Expressing Cytosine Deaminase Research Articles

Escherichia coli cytosine deaminase: Structural and biotechnological aspects.

Suicide gene therapy involves introducing viral or bacterial genes into tumor cells, which enables the conversion of a nontoxic prodrug into a toxic-lethal drug. The application of the bacterial cytosine deaminase (bCD)/5-fluorocytosine (5-FC) approach has been beneficial and progressive within the current field of cancer therapy because of the enhanced bystander effect. The basis of this method is the preferential deamination of 5-FC to 5-fluorouracil by cancer cells expressing cytosine deaminase (CD), which strongly inhibits DNA synthesis and RNA function, effectively targeting tumor cells. However, the poor binding affinity of toward 5-FC compared to the natural substrate cytosine and/or inappropriate thermostability limits the clinical applications of this gene therapy approach. Nowadays, many genetic engineering studies have been carried out to solve and improve the activity of this enzyme. In the current review, we intend to discuss the biotechnological aspects of Escherichia coli CD, including its structure, functions, molecular cloning, and protein engineering. We will also explore its relevance in cancer clinical trials. By examining these aspects, we hope to provide a thorough understanding of E. coli CD and its potential applications in cancer therapy.

Genetically engineered neural stem cells expressing cytosine deaminase and interferon-beta enhanced T cell-mediated antitumor immunity against gastric cancer in a humanized mouse model

AimsGastric cancer (GC) is an invasive, fatal disease with a poor prognosis. Gene-directed enzyme prodrug therapy via genetically engineered neural stem cells (GENSTECs) has been widely studied in various malignancies, such as breast, ovarian, and renal cancer. In this study, the human neural stem cells expressing cytosine deaminase and interferon beta (HB1.F3.CD.IFN-β) cells were applied to convert non-toxic 5-fluorocytosine to cytotoxic 5-fluorouracil and secrete IFN-β. Materials and methodsHuman lymphokine-activated killer cells (LAKs) were generated by stimulating human peripheral blood mononuclear cells (PBMCs) by interleukin-2, and we evaluated the cytotoxic activity and migratory ability of LAKs co-cultured with GNESTECs or their conditioned media in vitro. A GC-bearing human immune system (HIS) mouse model was generated by transplanting human PBMCs followed by subcutaneous engraftment of MKN45 cells in NSG-B2m mice to evaluate the involvement of T cell-mediated anti-cancer immune activity of GENSTECs. Key findingsIn vitro studies showed the presence of HB1.F3.CD.IFN-β cells facilitated the migration ability of LAKs to MKN45 cells and activated their cytotoxic potential. In MKN45-xenografted HIS mice, treatment with HB1.F3.CD.IFN-β cells resulted in increased cytotoxic T lymphocyte (CTL) infiltration throughout the tumor, including the central area. Moreover, the group treated to HB1.F3.CD.IFN-β showed increased granzyme B expression in the tumor, eventually enhancing the tumor-killing potential of CTLs and significantly delaying tumor growth. SignificanceThese results indicate that the HB1.F3.CD.IFN-β cells exert anti-cancer effects on GC by facilitating the T cell-mediated immune response, and GENSTECs are a promising therapeutic strategy for GC.

Engineering of mesenchymal stem cells to express cytosine deaminase gene with a selecable marker gene.

e14050 Background: Suicide genes induce apoptosis not only in the cell itself but also in surrounding cells. The former is called the suicide effect and the latter is called the bystander effect. Two major suicide gene strategies currently pursued, cytosine deaminase (CD)/5-fluorocytosine (5-FC) and the herpes simplex virus-thymidine kinase/ganciclovir. Both genes have similar potential to induce suicide effects, but bystander effect is higher in CD/5-FC. Here we show that the level of CD expression/activity influence the anti-cancer activity of CD-expressing cells and further demonstrate the need to use selectable markers during manufacturing of CD-expressing cells. Finally we test whether live microbes harboring the shed selectable marker genes are controllable by commonly used antibiotics. Methods: We introduced a microbial CD gene and puromycin-N-acetyltransferase ( pac) gene to bone-marrow derived mesenchymal stem cells MSCs) using a retroviral vector and selected the transduced cells with 4 ug/mL puromycin for one week. To determine the effect of purity, we varied the ratio of CD-expressing MSCs with naïve MSCs and 5-FC concentration in the culture and on co-cultured glioma cells. To mimic the situation in which the shed pac gene is transmitted to live microbes in vivo, we introduced the pac gene to E. coli and tested the growth of the pac-expressing E. coli using VITEK following the standard protocol M100-S32 in the presence of diverse antibiotics. Results: We found that selection of CD-expressing cells with puromycin during manufacturing process enhanced the bystander (anti-cancer effect). Lowering the purity of CD-expressing MSCs required more 5-FC with higher IC50. Growth of pac-expressing E. coli was completely inhibited by commonly used antibiotics in the hospital. Conclusions: We proved that antibiotic selection is necessary during manufacturing process. We also showed that the risk of transmission of shed pac gene can be manageable with commonly used antibiotics. We propose that using pac selectable marker gene can be beneficial to maintain the purity of engineered cells.

