A novel gene transfer strategy that combines promoter and transgene activities for improved tumor cell inhibition

Lentiviral transduction of neonatal rat ventricular myocytes preserves ultrastructural features of genetically modified cells

Preserving morphological features that are important for cell function and structure is a critical parameter for in vitro experiments with rat cardiomyocytes. Lentiviral vectors are commonly used as gene transfer tool because of its high flexibility, efficiency to deliver expression cassettes and versatility of transducing quiescent cells. The tropism of the recombinant viral particle can be determined depending on the virus envelope, which shows a specific binding to cell surface receptors on the target cell. The combination of promoter arrangement and viral envelope must be optimized to achieve a greater transduction efficiency and a higher transgene expression. In this study we explored the optimization of promoters and heterologous envelopes to transduce primary culture of neonatal rat ventricular myocytes. Our results suggest a robust expression driven by the cytomegalovirus promoter, and high efficiency transduction mediated by VSV-G envelope with no apparent compromising ultrastructural features of genetically modified cells.

Perspectives for cancer immunotherapy mediated by p19Arf plus interferon-beta gene transfer

While cancer immunotherapy has gained much deserved attention in recent years, many areas regarding the optimization of such modalities remain unexplored, including the development of novel approaches and the strategic combination of therapies that target multiple aspects of the cancer-immunity cycle. Our own work involves the use of gene transfer technology to promote cell death and immune stimulation. Such immunogenic cell death, mediated by the combined transfer of the alternate reading frame (p14ARF in humans and p19Arf in mice) and the interferon-β cDNA in our case, was shown to promote an antitumor immune response in mouse models of melanoma and lung carcinoma. With these encouraging results, we are now setting out on the road toward translational and preclinical development of our novel immunotherapeutic approach. Here, we outline the perspectives and challenges that we face, including the use of human tumor and immune cells to verify the response seen in mouse models and the incorporation of clinically relevant models, such as patient-derived xenografts and spontaneous tumors in animals. In addition, we seek to combine our immunotherapeutic approach with other treatments, such as chemotherapy or checkpoint blockade, with the goal of reducing dosage and increasing efficacy. The success of any translational research requires the cooperation of a multidisciplinary team of professionals involved in laboratory and clinical research, a relationship that is fostered at the Cancer Institute of Sao Paulo.

Improving adenoviral vectors and strategies for prostate cancer gene therapy

Gene therapy has been evaluated for the treatment of prostate cancer and includes the application of adenoviral vectors encoding a suicide gene or oncolytic adenoviruses that may be armed with a functional transgene. In parallel, versions of adenoviral vector expressing the p53 gene (Ad-p53) have been tested as treatments for head and neck squamous cell carcinoma and non-small cell lung cancer. Although Ad-p53 gene therapy has yielded some interesting results when applied to prostate cancer, it has not been widely explored, perhaps due to current limitations of the approach. To achieve better functionality, improvements in the gene transfer system and the therapeutic regimen may be required. We have developed adenoviral vectors whose transgene expression is controlled by a p53-responsive promoter, which creates a positive feedback mechanism when used to drive the expression of p53. Together with improvements that permit efficient transduction, this new approach was more effective than the use of traditional versions of Ad-p53 in killing prostate cancer cell lines and inhibiting tumor progression. Even so, gene therapy is not expected to replace traditional chemotherapy but should complement the standard of care. In fact, chemotherapy has been shown to assist in viral transduction and transgene expression. The cooperation between gene therapy and chemotherapy is expected to effectively kill tumor cells while permitting the use of reduced chemotherapy drug concentrations and, thus, lowering side effects. Therefore, the combination of gene therapy and chemotherapy may prove essential for the success of both approaches.

Autoregulated expression of p53 from an adenoviral vector confers superior tumor inhibition in a model of prostate carcinoma gene therapy

Alternative treatments for cancer using gene therapy approaches have shown promising results and some have even reached the marketplace. Even so, additional improvements are needed, such as employing a strategically chosen promoter to drive expression of the transgene in the target cell. Previously, we described viral vectors where high-level transgene expression was achieved using a p53-responsive promoter. Here we present an adenoviral vector (AdPGp53) where p53 is employed to regulate its own expression and which outperforms a traditional vector when tested in a model of gene therapy for prostate cancer. The functionality of AdPGp53 and AdCMVp53 were compared in human prostate carcinoma cell lines. AdPGp53 conferred greatly enhanced levels of p53 protein and induction of the p53 target gene, p21, as well as superior cell killing by a mechanism consistent with apoptosis. DU145 cells were susceptible to induction of death with AdPGp53, yet PC3 cells were quite resistant. Though AdCMVp53 was shown to be reliable, extremely high-level expression of p53 offered by AdPGp53 was necessary for tumor suppressor activity in PC3 and DU145. In situ gene therapy experiments revealed tumor inhibition and increased overall survival in response to AdPGp53, but not AdCMVp53. Upon histologic examination, only AdPGp53 treatment was correlated with the detection of both p53 and TUNEL-positive cells. This study points to the importance of improved vector performance for gene therapy of prostate cancer.

