Nanoparticle Formulation Derived from Carboxymethyl Cellulose, Polyethylene Glycol, and Cabazitaxel for Chemotherapy Delivery to the Brain.

Nanoparticles provide a unique opportunity to explore the benefits of selective distribution and release of cancer therapeutics at sites of disease through varying particle sizes and compositions that exploit the enhanced permeability of tumor-associated blood vessels. Though delivery of larger as opposed to smaller and/or actively transported molecules to the brain is prima facie a challenging endeavor, we wondered whether nanoparticles could improve the therapeutic index of existing drugs for use in treating brain tumors via these vascular effects. We therefore selected a family of nanoparticles composed of cabazitaxel-carboxymethyl cellulose amphiphilic polymers to investigate the potential for delivering a brain-penetrant taxane to intracranial brain tumors in mice. Among a small set of nanoparticle formulations, we found evidence for nanoparticle accumulation in the brain, and one such formulation demonstrated activity in an orthotopic model of glioma, suggesting that such nanoparticles could be useful for the treatment of glioma and brain metastases of other tumor types.

Cabazitaxel-conjugated nanoparticles for docetaxel-resistant and bone metastatic prostate cancer.

Effective treatment of metastatic castration resistant prostate cancer (mCRPC) remains an unmet challenge. Cabazitaxel (CBZ) is approved for mCRPC after docetaxel (DTX) failure, but the improvement in survival is only moderate (∼2 months) and patients suffer from significant side effects. Here, we report the development of a polymer based delivery system for CBZ to improve its safety and efficacy against DTX-resistant mCRPC. CBZ was conjugated to a carboxymethylcellulose-based polymer (Cellax-CBZ), which self-assembled into ∼100 nm particles in saline and exhibited sustained drug release in serum at 10%/day. Cellax-CBZ delivered 157-fold higher CBZ to PC3-RES prostate tumor in mice and could be safely administered at a 25-fold higher dose compared to free CBZ, resulting in superior tumor inhibition in multiple mice models of DTX-resistant CRPC. In a metastatic bone model of CRPC, Cellax-CBZ significantly improves overall survival with a 70% long-term survival rate to day 120, while mice treated with free CBZ had a median survival of 40 days. Cellax-CBZ induced mild and reversible neutropenia in mice but no other tissue damage. Cellax-CBZ showed significant potential for improving therapy of mCRPC over clinically approved CBZ.

Using Flash Nanoprecipitation To Produce Highly Potent and Stable Cellax Nanoparticles from Amphiphilic Polymers Derived from Carboxymethyl Cellulose, Polyethylene Glycol, and Cabazitaxel.

We report the use of flash nanoprecipitation (FNP) as an efficient and scalable means of producing Cellax nanoparticles. Cellax polymeric conjugates consisting of carboxymethyl cellulose functionalized with PEG and hydrophobic anticancer drugs, such as cabazitaxel (coined Cellax-CBZ), have been shown to have high potency against several oncology targets, including prostate cancer. FNP, a robust method used to create nanoparticles through rapid mixing, has been used to encapsulate several hydrophobic drugs with block copolymer stabilizers, but has never been used to form nanoparticles from random copolymers, such as Cellax-CBZ. To assess the potential of using FNP to produce Cellax nanoparticles, parameters such as concentration, mixing rate, solvent ratios, and subsequent dilution were tested with a target nanoparticle size range of 60 nm. Under optimized solvent conditions, particles were formed that underwent a subsequent rearrangement to form nanoparticles of 60 nm diameter, independent of Cellax-CBZ polymer concentration. This intraparticle relaxation, without interparticle association, points to a delicate balance of hydrophobic/hydrophilic domains on the polymer backbone. These particles were stable over time, and the random amphiphilicity did not lead to interparticle attractions, which would compromise the stability and corresponding narrow size distribution required for parenteral injection. The amphiphilic nature of these conjugates allows them to be processed into nanoparticles for sustained drug release and improved tumor selectivity. Preferred candidates were evaluated for plasma stability and cytotoxicity against the PC3 prostate cancer cell line in vitro. These parameters are important when assessing nanoparticle safety and for estimating potential efficacy, respectively. The optimal formulations showed plasma stability profiles consistent with long circulating nanoparticles, and cytotoxicity comparable to that of free CBZ. This study demonstrates that FNP is a promising technology for development of Cellax nanoparticles.