Pharmacokinetics and tolerance of repeated oral administration of 5-fluorocytosine in healthy dogs

Background5-fluorocytosine is a pyrimidine and a fluorinated cytosine analog mainly used as an antifungal agent. It is a precursor of 5-fluorouracil, which possesses anticancer properties. To reduce systemic toxicity of 5-fluorouracil during chemotherapy, 5- fluorocytosine can be used as a targeted anticancer agent. Expression of cytosine deaminase by a viral vector within a tumor allows targeted chemotherapy by converting 5-fluorocytosine into the cytotoxic chemotherapeutic agent 5-fluorouracil. However, little is known about the tolerance of 5-fluorocytosine in dogs after prolonged administration.ResultsIn three healthy Beagle dogs receiving 100 mg/kg of 5-fluorocytosine twice daily for 14 days by oral route, non-compartmental pharmacokinetics revealed a terminal elimination half-life of 164.5 ± 22.5 min at day 1 and of 179.2 ± 11.5 min, after 7 days of administration. Clearance was significantly decreased between day 1 and day 7 with 0.386 ± 0.031 and 0.322 ± 0.027 ml/min/kg, respectively. Maximal plasma concentration values were below 100 µg/ml, which is considered within the therapeutic margin for human patients. 5-fluorouracil plasma concentration was below the limit of detection at all time points. The main adverse events consisted of depigmented, ulcerated, exudative, and crusty cutaneous lesions 10 to 13 days after beginning 5-fluorocytosine administration. The lesions were localized to the nasal planum, the lips, the eyelids, and the scrotum. Histological analyses were consistent with a cutaneous lupoid drug reaction. Complete healing was observed 15 to 21 days after cessation of 5-fluorocytosine. No biochemical or hematological adverse events were noticed.ConclusionsLong term administration of 5-fluorocytosine was associated with cutaneous toxicity in healthy dogs. It suggests that pharmacotherapy should be adjusted to reduce the toxicity of 5-fluorocytosine in targeted chemotherapy.

ATR kinase activity promotes antibody class switch recombination in B cells through cell cycle regulation without suppressing DSB resection and microhomology usage.

Class switch recombination (CSR) changes the effector functions of antibodies and is carried out by classical and alternative nonhomologous end joining (c-NHEJ and A-EJ) of repetitive switch (S) region double-strand breaks (DSBs). The master DNA damage response (DDR) kinase ataxia-telangiectasia mutated (ATM) is critical for CSR in part by suppressing S region DSB resection. However, whether another related DDR kinase ATM- and Rad3-related (ATR) plays similar role in CSR remains elusive. In this study, we investigated the requirement for ATR kinase activity on CSR in both c-NHEJ competent and deficient B cell lines with high-throughput sequencing of S-S junctions. We found that ATR kinase inhibition efficiently blocked both c-NHEJ- and A-EJ-mediated CSR without affecting germline transcription and activation-induced cytosine deaminase expression. In contrast to ATM, ATR does not suppress S region DSB resection and microhomology usage. In addition, ATR kinase inhibition did not affect Cas9-generated DSB end joining by either c-NHEJ and A-EJ. ATR kinase-inhibited stimulated B cells proliferate much slower than controls and exhibited altered cell cycle profile with increased G1 and G2/M phase cells. In summary, our data revealed a role for ATR in promoting both c-NHEJ- and A-EJ-mediated CSR through regulating cell proliferation upon damage without negatively influencing DSB end-joining features.

