Phytochemical Diversity and Multi-Endpoint In Vitro Biological Evaluation of Sisymbrium irio L.: Chemical Radical-Scavenging, Antibacterial, α-Amylase-/α-Glucosidase-Inhibitory, Cytotoxic, and Apoptosis-Associated Activities

Sisymbrium irio L. (Brassicaceae) is an indigenous wild edible plant widely distributed in Saudi Arabia and the Mediterranean region and traditionally used in Unani and folk medicine to treat respiratory, digestive, and inflammatory ailments. However, its phytochemical diversity and organ-specific pharmacological potential remain insufficiently characterized. This study evaluated the phytochemical constituents; total phenolic and flavonoid contents; and in vitro antioxidant, antibacterial, cytotoxic/antiproliferative, apoptosis-associated and in vitro α-amylase- and α-glucosidase-inhibitory activities of methanolic leaf and stem extracts (SILEs and SISEs, respectively). GC–MS profiling putatively identified 82 compounds in SILE and 85 in SISE, revealing distinct organ-specific profiles. SISE showed higher FCRC and TFC (88.12 ± 1.15 and 45.18 ± 1.28 mg/g, respectively) and greater DPPH and ABTS+ radical-scavenging capacities. In contrast, SILE exhibited greater antibacterial activity, particularly against Staphylococcus aureus and Enterococcus faecalis, with MIC values as low as 6.25 µg/mL. Both extracts showed in vitro concentration-dependent cytotoxic/antiproliferative activity against MCF-7 and HepG2 cells, accompanied by changes in the expression of apoptosis-associated genes. These findings indicate apoptosis-associated transcriptional responses but do not establish functional apoptosis or tumor-selective/anticancer activity. SILE exhibited moderate in vitro α-amylase- and α-glucosidase-inhibitory activity (IC50 = 26.25 µg/mL (95% CI: 18.53–37.19 µg/mL) and 53.94 µg/mL (95% CI: 47.05–61.83 µg/mL), respectively). Overall, this study provides the first integrated comparison of SILE and SISE across multiple in vitro bioactivities, highlighting distinct organ-specific pharmacological potential that requires more investigation. These results do not prove therapeutic efficacy and should be viewed as first in vitro screening findings.