Spatiotemporal Concurrent Liberation of Cytotoxins from Dual-Prodrug Nanomedicine for Synergistic Antitumor Therapy

Platinum-based chemotherapy: trends in organic nanodelivery systems

Despite the investment in platinum drugs research, cisplatin, carboplatin and oxaliplatin are still the only Pt-based compounds used as first line treatments for several cancers, with a few other compounds being approved for administration in some Asian countries. However, due to the severe and worldwide impact of oncological diseases, there is an urge for improved chemotherapeutic approaches. Furthermore, the pharmaceutical application of platinum complexes is hindered by their inherent toxicity and acquired resistance. Nanodelivery systems rose as a key strategy to overcome these challenges, with recognized versatility and ability towards improving the safety, bioavailability and efficacy of the available drugs. Among the known nanocarriers, organic systems have been widely applied, taking advantage of their potential as drug vehicles. Researchers have mainly focused on the development of lipidic and polymeric carriers, including supramolecular structures, with an overall improvement of encapsulated platinum complexes. Herein, an overview of recent trends and strategies is presented, with the main focus on the encapsulation of platinum compounds into organic nanocarriers, showcasing the evolution in the design and development of these promising systems. This comprehensive review highlights formulation methods as well as characterization procedures, providing insights that may be helpful for the development of novel platinum nanocarriers aiming at future pharmaceutical applications.

Nordihydroguaiaretic Acid-Cross-Linked Phenylboronic Acid-Functionalized Polyplex Micelles for Anti-angiogenic Gene Therapy of Orthotopic and Metastatic Tumors

Polyplexes are required to be equipped with multiple functionalities to accomplish adequate structure stability and gene transfection efficacy for gene therapy. Herein, a 4-carboxy-3-fluorophenylboronic acid (FPBA)-functionalized block copolymer of PEG-b-PAsp(DET/FBA) and PAsp(DET/FBA) (abbreviated as PB and HB) was synthesized and applied for engineering functional polyplex micelles (PMs) through ionic complexation with pDNA followed by strategic cross-linking with nordihydroguaiaretic acid (NDGA) in respect to the potential linkage of polyphenol and FPBA moieties. In relation to polyplex micelles void of cross-linking, the engineered multifunctional polyplex micelles (PBHBN-PMs) were determined to possess improved structural tolerability against the exchange reaction with charged species. Besides, the FPBA/NDGA cross-linking appeared to be selectively cleaved in the acidic endosomal compartments but not the neutral milieu. Furthermore, the PBHB-PMs with the optimal FPBA/NDGA cross-linking degree were identified to possess appreciable cellular uptake and endosomal escape activities, eliciting a significantly high level of gene expression relative to P-PMs and PB-PMs. Eventually, in vivo antitumor therapy by our proposed multifunctional PMs appeared to be capable of facilitating expression of the antiangiogenic genomic payloads (sFlt-1 pDNA) via systemic administration. The enriched antiangiogenic sFlt-1 in the tumors could silence the activities of angiogenic cytokines for the inhibited neo-vasculature and the suppressed growth of orthotopic 4T1 tumors. Of note, the persistent expression of the antiangiogenic sFlt-1 is also presumed to migrate into the blood circulation, thereby accounting for an overall antiangiogenic environment in preventing the potential pulmonary metastasis. Hence, our elaborated multifaceted PMs inspired fascinating potential as an intriguing gene delivery system for the treatment of clinical solid tumors and metastasis.

Ultrasmall Single-Chain Nanoparticles Derived from Amphiphilic Alternating Copolymers

The collapse or folding of an individual polymer chain into a nanoscale particle gives rise to single-chain nanoparticles (SCNPs), which share a soft nature with biological protein particles. The precise control of their properties, including morphology, internal structure, size, and deformability, are a long-standing and challenging pursuit. Herein, a new strategy based on amphiphilic alternating copolymers for producing SCNPs with ultrasmall size and uniform structure is presented. SCNPs are obtained by folding the designed alternating copolymer in N,N-dimethylformamide (DMF) and fixing it through a photocatalyzed cycloaddition reaction of anthracene units. Molecular dynamics simulation confirms the solvophilic outer corona and solvophobic inner core structure of SCNPs. Furthermore, by adjusting the length of PEG units, precise control over the mean size of SCNPs is achieved within the range of 2.8 to 3.9 nm. These findings highlight a new synthetic strategy that enables enhanced control over morphology and internal structure while achieving ultrasmall and uniform size for SCNPs.

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 AUC_0-∞, and t_1/2 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.