Potentiated antitumor effects of APS001F/5-FC combined with anti-PD-1 antibody in a CT26 syngeneic mouse model

APS001F is a strain of Bifidobacterium longum genetically engineered to express cytosine deaminase that converts 5-fluorocytosine (5-FC) to 5-fluorouracil. In the present study, antitumor effects of APS001F plus 5-FC (APS001F/5-FC) in combination with anti-PD-1 monoclonal antibody were investigated using a CT26 syngeneic mouse model. Both of dosing of APS001F/5-FC before and after anti-PD-1 mAb in the combination dosing exhibited antitumor effects as well as prolonged survival over the nontreated control. The survival rate in the combination therapy significantly increased over the monotherapy with APS001F/5-FC and that with anti-PD-1 mAb. Regulatory T cells among CD4+ T cells in tumor decreased in the combination therapy, while the ratio of CD8+ T cells was maintained in all groups. Taken these results together, APS001F/5-FC not only demonstrates a direct antitumor activity, but also immunomodulatory effects once localized in the hypoxic region of the tumor, which allows anti-PD-1 mAb to exert potentiated antitumor effects.

Antitumor efficacy of oncolytic HSV-1 expressing cytosine deaminase is synergistically enhanced by DPD down-regulation and EMT inhibition in uveal melanoma xenograft.

Uveal melanoma (UM) is the most common intraocular tumor in adults and has a high incidence of metastases. Possible treatments remain limited in UM with enucleation and radiation, leading to poor prognosis in this chemo-resistant carcinoma. Thus, urging demand for novel treatment is needed. We examined the antitumor efficacy of a new recombinant oncolytic herpes simplex virus type 1 (oHSV-1) armed with E.coli cytosine deaminase (CD). We determined the efficacy of the oncolytic virus in UM cell lines. In vivo experiments showed that oHSV-CD/5-fluorocytosine (5-FC) treatment reduce tumor volume and prolonged survival. We further demonstrated the molecular mechanisms of oHSV-CD/5-FC treatment. The oncolytic virus down-regulated IL-6 expression and thereby reversed the epithelial-mesenchymal transition (EMT) phenotype. Dihydropyrimidine dehydrogenase (DPD), the rate-limiting enzyme in 5-fluorouracil (5-FU) metabolism, was also down-regulated. Therefore, the efficacy of oHSV-CD/5-FC was synergistically enhanced by DPD down-regulation and EMT inhibition. This study provides solid evidence for the antitumor efficacy of oHSV-CD/5-FC treatment in vitro and in vivo. The molecular mechanisms of this treatment may bring a new therapeutic approach for future treatment of UM.

Feasibility of intracerebrally administering multiple doses of genetically modified neural stem cells to locally produce chemotherapy in glioma patients.

Neural stem cells (NSCs) are tumor tropic and can be genetically modified to produce anti-cancer therapies locally in the brain. In a prior first-in-human study we demonstrated that a single dose of intracerebrally administered allogeneic NSCs, which were retrovirally transduced to express cytosine deaminase (CD), tracked to glioma sites and converted oral 5-fluorocytosine (5-FC) to 5-fluorouracil (5-FU). The next step in the clinical development of this NSC-based anti-cancer strategy was to assess the feasibility of administering multiple intracerebral doses of CD-expressing NSCs (CD-NSCs) in patients with recurrent high grade gliomas. CD-NSCs were given every 2 weeks using an indwelling brain catheter, followed each time by a 7-day course of oral 5-FC (and leucovorin in the final patient cohort). Fifteen evaluable patients received a median of 4 (range 2–10) intracerebral CD-NSC doses; doses were escalated from 50 x 106 to 150 x 106 CD-NSCs. Neuropharmacokinetic data confirmed that CD-NSCs continuously produced 5-FU in the brain during the course of 5-FC. There were no clinical signs of immunogenicity, and only three patients developed anti-NSC antibodies. Our results suggest intracerebral administration of serial doses of CD-NSCs is safe and feasible and identified a recommended dose for phase II testing of 150 x 106 CD-NSCs.

Antithyroid cancer effects of human neural stem cells expressing therapeutic genes on anaplastic thyroid cancer cells.

