Characterisation of systemic dissemination of nonreplicating adenoviral vectors from tumours in local gene delivery

Advanced gene nanocarriers/scaffolds in nonviral-mediated delivery system for tissue regeneration and repair

Tissue regeneration technology has been rapidly developed and widely applied in tissue engineering and repair. Compared with traditional approaches like surgical treatment, the rising gene therapy is able to have a durable effect on tissue regeneration, such as impaired bone regeneration, articular cartilage repair and cancer-resected tissue repair. Gene therapy can also facilitate the production of in situ therapeutic factors, thus minimizing the diffusion or loss of gene complexes and enabling spatiotemporally controlled release of gene products for tissue regeneration. Among different gene delivery vectors and supportive gene-activated matrices, advanced gene/drug nanocarriers attract exceptional attraction due to their tunable physiochemical properties, as well as excellent adaptive performance in gene therapy for tissue regeneration, such as bone, cartilage, blood vessel, nerve and cancer-resected tissue repair. This paper reviews the recent advances on nonviral-mediated gene delivery systems with an emphasis on the important role of advanced nanocarriers in gene therapy and tissue regeneration.

Silk-Gel Powered Adenoviral Vector Enables Robust Genome Editing of PD-L1 to Augment Immunotherapy across Multiple Tumor Models

Immune checkpoint blockade based on antibodies has shown great clinical success in patients, but the transitory working manner leads to restricted therapeutic benefits. Herein, a genetically engineered adenovirus is developed as the vector to deliver CRISPR/Cas9 (sgCas9-AdV) to achieve permanent PD-L1 gene editing with efficiency up to 78.7% exemplified in Hepa 1-6 liver cancer cells. Furthermore, the sgCas9-AdV is loaded into hydrogel made by silk fiber (SgCas9-AdV/Gel) for in vivo application. The silk-gel not only promotes local retention of sgCas9-AdV in tumor tissue, but also masks them from host immune system, thus ensuring effectively gene transduction over 9 days. Bearing these advantages, the sgCas9-AdV/Gel inhibits Hepa 1-6 tumor growth with 100% response rate by single-dose injection, through efficient PD-L1 disruption to elicit a T cell-mediated antitumor response. In addition, the sgCas9-AdV/Gel is also successfully extended into other refractory tumors. In CT26 colon tumor characterized by poor response to anti-PD-L1, sgCas9-AdV/Gel is demonstrated to competent and superior anti-PD-L1 antibody to suppress tumor progression. In highly aggressive orthotopic 4T1 mouse breast tumor, such a therapeutic paradigm significantly inhibits primary tumor growth and induces a durable immune response against tumor relapse/metastasis. Thus, this study provides an attractive and universal strategy for immunotherapy.

Ad5/3 is able to avoid neutralization by binding to erythrocytes and lymphocytes

Oncolytic adenoviruses are promising cancer therapeutic agents. Clinical data have shown adenoviruses' ability to transduce tumors after systemic delivery in human cancer patients, despite antibodies. In the present work, we have focused on the interaction of a chimeric adenovirus Ad5/3 with human lymphocytes and human erythrocytes. Ad5/3 binding with human lymphocytes and erythrocytes was observed to occur in a reversible manner, which allowed viral transduction of tumors, and oncolytic potency of Ad5/3 in vitro and in vivo, with or without neutralizing antibodies. Immunodeficient mice bearing xenograft tumors showed enhanced tumor transduction following systemic administration, when Ad5/3 virus was bound to lymphocytes or erythrocytes (P < 0.05). In conclusion, our findings reveal that chimeric Ad5/3 adenovirus reaches non-injected tumors in the presence of neutralizing antibodies: it occurs through reversible binding to lymphocytes and erythrocytes.

Is Viral Vector Gene Delivery More Effective Using Biomaterials?

