Combination of oncolytic adenovirotherapy and Bax gene therapy in human cancer xenografted models. Potential merits and hurdles for combination therapy

Oncolytic virus therapy in Japan: progress in clinical trials and future perspectives

Oncolytic virus therapy is a promising new option for cancer. It utilizes genetically engineered or naturally occurring viruses that selectively replicate in and kill cancer cells without harming normal cells. T-VEC (talimogene laherparepvec), a second-generation oncolytic herpes simplex virus type 1, was approved by the US Food and Drug Administration for the treatment of inoperable melanoma in 2015 and subsequently approved in Europe in 2016. Other oncolytic viruses using different parental viruses have also been tested in Phase III clinical trials and are ready for drug approval: Pexa-Vec (pexastimogene devacirepvec), an oncolytic vaccinia virus, CG0070, an oncolytic adenovirus, and REOLYSIN (pelareorep), an oncolytic reovirus. In Japan, as of May 2018, several oncolytic viruses have been developed, and some have already proceeded to clinical trials. In this review, we summarize clinical trials assessing oncolytic virus therapy that were conducted or are currently ongoing in Japan, specifically, T-VEC, the abovementioned oncolytic herpes simplex virus type 1, G47Δ, a third-generation oncolytic herpes simplex virus type 1, HF10, a naturally attenuated oncolytic herpes simplex virus type 1, Telomelysin, an oncolytic adenovirus, Surv.m-CRA, another oncolytic adenovirus, and Sendai virus particle. In the near future, oncolytic virus therapy may become an important and major treatment option for cancer in Japan.

Targeted CDX2 expression inhibits aggressive phenotypes of colon cancer cells in vitro and in vivo

Loss of caudal type homeobox 2 (CDX2) is associated with the development of human colorectal cancer, while human telomerase reverse transcriptase (hTERT) frequently occurs in variety of human cancers. We investigated the effects of restoration of CDX2 expression using a hypoxia-inducible hTERT promoter-driven vector (pLVX-5HRE-hTERTp-CDX2-3FLAG) on colon cancer cell viability, cell cycle distribution, apoptosis, colony formation, invasion ability and xenograft tumor growth in nude mice. CDX2 overexpression significantly inhibited viability, colony formation, and the invasion and migration ability of LoVo cells, and induced cell cycle arrest and apoptosis in vitro, especially under hypoxic culture conditions. Overexpression of CDX2 under normoxic conditions significantly suppressed the expression of TGF-β, cyclin D1, uPA, MMP-9, MMP-2, and Bcl-2, and stimulated the expression of collagen IV, laminin-1, and Bax. Overexpression of CDX2 reduced colon cancer xenograft tumor formation in nude mice which was associated with downregulation of Ki-67. In conclusion, overexpression of CDX2 using a hypoxia-inducible hTERT promoter-driven vector suppressed malignant progression of colon cancer cells in vitro and in vivo. These results suggest that pLVX-5HRE-hTERTp-CDX2-3FLAG gene therapy may be a promising novel approach to treat colon cancer.

Recombinant lentivirus with enhanced expression of caudal-related homeobox protein 2 inhibits human colorectal cancer cell proliferation in vitro

Caudal-related homeobox protein 2 (CDX2), a tumor suppressor in the adult colon, is overexpressed under a non-cancer specific cytomegalovirus promoter in certain tumor cells; furthermore, non-specific expression of CDX2 may result in aberrant side effects in normal cells. The human telomerase reverse transcriptase (hTERT) promoter is active in the majority of cancer cells but not in normal cells. Hypoxia is a key feature of solid tumors, and targeted genes may be significantly upregulated by five copies of hypoxia-response elements (HREs) under hypoxic conditions. However, the effect of CDX2 overexpression, as controlled by five copies of HREs and the hTERT promoter, on human colorectal cancer (CRC) cell proliferation in vitro remains to be fully elucidated. In the current study, a recombinant lentivirus containing the CDX2 gene under the control of five HREs and the hTERT promoter was generated. An immunofluorescence assay was used to detect CDX2 expression by the 5HhC lentivirus, whereas an MTT assay was used to detect the effects of CoCl₂ on the viability of LoVo cells. Western blot analysis was conducted in order to determine the relative ratios of recombinant CDX2 protein to the internal control β-actin, following 5HhC/LoVo cell culture under normoxic and hypoxic conditions (100, 200, 300, 400 or 500 µmol/l CoCl₂) for 24 h, then for 12, 24 or 36 h with the optimal concentration (300 µmol/l) of CoCl₂. Reverse transcription polymerase chain reaction analysis was used to determine the transcription of recombinant CDX2 mRNA following culture of 5HhC/LoVo cells under normoxic or hypoxic conditions. Finally, a cloning assay was used to detect the proliferative ability of 5HhC/LoVo and 5Hh cells. High CDX2 expression was observed in hTERT-positive LoVo cells under hypoxic conditions, an effect which was mimicked by treatment with CoCl₂ to inhibit LoVo cell proliferation in vitro. High expression of CDX2 therefore provides a promising strategy for the development of novel targeted treatments and gene therapy for CRC.

