantly higher risk of developing leprosy (relative hazard adjusted for age and sex [aRH], 7.2), notably multibacillary leprosy (aRH = 24), than seronegative contacts.

High efficiency transduction of dendritic cells by adenoviral vectors targeted to DC-SIGN

Dendritic cells (DCs) are a central element in the development of antigen-specific immune responses. The lack of a specific and efficient technique for the in vivo delivery of antigens to DCs remains a major obstacle limiting a vaccine's ability to induce an effective immune response. The efficacy of adenoviral (Ad) vectors in this regard can be enhanced through alterations in vector tropism such that DC-targeted transduction is achieved. Here, the efficiency of DC transduction by Ad vectors retargeted to DC-specific ICAM-3 grabbing nonintegrin (DC-SIGN) was studied and compared to that of Ad vectors retargeted through CD40. A comparable and significant enhancement of gene transfer to monocyte derived DCs (MDDCs) was accomplished by means of an Ad vector harboring the Fc-binding domain of Staphylococcus aureus protein A in combination with antibodies to DC-SIGN or to CD40 or with fused complexes of human Ig-Fc with their natural ligands, i.e., ICAM-3 or CD40L, respectively. Whereas CD40-targeted Ad transduction resulted in a more profound phenotypic DC maturation, DC-SIGN- and CD40-targeted Ad both induced similar levels of IL-12 secretion. These data demonstrate the usefulness of DC-SIGN as a DC-restricted targeting motif for Ad-mediated vaccination strategies.

Genetic replacement of the adenovirus shaft fiber reduces liver tropism in ovarian cancer gene therapy

Approaches to alter the native tropism of adenoviruses (Ads) are beneficial to increase their efficacy and safety profile. Liver tropism is important with regard to potential clinical toxicity in humans. Ad5/3 chimeras in which the Ad5 knob is substituted by the Ad3 knob, such as Ad5/3luc1, have been recently shown to increase infectivity of ovarian cancer cell lines and primary tumor cells, which express low levels of the coxsackie-adenovirus receptor (CAR), without increasing infectivity of liver cells. A novel strategy to address the problem of liver uptake and improve the tumor/liver ratio is genetic replacement of the Ad fiber shaft. Ad5.Ad3.SH.luc1 is an Ad5-based vector that contains the fiber shaft from Ad serotype 3 but the fiber knob from Ad serotype 5. To compare tumor/liver of Ad5.Ad3.SH.luc1 and Ad5/3luc1 in vivo, we created three different tumor and treatment models of ovarian cancer in mice, simulating intraperitoneal and intravenous administration of tumors. Ad5.Ad3.SH.luc1 displayed the lowest liver tropism of all viruses in all models tested. Intravenous administration of all viruses resulted in higher tumor transduction rates compared to intraperitoneal administration. Genetic shortening of the Ad5 fiber shaft significantly increases relative tumor/liver gene transfer. This could improve the effective tumor dose and reduce side effects, thereby increasing the bioavailability of therapeutic agents.

An adenovirus vector with a chimeric fiber derived from canine adenovirus type 2 displays novel tropism

Many clinically relevant tissues are refractory to Ad5 transduction because of negligible levels of the primary Ad5 receptor, the coxsackie and adenovirus receptor (CAR). Thus, development of Ad vectors that display CAR-independent tropism could lead directly to therapeutic gain. The Toronto strain of canine adenovirus type 2 (CAV2) exhibits native tropism that is augmented by, but not fully dependent upon, CAR for cellular transduction. We hypothesized that an Ad5 vector containing the nonhuman CAV2 knob would provide expanded tropism and constructed Ad5Luc1-CK, an E1-deleted Ad5 vector encoding the fiber knob domain from CAV2. Ad5Luc1-CK gene delivery to CAR-deficient cells was augmented up to 30-fold versus the Ad5 control vector, and correlated with increased cell surface binding. Further, we confirmed the importance of cellular integrins to Ad5Luc1-CK transduction. Herein, we present the rationale, design, purification, and characterization of a novel tropism modified, infectivity-enhanced Ad vector.

Single-chain antibodies: A therapeutic modality for cancer gene therapy (review)

Gene therapy has rapidly evolved into a field that is treating not only inborn errors of metabolism, but other diseases associated with poor outcomes such as malignancy, where transient gene expression can be therapeutic. Cancer gene therapy is a novel form of treatment that exploits differences at the molecular level between normal and malignant cells. Current gene therapy approaches that are being evaluated include the use of replication competent viruses, mutation compensation strategies, improved targeting with tumor specific promoters, and the utilization of enhanced infectivity viruses. An additional aspect of gene therapy that has gained increased interest in the last several years is the utilization of single-chain antibodies (scFv). Specifically, scFv have been utilized to target molecular processes associated with carcinogenesis, as well as to improve gene transfer efficiency. We will limit our discussion to the role of scFv in targeting molecular processes associated with carcinogenesis.

