Targeted in vivo knock-in of human alpha-1-antitrypsin cDNA using adenoviral delivery of CRISPR/Cas9

Serum deficiency diseases such as alpha-1-antitrypsin deficiency are characterized by reduced function of serum proteins, caused by deleterious genetic mutations. These diseases are promising targets for genetic interventions. Gene therapies using viral vectors have been used to introduce correct copies of the disease-causing gene in preclinical and clinical studies. However, these studies highlighted that disease-alleviating gene expression is lost over time. Integration into a specific chromosomal site could provide lasting therapeutic expression to overcome this major limitation. Additionally, targeted integration could avoid detrimental mutagenesis associated with integrative vectors, such as tumorigenesis or functional gene perturbation. To test if adenoviral vectors can facilitate long-term gene expression through targeted integration, we somatically incorporated the human alpha-1-antitrypsin gene into the ROSA26 "safe harbor" locus in murine livers, using CRISPR/Cas9. We found adenoviral-mediated delivery of CRISPR/Cas9 achieved gene editing outcomes persisting over 200 days. Furthermore, gene knock-in maintained greater levels of the serum protein than provided by episomal expression. Importantly, our "knock-in" approach is generalizable to other serum proteins and supports in vivo cDNA replacement therapy to achieve stable gene expression.

A new model of multi-visceral and bone metastatic prostate cancer with perivascular niche targeting by a novel endothelial specific adenoviral vector

While modern therapies for metastatic prostate cancer (PCa) have improved survival they are associated with an increasingly prevalent entity, aggressive variant PCa (AVPCa), lacking androgen receptor (AR) expression, enriched for cancer stem cells (CSCs), and evidencing epithelial-mesenchymal plasticity with a varying extent of neuroendocrine transdifferentiation. Parallel work revealed that endothelial cells (ECs) create a perivascular CSC niche mediated by juxtacrine and membrane tethered signaling. There is increasing interest in pharmacological metastatic niche targeting, however, targeted access has been impossible. Here, we discovered that the Gleason 7 derived, androgen receptor negative, IGR-CaP1 cell line possessed some but not all of the molecular features of AVPCa. Intracardiac injection into NOD/SCID/IL2Rg ^-/− (NSG) mice produced a completely penetrant bone, liver, adrenal, and brain metastatic phenotype; noninvasively and histologically detectable at 2 weeks, and necessitating sacrifice 4-5 weeks post injection. Bone metastases were osteoblastic, and osteolytic. IGR-CaP1 cells expressed the neuroendocrine marker synaptophysin, near equivalent levels of vimentin and e-cadherin, all of the EMT transcription factors, and activation of NOTCH and WNT pathways. In parallel, we created a new triple-targeted adenoviral vector containing a fiber knob RGD peptide, a hexon mutation, and an EC specific ROBO4 promoter (Ad.RGD.H5/3.ROBO4). This vector was expressed in metastatic microvessels tightly juxtaposed to IGR-CaP1 cells in bone and visceral niches. Thus, the combination of IGR-CaP1 cells and NSG mice produces a completely penetrant metastatic PCa model emulating end-stage human disease. In addition, the metastatic niche access provided by our novel Ad vector could be therapeutically leveraged for future disease control or cure.

Abstract 5210: Creation of endothelial-targeted adenoviral vectors for genetic engineering of the metastatic tumor microenvironment

The endothelium is an attractive gene therapy target for metastatic cancer, providing access to systemic tumors. Previous work has focused on either viral entry/attachment (transductional targeting), or cell type specific enhancer promoter vector transgene expression regulation (transcriptional targeting). While previous studies demonstrated endothelial targeting, the tumor wide extent and transgene expression level quantification have been uncertain. Indeed, obtaining robust and stringent tumor expression has been challenging due to: insufficient transduction, focal rather than widespread intratumoral vascular expression, viral particle liver sequestration, and host preformed immunity. We developed a set of adenoviral vectors, containing 3 kb of the human ROBO4 enhancer/promoter, that are expressed at high levels throughout tumor vasculature. We now have three vectors representing four tiers of genetic modification. Transgenes encoding fluorescent proteins allowed us to quantify endothelial expression frequency by image analysis, and expression level using whole tissue Western blotting. Our first vector was Ad5.ROBO4. Compared with Ad5.CMV, Ad5.ROBO4 evidenced complete retargeting from hepatocytes to low-level expression in host organ and tumor endothelial cells. Warfarin-mediated hepatocyte detargeting produced a striking increase in tumor and bone marrow sinusoidal endothelial expression, without change in other host organs. Our second vector is Ad.RGD.H5/H3.ROBO4. Insertion of a cyclized RGD peptide in the fiber/knob HI loop engages enhanced tumor endothelial transduction via αv/β3 and αv/β5. Swapping hexon hypervariable regions responsible for Ad Type 5-Factor X binding with corresponding regions from serotype 3 enables marked diminution of hepatocyte sequestration. Use of the ROBO4 enhancer promoter produces high-level pan-intratumoral vascular expression particularly in cancers with markedly elevated VEGF production, such as orthotopic and metastatic renal cell carcinoma, orthotopic colonic liver metastases, and prostate cancer bone, brain, and liver metastases. Most striking, was enhancement of Ad.RGD.H5/H3.ROBO4 vector expression within interior tumor regions undergoing hypoxic necrosis; regions notoriously resistant to radiation or chemotherapies. Our third vector contains a polycistronic array, enabling triple transgene expression from a single vector within the tumor vasculature. Thus, we have panel of endothelial-targeted vectors with distinctive vascular tropism for use in cancers metastatic to individual host organs. These vectors enable expression of a palette of transgenes that can manipulate the tumor microenvironment to achieve metastatic growth inhibition alone, or “staggered” with chemo- or irradiation therapies.

