p53-Armed Oncolytic Virotherapy Improves Radiosensitivity in Soft-Tissue Sarcoma by Suppressing BCL-xL Expression

Soft-tissue sarcoma (STS) is a heterogeneous group of rare tumors originating predominantly from the embryonic mesoderm. Despite the development of combined modalities including radiotherapy, STSs are often refractory to antitumor modalities, and novel strategies that improve the prognosis of STS patients are needed. We previously demonstrated the therapeutic potential of two telomerase-specific replication-competent oncolytic adenoviruses, OBP-301 and tumor suppressor p53-armed OBP-702, in human STS cells. Here, we demonstrate in vitro and in vivo antitumor effects of OBP-702 in combination with ionizing radiation against human STS cells (HT1080, NMS-2, SYO-1). OBP-702 synergistically promoted the antitumor effect of ionizing radiation in the STS cells by suppressing the expression of B-cell lymphoma-X large (BCL-xL) and enhancing ionizing radiation-induced apoptosis. The in vivo experiments demonstrated that this combination therapy significantly suppressed STS tumors' growth. Our results suggest that OBP-702 is a promising antitumor reagent for promoting the radiosensitivity of STS tumors.

Fluorescence-guided assessment of bone and soft-tissue sarcomas for predicting the efficacy of telomerase-specific oncolytic adenovirus

Bone and soft-tissue sarcomas are rare malignancies with histological diversity and tumor heterogeneity, leading to the lack of a common molecular target. Telomerase is a key enzyme for keeping the telomere length and human telomerase reverse transcriptase (hTERT) expression is often activated in most human cancers, including bone and soft-tissue sarcomas. For targeting of telomerase-positive tumor cells, we developed OBP-301, a telomerase-specific replication-competent oncolytic adenovirus, in which the hTERT promoter regulates adenoviral E1 gene for tumor-specific viral replication. In this study, we present the diagnostic potential of green fluorescent protein (GFP)-expressing oncolytic adenovirus OBP-401 for assessing virotherapy sensitivity using bone and soft-tissue sarcomas. OBP-401-mediated GFP expression was significantly associated with the therapeutic efficacy of OBP-401 in human bone and soft-tissue sarcomas. In the tumor specimens from 68 patients, malignant and intermediate tumors demonstrated significantly higher expression levels of coxsackie and adenovirus receptor (CAR) and hTERT than benign tumors. OBP-401-mediated GFP expression was significantly increased in malignant and intermediate tumors with high expression levels of CAR and hTERT between 24 and 48 h after infection. Our results suggest that the OBP-401-based GFP expression system is a useful tool for predicting the therapeutic efficacy of oncolytic virotherapy on bone and soft-tissue sarcomas.

LRRC15 expression indicates high level of stemness regulated by TWIST1 in mesenchymal stem cells

Mesenchymal stem cells (MSCs) are used as a major source for cell therapy, and its application is expanding in various diseases. On the other hand, reliable method to evaluate quality and therapeutic properties of MSC is limited. In this study, we focused on TWIST1 that is a transcription factor regulating stemness of MSCs and found that the transmembrane protein LRRC15 tightly correlated with the expression of TWIST1 and useful to expect TWIST1-regulated stemness of MSCs. The LRRC15-positive MSC populations in human and mouse bone marrow tissues highly expressed stemness-associated transcription factors and therapeutic cytokines, and showed better therapeutic effect in bleomycin-induced pulmonary fibrosis model mice. This study provides evidence for the important role of TWIST1 in the MSC stemness, and for the utility of the LRRC15 protein as a marker to estimate stem cell quality in MSCs before cell transplantation.

Mohawk is a transcription factor that promotes meniscus cell phenotype and tissue repair and reduces osteoarthritis severity

Meniscus tears are common knee injuries and a major osteoarthritis (OA) risk factor. Knowledge gaps that limit the development of therapies for meniscus injury and degeneration concern transcription factors that control the meniscus cell phenotype. Analysis of RNA sequencing data from 37 human tissues in the Genotype-Tissue Expression database and RNA sequencing data from meniscus and articular cartilage showed that transcription factor Mohawk (MKX) is highly enriched in meniscus. In human meniscus cells, MKX regulates the expression of meniscus marker genes, OA-related genes, and other transcription factors, including Scleraxis (SCX), SRY Box 5 (SOX5), and Runt domain-related transcription factor 2 (RUNX2). In mesenchymal stem cells (MSCs), the combination of adenoviral MKX (Ad-MKX) and transforming growth factor-β3 (TGF-β3) induced a meniscus cell phenotype. When Ad-MKX-transduced MSCs were seeded on TGF-β3-conjugated decellularized meniscus scaffold (DMS) and inserted into experimental tears in meniscus explants, they increased glycosaminoglycan content, extracellular matrix interconnectivity, cell infiltration into the DMS, and improved biomechanical properties. Ad-MKX injection into mouse knee joints with experimental OA induced by surgical destabilization of the meniscus suppressed meniscus and cartilage damage, reducing OA severity. Ad-MKX injection into human OA meniscus tissue explants corrected pathogenic gene expression. These results identify MKX as a previously unidentified key transcription factor that regulates the meniscus cell phenotype. The combination of Ad-MKX with TGF-β3 is effective for differentiation of MSCs to a meniscus cell phenotype and useful for meniscus repair. MKX is a promising therapeutic target for meniscus tissue engineering, repair, and prevention of OA.

Oncolytic virotherapy reverses chemoresistance in osteosarcoma by suppressing MDR1 expression

BACKGROUND

Osteosarcoma (OS) is a malignant bone tumor primarily affecting children and adolescents. The prognosis of chemotherapy-refractory OS patients is poor. We developed a tumor suppressor p53-expressing oncolytic adenovirus (OBP-702) that exhibits antitumor effects against human OS cells. Here, we demonstrate the chemosensitizing effect of OBP-702 in human OS cells.

MATERIALS AND METHODS

The in vitro and in vivo antitumor activities of doxorubicin (DOX) and OBP-702 were assessed using parental and DOX-resistant OS cells (U2OS, MNNG/HOS) and a DOX-resistant MNNG/HOS xenograft tumor model.

RESULTS

DOX-resistant OS cells exhibited high multidrug resistant 1 (MDR1) expression, which was suppressed by OBP-702 or MDR1 siRNA, resulting in enhanced DOX-induced apoptosis. Compared to monotherapy, OBP-702 and DOX combination therapy significantly suppressed tumor growth in the DOX-resistant MNNG/HOS xenograft tumor model.

CONCLUSION

Our results suggest that MDR1 is an attractive therapeutic target for chemoresistant OS. Tumor-specific virotherapy is thus a promising strategy for reversing chemoresistance in OS patients via suppression of MDR1 expression.

