An albumin-based tumor-targeted oxaliplatin prodrug with distinctly improved anticancer activity in vivo

Recent Advances in the Chemistry of Metal Carbamates

Following a related review dating back to 2003, the present review discusses in detail the various synthetic, structural and reactivity aspects of metal species containing one or more carbamato ligands, representing a large family of compounds across all the periodic table. A preliminary overview is provided on the reactivity of carbon dioxide with amines, and emphasis is given to recent findings concerning applications in various fields.

Stability, Reduction, and Cytotoxicity of Platinum(IV) Anticancer Prodrugs Bearing Carbamate Axial Ligands: Comparison with Their Carboxylate Analogues

Platinum(IV) complexes containing carboxylate and carbamate ligands at the axial position have been reported previously. A better understanding of the similarity and difference between the two types of ligands will provide us with new insights and more choices to design novel Pt(IV) complexes. In this study, we systematically investigated and compared the properties of Pt(IV) complexes bearing the two types of ligands. Ten pairs of unsymmetric Pt(IV) complexes bearing axial carbamate or carboxylate ligands were synthesized and characterized. The stability of these Pt(IV) complexes in a PBS buffer with or without a reducing agent was investigated, and most of these complexes exhibited good stability. Besides, most Pt(IV) prodrugs with carbamate axial ligands were reduced faster than the corresponding ones with carboxylate ligands. Furthermore, the aqueous solubilities and lipophilicities of these Pt(IV) complexes were tested. All the carbamate complexes showed better aqueous solubility and decreased lipophilicity as compared to those of the corresponding carboxylate complexes, due to the increased polarity of carbamate ligands. Biological properties of these complexes were also evaluated. Many carbamate complexes showed cytotoxicity similar to that of the carboxylate complexes, which may derive from the lower cellular accumulation but faster reduction of the former. Our research highlights the differences between the Pt(IV) prodrugs containing carbamate and carboxylate axial ligands and may contribute to the future rational design of Pt-based anticancer prodrugs.

Supramolecular combination chemotherapy: a pH-responsive co-encapsulation drug delivery system

Most cancer chemotherapy regimens rely on the use of two or more chemotherapeutic agents. However, achieving the best possible dosing of the individual drugs can be challenging due to differences in metabolism, uptake, and clearance among other factors. Here we describe a supramolecular strategy for achieving drug delivery in which the loading ratio of two active components is easily defined. Specifically, we report the formation of aggregates comprised of self-assembled amphiphiles between carboxylatopillar[6]arene (CP6A) and an oxaliplatin (OX)-type Pt(iv) prodrug (PtC10). The association constant (K a) for the underlying host-guest interaction at pH 7.4 ((1.16 ± 0.03) × 104 M-1) is an order of magnitude higher than at pH 5.0 ((1.73 ± 0.15) × 103 M-1). A second chemotherapeutic, doxorubicin (DOX), may be encapsulated in the resulting vesicles (PtC10⊂CP6A) to give a supramolecular combination chemotherapeutic system DOX@PtC10⊂CP6A. Drug release studies served to confirm that PtC10 and DOX are released in acidic environments. Support for a synergistic antiproliferative effect relative to PtC10 + DOX came from cellular studies of DOX@PtC10⊂CP6A using the human liver hepatocellular carcinoma (HepG-2) cell line. In vivo studies revealed that DOX@PtC10⊂CP6A is not only able to retard tumor growth efficiently but also reduce drug-related toxic side effects in BALB/c nude mice bearing HepG-2 subcutaneous tumor xenografts. These favorable findings are attributed to the formation of a ternary complex that benefits from an enhanced permeability and retention (EPR) effect in vivo while allowing for the pH-based release of PtC10 and DOX at the tumor site.

Engineering liposomal nanoparticles of cholesterol-tethered amphiphilic Pt(iv) prodrugs with prolonged circulation time in blood

Cisplatin is a platinum-based chemotherapeutic agent widely used in the treatment of various solid tumors. However, a major challenge in the use of cisplatin and in the development of cisplatin derivatives, namely Pt(iv) prodrugs, is their premature reduction in the bloodstream before reaching cancer cells. To circumvent this problem, we designed liposomal nanoparticles coupled with a cholesterol-tethered amphiphilic Pt(iv) prodrug. The addition of cholesterol served to stabilize the formation of the liposome, while selectively incorporating cholesterol as the axial ligand also allowed the Pt(iv) prodrug to readily migrate into the liposomal bilayer. Notably, upon embedding into the nanoparticles, the Pt(iv) prodrug showed marked resistance against premature reduction in human plasma in vitro. Pharmacokinetic analysis in a mouse model also showed that the nanoparticles significantly extend the half-life of the Pt(iv) prodrug to 180 min, which represents a >6-fold increase compared to cisplatin. Importantly, such lipid modification did not compromise the genotoxicity of cisplatin, as the Pt(iv) prodrug induced DNA damage and apoptosis in ovarian cancer cell lines efficiently. Taken together, our strategy provides a novel insight as to how to stabilize a platinum-based compound to increase the circulation time in vivo, which is expected to enhance the efficacy of drug treatment.

