Dense granule protein 16 (GRA16), an effector protein from Toxoplasma gondii, has been reported to enhance antitumor responses in several malignancies. However, whether GRA16 can enhance the inhibitory effects of standard anticancer drugs across diverse cancer types remains unclear. Gemcitabine, oxaliplatin, and irinotecan continue to play a key role in clinical oncology; however, their efficacy is limited by persistent tumor survival-promoting pathways. In this study, we stably expressed GRA16 in HepG2, PANC-1, and HCT116 cells and evaluated their responses to gemcitabine, oxaliplatin, and irinotecan under 50% inhibitory concentration-normalized dosing conditions. In vector control cells, baseline drug sensitivity was quantified using the CCK-8 assay across 0–64 μM after 48 h of exposure, and 50% inhibitory concentration was determined for each drug and cell line. Time-dependent proliferation assays (0–72 h) demonstrated that GRA16 reduced the basal growth rate and enhanced the growth inhibitory effects of all 3 drugs in all 3 cell models. Representative microscopy images at 48 h were consistent with reduced cell density in GRA16-expressing cultures under each treatment condition. These in vitro data indicate that GRA16 enhances the inhibitory effects of standard chemotherapeutic agents in hepatic, pancreatic, and colorectal cancer cell lines. This study provides a cross-cancer, multi-drug evaluation of GRA16-associated enhancement of drug response and includes, to our knowledge, the first assessment in a pancreatic cancer model. The underlying mechanism may involve pathway modulation, as suggested by previous studies and supported by the pancreatic cancer model although it was not comprehensively examined across all cell lines.

The dense granule protein of Toxoplasma gondii, inhibitor of signal transducer and activator of transcription 1 (IST) is an inhibitor of signal transducer and activator of transcription 1 (STAT1) transcriptional activity that binds to STAT1 and regulates the expression of inflammatory molecules in host cells. A sterile inflammatory liver injury in pathological acute liver failures occurs when excessive innate immune function, such as the massive release of IFN-γ and TNF-α, is activated without infection. In relation to inflammatory liver injury, we hypothesized that Toxoplasma gondii inhibitor of STAT1 transcription (TgIST) can inhibit the inflammatory response induced by activating the STAT1/IRF-1 mechanism in liver inflammation. This study used IFN-γ and TNF-α as inflammatory inducers at the cellular level of murine hepatocytes (Hepa-1c1c7) to determine whether TgIST inhibits the STAT1/IRF-1 axis. In stable cells transfected with TgIST, STAT1 expression decreased with a decrease in interferon regulatory factor (IRF)-1 levels. Furthermore, STAT1 inhibition of TgIST resulted in lower levels of NF-κB and COX2, as well as significantly lower levels of class II transactivator (CIITA), iNOS, and chemokines (CLXCL9/10/11). TgIST also significantly reduced the expression of hepatocyte proapoptotic markers (Caspase3/8/9, P53, and BAX), which are linked to sterile inflammatory liver injury. TgIST also reduced the expression of adhesion (ICAM-1 and VCAM-1) and infiltration markers of programmed death-ligand 1 (PD-L1) induced by hepatocyte and tissue damage. TgIST restored the cell apoptosis induced by IFN-γ/TNF-α stimulation. These results suggest that TgIST can inhibit STAT1-mediated inflammatory and apoptotic responses in hepatocytes stimulated with proinflammatory cytokines.