Kinetics of lactone hydrolysis in antitumor drugs of camptothecin series as studied by fluorescence spectroscopy

Quadruplex-duplex junction in LTR-III: A molecular insight into the complexes with BMH-21, namitecan and doxorubicin

Quadruplex-Duplex (Q-D) junctions are unique structural motifs garnering increasing interest as drug targets, due to their frequent occurrence in genomic sequences. The viral HIV LTR-III sequence was chosen as a Q-D junction model to study the affinity of the selected compounds BMH-21, namitecan (ST-1968), and doxorubicin (DOXO), all containing a planar polycyclic aromatic moiety, linked to either one short aminoalkyl or an aminoglycosyl group. A multidisciplinary approach that combines NMR spectroscopy, molecular modelling, circular dichroism (CD) and fluorescence spectroscopy was employed. The studied ligands induced moderate but clear stabilization to the Q-D junction by interacting with the interfacial tetrad. DOXO was found to be the best Q-D junction binder. Interestingly, the removal of the aminoglycosyl group significantly changed the pattern of the interactions, indicating that highly polar substituents have a stronger affinity with the exposed regions of the Q-D junction, particularly at the level of the interfacial tetrad.

Phosphorus and Silicon-Based Macromolecules as Degradable Biomedical Polymers

Synthetic polymers are indispensable in biomedical applications because they can be fabricated with consistent and reproducible properties, facile scalability, and customizable functionality to perform diverse tasks. However, currently available synthetic polymers have limitations, most notably when timely biodegradation is required. Despite there being, in principle, an entire periodic table to choose from, with the obvious exception of silicones, nearly all known synthetic polymers are combinations of carbon, nitrogen, and oxygen in the main chain. Expanding this to main-group heteroatoms can open the way to novel material properties. Herein the authors report on research to incorporate the chemically versatile and abundant silicon and phosphorus into polymers to induce cleavability into the polymer main chain. Less stable polymers, which degrade in a timely manner in mild biological environments, have considerable potential in biomedical applications. Herein the basic chemistry behind these materials is described and some recent studies into their medical applications are highlighted.

Discovery of indolizine lactones as anticancer agents and their optimization through late-stage functionalization

Indolizines fused with a seven-member lactone ring were identified as a promising scaffold in the search for new anticancer agents. Through a modular synthetic sequence, a library of cis and trans indolizines lactones had their antiproliferative activity evaluated against hormone-refractory prostate DU-145 and triple-negative breast MDA-MB-231 cancer cell lines. A methoxylated analogue was identified as an initial hit against MDA-MB-231 and late-stage functionalization of the indolizine core led to analogues within potencies up to twenty times higher than the parent precursor.

In Situ Encapsulation of Camptothecin by Self-Assembly of Poly(acrylic acid)-b-Poly(N-Isopropylacrylamide) and Chitosan for Controlled Drug Delivery

Camptothecin (CPT) has been shown to exhibit anticancer activity against several cancers. Nevertheless, CPT is very hydrophobic with poor stability, and thus its medical application is limited. Therefore, various drug carriers have been exploited for effectively delivering CPT to the targeted cancer site. In this study, a dual pH/thermo-responsive block copolymer of poly(acrylic acid-b-N-isopropylacrylamide) (PAA-b-PNP) was synthesized and applied to encapsulate CPT. At temperatures above its cloud point, the block copolymer self-assembled to form nanoparticles (NPs) and in situ encapsulate CPT, owing to their hydrophobic interaction as evidenced by fluorescence spectrometry. Chitosan (CS) was further applied on the surface through the formation of a polyelectrolyte complex with PAA for improving biocompatibility. The average particle size and zeta potential of the developed PAA-b-PNP/CPT/CS NPs in a buffer solution were 168 nm and -30.6 mV, respectively. These NPs were still stable at least for 1 month. The PAA-b-PNP/CS NPs exhibited good biocompatibility toward NIH 3T3 cells. Moreover, they could protect the CPT at pH 2.0 with a very slow-release rate. At pH 6.0, these NPs could be internalized by Caco-2 cells, followed by intracellular release of the CPT. They became highly swollen at pH 7.4, and the released CPT was able to diffuse into the cells at higher intensity. Among several cancer cell lines, the highest cytotoxicity was observed for H460 cells. As a result, these environmentally-responsive NPs have the potential to be applied in oral administration.

Optical properties of natural small molecules and their applications in imaging and nanomedicine

Natural small molecules derived from plants have fascinated scientists for centuries due to their practical applications in various fields, especially in nanomedicine. Some of the natural molecules were found to show intrinsic optical features such as fluorescence emission and photosensitization, which could be beneficial to provide spatial temporal information and help tracking the drugs in biological systems. Much efforts have been devoted to the investigation of optical properties and practical applications of natural molecules. In this review, optical properties of natural small molecules and their applications in fluorescence imaging, and theranostics will be summarized. First, we will introduce natural small molecules with different fluorescence emission, ranging from blue to near infrared emission. Second, imaging applications in biological samples will be covered. Third, we will discuss the applications of theranostic nanomedicines or drug delivering systems containing fluorescent natural molecules acting as imaging agents or photosensitizers. Finally, future perspectives in this field will be discussed.

