Design, Synthesis, and Integrated In Silico and In Vitro Evaluation of Chloro-Substituted Salicylaldehyde...

Background: Building on earlier work with methoxy-, dimethoxy-, bromo-, and nitro-substituted salicylaldehyde benzoylhydrazones, we synthesized and evaluated new 4-chloro- and 5-chloro derivatives bearing an additional chlorine substituent on the hydrazide-derived phenyl ring to further explore the impact of halogenation on cytotoxic activity. Methods: Chloro-hydrazones were obtained through a one-step condensation of 4- or 5-chlorosalicylaldehyde with benzhydrazide or 2-, 3-, and 4-chlorobenzhydrazides. Their physicochemical, pharmacokinetic, ADME, lead-likeness, and drug-likeness profiles were evaluated in silico using SwissADME, ACD/Labs v9.10, and MDL QSAR v2.2.0.0.446. The synthesized compounds were structurally characterized by IR, ¹H NMR, ¹³C NMR, and HR ESI-MS, and their cytotoxic activity was subsequently assessed by the MTT assay in selected cancer cell lines. Molecular docking was performed against ABL1 tyrosine kinase (ABL1 TK), a potential molecular target relevant to two of the investigated leukemia cell lines, using GOLD v.5.2.2 (CCDC Ltd., Cambridge, UK). Results: The chloro-substituted salicylaldehyde benzoylhydrazones exhibited pronounced, cell-type-dependent cytotoxicity, with leukemia cells being substantially more sensitive than breast carcinoma cells. Most derivatives showed low- to sub-micromolar IC₅₀ values against SKW-3 human T-cell prolymphocytic leukemia, K-562 human chronic myeloid (myelogenous) leukemia, and BV-173 human BCR::ABL1-positive leukemia cells, with K3 and K4 exhibiting the highest activity in SKW-3 cells (IC₅₀ = 0.5 ± 0.1 µM). K5 showed particularly strong activity against K-562 and BV-173 cells (IC₅₀ = 0.7 ± 0.1 and 0.9 ± 0.1 µM, respectively), compared with 26.9 ± 2.4 and 21.5 ± 3.3 µM for imatinib. HL-60 human acute promyelocytic leukemia cells showed intermediate sensitivity (IC₅₀ = 1.3-13.9 µM), whereas the activity against MCF-7 estrogen receptor-positive and MDA-MB-231 triple-negative breast carcinoma cells was more variable (1.5-32.1 and 4.1-62.5 µM, respectively). The derivatives showed high selectivity toward malignant cells relative to non-malignant CCL-1 non-malignant mouse fibroblasts, with lower-bound SI values frequently exceeding 50 and reaching >200 in SKW-3 cells. Conclusions: The chloro-substituted salicylaldehyde benzoylhydrazones exhibited pronounced and selective cytotoxicity, particularly toward leukemia cell lines, identifying this scaffold as a promising starting point for further anticancer drug-discovery studies.