A Red-Light-Responsive DASA-Polymer with High Water Stability for Controlled Release

Photoresponsive polymers hold vast potential in the realm of drug delivery. Currently, most photoresponsive polymers use ultraviolet (UV) light as the excitation source. However, the limited penetration ability of UV light within biological tissues serves as a significant hindrance to their practical applications. Given the strong penetration ability of red light in biological tissues, the design and preparation of a novel red-light-responsive polymer with high water stability, incorporating the reversible photoswitching compound and donor-acceptor Stenhouse adducts (DASA) for controlled drug release is demonstrated. In aqueous solutions, this polymer exhibits self-assembly into micellar nanovectors (~33 nm hydrodynamic diameter), facilitating the encapsulation of the hydrophobic model drug Nile red (NR) within the micellar core. Upon irradiation by a 660 nm LED light source, photons are absorbed by DASA, leading to the disruption of the hydrophilic-hydrophobic balance of the nanovector and thereby resulting in the release of NR. This newly designed nanovector incorporates red light as a responsive switch, successfully avoiding the problems of photodamage and limited penetration of UV light within biological tissues, thereby further promoting the practical applications of photoresponsive polymer nanomedicines.

Platinum Drug-Incorporating Polymeric Nanosystems for Precise Cancer Therapy

Platinum (Pt) drugs are widely used in clinic for cancer therapy, but their therapeutic outcomes are significantly compromised by severe side effects and acquired drug resistance. With the emerging immunotherapy and imaging-guided cancer therapy, precise delivery and release of Pt drugs have drawn great attention these days. The targeting delivery of Pt drugs can greatly increase the accumulation at tumor sites, which ultimately enhances antitumor efficacy. Further, with the combination of Pt drugs and other theranostic agents into one nanosystem, it not only possesses excellent synergistic efficacy but also achieves real-time monitoring. In this review, after the introduction of Pt drugs and their characteristics, the recent progress of polymeric nanosystems for efficient delivery of Pt drugs is summarized with an emphasis on multi-modal synergistic therapy and imaging-guided Pt-based cancer treatment. In the end, the conclusions and future perspectives of Pt-encapsulated nanosystems are given.

Older but Stronger: Development of Platinum-Based Antitumor Agents and Research Advances in Tumor Immunity

Platinum (Pt) drugs have developed rapidly in clinical applications because of their broad and highly effective antitumor effects. In recent years, with the rapid development of immunotherapy, Pt-based antitumor agents have gained new challenges and opportunities. Since the discovery of their pharmacological effects in immunotherapy and tumor microenvironment regulation, research into Pt drugs has progressed to multi-ligand and multi-functional Pt precursors and their own shortcomings have been further highlighted. With the development of antitumor immunotherapy and the rise of combination therapy, the development of Pt-based drugs has started to move in the direction of multi-targeting, nanocarrier modification, immunotherapy and photodynamic therapy. In this paper, we first overview the recent applications of Pt-based drugs in antitumor inorganic chemistry, with a focus on summarizing the application of Pt-based drugs and their precursors in the anticancer immune response. The paper also provides a reasonable outlook on the future development of Pt-based drugs from the chemical and immunological perspectives, relying on the existing content and problems of Pt-based drug development. On the basis of the gathered information, joint multidisciplinary programs on implementing comprehensive immune analyses for the future development of novel anticancer metal compounds should be initiated.

Simultaneous Knockdown of Immune Suppressive Markers by Tumor Microenvironment-Responsive Multifaceted Prodrug Nanomedicine

Tumors managing to exempt from immune clearance are attributable to their overexpressed immune suppressive molecules (CD47, PD-L1, etc.). Leadingly, the checkpoint blockade-based chemoimmunotherapy by means of knockdown of these immunosuppressive checkpoints, together with immunogenetic chemotherapeutics, is perceived to be a valid therapeutic strategy for improving anti-tumor outcomes. Herein, chemotherapeutic camptothecin was covalently introduced into an intriguing multifaceted nanomedicine. Note that the elaborated nanomedicine was chemically engineered to enable targeted transportation to the tumors via systemic administration, possessing intelligent responsiveness to sequential extracellular and intracellular microenvironments in the targeted tumors for prompted transcellular endocytosis owing to enzymolysis by the tumor-enriched matrix metalloproteinases and the selective liberation of cytocidal camptothecin in the cell interiors owing to thiolysis by glutathione. In addition, this chemotherapeutic nanomedicine allowed facile encapsulation of the negatively charged RNA interference payloads. Consequently, aiming for treatment of intractable triple-negative breast tumors, we attempted the small interfering RNA (siRNA) payloads aiming for CD47 and PD-L1 into the aforementioned nanomedicine. The subsequent investigations demonstrated drastic knockdown of these vital immune suppressive checkpoints by this siRNA-encapsulating chemotherapeutic nanomedicine, conducing to the reversal of the immune checkpoint suppressive microenvironment of triple-negative 4T1 tumors. Namely, the inhibited proceedings of the innate and adaptive anti-tumor immunities were revived, as supported by observation of the activated infiltration and retention of CD68⁺ macrophages and CD4⁺ and CD8⁺ lymphocytes into the tumors. Eventually, most potent anti-tumor efficacies were accomplished by systemic administration of this chemoimmunotherapeutic nanomedicine, which verified the amplified contribution from anti-tumor immunities by means of knockdown of the immune suppressive molecules to the ultimate anti-tumor efficacies. Note that the upregulation of the immune suppressive molecules was constantly reported in a variety of clinical therapies; hence, our facile chemoimmunotherapeutic platform should be emphasized in clinical translation for seeking improved therapeutic outcomes.