Antimicrobial Activity of Ca-Alginate/Chitosan Nanocomposite Loaded with Camptothecin

The main aim of this study was to prepare antimicrobial nanocomposites consisting of alginate, chitosan, and camptothecin (CPT). CPT-loaded calcium alginate (Ca-Alg₂) and calcium alginate/chitosan (Ca-Alg₂-CH) nanomaterials were synthesized and characterized using infrared (IR) spectroscopy, X-ray diffraction (XRD), UV-Vis spectroscopy, and scanning electron microscopy (SEM). The antimicrobial activity and the genetic effects of Ca-Alg₂/CPT and Ca-Alg₂-CH/CPT nanomaterials on Staphylococcus aureus, Escherichia coli, and Klebsiella pneumonia were studied. The repetitive element polymerase chain reaction analysis technique was used to assess the changes in the bacterial genetic material due to the processing of the nanomaterials. The results showed the presence of a strong chemical interaction between alginate and chitosan, and CPT was loaded successfully in both Ca-Alg₂/CPT and Ca-Alg₂-CH/CPT nanomaterials. Furthermore, the antimicrobial test showed that the Ca-Alg₂/CPT nanocomposite was susceptible to S. aureus, E. coli, and K. pneumonia; on the other hand, Ca-Alg₂-CH/CPT nanocomposite was more susceptible to E. coli and K. pneumonia and was resistant to S. aureus. The results showed that the Ca-Alg₂/CPT nanocomposite was less efficient than Ca-Alg₂-CH/CPT nanocomposite in killing Gram-negative treated bacteria. Moreover, results revealed that the PCR analysis revealed a polymorphic banding pattern. This observation provides an excellent guide to the ability of some polymers to induce point mutations in DNA.

Cancer theranostic platforms based on injectable polymer hydrogels

Theranostic platforms that combine therapy with diagnosis not only prevent the undesirable biological responses that may occur when these processes are conducted separately, but also allow individualized therapies for patients. Polymer hydrogels have been employed to provide well-controlled drug release and targeted therapy in theranostics, where injectable hydrogels enable non-invasive treatment and monitoring with a single injection, offering greater patient comfort and efficient therapy. Efforts have been focused on applying injectable polymer hydrogels in theranostic research and clinical use. This review highlights recent progress in the design of injectable polymer hydrogels for cancer theranostics, particularly focusing on the elements/components of theranostic hydrogels, and their cross-linking strategies, structures, and performance with regard to drug delivery/tracking. Therapeutic agents and tracking modalities that are essential components of the theranostic platforms are introduced, and the design strategies, properties and applications of the injectable hydrogels developed via two approaches, namely chemical bonds and physical interactions, are described. The theranostic functions of the platforms are highly dependent on the architecture and components employed for the construction of hydrogels. Challenges currently presented by theranostic platforms based on injectable hydrogels are identified, and prospects of acquiring more comfortable and personalized therapies are proposed.

Hyaluronic Acid-Coated Camptothecin Nanocrystals for Targeted Drug Delivery to Enhance Anticancer Efficacy

Tumor-targeted drug delivery via chemotherapy is very effective on cancer treatment. For potential anticancer agent such as Camptothecin (CPT), high chemotherapeutic efficacy and accurate tumor targeting are equally crucial. Inspired by special CD44 binding capability from hyaluronic acid (HA), in this study, novel HA-coated CPT nanocrystals were successfully prepared by an antisolvent precipitation method for tumor-targeted delivery of hydrophobic drug CPT. These HA-coated CPT nanocrystals demonstrated high drug loading efficiency, improved aqueous dispersion, prolonged circulation, and enhanced stability resulting from their nanoscaled sizes and hydrophilic HA layer. Moreover, as compared to crude CPT and naked CPT nanocrystals, HA-coated CPT nanocrystals displayed dramatically enhanced in vitro anticancer activity, apoptosis-inducing potency against CD44 overexpressed cancer cells, and lower toxic effect toward normal cells due to pH-responsive drug release behavior and specific HA-CD44 mediated endocytosis. Additionally, HA-coated CPT nanocrystals performed fairly better antimigration activity and biocompatibility. The possible molecular mechanism regarding this novel drug formulation might be linked to intrinsic mitochondria-mediated apoptosis by an increase of Bax to Bcl-2 ratio and upregulation of P53. Consequently, HA-coated CPT nanocrystals are expected to be an effective nanoplatform in drug delivery for cancer therapy.