Gene delivery has been extensively investigated for introducing foreign genetic material into cells to promote expression of therapeutic proteins or to silence relevant genes. This approach can regulate genetic or epigenetic disorders, offering an attractive alternative to pharmacological therapy or invasive protein delivery options. However, the exciting potential of viral gene therapy has yet to be fully realized, with a number of clinical trials failing to deliver optimal therapeutic outcomes. Reasons for this include difficulty in achieving localized delivery, and subsequently lower efficacy at the target site, as well as poor or inconsistent transduction efficiency. Thus, ongoing efforts are focused on improving local viral delivery and enhancing its efficiency. Recently, biomaterials have been exploited as an option for more controlled, targeted and programmable gene delivery. There is a growing body of literature demonstrating the efficacy of biomaterials and their potential advantages over other delivery strategies. This review explores current limitations of gene delivery and the progress of biomaterial-mediated gene delivery. The combination of biomaterials and gene vectors holds the potential to surmount major challenges, including the uncontrolled release of viral vectors with random delivery duration, poorly localized viral delivery with associated off-target effects, limited viral tropism, and immune safety concerns.

Monitoring of biodistribution and persistence of conditionally replicative adenovirus in a murine model of ovarian cancer using capsid-incorporated mCherry and expression of human somatostatin receptor subtype 2 gene

A significant limiting factor to the human clinical application of conditionally replicative adenovirus (CRAd)-based virotherapy is the inability to noninvasively monitor these agents and their potential persistence. To address this issue, we proposed a novel imaging approach that combines transient expression of the human somatostatin receptor (SSTR) subtype 2 reporter gene with genetic labeling of the viral capsid with mCherry fluorescent protein. To test this dual modality system, we constructed the Ad5/3Δ24pIXcherry/SSTR CRAd and validated its capacity to generate fluorescent and nuclear signals in vitro and following intratumoral injection. Analysis of 64Cu-CB-TE2A-Y3-TATE biodistribution in mice revealed reduced uptake in tumors injected with the imaging CRAd relative to the replication-incompetent, Ad-expressing SSTR2 but significantly greater uptake compared to the negative CRAd control. Optical imaging demonstrated relative correlation of fluorescent signal with virus replication as determined by viral genome quantification in tumors. Positron emission tomography/computed tomography studies demonstrated that we can visualize radioactive uptake in tumors injected with imaging CRAd and the trend for greater uptake by standardized uptake value analysis compared to control CRAd. In the aggregate, the plasticity of our dual imaging approach should provide the technical basis for monitoring CRAd biodistribution and persistence in preclinical studies while offering potential utility for a range of clinical applications.

Intratumoral delivery of CD154 homolog (Ad-ISF35) induces tumor regression: analysis of vector biodistribution, persistence and gene expression

Ad-ISF35 is an adenovirus (Ad) vector that encodes a mouse-human chimeric CD154. Ad-ISF35 induces activation of chronic lymphocytic leukemia (CLL) cells converting them into CLL cells capable of promoting immune recognition and anti-leukemia T-cell activation. Clinical trials in humans treated with Ad-ISF35-transduced leukemia cells or intranodal injection of Ad-ISF35 have shown objective clinical responses. To better understand the biology of Ad-ISF35 and to contribute to its clinical development, we preformed studies to evaluate biodistribution, persistence and toxicity of repeat dose intratumoral administration of Ad-ISF35 in a mouse model. Ad-ISF35 intratumoral administration induced tumor regression in more than 80% of mice bearing A20 tumors. There were no abnormalities in the serum chemistry. Mice receiving Ad-ISF35 presented severe extramedullary hematopoiesis and follicular hyperplasia in the spleen and extramedullary hematopoiesis with lymphoid hyperplasia in lymph nodes. After Ad-ISF35 injection, the vector was found primarily in the injected tumors with a biodistribution pattern that showed a rapid clearance with no evidence of Ad-ISF35 accumulation or persistence in the injected tumor or peripheral organs. Furthermore, pre-existing antibodies against Ad-5 did not abrogate Ad-ISF35 anti-tumor activity. In conclusion, intratumoral administration of Ad-ISF35 induced tumor regression in A20 tumor bearing mice without toxicities and with no evidence of vector accumulation or persistence.

