Cytotoxicity associated with artemis overexpression after lentiviral vector-mediated gene transfer

Parathyroid hormone 1 receptor signaling mediates breast cancer metastasis to bone in mice

Bone metastases are a common complication of breast cancer. We have demonstrated that intermittent administration of parathyroid hormone (PTH[1-34]) reduces the incidence of bone metastases in murine models of breast cancer by acting on osteoblasts to alter the bone microenvironment. Here, we examined the role of signaling mediated by PTH 1 receptor (PTH1R) in both osteoblasts and breast cancer cells in influencing bone metastases. In mice with impaired PTH1R signaling in osteoblasts, intermittent PTH did not reduce bone metastasis. Intermittent PTH also did not reduce bone metastasis when expression of PTH1R was knocked down in 4T1 murine breast cancer cells by shRNA. In 4T1 breast cancer cells, PTH decreased expression of PTH-related protein (PTHrP), implicated in the vicious cycle of bone metastases. Knockdown of PTHrP in 4T1 cells significantly reduced migration toward MC3T3-E1 osteoblasts, and migration was further inhibited by treatment with intermittent PTH. Conversely, overexpression of PTHrP in 4T1 cells increased migration toward MC3T3-E1 osteoblasts, and this was not inhibited by PTH. In conclusion, PTH1R expression is crucial in both osteoblasts and breast cancer cells for PTH to reduce bone metastases, and in breast cancer cells, this may be mediated in part by suppression of PTHrP.

AFB1 and OTA Promote Immune Toxicity in Human LymphoBlastic T Cells at Transcriptomic Level

Aflatoxin B1 (AFB1) and ochratoxin A (OTA) are typical contaminants of food and feed, which have serious implications for human and animal health, even at low concentrations. Therefore, a transcriptomic study was carried out to analyze gene expression changes triggered by low doses of AFB1 and OTA (100 nM; 7 days), individually and combined, in human lymphoblastic T cells. RNA-sequencing analysis showed that AFB1-exposure resulted in 99 differential gene expressions (DEGs), while 77 DEGs were obtained in OTA-exposure and 3236 DEGs in the combined one. Overall, 16% of human genome expression was altered. Gene ontology analysis revealed, for all studied conditions, biological processes and molecular functions typically associated with the immune system. PathVisio analysis pointed to ataxia telangiectasia mutated signaling as the most significantly altered pathway in AFB1-exposure, glycolysis in OTA-exposure, and ferroptosis in the mixed condition (Z-score > 1.96; adjusted p-value ≤ 0.05). Thus, the results demonstrated the potential DNA damage caused by AFB1, the possible metabolic reprogramming promoted by OTA, and the plausible cell death with oxidative stress prompted by the mixed exposure. They may be considered viable mechanisms of action to promote immune toxicity in vitro.

In Vivo Analysis of Heterogeneous Extracellular Vesicles Using a Red-Shifted Bioluminescence Resonance Energy Transfer Reporter Protein

Current methods for characterizing the biodistribution of extracellular vesicles (EVs) are not sensitive enough to track EVs in vivo, despite significant advances over the past decade. Commonly used lipophilic fluorescent dyes are convenient, but lack specificity and yield inaccurate spatiotemporal images in the long-term tracking of EVs. In contrast, protein-based fluorescent or bioluminescent EV reporters have more accurately revealed their distribution in cells and mouse models. Here, we describe a red-shifted bioluminescence resonance energy transfer (BRET) EV reporter, PalmReNL, to analyze the trafficking of small EVs (<200 nm; sEVs) and medium/large EVs (>200 nm; m/lEVs) in mice. Its advantages are that (i) background signals in bioluminescence imaging (BLI) are negligible and (ii) the photons PalmReNL emits have spectral wavelengths longer than 600 nm and can more efficiently penetrate tissues than reporters emitting shorter wavelength light.

Lentiviral Gene Therapy for Artemis-Deficient SCID

BACKGROUND

The DNA-repair enzyme Artemis is essential for rearrangement of T- and B-cell receptors. Mutations in DCLRE1C, which encodes Artemis, cause Artemis-deficient severe combined immunodeficiency (ART-SCID), which is poorly responsive to allogeneic hematopoietic-cell transplantation.

METHODS

We carried out a phase 1-2 clinical study of the transfusion of autologous CD34+ cells, transfected with a lentiviral vector containing DCLRE1C, in 10 infants with newly diagnosed ART-SCID. We followed them for a median of 31.2 months.

