Selective transduction of murine myelomonocytic leukemia cells (WEHI-3B) with regular and RGD-adenoviral vectors

Development of an in vitro model for the simultaneous study of the efficacy and hematotoxicity of antileukemic compounds

Hematopoietic system displays a wide spectrum of cell populations hierarchically organized in the bone marrow. Homeostasis in this system requires equilibrium between the self-renewal of the stem cells and their capacity of differentiation. Any failure on this equilibrium could lead to fatal consequences, such as the development of leukemia. Due to its rapid rate of renewal, hematopoietic tissue is a major target for antitumoral compounds and often becomes a dose limiting factor in the development of antineoplastics. Our aim was to develop an in vitro model for predicting the efficacy of antitumoral compounds on leukemic cells and their toxic effects on the healthy hematopoietic cells. The mouse myelomonocytic leukemia WEHI-3b was transduced with a lentiviral vector for expressing the green fluorescence protein. Mixed semisolid clonogenic cultures of transduced WEHI-3b and murine bone marrow cells were exposed to five pharmaceuticals: daunorubicin (positive control), atropine sulphate (negative control) and three in different stages of clinical development (trabectedin, Zalypsis(®) and PM01183). Colonies of leukemic cells were distinguishable from healthy CFU-GM under fluorescence microscope. The sensitivity of leukemic cells to daunorubicin, trabectedin, Zalypsis(®) and PM01183 was higher compared to healthy cells. The effect of a non-antitumoral compound, atropine sulphate, was the same on both populations. Our results show that this in vitro model is a valuable tool for studying the effect of antitumoral compounds in both tumoral and normal hematopoietic cells under the same toxic microenvironment and could safe time and facilitate the reduction of the number of animals used in preclinical development of pharmaceuticals.

Human basal cell carcinoma is associated with Foxp3+ T cells in a Th2 dominant microenvironment

Basal cell carcinoma (BCC), the most common human cancer, undergoes spontaneous regression in certain circumstances, which is potentially immune-mediated. To understand the immune response surrounding BCCs, we characterized the genomic, protein, and cellular microenvironment associated with BCC in comparison to normal skin. Our results demonstrated the following: (1) CD4+ CD25+ Foxp3+ surround epithelial tumor aggregates; (2) Immature dendritic cells (DCs) were abundant in the tumor microenvironment; (3) BCC showed increased expression of IL-4, IL-10, and CCL22 and increased expression of interferon-associated genes (IFI27, IRF1, IRF7, and G1P2) and IL-12/23, gene indicating a Th2 dominant microenvironment. Our findings suggest a dynamic state within the immune microenvironment associated with BCC. The finding of phenotypic T regs, in conjunction with immature DCs and Th2 cytokines, suggests an attenuated state of immunity to human BCC. In contrast, abundant CD8+ T cells, an interferon signal, and IL-12/23 suggest partial host antitumor response. A better understanding of these opposing forces within the immune microenvironment may facilitate development of more potent immune-based treatment for BCC and other human carcinomas.

Melanoma cultures show different susceptibility towards E1A-, E1B-19 kDa- and fiber-modified replication-competent adenoviruses

Replicating adenovirus (Ad) vectors with tumour tissue specificity hold great promise for treatment of cancer. We have recently constructed a conditionally replicating Ad5 AdDeltaEP-TETP inducing tumour regression in a xenograft mouse model. For further improvement of this vector, we introduced four genetic modifications and analysed the viral cytotoxicity in a large panel of melanoma cell lines and patient-derived melanoma cells. (1) The antiapoptotic gene E1B-19 kDa (Delta19 mutant) was deleted increasing the cytolytic activity in 18 of 21 melanoma cells. (2) Introduction of the E1A 122-129 deletion (Delta24 mutant), suggested to attenuate viral replication in cell cycle-arrested cells, did not abrogate this activity and increased the cytolytic activity in two of 21 melanoma cells. (3) We inserted an RGD sequence into the fiber to extend viral tropism to alphav integrin-expressing cells, and (4) swapped the fiber with the Ad35 fiber (F35) enhancing the tropism to malignant melanoma cells expressing CD46. The RGD-fiber modification strongly increased cytolysis in all of the 11 CAR-low melanoma cells. The F35 fiber-chimeric vector boosted the cytotoxicity in nine of 11 cells. Our results show that rational engineering additively enhances the cytolytic potential of Ad vectors, a prerequisite for the development of patient-customized viral therapies.