Antitumor effects of telomerase-specific replication-selective oncolytic viruses for adenoid cystic carcinoma cell lines

We evaluated the antitumor effect of a telomerase-specific replication-selective adenovirus (Telomelysin, OBP-301) for adenoid cystic carcinoma (ACC) in vitro and in vivo. Adenovirus E1 gene expression was controlled by human telomerase reverse transcription (hTERT). Infection of ACC cells by OBP-301 induced high E1A mRNA expression and subsequent oncolytic cell death in a dose-dependent manner. Using OBP-401 (TelomeScan), a genetically engineered adenovirus that carries the GFP gene under the control of the cytomegalovirus (CMV) promoter at the deleted E3 region of OBP-301, ACC cells expressed bright GFP fluorescence as early as 12 h after OBP-401 infection. The fluorescence intensity gradually increased in a time-dependent manner, followed by rapid cell death due to the cytopathic effect of OBP-401, as evidenced by the floating, highly light-refractive cells using phase-contrast microscopy. Effects of intratumorally injected OBP-401 against established Acc2 xenograft tumors were seen in BALB/c nu/nu mice. The levels of GFP expression following ex vivo infection of OBP-401 may be of value as a positive predictive marker for the outcome of telomerase-specific virotherapy. Our data clearly indicated that telomerase-specific oncolytic adenoviruses have significant therapeutic potential against human ACC in vitro and in vivo. These results suggest that treatment with OBP-301 and OBP-401 may improve the quality of life of oral cancer patients.

Telomerase-specific oncolytic adenoviral therapy for orthotopic hepatocellular carcinoma in HBx transgenic mice

The telomerase-specific replication-competent oncolytic adenovirus, Telomelysin, was developed for virus-mediated preferential lysis of tumor cells. Its selectivity is derived from a human telomerase reverse transcriptase (hTERT) promoter-driven active viral replication, which occurs in cancer cells with high telomerase activity but not in normal cells lacking such activity. Because the TERT activity is elevated in most cases of hepatocellular carcinoma (HCC), the current study aims to investigate whether Telomelysin can be used for treatment of HCC. The oncolytic effect of Telomelysin has been investigated both in vitro using cell culture and in vivo using an immunocompetent in situ orthotopic HCC model. In this model, HCC developed spontaneously in the liver of HBx transgenic mice, which is pathologically and genetically similar to human HCC. In cell culture assay, Telomelysin lyses HCC cell lines at a low multiplicity of infection (MOI), ranging 0.77-6.35 (MOI [PFU/cell]). In the orthotopic HCC model, Telomelysin showed a potent oncolytic effect on HCC but spared normal liver tissue. Dose escalation analysis identified a safety dose of 1.25 × 10(8) PFU for this model. The effect of multiple injections of Telomelysin was also evaluated in this immunocompetent HCC model. We found that the virus replicates in HCC after a second intratumoral injection despite an immune response induced by the previous injection. This preclinical study shows that Telomelysin can be used for treatment of human HCC at an appropriate dosage and that its tumor-killing activity persists after multiple injections.

Is telomerase a viable target in cancer?

The ideal cancer treatment would specifically target cancer cells yet have minimal or no adverse effects on normal somatic cells. Telomerase, the ribonucleoprotein reverse transcriptase that maintains the ends of human chromosome, is an attractive cancer therapeutic target for exactly this reason [1]. Telomerase is expressed in more than 85% of cancer cells, making it a nearly universal cancer marker, while the majority of normal somatic cells are telomerase negative. Telomerase activity confers limitless replicative potential to cancer cells, a hallmark of cancer which must be attained for the continued growth that characterizes almost all advanced neoplasms [2]. In this review we will summarize the role of telomeres and telomerase in cancer cells, and how properties of telomerase are being exploited to create targeted cancer therapies including telomerase inhibitors, telomerase-targeted immunotherapies and telomerase-driven virotherapies. A frank and balanced assessment of the current state of telomerase inhibitors with caveats and potential limitations will be included.