RESULTS

Marrow harvest, busulfan conditioning, and lentiviral-transduced CD34+ cell infusion produced the expected grade 3 or 4 adverse events. All the procedures met prespecified criteria for feasibility at 42 days after infusion. Gene-marked T cells were detected at 6 to 16 weeks after infusion in all the patients. Five of 6 patients who were followed for at least 24 months had T-cell immune reconstitution at a median of 12 months. The diversity of T-cell receptor β chains normalized by 6 to 12 months. Four patients who were followed for at least 24 months had sufficient B-cell numbers, IgM concentration, or IgM isohemagglutinin titers to permit discontinuation of IgG infusions. Three of these 4 patients had normal immunization responses, and the fourth has started immunizations. Vector insertion sites showed no evidence of clonal expansion. One patient who presented with cytomegalovirus infection received a second infusion of gene-corrected cells to achieve T-cell immunity sufficient for viral clearance. Autoimmune hemolytic anemia developed in 4 patients 4 to 11 months after infusion; this condition resolved after reconstitution of T-cell immunity. All 10 patients were healthy at the time of this report.

CONCLUSIONS

Infusion of lentiviral gene-corrected autologous CD34+ cells, preceded by pharmacologically targeted low-exposure busulfan, in infants with newly diagnosed ART-SCID resulted in genetically corrected and functional T and B cells. (Funded by the California Institute for Regenerative Medicine and the National Institute of Allergy and Infectious Diseases; ClinicalTrials.gov number, NCT03538899.).

Gene Therapy for Primary Immunodeficiency

Over the past 3 decades, there has been significant progress in refining gene therapy technologies and procedures. Transduction of hematopoietic stem cells ex vivo using lentiviral vectors can now create a highly effective therapeutic product, capable of reconstituting many different immune system dysfunctions when reinfused into patients. Here, we review the key developments in the gene therapy landscape for primary immune deficiency, from an experimental therapy where clinical efficacy was marred by adverse events, to a commercialized product with enhanced safety and efficacy. We also discuss progress being made in preclinical studies for challenging disease targets and emerging gene editing technologies that are showing promising results, particularly for conditions where gene regulation is important for efficacy.

Biosafety Studies of a Clinically Applicable Lentiviral Vector for the Gene Therapy of Artemis-SCID

Genetic deficiency of the nuclease DCLRE1C/Artemis causes radiosensitive severe combined immunodeficiency (RS-SCID) with lack of peripheral T and B cells and increased sensitivity to ionizing radiations. Gene therapy based on transplanting autologous gene-modified hematopoietic stem cells could significantly improve the health of patients with RS-SCID by correcting their immune system. A lentiviral vector expressing physiological levels of human ARTEMIS mRNA from an EF1a promoter without post-transcriptional regulation was developed as a safe clinically applicable candidate for RS-SCID gene therapy. The vector was purified in GMP-comparable conditions and was not toxic in vitro or in vivo. Long-term engraftment of vector-transduced hematopoietic cells was achieved in irradiated Artemis-deficient mice following primary and secondary transplantation (6 months each). Vector-treated mice displayed T and B lymphopoiesis and polyclonal T cells, had structured lymphoid tissues, and produced immunoglobulins. Benign signs of inflammation were noted following secondary transplants, likely a feature of the model. There was no evidence of transgene toxicity and no induction of hematopoietic malignancy. In vitro, the vector had low genotoxic potential on murine hematopoietic progenitor cells using an immortalization assay. Altogether, these preclinical data show safety and efficacy, and support further development of the vector for the gene therapy of RS-SCID.

Microvesicle-Mediated Delivery of Minicircle DNA Results in Effective Gene-Directed Enzyme Prodrug Cancer Therapy