PEAMOtecan, a novel chronotherapeutic polymeric drug for brain cancer

Glioblastoma multiforme (GBM) is an aggressive and difficult to treat form of brain cancer. In this work, we report on a novel chronotherapeutic polymeric drug, PEAMOtecan, for GBM therapy. PEAMOtecan was synthesized by conjugating camptothecin, a topoisomerase I inhibitor, to our proprietary, 'clickable' and modular polyoxetane polymer platform consisting of acetylene-functionalized 3-ethyl-3-(hydroxymethyl)oxetane (EAMO) repeat units (Patent No.: US 9,421,276) via the linker 3,3'-dithiodipropionic acid (DDPA) with a disulfide bond (SS) extended by short-chain polyethylene glycol (PEG). We show that PEAMOtecan is a highly modular polymer nanoformulation that protects covalently bound CPT until slowly being released over extended periods of time dependent on the cleavage of the disulfide and ester linkages. PEAMOtecan kills glioma cells by mitotic catastrophe with p53 mutant/knockdown cells being more sensitive than matched wild type cells potentially providing cancer-specific targeting. To establish proof-of-principle therapeutic effects, we tested PEAMOtecan as monotherapy for efficacy in a mouse orthotopic glioma model. PEAMOtecan was administered by one-time, convection-enhanced delivery (CED) intra-tumorally to achieve superior distribution and extended drug release over time. In addition, the near-infrared (NIR) dye Cy5.5 was coupled to the polymer providing live-animal imaging capability to track tissue distribution and clearance of the injected polymer over time. We show that PEAMOtecan significantly improves the survival of mice harboring intra-cranial tumors (p = .0074 compared to untreated group). Altogether, these results support further development and testing of our nanoconjugate platform.

A reversible decomposition approach for the formation of injectable, excipient-free, self-assembling nanocrystals

A chemical procedure to generate excipient-free SN38 nanocrystals with greater efficacy and less toxicity than CPT-11.

Developments in drug delivery of bioactive alkaloids derived from traditional Chinese medicine

The bioactive alkaloids (e.g. vincristine, hydroxycamptothecin, ligustrazine, and so on) from traditional Chinese medicine (TCM) have exerted potent efficacies (e.g. anti-tumor, anti-inflammation, immunosuppression, etc.). However, a series of undesirable physicochemical properties (like low solubility and weak stability) and baneful pharmacokinetic (PK) profiles (e.g. low bioavailability, short half time, rapid clearance, etc.) have severely restricted their applications in clinic. In addition, some side effects (like cumulative toxicities caused by high-frequency administration and their own toxicities) have recently been reported and also confined their clinical uses. Therefore, developments in drug delivery of such alkaloids are of significance in improving their drug-like properties and, thus, treatment efficiencies in clinic. Strategies, including (i) specific delivery via liposomes; (ii) sustained delivery via nanoparticles, gels, and emulsions; and (iii) transdermal delivery via ethosomes, solid lipid nanoparticles, and penetrating enhancers, have been reported to improve the pharmacokinetic and physicochemical characters of problematic TCM alkaloids, decline their adverse effects, and thus, boost their curative efficacies. In this review, the recent reports in this field were comprehensively summarized with the aim of providing an informative reference for relevant readers.

Nanomedicines for Malaria Chemotherapy: Encapsulation vs. Polymer Therapeutics

Malaria is one of the oldest infectious diseases that afflict humans and its history extends back for millennia. It was once prevalent throughout the globe but today it is mainly endemic to tropical regions like sub-Saharan Africa and South-east Asia. Ironically, treatment for malaria has existed for centuries yet it still exerts an enormous death toll. This contradiction is attributed in part to the rapid development of resistance by the malaria parasite to chemotherapeutic drugs. In turn, resistance has been fuelled by poor patient compliance to the relatively toxic antimalarial drugs. While drug toxicity and poor pharmacological potentials have been addressed or ameliorated with various nanomedicine drug delivery systems in diseases like cancer, no clinically significant success story has been reported for malaria. There have been several reviews on the application of nanomedicine technologies, especially drug encapsulation, to malaria treatment. Here we extend the scope of the collation of the nanomedicine research literature to polymer therapeutics technology. We first discuss the history of the disease and how a flurry of scientific breakthroughs in the latter part of the nineteenth century provided scientific understanding of the disease. This is followed by a review of the disease biology and the major antimalarial chemotherapy. The achievements of nanomedicine in cancer and other infectious diseases are discussed to draw parallels with malaria. A review of the current state of the research into malaria nanomedicines, both encapsulation and polymer therapeutics polymer-drug conjugation technologies, is covered and we conclude with a consideration of the opportunities and challenges offered by both technologies.

