Improved targeting of platinum chemotherapeutics

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.

A nanoformulation of cisplatin with arabinoxylan having enhanced activity against hepatocellular carcinoma through upregulation of apoptotic and necroptotic pathways

Cisplatin is a versatile drug used to treat various types of cancer, but it is associated with high toxicity and resistance problems. Several approaches, including nanotechnology, have been adopted to minimize the toxic effects and to overcome the resistance of cisplatin. Most of the nanoformulations involve the use of synthetic or semisynthetic polymers as drug carriers. In this study arabinoxylan nanoparticles have been investigated as drug reservoirs for intestinal drug delivery. The drug-loaded arabinoxylan nanoparticles (size: ∼1.8 nm, polydispersity index: 0.3 ± 0.04) were prepared and nanoformulation was characterized by various analytical techniques. The nanoformulation was found to be stable (zeta potential: 31.6 ± 1.1 mV). An in vitro cytotoxicity against HepG2 and HEK 293 cell lines was studied. The cell viability analysis showed greater efficacy than the standard cisplatin (IC50: cisplatin 2.4, arabinoxylan nanoformulation 1.3 μg mL-1). The expression profile of carcinogenic markers revealed a six-fold upregulation of MLKL and 0.9-fold down regulation of KRAS, suggesting the activation of the necroptotic pathway by the drug-loaded nanoparticles. The nanoformulation exhibited a sustained release of cisplatin with a cumulative release of ∼40 % (at pH 7.4) and ∼30 % (at pH 5.5) over a period of 12 h with very low initial burst. The study suggests that the use of the new nanoformulation can significantly reduce the required dose of cisplatin without compromising efficacy and more efficient release at basic pH.

Platinum-based targeted chemotherapies and reversal of cisplatin resistance in non-small cell lung cancer (NSCLC)

Lung cancer is the one of the most prevalent cancer in the world. It kills more people from cancer than any other cause and is especially common in underdeveloped nations. With 1.2 million instances, it is also the most prevalent cancer in men worldwide, making about 16.7% of the total cancer burden. Surgery is the main form of curative treatment for early-stage lung cancer. However, the majority of patients had incurable advanced non-small cell lung cancer (NSCLC) recurrence after curative purpose surgery, which is indicative of the aggressiveness of the illness and the dismal outlook. The gold standard of treatment for NSCLC patients includes drug targeting of specific mutated genes drive in development of lung cancer. Furthermore, patients with advanced NSCLC and those with early-stage illness needing adjuvant therapy should use cisplatin as it is the more active platinum drug. So, this review encompasses the non-small cell lung cancer microenvironment, treatment approaches, and use of cisplatin as a first-line regimen for NSCLC, its mechanism of action, cisplatin resistance in NSCLC and also the prevention strategies to revert the drug resistance.

Cisplatin-Loaded Tobacco Mosaic Virus for Ovarian Cancer Treatment

Ovarian cancer is the foremost cause of gynecological cancer and a major cause of cancer death in women. Treatment for advanced stage is surgical debulking followed by chemotherapy; however, most patients relapse with more aggressive and therapy-resistant tumors. There is a need to develop drug delivery approaches to deliver platinum therapies to tumors to increase efficacy while maintaining safety. Toward this goal, we utilized the protein nanotubes from the plant virus, tobacco mosaic virus (TMV), as a drug carrier. Specifically, the nanochannel of TMV was loaded with the active dication form of cisplatin (cisPt²⁺), making use of the negatively charged Glu acid side chains that line the interior channel of TMV. We achieved a loading efficiency with ∼2700 cisPt²⁺ per TMV; formulation stability was established with drug complexes stably loaded into the carrier for 2 months under refrigerated storage. TMV-cisPt maintained its efficacy against ovarian tumor cells with an IC₅₀ of ∼40 μM. TMV-cisPt exhibited superior efficacy vs free cisPt in ovarian tumor mouse models using intraperitoneal ID8-Defb29/Vegf-a-Luc (mouse) tumors and subcutaneous A2780 (human) xenografts. TMV-cisPt treatment led to reduced tumor burden and increased survival. Using ID8-Defb29/Vegf-a-Luc-bearing C57BL/6 mice, we also noted reduced tumor growth when animals were treated with TMV alone, which may indicate antitumor immunity induced by the immunomodulatory nature of the plant virus nanoparticle. Biodistribution studies supported the efficacy data, showing increased cisPt accumulation within tumors when delivered via the TMV carrier vs free cisPt administration. Finally, good safety profiles were noted. The study highlights the potential of TMV as a drug carrier against cancer and points to the opportunity to explore plant viruses as chemo-immuno combination cancer therapeutics.

