Multitargeted Platinum(IV) Anticancer Complexes Bearing Pyridinyl Ligands as Axial Leaving Groups.

Although multitargeted PtIV anticancer prodrugs have shown significant activities in reducing drug resistance, the types of bioactive ligands and drugs that can be conjugated to the Pt center remain limited to O-donors. Herein, we report the synthesis of PtIV complexes bearing axial pyridines via ligand exchange reactions. Unexpectedly, the axial pyridines are quickly released after reduction, indicating their potential to be utilized as axial leaving groups. We further expand our synthetic approach to obtaining two multitargeted PtIV prodrugs containing bioactive pyridinyl ligands: a PARP inhibitor and an EGFR tyrosine kinase inhibitor; these conjugates exhibit great potential for overcoming drug resistance, and the latter conjugate inhibits the growth of Pt-resistant tumor in vivo. This research adds to the array of synthetic methods for accessing PtIV prodrugs and significantly increases the types of bioactive axial ligands that can be conjugated to a PtIV center.

Enhancing Circulation and Tumor Accumulation of Carboplatin via an Erythrocyte-Anchored Prodrug Strategy.

The short circulatory half-lives and low tumor accumulation of carboplatin greatly limit the drug's efficacy in vivo. Herein, we address these challenges by using a prodrug strategy and present the rational design of a novel platinum(IV) anticancer prodrug that can hitchhike on erythrocytes. This prodrug, designated as ERY1-PtIV , can bind to erythrocytes efficiently and stably, possessing a circulatory half-life 18.5 times longer than that of carboplatin in mice. This elongated circulatory half-life enables platinum to accumulate at levels 7.7 times higher than with carboplatin, with steady levels in the tumors. As a consequence, the ERY1-PtIV prodrug is proved to exhibit significantly enhanced antitumor activity and reduced side effects compared with carboplatin. Collectively, our novel approach highlights an efficient strategy to utilize intrinsic erythrocytes as auto-binding carriers to enhance the tumor accumulation and subsequent antitumor efficacy of platinum drugs.

Delivery of Platinum(IV) Prodrugs via Bi2Te3 Nanoparticles for Photothermal-Chemotherapy and Photothermal/Photoacoustic Imaging.

Combinational administration of photothermal therapy (PTT) and chemotherapy (CT) shows great potential in improving the efficiency of tumor treatment. Herein, we designed a novel nanocomposite Pt@Bi2Te3 composed of bismuth telluride (Bi2Te3) nanoparticles and platinum(IV) prodrugs (Pt) for PTT-CT combination therapy. The obtained Bi2Te3 was synthesized by a simple solvothermal method and modified by polyethylene glycol, which exhibited excellent photothermal (PT) efficiency and stability and could also serve as a bimodal bioimaging contrast agent in PT and photoacoustic (PA) imaging. In vitro experiment results showed that the nanocomposite Pt@Bi2Te3 could effectively increase the uptake of platinum in cancer cells, which could kill tumor cells through the combined effect of PTT and CT. Furthermore, combination therapy of cancer in vivo was achieved with obvious tumor-growth inhibition without inducing observed side effects. We revealed the great potential of Bi2Te3 nanocomposites in increasing therapeutic efficiency by PTT-CT therapy and PA-PT imaging.

Redox-sensitive polyglutamic acid-platinum(IV) prodrug grafted nanoconjugates for efficient delivery of cisplatin into breast tumor.

Targeting cisplatin to the sites of action and decreasing its side effects are still major challenges. Here, we introduced a polyglutamic acid-platinum(IV) prodrug nanoconjugates (γ-PGA-CA-Pt(IV)) constructed by polyglutamic acid and modified platinum(IV) prodrug to reserve the anti-tumor efficacy of cisplatin with decreased side effects. We describe the synthesis, physico-chemical characterization, and redox- and pH-sensitive releasing behavior of the nanoconjugate. In vitro studies revealed that, when incubated with glutathione in advance, the γ-PGA-CA-Pt(IV) nanoconjugate induced significant apoptosis in human breast carcinoma MCF-7 cells. From in vivo antitumor efficacy evaluation, the γ-PGA-CA-Pt(IV) nanoconjugate obviously improved the survival rate of tumor-bearing mice with inhibition of the tumor growth compared with cisplatin. Meanwhile, the nanoconjugates showed remarkable improved safety profile than the free cisplatin.

Locally unlocks prodrugs by radiopharmaceutical in tumor for cancer therapy.

