Improved safety of induced pluripotent stem cell-derived antigen-presenting cell-based cancer immunotherapy

The tumorigenicity and toxicity of induced pluripotent stem cells (iPSCs) and their derivatives are major safety concerns in their clinical application. Recently, we developed granulocyte-macrophage colony-stimulating factor (GM-CSF)-producing proliferating myeloid cells (GM-pMCs) from mouse iPSCs as a source of unlimited antigen-presenting cells for use in cancer immunotherapy. As GM-pMCs are generated by introducing c-Myc and Csf2 into iPSC-derived MCs and are dependent on self-produced GM-CSF for proliferation, methods to control their proliferation after administration should be introduced to improve safety. In this study, we compared the efficacy of two promising suicide gene systems, herpes simplex virus-thymidine kinase (HSV-TK)/ganciclovir (GCV) and inducible caspase-9 (iCasp9)/AP1903, for safeguarding GM-pMCs in cancer immunotherapy. The expression of HSV-TK or iCasp9 did not impair the fundamental properties of GM-pMCs. Both of these suicide gene-expressing cells selectively underwent apoptosis after treatment with the corresponding apoptosis-inducing drug, and they were promptly eliminated in vivo. iCasp9/AP1903 induced apoptosis more efficiently than HSV-TK/GCV. Furthermore, high concentrations of GCV were toxic to cells not expressing HSV-TK, whereas AP1903 was bioinert. These results suggest that iCasp9/AP1903 is superior to HSV-TK/GCV in terms of both safety and efficacy when controlling the fate of GM-pMCs after priming antitumor immunity.

Novel hepatitis B virus infection mouse model using herpes simplex virus type 1 thymidine kinase transgenic mice

BACKGROUND AND AIM

The chronicity of hepatitis B virus (HBV) infection is the result of impaired HBV-specific immune responses that cannot eliminate or cure the infected hepatocytes efficiently. Previous studies have used immunodeficient mice such as herpes simplex virus type 1 thymidine kinase NOD/Scid/IL2Rr^null (HSV-TK-NOG) mice. However, it is difficult to analyze the immune response in the previous models. In the present study, we established a novel HBV infection model using herpes simplex virus type 1 thymidine kinase (HSV-TK) mice in which the host immune system was not impaired.

METHODS

Herpes simplex virus type 1 thymidine kinase mice were injected intraperitoneally with ganciclovir (GCV). Seven days after GCV injection, GCV-treated mice were transplanted with 1 × 10⁶ hepatocytes from HBV-transgenic (HBV-Tg) mice.

RESULTS

Serum alanine aminotransferase levels in HSV-TK mice increased 1 and 2 weeks after GCV injection. The number and viability of hepatocytes from the whole liver of HBV-Tg mice significantly increased using digestion medium containing liberase. Hepatitis B surface antigen (HBsAg)-positive areas in the liver tissue were observed for at least 20 weeks after HBsAg-positive hepatocyte transplantation. In addition, we measured HBsAg in the serum after transplantation. HBsAg levels in HBV-Tg hepatocyte-replaced mice increased 4 weeks after transplantation. Furthermore, we examined the immune response in HSV-TK mice. The increase in hepatitis B surface antibody levels in replaced mice was maintained for 20 weeks. Also, interferon-γ-producing cells were increased in non-replaced mice.

CONCLUSIONS

A novel HBV infection mouse model will help to understand the mechanisms of HBV tolerance similar to human chronic HBV-infected patients and can be used to develop a new strategy to treat chronic HBV infection.

Suicide Gene Therapy Against Malignant Gliomas by the Local Delivery of Genetically Engineered Umbilical Cord Mesenchymal Stem Cells as Cellular Vehicles

BACKGROUND

Glioblastoma (GBM) is a malignant tumor that is difficult to eliminate, and new therapies are thus strongly desired. Mesenchymal stem cells (MSCs) have the ability to locate to injured tissues, inflammation sites and tumors and are thus good candidates for carrying antitumor genes for the treatment of tumors. Treating GBM with MSCs that have been transduced with the herpes simplex virus thymidine kinase (HSV-TK) gene has brought significant advances because MSCs can exert a bystander effect on tumor cells upon treatment with the prodrug ganciclovir (GCV).