Alkyne Functionalization of a Photoactivated Ruthenium Polypyridyl Complex for Click-Enabled Serum Albumin Interaction Studies

Studying metal-protein interactions is key for understanding the fate of metallodrugs in biological systems. When a metal complex is not emissive and too weakly bound for mass spectrometry analysis, however, it may become challenging to study such interactions. In this work a synthetic procedure was developed for the alkyne functionalization of a photolabile ruthenium polypyridyl complex, [Ru(tpy)(bpy)(Hmte)](PF₆)₂, where tpy = 2,2′:6′,2′′-terpyridine, bpy = 2,2′-bipyridine, and Hmte = 2-(methylthio)ethanol. In the functionalized complex [Ru(HCC-tpy)(bpy)(Hmte)](PF₆)₂, where HCC-tpy = 4′-ethynyl-2,2′:6′,2′′-terpyridine, the alkyne group can be used for bioorthogonal ligation to an azide-labeled fluorophore using copper-catalyzed “click” chemistry. We developed a gel-based click chemistry method to study the interaction between this ruthenium complex and bovine serum albumin (BSA). Our results demonstrate that visualization of the interaction between the metal complex and the protein is possible, even when this interaction is too weak to be studied by conventional means such as UV–vis spectroscopy or ESI mass spectrometry. In addition, the weak metal complex-protein interaction is controlled by visible light irradiation, i.e., the complex and the protein do not interact in the dark, but they do interact via weak van der Waals interactions after light activation of the complex, which triggers photosubstitution of the Hmte ligand.

A “clickable” and photosubstitutionally active ruthenium complex has been prepared that bears a terminal alkyne group. In the dark, the saturated coordination sphere of the complex prevents it from interacting with serum albumin. Upon photosubstitution of one ligand, the complex interacts with the protein via weak interactions that were visualized using copper-catalyzed “click” chemistry postfunctionalization with an azide fluorophore on polyacrylamide gel electrophoresis. These studies demonstrate that the metal-protein interaction is triggered by light irradiation.

Multiaction Pt(IV) Carbamate Complexes Can Codeliver Pt(II) Drugs and Amine Containing Bioactive Molecules

Multiaction Pt(IV) prodrugs can overcome resistance associated with the FDA approved Pt(II) drugs like cisplatin. Intracellular reduction of the octahedral Pt(IV) derivatives of cisplatin releases cisplatin and the two axial ligands. When the released axial ligands act synergistically with cisplatin to kill the cancer cells, we have multiaction prodrugs. Most Pt(IV) multiaction prodrugs have bioactive ligands possessing a carboxylate that is conjugated to the Pt(IV) because breaking the Pt(IV)-ligand bond releases the active moiety. As many drugs that act synergistically with cisplatin do not have carboxylates, a major challenge is to prepare multiaction Pt(IV) complexes with drugs that have amino groups or hydroxyl groups such that following reduction, the drugs are released in their active form. Our objective was to prepare multiaction Pt(IV) prodrugs that release bioactive molecules having amino groups. Because we cannot conjugate amino groups to the axial position of Pt(IV), we developed a novel and efficient approach for the synthesis of Pt(IV)-carbamato complexes and demonstrated that following reduction of the Pt(IV), the released carbamates undergo rapid decarboxylation, releasing the free amine, as in the case of the PARP-1 inhibitor 3-aminobenzamide and the amino derivative of the HDAC inhibitor SAHA. Pt(IV)-carbamato complexes are stable in cell culture medium and are reduced by ascorbate. They are reduced slower than their carboxylato and carbonato analogues. We believe that this approach paves the way for preparing novel classes of multiaction Pt(IV) prodrugs with amino containing bioactive molecules that up to now were not accessible.