Targeted nanomedicine in cisplatin-based cancer therapeutics

Since its license in 1978, cisplatin has proved to be one of the most successful chemotherapeutic agents in the world. However, two acute challenges facing cisplatin, resistance and toxicity, have resulted in a bottleneck of clinical application. Targeted nanomedicine shows great promise in delivering cisplatin for maximizing efficacy while minimizing off-target toxicity. This article surveyed the recent progress and challenges of targeted nanomedicine in managing resistance and toxicity of cisplatin in both fundamental and clinical aspects. Particularly, we focused on three major mechanisms counteracting cisplatin sensitivity (decreased intracellular accumulation, increased cisplatin deactivation, and enhanced DNA repair/translesion synthesis) and correspondingly highlighted a few representative approaches to increase cisplatin sensitivity through improving the intracellular concentration of cisplatin and implementing combination therapy. Moreover, the requirements for future advancements in cisplatin delivery systems are rendered with emphasis on (i) understanding of nano-bio interaction and post-accumulation biological effects instead of overwhelmingly improving tumor accumulation, (ii) development of stimuli-responsive and/or actively-targeted nanomedicines, (iii) optimization of combination therapy, (iv) novel combinations targeting tumor microenvironment and immunotherapy. We postulate that cisplatin-based nanomedicines will continuously advance and potentially revolutionize oncological treatment.

Nanoparticle formulations of cisplatin for cancer therapy

The genotoxic agent cisplatin, used alone or in combination with radiation and/or other chemotherapeutic agents, is an important first-line chemotherapy for a broad range of cancers. The clinical utility of cisplatin is limited both by intrinsic and acquired resistance and dose-limiting normal tissue toxicity. That cisplatin shows little selectivity for tumor versus normal tissue may be a critical factor limiting its value. To overcome the low therapeutic ratio of the free drug, macromolecular, liposomal, and nanoparticle drug delivery systems have been explored toward leveraging the enhanced permeability and retention effect and promoting delivery of cisplatin to tumors. Here, we survey recent advances in nanoparticle formulations of cisplatin, focusing on agents that show promise in preclinical or clinical settings. WIREs Nanomed Nanobiotechnol 2016, 8:776-791. doi: 10.1002/wnan.1390 For further resources related to this article, please visit the WIREs website.

Development of nanoscale approaches for ovarian cancer therapeutics and diagnostics

Ovarian cancer is the deadliest of all gynecological cancers and the fifth leading cause of death due to cancer in women. This is largely due to late-stage diagnosis, poor prognosis related to advanced-stage disease, and the high recurrence rate associated with development of chemoresistance. Survival statistics have not improved significantly over the last three decades, highlighting the fact that improved therapeutic strategies and early detection require substantial improvements. Here, we review and highlight nanotechnology-based approaches that seek to address this need. The success of Doxil, a PEGylated liposomal nanoencapsulation of doxorubicin, which was approved by the FDA for use on recurrent ovarian cancer, has paved the way for the current wave of nanoparticle formulations in drug discovery and clinical trials. We discuss and summarize new nanoformulations that are currently moving into clinical trials and highlight novel nanotherapeutic strategies that have shown promising results in preclinical in vivo studies. Further, the potential for nanomaterials in diagnostic imaging techniques and the ability to leverage nanotechnology for early detection of ovarian cancer are also discussed.