An emerging approach for cancer treatment employs the use of extracellular vesicles, specifically exosomes and microvesicles, as delivery vehicles. We previously demonstrated that microvesicles can functionally deliver plasmid DNA to cells and showed that plasmid size and sequence, in part, determine the delivery efficiency. In this study, delivery vehicles comprised of microvesicles loaded with engineered minicircle (MC) DNA that encodes prodrug converting enzymes developed as a cancer therapy in mammary carcinoma models. We demonstrated that MCs can be loaded into shed microvesicles with greater efficiency than their parental plasmid counterparts and that microvesicle-mediated MC delivery led to significantly higher and more prolonged transgene expression in recipient cells than microvesicles loaded with the parental plasmid. Microvesicles loaded with MCs encoding a thymidine kinase (TK)/nitroreductase (NTR) fusion protein produced prolonged TK-NTR expression in mammary carcinoma cells. In vivo delivery of TK-NTR and administration of prodrugs led to the effective killing of both targeted cells and surrounding tumor cells via TK-NTR-mediated conversion of codelivered prodrugs into active cytotoxic agents. In vivo evaluation of the bystander effect in mouse models demonstrated that for effective therapy, at least 1% of tumor cells need to be delivered with TK-NTR-encoding MCs. These results suggest that MC delivery via microvesicles can mediate gene transfer to an extent that enables effective prodrug conversion and tumor cell death such that it comprises a promising approach to cancer therapy.

Functional DNA Delivery Enabled by Lipid-Modified Charge-Altering Releasable Transporters (CARTs)

Safe and effective DNA delivery systems are required to enable or enhance clinical strategies and research involving gene therapy and DNA vaccinations. To address this delivery problem, a series of charge-altering releasable transporters (CARTs) with varied lipid content were prepared and evaluated for plasmid DNA (pDNA) delivery into cultured cells. These lipid-modified CART co-oligomers were synthesized in only two steps via sequential organocatalytic ring-opening polymerization of lipid-containing cyclic carbonate monomers and morpholinone monomers. Lipid variations of the CARTs substantially impacted the delivery efficiency of pDNA, with oleyl- and linoleyl-based CARTs showing enhanced performance relative to the commercial transfection agent Lipofectamine 2000 (L2000). The best-performing oleyl CART was carried forward to study stable luciferase transfection with a Sleeping Beauty ( SB) transposon system. The oleyl CART outperformed the L2000 positive control with respect to stable transfection efficiency. CART-pDNA complexes represent a new DNA delivery system for research and clinical applications.

Local estrogen axis in the human bone microenvironment regulates estrogen receptor-positive breast cancer cells

BACKGROUND

Approximately 70% of all breast cancers express the estrogen receptor, and are regulated by estrogen. While the ovaries are the primary source of estrogen in premenopausal women, most breast cancer is diagnosed following menopause, when systemic levels of this hormone decline. Estrogen production from androgen precursors is catalyzed by the aromatase enzyme. Although aromatase expression and local estrogen production in breast adipose tissue have been implicated in the development of primary breast cancer, the source of estrogen involved in the regulation of estrogen receptor-positive (ER+) metastatic breast cancer progression is less clear.

METHODS

Bone is the most common distant site of breast cancer metastasis, particularly for ER+ breast cancers. We employed a co-culture model using trabecular  bone tissues obtained from total hip replacement (THR) surgery specimens to study ER+ and estrogen receptor-negative (ER-) breast cancer cells within the human bone microenvironment. Luciferase-expressing ER+ (MCF-7, T-47D, ZR-75) and ER- (SK-BR-3, MDA-MB-231, MCF-10A) breast cancer cells were cultured directly on bone tissue fragments or in bone tissue-conditioned media, and monitored over time with bioluminescence imaging (BLI). Bone tissue-conditioned media were generated in the presence vs. absence of aromatase inhibitors, and testosterone. Bone tissue fragments were analyzed for aromatase expression by immunohistochemistry.

RESULTS

ER+ breast cancer cells were preferentially sustained in co-cultures with bone tissues and bone tissue-conditioned media relative to ER- cells. Bone fragments analyzed by immunohistochemistry revealed expression of the aromatase enzyme. Bone tissue-conditioned media generated in the presence of testosterone had increased estrogen levels and heightened capacity to stimulate ER+ breast cancer cell proliferation. Pretreatment of cultured bone tissues with aromatase inhibitors, which inhibited estrogen production, reduced the capacity of conditioned media to stimulate ER+ cell proliferation.

CONCLUSIONS

These results suggest that a local estrogen signaling axis regulates ER+ breast cancer cell viability and proliferation within the bone metastatic niche, and that aromatase inhibitors modulate this axis. Although endocrine therapies are highly effective in the treatment of ER+ breast cancer, resistance to these treatments reduces their efficacy. Characterization of estrogen signaling networks within the bone microenvironment will identify new strategies for combating metastatic progression and endocrine resistance.