Chemotherapy is the first-line treatment for cancer, but its systemic toxicity can be severe. Tumor-selective prodrug activation offers promising opportunities to reduce systemic toxicity. Here, we present a strategy for activating prodrugs using radiopharmaceuticals. This strategy enables the targeted release of chemotherapeutic agents due to the high tumor-targeting capability of radiopharmaceuticals. [18F]FDG (2-[18F]-fluoro-2-deoxy-D-glucose), one of the most widely used radiopharmaceuticals in clinics, can trigger Pt(IV) complex for controlled release of axial ligands in tumors, it might be mediated by hydrated electrons generated by water radiolysis resulting from the decay of radionuclide 18F. Its application offers the controlled release of fluorogenic probes and prodrugs in living cells and tumor-bearing mice. Of note, an OxaliPt(IV) linker is designed to construct an [18F]FDG-activated antibody-drug conjugate (Pt-ADC). Sequential injection of Pt-ADC and [18F]FDG efficiently releases the toxin in the tumor and remarkably suppresses the tumor growth. Radiotherapy is booming as a perturbing tool for prodrug activation, and we find that [18F]FDG is capable of deprotecting various radiotherapy-removable protecting groups (RPGs). Our results suggest that tumor-selective radiopharmaceutical may function as a trigger, for developing innovative prodrug activation strategies with enhanced tumor selectivity.

Pt(IV) Prodrug Photoactivation: A Promising Strategy for Cancer Therapy.

Platinum (II) drugs, including cisplatin, carboplatin, and oxaliplatin, have achieved significant clinical success in cancer treatment. However, their clinical application has been greatly hindered by various adverse factors, such as non-specific activation and drug resistance. Compared with Pt(II) drugs, the axial ligands within Pt(IV) compounds can improve the pharmacokinetic properties, selectivity, and biological activity, implementing alternative cytotoxic mechanisms beyond DNA cross-linking and partially overcoming drug resistance. The controlled conversion of Pt(IV) prodrugs into Pt(II) agents at the tumor site has been extensively explored internationally. In this review, Pt(IV) prodrug modification strategies are first summarized, and the development of the predominant external and internal photosensitizers is listed. Finally, three representative photoreduction mechanisms and strategies for developing corresponding Pt(IV) prodrugs are discussed. This work provides constructive instruction for the subsequent molecular design of Pt(IV) prodrugs.

Novel Pt(IV) prodrug self-assembled nanoparticles with enhanced blood circulation stability and improved antitumor capacity of oxaliplatin for cancer therapy.

Pt(IV) compounds are regarded as prodrugs of active Pt(II) drugs (i.e. cisplatin, carboplatin, and oxaliplatin) and burgeoned as the most ideal candidates to substitute Pt(II) anticancer drugs with severe side effects. Nanoparticle drug delivery systems have been widely introduced to deliver Pt(IV) prodrugs more effectively and safely to tumors, but clinical outcomes were unpredictable owing to limited in vivo pharmacokinetics understanding. Herein, a novel Pt(IV) prodrug of oxaliplatin(OXA) was synthesized and prepared as self-assembled micellar nanoparticles(PEG-OXA NPs). In vitro, PEG-OXA NPs rapidly released biologically active OXA within 5 min in tumor cells while remaining extremely stable in whole blood or plasma. Importantly, the pharmacokinetic results showed that the AUC0-∞, and t1/2 values of PEG-OXA NPs were 1994 ± 117 h·µg/mL and 3.28 ± 0.28 h, respectively, which were much higher than that of free OXA solution (2.03 ± 0.55 h·µg/mL and 0.16 ± 0.07 h), indicating the longer drug circulation of PEG-OXA NPs in vivo. The altered pharmacokinetic behavior of PEG-OXA NPs remarkably contributed to improve antitumor efficacy, decrease systemic toxicity and increase tumor growth inhibition compared to free OXA. These findings establish that PEG-OXA NPs have the potential to offer a desirable self-delivery platform of platinum drugs for anticancer therapeutics.

Emerging platinum(IV) prodrug nanotherapeutics: A new epoch for platinum-based cancer therapy.

Owing to the unique DNA damaging cytotoxicity, platinum (Pt)-based chemotherapy has long been the first-line choice for clinical oncology. Unfortunately, Pt drugs are restricted by the severe dose-dependent toxicity and drug resistance. Correspondingly, Pt(IV) prodrugs are developed with the aim to improve the antitumor performance of Pt drugs. However, as "free" molecules, Pt(IV) prodrugs are still subject to unsatisfactory in vivo destiny and antitumor efficacy. Recently, Pt(IV) prodrug nanotherapeutics, inheriting both the merits of Pt(IV) prodrugs and nanotherapeutics, have emerged and demonstrated the promise to address the underexploited dilemma of Pt-based cancer therapy. Herein, we summarize the latest fronts of emerging Pt(IV) prodrug nanotherapeutics. First, the basic outlines of Pt(IV) prodrug nanotherapeutics are overviewed. Afterwards, how versatile Pt(IV) prodrug nanotherapeutics overcome the multiple biological barriers of antitumor drug delivery is introduced in detail. Moreover, advanced combination therapies based on multimodal Pt(IV) prodrug nanotherapeutics are discussed with special emphasis on the synergistic mechanisms. Finally, prospects and challenges of Pt(IV) prodrug nanotherapeutics for future clinical translation are spotlighted.

