Enhanced therapeutic efficacy of a novel liposome-based formulation of SN-38 against human tumor models in SCID mice

Recent advances in SN-38 drug delivery system

DNA topoisomerase I plays a key role in lubricatingthe wheels of DNA replication or RNA transcription through breaking and reconnecting DNA single-strand. It is widely known that camptothecin and its derivatives (CPTs) have inhibitory effects on topoisomerases I, and have obtained some clinical benefits in cancer treatment. The potent cytotoxicity makes 7-ethyl-10-hydroxycamptothecin (SN-38) become a brilliant star among these derivatives. However, some undesirable physical and chemical properties of this compound, including poor solubility and stability, seriously hinder its effective delivery to tumor sites. In recent years, strategies to alleviate these defects have aroused extensive research interest. By focusing on the loading mechanism, basic nanodrug delivery systems with SN-38 loaded, like nanoparticles, liposomes and micelles, are demonstrated here. Additionally, functionalized nanodrug delivery systems of SN-38 including prodrug and active targeted nanodrug delivery systems and delivery systems designed to overcome drug resistance are also reviewed. At last, challenges for future research in formulation development and clinical translation of SN-38 drug delivery system are discussed.

Promising Therapeutic Strategies for Colorectal Cancer Treatment Based on Nanomaterials

Colorectal cancer (CRC) is a global health problem responsible for 10% of all cancer incidences and 9.4% of all cancer deaths worldwide. The number of new cases increases per annum, whereas the lack of effective therapies highlights the need for novel therapeutic approaches. Conventional treatment methods, such as surgery, chemotherapy and radiotherapy, are widely applied in oncology practice. Their therapeutic success is little, and therefore, the search for novel technologies is ongoing. Many efforts have focused recently on the development of safe and efficient cancer nanomedicines. Nanoparticles are among them. They are uniquewith their properties on a nanoscale and hold the potential to exploit intrinsic metabolic differences between cancer and healthy cells. This feature allows them to induce high levels of toxicity in cancer cells with little damage to the surrounding healthy tissues. Graphene oxide is a promising 2D material found to play an important role in cancer treatments through several strategies: direct killing and chemosensitization, drug and gene delivery, and phototherapy. Several new treatment approaches based on nanoparticles, particularly graphene oxide, are currently under research in clinical trials, and some have already been approved. Here, we provide an update on the recent advances in nanomaterials-based CRC-targeted therapy, with special attention to graphene oxide nanomaterials. We summarise the epidemiology, carcinogenesis, stages of the CRCs, and current nanomaterials-based therapeutic approaches for its treatment.

SN38-based albumin-binding prodrug for efficient targeted cancer chemotherapy

Developing new therapeutic strategies that damage tumour cells without harming normal tissues is among the primary obstacles in chemotherapy. In this study, a novel β-glucuronidase-sensitive albumin-binding prodrug was designed and synthesized to selectively deliver the drug SN38 to tumour sites and maximize its efficacy. After intravenous administration, the prodrug Mal-glu-SN38 covalently bound to plasma albumin through the Michael addition, enabling it to accumulate in the tumour and release SN38 when triggered by extracellular β-glucuronidase. Compared to irinotecan, Mal-glu-SN38 displayed a slower plasma clearance and increased drug exposure over time. Moreover, Mal-glu-SN38 caused an increase in tumour-site accumulation of both the albumin-prodrug conjugate and free SN38 released from albumin conjugate when compared with irinotecan. After administration of multiple doses, Mal-glu-SN38 also significantly delayed the tumour growth, resulting in an impressive reduction or even disappearance of tumours (67% of mice cured) without causing any observable side effects.

Orally Administrable Therapeutic Nanoparticles for the Treatment of Colorectal Cancer

Colorectal cancer (CRC) is one of the most common and lethal human malignancies worldwide; however, the therapeutic outcomes in the clinic still are unsatisfactory due to the lack of effective and safe therapeutic regimens. Orally administrable and CRC-targetable drug delivery is an attractive approach for CRC therapy as it improves the efficacy by local drug delivery and reduces systemic toxicity. Currently, chemotherapy remains the mainstay modality for CRC therapy; however, most of chemo drugs have low water solubility and are unstable in the gastrointestinal tract (GIT), poor intestinal permeability, and are susceptible to P-glycoprotein (P-gp) efflux, resulting in limited therapeutic outcomes. Orally administrable nanoformulations hold the great potential for improving the bioavailability of poorly permeable and poorly soluble therapeutics, but there are still limitations associated with these regimes. This review focuses on the barriers for oral drug delivery and various oral therapeutic nanoparticles for the management of CRC.