Adenovirus-mediated gene delivery to skeletal muscle

Adenoviral vectors can be employed for gene delivery to skeletal muscle, both ex vivo and in vivo. Although the realization of the full potential of adenoviral vectors awaits the development of methods to allow safe and efficient targeted gene delivery to mature skeletal muscle upon intravenous vector administration (1), the current generation of vectors has nonetheless found utility in preclinical studies of gene therapy and in gene-transfer experiments designed to study muscle biology. Features of adenoviral vectors that have favored their use for gene delivery to skeletal muscle include the ability to infect both actively dividing and terminally differentiated cells, as well as their large insert capacity. Gutted adenoviral vectors are capable of carrying the large dystrophin gene together with regulatory sequences, and are therefore appropriate vehicles for gene-replacement therapy for Duchenne muscular dystrophy. In addition to their suitability for in vivo gene-therapy applications, adenoviral vectors have been used ex vivo to transfer genes to myoblasts prior to myoblast transplantation into muscle.

Adenovirus-mediated gene delivery: an overview

Adenoviruses, which were first isolated in the 1950s, have been developed as gene-delivery vehicles, or vectors, since the early 1980s. The adenoviruses constitute the Adenoviridae family, which is divided into two genera: the Aviadenovirus genus infects only birds, whereas the Mastadenovirus genus contains viruses that infect a range of mammalian species. Human adenoviruses are classified into six subgroups based on the percentage of guanine and cytosine in the DNA molecules and the ability to agglutinate red blood cells. They are further subdivided into more than 50 serotypes, primarily on the basis of neutralization assays.

Adenovirus-mediated gene delivery to dendritic cells

Dendritic cells (DCs) are "professional" antigen-presenting cells (APCs) that are uniquely capable of activating and instructing a naive immune system to mount a specific cellular and humoral response. Recognition of this crucial function makes the development of technologies for DC-based immuno-therapies a priority for the treatment of a wide variety of diseases. The most immediate impact of this emerging technology will be in the treatment of cancer and the development of third generation vaccines to protect against viral and intracellular pathogens. In addition to elicitation of immune responses, DCs also function to maintain tolerance to "self." Once the biological basis for this important function is understood, future applications of DC-based immuotherapies may be developed to ameliorate autoimmune diseases or enhance acceptance of transplanted organs. The feasibility of "engineering" the function of DCs has been realized by recent advances in ex vivo methodologies that allow selective DC propagation, antigen loading, and genetic modification in vitro for subsequent therapeutic transfer into the host. Ultimately, the ability to genetically modify these cells will allow us to design DC-mediated interventions that will direct predictable control of either immune activation or tolerance in vivo.

Retargeting of adenoviral infection to melanoma: combining genetic ablation of native tropism with a recombinant bispecific single-chain diabody (scDb) adapter that binds to fiber knob and HMWMAA

Gene therapy is an emerging and promising modality for the treatment of malignant melanoma and other neoplasms for which conventional therapies are inadequate. Various therapeutic genes have shown promise for tumor cell killing. However, successful gene therapy depends on the development of efficient and targeted gene transfer vectors. Here we describe a novel strategy for targeting of adenovirus-mediated gene transfer to melanoma cells. This strategy combines genetic ablation of native adenoviral tropism with redirected viral binding to melanoma cells via a bispecific adapter molecule, a bacterially expressed single-chain diabody, scDb MelAd, that binds to both the adenoviral fiber protein and to the high molecular weight melanoma-associated antigen (HMWMAA). This antigen is widely and specifically expressed on the surface of melanoma cells and its expression is associated with tumor development and progression. Our results showed specific and strong binding of the anti-HMWMAA scFv RAFT3 and the bispecific adapter scDb MelAd to melanoma cells. In adenoviral infection experiments, we demonstrated i) substantially (>50-fold) reduced infectivity of capsid mutant adenoviruses, ii) restored (up to 367-fold increase), CAR-independent and HMWMAA-mediated infectivity of these mutant viruses by scDb MelAd specifically in melanoma cells, and iii) higher levels of transgene expression in melanoma cells by fiber mutant virus complexed with scDbMelAd, relative to a vector with wild-type fibers. We confirmed the utility of this targeting strategy with human primary melanoma cells that represent clinically relevant substrates. These experiments established that the retargeting strategy mediates up to 54-fold increased adenoviral gene transfer to CAR-negative melanoma cells compared to the vector with native tropism. Hence, the HMWMAA-targeted adenoviral vector lacking native tropism exhibits both enhanced specificity and augmented infectivity of gene transfer to melanoma cells, suggesting that it is feasible to use this vector to improve gene therapy for malignant melanoma.