Efficient virotherapy for osteosarcoma by telomerase-specific oncolytic adenovirus

PURPOSE

A telomerase-specific oncolytic adenovirus, Telomelysin, can selectively kill cancer cells, and be attenuated in normal cells. We herein describe the oncolytic effect of Telomelysin on human osteosarcoma both in vitro and in vivo.

METHODS

The anti-tumor effects of Telomelysin were evaluated on human osteosarcoma cell lines in vitro and in a mouse xenograft model of human osteosarcoma in vivo. The replication efficiencies of Telomelysin in human osteosarcoma cell lines and normal cell lines and in osteosarcoma xenografts were determined by the expression levels of E1 mRNA and E1A protein using real-time quantitative PCR, Western blot analysis and immunohistochemistry. The in vitro telomerase-specific replication and the viral infection rate were also confirmed by TelomeScan (Telomelysin-GFP), using fluorescent microscopy and flow cytometry, respectively. The cell viabilities were examined by XTT assay, and the tumor volumes were measured every 2 days. The induction of apoptosis was assessed by Western blot analysis, as well as by TUNEL assay.

RESULTS

TelomeScan and Telomelysin were efficiently replicated in human osteosarcoma cell lines and led to a dose- and time-dependent expression of GFP, E1 mRNA and E1A protein. Telomelysin infection induced marked cytolysis and apoptosis in osteosarcoma cell lines in vitro. Neither cytotoxicity nor apoptosis were induced in normal human cell lines. In the human osteosarcoma cell xenograft model, intratumoral injection of Telomelysin resulted in increased viral replication, significant tumor growth suppression and distinct apoptotic cell death.

CONCLUSIONS

This study indicated that virotherapy with Telomelysin may provide a promising strategy for the treatment of human osteosarcoma.

Intraperitoneal administration of telomerase-specific oncolytic adenovirus sensitizes ovarian cancer cells to cisplatin and affects survival in a xenograft model with peritoneal dissemination

Despite tremendous development in chemotherapy for ovarian cancer over the past few decades, the prognosis of advanced cases with massive peritoneal dissemination is still unsatisfactory, and novel treatment modalities that can combine with chemotherapy are urgently needed. We recently developed virotherapy for solid tumors using telomerase-specific replication-selective adenoviruses (Telomelysin: OBP-301), in which the human telomerase reverse transcriptase (hTERT) gene promoter has been inserted to direct tumor-specific E1 gene expression. In this study, we investigated the anti-tumor effects of OBP-301, combined with cisplatin (CDDP), on ovarian cancer cells. In vitro treatment of SKOV3 cells with OBP-301 at a multiplicity of infection (MOI) of 0.01–100 induced significant cell death in a dose-dependent manner, with moderate cytotoxicity at an MOI of 1–10 and maximal cytotoxicity at an MOI of 100. In contrast, OBP-301 treatment of normal human cells showed no significant cell death at an MOI of 1–10 and exhibited modest cytotoxicity at an MOI of 100. The effects of low-dose CDDP at 0.5–1 μM, which induced only 20% cell death, were significantly augmented by combination with OBP-301 at an MOI of 1–10, finally achieving 40% cell death. Such enhancement of CDDP sensitivity was also observed in CDDP-resistant ovarian cancer cells. The combinatorial effects were further tested using a xenograft mouse model of SKOV3 with peritoneal dissemination. After intraperitoneal administration of OBP-301, we confirmed that injected OBP-301 fused with the green fluorescent protein (GFP) gene (OBP-401) was preferentially localized to peritoneal disseminations, as determined by fluorescence imaging. Treatment of mice with CDDP at low dose (0.5 mg kg^–1) had modest effects, showing a 10% decrease in disseminations, whereas combination with intraperitoneal administration of OBP-301 at an MOI of 10 led to enhanced effects, achieving an approximately 80% decrease in disseminations. Kaplan–Meier analysis showed improved overall survival of mice treated with CDDP plus OBP-301 compared with CDDP alone. These findings support the therapeutic potential of intraperitoneal administration of OBP-301 to sensitize ovarian cancer cells to CDDP.

hTERT-promoter-dependent oncolytic adenovirus enhances the transduction and therapeutic efficacy of replication-defective adenovirus vectors in pancreatic cancer cells