OBJECTIVE

In this study, we aimed to determine whether HSV-TK-expressing umbilical cord mesenchymal stem cells (MSCTKs) together with prodrug GCV treatment could exert a bystander killing effect on GBM.

METHODS AND RESULTS

Compared with MSCTK: U87 ratio at 1:10,1:100 and 1:100, GCV concentration at 2.5µM or 250µM, when MSCTKs were cocultured with U87 cells at a ratio of 1:1, 25 µM GCV exerted a more stable killing effect. Higher amounts of MSCTKs cocultured with U87 cells were correlated with a better bystander effect exerted by the MSCTK/GCV system. We built U87-driven subcutaneous tumor models and brain intracranial tumor models to evaluate the efficiency of the MSCTK/GCV system on subcutaneous and intracranial tumors and found that MSCTK/GCV was effective in both models. The ratio of MSCTKs and tumor cells played a critical role in this therapeutic effect, with a higher MSCTK/U87 ratio exerting a better effect.

CONCLUSION

This research suggested that the MSCTK/GCV system exerts a strong bystander effect on GBM tumor cells, and this system may be a promising assistant method for GBM postoperative therapy.

Complete regression of metastatic de-differentiated liposarcoma with engineered mesenchymal stromal cells with dTRAIL and HSV-TK

De-differentiated liposarcoma (DDLPS) is a rare cancer with high rates of recurrence and metastasis. Currently, treatment with doxorubicin-ifosphamide, following surgical resection, is routinely performed. However, clinical treatment of these refractory cancers require further study. We investigated the treatment of mesenchymal stromal cells (MSC) transduced with dodecameric tumor necrosis factor receptor apoptosis-inducing ligand (dTRAIL) and herpes simplex virus thymidine kinase (HSV-TK) (MSC-TR/TK), as a method to approach DDLPS therapy. First, in order to assess the efficacy of this therapy, cell viability was evaluated by apoptosis analysis of a DDLPS cell line co-cultured with patient-derived cells (PDCs) and MSC-TR/TK in vitro. In vivo, we established a lung metastasis model using the DDLPS cell line and assessed the anti-tumorigenic efficiency of dTRAIL-TK by injecting MSC-TR/TK. Results confirmed that liposarcoma cells resistant to dTRAIL in PDCs, transformed by HSV-TK, induced apoptosis effectively after treatment with toxic ganciclovir (GCV). Meanwhile, we observed that treatment of GCV after injection of MSC-TR/TK effectively eliminated lung nodules in a lung metastasis model established from LPS246 cells resistant to dTRAIL. When mice were treated with GCV two days after double injection with MSC-TR/TK, the tumor suppression effect was even more pronounced.

Depletion of Bone Marrow-Derived Fibrocytes Attenuates TAA-Induced Liver Fibrosis in Mice

Bone marrow-derived fibrocytes (FC) represent a unique cell type, sharing features of both mesenchymal and hematopoietic cells. FC were shown to specifically infiltrate the injured liver and participate in fibrogenesis. Moreover, FC exert a variety of paracrine functions, thus possibly influencing the disease progression. However, the overall contribution of FC to liver fibrosis remains unclear. We aimed to study the effect of a specific FC depletion, utilizing a herpes simplex virus thymidine kinase (HSV-TK)/Valganciclovir suicide gene strategy. Fibrosis was induced by oral thioacetamide (TAA) administration in C57BL/6J mice. Hepatic hydroxyproline content was assessed for the primary readout. The HSV-TK model enabled the specific depletion of fibrocytes. Hepatic hydroxyproline content was significantly reduced as a result of the fibrocyte ablation (−7.8%; 95% CI: 0.7–14.8%; p = 0.033), denoting a reduced deposition of fibrillar collagens. Lower serum alanine transaminase levels (−20.9%; 95% CI: 0.4–36.9%; p = 0.049) indicate a mitigation of liver-specific cellular damage. A detailed mode of action, however, remains yet to be identified. The present study demonstrates a relevant functional contribution of fibrocytes to chronic toxic liver fibrosis, contradicting recent reports. Our results emphasize the need to thoroughly study the biology of fibrocytes in order to understand their importance for hepatic fibrogenesis.