Ultrasound-triggered therapeutic microbubbles enhance the efficacy of cytotoxic drugs by increasing circulation and tumor drug accumulation and limiting bioavailability and toxicity in normal tissues

Most cancer patients receive chemotherapy at some stage of their treatment which makes improving the efficacy of cytotoxic drugs an ongoing and important goal. Despite large numbers of potent anti-cancer agents being developed, a major obstacle to clinical translation remains the inability to deliver therapeutic doses to a tumor without causing intolerable side effects. To address this problem, there has been intense interest in nanoformulations and targeted delivery to improve cancer outcomes. The aim of this work was to demonstrate how vascular endothelial growth factor receptor 2 (VEGFR2)-targeted, ultrasound-triggered delivery with therapeutic microbubbles (thMBs) could improve the therapeutic range of cytotoxic drugs. Methods: Using a microfluidic microbubble production platform, we generated thMBs comprising VEGFR2-targeted microbubbles with attached liposomal payloads for localised ultrasound-triggered delivery of irinotecan and SN38 in mouse models of colorectal cancer. Intravenous injection into tumor-bearing mice was used to examine targeting efficiency and tumor pharmacodynamics. High-frequency ultrasound and bioluminescent imaging were used to visualise microbubbles in real-time. Tandem mass spectrometry (LC-MS/MS) was used to quantitate intratumoral drug delivery and tissue biodistribution. Finally, 89Zr PET radiotracing was used to compare biodistribution and tumor accumulation of ultrasound-triggered SN38 thMBs with VEGFR2-targeted SN38 liposomes alone. Results: ThMBs specifically bound VEGFR2 in vitro and significantly improved tumor responses to low dose irinotecan and SN38 in human colorectal cancer xenografts. An ultrasound trigger was essential to achieve the selective effects of thMBs as without it, thMBs failed to extend intratumoral drug delivery or demonstrate enhanced tumor responses. Sensitive LC-MS/MS quantification of drugs and their metabolites demonstrated that thMBs extended drug exposure in tumors but limited exposure in healthy tissues, not exposed to ultrasound, by persistent encapsulation of drug prior to elimination. 89Zr PET radiotracing showed that the percentage injected dose in tumors achieved with thMBs was twice that of VEGFR2-targeted SN38 liposomes alone. Conclusions: thMBs provide a generic platform for the targeted, ultrasound-triggered delivery of cytotoxic drugs by enhancing tumor responses to low dose drug delivery via combined effects on circulation, tumor drug accumulation and exposure and altered metabolism in normal tissues.

Nanoparticles in Gastrooncology

BACKGROUND

Gastrointestinal malignancies have the greatest incidence and cancer-associated death rates worldwide. Routine therapeutic modalities include surgery, chemotherapy and radiation but they often fail to reach the goal of cancer-free survival.

SUMMARY

In the light of this urgent medical need for the treatment of GI tumors, nanotech-nology-based approaches, i.e. nanomedicine, promise new therapeutic options. Using nanoparticles instead of classically designed drugs, targeting anticancer agents directly to the tumor site may revolutionize both diagnostic and therapeutic tools thereby facilitating the identification and elimination of malignant cells. Importantly, diagnostic insight and therapeutic effects can be achieved simultaneously through the same nanoparticle. Additionally, a nanoparticle may be loaded with more than one agent, thereby further increasing the value and power of the nanotechnology approach in oncologic therapeutic concepts. Although most insight into mechanisms of nanomedicine has been gained from in vitro and preclinical in vivo models, few clinical trials have been conducted, and nanomedicine-based concepts are already part of standard treatment algorithms. However, despite substantial progress it remains a challenge to design nanoparticles that feature all desirable characteristics at the same time.

KEY MESSAGES

This review seeks to provide substantial insight into the current status of nanomedicine-based approaches employed for diagnostic and/or therapeutic purposes in the field of gastrointestinal cancers by highlighting achievements and pointing out unresolved issues that need to be further addressed by future research attempts.

