Crystal Structure and Anti-Proliferative and Mutagenic Evaluation of the Palladium(II) Complex of Deoxyalliin

Platinum(II) and palladium(II) complexes have been investigated as potential anticancer drugs since the serendipitous discovery of the antineoplastic activities of cisplatin in the 1960s. Skin cancer is considered the most common malignant neoplasm that affects humans, and melanoma is the most lethal type of skin cancer. Surgical excision is the main form of treatment, which also may include radiotherapy, systemic chemotherapy, and immunotherapy. In this work, new insights concerning the structural characterization and in vitro anti-proliferative activity of the palladium(II) complex with the amino acid deoxyalliin (Pd-sac) against a panel of thirteen human tumor cells, with emphasis on skin cancer cell lines, are presented. The composition of the complex was confirmed by elemental analysis as [Pd(C6H10NO2S)2]. The structure of the complex was elucidated for the first time by a single-crystal X-ray diffraction technique. Each deoxyalliin molecule coordinates in a bidentate N,S-mode to palladium(II) in a trans-configuration analogous to the platinum(II) deoxyalliin complex early reported. As the main result, the Pd-sac complex showed a selective anti-proliferative activity against melanoma (UACC-62, TGI = 63.5 µM), while both deoxyalliin and K2PdCl4 were inactive against all cell lines. Moreover, Pd-sac did not affect the proliferation of non-tumorigenic keratinocytes (HaCaT, TGI > 586 µM) and was non-mutagenic in the Ames assay. The results open new perspectives for in vivo studies concerning the application of the Pd-sac complex in the treatment of melanoma.