Prevention of breast cancer skeletal metastases with parathyroid hormone

Advanced breast cancer is frequently associated with skeletal metastases and accelerated bone loss. Recombinant parathyroid hormone [teriparatide, PTH(1-34)] is the first anabolic agent approved in the US for treatment of osteoporosis. While signaling through the PTH receptor in the osteoblast lineage regulates bone marrow hematopoietic niches, the effects of anabolic PTH on the skeletal metastatic niche are unknown. Here, we demonstrate, using orthotopic and intratibial models of 4T1 murine and MDA-MB-231 human breast cancer tumors, that anabolic PTH decreases both tumor engraftment and the incidence of spontaneous skeletal metastasis in mice. Microcomputed tomography and histomorphometric analyses revealed that PTH increases bone volume and reduces tumor engraftment and volume. Transwell migration assays with murine and human breast cancer cells revealed that PTH alters the gene expression profile of the metastatic niche, in particular VCAM-1, to inhibit recruitment of cancer cells. While PTH did not affect growth or migration of the primary tumor, it elicited several changes in the tumor gene expression profile resulting in a less metastatic phenotype. In conclusion, PTH treatment in mice alters the bone microenvironment, resulting in decreased cancer cell engraftment, reduced incidence of metastases, preservation of bone microarchitecture and prolonged survival.

Breast Cancer Cell Colonization of the Human Bone Marrow Adipose Tissue Niche

BACKGROUND/OBJECTIVES

Bone is a preferred site of breast cancer metastasis, suggesting the presence of tissue-specific features that attract and promote the outgrowth of breast cancer cells. We sought to identify parameters of human bone tissue associated with breast cancer cell osteotropism and colonization in the metastatic niche.

METHODS

Migration and colonization patterns of MDA-MB-231-fLuc-EGFP (luciferase-enhanced green fluorescence protein) and MCF-7-fLuc-EGFP breast cancer cells were studied in co-culture with cancellous bone tissue fragments isolated from 14 hip arthroplasties. Breast cancer cell migration into tissues and toward tissue-conditioned medium was measured in Transwell migration chambers using bioluminescence imaging and analyzed as a function of secreted factors measured by multiplex immunoassay. Patterns of breast cancer cell colonization were evaluated with fluorescence microscopy and immunohistochemistry.

RESULTS

Enhanced MDA-MB-231-fLuc-EGFP breast cancer cell migration to bone-conditioned versus control medium was observed in 12/14 specimens (P = .0014) and correlated significantly with increasing levels of the adipokines/cytokines leptin (P = .006) and IL-1β (P = .001) in univariate and multivariate regression analyses. Fluorescence microscopy and immunohistochemistry of fragments underscored the extreme adiposity of adult human bone tissues and revealed extensive breast cancer cell colonization within the marrow adipose tissue compartment.

CONCLUSIONS

Our results show that breast cancer cells migrate to human bone tissue-conditioned medium in association with increasing levels of leptin and IL-1β, and colonize the bone marrow adipose tissue compartment of cultured fragments. Bone marrow adipose tissue and its molecular signals may be important but understudied components of the breast cancer metastatic niche.

Lentivirus Mediated Correction of Artemis-Deficient Severe Combined Immunodeficiency

During B and T lymphocyte maturation, V(D)J recombination is initiated by creation of DNA double-strand breaks. Artemis is an exonuclease essential for their subsequent repair by nonhomologous end-joining. Mutations in DCLRE1C, the gene encoding Artemis, cause T^-B^-NK⁺ severe combined immunodeficiency (ART-SCID) and also confer heightened sensitivity to ionizing radiation and alkylating chemotherapy. Although allogeneic hematopoietic cell transplantation can treat ART-SCID, conditioning regimens are poorly tolerated, leading to early mortality and/or late complications, including short stature, endocrinopathies, and dental aplasia. However, without alkylating chemotherapy as preconditioning, patients usually have graft rejection or limited T cell and no B cell recovery. Thus, addition of normal DCLRE1C cDNA to autologous hematopoietic stem cells is an attractive strategy to treat ART-SCID. We designed a self-inactivating lentivirus vector containing human Artemis cDNA under transcriptional regulation of the human endogenous Artemis promoter (AProArt). Fibroblasts from ART-SCID patients transduced with AProArt lentivirus showed correction of radiosensitivity. Mobilized peripheral blood CD34⁺ cells from an ART-SCID patient as well as hematopoietic stem cells from Artemis-deficient mice demonstrated restored T and B cell development following AProArt transduction. Murine hematopoietic cells transduced with AProArt exhibited no increase in replating potential in an in vitro immortalization assay, and analysis of AProArt lentivirus insertions showed no predilection for sites that could activate oncogenes. These efficacy and safety findings support institution of a clinical trial of gene addition therapy for ART-SCID.