Docetaxel-carboxymethylcellulose nanoparticles target cells via a SPARC and albumin dependent mechanism.

Cellax, a polymer-docetaxel (DTX) conjugate that self-assembled into 120 nm particles, displayed significant enhancements in safety and efficacy over native DTX across a number of primary and metastatic tumor models. Despite these exciting preclinical data, the underlying mechanism of delivery of Cellax remains elusive. Herein, we demonstrated that serum albumin efficiently adsorbed onto the Cellax particles with a 4-fold increased avidity compared to native DTX, and the uptake of Cellax by cells was primarily driven by an albumin and SPARC (secreted protein acidic and rich in cysteine, an albumin binder) dependent internalization mechanism. In the SPARC-positive cells, a >2-fold increase in cellular internalization of Cellax was observed in the presence of albumin. In the SPARC-negative cells, no difference in Cellax internalization was observed in the presence or absence of albumin. Evaluation of the internalization mechanism using endocytotic inhibitors revealed that Cellax was internalized predominantly via a clathrin-mediated endocytotic mechanism. Upon internalization, it was demonstrated that Cellax was entrapped within the endo-lysosomal and autophagosomal compartments. Analysis of the tumor SPARC level with tumor growth inhibition of Cellax in a panel of tumor models revealed a positive and linear correlation (R(2) > 0.9). Thus, this albumin and SPARC-dependent pathway for Cellax delivery to tumors was confirmed both in vitro and in vivo.

A highly tumor-targeted nanoparticle of podophyllotoxin penetrated tumor core and regressed multidrug resistant tumors.

Podophyllotoxin (PPT) exhibited significant activity against P-glycoprotein mediated multidrug resistant (MDR) tumor cell lines; however, due to its poor solubility and high toxicity, PPT cannot be dosed systemically, preventing its clinical use for MDR cancer. We developed a nanoparticle dosage form of PPT by covalently conjugating PPT and polyethylene glycol (PEG) with acetylated carboxymethyl cellulose (CMC-Ac) using one-pot esterification chemistry. The polymer conjugates self-assembled into nanoparticles (NPs) of variable sizes (20-120 nm) depending on the PPT-to-PEG molar ratio (2-20). The conjugate with a low PPT/PEG molar ratio of 2 yielded NPs with a mean diameter of 20 nm and released PPT at ∼5%/day in serum, while conjugates with increased PPT/PEG ratios (5 and 20) produced bigger particles (30 nm and 120 nm respectively) that displayed slower drug release (∼2.5%/day and ∼1%/day respectively). The 20 nm particles exhibited 2- to 5-fold enhanced cell killing potency and 5- to 20-fold increased tumor delivery compared to the larger NPs. The biodistribution of the 20 nm PPT-NPs was highly selective to the tumor with 8-fold higher accumulation than all other examined tissues, while the larger PPT-NPs (30 and 120 nm) exhibited increased liver uptake. Within the tumor, >90% of the 20 nm PPT-NPs penetrated to the hypovascular core, while the larger particles were largely restricted in the hypervascular periphery. The 20 nm PPT-NPs displayed significantly improved efficacy against MDR tumors in mice compared to the larger PPT-NPs, native PPT and the standard taxane chemotherapies, with minimal toxicity.

Targeting of metastasis-promoting tumor-associated fibroblasts and modulation of pancreatic tumor-associated stroma with a carboxymethylcellulose-docetaxel nanoparticle.