Sequential administration of bovine and human adenovirus vectors to overcome vector immunity in an immunocompetent mouse model of breast cancer

The potential of a bovine adenovirus serotype 3 (BAd3)-based vector to bypass the human adenoviral serotype 5 (HAd5)-specific neutralizing immune response was evaluated in an immunocompetent mouse model of breast cancer. Initially we monitored vector biodistribution, genome persistence, transgene expression, and potential toxicity of HAd-GFP [HAd5 vector expressing green fluorescent protein (GFP)] or BAd-GFP (BAd3 vector expressing GFP) in FVB/n mice bearing tumors. A comparable biodistribution pattern for BAd-GFP and HAd-GFP was evident. In addition, following the development of vector-specific immune responses, animals were inoculated intratumorally (i.t.) with HAd-GFP or BAd-GFP. HAd-GFP immunity did not hamper the transduction and persistence of BAd-GFP into the tumors and other organs, and, similarly, BAd-GFP immunity did not hamper the transduction and persistence of HAd-GFP. Both BAd3 and HAd5 vectors showed relatively higher transgene expression in the presence of heterologous vector immunity. In contrast, the homologous vector immunity was associated with a rapid vector clearance and decline in transgene expression levels. Histopathological changes in BAd-GFP inoculated animals were generally mild with some acute but recoverable hepatic perturbations. Overall, the data suggest the importance of BAd3 vectors for sequential vector administration in overcoming the vector immunity for cancer gene therapy.

Influence of needle gauge on in vivo ultrasound and microbubble-mediated gene transfection

Ultrasound and microbubble-mediated gene transfection are potential tools for safe, site-selective gene therapy. However, preclinical trials have demonstrated a low transfection efficiency that has hindered the progression of the technique to clinical application. In this paper it is shown that simple changes to the method of intravenous injection can lead to an increase in transfection efficiency when using 6-MHz diagnostic ultrasound and the ultrasound contrast agent, SonoVue. By using needles of progressively smaller gauge, i.e., larger internal diameter (ID), from 29 G (ID 0.184 mm) to 25 G (ID 0.31 mm), the transfection of a luciferase plasmid (pGL4.13) was significantly increased threefold in heart-targeted female CD1 mice. In vitro work indicated that the concentration and size distribution of SonoVue were affected by increasing needle gauge. These results suggest that the process of systemic delivery alters the bubble population and adversely affects transfection. This is exacerbated by using high-gauge needles. These findings demonstrate that the needle with the largest possible ID should be used for systemic delivery of microbubbles and genetic material.

Preclinical evaluation of gene delivery methods for the treatment of loco-regional disease in breast cancer

Preclinical results with various gene therapy strategies indicate significant potential for new cancer treatments. However, many therapeutics fail at clinical trial, often due to differences in tissue physiology between animal models and humans, and tumor phenotype variation. Clinical data relevant to treatment strategies may be generated prior to clinical trial through experimentation using intact patient tissue ex vivo. We developed a novel tumor slice model culture system that is universally applicable to gene delivery methods, using a realtime luminescence detection method to assess gene delivery. Methods investigated include viruses (adenovirus [Ad] and adeno-associated virus), lipofection, ultrasound (US), electroporation and naked DNA. Viability and tumor populations within the slices were well maintained for seven days, and gene delivery was qualitatively and quantitatively examinable for all vectors. Ad was the most efficient gene delivery vector with transduction efficiency >50%. US proved the optimal non-viral gene delivery method in human tumor slices. The nature of the ex vivo culture system permitted examination of specific elements. Parameters shown to diminish Ad gene delivery included blood, regions of low viability and secondary disease. US gene delivery was significantly reduced by blood and skin, while tissue hyperthermia improved gene delivery. US achieved improved efficacy for secondary disease. The ex vivo model was also suitable for examination of tissue-specific effects on vector expression, with Ad expression mediated by the CXCR4 promoter shown to provide a tumor selective advantage over the ubiquitously active cytomegalovirus promoter. In conclusion, this is the first study incorporating patient tissue models in comparing gene delivery from various vectors, providing knowledge on cell-type specificity and examining the crucial biological factors determining successful gene delivery. The results highlight the importance of in-depth preclinical assessment of novel therapeutics and may serve as a platform for further testing of current, novel gene delivery approaches.

Multimodality imaging of gene transfer with a receptor-based reporter gene

Gene therapy trials have traditionally used tumor and tissue biopsies for assessing the efficacy of gene transfer. Noninvasive imaging techniques offer a distinct advantage over tissue biopsies in that the magnitude and duration of gene transfer can be monitored repeatedly. Human somatostatin receptor subtype 2 (SSTR2) has been used for the nuclear imaging of gene transfer. To extend this concept, we have developed a somatostatin receptor-enhanced green fluorescent protein fusion construct (SSTR2-EGFP) for nuclear and fluorescent multimodality imaging.