pH-responsive organic/inorganic hybrid nanocolloids for transcellular delivery of ribonucleolytic payloads toward targeted anti-glioma therapy

Proteins have been appreciated to be a superlative modality of therapeutics in view of their direct roles in regulating diverse sets of biological events, nonetheless, the clinical applications of the proteinic therapeutics have been strictly limited to act on the cell surface receptors owing to their inherent cell-impermeable character of the proteins. To this obstacle, we contrived carboxylation reaction upon the proteins (RNase A) into the overall negatively charged pro-RNase, followed by elaboration of intelligent pH-responsive pro-RNase delivery nanocolloids based on co-precipitation of pro-RNase and Arg-Gly-Asp (RGD)-functionalized poly(ethylene glycol) (PEG)-block-polyanion with aids of inorganic calcium phosphate (CaP). The resulting nanocolloids appeared to actively accumulate into glioma due to the specific binding affinities of RGD and glioma-enriched α_Vβ₃ and α_Vβ₅ integrins. Furthermore, the pH responsiveness to the acidic endolysosomal microenvironment of all compositions of nanocolloids (including: decarboxylation of pro-RNase composition to restore the native RNase A, ionization of CaP composition to elicit osmotic pressure, and charge reversal of PEG-block-polyanion into membrane-disruptive polycation) could stimulate not only efficient endolysosomal escape for translocation into the cytosol but also structural disassembly for ready liberation of the RNase A payloads, eventually exerting non-specific RNA degradation for apoptosis of the affected cells. Systemic dosage of the proposed nanocolloids demonstrated potent anti-tumor efficacies towards xenograft glioma due to massive RNA degradation. Therefore, our proposed RNase A prodrug nanocolloids could represent as a versatile platform for engineering transcellular protein delivery systems, which are expected to spur thriving emergence of a spectrum of proteins in precision intervention of intractable diseases.

The role of Platinum(IV)-based antitumor drugs and the anticancer immune response in medicinal inorganic chemistry. A systematic review from 2017 to 2022

Platinum-based antitumor drugs have been used in many types of tumors due to its broad antitumor spectrum in clinic. Encouraged by the cisplatin's (CDDP) worldwide success in cancer chemotherapy, the research in platinum-based antitumor drugs has evolved from traditional platinum drug to multi-ligand and multifunctional platinum prodrugs over half a century. With the rapid development of metal drugs and the anticancer immune response, challenges and opportunities in platinum drug research have been shifted from traditional platinum-based drugs to platinum-based hybrids and the direction of development is tending toward photodynamic therapy, nano-delivery therapy, drug combination, targeted therapy, diagnostic therapy, immune-combination therapy and tumor stem cell therapy. In this review, we first exhaustively overviewed the role of platinum-based antitumor prodrugs and the anticancer immune response in medicinal inorganic chemistry based on the special nanomaterials, the modification of specific ligands, and the multiple functions obtained that are beneficial for tumor therapy in the last five years. We also categorized them according to drug potency and function. There hasn't been a comprehensive evaluation of precursor platinum drugs in prior articles. And a multifarious approach to distinguish and detail the variety of alterations of platinum-based precursors in various valence states also hasn't been summarized. In addition, this review points out the main problems at the interface of chemistry, biology, and medicine from their action mechanisms for current platinum drug development, and provides up-to-date potential strategies from drug design perspectives to circumvent those drawbacks. And a promising idea is also enlightened for researchers in the development and discovery of platinum prodrugs.

