A novel PEGylated squid-derived protamine protein in combination with sorafenib effectively inhibits hepatocellular carcinoma growth.

In recent years, combination therapy has gained attention for improving hepatocellular carcinoma (HCC) treatment. However, the anticancer potential of marine-derived proteins combined with sorafenib remains largely unexplored. This study investigates, for the first time, the anticancer effects and mechanisms of Symplectoteuthis oualaniensis protamine (SOP), its PEG-modified form (SOP-PEG), and sorafenib in Hepa1-6 cells. Flow cytometry, Western blotting, and immunohistochemistry were employed to assess their effects on cell proliferation, cycle progression, apoptosis, and PI3K-Akt signaling. The IC₅₀ values of SOP, SOP-PEG, and sorafenib against Hepa1-6 cells were 10.14 μM, 9.23 μM, and 1.85 μM, respectively. Importantly, SOP and SOP-PEG showed no cytotoxicity toward LO2 normal liver cells within 0-10 μM. Combination treatments significantly suppressed Hepa1-6 cell proliferation and induced apoptosis. Notably, SOP-PEG combined with sorafenib led to the highest apoptotic rate (50.1 %), outperforming the SOP plus sorafenib group (43.8 %). The combination also inhibited PI3K-Akt pathway activation, disrupting proliferative and anti-apoptotic signaling. SOP-PEG plus sorafenib demonstrated superior efficacy compared to either agent alone. This study presents a promising therapeutic strategy for HCC by integrating naturally derived proteins with chemotherapy.