Pancreatic ductal adenocarcinomas are characterized by the desmoplastic reaction, a dense fibrous stroma that has been shown to be supportive of tumor cell growth, invasion, and metastasis, and has been associated with resistance to chemotherapy and reduced patient survival. Here, we investigated targeted depletion of stroma for pancreatic cancer therapy via taxane nanoparticles. Cellax-DTX polymer is a conjugate of docetaxel (DTX), polyethylene glycol (PEG), and acetylated carboxymethylcellulose, a construct which condenses into well-defined 120nm particles in an aqueous solution, and is suitable for intravenous injection. We examined Cellax-DTX treatment effects in highly stromal primary patient-derived pancreatic cancer xenografts and in a metastatic PAN02 mouse model of pancreatic cancer, focusing on specific cellular interactions in the stroma, pancreatic tumor growth and metastasis. Greater than 90% of Cellax-DTX particles accumulate in smooth muscle actin (SMA) positive cancer-associated fibroblasts which results in long-term depletion of this stromal cell population, an effect not observed with Nab-paclitaxel (Nab-PTX). The reduction in stromal density leads to a >10-fold increase in tumor perfusion, reduced tumor weight and a reduction in metastasis. Consentingly, Cellax-DTX treatment increased survival when compared to treatment with gemcitabine or Nab-PTX in a metastatic PAN02 mouse model. Cellax-DTX nanoparticles interact with the tumor-associated stroma, selectively interacting with and depleting SMA positive cells and macrophage, effects of which are associated with significant changes in tumor progression and metastasis.

Docetaxel-carboxymethylcellulose nanoparticles display enhanced anti-tumor activity in murine models of castration-resistant prostate cancer.

Docetaxel (DTX) remains the only effective drug for prolonging survival and improving quality of life of metastatic castration resistant prostate cancer (mCRPC) patients. Despite some clinical successes with DTX-based therapies, advent of cumulative toxicity and development of drug resistance limit its long-term clinical application. The integration of nanotechnology for drug delivery can be exploited to overcome the major intrinsic limitations of DTX therapy for mCRPC. We evaluated whether reformulation of DTX by facile conjugation to carboxymethylcellulose nanoparticles (Cellax) can improve the efficacy and safety of the drug in s.c. and bone metastatic models of CRPC. A single dose of the nanoparticles completely regressed s.c. PC3 tumor xenografts in mice. In addition, Cellax elicited fewer side effects compared to native DTX. Importantly, Cellax did not increase the expression of drug resistance molecules in androgen-independent PC3 prostate cancer cells in comparison with DTX. Lastly, in a bone metastatic model of CRPC, Cellax treatment afforded a 2- to 3-fold improvement in survival and enhancements in quality-of-life of the animals over DTX and saline controls. These results demonstrate the potential of Cellax in improving the treatment of mCRPC.

Recent progress in the development of polysaccharide conjugates of docetaxel and paclitaxel.

UNLABELLED: Taxanes are one of the most potent and broadest spectrum chemotherapeutics used clinically, but also induce significant side effects. Different strategies have been developed to produce a safer taxane formulation. Development of polysaccharide drug conjugates has increased in the recent years because of the demonstrated biocompatibility, biodegradability, safety, and low cost of the biopolymers. This review focuses on polysaccharide-taxane conjugates and provides an overview on various conjugation strategies and their effect on the efficacy. Detailed analyses on the designing factors of an effective polysaccharide-drug conjugate are provided with a discussion on the future direction of this field. For further resources related to this article, please visit the WIREs website. CONFLICT OF INTEREST: The authors have declared no conflicts of interest for this article.

Carboxymethylcellulose-based and docetaxel-loaded nanoparticles circumvent P-glycoprotein-mediated multidrug resistance.

Taxanes are a class of anticancer agents with a broad spectrum and have been widely used to treat a variety of cancer. However, its long-term use has been hampered by accumulating toxicity and development of drug resistance. The most extensively reported mechanism of resistance is the overexpression of P-glycoprotein (Pgp). We have developed a PEGylated carboxymethylcellulose conjugate of docetaxel (Cellax), which condenses into ∼120 nm nanoparticles. Here we demonstrated that Cellax therapy did not upregulate Pgp expression in MDA-MB-231 and EMT-6 breast tumor cells, whereas a significant increase in Pgp expression was measured with native docetaxel (DTX) treatment. Treatment with DTX led to 4-7-fold higher Pgp mRNA expression and 2-fold higher Pgp protein expression compared with Cellax treatment in the in vitro and in vivo system, respectively. Cellax also exhibited significantly increased efficacy compared with that of DTX in a taxane-resistant breast tumor model. Against the highly Pgp expressing EMT6/AR1 cells, Cellax exhibited a 6.5 times lower IC50 compared with that of native DTX, and in the in vivo model, Cellax exhibited 90% tumor growth inhibition, while native DTX had no significant antitumor activity.

