Novel Indole-Based Sulfonylhydrazones as Potential Anti-Breast Cancer Agents: Synthesis, In Vitro Evaluation, ADME, and QSAR Studies

Background: Breast cancer continues to pose a significant global health challenge despite advances in early detection and targeted therapies. The development of novel chemotherapeutic agents remains crucial, particularly those with selective cytotoxicity toward specific breast cancer subtypes. Methods: A series of ten hybrid indolyl-methylidene phenylsulfonylhydrazones and one bis-indole derivative were designed, synthesized, and structurally characterized using NMR and high-resolution mass spectrometry (HRMS). Prior to synthesis, in silico screening was performed to assess drug likeness and ADME-related properties. Single-crystal X-ray diffraction was conducted for compound 3e. The cytotoxic potential of the synthesized compounds was evaluated using the MTT assay against MCF-7 (ER-α⁺) and MDA-MB-231 (triple-negative) breast cancer cell lines. Additionally, quantitative structure–activity relationship (QSAR) analysis was conducted to identify key structural features contributing to activity. Results: Most compounds exhibited selective cytotoxicity against MCF-7 cells. Notably, compound 3b demonstrated the highest potency with an IC50 of 4.0 μM and a selectivity index (SI) of 20.975. Compound 3f showed strong activity against MDA-MB-231 cells (IC50 = 4.7 μM). QSAR analysis revealed that the presence of a non-substituted phenyl ring and specific indolyl substituents (5-methoxy, 1-acetyl, 5-chloro) significantly contributed to enhanced cytotoxic activity and ligand efficiency. Conclusion: The synthesized phenylsulfonylhydrazone hybrids exhibit promising and selective cytotoxicity, particularly against ER-α⁺ breast cancer cells. Structural insights from QSAR analysis provide a valuable foundation for the further optimization of this scaffold as a potential source of selective anticancer agents.