Targeting of adenovirus via genetic modification of the viral capsid combined with a protein bridge

A potential barrier to the development of genetically targeted adenovirus (Ad) vectors for cell-specific delivery of gene therapeutics lies in the fact that several types of targeting protein ligands require posttranslational modifications, such as the formation of disulfide bonds, which are not available to Ad capsid proteins due to their nuclear localization during assembly of the virion. To overcome this problem, we developed a new targeting strategy, which combines genetic modifications of the Ad capsid with a protein bridge approach, resulting in a vector-ligand targeting complex. The components of the complex associate by virtue of genetic modifications to both the Ad capsid and the targeting ligand. One component of this mechanism of association, the Fc-binding domain of Staphylococcus aureus protein A, is genetically incorporated into the Ad fiber protein. The ligand is comprised of a targeting component fused with the Fc domain of immunoglobulin, which serves as a docking moiety to bind to these genetically modified fibers during the formation of the Ad-ligand complex. The modular design of the ligand solves the problem of structural and biosynthetic compatibility with the Ad and thus facilitates targeting of the vector to a variety of cellular receptors. Our study shows that targeting ligands incorporating the Fc domain and either an anti-CD40 single-chain antibody or CD40L form stable complexes with protein A-modified Ad vectors, resulting in significant augmentation of gene delivery to CD40-positive target cells. Since this gene transfer is independent of the expression of the native Ad5 receptor by the target cells, this strategy results in the derivation of truly targeted Ad vectors suitable for tissue-specific gene therapy.

A mosaic adenovirus possessing serotype Ad5 and serotype Ad3 knobs exhibits expanded tropism

The efficiency of cancer gene therapy with recombinant adenoviruses based on serotype 5 (Ad5) has been limited partly because of variable, and often low, expression by human primary cancer cells of the primary cellular-receptor which recognizes the knob domain of the fiber protein, the coxsackie and adenovirus receptor (CAR). As a means of circumventing CAR deficiency, Ad vectors have been retargeted by utilizing chimeric fibers possessing knob domains of alternate Ad serotypes. We have reported that ovarian cancer cells possess a primary receptor for Ad3 to which the Ad3 knob binds independently of the CAR-Ad5 knob interaction. Furthermore, an Ad5-based chimeric vector, designated Ad5/3, containing a chimeric fiber proteins possessing the Ad3 knob, demonstrates CAR-independent tropism by virtue of targeting the Ad3 receptor. Based on these findings, we hypothesized that a mosaic virus possessing both the Ad5 knob and the Ad3 knob on the same virion could utilize either primary receptor, resulting in expanded tropism. In this study, we generated a dual-knob mosaic virus by coinfection of 293 cells with Ad5-based and Ad5/3-based vectors. Characterization of the resultant virions confirmed the incorporation of both Ad5 and Ad3 knobs in the same particle. Furthermore, this mosaic virus was able to utilize either receptor, CAR and the Ad3 receptor, for virus attachment to cells. Enhanced Ad infectivity with the mosaic virus was shown in a panel of cell lines, with receptor profiles ranging from CAR-dominant to Ad3 receptor-dominant. Thus, this mosaic virus strategy may offer the potential to improve Ad-based gene therapy approaches by infectivity enhancement and tropism expansion.

The coxsackievirus and adenovirus receptor acts as a tumour suppressor in malignant glioma cells

The coxsackievirus and adenovirus receptor (CAR) is a membrane glycoprotein with a cytoplasmic domain, a transmembrane domain and an extracellular region consisting of two immunoglobulin-like domains, an amino-terminal immunoglobulin variable (IgV)-related domain (D1), which is distal to the cell surface, and a proximal IgC2 domain (D2). The coxsackievirus and adenovirus receptor has been shown to exhibit tumour suppression activity in human bladder and prostate cancer cells. In the current paper, we demonstrate that CAR is a tumour suppressor in glioma cells and that the extracellular D2 domain is not required for this inhibitory effect. This finding provides a biological basis for the observation that expression of CAR is downregulated in malignant glioma cells. This suggests that strategies to redirect adenoviruses to achieve CAR-independent infection will be necessary to realise the full potential of adenoviral vectors for cancer gene therapy.

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.