A Multifunctional Nanotherapy for Targeted Treatment of Colon Cancer by Simultaneously Regulating Tumor Microenvironment

Colitis-associated colon cancer (CAC) is a widely recognized cancer, while treatment with the existing chemotherapeutic drugs affords limited clinical benefits. Herein we proposed a site-specific, combination nanotherapy strategy for targeted treatment of CAC by the oral route. Methods: A reactive oxygen species (ROS)-responsive and hydrogen peroxide-eliminating material OCD was synthesized, which was further produced into a functional nanoparticle (OCD NP). The antioxidative stress and anti-inflammatory effects of OCD NP were examined by in vitro and in vivo experiments. By packaging an anticancer drug camptothecin-11 (CPT-11) into OCD NP, a ROS-responsive nanotherapy CPT-11/OCD NP was obtained, and its antitumor activity was evaluated by both in vitro and in vivo studies. Preliminary safety studies were also performed for CPT-11/OCD NP in mice. Results: OCD NP significantly attenuated oxidative stress and inhibited inflammatory response in different cells and mice with induced colitis. CPT-11/OCD NP could selectively release drug molecules under intestinal pH conditions and at high levels of ROS. In C26 murine colon carcinoma cells, this nanotherapy showed significantly higher antitumor activity compared to free CPT-11 and a non-responsive CPT-11 nanotherapy. Correspondingly, oral delivery of CPT-11/OCD NP notably inhibited tumorigenesis and tumor growth in mice with induced CAC. By combination therapy with the nanovehicle OCD NP in the inflammatory phase, more desirable therapeutic effects were achieved. Furthermore, CPT-11/OCD NP displayed excellent safety profile for oral administration at a dose that is 87.3-fold higher than that employed in therapeutic studies. Conclusions: Anticancer nanotherapies derived from intrinsic anti-inflammatory nanocarriers are promising for targeted combination treatment of inflammation-associated tumors by simultaneously shaping pro-inflammatory microenvironment toward a relatively normal niche sensitive to chemotherapy.

In vitro and in vivo evaluation of SN-38 nanocrystals with different particle sizes

7-Ethyl-10-hydroxycamptothecin (SN-38) is a potent broad-spectrum antitumor drug derived from irinotecan hydrochloride (CPT-11). Due to its poor solubility and instability of the active lactone ring, its clinical use is significantly limited. As one of the most promising formulations for poorly water-soluble drugs, nanocrystals have attracted increasing attention. In order to solve these problems and evaluate the antitumor effect of SN-38 in vitro and in vivo, two nanocrystals with markedly different particle sizes were prepared. Dynamic light scattering and transmission electron microscopy were used to investigate the two nanocrystals. The particle sizes of SN-38 nanocrystals A (SN-38/NCs-A) and SN-38 nanocrystals B (SN-38/NCs-B) were 229.5±1.99 and 799.2±14.44 nm, respectively. X-ray powder diffraction analysis showed that the crystalline state of SN-38 did not change in the size reduction process. An accelerated dissolution velocity of SN-38 was achieved by nanocrystals, and release rate of SN-38/NCs-A was significantly faster than that of SN-38/NCs-B. Cellular uptake, cellular cytotoxicity, pharmacokinetics, animal antitumor efficacy, and tissue distribution were subsequently examined. As a result, enhanced intracellular accumulation in HT1080 cells and cytotoxicity on different tumor cells were observed for SN-38/NCs-A compared to that for SN-38/NCs-B and solution. Besides, compared to the SN-38 solution, SN-38/NCs-A had a higher bioavailability after intravenous injection; while the bioavailability of SN-38/NCs-B was even lower than that of the SN-38 solution. SN-38/NCs-A exhibited a significant inhibition of tumor growth compared to SN-38 solution and SN-38/NCs-B in vivo. The antitumor effect of SN-38/NCs-B was stronger than SN-38 solution. The tissue distribution study in tumor-bearing mice showed that nanocrystals could markedly improve the drug accumulation in tumor tissue by the enhanced permeability and retention effect compared to SN-38 solution, and the amount of SN-38 in tumors of SN-38/NCs-A group was much more than that of SN-38/NCs-B group. In conclusion, nanocrystals dramatically enhanced the anticancer efficacy of SN-38 in vitro and in vivo, and the particle size had a significant influence on the dissolution behavior, pharmacokinetic properties, and tumor inhibition of nanocrystals.