Lymphopoiesis in transgenic mice over-expressing Artemis

Artemis is a factor of the non-homologous end joining pathway involved in DNA double-strand break repair that has a critical role in V(D)J recombination. Mutations in DCLRE1C/ARTEMIS gene result in radiosensitive severe combined immunodeficiency in humans owing to a lack of mature T and B cells. Given the known drawbacks of allogeneic hematopoietic stem cell transplantation (HSCT), gene therapy appears as a promising alternative for these patients. However, the safety of an unregulated expression of Artemis has to be established. We developed a transgenic mouse model expressing human Artemis under the control of the strong CMV early enhancer/chicken beta actin promoter through knock-in at the ROSA26 locus to analyze this issue. Transgenic mice present a normal development, maturation and function of T and B cells with no signs of lymphopoietic malignancies for up to 15 months. These results suggest that the over-expression of Artemis in mice (up to 40 times) has no deleterious effects in early and mature lymphoid cells and support the safety of gene therapy as a possible curative treatment for Artemis-deficient patients.

Lentivirus technologies for modulation of the immune system

Lentiviral vectors (LVV) are important tools for the treatment of immune system disorders. Integration of therapeutic genetic material into the haematopoietic stem cell compartment using LVV can mediate long-term correction of haematopoietic lineages, thereby correcting disease phenotypes. Twenty years of vector development have successfully brought LVV to the clinic, with follow up studies of clinical trials treating primary immunodeficiencies now being reported. Results have demonstrated clear improvements in the quality of life for patients with a number of conditions in the absence of the severe adverse events observed in earlier retroviral gene therapy trials. Growing interest in gene modified adoptive T cell transfer as an alternative strategy has driven further technology innovation, including characterisation of novel viral envelopes. We will also discuss the progression of gene editing technology to preclinical investigations in models of immune deficiency.

Functional analysis of naturally occurring DCLRE1C mutations and correlation with the clinical phenotype of ARTEMIS deficiency

BACKGROUND

The endonuclease ARTEMIS, which is encoded by the DCLRE1C gene, is a component of the nonhomologous end-joining pathway and participates in hairpin opening during the V(D)J recombination process and repair of a subset of DNA double-strand breaks. Patients with ARTEMIS deficiency usually present with severe combined immunodeficiency (SCID) and cellular radiosensitivity, but hypomorphic mutations can cause milder phenotypes (leaky SCID).

OBJECTIVE

We sought to correlate the functional effect of human DCLRE1C mutations on phenotypic presentation in patients with ARTEMIS deficiency.

METHODS

We studied the recombination and DNA repair activity of 41 human DCLRE1C mutations in Dclre1c(-/-) v-abl kinase-transformed pro-B cells retrovirally engineered with a construct that allows quantification of recombination activity by means of flow cytometry. For assessment of DNA repair efficacy, resolution of γH2AX accumulation was studied after ionizing radiation.

RESULTS

Low or absent activity was detected for mutations causing a typical SCID phenotype. Most of the patients with leaky SCID were compound heterozygous for 1 loss-of-function and 1 hypomorphic allele, with significant residual levels of recombination and DNA repair activity. Deletions disrupting the C-terminus result in truncated but partially functional proteins and are often associated with leaky SCID. Overexpression of hypomorphic mutants might improve the functional defect.

CONCLUSIONS

Correlation between the nature and location of DCLRE1C mutations, functional activity, and the clinical phenotype has been observed. Hypomorphic variants that have been reported in the general population can be disease causing if combined in trans with a loss-of-function allele. Therapeutic strategies aimed at inducing overexpression of hypomorphic alleles might be beneficial.