Ligand Evolution in the Photoactivatable Platinum(IV) Anticancer Prodrugs.

Photoactivatable Pt(IV) anticancer prodrugs with the structure of [PtIV(N1)(N2)(L1)(L2)(A1)(A2)], where N1 and N2 are non-leaving nitrogen donor ligands, L1 and L2 are leaving ligands, and A1 and A2 are axial ligands, have attracted increasing attention due to their promising photo-cytotoxicity even to cisplatin-resistant cancer cells. These photochemotherapeutic prodrugs have high dark-stability under physiological conditions, while they can be activated by visible light restrained at the disease areas, as a consequence showing higher spatial and temporal controllability and much more safety than conventional chemotherapy. The coordinated ligands to the Pt center have been proved to be pivotal in determining the function and activity of the photoactivatable Pt(IV) prodrugs. In this review, we will focus on the development of the coordinated ligands in such Pt(IV) prodrugs and discuss the effects of diverse ligands on their photochemistry and photoactivity as well as the future evolution directions of the ligands. We hope this review can help to facilitate the design and development of novel photoactivatable Pt(IV) anticancer prodrugs.

A DNA damage nanoamplifier for the chemotherapy of triple-negative breast cancer via DNA damage induction and repair blocking.

Due to a powerful DNA damage repair system and a lack of surface markers, there is currently no effective chemotherapy or tailored targeted therapies available for triple-negative breast cancer (TNBC) treatment. Herein, a tailored DNA damage nanoamplifier (Lipo@Nir/Pt(IV)C18) was engineered to simultaneously induce DNA damage and inhibit DNA reparation for highly efficient TNBC treatment. A newly synthesized Pt(IV)C18 prodrug, the DNA damaging inducer, and the hydrophobic poly(ADP-ribose) polymerases (PARPs) inhibitor niraparib, which is used as the DNA repair blocker, were concurrently encapsulated in highly biocompatible PEGylated liposomes to prepare Lipo@Nir/Pt(IV)C18, for enhanced cancer therapy and future clinical translation. Lipo@Nir/Pt(IV)C18 with an appropriate size and excellent stability, effectively accumulated at the tumor site. After internalization by tumor cells, niraparib, a highly-selective hydrophobic PARP1 inhibitor, could exacerbate the accumulation of platinum-induced DNA lesions to induce excessive genome damage for synergistic cell apoptosis, which was evidenced by the upregulated γ-H2AX and cleaved-PARP levels. Importantly, Lipo@Nir/Pt(IV)C18 exhibited remarkable antitumor efficacy on TNBC without BRCA mutants in vivo with little systemic toxicity. Inspired by the concept of "synthetic lethality", this study provides an inspirational and clinically transformable nanobased DNA damaging amplification strategy for the expansion of TNBC beneficiaries and highly efficient TNBC treatment via DNA damage induction and DNA repair blocking.

Pt(IV) Prodrugs Designed to Embed in Nanotubes of a Polysaccharide for Drug Delivery.

Cisplatin exhibits a sufficient killing effect on cancer cells; however, it damages normal cells simultaneously. Herein, we developed a prodrug delivery system based on branched ß-(1→3)-d-glucan. This natural biomacromolecule-based polysaccharide nanotube was modified with cisplatin embedded in the hollow cavity (BFCP), showing high anticancer activity and low toxicity in vitro. It is a broad-prospect system, which is based on biocompatible nanomaterials loaded with Pt(IV) prodrugs for cancer cell absorption with subsequent release in tumors by utilizing the intracellular reducibility. BFCP chains adopted a nanotube conformation in water, observed by transmission electron microscopy. In comparison to cisplatin, the Pt(IV) prodrugs not only displayed better antitumor properties but also had significant tumor targeting. A potent natural complex conjugated with redox-responsive platinum prodrugs is a significantly efficient tumor drug demonstrated in vitro and in vivo.

The novel platinum(IV) prodrug with self-assembly property and structure-transformable character against triple-negative breast cancer.

