Reconstituting retroviral (ReCon) vectors facilitating delivery of cytotoxic genes in cancer gene therapy approaches

Conformational Differences Are Observed for the Active and Inactive Forms of Pinholin S21 Using DEER Spectroscopy

Bacteriophages have evolved with an efficient host cell lysis mechanism to terminate the infection cycle and release the new progeny virions at the optimum time, allowing adaptation with the changing host and environment. Among the lytic proteins, holin controls the first and rate-limiting step of host cell lysis by permeabilizing the inner membrane at an allele-specific time known as "holin triggering". Pinholin S²¹ is a prototype holin of phage Φ21 which makes many nanoscale holes and destroys the proton motive force, which in turn activates the signal anchor release (SAR) endolysin system to degrade the peptidoglycan layer of the host cell and destruction of the outer membrane by the spanin complex. Like many others, phage Φ21 has two holin proteins: active pinholin and antipinholin. The antipinholin form differs only by three extra amino acids at the N-terminus; however, it has a different structural topology and conformation with respect to the membrane. Predefined combinations of active pinholin and antipinholin fine-tune the lysis timing through structural dynamics and conformational changes. Previously, the dynamics and topology of active pinholin and antipinholin were investigated (Ahammad et al. JPCB 2019, 2020) using continuous wave electron paramagnetic resonance (CW-EPR) spectroscopy. However, detailed structural studies and direct comparison of these two forms of pinholin S²¹ are absent in the literature. In this study, the structural topology and conformations of active pinholin (S²¹68) and inactive antipinholin (S²¹68_IRS) in DMPC (1,2-dimyristoyl-sn-glycero-3-phosphocholine) proteoliposomes were investigated using the four-pulse double electron-electron resonance (DEER) EPR spectroscopic technique to measure distances between transmembrane domains 1 and 2 (TMD1 and TMD2). Five sets of interlabel distances were measured via DEER spectroscopy for both the active and inactive forms of pinholin S²¹. Structural models of the active pinholin and inactive antipinholin forms in DMPC proteoliposomes were obtained using the experimental DEER distances coupled with the simulated annealing software package Xplor-NIH. TMD2 of S²¹68 remains in the lipid bilayer, and TMD1 is partially externalized from the bilayer with some residues located on the surface. However, both TMDs remain incorporated in the lipid bilayer for the inactive S²¹68_IRS form. This study demonstrates, for the first time, clear structural topology and conformational differences between the two forms of pinholin S²¹. This work will pave the way for further studies of other holin systems using the DEER spectroscopic technique and will give structural insight into these biological clocks in molecular detail.

Enhancing titres of therapeutic viral vectors using the transgene repression in vector production (TRiP) system

A key challenge in the field of therapeutic viral vector/vaccine manufacturing is maximizing production. For most vector platforms, the ‘benchmark' vector titres are achieved with inert reporter genes. However, expression of therapeutic transgenes can often adversely affect vector titres due to biological effects on cell metabolism and/or on the vector virion itself. Here, we exemplify the novel ‘Transgene Repression In vector Production' (TRiP) system for the production of both RNA- and DNA-based viral vectors. The TRiP system utilizes a translational block of one or more transgenes by employing the bacterial tryptophan RNA-binding attenuation protein (TRAP), which binds its target RNA sequence close to the transgene initiation codon. We report enhancement of titres of lentiviral vectors expressing Cyclo-oxygenase-2 by 600-fold, and adenoviral vectors expressing the pro-apoptotic gene Bax by >150,000-fold. The TRiP system is transgene-independent and will be a particularly useful platform in the clinical development of viral vectors expressing problematic transgenes.

The maximum titre of therapeutic viral vectors can be adversely affected by the encoded transgene. Here the authors repress transgene expression in producing cells by employing the tryptophan RNA-binding attenuation protein and show that it improves titre of RNA- and DNA-based viral vectors expressing toxic transgenes.

Holins in bacteria, eukaryotes, and archaea: multifunctional xenologues with potential biotechnological and biomedical applications

Holins form pores in the cytoplasmic membranes of bacteria for the primary purpose of releasing endolysins that hydrolyze the cell wall and induce cell death. Holins are encoded within bacteriophage genomes, where they promote cell lysis for virion release, and within bacterial genomes, where they serve a diversity of potential or established functions. These include (i) release of gene transfer agents, (ii) facilitation of programs of differentiation such as those that allow sporulation and spore germination, (iii) contribution to biofilm formation, (iv) promotion of responses to stress conditions, and (v) release of toxins and other proteins. There are currently 58 recognized families of holins and putative holins with members exhibiting between 1 and 4 transmembrane α-helical spanners, but many more families have yet to be discovered. Programmed cell death in animals involves holin-like proteins such as Bax and Bak that may have evolved from bacterial holins. Holin homologues have also been identified in archaea, suggesting that these proteins are ubiquitous throughout the three domains of life. Phage-mediated cell lysis of dual-membrane Gram-negative bacteria also depends on outer membrane-disrupting "spanins" that function independently of, but in conjunction with, holins and endolysins. In this minireview, we provide an overview of their modes of action and the first comprehensive summary of the many currently recognized and postulated functions and uses of these cell lysis systems. It is anticipated that future studies will result in the elucidation of many more such functions and the development of additional applications.

