Insights into the mevalonate pathway in the anticancer effect of a platinum complex on human gastric cancer cells

Synthesis and Antitumor Activity of a GSH Inert Bisphosphonate Platinum (II) Complex

Osteosarcoma is a highly aggressive neoplasm. Traditional platinum chemotherapeutic agents for osteosarcoma inevitably have acquired drug resistance and serious side effects, which have limited their utility. To slow down the reaction of platinum drugs with glutathione (GSH) is a strategy to overcome the resistance of platinum chemotherapeutic agents. Herein, the unique design of a GSH inert bisphosphonate platinum complex cis-{di(amino)platinum[tetraethyl 2,2-bis(2-pyridinylmethyl)methylidene-1,1-bisphosphonate]} (DBPP) is reported. MTT assay demonstrates that DBPP showed moderate inhibition towards human osteosarcoma cell line U2OS cells. The cytostatic action of DBPP is related to conformational conversion from B-DNA to A-DNA and the unwinding of pUC19 DNA. DBPP could also destroy the tertiary structure of human serum albumin (HSA). Notably, 31P NMR and 1H NMR indicate that DBPP can hardly chelate with GSH, which could overcome the GSH-induced side effects. We envision that this unique design of the platinum complex would open up new ways to overcome GSH-induced resistance.

PT-112 Induces Mitochondrial Stress and Immunogenic Cell Death, Targeting Tumor Cells with Mitochondrial Deficiencies

Simple Summary

PT-112 is a novel pyrophosphate–platinum conjugate under Phase 1/2 clinical development for the treatment of several tumor types. In this study, using mouse tumor cells with well-characterized mitochondrial and metabolic status, we investigated the mechanisms underlying PT-112’s cancer cell death effects. Our results showed that cells with defective mitochondria were more sensitive to PT-112 when compared to cells with normal mitochondrial function. Moreover, PT-112 induced tumor cell death in those sensitive cells through non-conventional mechanisms, including increased mitochondrial stress, free radical generation and immunogenic cell death, a form of cell death that elicits an immune response. Taken together, the present findings suggest the potential for predictors of PT-112 sensitivity in the clinical setting on the basis of metabolic function.

Abstract

PT-112 is a novel pyrophosphate–platinum conjugate, with clinical activity reported in advanced pretreated solid tumors. While PT-112 has been shown to induce robust immunogenic cell death (ICD) in vivo but only minimally bind DNA, the molecular mechanism underlying PT-112 target disruption in cancer cells is still under elucidation. The murine L929 in vitro system was used to test whether differential metabolic status alters PT-112’s effects, including cell cytotoxicity. The results showed that tumor cells presenting mutations in mitochondrial DNA (mtDNA) (L929dt and L929^dt cybrid cells) and reliant on glycolysis for survival were more sensitive to cell death induced by PT-112 compared to the parental and cybrid cells with an intact oxidative phosphorylation (OXPHOS) pathway (L929 and dt^L929 cybrid cells). The type of cell death induced by PT-112 did not follow the classical apoptotic pathway: the general caspase inhibitor Z-VAD-fmk did not inhibit PT-112-induced cell death, alone or in combination with the necroptosis inhibitor necrostatin-1. Interestingly, PT-112 initiated autophagy in all cell lines, though this process was not complete. Autophagy is known to be associated with an integrated stress response in cancer cells and with subsequent ICD. PT-112 also induced a massive accumulation of mitochondrial reactive oxygen species, as well as changes in mitochondrial polarization—only in the sensitive cells harboring mitochondrial dysfunction—along with calreticulin cell-surface exposure consistent with ICD. PT-112 substantially reduced the amount of mitochondrial CoQ10 in L929 cells, while the basal CoQ10 levels were below our detection limits in L929dt cells, suggesting a potential relationship between a low basal level of CoQ10 and PT-112 sensitivity. Finally, the expression of HIF-1α was much higher in cells sensitive to PT-112 compared to cells with an intact OXPHOS pathway, suggesting potential clinical applications.

Enzymes in the Cholesterol Synthesis Pathway: Interactomics in the Cancer Context

A global protein interactome ensures the maintenance of regulatory, signaling and structural processes in cells, but at the same time, aberrations in the repertoire of protein-protein interactions usually cause a disease onset. Many metabolic enzymes catalyze multistage transformation of cholesterol precursors in the cholesterol biosynthesis pathway. Cancer-associated deregulation of these enzymes through various molecular mechanisms results in pathological cholesterol accumulation (its precursors) which can be disease risk factors. This work is aimed at systematization and bioinformatic analysis of the available interactomics data on seventeen enzymes in the cholesterol pathway, encoded by HMGCR, MVK, PMVK, MVD, FDPS, FDFT1, SQLE, LSS, DHCR24, CYP51A1, TM7SF2, MSMO1, NSDHL, HSD17B7, EBP, SC5D, DHCR7 genes. The spectrum of 165 unique and 21 common protein partners that physically interact with target enzymes was selected from several interatomic resources. Among them there were 47 modifying proteins from different protein kinases/phosphatases and ubiquitin-protein ligases/deubiquitinases families. A literature search, enrichment and gene co-expression analysis showed that about a quarter of the identified protein partners was associated with cancer hallmarks and over-represented in cancer pathways. Our results allow to update the current fundamental view on protein-protein interactions and regulatory aspects of the cholesterol synthesis enzymes and annotate of their sub-interactomes in term of possible involvement in cancers that will contribute to prioritization of protein targets for future drug development.