Note: This abstract was not presented at the meeting.

Citation Format: Zhi Hong Lu, Sergey Kaliberov, Lyudmila Kaliberova, Rebecca E. Sohn, Yingqui Du, David T. Curiel, Jeffrey M. Arbeit. Creation of endothelial-targeted adenoviral vectors for genetic engineering of the metastatic tumor microenvironment. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 5210. doi:10.1158/1538-7445.AM2015-5210

Altered expression of 15-hydroxyprostaglandin dehydrogenase in tumor-infiltrated CD11b myeloid cells: a mechanism for immune evasion in cancer

Many cancers are known to produce high amounts of PGE(2), which is involved in both tumor progression and tumor-induced immune dysfunction. The key enzyme responsible for the biological inactivation of PGE(2) in tissue is NAD(+)-dependent 15-hydroxyprostaglandin dehydrogenase (15-PGDH). It is well established that cancer cells frequently show down-regulated expression of 15-PGDH, which plays a major role in catabolism of the PGE(2). Here we demonstrate that tumor-infiltrated CD11b cells are also deficient for the 15-PGDH gene. Targeted adenovirus-mediated delivery of 15-PGDH gene resulted in substantial inhibition of tumor growth in mice with implanted CT-26 colon carcinomas. PGDH-mediated antitumor effect was associated with attenuated tumor-induced immune suppression and substantially reduced secretion of immunosuppressive mediators and cytokines such as PGE(2), IL-10, IL-13, and IL-6 by intratumoral CD11b cells. We show also that introduction of 15-PGDH gene in tumor tissue is sufficient to redirect the differentiation of intratumoral CD11b cells from immunosuppressive M2-oriented F4/80(+) tumor-associated macrophages (TAM) into M1-oriented CD11c(+) MHC class II-positive myeloid APCs. Notably, the administration of the 15-PGDH gene alone demonstrated a significant therapeutic effect promoting tumor eradication and long-term survival in 70% of mice with preestablished tumors. Surviving mice acquired antitumor T cell-mediated immune response. This study for the first time demonstrates an important role of the 15-PGDH in regulation of local antitumor immune response and highlights the potential to be implemented to enhance the efficacy of cancer therapy and immunotherapy.

Vascular endothelial growth factor promoter-based conditionally replicative adenoviruses for pan-carcinoma application

Treatment of advanced lung cancer is one of the major challenges in current medicine because of the high morbidity and mortality of the disease. Advanced stage lung cancer is refractory to conventional therapies and has an extremely poor prognosis. Thus, new therapeutic approaches are needed. Lung tumor formation depends on angiogenesis in which the vascular endothelial growth factor (VEGF) produced by cancer cells plays a pivotal role. Neutralizing VEGF with a soluble VEGF receptor suppresses tumor growth; however, the anticancer effect with this therapy is weakened after the intratumoral vascular network is completed. In this study, we turned the expression of VEGF by tumors to therapeutic advantage using a conditionally replication-competent adenovirus (CRAd) in which the expression of E1 is controlled by the human VEGF promoter. This virus achieved good levels of viral replication in lung cancer cells and induced a substantial anticancer effect in vitro and in vivo. As a further enhancement, the cancer cell killing effect was improved with tropism modification of the virus to express the knob domain of Ad3, which improved infectivity for cancer cells. These VEGF promoter-based CRAds also showed a significant cell killing effect for various types of cancer lines other than lung cancer. Conversely, the VEGF promoter has low activity in normal tissues, and the CRAd caused no damage to normal bronchial epithelial cells. Since tumor-associated angiogenesis via VEGF signalling is common in many types of cancers, these CRAds may be applicable to a wide range of tumors. We concluded that VEGF promoter-based CRAds have the potential to be an effective strategy for cancer treatment.