Oncolytic virotherapy promotes radiosensitivity in soft tissue sarcoma by suppressing anti-apoptotic MCL1 expression

Soft tissue sarcoma (STS) is a rare cancer that develops from soft tissues in any part of the body. Despite major advances in the treatment of STS, patients are often refractory to conventional radiotherapy, leading to poor prognosis. Enhancement of sensitivity to radiotherapy would therefore improve the clinical outcome of STS patients. We previously revealed that the tumor-specific, replication-competent oncolytic adenovirus OBP-301 kills human sarcoma cells. In this study, we investigated the radiosensitizing effect of OBP-301 in human STS cells. The in vitro antitumor effect of OBP-301 and ionizing radiation in monotherapy or combination therapy was assessed using highly radiosensitive (RD-ES and SK-ES-1) and moderately radiosensitive (HT1080 and NMS-2) STS cell lines. The expression of markers for apoptosis and DNA damage were evaluated in STS cells after treatment. The therapeutic potential of combination therapy was further analyzed using SK-ES-1 and HT1080 cells in subcutaneous xenograft tumor models. The combination of OBP-301 and ionizing radiation showed a synergistic antitumor effect in all human STS cell lines tested, including those that show different radiosensitivity. OBP-301 was found to enhance irradiation-induced apoptosis and DNA damage via suppression of anti-apoptotic myeloid cell leukemia 1 (MCL1), which was expressed at higher levels in moderately radiosensitive cell lines. The combination of OBP-301 and ionizing radiation showed a more profound antitumor effect compared to monotherapy in SK-ES-1 (highly radiosensitive) and HT1080 (moderately radiosensitive) subcutaneous xenograft tumors. OBP-301 is a promising antitumor reagent to improve the therapeutic potential of radiotherapy by increasing radiation-induced apoptosis in STS.

Liquid Biopsy Targeting Monocarboxylate Transporter 1 on the Surface Membrane of Tumor-Derived Extracellular Vesicles from Synovial Sarcoma

The lack of noninvasive biomarkers that can be used for tumor monitoring is a major problem for soft-tissue sarcomas. Here we describe a sensitive analytical technique for tumor monitoring by detecting circulating extracellular vesicles (EVs) of patients with synovial sarcoma (SS). The proteomic analysis of purified EVs from SYO-1, HS-SY-II, and YaFuSS identified 199 common proteins. DAVID GO analysis identified monocarboxylate transporter 1 (MCT1) as a surface marker of SS-derived EVs, which was also highly expressed in SS patient-derived EVs compared with healthy individuals. MCT1+CD9+ EVs were also detected from SS-bearing mice and their expression levels were significantly correlated with tumor volume (p = 0.003). Furthermore, serum levels of MCT1+CD9+ EVs reflected tumor burden in SS patients. Immunohistochemistry revealed that MCT1 was positive in 96.7% of SS specimens and its expression on the cytoplasm/plasma membrane was significantly associated with worse overall survival (p = 0.002). Silencing of MCT1 reduced the cellular viability, and migration and invasion capability of SS cells. This work describes a new liquid biopsy technique to sensitively monitor SS using circulating MCT1+CD9+ EVs and indicates the therapeutic potential of MCT1 in SS.

Radiographic and clinical assessment of unidirectional porous hydroxyapatite to treat benign bone tumors

Unidirectional porous hydroxyapatite (UDPHAp) was developed as an excellent scaffold with unidirectional pores oriented in the horizontal direction with interpore connections. The purpose of this study was to assess radiographic changes and clinical outcomes and complications following UDPHAp implantation to treat benign bone tumors. We retrospectively analyzed 44 patients treated with intralesional resection and UDPHAp implantation for benign bone tumors between 2010 and 2015. Clinical and radiographic findings were evaluated postoperatively at regular follow-up visits. The mean follow-up was 49 months. Radiographic changes were classified into five stages based on bone formation in the implanted UDPHAp according to Tamai’s classification. All patients showed excellent bone formation inside and around implanted UDPHAp. Absorption of UDPHAp and bone marrow cavity remodeling was identified in 20 patients at a mean of 17 months postoperatively, and was significantly more common in young patients. Preoperative cortical thinning was completely regenerated in 26 of 31 patients on average 10 months after surgery. There were no cases of delayed wound healing, postoperative infection, or allergic reaction related to implanted UDPHAp. UDPHAp is a useful bone-filling substitute for treating benign bone tumor, and the use of this material has a low complication rate.

Telomerase-specific oncolytic immunotherapy for promoting efficacy of PD-1 blockade in osteosarcoma

Immune checkpoint inhibitors including anti-programmed cell death 1 (PD-1) antibody have recently improved clinical outcome in certain cancer patients; however, osteosarcoma (OS) patients are refractory to PD-1 blockade. Oncolytic virotherapy has emerged as novel immunogenic therapy to augment antitumor immune response. We developed a telomerase-specific replication-competent oncolytic adenovirus OBP-502 that induces lytic cell death via binding to integrins. In this study, we assessed the combined effect of PD-1 blockade and OBP-502 in OS cells. The expression of coxsackie and adenovirus receptor (CAR), integrins αvβ3 and αvβ5, and programmed cell death ligand 1 (PD-L1) was analyzed in two murine OS cells (K7M2, NHOS). The cytopathic activity of OBP-502 in both cells was analyzed using the XTT assay. OBP-502-induced immunogenic cell death was assessed by analyzing the level of extracellular ATP and high-mobility group box protein B1 (HMGB1). Subcutaneous tumor models for K7M2 and NHOS cells were used to evaluate the antitumor effect and number of tumor-infiltrating CD8+ cells in combination therapy. K7M2 and NHOS cells showed high expression of integrins αvβ3 and αvβ5, but not CAR. OBP-502 significantly suppressed the viability of both cells, in which PD-L1 expression and the release of ATP and HMGB1 were significantly increased. Intratumoral injection of OBP-502 significantly augmented the efficacy of PD-1 blockade on subcutaneous K2M2 and NHOS tumor models via enhancement of tumor-infiltrating CD8+  T cells. Our results suggest that telomerase-specific oncolytic virotherapy is a promising antitumor strategy to promote the efficacy of PD-1 blockade in OS.

Bone and Soft-Tissue Sarcoma: A New Target for Telomerase-Specific Oncolytic Virotherapy

Adenovirus serotype 5 (Ad5) is widely and frequently used as a virus vector in cancer gene therapy and oncolytic virotherapy. Oncolytic virotherapy is a novel antitumor treatment for inducing lytic cell death in tumor cells without affecting normal cells. Based on the Ad5 genome, we have generated three types of telomerase-specific replication-competent oncolytic adenoviruses: OBP-301 (Telomelysin), green fluorescent protein (GFP)-expressing OBP-401 (TelomeScan), and tumor suppressor p53-armed OBP-702. These viruses drive the expression of the adenoviral E1A and E1B genes under the control of the hTERT (human telomerase reverse transcriptase-encoding gene) promoter, providing tumor-specific virus replication. This review focuses on the therapeutic potential of three hTERT promoter-driven oncolytic adenoviruses against bone and soft-tissue sarcoma cells with telomerase activity. OBP-301 induces the antitumor effect in monotherapy or combination therapy with chemotherapeutic drugs via induction of autophagy and apoptosis. OBP-401 enables visualization of sarcoma cells within normal tissues by serving as a tumor-specific labeling reagent for fluorescence-guided surgery via induction of GFP expression. OBP-702 exhibits a profound antitumor effect in OBP-301-resistant sarcoma cells via activation of the p53 signaling pathway. Taken together, telomerase-specific oncolytic adenoviruses are promising antitumor reagents that are expected to provide novel therapeutic options for the treatment of bone and soft-tissue sarcomas.

Abstract 3231: Oncolytic immunotherapy with PD-1 blockade and telomerase-specific oncolytic adenovirus in osteosarcoma

Background: Osteosarcoma (OS) is the most frequent primary malignant tumor of bone in children and adolescents. Although immune checkpoint inhibitor, anti-programmed death protein 1 (PD-1) antibody, has dramatically improved the clinical outcome in some cancer patients, OS patients are less sensitive to PD-1 blockade due to poor immune responses. Recently, oncolytic virotherapy has been shown to stimulate the immune system through induction of immunogenic cell death (ICD). We recently developed a RGD fiber-modified telomerase-specific oncolytic adenovirus OBP-502, which can enter into tumor cells by binding to cell surface integrin and induce oncolytic cell death in a telomerase-dependent manner. In this study, we assessed the in vitro and in vivo antitumor efficacy of combination therapy with PD-1 blockade and OBP-502 in OS cells.