Stem cells that express therapeutic proteins have been identified to have an anticancer effects on various types of cancer. In the present study study, human neural stem cells (hNSCs) that were genetically engineered to express cytosine deaminase (CD) and human interferon-β (IFN-β) were used for anaplastic thyroid cancer (ATC) treatment owing to their tumor-tropic properties and therapeutic effects. CD is an enzyme that converts 5-fluorocytosine (5-FC), a prodrug, to 5-fluorouracil (5-FU) which is a medication to suppress tumor growth through DNA synthesis inhibition. Also, IFN-β suppresses tumor growth by the induction of apoptotic process. In water soluble tetrazolium salt (WST) assay, SNU-80 cells which are human female ATC cells were cocultured with three cell types including engineered hNSCs such as HB1.F3, HB1.F3.CD, and HB1.F3.CD.IFN-β cells on transwells and treated with 5-FC for 72 hours. Finally, the SNU-80 cell viability was reduced by the coculture with HB1.F3.CD and HB1.F3.CD.IFN-β cells. In dichlorofluorescein diacetate (DCF-DA) and TdT-mediated dUTP nick-end labeling (TUNEL) assays, the production of reactive oxygen species (ROS) and the number of apoptotic cells were increased by HB1.F3.CD and HB1.F3.CD.IFN-β cells in the presence of 5-FC. In Western blot assay, ROS, and apoptosis-related genes were increased in SNU-80 cells when they were cocultured with HB1.F3.CD and HB1.F3.CD.IFN-β cells. In transwell migration assay, hNSCs selectively migrated to SNU-80 cells because hNSCs interacted with chemoattractant factors like SDF-1α, uPAR, and CCR2 secreted by SNU-80 cells. Taken together, engineered hNSCs were revealed to selectively migrate to ATC cells and to inhibit growth as well as to induce apoptosis of ATC cells via ROS production through the actions of transgenes such as CD and IFN-β. Therefore, these engineered hNSCs can be promising candidates for the treatment of metastatic ATC.

Labeling and Isolation of Fluorouracil Tagged RNA by Cytosine Deaminase Expression.

Tissues are comprised of different cell types whose interactions elicit distinct gene expression patterns that regulate tissue formation, regeneration, homeostasis and repair. Analysis of these gene expression patterns require methods that can capture as closely as possible the transcriptomes of cells of interest in their tissue microenvironment. Current technologies designed to study in situ transcriptomics are limited by their low sensitivity that require cell types to represent more than 1% of the total tissue, making it challenging to transcriptionally profile rare cell populations rapidly isolated from their native microenvironment. To address this problem, we developed fluorouracil-tagged RNA sequencing (Flura-seq) that utilizes cytosine deaminase (CD) to convert the non-natural pyrimidine fluorocytosine to fluorouracil. Expression of S. cerevisiae CD and exposure to fluorocytosine generates fluorouracil and metabolically labels newly synthesized RNAs specifically in cells of interest. Fluorouracil-tagged RNAs can then be immunopurified and used for downstream analysis. Here, we describe the detailed protocol to perform Flura-seq both in vitro and in vivo. The robustness, simplicity and lack of toxicity of Flura-seq make this tool broadly applicable to many studies in developmental, regenerative, and cancer biology.

The growth of K562 human leukemia cells was inhibited by therapeutic neural stem cells in cellular and xenograft mouse models

To confirm the anti-tumor effect of engineered neural stem cells (NSCs) expressing cytosine deaminase (CD) and interferon-β (IFN-β) with prodrug 5-fluorocytosine (FC), K562 chronic myeloid leukemia (CML) cells were co-cultured with the neural stem cell lines HB1.F3.CD and HB1.F3.CD.IFN-β in 5-FC containing media. A significant decrease in the viability of K562 cells was observed by the treatment of the NSC lines, HB1.F3.CD and HB1.F3.CD.IFN-β, compared with the control. A modified trans-well assay showed that engineered human NSCs significantly migrated toward K562 CML cells more than human normal lung cells. In addition, the important chemoattractant factors involved in the specific migration ability of stem cells were found to be expressed in K562 CML cells. In a xenograft mouse model, NSC treatments via subcutaneous and intravenous injections resulted in significant inhibitions of tumor mass growth and extended survival dates of the mice. Taken together, these results suggest that gene therapy using genetically engineered stem cells expressing CD and IFN-β may be effective for treating CML in these mouse models.