Targeted nanoparticles for colorectal cancer

Colorectal cancer (CRC) is highly prevalent worldwide, and despite notable progress in treatment still leads to significant morbidity and mortality. The use of nanoparticles as a drug delivery system has become one of the most promising strategies for cancer therapy. Targeted nanoparticles could take advantage of differentially expressed molecules on the surface of tumor cells, providing effective release of cytotoxic drugs. Several efforts have recently reported the use of diverse molecules as ligands on the surface of nanoparticles to interact with the tumor cells, enabling the effective delivery of antitumor agents. Here, we present recent advances in targeted nanoparticles against CRC and discuss the promising use of ligands and cellular targets in potential strategies for the treatment of CRCs.

Synthesis, characterization, and evaluation of mPEG-SN38 and mPEG-PLA-SN38 micelles for cancer therapy

7-Ethyl-10-hydroxy camptothecin (SN38) is a potent topoisomerase inhibitor and a metabolite of irinotecan. Its clinical development has been hampered by its poor solubility. To address this problem, methoxy poly(ethylene glycol)-2000 (mPEG2K)-SN38 and mPEG2K-poly(lactide) (PLA1.5K)-SN38 conjugates were prepared and then dispersed into an aqueous medium to form micelles. Physicochemical characteristics of SN38-polymer conjugate micelles, for example, micelle diameter, zeta potential, morphology, and drug content, were then evaluated. The results showed that the mean diameters of mPEG2K-SN38 and mPEG2K-PLA1.5K-SN38 micelles were ~130 and 20 nm, respectively. These two micelles had similar drug contents. mPEG2K-PLA1.5K-SN38 micelles were more homogeneous than mPEG2K-SN38 micelles. Moreover, in vitro drug release behavior of the micelles was studied by high performance liquid chromatography. SN38 release from mPEG2K-SN38 micelles was much faster than from mPEG2K-PLA1.5K-SN38 micelles. In vitro cytotoxicity, cellular uptake, and apoptosis assays of the SN38-polymer conjugate micelles were carried out on BEL-7402 human liver cancer cells. In vivo biodistribution and antitumor tumor efficacy studies were carried out in a nude mouse xenograft model derived from BEL-7402 cells. The results showed that mPEG2K-PLA1.5K-SN38 micelles were significantly more effective than mPEG2K-SN38 micelles in tumor inhibition, and the inhibitory effect of mPEG2K-PLA1.5K-SN38 micelles on tumor growth was significantly greater than that of mPEG2K-SN38 micelles (1,042 vs 1,837 mm) at 30 days. In conclusion, mPEG-PLA-SN38 is a promising anticancer agent that warrants further investigation.

Solid lipid nanoparticles containing 7-ethyl-10-hydroxycamptothecin (SN38): Preparation, characterization, in vitro, and in vivo evaluations

7-Ethyl-10-hydroxycamptothecin (SN38) is a biologically active metabolite of irinotecan. Due to the variability of irinotecan metabolism rate to SN38, and poor solubility of this compound in pharmaceutically acceptable solvents, SN38 has not been successfully used in the clinic. In the present study, we prepared solid lipid nanoparticle (SLN) formulations containing SN38 and evaluated the in vitro and in vivo efficacy of these nanoparticles. SLNs and PEGylated SLNs containing SN38 (SLN-SN38 and PEG-SLN-SN38) were prepared using ultrasonication technique. Nanoparticles were characterized for size, zeta potential, and drug encapsulation efficiency. In vitro cytotoxicity of these compounds was evaluated in two colorectal carcinoma cell lines, namely C-26 and HT-116. In vivo antitumor efficacy of the formulations was evaluated in C-26 xenograft tumor mice models. Mice survival was also explored through 60days post IV injection. Mean size of SLN-SN38 and PEG-SLN-SN38 was around 103 and 131nm, respectively. Polydispersity index (PDI) for all the formulations was around 0.2 and zeta potential was negative (-5 to -15mV). Nearly 90% of the drug was encapsulated in SLNs. SLN-SN38 and PEG-SLN-SN38 compared to irinotecan were significantly more toxic to C-26 and HT-116 cell lines after 48h of exposure. Calculation of IC50 suggests higher sensitivity of HT-116 cells than C-26 cells to SLN-SN38 and PEG-SLN-SN38. Tumor inhibitory efficacy presented the highest efficacy in SLN-SN38. However, both SLN-SN38 and PEG-SLN-SN38 carriers showed higher efficiency to inhibit tumors compared to irinotecan (25mg/kg).

Challenges in SN38 drug delivery: current success and future directions

INTRODUCTION

Clinical use of SN38 is limited by its poor aqueous solubility and hydrolysis of the lactone ring at pH > 6 to inactive carboxylate form. A variety of drug delivery systems have been developed to improve the solubility and stability of SN38, and reduce its toxicity. A few noteworthy formulations with some success in initial phases of clinical trials are reported.