Methods: We used 2 murine OS cell lines, K7M2 and NHOS. The expression of PD-L1, coxsackie and adenovirus receptor (CAR), and integrin on the cell surface was analyzed by flow cytometric analysis. We analyzed the in vitro antitumor effect of OBP-502 using XTT assay and western blot analysis. Virus-induced ICD was assessed by analyzing the level of extracellular ATP and high-mobility group box protein B1 (HMGB1). To evaluate the therapeutic potential of oncolytic immunotherapy, we investigated the in vivo antitumor effect of combination therapy with anti-PD-1 antibody and OBP-502 using a subcutaneous K7M2 xenograft tumor model. Moreover, the number of tumor-infiltrating CD8+, CD4+ and Foxp3+ T cells was analyzed by immunohistochemistry.

Results: Flow cytometric analysis demonstrated that K7M2 and NHOS cells had the expression of PD-L1 and integrin, but not CAR. XTT assay showed that OBP-502 efficiently suppressed the viability of K7M2 and NHOS cells in a dose-dependent manner. Western blot analysis revealed that OBP-502 induced the apoptosis-related cell death in K7M2 and NHOS cells. ELISA assay demonstrated that OBP-502 significantly increased the level of extracellular ATP and HMGB1 in K7M2 and NHOS cells. In vivo experiment using a subcutaneous K7M2 xenograft tumor model showed that combination of anti-PD-1 antibody and OBP-502 significantly reduced tumor growth compared to mock treatment or monotherapy. Immunohistochemical analysis revealed that OBP-502 significantly increased the number of tumor-infiltrating CD8+ T cells compared to mock treatment or monotherapy. By contrast, OBP-502 did not affect the number of CD4+ and Foxp3+ T cells in tumor tissues.

Conclusion: These results suggest that oncolytic immunotherapy with PD-1 blockade and telomerase-specific oncolytic adenovirus is a promising antitumor strategy to promote the therapeutic potential of PD-1 blockade in OS through stimulation of antitumor immune response.

Citation Format: Koji Demiya, Hiroshi Tazawa, Yusuke Mochizuki, Miho Kure, Joe Hasei, Toshiyuki Kunisada, Yasuo Urata, Toshifumi Ozaki, Toshiyoshi Fujiwara. Oncolytic immunotherapy with PD-1 blockade and telomerase-specific oncolytic adenovirus in osteosarcoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3231.

Involvement of ADAM12 in Chondrocyte Differentiation by Regulation of TGF-β1-Induced IGF-1 and RUNX-2 Expressions

A disintegrin and metalloproteinase 12 (ADAM12) is known to be involved in chondrocyte proliferation and maturation; however, the mechanisms are not fully understood. In this study, expression and localization of ADAM12 during chondrocyte differentiation were examined in the mouse growth plate by immunohistochemistry. Adam12 expression during ATDC5 chondrogenic differentiation was examined by real-time PCR and compared with the expression pattern of type X collagen. The clustered regularly interspaced short palindromic repeats (CRISPR)-Cas9 system was used to generate Adam12-knockout (KO) ATDC5 cells. Adam12-KO and Adam12 overexpressing cells were used for analyses of ADAM12 expression with or without TGF-β1 stimulation. ADAM12 was identified predominantly in chondrocytes of the proliferative zone in mouse growth plates by immunohistochemistry. Adam12 was upregulated prior to Col10a1 during chondrogenic differentiation in wild-type ATDC5 cells. In Adam12-KO ATDC5 cells, following initiation of chondrogenic differentiation, we observed a reduction in Igf-1 expression along with an upregulation of hypertrophy-associated Runx2, Col10a1, and type X collagen protein expressions. In ATDC5 wild-type cells, stimulation with TGF-β1 upregulated the expressions of Adam12 and Igf-1 and downregulated the expression of Runx2. In contrast, in Adam12-KO ATDC5 cells, these TGF-β1-induced changes were suppressed. Adam12 overexpression resulted in an upregulation of Igf-1 and downregulation of Runx2 expression in ATDC5 cells. The findings suggest that ADAM12 has important role in the regulation of chondrocyte differentiation, potentially by regulation of TGF-β1-dependent signaling and that targeting of ADAM12 may have a role in management of abnormal chondrocyte differentiation.

Mini-open excision of osteoid osteoma using intraoperative O-arm/Stealth navigation

BACKGROUND

Although osteoid osteomas have traditionally been treated by surgical excision, radiofrequency ablation (RFA) has gained favor as a less invasive procedure. However, RFA is contraindicated for osteoid osteomas close to the skin or crucial neurovascular structures, and is not covered by national health insurance in Japan. The aim of the present study was to evaluate the efficacy of surgical excision of osteoid osteomas using intraoperative navigation.

METHODS

We performed a retrospective review of five patients with osteoid osteoma who underwent a mini-open excision using O-arm/Stealth navigation at our institution. The osteoid osteomas were excised using a cannulated cutter or curetted out with the assistance of navigation.

RESULTS

Complete excision was achieved in all patients, which was confirmed by pathological examination. The mean skin incision was 2.1 cm (range, 1.5 to 3.0 cm) and the mean duration required for setup three-dimensional image was 15 min (range, 12 to 20 min). Although the mean visual analog scale score was 7 (range, 4 to 8) before surgery, all patients experienced relief from their characteristic pain immediately after surgery, with the mean scores of 2.2 (range, 1 to 3) and 0 at 2 days and 4 weeks after surgery, respectively. There was no intra-operative complication related to the navigation and no recurrence was observed during the mean follow-up period of 25 months (range, 13 to 33 months).

CONCLUSIONS

Mini-open excision using intraoperative O-arm/Stealth navigation is a safe and accurate procedure for patients with osteoid osteoma, which could cover the limitation of RFA.

Injury patterns of medial meniscus posterior root tears

INTRODUCTION

Medial meniscus posterior root tear (MMPRT) can occur in middle-aged patients who have a posteromedial painful popping during light activities. MMPRTs are more common in patients with increased age, female gender, sedentary lifestyle, obesity, and varus knee alignment. However, injury mechanisms of minor traumatic MMPRTs are still unclear. We hypothesized that high flexion activities are the major cause of MMPRTs. The aim of this study was to clarify injury patterns of MMPRTs.

MATERIALS AND METHODS

One hundred patients were diagnosed having MMPRTs after posteromedial painful popping episodes. Details of posteromedial painful popping episode, situation of injury, and position of injured leg were obtained from the patients by careful interviews. Injury patterns were divided into 8 groups: descending knee motion, walking, squatting, standing up action, falling down, twisting, light exercise, and minor automobile accident.

RESULTS

A descending knee motion was the most common cause of MMPRTs (38%) followed by a walking injury pattern (18%) and a squatting action related to high flexion activities of the knee (13%). The other injury patterns were less than 10%.

DISCUSSION

Descending knee motions associated with descending stairs, step, and downhill slope are the most common injury pattern of MMPRTs. High flexion activities of the knee are not the greatest cause of MMPRTs. Our results suggest that the descending action with a low knee flexion angle may trigger minor traumatic MMPRTs.