Role of transgene regulation in ex vivo lentiviral correction of artemis deficiency

Artemis is a single-stranded endonuclease, deficiency of which results in a radiation-sensitive form of severe combined immunodeficiency (SCID-A) most effectively treated by allogeneic hematopoietic stem cell (HSC) transplantation and potentially treatable by administration of genetically corrected autologous HSCs. We previously reported cytotoxicity associated with Artemis overexpression and subsequently characterized the human Artemis promoter with the intention to provide Artemis expression that is nontoxic yet sufficient to support immunodevelopment. Here we compare the human Artemis promoter (APro) with the moderate-strength human phosphoglycerate kinase (PGK) promoter and the strong human elongation factor-1α (EF1α) promoter to regulate expression of Artemis after ex vivo lentiviral transduction of HSCs in a murine model of SCID-A. Recipient animals treated with the PGK-Artemis vector exhibited moderate repopulation of their immune compartment, yet demonstrated a defective proliferative T lymphocyte response to in vitro antigen stimulation. Animals treated with the EF1α-Artemis vector displayed high levels of T lymphocytes but an absence of B lymphocytes and deficient lymphocyte function. In contrast, ex vivo transduction with the APro-Artemis vector supported effective immune reconstitution to wild-type levels, resulting in fully functional T and B lymphocyte responses. These results demonstrate the importance of regulated Artemis expression in immune reconstitution of Artemis-deficient SCID.

Methods for culturing human femur tissue explants to study breast cancer cell colonization of the metastatic niche

Bone is the most common site of breast cancer metastasis. Although it is widely accepted that the microenvironment influences cancer cell behavior, little is known about breast cancer cell properties and behaviors within the native microenvironment of human bone tissue.We have developed approaches to track, quantify and modulate human breast cancer cells within the microenvironment of cultured human bone tissue fragments isolated from discarded femoral heads following total hip replacement surgeries. Using breast cancer cells engineered for luciferase and enhanced green fluorescent protein (EGFP) expression, we are able to reproducibly quantitate migration and proliferation patterns using bioluminescence imaging (BLI), track cell interactions within the bone fragments using fluorescence microscopy, and evaluate breast cells after colonization with flow cytometry. The key advantages of this model include: 1) a native, architecturally intact tissue microenvironment that includes relevant human cell types, and 2) direct access to the microenvironment, which facilitates rapid quantitative and qualitative monitoring and perturbation of breast and bone cell properties, behaviors and interactions. A primary limitation, at present, is the finite viability of the tissue fragments, which confines the window of study to short-term culture. Applications of the model system include studying the basic biology of breast cancer and other bone-seeking malignancies within the metastatic niche, and developing therapeutic strategies to effectively target breast cancer cells in bone tissues.

Lentiviral vectors for the treatment of primary immunodeficiencies

In the last years important progress has been made in the treatment of several primary immunodeficiency disorders (PIDs) with gene therapy. Hematopoietic stem cell (HSC) gene therapy indeed represents a valid alternative to conventional transplantation when a compatible donor is not available and recent success confirmed the great potential of this approach. First clinical trials performed with gamma retroviral vectors were promising and guaranteed clinical benefits to the patients. On the other hand, the outcome of severe adverse events as the development of hematological abnormalities highlighted the necessity to develop a safer platform to deliver the therapeutic gene. Self-inactivating (SIN) lentiviral vectors (LVVs) were studied to overcome this hurdle through their preferable integration pattern into the host genome. In this review, we describe the recent advancements achieved both in vitro and at preclinical level with LVVs for the treatment of Wiskott-Aldrich syndrome (WAS), chronic granulomatous disease (CGD), ADA deficiency (ADA-SCID), Artemis deficiency, RAG1/2 deficiency, X-linked severe combined immunodeficiency (γchain deficiency, SCIDX1), X-linked lymphoproliferative disease (XLP) and immune dysregulation, polyendocrinopathy, enteropathy, X-linked (IPEX) syndrome.

Elevated expression of artemis in human fibroblast cells is associated with cellular radiosensitivity and increased apoptosis

BACKGROUND

The objective of this study was to determine the molecular mechanisms responsible for cellular radiosensitivity in two human fibroblast cell lines 84BR and 175BR derived from two cancer patients.

METHODS

Clonogenic assays were performed following exposure to increasing doses of gamma radiation to confirm radiosensitivity. γ-H2AX foci assays were used to determine the efficiency of DNA double-strand break (DSB) repair in cells. Quantitative PCR (Q-PCR) established the expression levels of key DNA DSB repair genes. Imaging flow cytometry using annexin V-FITC was used to compare artemis expression and apoptosis in cells.

RESULTS

Clonogenic cellular hypersensitivity in the 84BR and 175BR cell lines was associated with a defect in DNA DSB repair measured by the γ-H2AX foci assay. The Q-PCR analysis and imaging flow cytometry revealed a two-fold overexpression of the artemis DNA repair gene, which was associated with an increased level of apoptosis in the cells before and after radiation exposure. Overexpression of normal artemis protein in a normal immortalised fibroblast cell line NB1-Tert resulted in increased radiosensitivity and apoptosis.