Neural stem cells expressing cytosine deaminase and interferon-[beta] suppressed the growth and metastasis of anaplastic thyroid cancer cells

Searchable abstracts of presentations at key conferences in endocrinology ISSN 1470-3947 (print) | ISSN 1479-6848 (online)

Cancer-Specific Inhibitory Effects of Genetically Engineered Stem Cells Expressing Cytosine Deaminase and Interferon-β Against Choriocarcinoma in Xenografted Metastatic Mouse Models

Cancer treatments using stem cells expressing therapeutic genes have been identified for various types of cancers. In this study, we investigated inhibitory effects of HB1.F3.CD and HB1.F3.CD.IFN-β cells expressing Escherichia coli cytosine deaminase (CD) and human interferon-β (IFN-β) genes in intravenously (i.v.) injected mice with a metastasis model. In this treatment, pro-drug 5-fluorocytosine (5-FC) is converted to cytotoxic drug 5-fluorouracil by hNSCs expressing the CD gene, which inhibits DNA synthesis in cancer cells. Moreover, IFN-β induces apoptosis and reduces the growth of cancer cells. Upon MTT assay, proliferation of choriocarcinoma (JEG-3) cells decreased when co-cultured with hNSCs expressing CD and IFN-β genes. To confirm the cancer-tropic effect of these stem cells, chemoattractant factors (VEGF, CXCR4, and C-kit) secreted from JEG-3 cells were identified by polymerase chain reaction. hNSCs migrate toward JEG-3 cells due to ligand-receptor interactions of these factors. Accordingly, the migration capability of hNSCs toward JEG-3 cells was confirmed using an in vitro Trans-well assay, in vivo subcutaneously (s.c.) injected mice groups (xenograft model), and metastasis model. Intravenously injected hNSCs migrated freely to other organs when compared to s.c. injected hNSCs. Thus, we confirmed the inhibition of lung and ovarian metastasis of choriocarcinoma by i.v. injected HB1.F3.CD or HB1.F3.CD.IFN-β cells in the presence of 5-FC. Treatment of these stem cells also increased the survival rates of mice. In conclusion, this study showed that metastatic cancer was diminished by genetically engineered hNSCs and noncytotoxic drug 5-FC. This is the first report of the therapeutic potential of i.v. injected hNSCs in a metastasis model; therefore, the results indicate that this stem cell therapy can be used as an alternative novel tool to treat metastatic choriocarcinoma.

Abstract B13: A growth of human choriocarcinoma cells was selectively inhibited by therapeutic neural stem cells expressing cytosine deaminase and interferon-β in cellular and xenograft models

Abstract In this study, human neural stem cells (hNSCs) expressing Escherichia coli cytosine deaminase (CD) and human interferon-β (IFN-β) was used to cancer treatment strategy for human choriocarcinoma cancer. Prodrug 5-fluorocytosine (5-FC) is converted to 5-fluorouacil (5-FU) by CD, which induces an effect of killing the tumor cells through DNA synthesis inhibition. Also, IFN-β suppresses tumor growth through the apoptotic process. To manufacture animal models xenografted with choriocarcinoma, CMFDA pre-labeled JEG-3 cells (2×106) were injected intravenously (i.v.) into the tail vein of athymic nude mice (group A) and injected subcutaneously (s.c.) into the back of the mice (group B). Subcutaneously injected cancer cells were mixed with Matrigel (BD Biosciences, Bedford, MA, USA) at 1:1 volume ratio of Matrigel to PBS in 100 μl. On group A, CM-dil pre-labeled hNSCs (2×106) were injected intravenously after a week. On group B, when the tumor volume reached at 100mm3, CM-Dil pre-labeled hNSCs (2×106) were injected subcutaneously adjacent to the tumor mass. Every mice received i.p. injections of 5-FC (500 mg/kg/day) every day for 21 days. In a modified trans-well migration assay, NSCs selectively migrated to JEG-3 choriocarcinoma cells. It was revealed that the tumor-tropic properties of engineered NSCs were attributed to chemoattractant factors (CXCR4, SCF, SDF-1a, VEGF) secreted by JEG-3 cells. When JEG-3 cells co-cultured with engineered NSCs in the presence of 5-FC, the viability of JEG-3 cells was markedly decreased. The present results suggested that NSCs expressing CD gene and IFN-β gene have a potential therapeutic effect against choriocarcinoma. Consequently, hNSC therapy may be a clinically effective tool for the treatment of human choriocarcinoma cancer. In addition, we are currently studying on an in vivo model to demonstrate that selective anti-tumor effect of NSCs. Note: This abstract was not presented at the conference. Citation Format: Gyu-Sik Kim, Kyung-Chul Choi. A growth of human choriocarcinoma cells was selectively inhibited by therapeutic neural stem cells expressing cytosine deaminase and interferon-β in cellular and xenograft models [abstract]. In: Proceedings of the AACR International Conference: New Frontiers in Cancer Research; 2017 Jan 18-22; Cape Town, South Africa. Philadelphia (PA): AACR; Cancer Res 2017;77(22 Suppl):Abstract nr B13.