LEVEL OF EVIDENCE

IV, retrospective cohort study.

Clinical and Functional Significance of Intracellular and Extracellular microRNA-25-3p in Osteosarcoma

Although there is considerable evidence indicating that the dysregulation of microRNAs (miRNAs) in malignant tumors plays a role in tumor development, the overall function of miRNAs and their clinicopathological significance are not well understood. In this retrospective analysis of 45 biopsy specimens from osteosarcoma (OS) patients, we investigated the functional and clinical significance of miR-25-3p in OS, which we previously identified as a highly expressed miRNA in OS patients' serum. We observed that miR-25-3p dysregulation in human OS tissues was negatively correlated with the clinical prognosis, whereas the expression level of its target gene, Dickkopf WNT Signaling Pathway Inhibitor 3 (DKK3), was positively correlated with the clinical prognosis. Endogenous miR-25-3p upregulation promoted tumor growth, invasion, and drug resistance, which was consistent with DKK3 silencing in OS cells. In addition, secretory miR-25-3p was embedded in tumor-derived exosomes, where it promoted capillary formation and the invasion of vascular endothelial cells. Overall, our results show that miR-25-3p has intracellular and extracellular oncogenic functions as well as clinicopathological relevance in OS, indicating its potential as a novel diagnostic and therapeutic tool for the clinical management of this disease.

Abstract 4570: Telomerase-specific oncolytic virotherapy promotes therapeuticefficacy of PD-1 blockade in murine osteosarcoma

Background: Treatment with immune checkpoint inhibitor anti-programmed death protein 1 (PD-1) antibody has dramatically improved the clinical outcome in cancer patients. Then immunotherapy is the most exciting field for cancer treatment in recent years. However, PD-1 blockade therapy is limited to certain cancer types. Therefore, the enhancement of therapeutic efficacy in PD-1 blockade therapy is required. Recently, it has been suggested that the effect of PD-1 blockade therapy can be enhanced when combined with immunogenic antitumor therapy including chemotherapy and virotherapy. We recently developed a RGD fiber-modified telomerase-specific oncolytic adenovirus OBP-502, which can enter into tumor cells by binding to cell surface integrin and induce oncolytic cell death in a telomerase-dependent manner. In this study, we assessed the in vitro and in vivo antitumor efficacy of combination therapy with anti-PD-1 antibody and OBP-502 in murine osteosarcoma.

Methods: We used 2 murine osteosarcoma cell lines, K7M2 and NHOS. The expression of PD-L1, coxsackie and adenovirus receptor (CAR), and integrin on the cell surface was analyzed by flow cytometric analysis. The in vitro antitumor effect of OBP-502 was evaluated using a XTT assay. Virus-induced immunogenic cell death was assessed by analyzing the level of extracellular ATP and high-mobility group box protein B1 (HMGB1). To evaluate the therapeutic potential of anti-PD-1 antibody and OBP-502, we assessed the antitumor effect of combination therapy with anti-PD-1 antibody and OBP-502 using a subcutaneous K7M2 xenograft tumor model. Moreover, the number of tumor-infiltrating CD8+ and Foxp3+ T cells was analyzed by immunohistochemistry.

Results: K7M2 and NHOS cells showed the expression of PD-L1 and integrin, but not CAR, in flow cytometric analysis. OBP-502 efficiently suppressed the viability of K7M2 and NHOS cells in a dose-dependent manner. OBP-502 significantly increased the release of HMGB1 in K7M2 cells and the secretion of ATP in NHOS cells. Intratumoral injection of OBP-502 significantly induced the number of tumor-infiltrating CD8+ T cells and enhanced the suppression of tumor growth by PD-1 blockade in a subcutaneous K7M2 xenograft tumor model. Moreover, tumor free was observed in 6 out of 7 mice treated with anti-PD-1 antibody and OBP-502 even at 4 weeks after treatment.

Conclusion: These results suggest that telomerase-specific oncolytic virotherapy is a promising antitumor strategy to promote the therapeutic efficacy of PD-1 blockade therapy in osteosarcoma.

Citation Format: Yusuke Mochizuki, Hiroshi Tazawa, Koji Demiya, Tadashi Komatsubara, Kazuhisa Sugiu, Joe Hasei, Toshiyuki Kunisada, Yasuo Urata, Toshifumi Ozaki, Toshiyoshi Fujiwara. Telomerase-specific oncolytic virotherapy promotes therapeuticefficacy of PD-1 blockade in murine osteosarcoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4570.

Role of zoledronic acid in oncolytic virotherapy: Promotion of antitumor effect and prevention of bone destruction

Osteosarcoma is an aggressive malignant bone tumor that causes bone destruction. Although tumor‐specific replicating oncolytic adenovirus OBP‐301 induces an antitumor effect in an osteosarcoma tumor, it cannot prevent bone destruction. Zoledronic acid (ZOL) is a clinically available agent that inhibits bone destruction. In this study, we investigated the potential of combination therapy with OBP‐301 and ZOL against osteosarcomas with bone destruction. The antitumor activity of OBP‐301 and ZOL in monotherapy or combination therapy was assessed using three human osteosarcoma cell lines (143B, MNNG/HOS, SaOS‐2). The cytotoxic effect of OBP‐301 and/or ZOL was measured by assay of cell apoptosis. The effect of OBP‐301 and ZOL on osteoclast activation was investigated. The potential of combination therapy against tumor growth and bone destruction was analyzed using an orthotopic 143B osteosarcoma xenograft tumor model. OBP‐301 and ZOL decreased the viability of human osteosarcoma cells. Combination therapy with OBP‐301 and ZOL displayed a synergistic antitumor effect, in which OBP‐301 promoted apoptosis through suppression of anti‐apoptotic myeloid cell leukemia 1 (MCL1). Combination therapy significantly inhibited tumor‐mediated osteoclast activation, tumor growth and bone destruction compared to monotherapy. These results suggest that combination therapy of OBP‐301 and ZOL suppresses osteosarcoma progression via suppression of MCL1 and osteoclast activation.

Impact of Autophagy in Oncolytic Adenoviral Therapy for Cancer

Oncolytic virotherapy has recently emerged as a promising strategy for inducing tumor-specific cell death. Adenoviruses are widely and frequently used in oncolytic virotherapy. The mechanism of oncolytic adenovirus-mediated tumor suppression involves virus-induced activation of the autophagic machinery in tumor cells. Autophagy is a cytoprotective process that produces energy via lysosomal degradation of intracellular components as a physiologic response to various stresses, including hypoxia, nutrient deprivation, and disruption of growth signaling. However, infection with oncolytic adenoviruses induces autophagy and subsequent death of tumor cells rather than enhancing their survival. In this review, we summarize the beneficial role of autophagy in oncolytic adenoviral therapy, including the roles of infection, replication, and cell lysis. Numerous factors are involved in the promotion and inhibition of oncolytic adenovirus-mediated autophagy. Furthermore, recent evidence has shown that oncolytic adenoviruses induce autophagy-related immunogenic cell death (ICD), which enhances the antitumor immune response by inducing the activation of danger signal molecules and thus represents a novel cancer immunotherapy. Understanding the precise role of oncolytic adenovirus-induced autophagy and ICD could enhance the therapeutic potential of oncolytic adenoviral therapy for treating various cancers.