Graphene oxide-hydroxyapatite nanocomposites effectively deliver HSV-TK suicide gene to inhibit human breast cancer growth

Gene therapy with herpes simplex virus thymidine kinase gene (HSV-TK), which is also known as "suicide" gene therapy, is effective in various tumor models. The lack of a safe and efficient gene delivery system has become a major obstacle to "suicide" gene therapy. In this study, the cytotoxicity and transfection efficiency of graphene oxide-hydroxyapatite (GO-Hap) were analyzed by MTS and flow cytometry, respectively. A series of assays were performed to evaluate the effects of GO-HAp/p-HRE/ERE-Sur-TK combined with ganciclovir treatment on growth of human breast normal and cancer cells. The results showed that GO-HAp nanocomposites effectively transfected cells with minimum toxicity. GO-HAp/p-HRE/ERE-Sur-TK combined with ganciclovir treatment inhibited the proliferation and induced cell apoptosis in cancer cells, while the cytotoxic effects are tolerable in normal breast cells. We conclude that the GO-HAp nanocomposites have significant potential as a gene delivery vector for cancer therapy.

Treatment of advanced gastrointestinal cancer with genetically modified autologous mesenchymal stem cells: Results from the phase 1/2 TREAT-ME-1 trial

TREAT-ME-1, a Phase 1/2 open-label multicenter, first-in-human, first-in-class trial, evaluated the safety, tolerability and efficacy of treatment with genetically modified autologous mesenchymal stromal cells (MSC), MSC_ apceth_101, in combination with ganciclovir in patients with advanced gastrointestinal adenocarcinoma. Immunological and inflammatory markers were also assessed. All patients (3 in Phase 1; 7 in Phase 2) received three treatment cycles of MSC_apceth_101 at one dose level on Day 0, 7, and 14 followed by ganciclovir administration according to the manufacturer's instructions for 48─72 h after MSC_apceth_101 injection. Ten patients were treated with a total dose of 3.0 x 10⁶ cells/kg MSC_apceth_101. 36 adverse events and six serious adverse events were reported. Five patients achieved stable disease (change in target lesions of -2 to +28%). For all patients, the median time to progression was 1.8 months (95% CI: 0.5, 3.9 months). Median overall survival could not be estimated as 8/10 patients were still alive at the end of the study (1 year) and therefore censored. Post-study observation of patients showed a median overall survival of 15.6 months (ranging from 2.2─27.0 months). Treatment with MSC_apceth_101 and ganciclovir did not induce a consistent increase or decrease in levels of any of the tumor markers analyzed. No clear trends in the immunological markers assessed were observed. MSC_apceth_101 in combination with ganciclovir was safe and tolerable in patients with advanced gastrointestinal adenocarcinoma, with preliminary signs of efficacy in terms of clinical stabilization of disease.

Cancer Suicide Gene Therapy with TK.007

Cancer is a devastating disease characterized by uncontrolled and aggressive cell growth. Suicide gene therapy (SGT) facilitating induction of malignancy-specific cell death represents a novel therapeutic approach to treat cancer, which has been investigated in several cancer types with very promising results. In addition, SGT has been suggested as a safeguard in adoptive immunotherapy and regenerative-medicine settings. Generally, SGT consists of two steps-vector-mediated delivery of suicide genes into tumors and subsequent activation of the suicide mechanism, e.g., by administration of a specific prodrug. This chapter provides a framework of protocols for basic and translational research using the Herpes-simplex-virus thymidine kinase (HSV-TK)/ganciclovir (GCV) system, the most widely used suicide gene approach. The protocols provide standard guidelines for the preparation of high-titer third-generation lentiviral vectors encoding a genetically improved HSV-TK version known as TK.007 and its application in in vitro and in vivo treatment setups.