Nanocarriers for delivery of platinum anticancer drugs

Platinum based anticancer drugs have revolutionized cancer chemotherapy, and continue to be in widespread clinical use especially for management of tumors of the ovary, testes, and the head and neck. However, several dose limiting toxicities associated with platinum drug use, partial anti-tumor response in most patients, development of drug resistance, tumor relapse, and many other challenges have severely limited the patient quality of life. These limitations have motivated an extensive research effort towards development of new strategies for improving platinum therapy. Nanocarrier-based delivery of platinum compounds is one such area of intense research effort beginning to provide encouraging preclinical and clinical results and may allow the development of the next generation of platinum chemotherapy. This review highlights current understanding on the pharmacology and limitations of platinum compounds in clinical use, and provides a comprehensive analysis of various platinum-polymer complexes, micelles, dendrimers, liposomes and other nanoparticles currently under investigation for delivery of platinum drugs.

Cathepsin B-cleavable doxorubicin prodrugs for targeted cancer therapy (Review)

Doxorubicin (DOX) is one of the most effective cytotoxic anticancer drugs used for the treatment of hematological malignancies, as well as a broad range of solid tumors. However, the clinical applications of this drug have long been limited due to its severe dose-dependent toxicities. Therefore, DOX derivatives and analogs have been developed to address this issue. A type of DOX prodrug, cleaved by cathepsin B (Cat B), which is highly upregulated in malignant tumors and premalignant lesions, has been developed to achieve a higher DOX concentration in tumor tissue and a lower concentration in normal tissue, so as to enhance the efficacy and reduce toxicity to normal cells. In this review, we focused on Cat B-cleavable DOX prodrugs and discussed the efficacy of these prodrugs, demonstrated by preclinical and clinical developments.

Biological characterization of folate-decorated biodegradable polymer-platinum(II) complex micelles

A biodegradable and amphiphilic copolymer, poly(ethylene glycol)-block-poly(l-lactide-co-2-methyl-2-carboxyl-propylene carbonate) (mPEG-b-P(LA-co-MCC)), which contains pendant carboxyl groups, was chosen as a drug carrier for the active anticancer part (diaminocyclohexane platinum, DACH-Pt) of oxaliplatin to form mPEG-b-P(LA-co-MCC/Pt) complex. A folic acid-conjugated copolymer, folic acid-poly(ethylene glycol)-block-poly(L-lactide) (FA-PEG-PLA), with similar chemical structure was chosen for targeting. Multifunctional micelles were successfully prepared by a coassembling method. In vitro evaluation was performed by using SKOV-3 and MCF-7 cancer cells. In vivo blood clearance of platinum was studied, and the results show that micelles exhibit longer blood circulation after iv injection. Pt biodistribution was studied by measuring its levels in plasma, organs, and tumors, especially in tumor cell DNA, by atomic absorption and inductively coupled plasma mass spectrometry. Antitumor activity was assessed in mice bearing H22 liver cancers, and the results showed that the micelles with FA moieties exhibited greater antitumor efficacy than those without FA or oxaliplatin. Therefore, these novel multifunctional platinum micelles have great potential in future clinical application.

Cholesterol-tethered platinum II-based supramolecular nanoparticle increases antitumor efficacy and reduces nephrotoxicity

