Oncolytic viruses offer a promising approach to tumor treatment. These viruses not only have a direct lytic effect on tumor cells but can also modify the tumor microenvironment and activate antitumor immunity. Due to their high pathogenicity, flaviviruses have often been overlooked as potential antitumor agents. However, with recent advancements in genetic engineering techniques, an extensive history with vaccine strains, and the development of new attenuated vaccine strains, there has been a renewed interest in the Flavivirus genus. Flaviviruses can be genetically modified to express transgenes at acceptable levels, and the stability of such constructs has been greatly improving over the years. The key advantages of flaviviruses include their reproduction cycle occurring entirely within the cytoplasm (avoiding genome integration) and their ability to cross the blood–brain barrier, facilitating the systemic delivery of oncolytics against brain tumors. So far, the direct lytic effects and immunomodulatory activities of many flaviviruses have been widely studied in experimental animal models across various types of tumors. In this review, we delve into the findings of these studies and contemplate the promising potential of flaviviruses in oncolytic therapies.

Combined viral and photodynamic therapy for oncological diseases has great potential to treat aggressive tumors such as glioblastomas. A conjugate of vesicular stomatitis virus (VSV) with protoporphyrin IX was prepared, and its oncolytic effects were studied and compared to the effects of the individual components. The VSV showed an oncolytic effect on glioblastoma cell lines T98G and LN229 at a virus titer of 10⁵ TCID₅₀/mL. A VSV titer of 10⁴ TCID₅₀/mL was sufficient for neuroblastoma cell death. A study of the effect of VSV in tumor 3D cell modeling found that VSV had a clear viral cytopathic effect on spheroids of T98G and LN229 cells. Conjugation with the porphyrin significantly reduced the viral titer, but when irradiated, lysis of cells was observed. Photodynamic treatment of T98G and LN229 cells and spheroids with protoporphyrin IX as a photosensitizer also had a cytotoxic effect on cells and, to a lesser extent, on the tumoroids, as complete cell death was not achieved for the tumoroids. The combination therapy, which involved sequential photodynamic therapy using protoporphyrin IX as a photosensitizer and treatment with VSV, was shown to significantly enhance efficacy, resulting in complete cell death of both T98G and LN229 cells and tumoroids. The combination treatment allowed for the use of a lower viral titer (10³–10⁴ TCID₅₀/mL) and a lower porphyrin concentration (0.5 μg/mL) to achieve a significant cytotoxic effect. As a result, the implementation of this combination therapy would likely lead to fewer side effects from the treatment. This study clearly demonstrated the excellent perspectives of combination therapy for the treatment of highly aggressive tumors such as glioblastomas.

Objective: We evaluate the immunotherapeutic potential of the yellow fever virus vaccine strain 17D (YFV 17D) for intratumoral therapy of pancreatic cancer in mice. Methods: The cytopathic effect of YFV 17D on mouse syngeneic pancreatic cancers cells were studied both in vitro and in vivo and on human pancreatic cancers cells in vitro. Results: YFV 17D demonstrated a strong cytopathic effect against human cancer cells in vitro. Although YFV 17D did not exhibit a lytic effect against Pan02 mouse cells in vitro, a single intratumoral administration of 17D caused a delay in tumor growth and an increase in median survival by 30%. Multiple injections of 17D did not further improve the effect on tumor growth; however, it notably extended the median survival. Furthermore, preliminary immunization with 17D enhanced its oncotherapeutic effect. Conclusions: Intratumoral administration of yellow fever virus vaccine strain 17D delayed tumor in a murine model of pancreatic cancer. The fact that YFV 17D in vitro affected human cancer cells much more strongly than mouse cancer cells appears promising. Hence, we anticipate that the in vivo efficacy of YFV-17D-based oncolytic therapy will also be higher against human pancreatic carcinomas compared to its effect on the mouse pancreatic tumor.