Practical fluorimetric assay for the detection of anticancer drug SN-38 in human plasma

The implementation of therapeutic drug monitoring in the routine clinical practice in oncology is mainly limited by the lack of therapeutic indexes for the majority of the anticancer drugs, and by the absence of suitable analytical tools, which can accurately quantify in real time the concentration of the administered drugs and their relevant metabolites in biological fluids. In this work, a simple and efficient fluorimetric determination of SN-38, the active metabolite of the anticancer drug irinotecan, was developed and applied to human plasma samples. The intrinsic fluorescence of SN-38 allowed its quantification in the range 10-500 ng mL^-1 with a LOQ of 5.0 ng mL^-1 and a LOD of 1.5 ng mL^-1. Low interferences due to main metabolites of irinotecan and comedications, commonly associated with administration of irinotecan, were observed. A validation study, according to FDA and EMA guidelines for bioanalytical method validation, was carried out and, finally, blind samples were analyzed in parallel with a HPLC-MS method obtaining an excellent agreement between the two techniques.

A new targeted delivery approach by functionalizing drug nanocrystals through polydopamine coating

Tumor target specificity via chemotherapy is widely considered to be very effective on tumor treatment. For an ideal chemotherapeutic agent like Camptothecin (CPT) (CPT is the abbreviation for Camptothecin), improved therapeutic efficacy and high selectivity are equally important. Inspired by adhesive proteins in mussels, here we developed a novel tumor targeting peptide XQ1 grafted CPT nanocrystals with polydopamine coating as a spacer. In this study, CPT nanocrystals were coated by polymerization of dopamine that was induced by plasma-activated water under an acidic environment, and then the tumor targeting peptide was grafted onto polydopamine (PDA) (PDA is the abbreviation for polydopamine) coated CPT nanocrystals through catechol chemistry. The PDA layer had negligible effects on drug crystallinity and structure but resulted in drug nanocrystals with excellent dispersion properties, improved dissolution rate and drug stability by preventing water hydrolysis. More importantly, tumor targeting peptide XQ1 facilitated a rapid cross-membrane translocation of drug nanocrystals via receptor-mediated endocytosis, leading to efficient intracellular drug delivery. Moreover, this novel drug formulation demonstrated more potent anti-cancer activity against tumor cells in comparison with free CPT and naked CPT nanocrystals and exhibited high selectivity, all of which are attributed to the tumor target specificity property and inherent pH-dependent drug release behavior.

Preparation of Two Types of Polymeric Micelles Based on Poly(β-L-Malic Acid) for Antitumor Drug Delivery

Polymeric micelles represent an effective delivery system for poorly water-soluble anticancer drugs. In this work, two types of CPT-conjugated polymers were synthesized based on poly(β-L-malic acid) (PMLA) derivatives. Folic acid (FA) was introduced into the polymers as tumor targeting group. The micellization behaviors of these polymers and antitumor activity of different self-assembled micelles were investigated. Results indicate that poly(ethylene glycol)-poly(β-L-malic acid)-campotothecin-I (PEG-PMLA-CPT-I, P1) is a grafted copolymer, and could form star micelles in aqueous solution with a diameter of about 97 nm, also that PEG-PMLA-CPT-II (P2) is an amphiphilic block copolymer, and could form crew cut micelles with a diameter of about 76 nm. Both P1 and P2 micelles could improve the cellular uptake of CPT, especially the FA-modified micelles, while P2 micelles showed higher stability, higher drug loading efficiency, smaller size, and slower drug release rate than that of P1 micelles. These results suggested that the P2 (crew cut) micelles possess better stability than that of the P1 (star) micelles and might be a potential drug delivery system for cancer therapy.

Cyclodextrin-based nanosponges: a versatile platform for cancer nanotherapeutics development

Nanosponges (NSs) are a new age branched cyclodextrin (CD) polymeric systems exhibiting tremendous potential in pharmaceutical, agro science, and biomedical applications. Over the past decade, different varieties of NS based on the type of CD and the crosslinker have been developed tailored for specific applications. NS technology has been instrumental in achieving solubilization, stabilization, sustained release, enhancement of activity, permeability enhancement, protein delivery, ocular delivery, stimuli sensitive drug release, enhancement of bioavailability, etc. There is a major explosion of research in the area of NS-aided cancer therapeutics. A wide of anticancer molecules both from a pharmacological and physicochemical perspective have been developed as NS formulations by several groups including ours. Our objective in this review is to capture a systematic and comprehensive snapshot of the state-of-the-art of NS-aided cancer therapeutics reported so far. This review will provide an ideal platform for both the formulation scientists working on new polymeric/drug development and cancer biologists/scientists to understand the current nanotechnologies in CD-based NS-aided cancer therapeutics. The scope of the review is limited to small molecules and CD-based NS. The review covers in detail the problems associated with anticancer small molecules, and the solution provided by CD-based NS specifically for camptothecin, curcumin, paclitaxel, tamoxifen, resveratrol, quercetin, oxygen-NS, temozolomide, doxorubicin, and 5-Fluorouracil. WIREs Nanomed Nanobiotechnol 2016, 8:579-601. doi: 10.1002/wnan.1384 For further resources related to this article, please visit the WIREs website.