Comparison of the efficiency of transduction of leukemic cells by fiber-modified adenoviruses

Efficient gene transfer with adenoviral type 5 (Ad5) vectors depends on the initial attachment of their fiber, which binds the coxsackie-adenovirus receptor (CAR), and their subsequent internalization, mediated by the interaction of viral penton base with target cell alphav integrins. We previously demonstrated that human leukemic cells lack these receptors and are therefore resistant to Ad5 transduction, limiting efforts to genetically modify these cells. Human leukemic blasts are, however, susceptible to transduction with an adenovector made CAR independent by substitution of a chimeric Ad5/35 fiber [Yotnda et al. (2001). Gene Ther. 8, 930-937]. Other receptors can also be targeted with recombinant ligand moieties incorporated into adenovirus fiber. We have determined which of these fiber-modified adenovectors is most effective at modifying human primary leukemia cells, and lines. We used a replication-incompetent Ad5-beta-gal vector, in which the Ad5 fiber was replaced with fiber from various adenovirus serotypes (Ad35 and Ad11), or modified either with variable length polylysine (K4, K7, K21) or RGD-4C peptide. All the modified fiber vectors transduced primary leukemia cells and cell lines more efficiently than Ad5. Polylysine-substituted Ad5F/K21 and peptide-modified Ad5F/RGD vectors were most effective overall (up to 100% efficiency), whereas Ad5F/RGD was the most effective at transducing B cell acute lymphoblastic leukemia cells (90% efficiency). Ad5F/K21 and Ad5F/RGD should be of value for the genetic modification of human primary leukemia cells.

Approaches to improving the kinetics of adenovirus-delivered genes and gene products

Adenovirus (Ad) vectors have been expected to play a great role in gene therapy because of their extremely high transduction efficiency and wide tropism. However, due to the intrinsic deficiency of their immunogenic toxicities, Ad vectors are rapidly cleared from the host, transgene expression is transient, and readministration of the same serotype Ad vectors is problematic. As a result, Ad vectors are continually undergoing refinement to realize their potential for gene therapy application. Even after 1999, when a patient fatally succumbed to the toxicity associated with Ad vector administration at a University of Pennsylvania (U.S.) experimental clinic, enthusiasm of gene therapists for Ad vectors has not waned. With great efforts from various research groups, significant advances have been achieved through comprehensive approaches to improving the kinetics of Ad vector-delivered genes and gene products.

A soluble CAR-SCF fusion protein improves adenoviral vector-mediated gene transfer to c-Kit-positive hematopoietic cells

BACKGROUND

Although adenoviral vectors primarily derived from the adenovirus serotype 5 (Ad5) are widely used for many gene transfer applications, they cannot efficiently infect hematopoietic cells, since these cells do not express the coxsackie-adenoviral receptor (CAR).

METHODS

We have developed a soluble fusion protein that bridges adenoviral fibers and the c-Kit receptor to alter Ad5 tropism to immature hematopoietic cells. The CAR-SCF fusion protein consists of the extracellular domains of CAR and stem cell factor (SCF). The human megakaryoblastic leukemia cell lines UT-7 and M07e, human chronic myelogenous leukemia cell line K-562, and erythroleukemia cell line TF-1 were used to assess CAR-SCF-assisted Ad5-mediated gene transfer. Hematopoietic cell lines were infected with an Ad5 vector (Ad5-eGFP) or a fiber-mutant Ad5/F35 (Ad5/F35-eGFP) expressing the enhanced green fluorescent protein gene in the presence or absence of CAR-SCF.

RESULTS

Twenty-four hours after infection, more than 80% of M07e cells infected in the presence of CAR-SCF were eGFP-positive, compared with very few eGFP-positive cells following Ad5-eGFP infection in the absence of CAR-SCF. The enhancement of Ad5-eGFP infection by CAR-SCF was greater than that caused by Ad5/F35-eGFP (50%). The ability of CAR-SCF to enhance Ad5-eGFP infectivity was highly dependent on cellular c-Kit expression levels. Furthermore, CAR-SCF also enhanced Ad5-mediated gene transfer into human primary CD34(+) cells.

CONCLUSIONS

The CAR-SCF fusion protein assists Ad5-mediated transduction to c-Kit(+) CAR(-) hematopoietic cells. The use of this fusion protein would enhance a utility of Ad5-mediated hematopoietic cell transduction strategies.