Targeting drug delivery system for platinum(Ⅳ)-Based antitumor complexes

Classical platinum(II) anticancer agents are widely-used chemotherapeutic drugs in the clinic against a range of cancers. However, severe systemic toxicity and drug resistance have become the main obstacles which limit their application and effectiveness. Because divalent cisplatin analogues are easily destroyed in vivo, their bioavailability is low and no selective to tumor tissues. The platinum(IV) prodrugs are attractive compounds for cancer treatment because they have great advantages, e.g., higher stability in biological media, aqueous solubility and no cross-resistance with cisplatin, which may become the next generation of platinum anticancer drugs. In addition, platinum(IV) drugs could be taken orally, which could be more acceptable to cancer patients, breaking the current situation that platinum(II) drugs can only be given by injection. The coupling of platinum(IV) complexes with tumor targeting groups avoids the disadvantages such as instability in blood, irreversible binding to plasma proteins, rapid renal clearance, and non-specific distribution in normal tissues. Because of the above advantages, the combination of platinum complexes and tumor targeting groups has become the hottest field in the research and development of new platinum drugs. These approaches can be roughly categorized into two groups: active and passive targeted strategies. This review concentrates on various targeting and delivery strategies for platinum(IV) complexes to improve the efficacy and reduce the side effects of platinum-based anticancer drugs. We have made a summary of the related articles on platinum(IV) targeted delivery in recent years. We believe the results of the studies described in this review will provide new ideas and strategies for the development of platinum drugs.

Oxaliplatin-Based Platinum(IV) Prodrug Bearing Toll-like Receptor 7 Agonist for Enhanced Immunochemotherapy

A combination of platinum drugs with immunotherapy has shown promising anticancer effects, especially in the drug resistance cancer model. Herein, a new type of immunochemotherapeutic was designed by tethering the toll-like receptor 7 (TLR7) agonist on the axial position of oxaliplatin-based platinum(IV) prodrug. The prodrug simultaneously induced immunogenic cell death of 4T1 cancer cells to initiate an immune response and activate dendritic cells (DCs) to secrete proinflammatory cytokines including interferon-γ (IFN-γ), tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), and IL-12, to further enhance the adaptive immunity. The prodrug exhibited better in vivo anticancer effects than oxaliplatin in the 4T1 allograft mouse model, a later stage breast cancer model, which showed poor response to traditional chemotherapy. Mechanism studies revealed that enhanced activation of cytotoxic T cells within tumor contribute to the high in vivo anticancer efficiency of the prodrug. Moreover, the prodrug displayed much lower cytotoxicity to DCs compared with oxaliplatin, indicating its safety to normal cells. These results highlight the potential of the conjugation of TLR7 agonist with oxaliplatin-based Pt(IV) prodrug as an effective anticancer agent to overcome the toxic side effects and drug resistance of traditional platinum chemotherapy.

Sulfonamide-containing copper(ii) complexes: new insights on biophysical interactions and antibacterial activities

Cu–(N^N)–sulfonamide complexes are selective metallonucleases that bind tightly to BSA with no protease activity. These compounds have promising antibacterial properties.

Synthesis and Cytotoxicity of Water-Soluble Dual- and Triple-Action Satraplatin Derivatives: Replacement of Equatorial Chlorides of Satraplatin by Acetates

Pt(II) complexes, such as cisplatin and oxaliplatin, are in widespread use as anticancer drugs. Their use is limited by the toxic side effects and the ability of tumors to develop resistance to the drugs. A popular approach to overcome these drawbacks is to use their kinetically inert octahedral Pt(IV) derivatives that act as prodrugs. The most successful Pt(IV) complex in clinical trials to date is satraplatin, cct-[Pt(NH₃)(c-hexylamine)Cl₂(OAc)₂], that upon cellular reduction releases the cytotoxic cis-[Pt(NH₃)(c-hexylamine)Cl₂]. In an attempt to obtain water-soluble and more effective cytotoxic Pt(IV) complexes, we prepared a series of dual- and triple-action satraplatin analogues, where the equatorial chlorido ligands were replaced with acetates and the axial ligands include innocent and bioactive ligands. Replacement of the chlorides with acetates enhanced the water solubility of the compounds and, with one exception, all of the compounds were very stable in buffer. In general, compounds with one or two axial hydroxido ligands were reduced by ascorbate significantly more quickly than compounds with two axial carboxylates. While replacement of the chlorides with acetates in satraplatin led to a reduction in cytotoxicity, the dual- and triple-action analogues with equatorial acetates had low- to sub-micromolar IC₅₀ values in a panel of eight cancer cells. The triple-action compound cct-[Pt(NH₃)(c-hexylamine)(OAc)₂(PhB)(DCA)] was active in all cell lines, causing DNA damage that induced cell cycle inhibition and apoptosis. Its good activity against CT26 cells in vitro translated into good in vivo efficacy against the CT26 allograft, an in vivo model with intrinsic satraplatin resistance. This indicates that multiaction Pt(IV) derivatives of diamine dicarboxylates are interesting anticancer drug candidates.