Nanoscale drug delivery vehicles have been harnessed extensively as carriers for cancer chemotherapeutics. However, traditional pharmaceutical approaches for nanoformulation have been a challenge with molecules that exhibit incompatible physicochemical properties, such as platinum-based chemotherapeutics. Here we propose a paradigm based on rational design of active molecules that facilitate supramolecular assembly in the nanoscale dimension. Using cisplatin as a template, we describe the synthesis of a unique platinum (II) tethered to a cholesterol backbone via a unique monocarboxylato and O→Pt coordination environment that facilitates nanoparticle assembly with a fixed ratio of phosphatidylcholine and 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[amino (polyethylene glycol)-2000]. The nanoparticles formed exhibit lower IC(50) values compared with carboplatin or cisplatin in vitro, and are active in cisplatin-resistant conditions. Additionally, the nanoparticles exhibit significantly enhanced in vivo antitumor efficacy in murine 4T1 breast cancer and in K-Ras(LSL/+)/Pten(fl/fl) ovarian cancer models with decreased systemic- and nephro-toxicity. Our results indicate that integrating rational drug design and supramolecular nanochemistry can emerge as a powerful strategy for drug development. Furthermore, given that platinum-based chemotherapeutics form the frontline therapy for a broad range of cancers, the increased efficacy and toxicity profile indicate the constructed nanostructure could translate into a next-generation platinum-based agent in the clinics.

Synthetic polymers as drug-delivery vehicles in medicine

Cancerous diseases present a formidable health problem worldwide. While the chemotherapy of cancer, in conjunction with other treatment modalities, has reached a significant level of maturity, efficacious use of such agents is still restricted by numerous pharmacological deficiencies, such as poor water solubility, short serum circulation lifetimes, and low bioavailability resulting from lack of affinity to cancer tissue and inadequate mechanisms of cell entry. More critically still, most drugs suffer from toxic side effects and a risk of drug resistance. The class of platinum anticancer drugs, although outstandingly potent, is particularly notorious in that respect. Among the countless methods developed in recent years in an effort to overcome these deficiencies, the technology of polymer-drug conjugation stands out as a particularly advanced treatment modality. The strategy involves the bioreversible binding, conjugating, of a medicinal agent to a water-soluble macromolecular carrier. Following pharmacokinetic pathways distinctly different from those of the common, nonpolymeric drugs, the conjugate so obtained will act as a prodrug providing safe transport of the bioactive agent to and into the affected, that is, cancerous cell for its ultimate cell-killing activity. The present treatise will acquaint us with the pharmacological fundamentals of this drug delivery approach, applied here specifically to the metalorganic platinum-type drug systems and the organometallic ferrocene drug model. We will see just how this technology leads to conjugates distinctly superior in antiproliferative activity to cisplatin, a clinically used antitumor agent used here as a standard. Polymer-drug conjugation involving metal-based and other medicinal agents has unquestionably matured to a practical tool to the pharmaceutical scientist, and all indications point to an illustrious career for this nascent drug delivery approach in the fight against cancer and other human maladies.

Rationally engineered polymeric cisplatin nanoparticles for improved antitumor efficacy

The use of cisplatin, a first line chemotherapy for most cancers, is dose-limited due to nephrotoxicity. While this toxicity can be addressed through nanotechnology, previous attempts at engineering cisplatin nanoparticles have been limited by the impact on the potency of cisplatin. Here we report the rational engineering of a novel cisplatin nanoparticle by harnessing a novel polyethylene glycol-functionalized poly-isobutylene-maleic acid (PEG-PIMA) copolymer, which can complex with cis-platinum (II) through a monocarboxylato and a coordinate bond. We show that this complex self-assembles into a nanoparticle, and exhibits an IC(50) = 0.77 ± 0.11 µM comparable to that of free cisplatin (IC(50) = 0.44 ± 0.09 µM). The nanoparticles are internalized into the endolysosomal compartment of cancer cells, and release cisplatin in a pH-dependent manner. Furthermore, the nanoparticles exhibit significantly improved antitumor efficacy in a 4T1 breast cancer model in vivo, with limited nephrotoxicity, which can be explained by preferential biodistribution in the tumor with reduced kidney concentrations. Our results suggest that the PEG-PIMA-cisplatin nanoparticle can emerge as an attractive solution to the challenges in cisplatin chemotherapy.