Herein, a small library of Pt(IV) prodrugs based on cisplatin and chemosensitizer adjudin (ADD) were explored for efficient cisplatin resistant triple-negative breast cancer (TNBC) treatment. We further elucidated the detail relationship of chemical structure, alkyl chain length (ethyl to dodecyl) and ADD substituted degree, with respect to the self-assembly ability and cytotoxic effect of prodrugs. It demonstrated that all prodrugs could self-assemble into nanomedicine, which was in consist with the molecule structure building and self-assembly simulation. All nanomedicines possessed small particle size, uniform morphology and ultra-high drug loading content (84.0%-86.5%). Moreover, the length of alkyl chain was of great importance for the structure-transformable character and cytotoxicity of nanomedicines. Interestingly, ADD monosubstituted with butyl or hexyl contralateral substituted prodrug (C4-Pt-ADD or C6-Pt-ADD) assembled nanomedicine could convert to wire or sheet structure. These transformable nanoparticles showed great potential in improving the sensitivity of cisplatin to TNBC with up to 266-fold lower IC50 value and significantly enhanced in vivo tumor growth inhibition. Therefore, the self-assembled nanomedicine based on Pt(IV)-ADD could be a promising strategy for TNBC therapy.

Enhanced cytotoxicity to cancer cells by mitochondria-targeting MWCNTs containing platinum(IV) prodrug of cisplatin.

Among the arsenal of nano-materials, carbon nanotubes (CNTs) are becoming more prominent due to favorable attributes including their unique shape, which promotes cellular-uptake, and large aspect-ratio that facilitates functionalization of bioactive molecules on their surface. In this study, multi-walled carbon nanotubes (MWCNTs) were functionalized with either mitochondrial-targeting fluorescent rhodamine-110 (MWCNT-Rho) or non-targeting fluorescein (MWCNT-Fluo). Despite structural similarities, MWCNT-Rho associated well with mitochondria (ca. 80% co-localization) in contrast to MWCNT-Fluo, which was poorly localized (ca. 21% co-localization). Additionally, MWCNT-Rho entrapping platinum(IV) pro-drug of cisplatin (PtBz) displayed enhanced potency (IC50 = 0.34 ± 0.07 µM) compared to a construct based on MWCNT-Fluo (IC50 ≥ 2.64 µM). Concurrently, preliminary in vitro toxicity evaluation revealed that empty MWCNT-Rho neither decreased cell viability significantly nor interfered with mitochondrial membrane-potential, while seemingly being partially expelled from cells. Due to its targeting capability and apparent lack of cytotoxicity, MWCNT-Rho complex was used to co-encapsulate PtBz and a chemo-potentiator, 3-bromopyruvate (BP), and the resulting MWCNT-Rho(PtBz+BP) construct demonstrated superior efficacy over PtBz free drug in several cancer cell lines tested. Importantly, a 2-fold decrease in mitochondrial potential was observed, implying that mitochondrial targeting of compounds indeed incurred additional intended damage to mitochondria.

Gelatin-encapsulated iron oxide nanoparticles for platinum (IV) prodrug delivery, enzyme-stimulated release and MRI.

A facile method for transferring hydrophobic iron oxide nanoparticles (IONPs) from chloroform to aqueous solution via encapsulation of FITC-modified gelatin based on the hydrophobic-hydrophobic interaction is described in this report. Due to the existence of large amount of active groups such as amine groups in gelatin, the fluorescent labeling molecules of fluorescein isothiocyanate (FITC) and platinum (IV) prodrug functionalized with carboxylic groups can be conveniently conjugated on the IONPs. The nanoparticles carrying Pt(IV) prodrug exhibit good anticancer activities when the Pt(IV) complexes are reduced to Pt(II) in the intracellular environment, while the pure Pt(IV) prodrug only presents lower cytotoxicity on cancer cells. Meanwhile, fluorescence of FITC on the surface of nanoparticles was completely quenched due to the possible Förster Resonance Energy Transfer (FRET) mechanism and showed a fluorescence recovery after gelatin release and detachment from IONPs. Therefore FITC as a fluorescence probe can be used for identification, tracking and monitoring the drug release. In addition, adding pancreatic enzyme can effectively promote the gelatin release from IONPs owing to the degradation of gelatin. Noticeable darkening in magnetic resonance image (MRI) was observed at the tumor site after in situ injection of nanoparticles, indicating the IONPs-enhanced T2-weighted imaging. Our results suggest that the gelatin encapsulated Fe3O4 nanoparticles have potential applications in multi-functional drug delivery system for disease therapy, MR imaging and fluorescence sensor.