METHODS

An adenovirus containing SSTR2-EGFP (AdSSTR2-EGFP) was constructed and evaluated in vitro and in vivo. SCC-9 human squamous cell carcinoma cells were infected with AdEGFP, AdSSTR2, or AdSSTR2-EGFP for in vitro evaluation by saturation binding, internalization, and fluorescence spectroscopy assays. In vivo biodistribution and nano-SPECT imaging studies were conducted with mice bearing SCC-9 tumor xenografts directly injected with AdSSTR2-EGFP or AdSSTR2 to determine the tumor localization of (111)In-diethylenetriaminepentaacetic acid (DTPA)-Tyr3-octreotate. Fluorescence imaging was conducted in vivo with mice receiving intratumoral injections of AdSSTR2, AdSSTR2-EGFP, or AdEGFP as well as ex vivo with tissues extracted from mice.

RESULTS

The similarity between AdSSTR2-EGFP and wild-type AdSSTR2 was demonstrated in vitro by the saturation binding and internalization assays, and the fluorescence emission spectra of cells infected with AdSSTR2-EGFP was almost identical to the spectra of cells infected with wild-type AdEGFP. Biodistribution studies demonstrated that the tumor uptake of (111)In-DTPA-Tyr3-octreotate was not significantly different (P > 0.05) when tumors (n = 5) were injected with AdSSTR2 or AdSSTR2-EGFP but was significantly greater than the uptake in control tumors. Fluorescence was observed in tumors injected with AdSSTR2-EGFP and AdEGFP in vivo and ex vivo but not in tumors injected with AdSSTR2. Although fluorescence was observed, there were discrepancies between in vivo imaging and ex vivo imaging as well as between nuclear imaging and fluorescent imaging.

CONCLUSION

These studies showed that the SSTR2-EGFP fusion construct can be used for in vivo nuclear and optical imaging of gene transfer.

Adenovirus encoding human platelet-derived growth factor-B delivered to alveolar bone defects exhibits safety and biodistribution profiles favorable for clinical use

Platelet-derived growth factor (PDGF) gene therapy offers promise for tissue engineering of tooth-supporting alveolar bone defects. To date, limited information exists regarding the safety profile and systemic biodistribution of PDGF gene therapy vectors when delivered locally to periodontal osseous defects. The aim of this preclinical study was to determine the safety profile of adenovirus encoding the PDGF-B gene (AdPDGF-B) delivered in a collagen matrix to periodontal lesions. Standardized alveolar bone defects were created in rats, followed by delivery of matrix alone or containing AdPDGF-B at 5.5 x 10(8) or 5.5 x 10(9) plaque-forming units/ml. The regenerative response was confirmed histologically. Gross clinical observations, hematology, and blood chemistries were monitored to evaluate systemic involvement. Bioluminescence and quantitative polymerase chain reaction were used to assess vector biodistribution. No significant histopathological changes were noted during the investigation. Minor alterations in specific hematological and blood chemistries were seen; however, most parameters were within the normal range for all groups. Bioluminescence analysis revealed vector distribution at the axillary lymph nodes during the first 2 weeks with subsequent return to baseline levels. AdPDGF-B was well contained within the localized osseous defect area without viremia or distant organ involvement. These results indicate that AdPDGF-B delivered in a collagen matrix exhibits acceptable safety profiles for possible use in human clinical studies.

Viral shedding after p53 adenoviral gene therapy in 10 cases of esophageal cancer

We detected adenoviral DNA fragments in excretions of 10 esophageal cancer patients by DNA-PCR after tumor injection of Ad-CMV-vector. A total of 220 samples consisting of feces, gargling saliva, urine, and blood plasma were assessed. A total of 29.7% of feces samples and 13.2% of gargling saliva samples were positive for adenoviral DNA fragments, but 89.7% of the positive feces samples and all of the positive gargling saliva samples turned negative on day 12 after tumor injection. Although adenoviral DNA fragments may be pathogen-free, patients' feces and gargling saliva contain adenoviral DNA fragments for 12 days after injection.

