Evaluation of Newly Synthesized Schiff Base Pd(II) Complexes for Prostate Cancer Treatment through In Vitro Cytotoxicity and Molecular Mechanistic Studies

Damnjan Pantic^1,2Nikola Mirkovic^1,3Tatjana Vulovic^1,4*Danijela Jovanovic^1,4*Stefan Jakovljević^1,5Petar Canovic⁶Milan Zaric⁶Radica Zivkovic Zaric^7,8Marina Kostic⁹Jovana Dragojevic¹⁰Vera Divac¹⁰Ziko Milanovic⁹Kristina Milisavljevic⁹Marina Mitrovic⁶Ivanka Zelen⁶

• ¹Department of Surgery, Faculty of Medical Sciences, University of Kragujevac, Univerzitet u Kragujevcu, Kragujevac, Serbia
• ²Department of Urology, Clinic of Urology and Nephrology, University Clinical Center Kragujevac, Klinicki centar Kragujevac, Kragujevac, Serbia
• ³Department of Vascular Surgery Center, University Clinical Center Kragujevac, Klinicki centar Kragujevac, Kragujevac, Serbia
• ⁴Department of Anesthesia and Resuscitation, University Clinical Center Kragujevac, Klinicki centar Kragujevac, Kragujevac, Serbia
• ⁵Department of General Surgery, University Clinical Center Kragujevac, Klinicki centar Kragujevac, Kragujevac, Serbia
• ⁶Department of Biochemistry, Faculty of Medical Sciences, University of Kragujevac, Univerzitet u Kragujevcu, Kragujevac, Serbia
• ⁷Department of Pharmacology and Toxicology, Faculty of Medical Sciences, University of Kragujevac, Univerzitet u Kragujevcu, Kragujevac, Serbia
• ⁸Department of Clinical Pharmacology, University Clinical Center Kragujevac, Klinicki centar Kragujevac, Kragujevac, Serbia
• ⁹Department of Science, Institute for Information Technologies, University of Kragujevac, Univerzitet u Kragujevcu, Kragujevac, Serbia
• ¹⁰Department of Chemistry, Faculty of Sciences, University of Kragujevac, Univerzitet u Kragujevcu, Kragujevac, Serbia

Introduction: Palladium(II) complexes are promising anticancer agents with potential advantages over platinum drugs. This study aimed to synthesize and characterize three new Pd(II) complexes (2a-2c) with Schiff base ligands derived from salicylic acid and amine scaffolds, and to evaluate their antitumor activity against prostate cancer cells. Methods: The Pd(II) complexes were synthesized and structurally characterized. Cytotoxicity was tested on two human prostate cancer cell lines (PC-3, DU-145) and healthy fibroblasts (MRC-5). Apoptosis induction was assessed by flow cytometry, with a focus on Bcl-2 and caspase proteins. Molecular docking was used to examine binding to the androgen receptor (AR) and apoptotic regulators (CASP3, BCL2, BAX). DNA and human serum albumin (HSA) binding were also investigated. Results: All complexes showed significant cytotoxicity. Notably, complex 2c exhibited more potent cytotoxic activity than cisplatin in prostate cancer cell lines, with lower IC50 values after 72 h exposure in DU-145 (7.1 µM vs. 8.2 µM) and PC-3 cells (8.6 µM vs. 21.9 µM), while showing reduced toxicity in normal MRC-5 cells (42.3 µM vs. 24.4 µM). Apoptosis was confirmed as the primary cytotoxic mechanism, involving the activation of Bcl-2 and caspases. Docking studies revealed that complex 2c had the strongest binding affinity to AR and apoptotic proteins, mediated by hydrogen bonds, π-π stacking, and hydrophobic interactions. DNA and HSA binding supported their biological relevance. Conclusions: Complex 2c exhibits potent anticancer activity through the induction of apoptosis and dual targeting of the AR and apoptotic pathways, making it a promising candidate for further development of anticancer drugs.