AREAS COVERED

This work aims to provide a comprehensive review on the various techniques and strategies employed (physical, chemical and biological methods) to improve physicochemical properties and to deliver the drug efficiently to the cancer cells. Physical methods such as nanoparticle encapsulation, cyclodextrin complexation; chemical methods such as prodrugs, polymer-, albumin- and immunoconjugates; and enzyme activated prodrug therapy are discussed.

EXPERT OPINION

The challenges in SN38 drug delivery may be overcome by two ways: ensuring multiple layers of protection against degradation and slow but sustained release of therapeutically effective drug concentrations. It may also be achieved by preparing a polymer-drug conjugate and further encapsulating the conjugate in suitable carrier system; tumor-targeted SN38 delivery by using immunoconjugates, enzyme-activated prodrug therapy and antibody-directed nanoparticle delivery. However, selection of a suitable ligand for tumor targeting and use of safe and biocompatible nanoparticle systems play an important role in realizing this goal.

Synthesis, characterization, and antitumor evaluation of the albumin-SN38 conjugate

7-Ethyl-10-hydroxycamptothecin (SN38), the active metabolite of irinotecan, exerts a 100-fold to 1000-fold higher effect than irinotecan itself against several tumor cell lines. However, the water insolubility of SN38 has prevented its direct use as an antitumor drug in the clinic. To improve the water solubility and antitumor efficacy, SN38 was covalently attached to the only free sulfhydryl at cysteine-34 on the BSA site specifically through a thiol-binding linker to form a prodrug BSA-SN38 conjugate (BSA : SN38=1 : 1). The water solubility of this conjugate was similar to albumin using the current method. Also, SN38 loading in this conjugate became controllable. Size-exclusion chromatography purification and UV characterization of the SDS-PAGE electrophoresis product were carried out. Then, an MTT assay was carried out to test the antitumor effect of this conjugate on five colon cancer cell lines in vitro. The 72 h IC50 values of the BSA-SN38 conjugate ranged from 1.5 to 6.1 μmol/l. A colorectal peritoneal carcinomatosis model in mice was established to determine the intraperitoneal chemotherapy effect of the BSA-SN38 conjugate. The BSA-SN38 conjugate at an SN38 equivalent dose of 10 mg/kg/day was administrated every 4 days. Eighteen days after manipulation, the mice were euthanized and the tumors in the abdominal cavity were collected and weighed. Tumors in the BSA-SN38 conjugate treatment group (m=0.21 ± 0.15 g) were found to be significantly (P=5) lighter than those in the NS control group (m=4.74±0.73 g). The results indicated that this water-soluble BSA-SN38 conjugate exerted a strong antitumor effect on colorectal carcinoma.

Alpha-tocopheryl polyethylene glycol succinate-emulsified poly(lactic-co-glycolic acid) nanoparticles for reversal of multidrug resistance in vitro

Multidrug resistance (MDR) is one of the factors in the failure of anticancer chemotherapy. In order to enhance the anticancer effect of P-glycoprotein (P-gp) substrates, inhibition of the P-gp efflux pump on MDR cells is a good tactic. We designed novel multifunctional drug-loaded alpha-tocopheryl polyethylene glycol succinate (TPGS)/poly(lactic-co-glycolic acid) (PLGA) nanoparticles (TPGS/PLGA/SN-38 NPs; SN-38 is 7-ethyl-10-hydroxy-camptothecin), with TPGS-emulsified PLGA NPs as the carrier and modulator of the P-gp efflux pump and SN-38 as the model drug. TPGS/PLGA/SN-38 NPs were prepared using a modified solvent extraction/evaporation method. Physicochemical characterizations of TPGS/PLGA/SN-38 NPs were in conformity with the principle of nano-drug delivery systems (nDDSs), including a diameter of about 200 nm, excellent spherical particles with a smooth surface, narrow size distribution, appropriate surface charge, and successful drug-loading into the NPs. The cytotoxicity of TPGS/PLGA/SN-38 NPs to MDR cells was increased by 3.56 times compared with that of free SN-38. Based on an intracellular accumulation study relative to the time-dependent uptake and efflux inhibition, we suggest novel mechanisms of MDR reversal of TPGS/PLGA NPs. Firstly, TPGS/PLGA/SN-38 NPs improved the uptake of the loaded drug by clathrin-mediated endocytosis in the form of unbroken NPs. Simultaneously, intracellular NPs escaped the recognition of P-gp by MDR cells. After SN-38 was released from TPGS/PLGA/SN-38 NPs in MDR cells, TPGS or/and PLGA may modulate the efflux microenvironment of the P-gp pump, such as mitochondria and the P-gp domain with an ATP-binding site. Finally, the controlled-release drug entered the nucleus of the MDR cell to induce cytotoxicity. The present study showed that TPGS-emulsified PLGA NPs could be functional carriers in nDDS for anticancer drugs that are also P-gp substrates. More importantly, to enhance the therapeutic effect of P-gp substrates, this work might provide a new insight into the design of pharmacologically inactive excipients that can serve as P-gp modulators instead of drugs that are P-gp inhibitors.