Abstract 4299: Chemosensitizing effect of telomerase-dependent oncolytic adenovirus through virally induced microRNA-29-mediated MCL1 downregulation in osteosarcoma cells

Osteosarcoma is a rare highly malignant tumor. It is generally refractory to chemotherapy, which contributes to its poor prognosis. The enhancement of chemosensitivity is a potential approach to improve the prognostic outcome of osteosarcoma patients. We developed a telomerase-specific replication-competent oncolytic adenovirus, OBP-301. We recently confirmed the antitumor effect of OBP-301 monotherapy in human osteosarcoma cells. We also revealed the synergistic chemosensitizing effect of OBP-301 in human epithelial malignant tumor cells. In this study, we investigated the chemosensitizing effect of OBP-301 and its underlying mechanisms in human osteosarcoma cells. We used four human osteosarcoma cell lines, SaOS-2, MNNG/HOS, HOS and 143B. OBP-301 is an attenuated adenovirus, in which the hTERT promoter drives the expression of E1 gene, and causes tumor-selective lysis in a variety of human malignant tumor cells with telomerase activity. OBP-301 infection enhanced the cytotoxic effect of chemotherapeutic agents (cisplatin and doxorubicin). The calculation of combination index revealed the synergistic effects in all four human osteosarcoma cell lines. Combination of OBP-301 increased chemotherapy-induced apoptosis. To clarify the molecular mechanism underlying the chemosensitizing effect of OBP-301, we investigated whether OBP-301 affects the expression of anti-apoptotic BCL2 family proteins. In SaOS-2 and MNNG/HOS cells, the expression level of MCL1 was markedly decreased by OBP-301 infection. MCL1 knockdown by siRNA enhanced the chemotherapy-induced apoptosis as well as OBP-301. We recently revealed that OBP-301 increase the expression of cellular miRNAs in human cancer cells. To investigate the underlying mechanism of OBP-301-mediated MCL1 suppression, we determined whether OBP-301 upregulates MCL1-targeted miRNAs. OBP-301 dose-dependently upregulated the expression of MCL1 targeted miR-29 in SaOS-2 and MNNG/HOS cells. Exogenously introduced miR-29 efficiently suppressed MCL1 expression and enhanced the chemotherapy-induced apoptosis. Moreover, combination treatment significantly inhibited tumor growth, as compared to monotherapy, in a subcutaneous xenograft tumor model. MCL1 is overexpressed in various types of human tumor cells. Overexpression of anti-apoptotic proteins is an important factor to prevent chemotherapy-induced apoptosis in cancer. We demonstrated OBP-301 efficiently kills human osteosarcoma cells and markedly sensitizes them to chemotherapy. MCL1 suppression via OBP-301-induced miR-29 is critical as the underlying mechanism of the OBP-301 mediated chemosensitizing effect. These results suggest that replicative virus-mediated tumor specific MCL1 ablation may be a promising strategy to attenuate chemoresistance in osteosarcoma patients.

Citation Format: Shuhei Osaki, Hiroshi Tazawa, Joe Hasei, Yasuo Urata, Toshifumi Ozaki, Toshiyoshi Fujiwara. Chemosensitizing effect of telomerase-dependent oncolytic adenovirus through virally induced microRNA-29-mediated MCL1 downregulation in osteosarcoma cells [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 4299. doi:10.1158/1538-7445.AM2017-4299

Inflammation-induced miRNA-155 inhibits self-renewal of neural stem cells via suppression of CCAAT/enhancer binding protein β (C/EBPβ) expression

Intracerebral inflammation resulting from injury or disease is implicated in disruption of neural regeneration and may lead to irreversible neuronal dysfunction. Analysis of inflammation-related microRNA profiles in various tissues, including the brain, has identified miR-155 among the most prominent miRNAs linked to inflammation. Here, we hypothesize that miR-155 mediates inflammation-induced suppression of neural stem cell (NSC) self-renewal. Using primary mouse NSCs and human NSCs derived from induced pluripotent stem (iPS) cells, we demonstrate that three important genes involved in NSC self-renewal (Msi1, Hes1 and Bmi1) are suppressed by miR-155. We also demonstrate that suppression of self-renewal genes is mediated by the common transcription factor C/EBPβ, which is a direct target of miR-155. Our study describes an axis linking inflammation and miR-155 to expression of genes related to NSC self-renewal, suggesting that regulation of miR-155 may hold potential as a novel therapeutic strategy for treating neuroinflammatory diseases.

Abstract 4677: Tumor suppressor p53 reactivation by oncolytic adenovirus reverses chemoresistance in human osteosarcomas

Background: Osteosarcoma is a primary malignant bone tumor. Despite recent advances in multi-agent chemotherapy and aggressive surgical resection, the poor response to chemotherapy often contributes to poor prognosis in osteosarcoma patients. Therefore, the development of novel strategies for reversing the chemoresistance is a pivotal approach to improve the clinical outcome for osteosarcoma patients. We recently developed a tumor suppressor p53-expressing oncolytic adenovirus, OBP-702, which drives the adenoviral E1 gene under the control of the human telomerase reverse transcriptase promoter for tumor-specific virus replication and induces profound p53 expression for tumor-specific cell death. We recently found that OBP-702 effectively kills human osteosarcoma cells. In this study, we investigated the therapeutic potential of OBP-702 as a chemosensitizing reagent in human osteosarcoma cells with different p53 status.

Methods: We used 4 human osteosarcoma cell lines with different p53 status, including U2OS (p53 wild-type), MNNG/HOS (p53 mutant), 143B (p53 mutant), SaOS2 (p53 null). We also used the doxorubicin (DOX)-resistant U2OS cells, which were established by sequential exposure to DOX over 3 months. We performed the XTT assay to examine the antitumor effects of DOX and OBP-702. Combination efficacy between DOX and OBP-702 was assessed by calculating the combination index using CalcuSyn software (BioSoft, Inc.). We further investigated the DOX- and OBP-702-mediated apoptosis in parental and DOX-resistant U2OS cells using Western blot analysis.

Results: OBP-702 improved the sensitivity to DOX in a dose-dependent manner in all 4 osteosarcoma cell lines. The calculation of combination index revealed the synergistic effect in all 4 osteosarcoma cell lines. Combination with DOX and OBP-702 induced more profound apoptosis than monotherapy in all 4 osteosarcoma cell lines. Moreover, in DOX-resistant U2OS cells, OBP-702 induced the cytopathic effect as well as parental U2OS cells. Synergistic effect was also observed in DOX-resistant U2OS cells when we treated with DOX and OBP-702. Although DOX-resistant U2OS cells was more resistant to the DOX-mediated apoptosis than parental cells, OBP-702 enhanced the DOX-mediated apoptosis in DOX-resistant U2OS cells as well as parental cells.

Conclusions: These results suggest that OBP-702-mediated p53 reactivation reverses the chemoresistance in human osteosarcomas.

Citation Format: Kazuhisa Sugiu, Hiroshi Tazawa, Joe Hasei, Shuhei Osaki, Yasuaki Yamakawa, Toshinori Omori, Tadashi Komatsubara, Kouji Uotani, Tomohiro Fujiwara, Toshiyuki Kunisada, Yasuo Urata, Toshifumi Ozaki, Toshiyoshi Fujiwara. Tumor suppressor p53 reactivation by oncolytic adenovirus reverses chemoresistance in human osteosarcomas. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4677.

