Melatonin Derivative-Conjugated Formulations of Pd(II) and Pt(II) Thiazoline Complexes on Mesoporous Silica to Enhance Cytotoxicity and Apoptosis against HeLa Cells

The search for alternatives to cisplatin has led to the development of new metal complexes where thiazoline derivatives based on platinum(II) and palladium(II) stand out. In this sense, the Pt(II) and Pd(II) complexes coordinated with the thiazoline derivative ligand 2-(3,4-dichlorophenyl)imino-N-(2-thiazolin-2-yl)thiazolidine (TdTn), with formula [PtCl2(TdTn)] and [PdCl2(TdTn)], have previously shown good results against several cancer lines; however, in this work, we have managed to improve their activity by supporting them on mesoporous silica nanoparticles (MSN). The incorporation of metal compounds with a melatonin derivative (5-methoxytryptamine, 5MT), which is a well-known antioxidant and apoptosis inducer in different types of cancer, has been able to increase the cytotoxic activity of both MSN-supported and isolated complexes with only a very low amount (0.35% w/w) of this antioxidant. The covalently functionalized systems that have been synthesized are able to increase selectivity as well as accumulation in HeLa cells. The final materials containing the metal complexes and 5MT (MSN-5MT-PtTdTn and MSN-5MT-PdTdTn) required up to nine times less metal to achieve the same cytotoxic activity than their corresponding non-formulated counterparts did, thus reducing the potential side effects caused by the use of the free metal complexes.

Influence of ligand lipophilicity in Pt(II) complexes on their antiproliferative and apoptotic activities in tumour cell lines

One of the most widely used strategies for drug development is the coordination of bioactive ligands to transition metals, which could improve biological activity. Moreover, the incorporation of aromatic groups to ligands may allow an enhanced lipophilicity that can influence the cellular uptake and accumulation of the metallodrugs, thus increasing their activity. Herein, we have reported the synthesis and characterization of four Pt(II) complexes [PtCl₂(L)], where L = 2-(1-pyrazolyl)-2-thiazoline (PzTn), 2-(1-pyrazolyl)-1,3-thiazine (PzTz), 2-(3,5-diphenyl-1-pyrazolyl)-2-thiazoline (DPhPzTn) or 2-(3,5-diphenyl-1-pyrazolyl)-1,3-thiazine (DPhPzTz). The study was aimed at analysing their potential anticarcinogenic ability in epithelial cervix carcinoma HeLa, human promyelocytic leukemia HL-60 and human histiocytic lymphoma U-937 tumour cell lines as well as checking whether the structural factors of the organic ligand may influence their biological activity. Our findings showed that PtDPhPzTn and PtDPhPzTz were far more effective in terms of cytotoxicity than their less lipophilic counterparts (PtPzTn and PtPzTz), especially in cells derived from solid cervical tumours, thereby suggesting that modulating the lipophilicity of the ligands can help improve the cytotoxic effect of the metal complexes.

Synthesis and structure of a new thiazoline-based palladium(II) complex that promotes cytotoxicity and apoptosis of human promyelocytic leukemia HL-60 cells

Cisplatin is one of the most widely used chemotherapeutic agents in the treatment of different tumors but has high toxicity and side effects. Therefore, the synthesis of new chemotherapeutic agents is necessary, so that they are effective in the treatment of cancer while avoiding such toxicity. In this study, we have synthesized and characterized a palladium(II) complex, [PdCl2(µ-PyTT)2]Cl2·4H2O (PdPyTT), with 2-(2-pyridyl)imine-N-(2-thiazolin-2-yl)thiazolidine (PyTT) as a ligand; besides, its cytotoxicity and pro-apoptotic capacity was tested in human promyelocytic leukemia HL-60 cell line. Similar to cisplatin, PdPyTT produced a time- and dose-dependent decrease in cell viability. Additionally, the palladium complex increased both the proportion of cells with apoptotic morphology and the activation of caspase-3 and -9. PdPyTT, like cisplatin, also increased intracellular ROS production and DNA oxidative damage. Therefore, our findings demonstrated the promising application of palladium(II) complexes as novel anti-leukemic agents.