Investigations of the Kinetics and Mechanism of Reduction of a Carboplatin Pt(IV) Prodrug by the Major Small-Molecule Reductants in Human Plasma

The development of Pt(IV) anticancer prodrugs to overcome the detrimental side effects of Pt(II)-based anticancer drugs is of current interest. The kinetics and reaction mechanisms of the reductive activation of the carboplatin Pt(IV) prodrug cis,trans-[Pt(cbdca)(NH₃)₂Cl₂] (cbdca = cyclobutane-1,1-dicarboxylate) by the major small-molecule reductants in human plasma were analyzed in this work. The reductants included ascorbate (Asc), the thiol-containing molecules L-cysteine (Cys), DL-homocysteine (Hcy), and glutathione (GSH), and the dipeptide Cys–Gly. Overall second-order kinetics were established in all cases. At the physiological pH of 7.4, the observed second-order rate constants k′ followed the order Asc << Cys–Gly ~ Hcy < GSH < Cys. This reactivity order together with the abundances of the reductants in human plasma indicated Cys as the major small-molecule reductant in vivo, followed by GSH and ascorbate, whereas Hcy is much less important. In the cases of Cys and GSH, detailed reaction mechanisms and the reactivity of the various protolytic species at physiological pH were derived. The rate constants of the rate-determining steps were evaluated, allowing the construction of reactivity-versus-pH distribution diagrams for Cys and GSH. The diagrams unraveled that species III of Cys (⁻SCH₂CH(NH₃⁺)COO⁻) and species IV of GSH (⁻OOCCH(NH₃⁺)CH₂CH₂CONHCH(CH₂S⁻)- CONHCH₂COO⁻) were exclusively dominant in the reduction process. These two species are anticipated to be of pivotal importance in the reduction of other types of Pt(IV) prodrugs as well.

Expanding the Arsenal of PtIV Anticancer Agents: Multi-action PtIV Anticancer Agents with Bioactive Ligands Possessing a Hydroxy Functional Group

Most multi-action Pt^IV prodrugs have bioactive ligands containing carboxylates. This is probably due to the ease of carboxylating the OH axial ligands and because following reduction, the active drug is released. A major challenge is to expand the arsenal of bioactive ligands to include those without carboxylates. We describe a general approach for synthesis of Pt^IV prodrugs that release drugs with OH groups. We linked the OH groups of gemcitabine (Gem), paclitaxel (Tax), and estramustine (EM) to the Pt^IV derivative of cisplatin by a carbonate bridge. Following reduction, the axial ligands lost CO₂ , rapidly generating the active drugs. In contrast, succinate-linked drugs did not readily release the free drugs. The carbonate-bridged ctc-[Pt(NH₃ )₂ (PhB)(Gem-Carb)Cl₂ ] was significantly more cytotoxic than the succinate-bridged ctc-[Pt(NH₃ )₂ (PhB)(Gem-Suc)Cl₂ ], and more potent and less toxic than gemcitabine, cisplatin, and co-administration of cisplatin and gemcitabine.

A Dogma in Doubt: Hydrolysis of Equatorial Ligands of PtIV Complexes under Physiological Conditions

Due to their high kinetic inertness and consequently reduced side reactions with biomolecules, PtIV complexes are considered to define the future of anticancer platinum drugs. The aqueous stability of a series of biscarboxylato PtIV complexes was studied under physiologically relevant conditions. Unexpectedly and in contrast to the current chemical understanding, especially oxaliplatin and satraplatin complexes underwent fast hydrolysis in equatorial position (even in cell culture medium and serum). Notably, the resulting hydrolysis products strongly differ in their reduction kinetics, a crucial parameter for the activation of PtIV drugs, which also changes the anticancer potential of the compounds in cell culture. The discovery that intact PtIV complexes can hydrolyze at equatorial position contradicts the dogma on the general kinetic inertness of PtIV compounds and needs to be considered in the screening and design for novel platinum-based anticancer drugs.