Abstract B14: Injection of therapeutic stem cells expressing cytosine deaminase and interferon-beta resulted in the inhibition of K562 human chronic myeloid leukemia cells in a xenograft model

Abstract Gene-directed enzyme/prodrug therapies have been found to be more advantageous compared to conventional cancer treatment method. One of these, a cytosine deaminase (CD)/5-fluorocytosine (5-FC) system, is known to induce apoptosis of cancer cells by converting 5-FC, a prodrug, to its metabolically active form, 5-fluorouracil. In this study, human neural stem cells (hNSCs) derived enzyme/prodrug therapy was used to treat leukemia. The parental hNSCs, HB1.F3, were engineered to express E. coli CD and/or human interferon-β. To manufacture animal models xenografted with leukemia, K-562 cells (1×106) were mixed with Matrigel (BD Biosciences, Bedford, MA, USA) at 1:1 volume ratio of Matrigel to PBS in 100 μl and injected subcutaneously (s.c.) into the back of athymic nude mice. This animal study was performed for 24 days after hNSCs injections. When tumor volume reached 500 mm3, CM-Dil pre-labeled hNSCs (4 x 106 cells per mouse) were injected subcutaneously adjacent to the tumor mass. Another group, CM-dil pre-labeled hNSCs (4 x 106 cells per mouse) was injected intravenously. hNSCs were injected on the first day of each week. Two days after the injection of hNSCs, all mice received i.p. injections of 5-FC (500 mg/kg/day in 100 μl PBS) every day for 24 days. At 24 h after the last 5-FC treatment, the mice were euthanized and tumor masses were harvested for molecular analysis. In a xenografted mouse model administered with hNSCs intravenously or subcutaneously, hNSC significantly inhibits the growth of tumor mass and extends survival date in the presence of a prodrug. In addition, HB1.F3.CD.IFN-β treatment group showed more antitumor effect compared with HB1.F3.CD treatment group, indicating that IFN- β may have a synergistic effect for directly killing leukemia tumors. The present results represent that engineered hNSCs and prodrug treatment inhibited the proliferation of leukemia. These results suggest that gene therapy employing genetically engineered stem cells expressing CD and IFN-β may be effective for treating leukemia. Note: This abstract was not presented at the conference. Citation Format: Geon-Tae Park, Kyung-Chul Choi. Injection of therapeutic stem cells expressing cytosine deaminase and interferon-beta resulted in the inhibition of K562 human chronic myeloid leukemia cells in a xenograft model [abstract]. In: Proceedings of the AACR International Conference: New Frontiers in Cancer Research; 2017 Jan 18-22; Cape Town, South Africa. Philadelphia (PA): AACR; Cancer Res 2017;77(22 Suppl):Abstract nr B14.

Abstract 4564: Synergistic anti-tumor efficacy of combination therapy with APS001F, a cytosine deaminase (CD) expressing Bifidobacterium, 5-fluorocytosine (5-FC) and anti-mPD-1 antibody in syngeneic mice model