CONCLUSION

We conclude that elevated expression of artemis is associated with higher levels of DNA DSB, radiosensitivity and elevated apoptosis in two radio-hypersensitive cell lines. These data reveal a potentially novel mechanism responsible for radiosensitivity and show that increased artemis expression in cells can result in either radiation resistance or enhanced sensitivity.

Increased Artemis levels confer radioresistance to both high and low LET radiation exposures

BACKGROUND

Artemis has a defined role in V(D)J recombination and has been implicated in the repair of radiation induced double-strand breaks. However the exact function(s) of Artemis in DNA repair and its preferred substrate(s) in vivo remain undefined. Our previous work suggests that Artemis is important for the repair of complex DNA damage like that inflicted by high Linear Energy Transfer (LET) radiation. To establish the contribution of Artemis in repairing DNA damage caused by various radiation qualities, we evaluated the effect of over-expressing Artemis on cell survival, DNA repair, and cell cycle arrest after exposure to high and low LET radiation.

RESULTS

Our data reveal that Artemis over-expression confers marked radioprotection against both types of radiation, although the radioprotective effect was greater following high LET radiation. Inhibitor studies reveal that the radioprotection imparted by Artemis is primarily dependent on DNA-PK activity, and to a lesser extent on ATM kinase activity. Together, these data suggest a DNA-PK dependent role for Artemis in the repair of complex DNA damage.

CONCLUSIONS

These findings indicate that Artemis levels significantly influence radiation toxicity in human cells and suggest that Artemis inhibition could be a practical target for adjuvant cancer therapies.

Sleeping Beauty-mediated correction of Fanconi anemia type C

BACKGROUND

The Sleeping Beauty (SB) transposon system can insert defined sequences into chromosomes to direct the extended expression of therapeutic genes. Our goal is to develop the SB system for nonviral complementation of Fanconi anemia (FA), a rare autosomal recessive disorder accompanied by progressive bone marrow failure.

METHODS

We used a CytoPulse electroporation system (CytoPulse, Glen Burnie, MD, USA) to introduce SB transposons into human lymphoblastoid cells (LCL) derived from both Fanconi anemia type C (FA-C) defective and normal patients. Correction of the FA-C defect was assessed by resistance to mitomycin C, a DNA-crosslinking agent.

RESULTS

Culture of both cell types with the antioxidant N-acetyl- l-cysteine improved cell viability after electroporation. Co-delivery of enhanced green fluorescent protein (GFP) transposon with SB100X transposase-encoding plasmid supported a 50- to 90-fold increase in stable GFP expression compared to that observed in the absence of SB100X for normal LCL, but in FA-C defective LCL SB100X enhancement of stable GFP-expression was a more moderate five- to 13-fold. SB-mediated integration and expression of the FA-C gene was demonstrated by the emergence of a mitomycin C-resistant population bearing characteristic transposon-chromosome junction sequences and exhibiting a mitomycin dose response identical to that of normal LCL.

CONCLUSIONS

The SB transposon system achieved stable expression of therapeutic FA-C genes, complementing the genetic defect in patient-derived cells by nonviral gene transfer.

Lentivirus transduction of human osteoclast precursor cells and differentiation into functional osteoclasts

Gene transfer into stem cells has been an ongoing priority as a treatment for genetic disease and cancer for more than two decades. Methods described herein, form the basis for providing the cell source to determine if osteoclast precursor cells (OcP) can be used as therapeutic gene delivery systems in vivo. Osteoclasts and tumor associated macrophages or OcP, support survival, tumor progression and osteolysis in bone cancers. Two sources of precursor cells are compared: CD14+ cells, the standard OcP, found abundantly in peripheral blood and CD34+ cells, hematopoietic stem cells that are rare, but which can be expanded into OcP. Our findings characterize cell yield at each step of the transduction process and thus provide essential data for planning future in vivo experiments. In addition we demonstrate that essential functions of OcP are preserved following lentiviral transduction. Specifically, neither the transduction method nor the lentiviral transduction influence the OcP's ability to form osteoclasts, express the marker gene, EGFP, or resorb bone. Finally, we conclude that CD34+ cells yield significantly more transduced cells and form functionally superior osteoclasts in vitro. This study represents a step towards considering human gene therapy for bone cancer by demonstrating successful transduction of human OcP for use as cellular delivery vehicles to sites of bone cancer.