Thermosensitive liposomes for the delivery of gemcitabine and oxaliplatin to tumors.

The majority of ultrafast temperature sensitive liposome (uTSL) formulations reported in the literature deliver the highly membrane permeable drug, doxorubicin (DOX). Here we report on the study of the uTSL formulation, HaT (Heat activated cytoToxic, composed of the phospholipid DPPC and the surfactant Brij78) loaded with the water-soluble, but poorly membrane permeable anticancer drugs, gemcitabine (GEM) and oxaliplatin (OXA). The HaT formulation displayed ultrafast release of these drugs in response to temperature, whereas attempts with LTSL (Lyso-lipid Temperature Sensitive Liposome, composed of DPPC, MSPC, and DSPE-PEG) were unsuccessful. HaT-GEM and HaT-OXA both released >80% of the encapsulated drug within 2 min at 40-42 °C, with <5% drug leakage at 37 °C after 30 min in serum. The pharmacokinetic profile of both drugs was improved by formulating with HaT relative to the free drug, with clearance reduced by 50-fold for GEM and 3-fold for OXA. HaT-GEM and HaT-OXA both displayed improved drug uptake in the heated tumor relative to the unheated tumor (by 9-fold and 3-fold, respectively). In particular, HaT-GEM showed 25-fold improved delivery to the heated tumor relative to free GEM and significantly enhanced antitumor efficacy with complete tumor regression after a single dose of HaT-GEM. These data suggest that uTSL technology can also be used to deliver nonmembrane permeable drugs via an intravascular ultrafast release mechanism to great effect.

Factors controlling the pharmacokinetics, biodistribution and intratumoral penetration of nanoparticles.

Nanoparticle drug delivery to the tumor is impacted by multiple factors: nanoparticles must evade clearance by renal filtration and the reticuloendothelial system, extravasate through the enlarged endothelial gaps in tumors, penetrate through dense stroma in the tumor microenvironment to reach the tumor cells, remain in the tumor tissue for a prolonged period of time, and finally release the active agent to induce pharmacological effect. The physicochemical properties of nanoparticles such as size, shape, surface charge, surface chemistry (PEGylation, ligand conjugation) and composition affect the pharmacokinetics, biodistribution, intratumoral penetration and tumor bioavailability. On the other hand, tumor biology (blood flow, perfusion, permeability, interstitial fluid pressure and stroma content) and patient characteristics (age, gender, tumor type, tumor location, body composition and prior treatments) also have impact on drug delivery by nanoparticles. It is now believed that both nanoparticles and the tumor microenvironment have to be optimized or adjusted for optimal delivery. This review provides a comprehensive summary of how these nanoparticle and biological factors impact nanoparticle delivery to tumors, with discussion on how the tumor microenvironment can be adjusted and how patients can be stratified by imaging methods to receive the maximal benefit of nanomedicine. Perspectives and future directions are also provided.

Docetaxel conjugate nanoparticles that target α-smooth muscle actin-expressing stromal cells suppress breast cancer metastasis.

Docetaxel-conjugate nanoparticles, known as Cellax, were synthesized by covalently conjugating docetaxel and polyethylene glycol to acetylated carboxymethylcellulose via ester linkages, yielding a polymeric conjugate that self-assembled into 120 nm particles suitable for intravenous administration. In 4T1 and MDA-MB-231 orthotopic breast tumor models, Cellax therapy reduced α-smooth muscle actin (α-SMA) content by 82% and 70%, respectively, whereas native docetaxel and nab-paclitaxel (albumin-paclitaxel nanoparticle, Abraxane) exerted no significant antistromal activity. In Cellax-treated mice, tumor perfusion was increased by approximately 70-fold (FITC-lectin binding), tumor vascular permeability was enhanced by more than 30% (dynamic contrast-enhanced magnetic resonance imaging), tumor matrix was decreased by 2.5-fold (immunohistochemistry), and tumor interstitial fluid pressure was suppressed by approximately 3-fold after Cellax therapy compared with the control, native docetaxel, and nab-paclitaxel groups. The antistromal effect of Cellax treatment corresponded to a significantly enhanced antimetastatic effect: lung nodules were reduced by 7- to 24-fold by Cellax treatment, whereas native docetaxel and nab-paclitaxel treatments were ineffective. Studies of the 4T1 tumor showed that more than 85% of the Cellax nanoparticles were delivered to the α-SMA+ stroma. Significant tumor stromal depletion occurred within 16 hours (∼50% depletion) postinjection, and the α-SMA+ stroma population was almost undetectable (∼3%) by 1 week. The 4T1 tumor epithelial cell population was not significantly reduced in the week after Cellax injection. These data suggest that Cellax targets tumor stroma and performs more efficaciously than docetaxel and nab-paclitaxel.