Abstract Immune checkpoint blockers like anti-PD-1 antibody are leading the new generation in anti-cancer drug development. A lot of scientific evidences have demonstrated that immune checkpoint antibodies have promising clinical response in patients with multiple cancer types. Nevertheless, limited fraction of patients responds to the antibody immunotherapy, and moreover, immune related serious adverse events caused by nonspecific reaction with immune checkpoint blockers result in treatment discontinuation. Many approaches have been attempted to improve therapeutic outcomes of antibody immunotherapy, particularly a combination of antibody treatment and other therapies is one of worth-trying ideas. APS001F is a live recombinant Bifidobacterium longum expressing cytosine deaminase (CD), which is an enzyme to catalyze the hydrolytic deamination of cytosine to uracil. Bifidobacterium is a non-pathogenic anaerobic bacterium derived from normal human intestinal flora. It can only survive and grow at low oxygen environment such as solid tumor. Intravenous administration of APS001F to patients leads to colonization of the B.longum and production of CD enzyme only inside the solid tumor. Locally expressed CD enzyme converts orally taken prodrug, 5-FC, into anti-tumor drug 5-FU, which increases 5-FU concentration specifically inside tumor and results in alleviation of side effects caused by attacking normal organs. The phase 1 clinical trial for APS001F is conducted in the US sponsored by us. 5-FU has been shown to alleviate Myeloid Derived Suppressor Cells (MDSC) in the tumor site and release immune suppression in tumor [1]. Furthermore, Van Der Kraak et. al. have reported that 5-FU upregulated PD-L1 expression on the surface of tumor cells [2]. These findings drove us to combine anti-PD-1 antibody with the APS001F therapy. At this present study, systemic administration of APS001F and 5-FC significantly suppressed tumor growth in CT26 bearing syngeneic mice model, which is consistent with our previous finding. Additionally, anti-murine PD-1 antibody combined with APS001F and 5-FC further suppressed tumor progression and some of individual samples achieved complete regression of CT26 tumors. The combination treatment effect of anti-murine PD-1 antibody and APS001F with 5-FC showed statistical significance in comparison with either treatment group, which encourages us to expect much effective results and less side effects in clinic. Reference: 1. Vincent J. et. al., Cancer Res. 2010 Apr 15;70(8):3052-61, 5-Fluorouracil selectively kills tumor-associated myeloid-derived suppressor cells resulting in enhanced T cell-dependent antitumor immunity. 2. Van Der Kraak et. al., J Immunother Cancer., 2016 Oct 18;4:65. 5-Fluorouracil upregulates cell surface B7-H1 (PD-L1) expression in gastrointestinal cancers. Citation Format: Koichiro Shioya, Yuji Seki, Tomio Matsumura, Yuko Shimatani, Shun'ichiro Taniguchi, Minoru Fujimori. Synergistic anti-tumor efficacy of combination therapy with APS001F, a cytosine deaminase (CD) expressing Bifidobacterium, 5-fluorocytosine (5-FC) and anti-mPD-1 antibody in syngeneic mice model [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4564. doi:10.1158/1538-7445.AM2017-4564

IPS-derived MSCs from an expandable bank to deliver a prodrug-converting enzyme that limits growth and metastases of human breast cancers

One attractive strategy to treat cancers is to deliver an exogenous enzyme that will convert a non-toxic compound to a highly toxic derivative. The strategy was tested with viral vectors but was disappointing because the efficiency of transduction into tumor cells was too low. Recent reports demonstrated that the limitation can be addressed by using tissue-derived mesenchymal stromal cells (MSCs) to deliver enzyme/prodrug systems that kill adjacent cancer cells through bystander effects. Here we addressed the limitation that tissue-derived MSCs vary in their properties and are difficult to generate in the large numbers needed for clinical applications. We prepared a Feeder Stock of MSCs from induced pluripotent stem cells (iPSs) that provided an extensively expandable source of standardized cells. We then transduced the iPS-derived MSCs to express cytosine deaminase and injected them locally into a mouse xenogeneic model of human breast cancer. After administration of the prodrug (5-fluorocytosine), the transduced iPS-MSCs both limited growth of preformed tumors and decreased lung metastases.

Vectorized gene therapy of liver tumors: proof-of-concept of TG4023 (MVA-FCU1) in combination with flucytosine

TG4023 is a modified vaccinia virus Ankara (MVA) containing the yeast-originated transgene FCU1, expressing cytosine deaminase and uracil phosphoribosyltransferase enzymes that transform the prodrug flucytosine (5-FC) into cytotoxic 5-fluorouracil (5-FU) and 5-fluorouridine-5′-monophosphate, respectively. This first-in-human study aimed to assess the maximum tolerated dose (MTD) of intratumoral (IT) TG4023 and the safety, feasibility, and proof-of-concept (PoC) of TG4023/5-FC combination to deliver high 5-FU concentrations in tumors. Cancer patients without further therapeutic option and with at least one injectable primary or metastatic liver tumor underwent on day 1 a percutaneous IT injection of TG4023 at doses of 107, 108, or 4.108 plaque forming units (p.f.u.) using ultrasound imaging guidance, after a dose-limiting toxicities (DLTs)-driven 3 + 3 dose-escalating design. On day 2, patients were given intravenous and/or oral 5-FC at a dose of 200 mg/kg/day for 14 days and were followed for safety through day 43. Tumor response was assessed at week 6, according to RECIST. Plasma and tumor 5-FU concentrations were measured to establish the PoC. In total, 16 patients completed treatment with TG4023 and 5-FC. One DLT/7 patients (ALT/aspartate aminotransferase transient increase) was observed at 4 × 108 p.f.u.; MTD was therefore not reached. The most frequent adverse events were pyrexia, asthenia, vomiting, and decreased appetite. Eight of 16 patients had stable disease. Mean 5-FU concentrations in plasma were 1.9 ± 2.6 ng/ml and 56 ± 30 ng/g in tumors. Seroconversion for anti-FCU1 antibodies was found for one patient from each cohort (16%, overall). This phase I study demonstrated that IT injections of TG4023 were feasible and well tolerated; MTD was defined as 4 × 108 p.f.u. Therapeutic 5-FU concentrations in tumors established the virus-directed enzyme-prodrug therapy PoC. NCT00978107.