Characterization of the human artemis promoter by heterologous gene expression in vitro and in vivo

Artemis is an endonucleolytic enzyme involved in nonhomologous double-strand break repair and V(D)J recombination. Deficiency of Artemis results in a B- T- radiosensitive severe combined immunodeficiency, which may potentially be treatable by Artemis gene transfer into hematopoietic stem cells. However, we recently found that overexpression of Artemis after lentiviral transduction resulted in global DNA damage and increased apoptosis. These results imply the necessity of effecting natural levels of Artemis expression, so we isolated a 1 kilobase DNA sequence upstream of the human Artemis gene to recover and characterize the Artemis promoter (APro). The sequence includes numerous potential transcription factor-binding sites, and several transcriptional start sites were mapped by 5' rapid amplification of cDNA ends. APro and deletion constructs conferred significant reporter gene expression in vitro that was markedly reduced in comparison to expression regulated by the human elongation factor 1-α promoter. Ex vivo lentiviral transduction of an APro-regulated green fluorescent protein (GFP) construct in mouse marrow supported GFP expression throughout hematopoeitic lineages in primary transplant recipients and was sustained in secondary recipients. The human Artemis promoter thus provides sustained and moderate levels of gene expression that will be of significant utility for therapeutic gene transfer into hematopoeitic stem cells.

Restoration of G1 chemo/radioresistance and double-strand-break repair proficiency by wild-type but not endonuclease-deficient Artemis

Deficiency in Artemis is associated with lack of V(D)J recombination, sensitivity to radiation and radiomimetic drugs, and failure to repair a subset of DNA double-strand breaks (DSBs). Artemis harbors an endonuclease activity that trims both 5′- and 3′-ends of DSBs. To examine whether endonucleolytic trimming of terminally blocked DSBs by Artemis is a biologically relevant function, Artemis-deficient fibroblasts were stably complemented with either wild-type Artemis or an endonuclease-deficient D165N mutant. Wild-type Artemis completely restored resistance to γ-rays, bleomycin and neocarzinostatin, and also restored DSB-repair proficiency in G0/G1 phase as measured by pulsed-field gel electrophoresis and repair focus resolution. In contrast, cells expressing the D165N mutant, even at very high levels, remained as chemo/radiosensitive and repair deficient as the parental cells, as evidenced by persistent γ-H2AX, 53BP1 and Mre11 foci that slowly increased in size and ultimately became juxtaposed with promyelocytic leukemia protein nuclear bodies. In normal fibroblasts, overexpression of wild-type Artemis increased radioresistance, while D165N overexpression conferred partial repair deficiency following high-dose radiation. Restoration of chemo/radioresistance by wild-type, but not D165N Artemis suggests that the lack of endonucleolytic trimming of DNA ends is the principal cause of sensitivity to double-strand cleaving agents in Artemis-deficient cells.

Inhibition of angiogenesis and suppression of colorectal cancer metastatic to the liver using the Sleeping Beauty Transposon System

Background

Metastatic colon cancer is one of the leading causes of cancer-related death worldwide, with disease progression and metastatic spread being closely associated with angiogenesis. We investigated whether an antiangiogenic gene transfer approach using the Sleeping Beauty (SB) transposon system could be used to inhibit growth of colorectal tumors metastatic to the liver.

Results

Liver CT26 tumor-bearing mice were hydrodynamically injected with different doses of a plasmid containing a transposon encoding an angiostatin-endostatin fusion gene (Statin AE) along with varying amounts of SB transposase-encoding plasmid. Animals that were injected with a low dose (10 μg) of Statin AE transposon plasmid showed a significant decrease in tumor formation only when co-injected with SB transposase-encoding plasmid, while for animals injected with a higher dose (25 μg) of Statin AE transposon, co-injection of SB transposase-encoding plasmid did not significantly affect tumor load. For animals injected with 10 μg Statin AE transposon plasmid, the number of tumor nodules was inversely proportional to the amount of co-injected SB plasmid. Suppression of metastases was further evident in histological analyses, in which untreated animals showed higher levels of tumor cell proliferation and tumor vascularization than animals treated with low dose transposon plasmid.

Conclusion

These results demonstrate that hepatic colorectal metastases can be reduced using antiangiogenic transposons, and provide evidence for the importance of the transposition process in mediating suppression of these tumors.