Design, Synthesis, and Evaluation of Novel Adenine-Based Hydrazones as Potential Anticancer Agents: Cytotoxicity Against A549 and MRC-5 Cell Lines with In Silico Insights

Background/Objectives: Lung cancer remains a leading cause of global cancer-related mortality, necessitating the development of new therapeutic candidates. In this study, we aimed to design, synthesize, and biologically evaluate novel adenine-based hydrazone derivatives as potential anticancer candidates. Methods: A series of novel adenine–hydrazones were synthesized via the condensation of 2-(6-amino-9H-purin-9-yl)acetohydrazide with various aldehydes and isatin derivatives. Their antiproliferative activities against human lung adenocarcinoma (A549) and normal lung fibroblast (MRC-5) cell lines were evaluated using the MTT assay. Mechanistic investigations—including cell membrane damage (LDH release), oxidative stress (TOS, iROS), mitochondrial membrane potential (MMP, ΔΨm), cell cycle distribution, and apoptosis (Annexin V/PI)—were conducted for the lead derivatives, complemented by multi-target in silico molecular docking against PLK1, TrxR1, and MDM2. Results: Compounds 3d, 3c, and 4j showed the strongest antiproliferative activity within the synthesized series against A549 cells, with IC50 values of 37.2 ± 1.8 µM, 41.8 ± 1.9 µM, and 42.9 ± 1.7 µM, respectively, together with comparatively more favorable A549/MRC-5 activity profiles than several other derivatives. These compounds induced oxidative stress-associated cellular injury, accompanied by mitochondrial depolarization, G2/M phase accumulation, and Annexin V-confirmed apoptotic cell death. Complementary multi-target in silico molecular docking provided theoretical insights into potential binding interactions with PLK1, TrxR1, and MDM2. Conclusions: Adenine–hydrazone hybrids, particularly 5-halogenated isatin derivatives such as compound 3d, provide preliminary lead scaffolds with moderate in vitro cytotoxicity against lung cancer cells, serving as a platform for future structural optimization to enhance potency and selectivity.