FOLFOXIRI chemotherapy is a first-line therapy for advanced or metastatic colorectal cancer (CRC), yet its therapeutic efficacy remains limited. Immunostimulatory therapies like oncolytic viruses can complement chemotherapies by fostering the infiltration of the tumor by immune cells and enhancing drug cytotoxicity. In this study, we explored the effect of combining the FOLFOXIRI chemotherapeutic agents with the oncolytic coxsackievirus B3 (CVB3) PD-H in the CRC cell line Colo320. Additionally, we examined the impact of the drugs on the expression of microRNAs (miRs), which could be used to increase the safety of oncolytic CVB3 containing corresponding miR target sites (miR-TS). The measurement of cytotoxic activity using the Chou–Talalay combination index approach revealed that PD-H synergistically enhanced the cytotoxic activity of oxaliplatin (OX), 5-fluorouracil (5-FU) and SN-38. PD-H replication was not affected by OX and SN-38 but inhibited by high concentrations of 5-FU. MiR expression levels were not or only slightly elevated by the drugs or with drug/PD-H combinations on Colo320 cells. Moreover, the drug treatment did not increase the mutation rate of the miR-TS inserted into the PD-H genome. The results demonstrate that the combination of FOLFOXIRI drugs and PD-H may be a promising approach to enhance the therapeutic effect of FOLFOXIRI therapy in CRC.

Pancreatic ductal adenocarcinoma (PDAC) is a highly aggressive cancer characterized by a dense desmoplastic stroma and a highly immunosuppressive tumor microenvironment (TME). The focal adhesion kinase (FAK), a non-receptor tyrosine kinase, is considered a critical regulator of various cellular processes involved in cancer development. FAK inhibitors (FAKi) have proven to be promising therapeutics for cancer treatment including for pancreatic cancer. As monotherapy, however, FAKi showed only a modest effect in clinical studies. In this study, we investigated the cytotoxicity of six FAKi (Defactinib, CEP-37440, VS-4718, VS-6062, Ifebemtinib and GSK2256098) used in clinical trials on five pancreatic tumor cell lines. We further examined whether their anti-tumor activity can be enhanced by combination with the oncolytic coxsackievirus B3 (CVB3) strain PD-H. IC₅₀ analyses identified Defactinib and CEP-37440 as the most potent inhibitors of tumor cell growth. VS-4718, VS-6062, and Ifebemtinib showed slightly lower activity, while GSK2256098 was largely ineffective. The combination of Defactinib, CEP-37440, VS-4718, and VS-6062 with PD-H resulted in varying effects on cytotoxicity, depending on the cell line and the specific FAKi, ranging from no enhancement to a pronounced increase. Using the Chou–Talalay method, we determined combination indices (CI), revealing synergistic, additive, but also antagonistic interactions between the respective FAKi and PD-H. Considering both oncolytic efficacy and the CI, the greatest enhancement in oncolytic activity was achieved when VS-4718 or CEP-37440 was combined with PD-H. These findings indicate that co-treatment with PD-H can potentiate the therapeutic activity of the selected FAKi and may represent a novel strategy to improve treatment outcomes in PDAC.

Recently, we demonstrated that the oncolytic Coxsackievirus B3 (CVB3) strain PD-H can be efficiently adapted to resistant colorectal cancer cells through dose-dependent passaging in colorectal cancer cells. However, the method is time-consuming, which limits its clinical applicability. Here, we investigated whether the manufacturing time of the adapted virus can be reduced by replacing the dose-based passaging with volume-based passaging. For this purpose, the murine colorectal carcinoma cell line MC38, resistant to PD-H-induced lysis, was initially infected with PD-H at 0.1 multiplicity of infection (MOI). For subsequent passages, 15–30 µL of a 1:10 dilution of the cell culture supernatant was transferred to fresh MC38 cells early after virus-induced cell lysis became visible. By virus passage 10, complete cell lysis of MC38 cells was achieved. Sequencing of the passage 10 virus (P-10) revealed two nucleotide substitutions in the 5′ UTR and six amino acid changes in the viral polyprotein compared to the PD-H founder. P-10, however, consisted of a heterogeneous virus population. Therefore, the detected mutations were introduced into the cDNA of PD-H, from which the recombinant virus PD-MC38 was generated. PD-MC38 exhibited significantly enhanced replication and lytic activity in MC38 cells compared to PD-H, whereas its oncolytic activity in other colorectal cancer cell lines was comparable to or even lower than that of PD-H. These findings demonstrate that volume-based passaging is suitable to generate tumor cell-specific adapted PD-H. Moreover, compared to the dose-dependent passaging, volume-based passaging significantly reduced the time required to generate the adapted virus.