Adenovirus-mediated gene therapy shows promise for cancer therapy, but transgene expression of replication-defective adenovirus may be low and transient in clinical settings. Recent reports have shown that the use of a conditionally replication-competent adenovirus (CRAd) enhanced the gene transduction of a replication-defective adenovirus vector. The control of tumor-stromal interactions has also been determined to be important in cancer therapy. In this study, we investigated the effect of the human telomerase reverse transcriptase (hTERT)-CRAd, Ad5/3hTERTE1, which possesses the tumor-specific hTERT promoter with the chimeric fiber 5/3, on the transgene expression and therapeutic efficacy of a replication-defective adenovirus vector expressing NK4 under the control of the CMV promoter, Ad-NK4. In addition, we established a new strategy to target both cancer cells and cancer-stromal interactions. Human pancreatic cancer cells were infected with Ad-NK4 and either Ad5/3hTERTE1 (CRAd-combination group) or Ad5/3hTERTLuc (control-combination group). In the CRAd-combination group, Ad-NK4-delivered transgene expression was increased, leading to an enhanced inhibitory effect on the invasion of cancer cells. In in vivo experiments, NK4 expression within tumors and its inhibitory effect on tumor growth, angiogenesis, and metastasis were enhanced in the CRAd-combination group. These results suggest that hTERT-CRAd enhances the transgene expression and therapeutic efficacies of Ad-NK4, possibly through the in-trans replication of Ad-NK4 induced by adenovirus E1 derived from co-infected hTERT-CRAd. This approach may be a promising combination therapy against advanced pancreatic cancer.

Apoptosis in cancer: key molecular signaling pathways and therapy targets

Apoptosis is a physiological process vital for embryologic development and the maintenance of homeostasis in multicellular organisms, but it is also involved in a wide range of pathological processes, including cancer. In mammalian cells, apoptosis has been divided into two major pathways: the extrinsic pathway, activated by proapoptotic receptor signals at the cellular surface, and the intrinsic pathway, which involves the disruption of mitochondrial membrane integrity. Although many of the proteins vital for apoptosis have been identified, the molecular pathways of cellular death still remain to be elucidated. This review provides references concerning the apoptotic molecules, their interactions, the mechanisms involved in apoptosis resistance, and also the modulation of apoptosis for the treatment of cancer.

Selective metastatic tumor labeling with green fluorescent protein and killing by systemic administration of telomerase-dependent adenoviruses

We previously constructed telomerase-dependent, replication-selective adenoviruses OBP-301 (Telomelysin) and OBP-401 [Telomelysin-green fluorescent protein (GFP); TelomeScan], the replication of which is regulated by the human telomerase reverse transcriptase promoter. By intratumoral injection, these viruses could replicate within the primary tumor and subsequent lymph node metastasis. The aim of the present study was to evaluate the possibility of systemic administration of these telomerase-dependent adenoviruses. We assessed the antitumor efficacy of OBP-301 and the ability of OBP-401 to deliver GFP in hepatocellular carcinoma (HCC) and metastatic colon cancer nude mouse models. We showed that i.v. administration of OBP-301 significantly inhibited colon cancer liver metastases and orthotopically implanted HCC. Further, we showed that OBP-401 could visualize liver metastases by tumor-specific expression of the GFP gene after portal venous or i.v. administration. Thus, systemic administration of these adenoviral vectors should have clinical potential to treat and detect liver metastasis and HCC.

E2F promoter-regulated oncolytic adenovirus with p16 gene induces cell apoptosis and exerts antitumor effect on gastric cancer

Replication-competent adenovirus (RCAd) constitutes an alternative in cancer therapy. For obtaining advanced RCAd generations with high oncolytic capability and a good safety profile, we constructed an E2F promoter-regulated RCAd carrying p16 gene, AdE2F-p16, in which the E1a gene was controlled by the E2F promoter. The experimental data showed that the E2F promoter endowed AdE2F-p16 with high specificity in cancer cells. While rarely replicating in normal cells, AdE2F-p16 could replicate in p16-deficient cancer cells, with 2,937- to 160,000-fold increased replicative capability in different cancer cell lines. AdE2F-p16 expressed p16 within cancer cells and led to potent antitumor efficacy in gastric cancer xenografts in nude mice, with a tumor inhibition rate of 59.14%. Due to the combined effects of cancer cell apoptosis induced by p16 expression and oncolysis by virus replication, the E2F promoter-regulated, p16-armed RCAd provides a promising strategy for cancer gene therapy.