Abstract 1794: Preclinical evaluation of radiotherapy in combination with radio-sensitizing telomerase-specific oncolytic virus for human bone and soft tissue sarcomas

Background: Despite major advances in the treatment of bone and soft tissue sarcomas, including surgery, chemotherapy, and radiation, some sarcoma patients show poor prognosis due to resistance to conventional therapy. Therefore, the development of a novel therapeutic strategy for sarcoma patients is needed. We recently revealed that a telomerase-specific, replication-competent oncolytic adenovirus OBP-301 efficiently killed human sarcoma cells. Moreover, combination therapy with OBP-301 and radiation has been confirmed to show synergistic antitumor effect in epithelial malignant tumor cells; however, its effect in human sarcoma cells remains elusive. In this study, we investigated the antitumor effect of OBP-301 in combination with radiation against human sarcoma cells.

Methods: We used five human sarcoma cell lines, SK-ES-1 (Ewing sarcoma), RD-ES (Ewing sarcoma) SYO-1 (synovial sarcoma), U2OS (osteosarcoma) and HOS (osteosarcoma). Cells were irradiated 24 h after infection with OBP-301, and cell viability was assessed by XTT assay 4 days after irradiation. Combined effect of radiation with OBP-301 was analyzed with the CalcuSyn software (BioSoft). These cells were analyzed for apoptosis using western blot analysis. To analyze the effect of OBP-301 in DNA repair process, immunofluorescence staining was performed after treatment of irradiation with or without OBP-301 infection on SK-ES-1 cell. We further investigated the in vivo combined effect of OBP-301 and radiation. The SK-ES-1 tumor-bearing mice were irradiated at a dosage of 1 Gy/tumor once per week for three cycles, and OBP-301 (1 × 108 plaque-forming units per tumor), or PBS was injected into the tumor 3 times per week for three cycles.

Results: Combination treatment with OBP-301 and radiation showed synergistic or additive antitumor effect in all human sarcoma cells. Western blot analysis showed that combination treatment increased the expression of cleaved-PARP, and prolonged the level of γH2AX protein than radiation treatment. Combination therapy of OBP-301 with radiation showed antitumor effect more significantly than monotherapy in SK-ES-1 xenograft tumor model.

Conclusions: These results suggest that combination therapy of OBP-301 with radiation is a promising antitumor strategy for bone and soft tissue sarcomas.

Citation Format: Toshinori Omori, Yasuaki Yamakawa, Joe Hasei, Hiroshi Tazawa, Shuhei Osaki, Tusyoshi Sasaki, Kazuhisa Sugiu, Tomohiro Fujiwara, Toshiyuki Kunisada, Yasuo Urata, Toshifumi Ozaki, Toshiyoshi Fujiwara. Preclinical evaluation of radiotherapy in combination with radio-sensitizing telomerase-specific oncolytic virus for human bone and soft tissue sarcomas. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1794. doi:10.1158/1538-7445.AM2015-1794

Abstract 342: Telomerase-dependent oncolytic adenovirus sensitizes human osteosarcoma cells to chemotherapy through Mcl-1 downregulation

Osteosarcoma is the most common malignant primary bone tumor. Despite advances in multi-agent chemotherapy, poor response to chemotherapy is one of the critical prognostic factors in osteosarcoma. Therefore, enhancement of chemosensitivity is one approach to improve the survival of osteosarcoma patients. We recently developed a telomerase-specific replication-competent oncolytic adenovirus, Telomelysin (OBP-301). A Phase I clinical trial in the U.S. showed the safety of OBP-301 in advanced cancer patients, and a Phase I/II clinical trial for malignant thoracic tumors is currently undergoing. We recently confirmed the antitumor effect of OBP-301 monotherapy in human osteosarcoma cells. In this study, we investigated the chemosensitizing effect of OBP-301 in human osteosarcoma cells and the molecular mechanism in the OBP-301-mediated enhancement of cell death. We used four human osteosarcoma cell lines, HOS, MNNG/HOS, 143B and SaOS-2. OBP-301 is an attenuated adenovirus, in which the hTERT promoter drives the expression of E1 gene, and causes tumor-selective lysis in a variety of human malignant tumor cells with telomerase activity. OBP-301 infection enhanced the cytotoxic effect of chemotherapeutic agents, cisplatin and doxorubicin, that are commonly used for the treatment of osteosarcomas. The calculation of combination index revealed the synergistic effects in all human osteosarcoma cell lines. Combination of OBP-301 increased apoptosis in the chemotherapeutic agents-treated cells. To clarify the molecular mechanism for the chemosensitizing effect of OBP-301, the expression of Bcl-2 family proteins, which are critical regulators of apoptosis, were investigated. In OBP-301-infected MNNG/HOS and SaOS-2 cells, the expression level of Mcl-1 was markedly decreased by OBP-301 infection. Downregulation of Mcl-1 expression by siRNA enhanced the chemotherapeutic agents-induced apoptosis. Moreover, combination therapy of chemotherapeutic agents with OBP-301 significantly suppressed tumor growth in a subcutaneous xenograft tumor model compared to monotherapy with chemotherapeutic agents or OBP-301. Anti-apoptotic Mcl-1 protein has been shown to be frequently overexpressed in human sarcomas. Overexpression of anti-apoptotic proteins is an important factor to prevent chemotherapy-induced apoptosis in cancer. We demonstrated the involvement of Mcl-1 suppression in the chemosensitizing effect of OBP-301 in human osteosarcoma cells. These results suggest that Mcl-1 is a critical target for improvement of the chemosensitivity in human osteosarcoma cells and the combination of chemotherapy with OBP-301 may be a novel therapeutic strategy for osteosarcoma patients.

Citation Format: Shuhei Osaki, Toshinori Omori, Hiroshi Tazawa, Joe Hasei, Yasuaki Yamakawa, Tsuyoshi Sasaki, Toshiyuki Kunisada, Yasuo Urata, Toshifumi Ozaki, Toshiyoshi Fujiwara. Telomerase-dependent oncolytic adenovirus sensitizes human osteosarcoma cells to chemotherapy through Mcl-1 downregulation. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 342. doi:10.1158/1538-7445.AM2014-342

Abstract 725: Combination therapy of telomerase-specific oncolytic adenovirus and zoledronic acid in human osteosarcoma cells

Osteosarcoma is one of the primary malignant bone tumors that often occur around the ages of 15 to 20. Despite advances in combined chemotherapy and surgical resection, 30% of osteosarcoma patients still die from tumor or metastasis. Therefore, new treatment strategy is being required. We previously reported that telomerase-specific, replication-competent oncolytic adenovirus (Telomelysin, OBP-301), showed the in vitro and in vivo antitumor effects in human bone and soft tissue sarcoma cells; however OBP-301 could not efficiently prevent bone destruction in an orthotopic xenograft tumor model. Recently, third-generation bisphosphonates, zoledronic acid (ZOL), is widely used to inhibit bone destruction in metastatic bone tumors in the clinical settings. Moreover, ZOL has been shown to induce the antitumor effect synergistically in combination with chemotherapeutic agents in human sarcoma cells. In this study, we investigated the in vitro and in vivo antitumor effects of combination therapy with ZOL and OBP-301 in human osteosarcoma cells. Four human osteosarcoma cell lines, HOS, SaOS-2, U2OS and MNNG/HOS were used. We used XTT assay to examine the antitumor effect of ZOL and OBP-301 individually and combinatory on days 2,3,5. ZOL was treated at concentration of 0 to 10µM, and OBP-301 was infected at multiplicity of infections (MOI) of 0 to 100 plaque forming units (PFU)/cell. Combination index was calculated with the CalcuSyn software (BioSoft) and combined antitumor effect between ZOL and OBP-301 was analyzed. XTT assay revealed that combination treatment of ZOL and OBP-301 showed synergistic and additive effects. To analyze the molecular mechanism in the synergistic effect of ZOL and OBP-301, western blot analysis for apoptosis (PARP) and autophagy (LC3, p62) was performed. Treatment with ZOL induced apoptosis, which was confirmed by the cleavage of PARP, and OBP-301infection induced both apoptosis and autophagy, which is confirmed by conversion of LC3- I to LC3- II and p62 downregulation. Combination treatment showed increased apoptotic cell death in all human osteosarcoma cells. Moreover, in vivo antitumor effect of combination therapy was investigated in an orthotopic xenograft tumor model, in which MNNG/HOS cells (2×106 cells per site) were inoculated into the left tibias of female athymic nude mice. ZOL and OBP-301 were injected subcutaneously and intratumorally, respectively, for three times every week. Tumor volume was measured once a week and bone destruction status was analyzed using 3D-CT imaging system at final assessment. Combination treatment showed increased antitumor effect and efficiently prevented bone destruction compared to monotherapy in an orthotopic xenograft MNNG/HOS tumor model. These results suggest that combination treatment of ZOL and OBP-301 is a promising antitumor strategy for improvement of clinical outcome in patients with osteosarcomas.