Influence of supramolecular encapsulation of camptothecin by cucurbit[7]uril: reduced toxicity and preserved anti-cancer activity

Encapsulation of camptothecin by cucurbit[7]uril significantly inhibited the systemic toxicities of the free drug, while maintaining its antitumor/anti-angiogenic activities.

Polyprodrug amphiphiles: hierarchical assemblies for shape-regulated cellular internalization, trafficking, and drug delivery

Solution self-assembly of block copolymers (BCPs) typically generates spheres, rods, and vesicles. The reproducible bottom-up fabrication of stable planar nanostructures remains elusive due to their tendency to bend into closed bilayers. This morphological vacancy renders the study of shape effects on BCP nanocarrier-cell interactions incomplete. Furthermore, the fabrication of single BCP assemblies with built-in drug delivery functions and geometry-optimized performance remains a major challenge. We demonstrate that PEG-b-PCPTM polyprodrug amphiphiles, where PEG is poly(ethylene glycol) and PCPTM is polymerized block of reduction-cleavable camptothecin (CPT) prodrug monomer, with >50 wt % CPT loading content can self-assemble into four types of uniform nanostructures including spheres, large compound vesicles, smooth disks, and unprecedented staggered lamellae with spiked periphery. Staggered lamellae outperform the other three nanostructure types, exhibiting extended blood circulation duration, the fastest cellular uptake, and unique internalization pathways. We also explore shape-modulated CPT release kinetics, nanostructure degradation, and in vitro cytotoxicities. The controlled hierarchical organization of polyprodrug amphiphiles and shape-tunable biological performance opens up new horizons for exploring next-generation BCP-based drug delivery systems with improved efficacy.

Supramolecular nanostructures formed by anticancer drug assembly

We report here a supramolecular strategy to directly assemble the small molecular hydrophobic anticancer drug camptothecin (CPT) into discrete, stable, well-defined nanostructures with a high and quantitative drug loading. Depending on the number of CPTs in the molecular design, the resulting nanostructures can be either nanofibers or nanotubes, and have a fixed CPT loading content ranging from 23% to 38%. We found that formation of nanostructures provides protection for both the CPT drug and the biodegradable linker from the external environment and thus offers a mechanism for controlled release of CPT. Under tumor-relevant conditions, these drug nanostructures can release the bioactive form of CPT and show in vitro efficacy against a number of cancer cell lines. This strategy can be extended to construct nanostructures of other types of anticancer drugs and thus presents new opportunities for the development of self-delivering drugs for cancer therapeutics.

Preparation, characterization, and cytotoxicity of CPT/Fe₂O₃-embedded PLGA ultrafine composite fibers: a synergistic approach to develop promising anticancer material

The aim of this study was to fabricate camptothecin/iron(III) oxide (CPT/Fe₂O₃)-loaded poly(D,L-lactide-co-glycolide) (PLGA) composite mats to modulate the CPT release and to improve the structural integrity and antitumor activity of the released drug. The CPT/Fe₂O₃-loaded PLGA ultrafine fibers were prepared for the first time by electrospinning a composite solution of CPT/Fe₂O₃ and neat PLGA (4 weight percent). The physicochemical characterization of the electrospun composite mat was carried out by scanning electron microscopy, energy dispersive X-ray spectroscopy, electron probe microanalysis, thermogravimetry, transmission electron microscopy, ultraviolet-visible spectroscopy, and X-ray diffraction pattern. The medicated composite fibers were evaluated for their cytotoxicity on C2C12 cells using Cell Counting Kit-8 assay (Sigma-Aldrich Corporation, St Louis, MO). The in vitro studies indicated a slow and prolonged release over a period of 96 hours with mild initial burst. Scanning electron microscopy, thermogravimetry, and X-ray diffraction studies confirmed the interaction of CPT/Fe₂O₃ with the PLGA matrix and showed that the crystallinity of CPT decreased after loading. Incorporation of CPT in the polymer media affected both the morphology and the size of the CPT/Fe₂O₃-loaded PLGA composite fibers. Electron probe microanalysis and energy dispersive X-ray spectroscopy results confirmed well-oriented composite ultrafine fibers with good incorporation of CPT/Fe₂O₃. The cytotoxicity results illustrate that the pristine PLGA did not exhibit noteworthy cytotoxicity; conversely, the CPT/Fe₂O₃ composite fibers inhibited C2C12 cells significantly. Thus, the current work demonstrates that the CPT/Fe₂O₃-loaded PLGA composite fibers represent a promising chemotherapeutic system for enhancing anticancer drug efficacy and selectively targeting cancer cells in order to treat diverse cancers.