Novel strategies to augment genetically delivered immunotoxin molecular therapy for cancer therapy

Immunotoxin therapy is a promising molecular cancer treatment strategy. Its main advantage is seletive cytotoxicity towards tumor cells and minimal toxicity in normal tissues. However, a short half-life and rapid clearance severely hampers its clinical application. We report here a novel genetic approach in which a recombinant adenovirus vector was used to deliver an immunotoxin gene e23(scFv)-PE40 targeted to the oncogene c-erbB-2 (also known as Her2/neu). This vector, when combined with a low dose of a conditionally replicative adenovirus vector (CRAd), has enhanced tumor-killing ability either alone or in combination with the chemotherapeutic agent etoposide. Our data show that low-dose CRAd facilitated the replication of replication-deficient Ad-e23(scFv)-PE40 up to 6-20 times and the transcription of e23(scFv)-PE40 gene up to 12 times. Moreover, etoposide increased the e23(scFv)-PE40 transcription up to 8.5 times. Furthermore, we show that systemic application of Ad-e23(scFv)-PE40 and enhanced expression of the immunotoxin gene was well tolerated as determined by serum biochemical markers and histological examination of most vital organs. Taken together, our data support a novel genetic immunotoxin delivery approach that may yield enhanced efficacy against a variety of Her2/neu-expressing tumors.

PDGF-B gene therapy accelerates bone engineering and oral implant osseointegration

Platelet-derived growth factor-BB (PDGF-BB) stimulates repair of healing-impaired chronic wounds such as diabetic ulcers and periodontal lesions. However, limitations in predictability of tissue regeneration occur due in part to transient growth factor bioavailability in vivo. Here, we report that gene delivery of PDGF-B stimulates repair of oral implant extraction socket defects. Alveolar ridge defects were created in rats and were treated at the time of titanium implant installation with a collagen matrix containing an adenoviral (Ad) vector encoding PDGF-B (5.5×10⁸ or 5.5×10⁹ pfu/ml), Ad encoding luciferase (Ad-Luc; 5.5×10⁹ pfu/ml; control) or recombinant human PDGF-BB protein (rhPDGF-BB, 0.3 mg/ml). Bone repair and osseointegration were measured via backscattered SEM, histomorphometry, microcomputed tomography, and biomechanical assessments. Further, a panel of local and systemic safety assessments was performed. Results demonstrated bone repair was accelerated by Ad-PDGF-B and rhPDGF-BB delivery compared to Ad-Luc, with the high dose of Ad-PDGF-B more effective than the low dose. No significant dissemination of the vector construct or alteration of systemic parameters was noted. In summary, gene delivery of Ad-PDGF-B demonstrates regenerative and safety capabilities for bone tissue engineering and osseointegration in alveolar bone defects comparable to rhPDGF-BB protein delivery in vivo.

Dynamic distribution and expression in vivo of the human interferon gamma gene delivered by adenoviral vector

BACKGROUND

We previously found that r-hu-IFNgamma exerts a potent anti-tumor effect on human nasopharyngeal carcinoma xenografts in vivo. Considering the fact that the clinical use of recombinant IFNgamma is limited by its short half-life and systemic side effects, we developed a recombinant adenovirus, Ad-IFNgamma.

METHODS

Dynamic distribution of the adenovirus vector and expression of IFNgamma were evaluated by Q-PCR and ELISA after intratumoral administration of Ad-IFNgamma into CNE-2 xenografts.

RESULTS

Ad-IFNgamma DNA was mainly enriched in tumors where the Ad-IFNgamma DNA was injected (P < 0.05, compared to blood or parenchymal organs), as well as in livers (P < 0.05). Concentrations of Ad-IFNgamma DNA in other organs and blood were very low. Intratumoral Ad-IFNgamma DNA decreased sharply at high concentrations (9 x 10(5) copies/microg tissue DNA), and slowly at lower concentrations (1.7-2.9 x 10(5) copies/microg tissue DNA). IFNgamma was detected in the tumors and parenchymal organs. The concentration of IFNgamma was highest in the tumor (P < 0.05), followed by the liver and kidney (P < 0.05). High-level intratumoral expression of IFNgamma was maintained for at least 7 days, rapidly peaking on day 3 after injection of Ad-IFNgamma DNA.