Combined treatment of cholangiocarcinoma with interventional radiofrequency hyperthermia and heat shock protein promoter-mediated HSV-TK gene therapy

Cholangiocarcinoma is a most lethal malignancy frequently resistant to chemotherapy. Herpes simplex virus thymidine kinase/Ganciclovir (HSV-TK/GCV) suicide gene therapy is a promising approach to treat different cancers, including cholangiocarcinoma. However drawbacks including low therapeutic gene expression and lack of precise targeted gene delivery limit the wide clinical utilization of the suicide gene therapy. We attempted to overcome these obstacles. We established the "proof-of-principle" of this concept via serial in-vitro experiments using human cholangiocarcinoma cells and then validated the new interventional oncology technique in vivo using mice harboring the same patient derived cholangiocarcinomas. Curative effects were evaluated by magnetic resonance imaging and confirmed by pathology and laboratory examinations. Intratumoral radiofrequency hyperthermia (RFH) significantly elevated the targeted expression of HSV-TK gene and further enhanced the therapeutic effects of direct intratumoral HSV-TK/GCV gene therapy, evident as the least number of survival tumor cells, smallest tumor size, and the highest apoptosis index in the combination treatment of HSV-TK plus RFH, compared to other control treatments. The novel combination of image-guided interventional oncology, RFH technology, and direct gene therapy may be valuable for the effective treatment of cholangiocarcinoma.

Radiofrequency hyperthermia promotes the therapeutic effects on chemotherapeutic-resistant breast cancer when combined with heat shock protein promoter-controlled HSV-TK gene therapy: Toward imaging-guided interventional gene therapy

Objective

Gene therapy is a frontier in modern medicine. In the present study, we explored a new technique for the effective treatment of multidrug-resistant (MDR) breast cancer by combining fully the advantages of multidisciplinary fields, including image-guided minimally invasive interventional oncology, radiofrequency technology, and direct intratumoral gene therapy.

Results

Combination treatment with P_HSP-TK plus RFH resulted in significantly higher TK gene transfection/expression, as well as a lower cell proliferation rate and a higher cell apoptosis index, than those of control groups. In vivo validation experiments with MRI confirmed that combination therapy resulted in a significant reduction of relative tumor volume compared with those of control animals, which was supported by the results of histologic and apoptosis analyses.

Materials and methods

The heat shock protein promoter (P_HSP) was used to precisely control the overexpression of thymidine kinase (TK) (P_HSP-TK). Serial in vitro experiments were performed to confirm whether radiofrequency hyperthermia (RFH) could enhance P_HSP-TK transfection and expression in a MDR breast cancer cell line (MCF7/Adr). Serial in vivo experiments were then carried out to validate the feasibility of the new technique, termed interventional RFH-enhanced direct intratumoral P_HSP-TK gene therapy. The therapeutic effect of combination therapy was evaluated by MRI and confirmed by subsequent laboratory correlation.

Conclusions

This study has established “proof-of-principle” of a new technique, interventional RFH-enhanced local gene therapy for MDR breast cancer, which may open new avenues for the effective management of MDR breast cancers via the simultaneous integration of interventional oncology, RF technology, and direct intratumoral gene therapy.

Thymidine Kinase PET Reporter Gene Imaging of Cancer Cells In Vivo

Positron emission tomography (PET) is a three dimensional imaging modality that detects the accumulation of radiolabeled isotopes in vivo. Ectopic expression of a thymidine kinase reporter gene allows for the specific detection of reporter cells in vivo by imaging with the reporter specific probe. PET reporter imaging is sensitive, quantitative and can be scaled into larger tumors or animals with little to no tissue diffraction. Here, we describe how thymidine kinase PET reporter genes can be used to noninvasively image cancer cells in vivo.

Deciphering fact from artifact when using reporter assays to investigate the roles of host factors on L1 retrotransposition

Background

The Long INterspersed Element-1 (L1, LINE-1) is the only autonomous mobile DNA element in humans and has generated as much as half of the genome. Due to increasing clinical interest in the roles of L1 in cancer, embryogenesis and neuronal development, it has become a priority to understand L1-host interactions and identify host factors required for its activity. Apropos to this, we recently reported that L1 retrotransposition in HeLa cells requires phosphorylation of the L1 protein ORF1p at motifs targeted by host cell proline-directed protein kinases (PDPKs), which include the family of mitogen-activated protein kinases (MAPKs). Using two engineered L1 reporter assays, we continued our investigation into the roles of MAPKs in L1 activity.