Soluplus--solubilized citrated camptothecin--a potential drug delivery strategy in colon cancer

Camptothecin (CPT), a potent antitumor drug, exhibits poor aqueous solubility and rapid conversion from the pharmacologically active lactone form to inactive carboxylate form at physiological pH. Solid dispersion of CPT in Soluplus®, an amphiphilic polymeric solubilizer, was prepared to increase the aqueous solubility of CPT and the resultant solid dispersion along with citric acid was formulated as hard gelatin capsules that were subsequently coated with Eudragit S100 polymer for colonic delivery. FTIR spectrum of the solid dispersion confirmed the presence of CPT. PXRD and DSC revealed the semicrystalline nature of solid dispersion. The solubility of the drug was found to increase ~40 times in the presence of Soluplus and ~75 times in solid dispersion. The capsules showed no drug release in 0.01 N HCl but released 86.4% drug in lactone form in phosphate buffer (pH 7.4) and the result appears to be due to citric acid-induced lowering of pH of buffer from 7.4 to 6.0. Thus the presence of citric acid in the formulation led to stabilization of the drug in its pharmacologically active lactone form. Cytotoxicity studies conducted with the formulation of solid dispersion with citric acid, utilizing cell cytotoxicity test (MTT test) on Caco-2 cells, confirmed cytotoxic nature of the formulation.

Antitumor activity of peptide amphiphile nanofiber-encapsulated camptothecin

Self-assembling peptide amphiphile (PA) nanofibers were used to encapsulate camptothecin (CPT), a naturally occurring hydrophobic chemotherapy agent, using a solvent evaporation technique. Encapsulation by PA nanofibers was found to improve the aqueous solubility of the CPT molecule by more than 50-fold. PAs self-assembled into nanofibers in the presence of CPT as demonstrated by transmission electron microscopy. Small-angle X-ray scattering results suggest a slight increase in diameter of the nanofiber to accommodate the hydrophobic cargo. In vitro studies using human breast cancer cells show an enhancement in antitumor activity of the CPT when encapsulated by the PA nanofibers. In addition, using a mouse orthotopic model of human breast cancer, treatment with PA nanofiber-encapsulated CPT inhibited tumor growth. These results highlight the potential of this model PA system to be adapted for delivery of hydrophobic therapies to treat a variety of diseases including cancer.

Modified hydrolysis kinetics of the active lactone moiety of 10-hydroxycamptothecin by liposomal encapsulation

The key structural requirement for the antitumor activity of 10-hydroxycamptothecin (HCPT) is the intact lactone moiety which is always instability and suffered from pH-dependent hydrolysis. The aim of this study was to evaluate the protection effects of liposomal encapsulation on the labile lactone ring. Mono-modal dispersed quasi-spherical liposomes with mean diameter of 145 nm and high drug entrapment efficiency of 90% were obtained under optimal conditions. The in vitro hydrolysis kinetics behaviors of lactone were studied in varied pH buffers. Compared to that of free HCPT in solution formulation, both the hydrolysis half-life and observed equilibrium constant of liposomal HCPT were increased significantly along with the decreased apparent hydrolysis rate constant. The plasma pharmacokinetics was studied by assessing the lactone stability versus time profiles in vivo following intravenous administration of free and liposomal HCPT. The liposomal encapsulation led to a twofold increase in the AUC values and significant decrease in the plasma clearance of lactone (P < 0.05). There was a good correlation between in vitro and in vivo stability of HCPT-lactone. These results suggested a potential application of the novel liposome formulation for the stable delivery system of HCPT.

PEGylated nanostructured lipid carriers loaded with 10-hydroxycamptothecin: an efficient carrier with enhanced anti-tumour effects against lung cancer

Most drugs do not have the pharmacokinetic features required for optimal pulmonary delivery. In this study, we developed PEGylated nanostructured lipid carriers (PEG-NLCs) to improve the delivery of anti-tumour agents to lung tumours. PEG-40 NLCs modified with PEG-40 stearate (molecular weight 2000 Da), PEG-100 NLCs modified with PEG-100 stearate (molecular weight 5000 Da) and NLCs without PEG modification were prepared by melt-emulsification and homogenization, and were loaded with 10-hydroxycamptothecin (HCPT). They were investigated in terms of physiological characteristics, biodistribution, cellular uptake, and anti-tumour effect in-vivo. PEG-NLCs exhibited regular morphology, with a spherical shape. The particle size (measured by laser diffraction) was approximately 100 nm. Encapsulation in PEG-NLCs protected the active lactone form of HCPT compared with HCPT solution after incubation with plasma. In biodistribution studies, PEG-NLCs, especially PEG-40 NLCs, had longer circulation time and decreased uptake by the reticuloendothelial system (RES) compared with unmodified NLCs. PEG-NLCs accumulated in the lungs after i.v. injection in mice. PEG-NLCs showed enhanced cellular uptake by human lung adenocarcinoma epithelial A549 cells. In-vivo experiments indicated that PEG-NLCs loaded with HCPT have superior efficacy against A549 lung cancer compared with HCPT solution and NLCs. These results suggest that PEG-NLCs is a promising delivery system for HCPT in the treatment of lung cancer.

