Novel Adenine–Hydrazone Hybrids Against Human Lung Adenocarcinoma (A549): Design, Synthesis, Cellular Mechanistic Investigation and Molecular Docking Studies

<b>Background/Objectives</b>: Adenine derivatives are promising anticancer scaffolds, but their cellular mechanisms remain unclear. This study aimed to synthesize adenine-hydrazone hybrids and evaluate their cytotoxic effects in human lung adenocarcinoma (A549) cells. <b>Methods</b>: A series of adenine-hydrazone compounds (<b>3a</b>-<b>r</b>) was synthesized and tested for cytotoxicity in A549 and MRC-5 cells. Selected compounds were further analyzed for LDH release, oxidative stress markers, ROS production, mitochondrial membrane potential, cell-cycle distribution, apoptosis, and in silico docking against VEGFR2, ALK5, and EGFR. <b>Results</b>: Compounds with electron-withdrawing or donor-acceptor substituents showed the highest cytotoxicity, while halogenated and methoxy analogs were moderately active. Among the synthesized derivatives, 4F-substituted derivatives (<b>3c</b>) showed more activity than 2F- and 3F-substituted ones (<b>3a</b> and <b>3b</b>). 4F- and 3Br-substituted derivatives (<b>3f</b>) showed more activity than only 4F-substituted ones (<b>3c</b>). 4-Nitro-substituted derivative (<b>3i</b>) showed more activity than 4F- (<b>3c</b>), 4Cl- (<b>3d</b>) and 4OMe- (<b>3h</b>) derivatives. Trimethoxy-substituted derivative (<b>3l</b>) showed more activity than di- and mono-substituted methoxy derivatives (<b>3g</b>, <b>3h</b>, <b>3j</b> and <b>3k</b>). Among the salicyl aldehydederivatives (<b>3m</b>-<b>r</b>), 4-N(et)₂-substituted derivative (<b>3r</b>) showed more activity than non-substituted (<b>3m</b>), 5Br-(<b>3n</b>), 5Cl-(<b>3o</b>), 5Me (<b>3p</b>) and 3OCH₃ (<b>3q</b>) derivatives. Treatment induced oxidative stress, mitochondrial depolarization, Sub-G1 cell-cycle accumulation, and apoptosis. Docking studies indicated strong binding to VEGFR2 and ALK5, suggesting dual inhibition as a potential mechanism. <b>Conclusions</b>: Adenine-hydrazone derivatives exert substituent-dependent anticancer effects by inducing redox imbalance-associated mitochondrial dysfunction and regulated cell death. These results highlight their potential as lead structures for lung cancer therapy.