Citation Format: Yasuaki Yamakawa, Joe Hasei, Hiroshi Tazawa, Toshinori Omori, Shuhei Osaki, Tsuyoshi Sasaki, Aki Yoshida, Toshiyuki Kunisada, Yasuo Urata, Toshifumi Ozaki, Toshiyoshi Fujiwara. Combination therapy of telomerase-specific oncolytic adenovirus and zoledronic acid in human osteosarcoma cells. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 725. doi:10.1158/1538-7445.AM2014-725

Abstract 3320: Combined effect of zoledronic acid and telomerase-specific oncolytic virotherapy for human osteosarcoma cells

Osteosarcoma is the most frequent type of primary malignant bone tumor and common between the ages of 10 to 25. Based on preoperative and postoperative chemotherapy, the prognosis of osteosarcoma patients has improved. However, 30% of osteosarcoma patients who become refractory to chemotherapy still die from tumor or metastasis. We previously reported that telomerase-specific, replication-competent oncolytic adenovirus (Telomelysin, OBP-301), efficiently killed human bone and soft tissue sarcoma cells but not normal human somatic cells. Recently, third-generation bisphosphonates, zoledronic acid (ZOL), is widely used to inhibit bone destruction in metastatic bone tumor through induction of apoptosis in osteoclast cells in the clinical settings. Moreover, ZOL has been shown to induce the antitumor effect synergistically in combination with chemotherapeutic agents in human sarcoma cells. In this study, we investigated the combined antitumor effect of ZOL and OBP-301 in human osteosarcoma cells. Three human osteosarcoma cell lines, HOS, SaOS-2, U2OS, were used. We used XTT assay to examine the antitumor effect of ZOL and OBP-301 individually and combinatory on days 2, 3, 5 after treatment. ZOL was treated at concentration of 0 to 10μM, and OBP-301 was infected at multiplicity of infections (MOI) of 0 to 50 plaque forming units (PFU)/cell. Synergy between ZOL and OBP-301 was analyzed with the CalcuSyn software (BioSoft). XTT assay showed that treatment of ZOL or OBP-301 decreased the cell viability in a time- and dose-dependent manner. Combination treatment of ZOL and OBP-301 showed synergy and additive effects. After calculation of the half maximal (50%) inhibitory concentration (IC50) of ZOL and dose (ID50) of OBP-301 for each cell, cells were treated with ZOL and OBP-301 for 3 days at concentration of IC50 and ID50, respectively. Whole cell lysates were subjected to western blot analysis for the cleaved PARP (C-PARP) and PARP, LC3, p62 and β-actin. Western blot analysis revealed that ZOL induced apoptosis, which was confirmed by increasing of C- PARP, and OBP-301 induced not only apoptosis but also autophagy, which is confirmed by conversion of LC3- I to LC3- II and p62 down-regulation. Combination treatment showed increasing of these effects synergistically or additively in each cell. These results suggest that combination treatment of ZOL and OBP-301 is a promising antitumor strategy for patients with osteosarcomas. We are now planning to investigate the antitumor and bone-protective effects of combination treatment in an orthotopic xenograft tumor model using 3D-CT imaging system.

Citation Format: Yasuaki Yamakawa, Joe Hasei, Hiroshi Tazawa, Shuhei Osaki, Tsuyoshi Sasaki, Toshiyuki Kunisada, Aki Yoshida, Yasuo Urata, Toshifumi Ozaki, Toshiyoshi Fujiwara. Combined effect of zoledronic acid and telomerase-specific oncolytic virotherapy for human osteosarcoma cells. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3320. doi:10.1158/1538-7445.AM2013-3320

Abstract 584: Enhanced chemosensitivity of osteosarcoma cells by telomerase-specific oncolytic adenovirus in combination therapy

Osteosarcomas are the most common malignant bone tumors. Although the multi-agent chemotherapy has improved the long-term survival rate of osteosarcoma patients, some patients show a poor response to chemotherapy, leading to recurrence and poor prognosis. Therefore, the enhancement of chemosensitivity is required to cure patients with osteosarcomas. We recently developed a telomerase-specific replication-competent oncolytic adenovirus, Telomelysin (OBP-301), and confirmed the antitumor effect of OBP-301 in human osteosarcoma cells. A phase I clinical trial in US has also shown the safety of OBP-301 in cancer patients. In this study, we investigated whether OBP-301 enhances the antitumor effect of chemotherapeutic agents, doxorubicin and cisplatin, that are used for the treatment of osteosarcomas, and the molecular mechanism of chemotherapy- and OBP-301-mediated cell death pathway, autophagy and apoptosis, in human osteosarcoma cell lines. We used four human osteosarcoma cell lines, HOS, MNNG/HOS, 143B and SaOS2. OBP-301 is an attenuated adenovirus, in which the human telomerase reverse transcriptase (hTERT) promoter element drives expression of E1A and E1B genes, and causes tumor-selective lysis in a variety of human malignant tumor cells with high telomerase activity. OBP-301 infection enhanced the cytotoxic effect of chemotherapeutic agents and the calculation of combination index revealed the synergistic effects in all human osteosarcoma cell lines. To analyze the molecular mechanism in the synergistic effect induced by combination therapy, western blot analysis for apoptosis (PARP) and autophagy (LC3, p62) was performed. Combination of OBP-301 increased both apoptosis (the cleavage of PARP) and autophagy (conversion of LC3-I to LC3-II and p62 downregulation) in the chemotherapeutic agents-treated human osteosarcoma cells. In contrast, the replication of OBP-301 was not suppressed by chemotherapeutic agents. Moreover, combination therapy of chemotherapeutic agents with OBP-301 significantly suppressed tumor growth in a subcutaneous xenograft tumor model compared to monotherapy with chemotherapeutic agents or OBP-301. These results suggest that combination therapy of chemotherapeutic agents with OBP-301 provides a novel therapeutic strategy for human osteosarcomas.