Pt(IV) Bifunctional Prodrug Containing 2-(2-Propynyl)octanoato Axial Ligand: Induction of Immunogenic Cell Death on Colon Cancer

The synthesis, characterization, and in vitro activity of a cyclohexane-1 R,2 R-diamine-based Pt(IV) derivative containing the histone deacetylase inhibitor rac-2-(2-propynyl)octanoato, namely, ( OC-6-44)-acetatodichlorido(cyclohexane-1 R,2 R-diamine)( rac-2-(2-propynyl)octanoato)platinum(IV), are reported together with those of its isomers containing enantiomerically enriched axial ligands. These Pt(IV) complexes showed comparable activity, of 2 orders of magnitude higher than reference drug oxaliplatin on three human (HCT 116, SW480, and HT-29) and one mouse (CT26) colon cancer cell lines. In vivo experiments were carried out on immunocompetent BALB/c mice bearing the same syngeneic tumor. The complex ( OC-6-44)-acetatodichlorido(cyclohexane-1 R,2 R-diamine)( rac-2-(2-propynyl)octanoato)platinum(IV) showed higher tumor mass Pt accumulation than oxaliplatin, due to its higher lipophilicity, with negligible nephro- and hepatotoxicities when administered intravenously. A remarkable tumor mass invasion by cytotoxic CD8+ T lymphocytes, following the Pt(IV) treatment, indicated a strong induction of immunogenic cell death.

Synthesis, characterization and biological investigation of platinum(ii) complexes with asparagusic acid derivatives as ligands

After more than 50 years of platinum-based anticancer research only three compounds are in clinical use worldwide. The use of the well-known lead compound of this class of anticancer agents, cisplatin, is limited by its side effects and varying resistance mechanisms. Therefore, we report on platinum(ii) compounds with asparagusic acid derivatives as ligands which show interesting anticancer results on cisplatin resistant cell lines.

Synthesis and characterization of cyclohexane-1R,2R-diamine-based Pt(iv) dicarboxylato anticancer prodrugs: their selective activity against human colon cancer cell lines

Three pairs of asymmetric dicarboxylato derivatives based on the cisplatin and oxaliplatin-like skeletons have been synthesized de novo or re-synthesized. The axial ligands consist of one medium-chain fatty acid (MCFA), namely clofibrate (i.e. 2-(p-chlorophenoxy)-2-methylpropionic acid, CA), heptanoate (HA) or octanoate (OA), respectively, and an inactive acetato ligand that imparts acceptable water solubility to such conjugates. Stability tests provided evidence for the partial formation of two hydrolyzed products, corresponding to two monoaqua diastereomers derived from the substitution of an equatorial chlorido ligand with a water molecule. The complexes have been tested on three different colon cancer cell lines having different histological history, and also on the cisplatin-sensitive A2780 ovarian cancer cell line for comparison. This allowed the evaluation not only of the increase in activity on passing from Pt(ii) to Pt(iv) derivatives, but also the selectivity towards colon cancer cells brought about by the cyclohexane-1R,2R-diamine carrier ligand.

Glucose-conjugated platinum(IV) complexes as tumor-targeting agents: design, synthesis and biological evaluation

A new series of glucose-conjugated Pt(IV) complexes that target tumor-specific glucose transporters (GLUTs) was designed, synthesized, and evaluated for their anticancer activities. All six compounds, namely, A1-A6, exhibited increased cytotoxicity that were almost six fold higher than that of oxaliplatin to MCF-7 cells. These Pt(IV) complexes can be reduced to release Pt(II) complexes and cause the death of tumor cells. Simultaneously, the glycosylated Pt(IV) complexes (30.21-91.33 μM) showed lower cytotoxicity that normal LO2 cells compared with cisplatin (5.25 μM) and oxaliplatin (8.34 μM). The intervention of phlorizin as a GLUTs inhibitor increased the IC₅₀ value of the glycosylated Pt(IV) complexes, thereby indicating the potential GLUT transportability. The introduction of glucose moiety to Pt(IV) complexes can effectively enhance the Pt cellular uptake and DNA platination. Results suggested glucose-conjugated Pt(IV) complexes had potential for further study as new anticancer agents.

Nucleus-Targeted Organoiridium-Albumin Conjugate for Photodynamic Cancer Therapy

An organoiridium-albumin bioconjugate (Ir1-HSA) was synthesized by reaction of a pendant maleimide ligand with human serum albumin. The phosphorescence of Ir1-HSA was enhanced significantly compared to parent complex Ir1. The long phosphorescence lifetime and high 1 O2 quantum yield of Ir1-HSA are highly favorable properties for photodynamic therapy. Ir1-HSA mainly accumulated in the nucleus of living cancer cells and showed remarkable photocytotoxicity against a range of cancer cell lines and tumor spheroids (light IC50 ; 0.8-5 μm, photo-cytotoxicity index PI=40-60), while remaining non-toxic to normal cells and normal cell spheroids, even after photo-irradiation. This nucleus-targeting organoiridium-albumin is a strong candidate photosensitizer for anticancer photodynamic therapy.