Harnessing structure-activity relationship to engineer a cisplatin nanoparticle for enhanced antitumor efficacy

Cisplatin is a first line chemotherapy for most types of cancer. However, its use is dose-limited due to severe nephrotoxicity. Here we report the rational engineering of a novel nanoplatinate inspired by the mechanisms underlying cisplatin bioactivation. We engineered a novel polymer, glucosamine-functionalized polyisobutylene-maleic acid, where platinum (Pt) can be complexed to the monomeric units using a monocarboxylato and an O --> Pt coordinate bond. We show that at a unique platinum to polymer ratio, this complex self-assembles into a nanoparticle, which releases cisplatin in a pH-dependent manner. The nanoparticles are rapidly internalized into the endolysosomal compartment of cancer cells, and exhibit an IC50 (4.25 +/- 0.16 microM) comparable to that of free cisplatin (3.87 +/- 0.37 microM), and superior to carboplatin (14.75 +/- 0.38 microM). The nanoparticles exhibited significantly improved antitumor efficacy in terms of tumor growth delay in breast and lung cancers and tumor regression in a K-ras(LSL/+)/Pten(fl/fl) ovarian cancer model. Furthermore, the nanoparticle treatment resulted in reduced systemic and nephrotoxicity, validated by decreased biodistribution of platinum to the kidney as quantified using inductively coupled plasma spectroscopy. Given the universal need for a better platinate, we anticipate this coupling of nanotechnology and structure-activity relationship to rationally reengineer cisplatin could have a major impact globally in the clinical treatment of cancer.

ProLindac (AP5346): a review of the development of an HPMA DACH platinum Polymer Therapeutic

ProLindac (AP5346) is DACH (diaminocyclohexane) platinum polymer prodrug currently in phase II clinical development. It uses a 25 kDa polymer delivery vehicle based on hydroxypropylmethacrylamide (HPMA) to target the active form of the approved drug oxaliplatin to tumors. The pH-sensitive linker that binds platinum to the polymer releases platinum more rapidly in low pH environments, as found typically in many tumors. This review summarizes the development of ProLindac to date, including preclinical efficacy studies, the phase I monotherapy clinical study in patients with solid tumors, and the phase I/II monotherapy study in patients with recurrent ovarian cancer. Both preclinical and clinical study data indicate that ProLindac exhibits efficacy at least equal to, and likely superior to oxaliplatin, while demonstrating excellent tolerability. Additional clinical studies of ProLindac used in combination with other chemotherapeutic agents are planned.

Development of HPMA copolymer-anticancer conjugates: clinical experience and lessons learnt

The concept of polymer-drug conjugates was proposed more than 30 years ago, and an N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer conjugate of doxorubicin covalently bound to the polymer backbone by a Gly-Phe-Leu-Gly peptidyl linker (FCE28068) became the first synthetic polymer-based anticancer conjugate to enter clinical trial in 1994. This conjugate arose from rational design attempting to capitalise on passive tumour targeting by the enhanced permeability and retention effect and, at the cellular level, lysosomotropic drug delivery to improve therapeutic index. Early clinical results were promising, confirming activity in chemotherapy refractory patients and the safety of HPMA as a new polymer platform. Subsequent Phase I/II trials have investigated an HPMA copolymer-based conjugate containing a doxorubicin and additionally galactose as a targeting moiety to promote liver targeting (FCE28069), and also HPMA copolymer conjugates of paclitaxel (PNU 166945), camptothecin (PNU 166148) and two platinates (AP5280 and AP5346- ProLindac). The preclinical and clinical observations made in these, and clinical studies with other polymer conjugates, should shape the development of next generation anticancer polymer therapeutics.