A docetaxel-carboxymethylcellulose nanoparticle outperforms the approved taxane nanoformulation, Abraxane, in mouse tumor models with significant control of metastases.

Cellax is a PEGylated carboxymethylcellulose conjugate of docetaxel (DTX) which condenses into a 120-nm nanoparticle, and was compared against the approved clinical taxane nanoformulation (Abraxane®) in mouse models. Cellax increased the systemic exposure of taxanes by 37× compared to Abraxane, and improved the delivery specificity: Cellax uptake was selective to the tumor, liver and spleen, with a 203× increase in tumor accumulation compared to Abraxane. The concentration of released DTX in Cellax treated tumors was well above the IC50 for at least 10 d, while paclitaxel released from Abraxane was undetectable after 24h. In s.c. PC3 (prostate) and B16F10 (melanoma) models, Cellax exhibited enhanced efficacy and was better tolerated compared to Abraxane. In an orthotopic 4T1 breast tumor model, Cellax reduced the incidence of lung metastasis to 40% with no metastasic incidence in other tissues. Mice treated with Abraxane displayed increased lung metastasic incidence (>85%) with metastases detected in the bone, liver, spleen and kidney. These results confirm that Cellax is a more effective drug delivery strategy compared to the approved taxane nanomedicine.

A thermosensitive liposome prepared with a Cu²âº gradient demonstrates improved pharmacokinetics, drug delivery and antitumor efficacy.

Here we report the development of an enhanced thermosensitive formulation composed of DPPC and Brij78, loaded with doxorubicin (DOX) using a Cu²âº gradient and post-inserted with an additional amount of Brij78. This optimal formulation (HaT-II: Hyperthermia-activated cytoToxic) displayed significantly improved stability in serum at 37 °C, and enhanced drug release rates at 41-42 °C, compared to LTSL (lyso-lipid temperature sensitive liposomes, DPPC/MSPC/DSPE-PEG2000=86/10/4, pH gradient drug loading). HaT-II released 100% DOX within 15-40s at 40-42 °C, with only 5% drug leakage at 37 °C after 30 min in serum, while LTSL lost 30% of its drug content at 37 °C and exhibited ~2-fold decreased release rate constants at 41-42 °C under the same conditions. The pharmacokinetics of DOX was significantly improved in non-heated HaT-II treated healthy mice with 2.5-fold increased area under the curve and 2-fold prolonged circulation half life compared to LTSL. This led to 2-fold improved drug delivery to the heated tumor by HaT-II (~20% injected dose/g tissue), relative to LTSL and significantly enhanced antitumor efficacy with complete inhibition of tumor growth after a single dose of HaT-II. Finally, HaT-II exhibited little toxicity in mice, inducing no body weight loss and no abnormality in the blood chemistry (10 mg DOX/kg).

Tumor-targeted drug delivery using MR-contrasted docetaxel - carboxymethylcellulose nanoparticles.

A carboxymethylcellulose-based polymer conjugate with nanoparticle forming properties (Cellax) has been shown to enhance the pharmacokinetics, specificity of biodistribution, anti-tumor efficacy and safety of docetaxel (DTX) in comparison to the Taxotere™ formulation. We examined Cellax and Taxotere efficacy in four tumor models (EMT-6, B16F10, PC3, and MDA-MB-231), and observed variances in efficacy. To explore whether differences in tumor uptake of Cellax were responsible for these effects, we incorporated superparamagnetic iron oxide nanoparticles (SPIONs) into Cellax particles to enable magnetic resonance (MR) imaging (Cellax-MR). In the EMT-6 tumor model, Cellax-MR nanoparticles exhibited peak tumor accumulation 3-24 h post intravenous injection, and 3 days post-treatment, significant MR contrast was still detected. The amount of Cellax-MR deposited in the EMT-6 tumors was quantifiable as a hypointense volume fraction, a value positively correlated with drug content as determined by LC/MS analysis (R(2) = 0.97). In the four tumor models, Cellax-MR uptake was linearly associated with anti-tumor efficacy (R(2) > 0.9), and was correlated with blood vessel density (R(2) > 0.9). We have affirmed that nanoparticle uptake is variable in tumor physiology, and that this efficacy-predictive parameter can be non-invasively estimated in real-time using a theranostic variant of Cellax.