Phase I trial of poly-L-glutamate camptothecin (CT-2106) administered weekly in patients with advanced solid malignancies

PURPOSE

CT-2106 is a 20(S)-camptothecin poly-L-glutamate conjugate. This linkage stabilizes the active lactone form of camptothecin and enhances aqueous solubility. In addition, poly-L-glutamate is postulated to increase tumor delivery of the active compound through enhanced permeability and retention effect in tumor. We studied a weekly schedule of CT-2106 in patients with refractory solid tumor malignancies.

EXPERIMENTAL DESIGN

CT-2106 was infused (10 min i.v. infusion) on days 1, 8, and 15 of each 28-day cycle. Plasma and urine were analyzed for total and unconjugated camptothecin by high-performance liquid chromatography equipped with a fluorescence detector. Toxicity and response assessments were done with Common Toxicity Criteria for Adverse Events version 3 and Response Evaluation Criteria in Solid Tumors, respectively.

RESULTS

Twenty-six patients were enrolled. Median age was 58 years (range, 36-83) and median number of doses was 6 (range, 1-9). The most frequent tumor type (50%) was melanoma. Dose limiting toxicities were thrombocytopenia and fatigue. A weekly dose of 25 mg/m2 given every 3 of 4 weeks was the maximum tolerated dose. The majority of grade 3 and 4 toxicities were hematologic. The pharmacokinetic profile of conjugated and unconjugated camptothecin showed a polyexponential decline with similar terminal half life (t1/2 range was 44-63 and 31-48 h for conjugated and unconjugated, respectively). Pharmacokinetics of conjugated and unconjugated camptothecin were dose and time independent in the tested dose range. Urinary excretion of conjugated and unconjugated camptothecin accounted for about 30% and 4% of the administered dose, respectively.

CONCLUSIONS

CT-2106 has a more manageable toxicity profile compared with unconjugated camptothecin. The maximum tolerated dose is 25 mg/m2 weekly given 3 of 4 weeks. This compound results in prolonged release of unconjugated camptothecin.

Role of copper gluconate/triethanolamine in irinotecan encapsulation inside the liposomes

A novel method for encapsulating irinotecan into liposomes containing copper gluconate buffered to pH 7.0 with triethanolamine (TEA) has recently been developed. In the present study, the mechanism dictating drug encapsulation and retention inside those liposomes was investigated. Spectroscopic analyses revealed that irinotecan interacted with copper gluconate/TEA in solution. Fourier transformed infrared (FT-IR) spectroscopy indicated a strengthening of the hydrogen bonds involving the hydroxyl groups when solutions of irinotecan and copper gluconate/TEA are mixed at a 1:1 molar ratio. The intensity of the circular dichroism (CD) signal of copper gluconate/TEA increased in the presence of equimolar amounts of irinotecan. The addition of irinotecan to liposomes containing copper gluconate/TEA at 50 degrees C induced a shift of the absorption bands from 370 nm to 378 nm as well as a 60% quenching of the drug fluorescence at 440 nm suggesting the occurrence of irinotecan self association. Irinotecan encapsulation was found to be kinetically and stoichiometrically correlated with the release of TEA from the liposomes. The results suggested that the encapsulation of irinotecan was mediated by TEA in association with copper gluconate, leading to a final drug complex that is retained inside the liposomes. A neutral antiport exchange loading mechanism between irinotecan and TEA is proposed.

Topoisomerase I-mediated DNA cleavage induced by the minor groove-directed binding of bibenzimidazoles to a distal site

Many agents (e.g. camptothecins, indolocarbazoles, indenoisoquinolines, and dibenzonaphthyridines) stimulate topoisomerase I (TOP1)-mediated DNA cleavage (a behavior termed topoisomerase I poisoning) by interacting with both the DNA and the enzyme at the site of cleavage (typically by intercalation between the -1 and +1 base-pairs). The bibenzimidazoles, which include Hoechst 33258 and 33342, are a family of DNA minor groove-directed agents that also stimulate topoisomerase I-mediated DNA cleavage. However, the molecular mechanism by which these ligands poison TOP1 is poorly understood. Toward this goal, we have used a combination of mutational, footprinting, and DNA binding affinity analyses to define the DNA binding site for Hoechst 33258 and a related derivative that results in optimal induction of TOP1-mediated DNA cleavage. We show that this DNA binding site is located downstream from the site of DNA cleavage, encompassing the base-pairs from position +4 to +8. The distal nature of this binding site relative to the site of DNA cleavage suggests that minor groove-directed agents like the bibenzimidazoles poison TOP1 via a mechanism distinct from compounds like the camptothecins, which interact at the site of cleavage.