Delivery process and effective design of vectors for cancer therapy

In recent years, the efficacy of nano-drugs has not been significantly better than that of the drugs themselves, mainly because nano-drugs enter the tumor vasculature, stay near the blood vessels, and cannot enter the tumor tissues or tumor cells to complete the drug delivery process. Although intratumor injection can significantly decrease this risk, the side effects are strong. The advent of drug delivery carrier materials offers an opportunity to avoid the side effects of systemic drug delivery and the damage caused by tumor resection, holding great promise for the future of cancer therapy. Here, we systematically review recent research advances in the classification of drug delivery carrier materials and the delivery process in drug delivery systems. This review is divided into several main sections, first, we summarize the classification of tumor drug carrier materials, including drug delivery vectors and gene delivery vectors, etc., which are introduced in detail, respectively. Then we describe the carrier materials to deliver the drug cascade and the transition pathways for drug delivery, including stabilization transitions, charge inversions, and size changes. Finally, we discuss the current design strategies and research progress of drug vectors and provide a summary and outlook. This review aims to summarize different drug delivery vehicles and delivery processes to provide ideas for effective cancer therapy.

Alantolactone-Loaded Pegylated Prodrug Nanocarriers for Synergistic Treatment of Cisplatin-Resistant Ovarian Cancer via Reactivating Mitochondrial Apoptotic Pathway

Ovarian cancer (OV) seriously damages women's health because of refractory OV and the development of platinum (Pt) resistance. New treatment strategies are urgently needed to deal with the treatment of cisplatin-resistant OV. Here, a reduction-sensitive pegylated Pt(IV) prodrug was synthesized by amidation of methoxy polyethylene glycol amine (PEG₇₅₀-NH₂) with monocarboxylic Pt(IV) prodrug (Pt(IV)-COOH). Then alantolactone (AL) loaded PEG-Pt(IV) nanocarriers (NP(Pt)@AL) were prepared. In the cisplatin-resistant model of OV, cancer cells actively ingest NP(Pt)@AL through endocytosis, and AL and Pt(II) were disintegrated and released under high intracellular reductant condition. The activity of thioredoxin reductase 1 (TrxR1) inhibited by AL and the adducts of Pt(II) with mitochondrial DNA (mDNA) can costimulate reactive oxygen species (ROS) and reactivate the mitochondrial pathway of apoptosis. Meanwhile, Pt(II) binds with nuclear DNA (nDNA) to jointly promote cell apoptosis. Both in vitro and in vivo results demonstrated that NP(Pt)@AL could effectively reverse the drug resistance and displayed excellent synergistic therapeutic efficacy on platinum-resistant OV with high safety. Therefore, reactivation of the mitochondrial pathway of apoptosis would be a potential strategy to improve the therapeutic effect of Pt-based chemotherapy and even reverse drug resistance.

Multi-functional polymeric micelles for chemotherapy-based combined cancer therapy

Currently, the therapeutic performance of traditional mono-chemotherapy on cancers remains unsatisfactory because of the tumor heterogeneity and multidrug resistance. In light of intricate tumor structures and distinct tumor microenvironments (TMEs), combinational therapeutic strategies with multiple anticancer drugs from different mechanisms can synergistically optimize the outcomes and concomitantly minimize the adverse effects during the therapy process. Extensive research on polymeric micelles (PMs) for biomedical applications has revealed the growing importance of nanomedicines for cancer therapy in the recent decade. Starting from traditional simple delivery systems, PMs have been extended to multi-faceted therapeutic strategies. Here we review and summarize the most recent advances in combinational therapy based on multifunctional PMs including a combination of multiple anticancer drugs, chemo-gene therapy, chemo-phototherapy and chemo-immunotherapy. The design approaches, action mechanisms and therapeutic applications of these nanodrugs are summarized. In addition, we highlight the opportunities and potential challenges associated with this promising field, which will provide new guidelines for advanced combinational cancer chemotherapy.

Prodrug-based nano-delivery strategy to improve the antitumor ability of carboplatin in vivo and in vitro

Chemotherapy plays a major role in the treatment of cancer, but it still has great limitations in anti-tumor effect. Carboplatin (CAR) is the first-line drug in the treatment of non-small cell lung cancer, but the therapeutic effect is demonstrated weak. Therefore, we modified CAR with hexadecyl chain and polyethylene glycol, so as to realize its liposolubility and PEGylation. The synthesized amphiphilic CAR prodrugs could self-assemble into polymer micelles in water with an average particle size about 11.8 nm and low critical micelles concentration (0.0538 mg·mL^-1). In vivo pharmacodynamics and cytotoxicity experiment evidenced that the polymer micelles were equipped with preferable anti-tumor effect, finally attained the aim of elevating anti-tumor effect and prolonging retention time in vivo. The self-assembled micelles skillfully solve the shortcomings of weak efficacy of CAR, which provides a powerful platform for the application of chemical drug in oncology.