Citation Format: Shuhei Osaki, Tsuyoshi Sasaki, Hiroshi Tazawa, Joe Hasei, Yasuaki Yamakawa, Yuuri Hashimoto, Toshiyuki Kunisada, Yasuo Urata, Toshifumi Ozaki, Toshiyoshi Fujiwara. Enhanced chemosensitivity of osteosarcoma cells by telomerase-specific oncolytic adenovirus in combination therapy. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 584. doi:10.1158/1538-7445.AM2013-584

Dual programmed cell death pathways induced by p53 transactivation overcome resistance to oncolytic adenovirus in human osteosarcoma cells

Tumor suppressor p53 is a multifunctional transcription factor that regulates diverse cell fates, including apoptosis and autophagy in tumor biology. p53 overexpression enhances the antitumor activity of oncolytic adenoviruses; however, the molecular mechanism of this occurrence remains unclear. We previously developed a tumor-specific replication-competent oncolytic adenovirus, OBP-301, that kills human osteosarcoma cells, but some human osteosarcoma cells were OBP-301-resistant. In this study, we investigated the antitumor activity of a p53-expressing oncolytic adenovirus, OBP-702, and the molecular mechanism of the p53-mediated cell death pathway in OBP-301-resistant human osteosarcoma cells. The cytopathic activity of OBP-702 was examined in OBP-301-sensitive (U2OS and HOS) and OBP-301-resistant (SaOS-2 and MNNG/HOS) human osteosarcoma cells. The molecular mechanism in the OBP-702-mediated induction of two cell death pathways, apoptosis and autophagy, was investigated in OBP-301-resistant osteosarcoma cells. The antitumor effect of OBP-702 was further assessed using an orthotopic OBP-301-resistant MNNG/HOS osteosarcoma xenograft tumor model. OBP-702 suppressed the viability of OBP-301-sensitive and -resistant osteosarcoma cells more efficiently than OBP-301 or a replication-deficient p53-expressing adenovirus (Ad-p53). OBP-702 induced more profound apoptosis and autophagy when compared with OBP-301 or Ad-p53. E1A-mediated miR-93/106b upregulation induced p21 suppression, leading to p53-mediated apoptosis and autophagy in OBP-702-infected cells. p53 overexpression enhanced adenovirus-mediated autophagy through activation of damage-regulated autophagy modulator (DRAM). Moreover, OBP-702 suppressed tumor growth in an orthotopic OBP-301-resistant MNNG/HOS xenograft tumor model. These results suggest that OBP-702-mediated p53 transactivation is a promising antitumor strategy to induce dual apoptotic and autophagic cell death pathways via regulation of miRNA and DRAM in human osteosarcoma cells.

Abstract 4065: A simple biological imaging system for detecting adenovirus receptor expression in tumor cells using a telomerase-specific replication-competent adenovirus

Adenovirus serotype 5 (Ad5) is frequently used as an effective vector for induction of therapeutic transgenes in cancer gene therapy or of tumor cell lysis in oncolytic virotherapy. Ad5 can infect target cells through binding with the coxsackie and adenovirus receptor (CAR). Thus, the infectious ability of Ad5-based vectors depends on the CAR expression level in target cells. There are conventional methods to evaluate the CAR expression level in human target cells, including flow cytometry, western blotting and immunocytochemistry. We recently generated a green fluorescent protein (GFP)-expressing telomerase-specific replication-competent adenovirus OBP-401, which induces ectopic GFP expression in tumor cells, but not in normal cells. In this study, we evaluated whether induction of GFP expression by OBP-401 infection is associated with CAR expression in tumor cells. OBP-401-mediated GFP induction was further examined in xenograft tumor tissues that have different levels of CAR expression and in surrounding normal tissues. We used six human sarcoma cell lines that have different levels of CAR expression and CAR-positive normal human lung fibroblasts (NHLF). Flow cytometry analysis confirmed that cells of four of the sarcoma cell lines (OST, U2OS, NOS-10 and MNNG/HOS) as well as the NHLF cells showed detectable CAR expression, whereas cells of the NMFH-1 and OUMS-27 sarcoma cell lines had no detectable CAR expression. To determine suitable conditions for OBP-401 infection, all tumor and normal cells was infected with OBP-401 at multiplicity of infections of 1, 10 and 100 plaque forming units/cell. OBP-401 infection induced detectable GFP expression in CAR-expressing tumor cells, but not in CAR-negative tumor cells, nor in CAR-positive normal fibroblasts, 24 hours after infection. OBP-401-mediated GFP expression was significantly associated with CAR expression in tumor cells. OBP-401 infection detected tumor cells with low CAR expression more efficiently than conventional methods. We further examined the potential of the OBP-401-mediated method for the detection of CAR expression in tumor and normal tissues, we used this method to analyze CAR expression of human xenograft tumor tissues. OBP-401 infection induced GFP expression in OST tumor tissues, but not in OUMS-27 tumor tissues or in normal muscle tissue. OBP-401 also distinguished CAR-positive tumor tissues from CAR-negative tumor and normal tissues in biopsy samples. These results suggest that GFP-expressing telomerase-specific replication-competent adenovirus is a very potent diagnostic tool for assessment of functional CAR expression in tumor cells for Ad5-based antitumor therapy.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4065. doi:1538-7445.AM2012-4065

Abstract 5651: p53-mediated apoptotic signaling overcomes the resistance to oncolytic adenovirus in human osteosarcoma cells

Despite major advances in the treatment of bone and soft tissue sarcomas, about one fourth of the patients show a poor response to conventional therapy, resulting in subsequent recurrence and leading to a poor prognosis. Therefore, the development of a novel therapeutic strategy is required to cure patients with bone and soft tissue sarcomas. We previously developed an oncolytic adenovirus, OBP-301, in which human telomerase reverse transcriptase (hTERT) gene promoter drives viral E1 gene for replication. OBP-301 induces tumor-specific oncolytic cell death in a telomerase-dependent manner. Recently, we revealed that OBP-301 shows cytopathic activity in human bone and soft tissue sarcoma cells. However, some human osteosarcoma cells were less sensitive to cytopathic activity of OBP-301. To enhance the cytopathic activity of OBP-301, we recently developed a novel telomerase-specific oncolytic adenovirus, OBP-702, which expresses tumor suppressor p53 gene. In this study, we investigated the antitumor effect of OBP-702 in OBP-301-sensitive (OST, HOS and U2OS) and OBP-301-resistant (MNNG/HOS and SaOS-2) human osteosarcoma cells. We compared the antitumor effects of OBP-702 and OBP-301 using XTT assay. The 50% inhibiting dose (ID50) value of OBP-702 and OBP-301 for each cell was calculated using cell viability data obtained on day 5 after virus infection. We further evaluated the expression of p53, p21 and cleaved poly (ADP-ribose) polymerase (PARP) proteins using western blot analysis in both OBP-301-sensitive and OBP-301-resistant osteosarcoma cells after infection with OBP-702 or Ad-p53, which is a p53-expressing replication-defective adenovirus. OBP-702 showed more cytopathic activity compared to OBP-301 in both OBP-301-sensitive and OBP-301-resistant osteosarcoma cells. The ID50 value of OBP-702 was lower than that of OBP-301 in all cell lines. OBP-702 induced not only oncolysis, but also apoptotic cell death with the cleavage of PARP. OBP-702 infection induced more profound p53 expression than Ad-p53. However, p53-downstream target p21 proteins were not activated by OBP-702. Taken together, we demonstrated that the p53-expressing oncolytic adenovirus OBP-702 has a much stronger antitumor effect than OBP-301 in human osteosarcoma cells. Oncolytic adenovirus-mediated p53 gene transduction would induce profound apoptosis through p53 upregulation without p21 activation, resulting in the enhancement of antitumor effect by OBP-301. OBP-702 would be a promising antitumor reagent for the treatment of OBP-301-resistant human osteosarcoma cells.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 5651. doi:1538-7445.AM2012-5651