Preclinical pharmacokinetic, biodistribution, and anti-cancer efficacy studies of a docetaxel-carboxymethylcellulose nanoparticle in mouse models.

We have developed a polymer conjugate (Cellax) composed of acetylated carboxymethylcellulose (CMC), docetaxel (DTX), and PEG, designed to enhance the pharmacokinetics (PK) and antitumor efficacy of DTX. Our design placed an emphasis on nanoparticle self-assembly to protect DTX during blood transport, stability of the nanoparticle, and PEGylation to enhance PK. Compared to Taxotere, Cellax exhibited a 38.6 times greater area under the curve (AUC), and significantly lower clearance (2.5%) in PK. Less than 10% of DTX was released from Cellax in the blood circulation, indicating that Cellax were stable during blood transport. Cellax reduced non-specific distribution of DTX to the heart, lung and kidney by 48, 90, and 90%, respectively, at 3 h, compared to Taxotere. The uptake of Cellax at 3 h in the liver and spleen was high (15-45 µg DTX/g) but declined rapidly to <10 µg DTX/g in 24 h, and induced no measurable toxicity at 170 mg DTX/kg. Taxotere, on the other hand, displayed non-specific uptake in all the examined normal tissues and induced significant apoptosis in the lung and kidney at 40 mg DTX/kg. The tumor uptake of Cellax was 5.5-fold more than that by Taxotere and the uptake occurred within 3 h after injection and persisted for 10 days. The conjugate exhibited enhanced efficacy in a panel of primary and metastatic mouse tumor models. These results clearly demonstrated that Cellax improved the pharmacokinetics, biodistribution and efficacy of DTX compared to Taxotere with reduced toxicity.

Synthetic modification of carboxymethylcellulose and use thereof to prepare a nanoparticle forming conjugate of docetaxel for enhanced cytotoxicity against cancer cells.

A nanoparticle formulation of docetaxel (DTX) was designed to address the strengths and limitations of current taxane delivery systems: PEGylation, high drug conjugation efficiency (>30 wt %), a slow-release mechanism, and a well-defined and stable nanoparticle identity were identified as critical design parameters. The polymer conjugate was synthesized with carboxymethylcellulose (CMC), an established pharmaceutical excipient characterized by a high density of carboxylate groups permitting increased conjugation of a drug. CMC was chemically modified through acetylation to eliminate its gelling properties and to improve solvent solubility, enabling high yield and reproducible conjugation of DTX and poly(ethylene glycol) (PEG). The optimal conjugate formulation (Cellax) contained 37.1 ± 1.5 wt % DTX and 4.7 ± 0.8 wt % PEG, exhibited a low critical aggregation concentration of 0.6 µg/mL, and formed 118-134 nm spherical nanoparticles stable against dilution. Conjugate compositions with a DTX degree of substitution (DS) outside the 12.3-20.8 mol % range failed to form discrete nanoparticles, emphasizing the importance of hydrophobic and hydrophilic balance in molecular design. Cellax nanoparticles released DTX in serum with near zero order kinetics (100% in 3 weeks), was internalized in murine and human cancer cells, and induced significantly higher toxic effects against a panel of tumor cell lines (2- to 40-fold lower IC50 values) compared to free DTX.

MRI monitoring of intratumoral drug delivery and prediction of the therapeutic effect with a multifunctional thermosensitive liposome.