Synthesis, crystal structure, DFT calculations, protein interaction, anticancer potential and bromoperoxidase mimicking activity of oxidoalkoxidovanadium(v) complexes

Intriguing structure–activity relationships (SARs) indicating an apparent dependence of anticancer and haloperoxidase activities on the carbon chain length of the alkoxo group.

H2O2-activated oxidative stress amplifier capable of GSH scavenging for enhancing tumor photodynamic therapy

An oxidative stress amplifier (OSA) capable of GSH scavenging and accelerated release by positive feedback was fabricated for enhancing the efficacy of tumor photodynamic therapy (PDT).

Cysteine-Directed Bioconjugation of a Platinum(II)-Acridine Anticancer Agent

Classical maleimide Michael addition chemistry in conjunction with copper-free click chemistry was investigated as a synthetic strategy to attach cytotoxic platinum-acridine hybrid agents to carrier proteins. The structural integrity and selectivity of the model payloads, which were validated in human serum albumin (HSA) using mass spectrometric analysis and heteronuclear 2D ¹H-¹⁵N HSQC NMR experiments, may have broad utility for the targeted delivery of highly cytotoxic platinum acridines and other nonclassical platinum containing anticancer agents.

Supramolecular chemotherapy based on host-guest molecular recognition: a novel strategy in the battle against cancer with a bright future

Chemotherapy is currently one of the most effective ways to treat cancer. However, traditional chemotherapy faces several obstacles to clinical trials, such as poor solubility/stability, non-targeting capability and uncontrollable release of the drugs, greatly limiting their anticancer efficacy and causing severe side effects towards normal tissues. Supramolecular chemotherapy integrating non-covalent interactions and traditional chemotherapy is a highly promising candidate in this regard and can be appropriately used for targeted drug delivery. By taking advantage of supramolecular chemistry, some limitations impeding traditional chemotherapy for clinical applications can be solved effectively. Therefore, we present here a review summarizing the progress of supramolecular chemotherapy in cancer treatment based on host-guest recognition and provide guidance on the design of new targeting supramolecular chemotherapy combining diagnostic and therapeutic functions. Based on a large number of state-of-the-art studies, our review will advance supramolecular chemotherapy on the basis of host-guest recognition and promote translational clinical applications.

Critical assessment of different methods for quantitative measurement of metallodrug-protein associations

Quantitative screening for potential drug-protein binding is an essential step in developing novel metal-based anticancer drugs. ICP-MS approaches are at the core of this task; however, many applications lack in the capability of large-scale high-throughput screenings and proper validation. In this work, we critically discuss the analytical figures of merit and the potential method-based quantitative differences applying four different ICP-MS strategies to ex vivo drug-serum incubations. Two candidate drugs, more specifically, two Pt(IV) complexes with known differences of binding affinity towards serum proteins were selected. The study integrated centrifugal ultrafiltration followed by flow injection analysis, turbulent flow chromatography (TFC), and size exclusion chromatography (SEC), all combined with inductively coupled plasma-mass spectrometry (ICP-MS). As a novelty, for the first time, UHPLC SEC-ICP-MS was implemented to enable rapid protein separation to be performed within a few minutes at > 90% column recovery for protein adducts and small molecules. Graphical abstract Quantitative screening for potential drug-protein binding is an essential step in developingnovel metal-based anticancer drugs.

In vivo tailor-made protein corona of a prodrug-based nanoassembly fabricated by redox dual-sensitive paclitaxel prodrug for the superselective treatment of breast cancer

Prodrug self-nanoassemblies have many advantages for anticancer drug delivery, including high drug loading rate, resistance to recrystallization, and on-demand drug release. However, few studies have focused on their protein corona, which is inevitably formed after entering the blood and determines their subsequent fates in vivo. To actively tune the protein corona of prodrug nanoassemblies, three maleimide-paclitaxel prodrugs were synthesized via different redox-sensitive linkers (ester bond, thioether bond and disulfide bond). After incubation with rat plasma, the surface maleimide groups effectively captured albumins, resulting in albumin-enriched protein corona. The recruited albumin corona enabled enhanced tumor accumulation and facilitated cellular uptake, ensuring the high-efficiency delivery of nanoassemblies to tumor cells. Surprisingly, we found that the traditionally reduction-sensitive disulfide bond could also be triggered by reactive oxygen species (ROS). Such a redox dual-responsive drug release property of the disulfide bond-containing prodrug nanoassemblies further increased the selectivity in cytotoxicity between normal and tumor cells. Moreover, the disulfide bond-containing prodrug nanoassemblies exhibited the highest antitumor efficacy in vivo compared to marketed Abraxane® and other prodrug nanoassemblies. Thus, the fabrication of the maleimide-decorated disulfide bond bridged prodrug nanoassembly, integrating a tunable protein corona and on-demand drug release, is a promising strategy for improved cancer chemotherapy.