Results

We found that the MAPK p38δ phosphorylated ORF1p on three of its four PDPK motifs required for L1 activity. In addition, we found that a constitutively active p38δ mutant appeared to promote L1 retrotransposition in HeLa cells. However, despite the consistency of these findings with our earlier work, we identified some technical concerns regarding the experimental methodology. Specifically, we found that exogenous expression of p38δ appeared to affect at least one heterologous promoter in an engineered L1 reporter, as well as generate opposing effects on two different reporters. We also show that two commercially available non-targeting control (NTC) siRNAs elicit drastically different effects on the apparent retrotransposition reported by both L1 assays, which raises concerns about the use of NTCs as normalizing controls.

Conclusions

Engineered L1 reporter assays have been invaluable for determining the functions and critical residues of L1 open reading frames, as well as elucidating many aspects of L1 replication. However, our results suggest that caution is required when interpreting data obtained from L1 reporters used in conjunction with exogenous gene expression or siRNA.

Suicide plus immune gene therapy prevents post-surgical local relapse and increases overall survival in an aggressive mouse melanoma setting

In an aggressive B16-F10 murine melanoma model, we evaluated the effectiveness and antitumor mechanisms triggered by a surgery adjuvant treatment that combined a local suicide gene therapy (SG) with a subcutaneous genetic vaccine (Vx) composed of B16-F10 cell extracts and lipoplexes carrying the genes of human interleukin-2 and murine granulocyte and macrophage colony stimulating factor. Pre-surgical SG treatment, neither alone nor combined with Vx was able to slow down the fast evolution of this tumor. After surgery, both SG and SG + Vx treatments, significantly prevented (in 50% of mice) or delayed (in the remaining 50%) post-surgical recurrence, as well as significantly prolonged recurrence-free (SG and SG + Vx) and overall median survival (SG + Vx). The treatment induced the generation of a pseudocapsule wrapping and separating the tumor from surrounding host tissue. Both, SG and the subcutaneous Vx, induced this envelope that was absent in the control group. On the other hand, PET scan imaging of the SG + Vx group suggested the development of an effective systemic immunostimulation that enhanced (18)FDG accrual in the thymus, spleen and vertebral column. When combined with surgery, direct intralesional injection of suicide gene plus distal subcutaneous genetic vaccine displayed efficacy and systemic antitumor immune response without host toxicity. This suggests the potential value of the assayed approach for clinical purposes.

2,3-Dihydroxy-quinoxaline induces ATPase activity of Herpes Simplex Virus thymidine kinase

2,3-Dihydroxy-quinoxaline, a small molecule that promotes ATPase catalytic activity of Herpes Simplex Virus thymidine kinase (HSV-TK), was identified by virtual screening. This compound competitively inhibited HSV-TK catalyzed phosphorylation of acyclovir with Ki=250 μM (95% CI: 106-405 μM) and dose-dependently increased the rate of the ATP hydrolysis with KM=112 μM (95% CI: 28-195 μM). The kinetic scheme consistent with this experimental data is proposed.

Gene-modified hematopoietic stem cells for cancer immunotherapy

The rapid expansion of available cancer immunotherapies has resulted in favorable early outcomes. Specifically the use of gene therapy to introduce chimeric antigen receptors (CARs) and T cell receptors (TCRs) in T cells creates new immunotherapy options for patients. While showing early success with these approaches, limitations remain that can be overcome by the use of modification of hematopoietic stem cells (HSCs) to express CARs and TCRs. With modern gene therapy technologies, increased safety and control of the modification of the HSCs can be achieved through the use of a suicide gene.

Inhibition of homologous recombination with vorinostat synergistically enhances ganciclovir cytotoxicity