Purging of leukemia-contaminated bone marrow grafts using suicide adenoviral vectors: an in vivo murine experimental model

Autologous bone marrow transplantation is an alternative therapeutic option for acute myeloid leukemia patients lacking a compatible donor. However, bone marrow from these patients may contain residual leukemic cells that should be ideally eliminated prior to the infusion of the graft. With the aim of developing more efficient protocols of graft purging, adenoviral-mediated gene transfer protocols have been conducted. We studied whether suicide adenoviral vectors expressing the cytosine deaminase gene (AdCD) could be used for selectively killing leukemic WEHI-3B cells. The AdCD transduction followed by the 5-fluorocytosine exposure abrogated the growth of WEHI-3B cells in vitro, with a minimal effect on normal hematopietic progenitors. To test the efficacy of the purging protocol in vivo, bone marrow cells were mixed with syngenic WEHI-3B cells and this chimeric cell population was transduced with AdCD vectors. Infected cells were injected into myeloablated Balb-c mice, which then received a 5-fluorocytosine treatment for 4 days. All mice transplanted with unpurged bone marrow developed leukemia and died. However, 90% of recipients receiving the purging treatment were healthy up to 9 months post-transplantation and had a perfectly re-established hematopoietic system, without any signal of leukemic cell presence. In conclusion, suicide adenoviral vectors are proposed as a tool for the purging of Adenoviral-susceptible myeloid leukemia cells contaminating autologous bone marrow grafts.

Adenoviral transduction of mouse hematopoietic stem cells

Hematopoietic stem cells (HSC) are quiescent, self-renewing cells that can give rise to all blood cell lineages. HSC are an attractive target for gene therapy, due to their differentiation capacity and the number of diseases that result from abnormal HSC function. While human HSC have been shown to be transduced with adenoviral vectors, the adenoviral transduction of mouse HSC has not been extensively studied. We show here that a population of mouse bone marrow highly enriched for HSC (called side population, or SP, cells) can be transduced with adenovirus type 5 (Ad5) at a low multiplicity of infection. Transduced SP cells showed normal in vitro myeloid differentiation potential compared to mock-transduced SP cells. Transduced SP cells retained substantial but reduced in vivo long-term repopulating activity and contributed to all blood cell lineages. Ad5 transduction of mouse SP cells was dependent on coxsackie and adenovirus receptor (CAR), as an anti-CAR blocking antibody greatly reduced transduction. Therefore, adenoviral transduction of mouse HSC can be achieved without ablation of the hematopoietic repopulating activity.

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

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

Targeted adenoviral vectors

Replication-defective vectors based on human adenovirus serotypes 2 and 5 (Ad2 and Ad5) possess a number of attributes which favor their use as gene delivery vehicles in gene therapy applications. However, the widespread distribution of the primary cellular receptor for Ad, the coxsackievirus and adenovirus receptor (CAR), allows Ad vectors to infect a broad range of cells in the host. Conversely, a number of tissues which represent important targets for gene therapy, such as the airway epithelium and cancer cells, are refractory to Ad infection due a paucity of CAR. Thus, there is a strong rationale for the development of CAR-independent Ad vectors capable of enhanced specificity and efficiency of gene transfer to target cells. In this article we review the approaches which have been employed to generate tropism-modified Ad vectors. These targeting strategies have led to improvements in the safety and efficacy of Ad vectors and have the potential to yield an increased therapeutic benefit in the human clinical context.

Histone deacetylase inhibitor FR901228 enhances adenovirus infection of hematopoietic cells

Adenovirus infection of hematopoietic cells frequently requires high virus concentrations and long incubation times to obtain moderate infection levels because these cells have low levels of Coxsackie and adenovirus receptor (CAR) and alpha(v) integrin. The effect of treatment with FR901228 (depsipeptide), a histone deacetylase inhibitor in phase 2 clinical trials, was studied in K562 cells, granulocyte-colony-stimulating factor-mobilized peripheral blood mononuclear cells (PBMCs), and CD34+ peripheral blood stem cells (PBSCs). FR901228 increased CAR and alpha(v) integrin RNA levels and histone H3 acetylation. FR901228 treatment before adenovirus infection was associated with at least a 10-fold increase in transgene expression from a beta-galactosidase-expressing adenoviral vector. More than 80% of the PBMCs or CD34+ PBSCs from 7 different donors were beta-galactosidase-positive after adenovirus infection with a multiplicity of infection of 10 for 60 minutes. Increased CAR, alpha(v) integrin, and acetylated histone H3 levels were observed in PBMCs from a patient treated with FR901228. These studies suggest that FR901228 can increase the efficiency of adenoviral infection in hematopoietic cells.