Precisely albumin-hitchhiking tumor cell-activated reduction/oxidation-responsive docetaxel prodrugs for the hyperselective treatment of breast cancer

The anticancer efficacy of chemotherapy is greatly limited by short blood circulation and poor tumor selectivity. Thus, anticancer prodrugs with prolonged systemic circulation, tumor-specific distribution and bioactivation, could significantly strengthen the chemotherapy efficacy. Herein, we design two novel tumor cell reduction/oxidation-responsive docetaxel (DTX) prodrugs, DTX-maleimide conjugates with disulfide bond (DSSM) or thioether bond (DSM) linkages, to evaluate the roles of different sensitive linkages in drug release, pharmacokinetics and therapeutic efficacy. An ester bond-linkage prodrug (DM) is utilized as a non-sensitive control. DSSM and DSM show reduction- or oxidation-sensitive release behavior, respectively, and exhibit hyperselective bioactivation and cytotoxicities between cancerous and normal cells. They could instantly hitchhike blood circulating albumin after i.v. administration with albumin-binding half-lives as short as 1 min, resulting in prolonged systemic circulation, increased tumor accumulation. In response to the upregulated reduction/oxidation environment within tumor cells, DSSM and DSM exhibit selectively release capacity in tumor tissues, their TAITumor/Liver values are over 30-fold greater than DM. Combining the above delivery advantages into one, DSSM and DSM achieve enhanced antitumor efficacy of DTX. Such a uniquely developed strategy, integrating high albumin-binding capability and reduction/oxidation-sensitive drug superselective release in tumors, has great potential to be applied in clinical cancer therapy.

Design and synthesis of a new series of low toxic naphthalimide platinum(IV) antitumor complexes with dual DNA damage mechanism

Naphthalimide platinum(IV) antitumor complexes with potential dual DNA damage mechanism were designed, synthesized and evaluated for antitumor activities. The incorporation of DNA targeted naphthalimide group to the platinum(IV) system exerts much positive impacts on their antitumor efficacy. The mechanism research reveals that the title compounds could interact with dsDNA in platinum(IV) form via the naphthalimide group and cause DNA lesion. The further reduction would release platinum(II) complexes and naphthalimide acids which would induce remarkable secondary damage to DNA. Furthermore, the naphthalimide platinum(IV) compounds could combine with human serum albumin via electrostatic force, which are favourable for their storage and transport in blood. Moreover, the title compounds exhibit higher accumulation in tumor cells, and exert lower toxic and higher safe properties than oxaliplatin in vivo.

Serum-binding properties of isosteric ruthenium and osmium anticancer agents elucidated by SEC-ICP-MS

ABSTRACT

Size-exclusion chromatography-inductively coupled plasma-mass spectrometry (SEC-ICP-MS) was used to study the serum-binding preferences of two metallodrugs with anticancer activities in vivo, namely the organoruthenium compound plecstatin-1 and its isosteric osmium analog. The complexes were administered intraperitoneally into mice bearing a CT-26 tumor. Comparing the total metal content of mouse whole blood and serum underlined that the metallodrugs are mainly located in serum and not in the cellular fraction of the blood samples. In mouse serum, both compounds were not only found to bind extensively to the serum albumin/transferrin fraction but also to immunoglobulins. Free drug was not observed in any of the samples indicating rapid protein binding of the metallodrugs. These findings were validated by spiking human serum with the respective compounds ex vivo. An NCI-60 screen is reported for the osmium analog, which revealed a relative selectivity for cancer cell lines of the ovary and the central nervous system with respect to plecstatin-1. Finally, a COMPARE 170 analysis revealed disruption of DNA synthesis as a possible treatment effect of the osmium-based drug candidate.