CONCLUSION

An IFNgamma gene delivered by an adenoviral vector achieved high and consistent intratumoral expression. Disseminated Ad-IFNgamma DNA and the transgene product were mainly enriched in the liver.

Drug-virus interaction: effect of administration of recombinant adenoviruses on the pharmacokinetics of docetaxel in a rat model

Modern cancer therapy combines recombinant viruses with traditional chemotherapeutic agents that are metabolized by hepatic cytochrome P450 3A4 (CYP3A4). A single dose of recombinant adenovirus (Ad) expressing beta-galactosidase (AdlacZ) significantly alters CYP3A2, the correlate of CYP3A4, in rats for 14 days. Recombinant adenovirus expressing human p53 (Adp53) also suppresses CYP3A2. Plasma clearance of docetaxel (DTX) in animals given AdlacZ (3.38 ± 0.22 L/h/kg) was significantly lower than that of those given DTX alone (6.41 ± 1.10 L/h/kg, p≤0.05). Area under the plasma concentration-time curve of DTX in rats given AdlacZ (2,987.37 ± 197.97 ng/ml/h) was significantly greater than those given drug alone (1,666.59 ± 317.04 ng/ml/h, p≤0.05). Both viruses prolonged DTX half-life (t_1/2). Ad infection may cause significant variability in the pharmacokinetics and pharmacodynamics of anti-cancer agents and should be considered when designing therapeutic regimens for patients with viral infection and those enrolled in clinical trials employing recombinant viruses.

Relaxin treatment of solid tumors: effects on electric field-mediated gene delivery

Pulsed electric fields have been shown to enhance interstitial transport of plasmid DNA (pDNA) in solid tumors in vivo. However, the extent of enhancement is still limited partly due to the collagen component in extracellular matrix. To this end, effects of collagen remodeling on interstitial electrophoresis were investigated by pretreatment of tumor-bearing mice with a recombinant human relaxin (rh-Rlx). In the study, two tumor lines (4T1 and B16.F10) were examined and implanted s.c. to establish two murine models: dorsal skin-fold chamber (DSC) and hind leg. Effects of rh-Rlx on pDNA electrophoresis were measured either directly in the DSC model or indirectly in the hind leg model via reporter gene expression. It was observed that rh-Rlx treatment reduced collagen levels in the hind leg tumors but not in the DSC tumors. The observation correlated with the results from electromobility experiments, where rh-Rlx treatment enhanced transgene expression in 4T1 hind leg tumors but did not increase the electromobility of pDNA in the DSC tumors. In addition, it was observed that pDNA binding to collagen could block its diffusion in collagen gel in vitro. These observations showed that effects of rh-Rlx on the collagen content depended on microenvironment in solid tumors and that rh-Rlx treatment would enhance electric field-mediated gene delivery only if it could effectively reduce the collagen content in collagen-rich tumors.

Ultrasound mediated delivery of drugs and genes to solid tumors

It has long been shown that therapeutic ultrasound can be used effectively to ablate solid tumors, and a variety of cancers are presently being treated in the clinic using these types of ultrasound exposures. There is, however, an ever-increasing body of preclinical literature that demonstrates how ultrasound energy can also be used non-destructively for increasing the efficacy of drugs and genes for improving cancer treatment. In this review, a summary of the most important ultrasound mechanisms will be given with a detailed description of how each one can be employed for a variety of applications. This includes the manner by which acoustic energy deposition can be used to create changes in tissue permeability for enhancing the delivery of conventional agents, as well as for deploying and activating drugs and genes via specially tailored vehicles and formulations.

Field distribution and DNA transport in solid tumors during electric field-mediated gene delivery

Gene therapy has a great potential in cancer treatment. However, the efficacy of cancer gene therapy is currently limited by the lack of a safe and efficient means to deliver therapeutic genes into the nucleus of tumor cells. One method under investigation for improving local gene delivery is based on the use of pulsed electric field. Despite repeated demonstration of its effectiveness in vivo, the underlying mechanisms behind electric field-mediated gene delivery remain largely unknown. Without a thorough understanding of these mechanisms, it will be difficult to further advance the gene delivery. In this review, the electric field-mediated gene delivery in solid tumors will be examined by following individual transport processes that must occur in vivo for a successful gene transfer. The topics of examination include: (i) major barriers for gene delivery in the body, (ii) distribution of electric fields at both cell and tissue levels during the application of external fields, and (iii) electric field-induced transport of genes across each of the barriers. Through this approach, the review summarizes what is known about the mechanisms behind electric field-mediated gene delivery and what require further investigations in future studies.

