M. Guillaume Wientjes

Delivery of siRNA Therapeutics: Barriers and Carriers

RNA interference is a naturally occurring endogenous regulatory process where short double-stranded RNA causes sequence-specific posttranscriptional gene silencing. Small interference RNA (siRNA) represents a promising therapeutic strategy. Clinical evaluations of siRNA therapeutics in locoregional treatment settings began in 2004. Systemic siRNA therapy is hampered by the barriers for siRNA to reach their intended targets in the cytoplasm and to exert their gene silencing activity. The three goals of this review were to provide an overview of (a) the barriers to siRNA delivery, from the perspectives of physicochemical properties of siRNA, pharmacokinetics and biodistribution, and intracellular trafficking; (b) the non-viral siRNA carriers including cell-penetrating peptides, polymers, dendrimers, siRNA bioconjugates, and lipid-based siRNA carriers; and (c) the current status of the clinical trials of siRNA therapeutics.

Drug Delivery and Transport to Solid Tumors

AbstractPurpose. The purpose of this review is to provide an overview of the principles of and barriers to drug transport and delivery to solid tumors. Methods. This review consists of four parts. Part I provides an overview of the differences in the vasculature in normal and tumor tissues, and the relationship between tumor vasculature and drug transport. Part II describes the determinants of transport of drugs and particles across tumor vasculature into surrounding tumor tissues. Part III discusses the determinants and barriers of drug transport, accumulation, and retention in tumors. Part IV summarizes the experimental approaches used to enhance drug delivery and transport in solid tumors. Results. Drug delivery to solid tumors consists of multiple processes, including transport via blood vessels, transvascular transport, and transport through interstitial spaces. These processes are dynamic and change with time and tumor properties and are affected by multiple physicochemical factors of a drug, multiple tumor biologic factors, and as a consequence of drug treatments. The biologic factors, in turn, have opposing effects on one or more processes in the delivery of drugs to solid tumors. Conclusion. The effectiveness of cancer therapy depends in part on adequate delivery of the therapeutic agents to tumor cells. A better understanding of the processes and contribution of these factors governing drug delivery may lead to new cancer therapeutic strategies.

Evaluation of Combination Chemotherapy: Integration of Nonlinear Regression, Curve Shift, Isobologram, and Combination Index Analyses

Isobologram and combination index (CI) analyses are the two most popular methods for evaluating drug interactions in combination cancer chemotherapy. As the commonly used CI-based software program uses linear regression, our first objective was to evaluate the effects of logarithmic data transformation on data analysis and conclusions. Monte-Carlo simulations were conducted with experimentally relevant parameter values to generate error-containing effect or concentration-effect data of single agents and combinations. The simulated data were then analyzed with linear and nonlinear regression. The results showed that data transformation reduced the accuracy and precision of the regression-derived IC50, curve shape parameter and CI values. Furthermore, as neither isobologram nor CI analyses provide output of concentration-effect curves for investigator evaluation, our second objective was to develop a method and the associated computer program/algorithm to (a) normalize drug concentrations in IC50 equivalents and thereby enable simultaneous presentation of the curves for single agents and combinations in a single plot for visual inspection of potential curve shifts, (b) analyze concentration-effect data with nonlinear regression, and (c) use the curve shift analysis simultaneously with isobologram and CI analyses. The applicability of this method was shown with experimentally obtained data for single agent doxorubicin and suramin and their combinations in cultured tumor cells. In summary, this method, by incorporating nonlinear regression and curve shift analysis, although retaining the attractive features of isobologram and CI analyses, reduced the potential errors introduced by logarithmic data transformation, enabled visual inspection of data variability and goodness of fit of regression analysis, and simultaneously provided information on the extent of drug interaction at different combination ratios/concentrations and at different effect levels.

Delivery of nanomedicines to extracellular and intracellular compartments of a solid tumor.

Advances in molecular medicines have led to identification of promising targets on cellular and molecular levels. These targets are located in extracellular and intracellular compartments. The latter include cytosol, nucleus, mitochondrion, Golgi apparatus and endoplasmic reticulum. This report gives an overview on the barriers to delivering nanomedicines to various target sites within a solid tumor, the experimental approaches to overcome such barriers, and the potential utility of nanotechnology.