Radiopharmacological evaluation of a caspase-3 responsive probe with optimized pharmacokinetics for PET imaging of tumor apoptosis

Early evaluation of the therapy efficiency can promote the development of anti-tumor drugs and optimization of the treatment method. Caspase-3 is a key biomarker for early apoptosis. Detection of caspase-3 activity is essential for quick assessment of the curative effect. We have reported a PET probe that could image drug-induced tumor apoptosis in vivo. However, high liver uptake limits its application. In order to optimize the pharmacokinetics of the previous probe, we introduced a hydrophilic peptide sequence to minimize liver uptake. The structure of the new probe was confirmed by mass spectrometry and nuclear magnetic resonance. This probe was able to cross the cell membrane freely and could be converted into a dimer through the condensation reaction of 2-cyano-6-aminobenzothiazole (CBT) and cysteine in response to intracellular activated caspase-3 and glutathione (GSH). The hydrophobic dimers further self-assembled into nanoparticles, which could enhance the probe aggregation in apoptotic tumor tissues. In vivo experiments showed that the tumor uptake of the new probe was higher than that of the previous probe, while the liver uptake of the new probe was significantly reduced. The new probe might be promising in imaging apoptotic tumors with suitable pharmacokinetics.

Proteomic profiling of MIN6 cell-derived exosomes

Exosomes have been widely used in research on the early clinical diagnosis, prognosis and treatment of various cancers due to their features of small size (30-120 nm), non-immunogenicity and ability to cross biological barriers. However, few studies have investigated exosomes involved in metabolic diseases. Early studies have found that adipose tissue can be a source of exosomes regulating metabolism, but the related functions of exosomes secreted by other tissues in the regulation of metabolic diseases have not been determined. In addition, islets were found to be able to secrete miRNA via exosomes, suggesting that islet exosomes may be among the sources of exosomes involved in the regulation of metabolic diseases and that the relevant protein profiles have not been characterized to date. Therefore, identifying the protein contents of pancreatic β cell-derived exosomes would benefit further research investigating the protein functions and mechanisms associated with diabetes-related metabolic diseases. SIGNIFICANCE: Exosomes are emerging tools for investigating metabolic diseases in recent years, but little research has been done. In our work, functional identification of MIN6 cell-derived exosomal proteins and comparative analysis of islet β cell exosomal protein data from different cell lines or from different species revealed that exosomes secreted by islet β cells may be involved in the regulation of glucose metabolism. These results may suggest that intercellular communication induced by exosome transfer among tissues may account for the major reason of diabetic metabolic disorder. In addition, these results may provide a theoretical basis for the study of the physiological and pathological functions of islet β cell exosomes for the future studies.

Toward Multi-Targeted Platinum and Ruthenium Drugs-A New Paradigm in Cancer Drug Treatment Regimens?

While medicinal inorganic chemistry has been practised for over 5000 years, it was not until the late 1800s when Alfred Werner published his ground-breaking research on coordination chemistry that we began to truly understand the nature of the coordination bond and the structures and stereochemistries of metal complexes. We can now readily manipulate and fine-tune their properties. This had led to a multitude of complexes with wide-ranging biomedical applications. This review will focus on the use and potential of metal complexes as important therapeutic agents for the treatment of cancer. With major advances in technologies and a deeper understanding of the human genome, we are now in a strong position to more fully understand carcinogenesis at a molecular level. We can now also rationally design and develop drug molecules that can either selectively enhance or disrupt key biological processes and, in doing so, optimize their therapeutic potential. This has heralded a new era in drug design in which we are moving from a single- toward a multitargeted approach. This approach lies at the very heart of medicinal inorganic chemistry. In this review, we have endeavored to showcase how a "multitargeted" approach to drug design has led to new families of metallodrugs which may not only reduce systemic toxicities associated with modern day chemotherapeutics but also address resistance issues that are plaguing many chemotherapeutic regimens. We have focused our attention on metallodrugs incorporating platinum and ruthenium ions given that complexes containing these metal ions are already in clinical use or have advanced to clinical trials as anticancer agents. The "multitargeted" complexes described herein not only target DNA but also contain either vectors to enable them to target cancer cells selectively and/or moieties that target enzymes, peptides, and intracellular proteins. Multitargeted complexes which have been designed to target the mitochondria or complexes inspired by natural product activity are also described. A summary of advances in this field over the past decade or so will be provided.

A Potential Bone-Targeting Hypotoxic Platinum(II) Complex with an Unusual Cytostatic Mechanism toward Osteosarcoma Cells

Osteosarcoma (OS) is the most common primary pediatric bone tumor lethal to children and adolescents. Chemotherapeutic agents such as cisplatin are not effective for OS because of their poor accessibility to this cancer and severe systemic toxicity. In this study, a lipophilic platinum(II) complex bearing a bisphosphonate bone-targeting moiety, cis-[PtL(NH₃)₂Cl]NO₃ {BPP; L = tetraethyl [2-(pyridin-2-yl)ethane-1,1-diyl]bisphosphonate}, was prepared and characterized by NMR, electrospray ionization mass spectrometry, and single-crystal X-ray crystallography. The cytotoxicity of BPP toward OS cell lines U2OS and MG-63 was tested by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. BPP exhibits moderate inhibition against U2OS cells through a mechanism involving both DNA binding and a mevalonate pathway. The acute toxicity of BPP to mice is 7-fold lower than that of cisplatin. The relative low systemic toxicity may result from the steric hindrance of the ligand, which blocks BPP approaching the bases of DNA. The results suggest that incorporating bisphosphonates into a platinum complex not only enhances its bone-targeting property but also minimizes its reactivity toward DNA and thereby lowers the systematic toxicity of the complex. The diminished cytotoxicity of BPP could be compensated for by increasing the therapeutic dose with marginal harm. This strategy provides a new possibility for overcoming the ineffectiveness and systemic toxicity of platinum drugs in the treatment of OS.