High intensity focused ultrasound-induced gene activation in solid tumors

In this work, the activation of heat-sensitive trans-gene by high-intensity focused ultrasound (HIFU) in a tumor model was investigated. 4T1 cancer cells (2 x 10(6)) were inoculated subcutaneously in the hind limbs of Balb/C mice. The tumors were subsequently transducted on day 10 by intratumoral injection of a heat-sensitive adenovirus vector (Adeno-hsp70B-Luc at 2 x 10(8) pfu/tumor). On day 11, the tumors were heated to a peak temperature of 55, 65, 75, or 85 degrees C within 10-30 s at multiple sites around the center of the tumor by a 1.1- or 3.3-MHz HIFU transducer. Inducible luciferase gene expression was increased from 15-fold to 120-fold of the control group following 1.1-MHz HIFU exposure. Maximum gene activation (120-fold) was produced at a peak temperature of 65-75 degrees C one day following HIFU exposure and decayed to baseline within 7 days. HIFU-induced gene activation (75 degrees C-10 s) could be further improved by using a 3.3-MHz transducer and a dense scan strategy to 170-fold. Thermal stress, rather than nonthermal mechanical stress, was identified as the primary physical mechanism for HIFU-induced gene activation in vivo. Overall, these observations open up the possibility for combining HIFU thermal ablation with heat-regulated gene therapy for cancer treatment.

Differential biodistribution of adenoviral vector in vivo as monitored by bioluminescence imaging and quantitative polymerase chain reaction

A better understanding of the in vivo biodistribution of adenoviral vectors would enable the researcher to anticipate potential side effects due to off-targeted site of transduction, and aid in the strategic design of gene therapy. We combined real-time polymerase chain reaction with in vivo optical imaging to examine viral transduction in liver, lung, spleen, kidney, prostate, and lymph nodes. A replication-deficient serotype 5 adenoviral vector expressing the firefly luciferase gene under the control of a constitutive cytomegalovirus promoter was administered in vivo via different routes. Intravenous and intraperitoneal injections resulted in greatest gene expression and viral DNA in the liver, whereas intraperitoneal injections led to a greater extent of gene delivery to the prostate. Although prostate-directed injection resulted in dominant gene expression in the targeted site, leakage of the vector to other organs was also observed. Vector injection into the lymphatic-rich paw tissue or the subcutaneous tissue of shoulder or chest followed the expected lymphatic drainage pattern, resulting in the accumulation of viral vector in ipsilateral brachial and axillary lymph nodes. Collectively, this study demonstrates that each tissue retains various amounts of adenoviral vector, depending on the route of administration. This knowledge is useful in the strategic design and implementation of adenovirus-mediated gene therapies.

Preclinical safety and biodistribution of adenovirus-based cancer vaccines after intradermal delivery

The recombinant adenoviral (Ad) vector is being considered as a cancer vaccine platform because it efficiently induces immune responses to tumor antigens by intradermal immunization. The aims of this study were to evaluate the potential toxicities and biodistribution after a single dose or six weekly intradermal doses of Ad2/gp100v2 and Ad2/MART-1v2, which encode tumor-associated antigens gp100 and MelanA/MART-1, respectively. The only dose-related toxicities associated with intradermal administration of these Ad vectors were inflammatory cell infiltrates in the draining lymph nodes and injection sites that persisted 83 days after administration. The biodistribution of Ad DNA as detected by real-time polymerase chain reaction was largely confined to the injection sites and draining lymph nodes of mice treated with either a single dose or multiple doses of Ad vector and in the spleens of mice treated with multiple doses of Ad vector. Adenoviral DNA was transiently detected in the bone marrow, lung, or blood of only one animal for each site and was below the limit of assay quantification (<10 copies/microg DNA). The vector persisted in the skin and lymph nodes as long as 92 days after the last dose. We conclude that Ad vectors delivered by intradermal administration provide a safe, genetic vaccine delivery platform that induces desirable immune responses at the immunization sites and the lymph nodes that, ultimately, result in immune responses specific to the tumor antigens.