TUMOR PRIMING ENHANCES DELIVERY AND EFFICACY OF NANOMEDICINES

We have shown that high epithelial cell density is a major barrier to the distribution of protein-bound drugs in solid tumors, and tumor priming (expansion of interstitial space using an apoptosis-inducing pretreatment) can promote drug delivery. This study evaluated the optimal conditions of paclitaxel tumor priming (time window, particle size) and its effects on the delivery and efficacy of nanomedicines. Paclitaxel tumor priming was applied to mice bearing human xenograft tumors. The kinetics of paclitaxel-induced apoptosis was evaluated to identify the time window of tumor priming. The effects of tumor priming on the tumor delivery and interstitial dispersion of fluorescence-labeled nanoparticles of various sizes, the perfusion of tumor and normal tissues, the delivery of doxorubicin HCl liposomes to tumor and host tissues, and the antitumor activity and host toxicity were studied. Tumor priming by a single i.v. injection of paclitaxel induced apoptosis, expanded the interstitial space, vessel diameter and blood-perfused area, and promoted the delivery and interstitial dispersion of nanoparticles (100- and 200-nm diameter, administered 48 h after paclitaxel) in a tumor-selective manner. Tumor priming also enhanced the tumor delivery and antitumor activity of doxorubicin HCl liposomes (85 nm) without affecting the delivery to noncancerous host tissues or enhancing host toxicity. Tumor priming represents a potentially useful means to promote tumor-selective delivery and efficacy of nanomedicines. The current study will have significant impact on enhancing delivery and efficacy of nanomedicines and dosing regimen optimization of combination chemotherapy in the clinical setting.

Intravesical Treatments of Bladder Cancer: Review

For bladder cancer, intravesical chemo/immunotherapy is widely used as adjuvant therapies after surgical transurethal resection, while systemic therapy is typically reserved for higher stage, muscle-invading, or metastatic diseases. The goal of intravesical therapy is to eradicate existing or residual tumors through direct cytoablation or immunostimulation. The unique properties of the urinary bladder render it a fertile ground for evaluating additional novel experimental approaches to regional therapy, including iontophoresis/electrophoresis, local hyperthermia, co-administration of permeation enhancers, bioadhesive carriers, magnetic-targeted particles and gene therapy. Furthermore, due to its unique anatomical properties, the drug concentration-time profiles in various layers of bladder tissues during and after intravesical therapy can be described by mathematical models comprised of drug disposition and transport kinetic parameters. The drug delivery data, in turn, can be combined with the effective drug exposure to infer treatment efficacy and thereby assists the selection of optimal regimens. To our knowledge, intravesical therapy of bladder cancer represents the first example where computational pharmacological approach was used to design, and successfully predicted the outcome of, a randomized phase III trial (using mitomycin C). This review summarizes the pharmacological principles and the current status of intravesical therapy, and the application of computation to optimize the drug delivery to target sites and the treatment efficacy.

Effects of carrier on disposition and antitumor activity of intraperitoneal Paclitaxel.

PurposeThe rationale for intraperitoneal (IP) chemotherapy is to expose peritoneal tumors to high drug concentrations. While multiple phase III trials have established the significant survival advantage by adding IP therapy to intravenous therapy in optimally debulked ovarian cancer patients, the use of IP chemotherapy is limited by the complications associated with indwelling catheters and by the local chemotherapy-related toxicity. The present study evaluated the effects of drug carrier on the disposition and efficacy of IP paclitaxel, for identifying strategies for further development of IP treatment.Materials and MethodsThree paclitaxel formulations, i.e., Cremophor micelles, Cremophor-free paclitaxel-loaded gelatin nanoparticles and polymeric microparticles, were evaluated for peritoneal targeting advantage and antitumor activity in mice after IP injection. Whole body autoradiography and scanning electron microscopy were used to visualize the spatial drug distribution in tissues. A kinetic model, depicting the multiple processes involved in the peritoneal-to-plasma transfer of paclitaxel and its carriers, was established to determine the mechanisms by which a drug carrier alters the peritoneal targeting advantage.ResultsAutoradiographic results indicated that IP injection yielded much higher paclitaxel concentrations in intestinal tissues relative to intravenous injection. Compared to the Cremophor and nanoparticle formulations, the microparticles showed slower drug clearance from the peritoneal cavity, slower absorption into the systemic circulation, longer residence time, 10- to 45-times greater peritoneal targeting advantage and ∼2-times longer increase in survival time (p < 0.01 for all parameters).ConclusionsOur results indicate the important roles of drug carrier in determining the peritoneal targeting advantage and antitumor activity of IP treatment.