Introduction. Flaviviruses, possessing natural neurotropicity could be used in glioblastoma therapy using attenuated strains or as a delivery system for antitumor agents in an inactivated form. Objective. To investigate the sensitivity of glioblastoma and pancreatic carcinoma cell lines to vaccine strains of yellow fever and tick-borne encephalitis viruses. Materials and methods. Cell lines: glioblastoma GL-6, T98G, LN-229, pancreatic carcinoma MIA RaCa-2 and human pancreatic ductal carcinoma PANC-1. Viral strains: 17D yellow fever virus (YF), Sofjin tick-borne encephalitis virus (TBEV). Virus concentration were determined by plaque assay and quantitative PCR. Determination of cell sensitivity to viruses by MTT assay. Results. 17D YF was effective only against pancreatic carcinoma tumor cells MIA Paca-2 and had a limited effect against PANC-1. In glioblastoma cell lines (LN229, GL6, T98G), virus had no oncolytic effect and the viral RNA concentration fell in the culture medium. Sofjin TBEV showed CPE50 against MIA Paca-2 and a very limited cytotoxic effect against PANC-1. However, it had no oncolytic effect against glioblastoma cell lines (LN229, T98G and GL6), although virus reproduction continued in these cultures. For the GL6 glioblastoma cell line, the viral RNA concentration at the level with the infection dose was determined within 13 days, despite medium replacement, while in the case of the LN229 cell line, the virus concentration increased from 1 × 109 to 1 × 1010 copies/ml. Conclusion. Tumor behavior in organism is more complex and is determined by different microenvironmental factors and immune status. In the future, it is advisable to continue studying the antitumor oncolytic and immunomodulatory effects of viral strains 17D YF and Sofjin TBEV using in vivo models.

Introduction. Overcoming the immunosuppressive microenvironment of pancreatic cancer (PC) using oncolytic viruses appears to be a promising therapeutic approach. However, tumor cells are characterized by significant heterogeneity, including populations of resistant cells with high basal JAK/STAT signaling activity. One potential approach to overcoming this resistance is the use of JAK1/2 kinase inhibitors, such as ruxolitinib, the efficacy of which has already been demonstrated in several studies. Objective. To study the effect of ruxolitinib (a JAK1/2 kinase inhibitor) on the replicative activity of certain oncolytic flaviviruses (YFV 17D) and alphaviruses (SINV K1487) in human pancreatic adenocarcinoma cell lines AsPC-1, BxPC-3, and Capan-2, which are characterized by high resistance to viral oncolysis. Materials and methods. Human pancreatic adenocarcinoma cell lines: AsPC-1, BxPC-3, and Capan-2 from the collection of Laboratory of Tick-Borne Encephalitis Chumakov FSC RD IBP RAS (Institute of Poliomyelitis). Viruses: yellow fever virus strain 17D and Sindbis virus strain K1487 (GenBank AC № PZ244961.1). Virus quantification was performed using the plaque assay on Vero cell culture and real-time PCR. Results. In this study, we investigated the effect of ruxolitinib (a JAK1/2 kinase inhibitor) on the replicative activity of certain oncolytic flaviviruses (YFV 17D) and alphaviruses (SINV K1487) in virus-resistant human pancreatic adenocarcinoma cell lines AsPC-1, BxPC-3, and Capan-2. A significant dose-dependent increase in infectious titers (by 2–3 orders of magnitude) of YFV 17D and SINV K1487 was demonstrated in the studied cultures in the presence of various concentrations of ruxolitinib (0.1 μM, 0.5 μM, 1.0 μM, and 5.0 μM). Conclusion. Enhanced replication of oncolytic flaviviruses and alphaviruses in the presence of ruxolitinib could significantly improve the efficacy of therapy for resistant and highly immunosuppressive pancreatic cancer. This combined virotherapy approach can activate powerful immunomediated cell death mechanisms even without an overt cytopathic effect in culture.

Introduction. There are three antigenic subtypes of tick-borne encephalitis virus (TBEV): the European, Far Eastern and Siberian subtypes. The article discusses the topic of cross-protective neutralizing antibodies against different subtypes of TBEV. Objective ‒ the study of the immune response after vaccination against TBE in recipients immunized with Russian-made vaccines in relation to Siberian, Far Eastern, and European subtypes. Materials and methods. 100 serum samples obtained from recipients vaccinated against TBE. ELISA reagent kit was used to detect IgG antibodies to TBEV. The neutralization reaction on cell culture was used to analyze the titer of neutralizing antibodies. The following TBEV strains were used: Sofyin; Vasilchenko; Absettarov; Ekb_1887_1. Results. A decrease in the levels of neutralizing antibodies against heterologous strains compared to the vaccine strain was observed: for the Siberian strains Ekb_1887_1 and the Vasilchenko, a decrease was of 3.9 and 2.4 times, respectively; for the European strain, a 4.9-fold decrease compared to vaccine strain was observed. In case when IgG antibody titers were below 1 : 500, the titers of antibodies to TBEV strains heterologous to the vaccine did not exceed the minimum detectable value of 1 : 10. For individuals with IgG antibody titers below 1 : 100, antibodies to Sofyin strain were not detected. Individuals with reduced titers of virus-specific antibodies more often had deviations from the recommended vaccination schedule. Conclusion. Given the widespread distribution and genetic variability of the Siberian subtype, as well as the limited cross-neutralization capabilities of existing vaccines, the task of developing a combined vaccine that includes antigens of several virus subtypes seems relevant.