Preparation And Antitumor Activity Of Polyoxometalate-based Lipid Compounds

In recent years, the development of cancer treatment with high accuracy and efficacy shows significant importance due to the increasing incidence of malignant tumors. Polyoxometalates(POMs) as a promising chemotherapeutic drug candidate with remarkable antitumor and antiviral activities are drawing special attention from researchers owing to their tunability in chemical structures and physicochemical properties. However, the application of POMs in medical study are far less than that of cisplatin or other drugs, which could be attributed to the following issues: Inorganic POMs exhibit lower bioactivity than small molecular organic drugs; POMs with high negative surface charge are difficult to penetrate into cells, and could easily interact with plasma proteins to generate toxic side effects; Some POMs are instable under physiological conditions to exhibit poor antitumor bioactivity. Therefore, the stability under physiological conditions and antitumor bioactivity of POMs are required to be improved to achieve enhanced bioactivity and decreased cytotoxicity for their clinical application. Moreover, research on pharmacokinetics and mechanism of the interaction between POMs and biomembranes still lacks novel theoretical supports.Herein, we reported synthesis of organic-inorganic amphiphilic compounds based on three types of POMs(Keggin, Dawson and Preyssler) through covalent derivatization with a novel long-chain organoalkoxysilane lipid. The POM-based lipid compounds could self-assemble into vesicles, and the interaction between the POM drugs and supported bilayer lipid membranes(s-BLM) was evaluated by surface plasmon resonance imaging(SPRi) to explain the transmembrane process of POM drugs. Thereafter, the antitumor activities and cytological behaviors of POMs and the POM-based lipid compounds were assessed in vitro to investigate the antitumor efficacy of POM drugs on different tumor cell lines. The results could boost the exploration of antitumor mechanism and potential clinical application of the novel POM drugs. The research contents in detail are listed as follows.Firstly, the organic-inorganic amphiphilic compounds and their cation-exchanged products were successfully synthesized by conjugating long-chain organoalkoxysilane lipids to lacunary Keggin, Dawson and Preyssler-type POMs. The obtained compounds were thoroughly characterized by infrared spectroscopy(IR), 31 P nuclear magnetic resonance spectroscopy(NMR) and mass spectroscopy. And then dynamic light scattering(DLS) measurement and transmission electron microscope(TEM) results indicated that three Na-type compounds exhibited amphiphilic nature and spontaneously organized into stable vesicles in an aqueous medium with diameters of 79.8?12.4 nm, 162.2?30.2 nm, 113.3?31.6 nm, respectively.Using s-BLM as a mimic of natural membrane, the association and dissociation processes between Keggin, Dawson and Preyssler-type POM-based lipid compounds and biomembranes were investigated by SPRi. The results showed that the interactions between pure Keggin, Dawson, Preyssler-type POMs and s-BLM were reversible, and there were no stable complexes generated between POMs and s-BLM. Preyssler-type POMs were more easily to bind to s-BLM. In the contrary, the irreversible interaction between POM-based lipid compound vesicles and s-BLM would disturb the phospholipid bilayer when the vesicles bound to the hydrophilic heads of the phospholipids, prompting POM vesicles overturn into the interior region of lipid bilayer to eventually form stable complexes. The stability of POM/lipid complexes was related to the surface charge density of POMs, which also affected the binding equilibrium constants of POMs to s-BLM. The affinity between POMs and s-BLM was strengthened when surface charge density increased.The antitumor activity and cytotoxicity of Keggin, Dawson and Preyssler-type POMs and POM-based lipid compound vesicles were assessed by MTT assay. The results indicated that Na-P2W17-Lipid vesicles and P2W18 showed more efficient antitumor activity against He La cells, while Na-P5W29-Lipid vesicles and P5W30 exhibited time-/ concentration-dependent higher inhibition activity on HT29 cells. POM-based organic-inorganic lipid compound vesicles showed rapid endocytosis and higher inhibition rate when shortly incubated with cancer cells, and the higher antitumor activity compared to pure POMs declined when the incubation time increased. Meanwhile, Preyssler-type POMs and POM-based lipid compound vesicles exhibited little cytotoxicity on normal cell line HUVEc. Na-P5W29-Lipid vesicles showed efficient cellular uptake on HT29 cancer cells via rapid endocytosis through the membranes, and located in the cytoplasm. They could make HT29 cells nucleus crenulated in short incubation times and eventually apoptosis. Furthermore, modified POM-based lipid compound vesicles exhibited higher capabilities to induce membrane destruction and apoptosis of cancer cells, indicating that the amphiphilic POM compound vesicles can improve the cellular uptake to generate improved antitumor activity.Our study provides theoretical and experimental bases for the development and application of POM drugs, with potential impact on the future exploration about the antitumor mechanism of POM drugs.