Magnetic-Fe/Fe(3)O(4)-nanoparticle-bound SN38 as carboxylesterase-cleavable prodrug for the delivery to tumors within monocytes/macrophages

The targeted delivery of therapeutics to the tumor site is highly desirable in cancer treatment, because it is capable of minimizing collateral damage. Herein, we report the synthesis of a nanoplatform, which is composed of a 15 ± 1 nm diameter core/shell Fe/Fe(3)O(4) magnetic nanoparticles (MNPs) and the topoisomerase I blocker SN38 bound to the surface of the MNPs via a carboxylesterase cleavable linker. This nanoplatform demonstrated high heating ability (SAR = 522 ± 40 W/g) in an AC-magnetic field. For the purpose of targeted delivery, this nanoplatform was loaded into tumor-homing double-stable RAW264.7 cells (mouse monocyte/macrophage-like cells (Mo/Ma)), which have been engineered to express intracellular carboxylesterase (InCE) upon addition of doxycycline by a Tet-On Advanced system. The nanoplatform was taken up efficiently by these tumor-homing cells. They showed low toxicity even at high nanoplatform concentration. SN38 was released successfully by switching on the Tet-On Advanced system. We have demonstrated that this nanoplatform can be potentially used for thermochemotherapy. We will be able to achieve the following goals: (1) Specifically deliver the SN38 prodrug and magnetic nanoparticles to the cancer site as the payload of tumor-homing double-stable RAW264.7 cells; (2) Release of chemotherapeutic SN38 at the cancer site by means of the self-containing Tet-On Advanced system; (3) Provide localized magnetic hyperthermia to enhance the cancer treatment, both by killing cancer cells through magnetic heating and by activating the immune system.

Development and characterization of a novel lipid nanocapsule formulation of Sn38 for oral administration

The purpose of this work was to encapsulate 7-Ethyl-10-hydroxy-camptothecin (Sn38) in lipid nanocapsules (LNCs) using phase inversion-based method in order to deliver Sn38 by oral route. LNCs were prepared by a low-energy emulsification method and were characterized for size, polydispersity index (PDI), surface charge, drug payload, in vitro drug release, and storage stability. Moreover, in view of an oral administration, in vitro stability in gastrointestinal fluid and permeability across Caco-2 cells were tested. Sn38-loaded LNCs with a mean particle size of 38±2 nm were obtained. The particles displayed a narrow size distribution and a drug payload of 0.40±0.07 mg/g of LNC dispersion. In vitro stability in simulated gastric and intestinal media was also observed. Finally, Sn38-loaded LNCs improved permeability of Sn38 across Caco-2 cells (5.69±0.87×10(6) cm s(-1) at 6h vs 0.31±0.02×10(6) cm s(-1)) and intracellular concentration compared with free Sn38. In conclusion, Sn38 nanocarriers have been developed and display a strong potential for oral administration.