Development of chitosan-ellagic acid films as a local drug delivery system to induce apoptotic death of human melanoma cells

This study was designed to develop a local chemotherapy device using chitosan as a local drug carrier and ellagic acid (EA) as an anticancer drug. We fabricated chitosan-ellagic acid (Ch-EA) films with concentrations of 0, 0.05, 0.1, 0.5, and 1% (w/v) of EA and examined the films using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and contact angle measurement. The WM115 human melanoma cell line as a skin cancer model was used to evaluate cell response to the films with the MTS assay and apoptosis assay, and HS68 human newborn fibroblast cell line as a control. With the increase in the concentration of the EA, the composite films exhibit increasing amide and ester groups and diffraction peaks of the crystallized EA and greater surface roughness and hydrophilicity. The chitosan films with 0.5 and 1% (w/v) of EA were found to have a potent antiproliferative effect on the melanoma cells by inducing apoptotic cell death. Localized effect of composites on cell behaviors has been clearly demonstrated. Our study demonstrated that the novel Ch-EA film can be potentially used in local chemotherapy.

Polymeric drug delivery of platinum-based anticancer agents

Platinum-based anticancer agents such as cisplatin and carboplatin are in widespread clinical use but associated with many side effects. Improving the delivery of cytotoxic platinum compounds may lead to reduced side effects and achieve greater efficacy at lower doses. Polymer-based therapeutics have been investigated as potential drug delivery vehicles for platinum-based drugs. Against a background of the chemistry and pharmacology of cytotoxic platinum compounds, this review discusses the formation and properties of platinum-polymer complexes, dendrimers, micelles, and microparticulates.

Preclinical efficacy studies of a novel nanoparticle-based formulation of paclitaxel that out-performs Abraxane

Purpose

Poly-(γ-l-glutamylglutamine)–paclitaxel (PGG–PTX) is a novel polymer-based formulation of paclitaxel (PTX) in which the PTX is linked to the polymer via ester bonds. PGG–PTX is of interest because it spontaneously forms very small nanoparticles in plasma. In mouse models, PGG–PTX increased tumor exposure to PTX by 7.7-fold relative to that produced by PTX formulated in Cremophor. In this study, the efficacy of PGG–PTX was compared to that of Abraxane, an established nanoparticular formulation of PTX, in three different tumor models.

Methods

Efficacy was quantified by delay in tumor growth of NCI H460 human lung cancer, 2008 human ovarian cancer and B16 melanoma xenografts growing in athymic mice following administration of equitoxic doses of PGG–PTX and Abraxane administered on either a single dose or every 7 day schedule. Toxicity was assessed by change in total body weight.

Results

The efficacy and toxicity of PGG–PTX was shown to increase with dose in the H460 model. PGG–PTX was ~1.5-fold less potent than Abraxane. PGG–PTX produced statistically significantly greater inhibition of tumor growth than Abraxane in all three tumor models when mice were given single equitoxic doses of drug. When given every 7 days for 3 doses, PGG–PTX produced greater inhibition of tumor growth while generating much less weight loss in mice bearing H460 tumors.

Conclusion

PGG–PTX has activity that is superior to that of Abraxane in multiple tumor models. PGG–PTX has the potential to out-perform Abraxane in enhancing the delivery of PTX tumors while at the same time further reducing the toxicity of both single dose and weekly treatment regimens.

Pharmacokinetics and tissue distribution of PGG-paclitaxel, a novel macromolecular formulation of paclitaxel, in nu/nu mice bearing NCI-460 lung cancer xenografts

Purpose

PGG–PTX is a water-soluble formulation of paclitaxel (PTX), made by conjugating PTX to poly(l-γ-glutamylglutamine) acid (PGG) via ester bonds, that spontaneously forms a nanoparticle in aqueous environments. The purpose of this study was to compare the pharmacokinetics and tissue distribution of PTX following injection of either free PTX or PGG–PTX in mice.

Experimental design

Both [³H]PTX and PGG–[³H]PTX were administered as an IV bolus injection to mice bearing SC NCI-H460 lung cancer xenografts at a dose of 40-mg PTX equivalents/kg. Plasma, tumor, major organs, urine, and feces were collected at intervals out to 340 h. Total taxanes, taxane extractable into ethyl acetate, and native PTX were quantified by liquid scintillation counting and HPLC.