Non-invasive in vivo imaging of drug distribution enables real-time monitoring and prediction of therapeutic responses to treatment. We have developed a thermosensitive liposomal formulation (HaT: Hyperthermia-activated-cytoToxic) consisting of DPPC and Brij78, a formulation that enhanced drug delivery compared to the lyso-lipid temperature sensitive liposomes (LTSL). Here we report the development of a multifunctional HaT liposome co-encapsulating Gd-DTPA (an MRI probe) and doxorubicin (DOX), which simultaneously releases and reports on drug delivery in a locally heated tumor. The temperature-dependent release profiles of DOX from HaT were closely related to the change in the MR T(1) relaxation time, in which DOX was 100% released at 40-42 °C in 3 min, accompanied by a 60% reduction in T(1). By T(1) relaxometry analysis, no Gd-DTPA leakage was detected in 30 min at 30-37 °C. In the in vivo study, DOX uptake in the tumor was quantitatively correlated with T(1) response (R(2) = 0.98) and the patterns of the T(1) image and the intratumoral DOX uptake were matched, in which both signals were predominantly detected in the highly perfused tumor periphery. Finally, the extent of T(1) relaxation enhancement in the heated tumor successfully predicted the antitumor efficacy in a standard pharmacological response model (R(2) = 0.98).

Optimization of a novel and improved thermosensitive liposome formulated with DPPC and a Brij surfactant using a robust in vitro system.

The combination of thermosensitive liposomes and local heating has been shown to improve anticancer drug delivery in both animal models and human patients. The lyso-lipid temperature sensitive liposomes (LTSL) consisting of DPPC, MSPC and DSPE-PEG(2000) is currently under evaluation in clinical trials. We hypothesized that Brij surfactants resembling the chemical structures of MSPC and DSPE-PEG(2000) could be utilized for generating a thermosensitive formulation with DPPC. Here, we report using a robust in vitro system to efficiently screen a series of liposomal candidates composed of DPPC and a Brij surfactant for thermosensitive delivery of doxorubicin. The data indicated that the optimal acyl chain length of the surfactant was between C(16) and C(18) with a saturated carbon chain, a PEG repeating unit ranging between 10 and 100 and a molecule weight above 600Da. The linking chemistry between the acyl chain and the PEG chain did not influence thermosensitivity. In the panel of surfactants tested, Brij78 was optimal and could be incorporated into the liposomes by the thin film hydration or the post-insertion method with an optimal range of 1 to 8mol%. Doxorubicin was incorporated into the formulation by pH gradient with >95% loading efficiency at drug/lipid of 1/20 (w/w). The transition temperature of the Brij78-liposomes was slightly lower than that of LTSL (41 v.s. 41.5°C), leading to enhanced drug release at the low end of the hyperthermic temperatures (40°C) with similar stability at 37°C, which was confirmed by cell based assays. Finally, the Brij78-liposomes and LTSL displayed comparable blood compatibility with mild hemolytic activity. This in vitro system allowed for efficient screening and optimization to produce an optimal formulation.

Efficient tumor regression by a single and low dose treatment with a novel and enhanced formulation of thermosensitive liposomal doxorubicin.

We have developed a novel and simplified thermosensitive liposomal formulation (HaT: Hyperthermia-activated cytoToxic) composed of DPPC lipid and Brij78 (96:4, molar ratio). The HaT nanoparticles were loaded with doxorubicin (DOX) with >95% efficiency when a pH gradient method and a drug/lipid ratio of 1/20 (w/w) were applied. Drug release from the HaT formulation was significantly faster at 40-41°C (100% release in 2-3min) with 3.4-fold increased membrane permeability compared to the LTSL (lyso-lipid temperature sensitive liposomes; DPPC: MSPC: DSPE-PEG(2000)=86:10:4, molar ratio), a formulation that is currently in clinical trials. Both formulations displayed similar stability at 37°C in serum (10-20% release in 30min), which corresponds to their comparable pharmacokinetics in the unheated mice. An approximately 1.4-fold increased drug delivery to the locally heated tumor (~43°C) was detected with HaT-DOX compared to LTSL-DOX. Moreover, when compared with free DOX, HaT enhanced drug uptake in the heated tumor by 5.2-fold and reduced drug delivery to the heart by 15-fold. A single i.v. treatment with HaT-DOX at 3mg DOX/kg in combination with localized hyperthermia demonstrated enhanced tumor regression compared to LTSL-DOX and free DOX, and exhibited little toxicity.