Cancer therapies utilizing the camptothecins: a review of the in vivo literature

This review summarizes the in vivo assessment-preliminary, preclinical, and clinical-of chemotherapeutics derived from camptothecin or a derivative. Camptothecin is a naturally occurring, pentacyclic quinoline alkaloid that possesses high cytotoxic activity in a variety of cell lines. Major limitations of the drug, including poor solubility and hydrolysis under physiological conditions, prevent full clinical utilization. Camptothecin remains at equilibrium in an active lactone form and inactive hydrolyzed carboxylate form. The active lactone binds to DNA topoisomerase I cleavage complex, believed to be the single site of activity. Binding inhibits DNA religation, resulting in apoptosis. A series of small molecule camptothecin derivatives have been developed that increase solubility, lactone stability and bioavailability to varying levels of success. A number of macromolecular agents have also been described wherein camptothecin(s) are covalently appended or noncovalently associated with the goal of improving solubility and lactone stability, while taking advantage of the tumor physiology to deliver larger doses of drug to the tumor with lower systemic toxicity. With the increasing interest in drug delivery and polymer therapeutics, additional constructs are anticipated. The goal of this review is to summarize the relevant literature for others interested in the field of camptothecin-based therapeutics, specifically in the context of biodistribution, dosing regimens, and pharmacokinetics with the desire of providing a useful source of comparative data. To this end, only constructs where in vivo data is available are reported. The review includes published reports in English through mid-2009.

Current trends in liposome research

Among the several drug delivery systems, liposomes--phospholipid nanosized vesicles with a bilayered membrane structure--have drawn a lot of interest as advanced and versatile pharmaceutical carriers for both low and high molecular weight pharmaceuticals. At present, liposomal formulations span multiple areas, from clinical application of the liposomal drugs to the development of various multifunctional liposomal systems to be used in therapy and diagnostics. This chapter provides a brief overview of various liposomal products currently under development at experimental and preclinical level.

Concept and clinical evaluation of carrier-mediated anticancer agents

Major advances in the use of carrier vehicles delivering pharmacologic agents and enzymes to sites of disease have occurred over the past 10 years. This review focuses on the concepts and clinical evaluation of carrier-mediated anticancer agents that are administered i.v. or orally. The primary types of carrier-mediated anticancer agents are nanoparticles, nanosomes, which are nanoparticle-sized liposomes, and conjugated agents. Nanosomes are further subdivided into stabilized and nonstabilized or conventional nanosomes. Nanospheres and dendrimers are subclasses of nanoparticles. Conjugated agents consist of polymer-linked and pegylated agents. The theoretical advantages of carrier-mediated drugs are greater solubility, longer duration of exposure, selective delivery of entrapped drug to the site of action, superior therapeutic index, and the potential to overcome resistance associated with the regular anticancer agent. The pharmacokinetic disposition of carrier-mediated agents depends on the physiochemical characteristics of the carrier, such as size, surface charge, membrane lipid packing, steric stabilization, dose, and route of administration. The primary sites of accumulation of carrier-mediated agents are the tumor, liver, and spleen, compared with noncarrier formulations. The drug that remains encapsulated in or linked to the carrier (e.g., the nanosome or nanoparticle) is an inactive prodrug, and thus the drug must be released from the carrier to be active. The factors affecting the pharmacokinetic and pharmacodynamic variability of these agents remain unclear, but most likely include the reticuloendothelial system, which has also been called the mononuclear phagocyte system. Future studies need to evaluate the mechanism of clearance of carrier-mediated agents and identify the factors associated with the pharmacokinetic and pharmacodynamic variability of carrier agents in patients and specifically in tumors.

Novel delivery of SN38 markedly inhibits tumor growth in xenografts, including a camptothecin-11-refractory model

PURPOSE

Clinical development of SN38, the active metabolite of camptothecin-11 (CPT-11), has been hampered due to its poor solubility. We have developed a novel polymer-drug conjugate, EZN-2208, made by linking SN38 with a multiarm polyethylene glycol via a glycine linker.

EXPERIMENTAL DESIGN

The in vitro cytotoxicity of EZN-2208 was tested using the 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium assay. The therapeutic efficacy of EZN-2208 was evaluated in various xenografts, including an in vivo-selected CPT-11-refractory model. Tumor and blood concentration of EZN-2208, CPT-11, and SN38 was determined by high-performance liquid chromatography.

RESULTS

In vitro, EZN-2208 was 10- to 245-fold more potent than CPT-11 in a panel of human tumor cell lines. In xenograft models of MX-1 breast, MiaPaCa-2 pancreatic, or HT-29 colon carcinoma, treatment with either a single dose or multiple injections of EZN-2208 was more efficacious (and in some cases produced tumor eradication for >16 weeks) compared with CPT-11 at their respective maximum tolerated doses or corresponding dose levels (P < 0.01). Most interestingly, EZN-2208 showed marked antitumor activity in animals that developed resistance to an 8-day course of CPT-11 treatment, as well as outperformed CPT-11 as second-round therapy in mice initially sensitive to CPT-11. EZN-2208 had prolonged circulation in the blood compared with CPT-11, resulting in high tumor exposure. This resulted in higher and longer-lasting tumor exposure of free SN38 in mice given EZN-2208 compared with those given CPT-11.