GRAPHICAL ABSTRACT

Structure elucidation and quantification of the reduction products of anticancer Pt(iv) prodrugs by electrochemistry/mass spectrometry (EC-MS)

Pt(iv) prodrugs are a class of promising anticancer agents, which are activated by reduction to the active Pt(ii) species. Consequently, the reduction process is a crucial parameter. Herein, a new approach using electrochemistry (EC) coupled to liquid chromatography (LC) and electrospray ionization-mass spectrometry (ESI-MS) or inductively coupled plasma (ICP)-MS was applied. This enabled getting insights into the differences in the reduction and ligand release of platinum(iv) complexes with varying equatorial core structures.

Cytosine arabinoside prodrug designed to bind plasma serum albumin for drug delivery

Rational design of anticancer prodrugs for efficient albumin binding can show distinct advantages in drug delivery in terms of high drug availability, long systemic circulation, potential targeting effect, and enhanced chemotherapy effect. In the present study, we reported a cytosine arabinoside (Ara-C) prodrug which could well formulate in solution and instantly transform into long-circulating nanocomplexes by hitchhiking blood-circulating albumin after i.v. administration. Specifically, Ara-C was conjugated with an albumin-binding maleimide derivative, the resulting Ara-C maleimide caproic acid conjugate (AM) was well formulated in aqueous solution, conferring high albumin-binding ability in vitro albumin-binding studies. Moreover, in vivo fluorescence images of sulfo-cyanine5 maleimide indirectly demonstrated that AM showed better accumulation in tumors, exhibiting superior tumor targeting ability and antitumor activity compared to Ara-C. Such a uniquely developed strategy, integrating high albumin-binding capability, has great potential to be applied in clinical cancer therapy.

Anticancer metallodrugs: where is the next cisplatin?

Despite the severe side effects and the emergence of drug resistance, the use of DNA-targeting platinum drugs remains strong either alone or in a combination chemotherapy regimen. New strategies and formulations are being explored in the design of anticancer metal complexes that exhibit nonclassical modes of action, selectively hit precise biomolecular targets or are even able to induce immunogenic anticancer activity. These developments will ameliorate the systemic toxicity of metal-based drugs and widen the range of treatable cancers.

Multifunctional αvβ6 Integrin-Specific Peptide-Pt(IV) Conjugates for Cancer Cell Targeting

Increasing the specificity of cancer therapy, and thereby decreasing damage to normal cells, requires targeting to cancer-cell specific features. The α_vβ₆ integrin is a receptor involved in cell adhesion and is frequently up-regulated in cancer cells compared to normal cells. We have selected a peptide ligand reported to bind specifically to the β₆ integrin and have synthesized a suite of multispecific molecules to explore the potential for targeting of cancer cells. A combination of solid-phase peptide synthesis and chemoselective ligations was used to synthesize multifunctional molecules composed of integrin-targeting peptides, cytotoxic platinum(IV) prodrugs, and fluorescent or affinity probes joined with flexible linkers. The modular synthesis approach facilitates the construction of peptide-drug conjugates with various valencies and properties in a convergent manner. The binding and specificity of the multifunctional peptide conjugates were investigated using a cell line transfected with the β₆ integrin and fluorescence microscopy. This versatile and highly controlled approach to synthesizing labeled peptide-drug conjugates has the potential to target potent cytotoxic drugs specifically to cancer cells, reducing the doses required for effective treatment.

EGFR-targeting peptide-coupled platinum(IV) complexes

The high mortality rate of lung cancer patients and the frequent occurrence of side effects during cancer therapy demonstrate the need for more selective and targeted drugs. An important and well-established target for lung cancer treatment is the occasionally mutated epidermal growth factor receptor (EGFR). As platinum(II) drugs are still the most important therapeutics against lung cancer, we synthesized in this study the first platinum(IV) complexes coupled to the EGFR-targeting peptide LARLLT (and the shuffled RTALLL as reference). Notably, HPLC–MS measurements revealed two different peaks with the same molecular mass, which turned out to be a transcyclization reaction in the linker between maleimide and the coupled cysteine moiety. With regard to the EGFR specificity, subsequent biological investigations (3-day viability, 14-day clonogenic assays and platinum uptake) on four different cell lines with different verified EGFR expression levels were performed. Unexpectedly, the results showed neither an enhanced activity nor an EGFR expression-dependent uptake of our new compounds. Consequently, fluorophore-coupled peptides were synthesized to re-evaluate the targeting ability of LARLLT itself. However, also with these molecules, flow cytometry measurements showed no correlation of drug uptake with the EGFR expression levels. Taken together, we successfully synthesized the first platinum(IV) complexes coupled to an EGFR-targeting peptide; however, the biological investigations revealed that LARLLT is not an appropriate peptide for enhancing the specific uptake of small-molecule drugs into EGFR-overexpressing cancer cells.