The nucleoside analog ganciclovir (GCV) elicits cytotoxicity in tumor cells via a novel mechanism in which drug incorporation into DNA produces minimal disruption of replication, but numerous DNA double strand breaks occur during the second S-phase after drug exposure. We propose that homologous recombination (HR), a major repair pathway for DNA double strand breaks, can prevent GCV-induced DNA damage, and that inhibition of HR will enhance cytotoxicity with GCV. Survival after GCV treatment in cells expressing a herpes simplex virus thymidine kinase was strongly dependent on HR (>14-fold decrease in IC50 in HR-deficient vs. HR-proficient CHO cells). In a homologous recombination reporter assay, the histone deacetylase inhibitor, suberoylanilide hydroxamic acid (SAHA; vorinostat), decreased HR repair events up to 85%. SAHA plus GCV produced synergistic cytotoxicity in U251tk human glioblastoma cells. Elucidation of the synergistic mechanism demonstrated that SAHA produced a concentration-dependent decrease in the HR proteins Rad51 and CtIP. GCV alone produced numerous Rad51 foci, demonstrating activation of HR. However, the addition of SAHA blocked GCV-induced Rad51 foci formation completely and increased γH2AX, a marker of DNA double strand breaks. SAHA plus GCV also produced synergistic cytotoxicity in HR-proficient CHO cells, but the combination was antagonistic or additive in HR-deficient CHO cells. Collectively, these data demonstrate that HR promotes survival with GCV and compromise of HR by SAHA results in synergistic cytotoxicity, revealing a new mechanism for enhancing anticancer activity with GCV.

Turning an antiviral into an anticancer drug: nanoparticle delivery of acyclovir monophosphate

Anti-herpes simplex virus (HSV) drug acyclovir (ACV) is phosphorylated by the viral thymidine kinase (TK), but not the cellular TK. Phosphorylated ACV inhibits cellular DNA synthesis and kills the infected cells. We hypothesize that ACV monophosphate (ACVP), which is an activated metabolite of ACV, should be efficient in killing cells independent of HSV-TK. If so, ACVP should be a cytotoxic agent if properly delivered to the cancer cells. The Lipid/Calcium/Phosphate (LCP) nanoparticles (NPs) with a membrane/core structure were used to encapsulate ACVP to facilitate the targeted delivery of ACVP to the tumor. The LCP NPs showed entrapment efficiency of ~70%, the nano-scaled particle size and positive zeta potential. Moreover, ACVP-loaded LCP NPs (A-LCP NPs) exhibited concentration-dependent cytotoxicity against H460 cells and increased S-phase arrest. More importantly, a significant reduction of the tumor volume over 4 days following administration (p<0.05-0.005) of A-LCP NPs, suggests excellent in vivo efficacy. Whereas, two free drugs (ACV and ACVP) and blank LCP NPs showed little or no therapeutic effect. It was also found that the high efficacy of A-LCP NPs was associated with the ability to induce dramatic apoptosis of the tumor cells, as well as significantly inhibit tumor cell proliferation and cell cycle progression. In conclusion, with the help of LCP NPs, monophosphorylation modification of ACV can successfully modify an HSV-TK-dependent antiviral drug into an anti-tumor drug.

History of gene therapy

Two decades after the initial gene therapy trials and more than 1700 approved clinical trials worldwide we not only have gained much new information and knowledge regarding gene therapy in general, but also learned to understand the concern that has persisted in society. Despite the setbacks gene therapy has faced, success stories have increasingly emerged. Examples for these are the positive recommendation for a gene therapy product (Glybera) by the EMA for approval in the European Union and the positive trials for the treatment of ADA deficiency, SCID-X1 and adrenoleukodystrophy. Nevertheless, our knowledge continues to grow and during the course of time more safety data has become available that helps us to develop better gene therapy approaches. Also, with the increased understanding of molecular medicine, we have been able to develop more specific and efficient gene transfer vectors which are now producing clinical results. In this review, we will take a historical view and highlight some of the milestones that had an important impact on the development of gene therapy. We will also discuss briefly the safety and ethical aspects of gene therapy and address some concerns that have been connected with gene therapy as an important therapeutic modality.

Trojan horse at cellular level for tumor gene therapies

Among innovative strategies developed for cancer treatments, gene therapies stand of great interest despite their well-known limitations in targeting, delivery, toxicity or stability. The success of any given gene-therapy is highly dependent on the carrier efficiency. New approaches are often revisiting the mythic trojan horse concept to carry therapeutic nucleic acid, i.e. DNAs, RNAs or small interfering RNAs, to pathologic tumor site. Recent investigations are focusing on engineering carrying modalities to overtake the above limitations bringing new promise to cancer patients. This review describes recent advances and perspectives for gene therapies devoted to tumor treatment, taking advantage of available knowledge in biotechnology and medicine.