CONCLUSIONS

Preclinical data suggest that EZN-2208 may be a promising anticancer agent in a wide variety of clinical settings, including tumors refractory to CPT-11 treatment.

Novel SN-38-incorporating polymeric micelles, NK012, eradicate vascular endothelial growth factor-secreting bulky tumors

7-Ethyl-10-hydroxy-camptothecin (SN-38), a biological active metabolite of irinotecan hydrochloride (CPT-11), has potent antitumor activity but has not been used clinically because it is a water-insoluble drug. For delivery by i.v. injection, we have successfully developed NK012, a SN-38-releasing nanodevice. The purpose of this study is to investigate the pharmacologic character of NK012 as an anticancer agent, especially in a vascular endothelial growth factor (VEGF)-secreting tumor model. The particle size of NK012 was approximately 20 nm with a narrow size distribution. NK012 exhibited a much higher cytotoxic effect against lung and colon cancer cell lines as compared with CPT-11. NK012 showed significantly potent antitumor activity against a human colorectal cancer HT-29 xenograft as compared with CPT-11. Enhanced and prolonged distribution of free SN-38 in the tumor was observed after the injection of NK012. NK012 also had significant antitumor activity against bulky SBC-3/Neo (1,533.1 +/- 1,204.7 mm(3)) and SBC-3/VEGF tumors (1,620.7 +/- 834.0 mm(3)) compared with CPT-11. Furthermore, NK012 eradicated bulky SBC-3/VEGF tumors in all mice but did not eradicate SBC-3/Neo tumors. In the drug distribution analysis, an increased accumulation of SN-38 in SBC-3/VEGF tumors was observed as compared with that in SBC-3/Neo tumors. NK012 markedly enhanced the antitumor activity of SN-38, especially in highly VEGF-secreting tumors, and could be a promising SN-38-based formulation.

Novel Therapeutic Developments Other Than EGFR and VEGF Inhibition in Colorectal Cancer

Developments that may improve existing cytotoxic therapy for colorectal cancer (CRC) include alternatives to 5-fluorouracil (5-FU) such as the liposomal Thymidylate Synthase inhibitor OSI-7904L and the multitargeted antifolate pemetrexed. Studies have explored means of reformulating irinotecan, modulating its pharmacokinetics, and enhancing its activity by maximizing DNA damage through poly(ADP-ribose) polymerase inhibition. Cell cycle inhibitors may offer an alternative to combination with 5-FU. However, as standard regimens become more complex, so do the clinical trials needed to develop new agents, and the path to registration becomes ever more tortuous. It is therefore likely that several drugs with promise in CRC will not be developed for this indication.

Synthesis of cationic cardiolipin analogues

An approach was developed to synthesize a new class of cationic cardiolipin analogues containing two quaternary ammonium groups with tetra alkyl groups retaining "glycerol" moiety, the central core of the molecule. Cationic cardiolipin analogues were modified via introduction of either two or four oxyethylene groups to enhance the solubility in polar solvents. These newly synthesized cationic cardiolipin analogues can be applied to a broad range of drug delivery systems such as transfection reagents.

Novel cationic cardiolipin analogue-based liposome for efficient DNA and small interfering RNA delivery in vitro and in vivo

Cationic liposomes have been successfully used as an alternative approach to viral systems to deliver nucleic acids. However, high toxicity and inconsistent transfection efficiency have been associated with the currently available liposomes. Therefore, a novel cationic liposome was developed based on a synthetic cationic cardiolipin analogue (CCLA) to test the DNA transfection efficiency. This CCLA-based liposome was also used to determine the therapeutic efficacy of c-raf small interfering RNA (siRNA) in mice. In this report, we showed that the CCLA-based liposome was less toxic and effectively transfected reporter genes in vitro and in vivo. The transfection efficiency in mice was seven-fold higher than the commercially available DOTAP-based liposome. In addition, c-raf siRNA in the presence of CCLA-based liposome induced up to 62% of growth inhibition in cancer cells. Treatment of c-raf siRNA/CCLA complex in SCID mice bearing human breast xenograft tumors resulted in 73% of tumor growth suppression as compared to free c-raf siRNA group. In conclusion, a novel CCLA-based liposome showed less toxicity and broad usage both in vitro and in vivo with DNA and siRNA.