Preservation of cardiac function in left ventricle cardiac hypertrophy using an AAV vector which provides VEGF-A expression in response to p53

Here we present the application of our adeno-associated virus (AAV2) vector where transgene expression is driven by a synthetic, p53-responsive promoter, termed PG, used to supply human vascular endothelial growth factor-A165 (VEGF-A). Thus, p53 is harnessed to promote the beneficial expression of VEGF-A encoded by the AAVPG vector, bypassing the negative effect of p53 on HIF-1α which occurs during cardiac hypertrophy. Wistar rats were submitted to pressure overload induced by thoracic aorta coarctation (TAC) with or without concomitant gene therapy (intramuscular delivery in the left ventricle). After 12 weeks, rats receiving AAVPG-VEGF gene therapy were compared to those that did not, revealing significantly improved cardiac function under hemodynamic stress, lack of fibrosis and reversal of capillary rarefaction. With these functional assays, we have demonstrated that application of the AAVPG-VEGF vector under physiologic conditions known to stimulate p53 resulted in the preservation of cardiac performance.

Combined p19Arf and interferon-beta gene transfer enhances cell death of B16 melanoma in vitro and in vivo

Approximately 90% of melanomas retain wild-type p53, a characteristic that may help shape the development of novel treatment strategies. Here, we employed an adenoviral vector where transgene expression is controlled by p53 to deliver the p19 alternate reading frame (Arf) and interferon-β (IFNβ) complementary DNAs in the B16 mouse model of melanoma. In vitro, cell death was enhanced by combined gene transfer (63.82±15.30% sub-G0 cells); yet introduction of a single gene resulted in significantly fewer hypoploid cells (37.73±7.3% or 36.96±11.58%, p19Arf or IFNβ, respectively, P<0.05). Annexin V staining and caspase-3 cleavage indicate a cell death mechanism consistent with apoptosis. Using reverse transcriptase quantitative PCR, we show that key transcriptional targets of p53 were upregulated in the presence of p19Arf, although treatment with IFNβ did not alter expression of the genes studied. In situ gene therapy revealed significant inhibition of subcutaneous tumors by IFNβ (571±25 mm3) or the combination of p19Arf and IFNβ (489±124 mm3) as compared with the LacZ control (1875±33 mm3, P<0.001), whereas p19Arf yielded an intermediate result (1053±169 mm3, P<0.01 vs control). However, only the combination was associated with increased cell death and prolonged survival (P<0.01). As shown here, the combined transfer of p19Arf and IFNβ using p53-responsive vectors enhanced cell death both in vitro and in vivo.

Activation of endogenous p53 by combined p19Arf gene transfer and nutlin-3 drug treatment modalities in the murine cell lines B16 and C6

Background

Reactivation of p53 by either gene transfer or pharmacologic approaches may compensate for loss of p19Arf or excess mdm2 expression, common events in melanoma and glioma. In our previous work, we constructed the pCLPG retroviral vector where transgene expression is controlled by p53 through a p53-responsive promoter. The use of this vector to introduce p19Arf into tumor cells that harbor p53wt should yield viral expression of p19Arf which, in turn, would activate the endogenous p53 and result in enhanced vector expression and tumor suppression. Since nutlin-3 can activate p53 by blocking its interaction with mdm2, we explored the possibility that the combination of p19Arf gene transfer and nutlin-3 drug treatment may provide an additive benefit in stimulating p53 function.

Methods

B16 (mouse melanoma) and C6 (rat glioma) cell lines, which harbor p53wt, were transduced with pCLPGp19 and these were additionally treated with nutlin-3 or the DNA damaging agent, doxorubicin. Viral expression was confirmed by Western, Northern and immunofluorescence assays. p53 function was assessed by reporter gene activity provided by a p53-responsive construct. Alterations in proliferation and viability were measured by colony formation, growth curve, cell cycle and MTT assays. In an animal model, B16 cells were treated with the pCLPGp19 virus and/or drugs before subcutaneous injection in C57BL/6 mice, observation of tumor progression and histopathologic analyses.

Results

Here we show that the functional activation of endogenous p53wt in B16 was particularly challenging, but accomplished when combined gene transfer and drug treatments were applied, resulting in increased transactivation by p53, marked cell cycle alteration and reduced viability in culture. In an animal model, B16 cells treated with both p19Arf and nutlin-3 yielded increased necrosis and decreased BrdU marking. In comparison, C6 cells were quite susceptible to either treatment, yet p53 was further activated by the combination of p19Arf and nutlin-3.