Retroviral Replicating Vector Delivery of miR-PDL1 Inhibits Immune Checkpoint PDL1 and Enhances Immune Responses InVitro.

Tumor cells express a number of immunosuppressive molecules that can suppress anti-tumor immune responses. Efficient delivery of small interfering RNAs to treat a wide range of diseases including cancers remains a challenge. Retroviral replicating vectors (RRV) can be used to stably and selectively introduce genetic material into cancer cells. Here, we designed RRV to express shRNA (RRV-shPDL1) or microRNA30-derived shRNA (RRV-miRPDL1) using Pol II or Pol III promoters to downregulate PDL1 in human cancer cells. We also designed RRV expressing cytosine deaminase (yCD2) and miRPDL1 for potential combinatorial therapy. Among various configurations tested, we showed that RRV-miRPDL1 vectors with Pol II or Pol III promoter replicated efficiently and exhibited sustained downregulation of PDL1 protein expression by more than 75% in human cancer cell lines with high expression of PDL1. Immunologic effects of RRV-miRPDL1 were assessed by a trans-suppression lymphocyte assay. In vitro data showed downregulation of PDL1+ tumor cells restored activation of CD8+ T cells and bio-equivalency compared to anti-PDL1 antibody treatment. These results suggest RRV-miRPDL1 may be an alternative therapeutic approach to enhance anti-tumor immunity by overcoming PDL1-induced immune suppression from within cancer cells and this approach may also be applicable to other cancer targets.

Combined treatment, based on lysomustine administration with mesenchymal stem cells expressing cytosine deaminase therapy, leads to pronounced murine Lewis lung carcinoma growth inhibition.

The combination of stem cell-based gene therapy with chemotherapy comprises an advantageous strategy that results in a reduction of system toxicity effects and an improvement in the general efficacy of treatment. In the present study, we estimated the efficacy of adipose tissue-derived mesenchymal stem cells (AT-MSCs) expressing cytosine deaminase (CDA) combined with lysomustine chemotherapy in mice bearing late stage Lewis lung carcinoma (LLC). Adipose tissue-derived mesenchymal stem cells were transfected with non-insert plasmid construct transiently expressing fused cytosine deaminase-uracil phosphoribosyltransferase protein (CDA/UPRT) or the same construct fused with Herpes Simplex Virus Type1 tegument protein VP22 (CDA/UPRT/VP22). Systemic administration of 5-fluorocytosine (5FC) and lysomustine was implemented after a single intratumoral injection of transfected AT-MSCs. We demonstrated that direct intratumoral transplantation of AT-MSCs expressing CDA/UPRT or CDA/UPRT/VP22 followed by systemic administration of 5FC resulted in a significant tumor growth inhibition. There was a 56% reduction in tumor volume in mice treated by AT-MSCs-CDA/UPRT + 5FC or with AT-MSCs-CDA/UPRT/VP22 + 5FC compared to control animals grafted with lung carcinoma alone. Transplantation of AT-MSCs-CDA/UPRT + 5FC and AT-MSCs-CDA/UPRT/VP22 + 5FC prolonged the life span of mice bearing LLC by 27% and 31%, respectively. Co-administration of lysomustine and AT-MSCs-CDA/UPRT + 5FC led to tumor growth inhibition (by 86%) and life span extension (by 60%) compared to the control group. Our data indicate that a combination CDA/UPRT-expressing AT-MSCs with lysomustine has a superior antitumor effect in the murine lung carcinoma model compared to monotherapies with transfected AT-MSCs or lysomustine alone, possibly because of a synergistic effect of the combination therapy. Copyright © 2016 John Wiley & Sons, Ltd.