An issue of concern is that no current HER2-targeted therapeutic agent is effective against Trastuzumab (Tmab)-resistant gastric cancer. Gold nanoparticles (AuNPs) are promising drug carriers with unique characteristics of a large surface area available for attachment of materials such as antibodies. Here, we created HER2-targeted AuNPs (T-AuNPs) and examined their therapeutic efficacy and cytotoxic mechanisms using HER2-postive Tmab-resistant (MKN7) or Tmab-sensitive (NCI-N87) gastric cancer cell lines. In vitro, T-AuNPs showed stronger cytotoxic effects than controls against MKN7 and NCI-N87 cells although Tmab had no effect on MKN7 cells. Autophagy played an important role in T-AuNP cytotoxic mechanisms, which was considered to be driven by internalization of T-AuNPs. Finally, T-AuNPs displayed potent antitumor effects against NCI-N87 and MKN7 subcutaneous tumors in in vivo mouse models. In conclusion, HER2-targeted AuNPs with conjugated Tmab is a promising strategy for the development of novel therapeutic agents to overcome Tmab resistance in gastric cancer.

The clinical benefit of monotherapy involving immune checkpoint inhibitors (ICIs) such as anti-programmed death-1 antibody (PD-1 Ab) is limited to small populations. We previously developed a telomerase-specific oncolytic adenovirus, Telomelysin (OBP-301), the safety of which was confirmed in a phase I clinical study. Here, we examined the potential of OBP-502, an OBP-301 variant, as an agent for inducing immunogenic cell death (ICD) and synergistically enhancing the efficacy of OBP-502 with PD-1 Ab using CT26 murine colon cancer and PAN02 murine pancreatic cancer cell lines. OBP-502 induced the release of ICD molecules such as ATP and HMGB1 from CT26 and PAN02 cells, leading to recruitment of CD8-positive lymphocytes and inhibition of Foxp3-positive lymphocyte infiltration into tumors. Combination therapy involving OBP-502 intratumoral administration and PD-1 Ab systemic administration significantly suppressed the growth of not only OBP-502-treated tumors but also tumors not treated with OBP-502 (so-called abscopal effect) in CT26 and PAN02 bilateral subcutaneous tumor models, in which active recruitment of CD8-positve lymphocytes was observed even in tumors not treated with OBP-502. This combined efficacy was similar to that observed in a CT26 rectal orthotopic tumor model involving liver metastases. In conclusion, telomerase-specific oncolytic adenoviruses are promising candidates for combined therapies with ICIs.

While the importance of programmed death-ligand 1 (PD-L1), mutation burden caused by microsatellite instability (MSI), and CD8+ tumor infiltrating lymphocytes (TILs) has become evident, the significance of PD-L1 expression on prognosis still remains controversial. We evaluated the usefulness of combined markers of PD-L1 and MSI or CD8+ TILs as a prognostic biomarker in gastric cancer. A total of 283 patients with gastric cancer were reviewed retrospectively. PD-L1 expression on >5% tumor cells was defined as PD-L1-positive. PD-L1-positive rate was 15.5% (44/283). PD-L1 positivity was significantly correlated with invasive and advanced cancer and also significantly correlated with MSI, whereas no significance was observed with CD8+ TILs. Kaplan–Meier analysis showed that PD-L1 positivity significantly correlated with a poor prognosis (p = 0.0025). Multivariate analysis revealed that PD-L1 positivity was an independent poor prognostic factor (hazard ratio [HR]: 1.97, p = 0.0106) along with diffuse histological type and lymph node metastases. Combinations of PD-L1 and MSI (HR: 2.18) or CD8+ TILs (HR: 2.57) were stronger predictive factors for prognosis than PD-L1 alone. In conclusion, combined markers of PD-L1 and MSI or CD8+ TILs may be more useful prognostic biomarkers in gastric cancer, and better clarify the immune status of gastric cancer patients.

Oncolytic virotherapy has the disadvantage of being unsuitable for systemic delivery due to immune elimination. Liposomal encapsulation is well-recognized to reduce immune elimination and enhance the stability of drugs in the bloodstream. In the present study, the potential of liposome-encapsulated plasmid DNA of telomerase-specific oncolytic adenovirus (TelomeScan) expressing GFP (Lipo-pTS) as an oncolytic adenoviral agent suitable for systemic delivery was investigated. Lipo-pTS, which has a diameter of 40–50 nm, showed potent antitumor effects on HCT116 colon carcinoma cells in vitro and in vivo. Tumor selectivity of Lipo-pTS was independent of coxsackie and adenovirus receptor (CAR). Importantly, Lipo-pTS reduced production of adenovirus-neutralizing antibodies (AdNAbs) after intravenous administration into immune-competent mice compared to TelomeScan, and even in the presence of AdNAbs, Lipo-pTS maintained strong cytotoxicity. In conclusion, Lipo-pTS has the potential to become an oncolytic adenoviral agent suitable for systemic delivery with the characteristics of CAR-independent antitumor activity and a stealth effect on the immune system.

Orthotopic models of various types of tumors are widely used in anti-tumor therapeutic experiments in preclinical studies. However, there are few ways to appropriately monitor therapeutic effect in orthotopic tumor models, especially for tumors invisible from the outside. In this study we aimed to establish a non-invasive semi-quantitative bioluminescent imaging method of monitoring an orthotopic esophageal cancer mouse model. We confirmed that the TE8 esophageal cancer cell line implanted orthotopically into the abdominal esophagus of nu/nu mice (n = 5) developed not only a main tumor at the implanted site, but also local lymph node metastases and peritoneal disseminations within 6 weeks after inoculation. We established a TE8 cell line that stably expressed the firefly luciferase gene (TE8-Luc). We showed that TE8-Luc cells implanted subcutaneously into nu/nu mice (n = 5) grew over time until 5 weeks after inoculation. Tumor volume was strongly correlated with luminescent intensity emitted from the tumor, which was quantified using the IVIS imaging system. We then showed that TE8-Luc cells implanted orthotopically into the mouse abdominal esophagus (n = 8) also formed a tumor and that the luminescent intensity of such a tumor, as detected by IVIS, increased over time until 7 weeks after inoculation and was therefore likely to reflect tumor progression. We therefore propose that this orthotopic esophageal cancer model, monitored using the non-invasive semi-quantitative IVIS imaging system, will be useful for in vivo therapeutic experiments against esophageal cancer. This experimental setting is expected to contribute to the development of novel therapeutic technologies for esophageal cancer in preclinical studies.