Conclusions

To the best of our knowledge, this is the first study to apply both p19Arf and nutlin-3 for the stimulation of p53 activity. These results support the notion that a p53 responsive vector may prove to be an interesting gene transfer tool, especially when combined with p53-activating agents, for the treatment of tumors that retain wild-type p53.

Serial bone marrow transplantation reveals in vivo expression of the pCLPG retroviral vector

Background

Gene therapy in the hematopoietic system remains promising, though certain aspects of vector design, such as transcriptional control elements, continue to be studied. Our group has developed a retroviral vector where transgene expression is controlled by p53 with the intention of harnessing the dynamic and inducible nature of this tumor suppressor and transcription factor. We present here a test of in vivo expression provided by the p53-responsive vector, pCLPG. For this, we used a model of serial transplantation of transduced bone marrow cells.

Results

We observed, by flow cytometry, that the eGFP transgene was expressed at higher levels when the pCLPG vector was used as compared to the parental pCL retrovirus, where expression is directed by the native MoMLV LTR. Expression from the pCLPG vector was longer lasting, but did decay along with each sequential transplant. The detection of eGFP-positive cells containing either vector was successful only in the bone marrow compartment and was not observed in peripheral blood, spleen or thymus.

Conclusions

These findings indicate that the p53-responsive pCLPG retrovirus did offer expression in vivo and at a level that surpassed the non-modified, parental pCL vector. Our results indicate that the pCLPG platform may provide some advantages when applied in the hematopoietic system.

Development of an adenoviral vector with robust expression driven by p53

Here we introduce a new adenoviral vector where transgene expression is driven by p53. We first developed a synthetic promoter, referred to as PGTxbeta, containing a p53-responsive element, a minimal promoter and the first intron of the rabbit beta-globin gene. Initial assays using plasmid-based vectors indicated that expression was tightly controlled by p53 and was 5-fold stronger than the constitutive CMV immediate early promoter/enhancer. The adenoviral vector, AdPG, was also shown to offer p53-responsive expression in prostate carcinoma cells LNCaP (wt p53), DU-145 (temperature sensitive mutant of p53) and PC3 (p53-null, but engineered to express temperature-sensitive p53 mutants). AdPG served as a sensor of p53 activity in LNCaP cells treated with chemotherapeutic agents. Since p53 can be induced by radiotherapy and chemotherapy, this new vector could be further developed for use in combination with conventional therapies to bring about cooperation between the genetic and pharmacologic treatment modalities.

A lentiviral vector with expression controlled by E2F-1: A potential tool for the study and treatment of proliferative diseases

We have constructed a lentiviral vector with expression limited to cells presenting active E2F-1 protein, a potential advantage for gene therapy of proliferative diseases. For the FE2FLW vector, the promoter region of the human E2F-1 gene was utilized to drive expression of luciferase cDNA, included as a reporter of viral expression. Primary, immortalized, and transformed cells were transduced with the FE2FLW vector and cell cycle alterations were induced with serum starvation/replacement, contact inhibition or drug treatment, revealing cell cycle-dependent changes in reporter activity. Forced E2F-1 expression, but not E2F-2 or E2F-3, increased reporter activity, indicating a major role for this factor in controlling expression from the FE2FLW virus. We show the utility of this vector as a reporter of E2F-1 and proliferation-dependent cellular alterations upon cytotoxic/cytostatic treatment, such as the introduction of tumor suppressor genes. We propose that the FE2FLW vector may be a starting point for the development of gene therapy strategies for proliferative diseases, such as cancer or restinosis.

The DU145 human prostate carcinoma cell line harbors a temperature-sensitive allele of p53

BACKGROUND

Some nuances of mutant and wild-type p53 activity have been uncovered utilizing temperature sensitive (TS) alleles. However, few human tumor derived cell lines possess a TS p53 mutant.

METHODS

The cell lines DU145 (heterozygous p53, P223L, and V274F) and PC3 (p53-null, where exogenous P223L and V274F were introduced individually or in combination) were examined for TS p53 activity as revealed by reporter construct and target gene activation.

RESULTS

TS p53 function was observed in DU145 and expression of the P223L allele in PC3 conferred a TS p53 profile. Activation of p21Waf1 demonstrated that P223L TS activity may have been influenced by cellular context.

CONCLUSIONS

The DU145 cell line harbors a TS mutant of p53 and, in addition to being a widely used model of human prostate carcinoma, may also reveal new insights into p53 function due to the unique transcriptional properties of its TS phenotype.