Synergistic antitumoral effect of combination E gene therapy and Doxorubicin in MCF-7 breast cancer cells

The low effectiveness of conventional therapies to achieve the long-term survival of metastatic breast cancer patients calls for the development of novel options. Genes encoding cytotoxic proteins have been proposed as a new strategy to enhance the antiproliferative activity of drugs. Combined therapy using these genes and classical antitumoral drugs are under intensive study. The E gene from ϕX174 encodes a membrane protein with a toxic domain that leads to a decrease in the tumour cell growth rate. With the aim of improving the anti-tumour effect on breast cancer cells of the currently used chemotherapeutic drugs (Paclitaxel, Docetaxel and Doxorubicin), we investigated the association of E suicide gene with these drugs. The effect of the combined therapy (gene therapy and cytotoxic) was determined by treating transfected MCF-7 cells and multicellular tumour spheroids (MTS) with drugs gradient concentrations. Our results showed that E gene has a direct oncolytic effect inducing a significant decrease in the proliferation rate of the MCF-7 cells. The E gene antitumoral activity was mediated by the induction of apoptosis (mitochondrial pathway). In addition, a significant enhancement of proliferation inhibition was observed when E gene transfection was associated with cytotoxic drugs in comparison to single treatments. The use of the combined therapy E gene-Doxorubicin obtained the greatest effect on the MCF-7 growth arrest. This therapeutic association also induced a significant enhancement of the MTS volume growth inhibition. Anti-tumour activity of the chemotherapeutic drugs classically used in the treatment of breast cancer was enhanced by E gene. Our in vitro results indicate that experimental therapeutic strategy based in the combined therapy E gene and cytotoxic drugs may be of potential therapeutic value as a new strategy for patients with advanced breast cancer.

Gef gene therapy enhances the therapeutic efficacy of doxorubicin to combat growth of MCF-7 breast cancer cells

PURPOSE

The potential use of combined therapy is under intensive study including the association between classical cytotoxic and genes encoding toxic proteins which enhanced the antitumour activity. The main aim of this work was to evaluate whether the gef gene, a suicide gene which has a demonstrated antiproliferative activity in tumour cells, improved the antitumour effect of chemotherapeutic drugs used as first-line treatment in the management of advanced breast cancer.

METHODS

MCF-7 human breast cancer cells were transfected with gef gene using pcDNA3.1-TOPO expression vector. To determine the effect of the combined therapy, MCF-7 transfected and non-transfected cells were exposed to paclitaxel, docetaxel and doxorubicin at different concentrations. The growth-inhibitory effect of gef gene and/or drugs was assessed by MTT assay. Apoptosis modulation was determined by flow cytometric analysis, DNA fragmentation and morphological analysis. Multicellular tumour spheroids (MTS) from MCF-7 cells were used to confirm effectiveness of combined therapy (gef gene and drug).

RESULTS

Our results demonstrate that combined therapy gef gene/drugs (paclitaxel, docetaxel or doxurubicin) caused a decrease in cell viability. However, only the gef-doxorubicin (10 microM) combination induced a greater enhancement in the antitumour activity in MCF-7 cells. Most importantly, this combined strategy resulted in a significant synergistic effect, thus allowing lower doses of the drug to be used to achieve the same therapeutic effect. These results were confirmed using MTS in which volume decrease with combined therapy was greater than obtained using the gene therapy or chemotherapy alone, or the sum of both therapies.

CONCLUSIONS

The cytotoxic effect of gef gene in breast cancer cells enhances the chemotherapeutic effect of doxorubicin. This therapeutic approach has the potential to overcome some of the major limitations of conventional chemotherapy, and may therefore constitute a promising strategy for future applications in breast cancer therapy.

Regression of established subcutaneous B16-F10 murine melanoma tumors after gef gene therapy associated with the mitochondrial apoptotic pathway

Novel treatment modalities, including gene therapy, are needed for patients with advanced melanoma. We evaluated whether the gef gene, a suicide gene from Escherichia coli, had a significant cytotoxic impact on melanoma in vivo. First, we used a non-viral gene delivery approach (pcDNA3.1/gef) to study the inhibition of melanoma cells (B16-F10) proliferation in vitro. Secondly, we used direct intra-tumoral injection of pcDNA3.1/gef complexed with jetPEI to deliver gef cDNA to rapidly growing murine melanomas. We demonstrated that gef gene not only has an antiproliferative effect on B16-F10 cells in vitro, but also induces an important decrease in melanoma tumor volume (77.7% in 8 days) in vivo. Interestingly, after gef gene treatment, melanoma showed apoptosis activation associated with the mitochondrial pathway, suggesting that the induction of this death mechanism may be an effective strategy for its treatment. Our in vivo results indicate that gef gene might become a suitable therapeutic strategy for patients with advanced melanoma.

The cytotoxic activity of the phage E protein suppress the growth of murine B16 melanomas in vitro and in vivo

Novel treatment modalities, including gene therapy, are needed for patients with advanced melanoma. The E gene from the phage varphiX174 encodes a 91-aa protein which lyses Escherichia coli by formation of a transmembrane tunnel structure. To evaluate whether this E gene has a cytotoxic impact on melanoma cells in vitro and in vivo, and could therefore be used as a new therapeutic strategy for this tumor type, we selected the B16-F10 murine melanoma cell line as a model. We used a nonviral gene delivery approach (pcDNA3.1/E plasmid) to study the inhibition of melanoma cells' proliferation in vitro and direct intratumoral injection of pcDNA3.1/E complexed with jetPEI to deliver E cDNA to rapidly growing murine melanomas, and found that the E gene has both a strong antiproliferative effect in B16-F10 cells in vitro and induces an efficient decrease in melanoma tumor volume in vivo (90% in 15 days). Interestingly, the GFP-E fusion protein expressed in melanoma cells was located in the mitochondria. In vitro and in vivo analysis demonstrated significant functional and morphological mitochondrial alterations accompanied by a significant increase of cytochrome c and active caspase-3 and -9 in transfected cells, which suggests that tumoral cell death is mediated by the mitochondrial apoptotic pathway. These results show that E gene expression in melanoma cells has an extraordinary antitumor effect, which means it may be a new candidate for an effective strategy for melanoma treatment.