Polyoxovanadates as new P-glycoprotein inhibitors: insights into the mechanism of inhibition

Non-Covalent and Covalent Binding of New Mixed-Valence Cage-like Polyoxidovanadate Clusters to Lysozyme

The high-resolution X-ray structures of the model protein lysozyme in the presence of the potential drug [VIVO(acetylacetonato)2] from crystals grown in 1.1 M NaCl, 0.1 M sodium acetate at pH 4.0 reveal the binding to the protein of different and unexpected mixed-valence cage-like polyoxidovanadates (POVs): [V15O36(OH2)]5-, which non-covalently interacts with the lysozyme surface, [V15O33(OH2)]+ and [V20O51(OH2)]n- (this latter based on an unusual {V18O43} cage) which covalently bind the protein. EPR spectroscopy confirms the partial oxidation of VIV to VV and the formation of mixed-valence species. The results indicate that the interaction with proteins can stabilize the structure of unexpected - both for dimension and architecture - POVs, not observed in aqueous solution.

Advances in the structure, mechanism and targeting of chemoresistance-linked ABC transporters

Cancer cells frequently display intrinsic or acquired resistance to chemically diverse anticancer drugs, limiting therapeutic success. Among the main mechanisms of this multidrug resistance is the overexpression of ATP-binding cassette (ABC) transporters that mediate drug efflux, and, specifically, ABCB1, ABCG2 and ABCC1 are known to cause cancer chemoresistance. High-resolution structures, biophysical and in silico studies have led to tremendous progress in understanding the mechanism of drug transport by these ABC transporters, and several promising therapies, including irradiation-based immune and thermal therapies, and nanomedicine have been used to overcome ABC transporter-mediated cancer chemoresistance. In this Review, we highlight the progress achieved in the past 5 years on the three transporters, ABCB1, ABCG2 and ABCC1, that are known to be of clinical importance. We address the molecular basis of their broad substrate specificity gleaned from structural information and discuss novel approaches to block the function of ABC transporters. Furthermore, genetic modification of ABC transporters by CRISPR-Cas9 and approaches to re-engineer amino acid sequences to change the direction of transport from efflux to import are briefly discussed. We suggest that current information regarding the structure, mechanism and regulation of ABC transporters should be used in clinical trials to improve the efficiency of chemotherapeutics for patients with cancer.

In Vitro, Oral Acute, and Repeated 28-Day Oral Dose Toxicity of a Mixed-Valence Polyoxovanadate Cluster

Polyoxovanadates (POV) are a subgroup of polyoxometalates (POM), which are nanosized clusters with reported biological activities. This manuscript describes the first toxicity evaluation of a mixed-valence polyoxovanadate, pentadecavanadate, (Me4N)6[V15O36Cl], abbreviated as V15. Cytotoxicity experiments using peripheral blood mononuclear cells (PBMC), larvae of Artemia salina Leach, and in vivo oral acute and repeated 28-day doses in mice was carried out. The LC50 values in PBMC cells and A. salina were 17.5 ± 5.8 μmol L-1, and 17.9 µg L-1, respectively, which indicates high cytotoxic activity. The toxicity in mice was not observed upon acute exposure in a single dose, however, the V15 repeated 28-day oral administration demonstrated high toxicity using 25 mg/kg, 50 mg/kg and, 300 mg/kg doses. The biochemical and hematological analyses during the 28-day administration of V15 showed significant alteration of the metabolic parameters related to the kidney and liver, suggesting moderate toxicity. The V15 toxicity was attributed to the oxidative stress and lipid peroxidation, once thiobarbituric acid (TBAR) levels significantly increased in both males and females treated with high doses of the POV and also in males treated with a lower dose of the POV. This is the first study reporting a treatment-related mortality in animals acutely administrated with a mixed-valence POV, contrasting with the well-known, less toxic decavanadate. These results document the toxicity of this mixed-valence POV, which may not be suitable for biomedical applications.