Fish waste accounts for almost one-third of the total fish production annually. The main objective of this study was to upcycle fish by-products to produce biodegradable packaging materials. Fish protein concentrate (FPC) was extracted from gilthead seabream by-catch (flesh and skin). FPC (3%) and gelatin (3%) were used to produce film-forming solutions. The films were produced according to the solvent casting method. The produced films were tested as packaging materials via the determination of different film properties. The wettability of the packaging materials was characterized based on the determination of the contact angle. Water vapor permeability was evaluated using the ASTM E96/E96M standardized method. The evaluation of mechanical properties was based on the Young’s modulus, tensile strength, and elongation at break. Color was measured using a CIELab system. The incorporation of FPC into the produced membranes resulted in a reduced contact angle from 108.5° to 90.6°; however, both films were characterized as hydrophobic materials. Films supplemented with FPC had lower tensile strength values compared to pure gelatin films, but higher elongation values without statistically significant differences. The color parameters (L,a,b) indicated that gelatin films and FPC–gelatin films were colorless and transparent (L > 90), an important parameter for food packaging materials. The production of biodegradable packaging materials from FPC and gelatin may effectively reduce petroleum-based plastics under the circular economy model.

Liver cancer ranks among the most prevalent malignancies globally and stands as a leading cause of cancer-related mortality. Numerous isothiazolone derivatives and analogues have been synthesized and investigated for their potential as anticancer agents; however, limited data exist regarding their efficacy against liver cancer. In the present study, two nitrophenyl-isothiazolones, the 5-benzoyl-2-(4-nitrophenyl)isothiazol-3(2H)-one (IsoA) and the 2-(4-nitrophenyl)isothiazol-3(2H)-one (IsoB), were preliminarily investigated for their cytotoxicity against hepatoma human (Huh7) cells as a liver cancer model and Immortalized Human Hepatocytes (IHHs) as a model of non-cancerous hepatocytes. IsoB, derived from IsoA after removal of the benzoyl moiety, demonstrated the highest cytotoxic effect against Huh7 cells with CC₅₀ values of 19.3 μΜ at 24 h, 16.4 μΜ at 48 h, and 16.2 μΜ at 72 h of incubation, respectively. IsoB also exhibited selective toxicity against the liver cancerous Huh7 cells compared to IHH cells, reinforcing its role as a potent and selective anticancer agent. Remarkably, the cytotoxicity of IsoB was higher when compared with the standard chemotherapeutical agent 5-fluorouracil (5-FU), which also failed to exhibit higher toxicity against the liver cancerous cell lines. Moreover, IsoB-treated Huh7 cells presented a noteworthy reduction in mitochondrial membrane potential (ΔΨm) after 48 and 72 h, while mitochondrial superoxide levels showed an increase after 24 h of incubation. The molecular mechanism of the IsoB cytotoxic effect was also investigated using RT-qPCR, revealing an apoptosis-mediated cell death along with tumor suppressor TP53 overexpression and key-oncogene MYCN downregulation.