Convection-enhanced delivery of Ls-TPT enables an effective, continuous, low-dose chemotherapy against malignant glioma xenograft model

Treatment of malignant gliomas represents one of the most formidable challenges in oncology. The combination of surgery, radiation, and chemotherapy yields median survivals of less than one year. Here we demonstrate the use of a minimally invasive surgical technique, convection-enhanced delivery (CED), for local administration of a novel nanoparticle liposome containing topotecan. CED of this liposomal topotecan (Ls-TPT) resulted in extended brain tissue retention (t1/2 = 1.5 days), whereas free topotecan was rapidly cleared (t1/2 = 0.1 days) after CED. The favorable pharmacokinetic profile of extended topotecan release for about seven days, along with biodistribution featuring perivascular accumulation of the nanoparticles, provided, in addition to the known topoisomerase I inhibition, an effective antiangiogenic therapy. In the rat intracranial U87MG tumor model, vascular targeting of Ls-TPT with CED was associated with reductions in laminin expression and vascular density compared to free topotecan or control treatments. A single CED treatment on day 7 showed that free topotecan conferred no survival benefit versus control. However, Ls-TPT produced a significant (P = 0.0002) survival benefit, with six of seven complete cures. Larger U87MG tumors, where CED of Ls-TPT on day 12 resulted in one of six cures, indicated the necessity to cover the entire tumor with the infused therapeutic agent. CED of Ls-TPT was also efficacious in the intracranial U251MG tumor model (P = 0.0005 versus control). We conclude that the combination of a novel nanoparticle Ls-TPT and CED administration was very effective in treating experimental brain tumors.

Human Multidrug Resistance Associated Protein 4 Confers Resistance to Camptothecins

PURPOSE

The multidrug resistance associated protein (MRP) 4 is a member of the adenosine triphosphate (ATP)-binding cassette transporter family. Camptothecins (CPTs) have shown substantial anticancer activity against a broad spectrum of tumors by inhibiting DNA topoisomerase I, but tumor resistance is one of the major reasons for therapeutic failure. P-glycoprotein, breast cancer resistance protein, MRP1, and MRP2 have been implicated in resistance to various CPTs including CPT-11 (irinotecan), SN-38 (the active metabolite of CPT-11), and topotecan. In this study, we explored the resistance profiles and intracellular accumulation of a panel of CPTs including CPT, CPT-11, SN-38, rubitecan, and 10-hydroxy-CPT (10-OH-CPT) in HepG2 cells with stably overexpressed human MRP4. Other anticancer agents such as paclitaxel, cyclophosphamide, and carboplatin were also included.

METHODS

HepG2 cells were transfected with an empty vehicle plasmid (V/HepG2) or human MRP4 (MRP4/HepG2). The resistance profiles of test drugs in exponentially growing V/HepG2 and MRP4/HepG2 cells were examined using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazonium bromide (MTT) assay with 4 or 48 h exposure time of the test drug in the absence or presence of various MRP4 inhibitors. The accumulation of CPT-11, SN-38, and paclitaxel by V/HepG2 and MRP4/HepG2 cells was determined by validated high-performance liquid chromatography methods.

RESULTS

Based on the resistance folds from the MTT assay with 48 h exposure time of the test drug, MRP4 conferred resistance to CPTs tested in the order 10-OH-CPT (14.21) > SN-38 carboxylate (9.70) > rubitecan (9.06) > SN-38 lactone (8.91) > CPT lactone (7.33) > CPT-11 lactone (5.64) > CPT carboxylate (4.30) > CPT-11 carboxylate (2.68). Overall, overexpression of MRP4 increased the IC50 values 1.78- to 14.21-fold for various CPTs in lactone or carboxylate form. The resistance of MRP4 to various CPTs tested was significantly reversed in the presence of dl-buthionine-(S,R)-sulfoximine (BSO, a gamma-glutamylcysteine synthetase inhibitor), MK571, celecoxib, or diclofenac (all MRP4 inhibitors). In addition, the accumulation of CPT-11 and SN-38 over 120 min in MRP4/HepG2 cells was significantly reduced compared to V/HepG2 cells, whereas the addition of celecoxib, MK571, or BSO significantly increased their accumulation in MRP4/HepG2 cells. There was no significant difference in the intracellular accumulation of paclitaxel in V/HepG2 and MRP4/HepG2 cells, indicating that P-glycoprotein was not involved in the observed resistance to CPTs in this study. MRP4 also conferred resistance to cyclophosphamide and this was partially reversed by BSO. However, MRP4 did not increase resistance to paclitaxel, carboplatin, etoposide (VP-16), 5-fluorouracil, and cyclosporine.

CONCLUSIONS

Human MRP4 rendered significant resistance to cyclophosphamide, CPT, CPT-11, SN-38, rubitecan, and 10-OH-CPT. CPT-11 and SN-38 are substrates for MRP4. Further studies are needed to explore the role of MRP4 in resistance, toxicity, and pharmacokinetics of CPTs and cyclophosphamide.