Nonlinear dependence of hydraulic conductivity on tissue deformation during intratumoral infusion

Efficiency of intratumoral infusion for drug and gene delivery depends on intrinsic tissue structures as well as infusion-induced changes in these structures. To this end, we investigated effects of infusion pressure (P(inf)) and infusion-induced tissue deformation on infusion rate (Q) in three mouse tumor models (B16.F10, 4T1, and U87) and developed a poroelastic model for interpreting data and understanding mechanisms of fluid transport in tumors. The collagen concentrations in these tumors were 2.9+/-1.2, 12.2+/-0.9, and 18.1+/-3.5 microg/mg wet wt. of tissues, respectively. During the infusion, there existed a threshold infusion pressure (P(t)), below which fluid flow could not be initiated. The values of P(t) for these tumors were 7.36, 36.8, and 29.4 mmHg, respectively. Q was a bell-shaped function of P(inf) in 4T1 tumors but increased monotonically with increasing P(inf) in other tumors. These observations were consistent with results from numerical simulations based on the poroelastic model, suggesting that both the existence of P(t) and the nonlinear relationships between Q and P(inf) could be explained by infusion-induced tissue deformation that anisotropically affected the hydraulic conductivity of tissues. These results may be useful for further investigations of intratumoral infusion of drugs and genes.

Delivery of viral vectors to tumor cells: extracellular transport, systemic distribution, and strategies for improvement

It is a challenge to deliver therapeutic genes to tumor cells using viral vectors because (i) the size of these vectors are close to or larger than the space between fibers in extracellular matrix and (ii) viral proteins are potentially toxic in normal tissues. In general, gene delivery is hindered by various physiological barriers to virus transport from the site of injection to the nucleus of tumor cells and is limited by normal tissue tolerance of toxicity determined by local concentrations of transgene products and viral proteins. To illustrate the obstacles encountered in the delivery and yet limit the scope of discussion, this review focuses only on extracellular transport in solid tumors and distribution of viral vectors in normal organs after they are injected intravenously or intratumorally. This review also discusses current strategies for improving intratumoral transport and specificity of viral vectors.

Effects of rate, volume, and dose of intratumoral infusion on virus dissemination in local gene delivery

Recent studies have shown that up to 90% of viral vectors could disseminate to normal organs following intratumoral infusion. The amount of dissemination might be dependent on the infusion conditions. Therefore, we investigated the effects of infusion rate, volume, and dose on transgene expression in liver and tumor tissues after intratumoral infusion of an adenoviral vector encoding luciferase. Luciferase expression was determined through bioluminescence intensity measurement. We observed that the luciferase expression in the liver was independent of the infusion rate but increased with the infusion dose, whereas the luciferase expression in the tumor was a bell-shaped function of the infusion rate. The latter observation was consistent with the distribution pattern of Evans blue-labeled albumin after its solution was infused into tumors at the same infusion rates. We also observed that the infusion volume could affect luciferase expression in the tumor but not in the liver. These observations implied that virus dissemination was determined mainly by the infusion dose, whereas the amount of transgene expression in the tumor depended on the distribution volume of viral vectors in the tumor as well as the infusion dose.

A novel method for viral gene delivery in solid tumors

Intratumoral infusion is the most commonly used method for viral gene delivery in clinical trials for cancer treatment. However, a potential problem in this approach is that viral vectors may disseminate from tumor to normal tissues during and after the infusion. To reduce the dissemination, we developed a novel method based on a biocompatible polymer, poloxamer 407, which could significantly increase the viscosity of virus suspension when the temperature was changed from 4 degrees C to 37 degrees C. With this method, we could significantly increase transgene expression in solid tumors and reduce virus dissemination by 2 orders of magnitude after intratumoral infusion of adenoviral vectors. The mechanism of reduction was likely to be that the viscous poloxamer solution blocked convection of viral vectors in the interstitial space and the lumen of microvessels in the vicinity of the infusion site. This method has a potential to be used in the clinic for enhancing efficacy and reducing toxicity in viral gene therapy.