Intraperitoneal therapy for peritoneal cancer

Cancers originating from organs in the peritoneal cavity (e.g., ovarian, pancreatic, colorectal, gastric and liver) account for approximately 250,000 new cancer cases annually in the USA. Peritoneal metastases are common owing to locoregional spread and distant metastases of extraperitoneal cancers. A logical treatment is intraperitoneal therapy, as multiple studies have shown significant targeting advantage for this treatment, including significant survival benefits in stage III, surgically debulked ovarian cancer patients. However, the clinical use of intraperitoneal therapy has been limited, in part, by toxicity, owing to the use of indwelling catheters or high drug exposure, by inadequate drug penetration into bulky tumors (>1 cm) and by the lack of products specifically designed and approved for intraperitoneal treatments. This article provides an overview on the background of peritoneal metastasis, clinical research on intraperitoneal therapy, the pharmacokinetic basis of drug delivery in intraperitoneal therapy and our development of drug-loaded tumor-penetrating microparticles.

Use of pharmacologic data and computer simulations to design an efficacy trial of intravesical mitomycin C therapy for superficial bladder cancer

SummaryTreatment of superficial bladder cancers by intravesical mitomycin C (MMC) chemotherapy gives a varying and incomplete response. Our recent pharmacokinetics and pharmacodynamics studies have shown that treatment effectiveness is limited by drug degradation in acidic urine and by drug dilution due to residual urine volume and urine production. A model was developed to predict drug exposure in tumors in the bladder wall and to correlate drug exposure with antitumor effect. The model is based on the known pharmacokinetic data in patients treated with intravesical chemotherapy, drug-penetration data in the bladder wall of patients undergoing radical cystectomy, and pharmacodynamic data on patients bladder-tumor chemosensitivity. Computer simulations based on the model were generated. The simulations predicted that changes in treatment parameters would affect the therapeutic outcome in the following rank order: dose>residual volume>urine production>dosing volume>urine pH>dwell time. Tissue exposure could be enhanced by increased dose, complete bladder emptying, reduced fluid intake, use of the minimal dosing volume, and alkalinization of the urine to a neutral pH. Increasing the dwell time from 2 to 4 h gave an insignificant improvement and posed a compliance problem. The selected optimized regimen of a 40-mg dose, no residual volume, 0.62-ml/min urine production, a 20-ml dosing volume, and alkaline urine pH yielded a calculated 8.5-fold increase in tissue exposure over that achieved by the standard regimen, which consisted of a 20-mg dose, 32-ml residual volume, 1.5-ml/min urine production, a 20-ml dosing volume, and acidic urine pH. On the basis of previously established pharmacodynamic data, we hypothesize that the increase in tissue exposure in the optimized treatment would result in a 20% improvement over the standard therapy along with an increase in the recurrence-free rate from 56% to 76% of patients. A phase III efficacy trial comparing the optimized and standard regimens is proposed.

Pancreatic Cancer: Pathobiology, Treatment Options, and Drug Delivery

Pancreatic cancer is the fourth leading cause of cancer-related deaths in the USA. The high mortality rate is partly due to lack of effective treatments. This review summarizes the pathobiology and current treatment options for pancreatic cancer. Moreover, the review discusses the opportunities of developing novel therapies for pancreatic cancer provided by the progress in understanding the genetic mutations, tumor microenvironment, cancer stem cells, and drug delivery.