Results

Conjugation of PTX to the PGG polymer increased plasma and tumor C_max, prolonged plasma half-life and the period of accumulation in tumor, and reduced washout from tumor. In plasma injection of PGG–PTX increased total taxane AUC_0–340 by 23-fold above that attained with PTX. In tumors, it increased the total taxane by a factor of 7.7, extractable taxane by 5.7, and native PTX by a factor of 3.5-fold. Conjugation delayed and reduced total urinary and fecal excretion of total taxanes.

Conclusions

Incorporation of PTX into the PGG–PTX polymer significantly prolonged the half-life of total taxanes, extractable taxane, and native PTX in both the plasma and tumor compartments. This resulted in a large increase in the amount of active PTX delivered to the tumor. PGG–PTX is an attractive candidate for further development.

Degradable Cisplatin-Releasing Core-Shell Nanogels from Zwitterionic Poly(β -Aminoester)-Graft-PEG for Cancer Chemotherapy

Cisplatin conjugated onto macromolecules or loaded in micelles can be preferentially delivered to tumors to minimize its toxicity to healthy tissues and increase its drug efficacy. Herein, we report cisplatin-containing nanogels possibly useful for targeted delivery of cisplatin. Carboxylic acid-functionalized poly(beta -aminoester)graft-poly(ethylene glycol) copolymers were synthesized by cocondensation polymerization of piperazine with 2,2-bis(acryloxymethyl)propionic acid, PEG 2,2-bis(acryloxymethyl)propionate macromonomer (mPEG). The graft copolymers formed 100-200 nm nanogels with low size-distribution by the complexation of their carboxylic groups with cisplatin. The nanogels were negatively charged and had a PEG outer layer. Thus, they had "stealth properties" suitable for in vivo applications. The nanogels had significantly lower in vitro cytotoxicity to SKOV-3 ovarian cancer cells than free cisplatin, but similar anticancer activity toward SKOV-3 tumors xenografted to immunocompromised mice.

Optimization of (1,2-diamino-cyclohexane)platinum(II)-loaded polymeric micelles directed to improved tumor targeting and enhanced antitumor activity

Polymeric micelles are promising nanocarriers, which might enhance the efficacy of antitumor drugs. Herein, polymeric micelles incorporating dichloro(1,2-diamino-cyclohexane)platinum(II) (DACHPt), the oxaliplatin parent complex, were prepared through the polymer-metal complex formation of DACHPt with poly(ethylene glycol)-b-poly(glutamic acid) [PEG-b-P(Glu)] block copolymer having different lengths of the poly(glutamic acid) block [p(Glu): 20, 40, and 70 U]. The resulting micelles were studied with the aim of optimizing the system's biological performance. DACHPt-loaded micelles (DACHPt/m) were approximately 40 nm in diameter and had a narrow size distribution. In vivo biodistribution and antitumor activity experiments (CDF1 mice bearing the murine colon adenocarcinoma C-26 inoculated subcutaneously) showed 20-fold greater accumulation of DACHPt/m at the tumor site than free oxaliplatin to achieve substantially higher antitumor efficacy. Moreover, the micelles prepared from PEG-b-P(Glu) with 20 U of P(Glu) exhibited the lowest non-specific accumulation in the liver and spleen to critically reduce non-specific accumulation, resulting in higher specificity to solid tumors. The antitumor effect of DACHPt/m was also evaluated on multiple metastases generated from intraperitoneally injected bioluminescent HeLa (HeLa-Luc) cells. The in vivo bioluminescent data indicated that DACHPt/m decreased the signal 10-to 50-fold compared to the control indicating a very strong antitumor activity. These results suggest that DACHPt/m could be an outstanding drug delivery system for oxaliplatin in the treatment of solid tumors.