Generation of an adenoviral vector containing an addition of a heterologous ligand to the serotype 3 fiber knob

As an initial assessment of the feasibility of employing the adenovirus serotype 3 (Ad3) fiber knob as a locale for introducing a tropism-modifying motif, we generated an adenoviral vector containing a six-histidine tag genetically fused to the carboxy-terminus of the Ad3 fiber knob. The heterologous tag proved to be accessible for binding in the context of the virion and, moreover, had rendered the modified vector capable of mediating gene transfer through an artificial, non-Ad3 receptor.

Dual targeting of adenoviral vectors at the levels of transduction and transcription enhances the specificity of gene expression in cancer cells

Adenoviral (Ad) vector-mediated strategies for cancer gene therapy mandate a vector that is capable of efficient expression of the therapeutic gene specifically within the target tumor cells. In one approach to the development of cancer cell-specific vectors, Ad vectors have been targeted at the level of transduction to achieve the selective delivery of the therapeutic gene. In an alternative approach to the derivation of cancer cell-specific vectors, Ad vectors have been targeted at the level of transcription by placing the therapeutic gene under the control of transcriptional regulatory sequences that are activated in tumor cells, but not in normal cells, and therefore target expression selectively to the tumor cell. In this report, we demonstrate that a higher degree of specificity for cancer cells can be achieved by combining the complementary approaches of transductional and transcriptional targeting, each of which is imperfect or "leaky" by itself.

The therapeutic efficacy of adenoviral vectors for cancer gene therapy is limited by a low level of primary adenovirus receptors on tumour cells

Replication-defective adenoviral vectors are currently being employed as gene delivery vehicles for cancer gene therapy. To address the hypothesis that the therapeutic efficacy of adenoviral vectors is restricted by their inability to infect tumour cells expressing low levels of the primary cellular receptor for adenoviruses, the coxsackievirus and adenovirus receptor (CAR), we have employed a pair of ovarian cancer cell lines differing only in the expression of a primary receptor for Ad5. This novel system thus allowed the direct evaluation of the relationship between the efficacy of an adenoviral vector and the primary receptor levels of the host cancer cell, without the confounding influence of other variable cellular factors. We demonstrate that a deficiency of the primary cellular receptor on the tumour cells restricts the efficacy of adenoviral vectors in two distinct cancer gene therapy approaches, TP53 gene replacement therapy and herpes simplex virus thymidine kinase/ganciclovir suicide gene therapy. Moreover, we show that a deficiency of the primary receptor on the tumour cells limits the efficiency of adenovirus-mediated gene transfer in vivo. Since a number of studies have reported that primary cancer cells express only low levels of CAR, our results suggest that strategies to redirect adenoviruses to achieve CAR-independent infection will be necessary to realize the full potential of adenoviral vectors in the clinical setting.

Soluble coxsackievirus adenovirus receptor is a putative inhibitor of adenoviral gene transfer in the tumor milieu

PURPOSE

Several barriers that collectively restrict gene delivery by viral vectors in vivo have been described. Previously, we identified soluble chondroitin sulfate-proteoglycans/glycosaminoglycans in malignant pleural effusions (MPEs) as inhibitors of retroviral vector transduction. Soluble components of MPE also inhibited adenoviral (Ad) gene transfer, and the factors were characteristically filterable, titrable, stable at 56 degrees C, and blocked the binding of Ad to target cells. Depleting immunoglobulin from MPE, partially reversed the block to Ad transduction, instigating a search for additional factors that bound Ad in MPE.

EXPERIMENTAL DESIGN

Vector-protein interactions were identified after the resolution of MPE-components by SDS-PAGE. Viral overlays and immunoblots delineated significant interactions, and the potential relevance of those interactions was tested in transduction efficiency bioassays.

RESULTS

Immunoglobulin is the predominant factor inhibiting Ad gene transfer in MPE. Albumin also interacted with Ad, although at predicted serum concentrations, it did not effect Ad transduction efficiency in vitro. Soluble coxsackievirus-Ad receptor (sCAR) was then identified in MPE. In a survey of 18 MPE, the mean concentration of sCAR was variable and estimated to be 3.51 +/- 5.02 ng/ml by ELISA. The impact of sCAR on transduction efficiency in this milieu was next assessed. Whereas immunodepletion of sCAR from MPE by affinity chromatography resulted in enhanced gene transfer within MPE, the inhibition of adenoviral gene transfer was not evident when the predicted concentrations of recombinant sCAR were added into the transduction medium.

CONCLUSIONS

These studies indicate that, in addition to anti-Ad antibodies, other specific and nonspecific factors interact with viral vectors and may impair gene transfer in the tumor milieu. The presence of sCAR in MPE puts forward the notion that in certain contexts (e.g., within the extracellular matrix of solid tumors) the concentrations of secreted (or shed) CAR may be high enough to effectively compete with Ad gene delivery.