Transcriptional targeting of adenoviral vector through the CXCR4 tumor-specific promoter

Adenoviral vectors are considered to be good gene delivery vectors for cancer gene therapy due to their wide host tissue range and cell cycle-independent infectivity. However, the disadvantages include the lack of specificity for cancer cells and the high liver accumulation in vivo. The human CXCR4 gene is expressed at high levels in many types of cancers, but is repressed in the liver. We explored the CXCR4 promoter as a candidate to restrict adenoviral transgene expression to tumor cells with a low expression in host tissues. The luciferase activities in multiple cancer cell lines infected with recombinant adenovirus reAdGL3BCXCR4 or the control vector reAdGL3BCMV revealed that the CXCR4 promoter exhibited relatively high transcriptional activity in a breast cancer cell line, MDA-MB-361, and two ovarian cancer cell lines, OVCAR-3 and SKOV3. ip1, 65% (P=0.0087), 16.7% (P=0.1) and 20% (P=0.0079) compared to that of the CMV promoter, respectively, and low expression, 4.9 and 0.1%, respectively, in both normal cell lines HFBC and HMEC. In addition, CXCR4 had a low expression of luciferase (0.32%) compared to that of the CMV promoter in mouse liver in vivo. The data also revealed that the CXCR4 promoter was a stronger tumor-specific promoter (TSP) than the Cox-2M promoter in primary melanomas obtained from two patients. The CXCR4 promoter is shown to have a 'tumor-on' and 'liver-off' status in vitro and in vivo, and CXCR4 may prove to be a good candidate TSP for cancer gene therapy approaches for melanoma and breast cancers.

Enhanced apoptosis following treatment with TRA-8 anti-human DR5 monoclonal antibody and overexpression of exogenous Bax in human glioma cells

Specific activation of apoptosis in tumor cells offers a promising approach for cancer therapy. Induction of apoptosis leads to activation of specific proteases. Two major pathways for caspase activation in mammalian cells have been described. One apoptotic pathway involves members of the tumor necrosis factor family of cytokine receptors (eg death receptor 5 (DR5)). The other pathway is controlled by the Bcl-2 family of proteins. The purpose of this study was to investigate whether increased apoptosis occurs in human glioma cells following infection with a recombinant adenoviral vector encoding the human Bax gene under the control of human vascular endothelial growth factor (VEGF) promoter element (AdVEGFBax) in combination with an anti-human DR5 monoclonal antibody (TRA-8). Specific overexpression of exogenous Bax protein induced apoptosis and cell death in glioma cell lines, through activation of both caspase-8 and -9, leading to activation of downstream caspase-3. The relative sensitivity to AdVEGFBax for the glioma cell lines was U251MG>U373MG>U87MG>D54MG. The recently characterized TRA-8 monoclonal antibody induces apoptosis of most TRAIL-sensitive tumor cells by specific binding to DR5 receptors on the cellular membrane. TRA-8 induced rapid apoptosis and cell death in glioma cells, but did not demonstrate detectable cytotoxicity of primary normal human astrocytes. The efficiency of TRA-8-induced apoptosis was variable in different glioma cell lines. The relative sensitivity to TRA-8 was U373MG>U87MG>U251MG>D54MG. The combination of TRA-8 treatment and overexpression of Bax overcame TRA-8 resistance of glioma cells in vitro. Cell viability of U251MG cells was 71.1% for TRA-8 (100 ng/ml) alone, 75.9% for AdVEGFBax (5 MOI) alone and 41.1% for their combination as measured by MTS assay. Similar enhanced apoptosis results were obtained for the other glioma cell lines. In vivo studies demonstrated that the combined treatment significantly (P<0.05) suppressed the growth of U251MG xenografts and produced 60% complete tumor regressions without recurrence. These data suggest that the combination of TRA-8 treatment with specific overexpression of Bax using AdVEGFBax may be an effective approach for the treatment of human malignant gliomas.

Combined transductional and transcriptional targeting improves the specificity of transgene expression in vivo

The promise of gene therapy for health care will not be realized until gene delivery systems are capable of achieving efficient, cell-specific gene delivery in vivo. Here we describe an adenoviral system for achieving cell-specific transgene expression in pulmonary endothelium. The combination of transductional targeting to a pulmonary endothelial marker (angiotensin-converting enzyme, ACE) and an endothelial-specific promoter (for vascular endothelial growth factor receptor type 1, flt-1) resulted in a synergistic, 300,000-fold improvement in the selectivity of transgene expression for lung versus the usual site of vector sequestration, the liver. This combined approach should be useful for the design of other gene delivery systems.

A novel system for mitigation of ectopic transgene expression induced by adenoviral vectors

Adenoviral (Ad) vectors are good candidates for gene therapy in view of their high in vivo gene delivery efficiency. However, greater control over the tissue distribution of transgene expression is required to avoid potentially deleterious effects in non-target organs. In this regard, the liver is particularly at risk due to the high natural tropism of Ad for this organ, where dose limiting toxicity has been seen due to toxic transgene expression. We hypothesized that the cre/loxP system could be utilized to reduce unintended transgene expression at this site. This concept was tested using an Ad vector (AdLCLLL) carrying a reporter gene cassette in which the promoter and luciferase gene were flanked by LoxP sequences. Co-administration of this vector with a second vector carrying the cre recombinase gene in vitro and in vivo resulted in specific down-regulation of transgene expression. This novel approach thus has the potential to improve the safety of gene therapy strategies that rely upon the delivery of genes which may be hepatotoxic.