Acidic hydrolysis of N-Ethoxybenzylimidazoles (NEBIs): potential applications as pH-sensitive linkers for drug delivery

This paper describes the development of a new class of N-linked imidazoles as potential pH-sensitive, cleavable linkers for use in cancer drug delivery systems. Kinetic analysis of eight derivatives of N-ethoxybenzylimidazoles (NEBIs) showed that their rates of hydrolysis are accelerated in mild aqueous acidic solutions compared to in solutions at normal, physiological pH. Incorporation of electron donating or electron withdrawing substituents on the phenyl ring of the NEBI resulted in the ability to tune the rates of hydrolysis under mild acidic conditions with half-lives ranging from minutes to months. A derivative of NEBI carrying doxorubicin, a widely used anticancer agent, also showed an increased rate of hydrolysis under mild acid compared to that at normal physiological pH. The doxorubicin analogue resulting from hydrolysis from the NEBI exhibited good cytotoxic activity when exposed to human ovarian cancer cells. These results demonstrate a potentially useful, general strategy for conjugating a wide range of drugs to imidazole-containing delivery vessels via NEBI functionalities for controlled release of therapeutics for drug delivery applications.

Cisplatin delivery from poly(acrylic acid-co-methyl methacrylate) microparticles

To develop a platform for tumor chemotherapy, poly(acrylic acid-co-methyl methacrylate) microparticles have been synthesized. Carboxylate containing monomers were included to complex therapeutic agents, specifically cisplatin. Microparticles were prepared by free radical emulsion polymerization in aqueous media. Particle diameter, zeta-potential, in vitro cytotoxicity, and in vivo acute toxicity were characterized for both cisplatin-loaded microparticles and unloaded microparticles. In vitro cytotoxicity and FT-IR were used to characterize cisplatin released from cisplatin-loaded microparticles. Acrylic acid feed mole fraction determined several key microparticle properties, including particle size, zeta-potential, and yield. A burst release of cisplatin (40%) in the first day was followed by a zero-order release phase. The interaction between cisplatin and microparticles allowed approximately 20% additional cisplatin release in the next five days. Cisplatin-loaded and unloaded microparticles are non-toxic (LC50>15 mM) to the cell line used in in vitro tests. Cisplatin released from cisplatin-loaded microparticles retained activity, but that activity was slightly lower than freshly prepared cisplatin. Other than a slight reduction in cisplatin activity, microparticles exhibited low in vivo acute toxicity (LD50>170 mg/kg), which suggests that this hydrogel particulate system and the hydrogel complexation mechanism should further be studied for drug delivery.

Effect of physicochemical modification on the biodistribution and tumor accumulation of HPMA copolymers

Copolymers of N-(2-hydroxypropyl)methacrylamide (HPMA) are prototypic and well-characterized polymeric drug carriers that are being broadly implemented in the delivery of anticancer therapeutics. To better predict the in vivo potential of the copolymers and to describe the biodistributional consequences of functionalization, 13 physicochemically different HPMA copolymers were synthesized, varying in molecular weight and in the nature and amount of functional groups introduced. Upon radiolabeling, the copolymers were injected i.v., and their circulation kinetics, tissue distribution and tumor accumulation were monitored in rats bearing subcutaneous Dunning AT1 tumors. It was found that increasing the average molecular weight of HPMA copolymers resulted in prolonged circulation times and in increased tumor concentrations. Conjugation of carboxyl and hydrazide groups, as well as introduction of spacer, drug and peptide moieties reduced the long-circulating properties of the copolymers and as a result, lower levels were found in tumors and in all organs other than kidney. Interestingly, however, in spite of the reduced (absolute) tumor concentrations, hardly any reduction in the relative levels localizing to tumors was found. Tumor-to-organ ratios were comparable to unmodified control for the majority of chemically modified copolymers, indicating that functionalization does not necessarily affect the tumor targeting ability of the copolymers and suggesting that HPMA copolymer-based drug delivery systems may prove to be attractive tools for more effectively treating various forms of advanced solid malignancy.