Local carboplatin delivery and tissue distribution in livers after radiofrequency ablation

Liver Cancer: Current and Future Trends Using Biomaterials

Hepatocellular carcinoma (HCC) is the fifth most common type of cancer diagnosed and the second leading cause of death worldwide. Despite advancement in current treatments for HCC, the prognosis for this cancer is still unfavorable. This comprehensive review article focuses on all the current technology that applies biomaterials to treat and study liver cancer, thus showing the versatility of biomaterials to be used as smart tools in this complex pathologic scenario. Specifically, after introducing the liver anatomy and pathology by focusing on the available treatments for HCC, this review summarizes the current biomaterial-based approaches for systemic delivery and implantable tools for locally administrating bioactive factors and provides a comprehensive discussion of the specific therapies and targeting agents to efficiently deliver those factors. This review also highlights the novel application of biomaterials to study HCC, which includes hydrogels and scaffolds to tissue engineer 3D in vitro models representative of the tumor environment. Such models will serve to better understand the tumor biology and investigate new therapies for HCC. Special focus is given to innovative approaches, e.g., combined delivery therapies, and to alternative approaches-e.g., cell capture-as promising future trends in the application of biomaterials to treat HCC.

Intratumoral delivery of beta-lapachone via polymer implants for prostate cancer therapy

PURPOSE

beta-Lapachone (ARQ 501, a formulation of beta-lapachone complexed with hydroxypropyl-beta-cyclodextrin) is a novel anticancer agent with selectivity against prostate cancer cells overexpressing the NAD(P)H:quinone oxidoreductase-1 enzyme. Lack of solubility and an efficient drug delivery strategy limits this compound in clinical applications. In this study, we aimed to develop beta-lapachone-containing polymer implants (millirods) for direct implantation into prostate tumors to test the hypothesis that the combination of a tumor-specific anticancer agent with site-specific release of the agent will lead to significant antitumor efficacy.

EXPERIMENTAL DESIGN

Survival assays in vitro were used to test the killing effect of beta-lapachone in different prostate cancer cells. beta-Lapachone release kinetics from millirods was determined in vitro and in vivo. PC-3 prostate tumor xenografts in athymic nude mice were used for antitumor efficacy studies in vivo.

RESULTS

beta-Lapachone killed three different prostate cancer cell lines in an NAD(P)H:quinone oxidoreductase-1-dependent manner. Upon incorporation of solid-state inclusion complexes of beta-lapachone with hydroxypropyl-beta-cyclodextrin into poly(D,L-lactide-co-glycolide) millirods, beta-lapachone release kinetics in vivo showed a burst release of approximately 0.5 mg within 12 hours and a subsequently sustained release of the drug ( approximately 0.4 mg/kg/d) comparable with that observed in vitro. Antitumor efficacy studies showed significant tumor growth inhibition by beta-lapachone millirods compared with controls (P < 0.0001; n = 10 per group). Kaplan-Meier survival curves showed that tumor-bearing mice treated with beta-lapachone millirods survived nearly 2-fold longer than controls, without observable systemic toxicity.

CONCLUSIONS

Intratumoral delivery of beta-lapachone using polymer millirods showed the promising therapeutic potential for human prostate tumors.

Drug-eluting polymer implants in cancer therapy

BACKGROUND

Drug-eluting polymer implants present a compelling parenteral route of administration for cancer chemotherapy. With potential for minimally invasive, image-guided placement and highly localized drug release, these delivery systems are playing an increasingly important role in cancer management. This is particularly true as the use of labile proteins and other bioactive molecules is likely to increase in the upcoming years.

OBJECTIVE

In this review, we present the current trends in the application of Pre-formed and in situ-forming systems as drug-eluting implants for cancer chemotherapy.

METHODS

We outline the clinically available options as well as up-and-coming technologies and their advantages and challenges. We also describe ongoing related innovations with image-guided drug delivery, mathematical modeling of implanted delivery systems and implanted drug delivery in combination with other therapies.

RESULTS/CONCLUSION

Whether used alone or combined with other minimally invasive procedures, drug-eluting polymeric implants will play a significant role in the future of cancer management.

Model simulation and experimental validation of intratumoral chemotherapy using multiple polymer implants

Radiofrequency ablation has emerged as a minimally invasive option for liver cancer treatment, but local tumor recurrence is common. To eliminate residual tumor cells in the ablated tumor, biodegradable polymer millirods have been designed for local drug (e.g., doxorubicin) delivery. A limitation of this method has been the extent of drug penetration into the tumor (<5 mm), especially in the peripheral tumor rim where thermal ablation is less effective. To provide drug concentration above the therapeutic level as needed throughout a large tumor, implant strategies with multiple millirods were devised using a computational model. This dynamic, 3-D mass balance model of drug distribution in tissue was used to simulate the consequences of various numbers of implants in different locations. Experimental testing of model predictions was performed in a rabbit VX2 carcinoma model. This study demonstrates the value of multiple implants to provide therapeutic drug levels in large ablated tumors.

Polymer Implants for Intratumoral Drug Delivery and Cancer Therapy

To address the need for minimally invasive treatment of unresectable tumors, intratumoral polymer implants have been developed to release a variety of chemotherapeutic agents for the locoregional therapy of cancer. These implants, also termed "polymer millirods," were designed to provide optimal drug release kinetics to improve drug delivery efficiency and antitumor efficacy when treating unresectable tumors. Modeling of drug transport properties in different tissue environments has provided theoretical insights on rational implant design, and several imaging techniques have been established to monitor the local drug concentrations surrounding these implants both ex vivo and in vivo. Preliminary antitumor efficacy and drug distribution studies in a rabbit liver tumor model have shown that these implants can restrict tumor growth in small animal tumors (diameter < 1 cm). In the future, new approaches, such as three-dimensional (3-D) drug distribution modeling and the use of multiple drug-releasing implants, will be used to extend the efficacy of these implants in treating larger tumors more similar to intractable human tumors.

Modeling doxorubicin transport to improve intratumoral drug delivery to RF ablated tumors

A mathematical model of drug transport provides an ideal strategy to optimize intratumoral drug delivery implants to supplement radiofrequency (RF) ablation for tumor treatment. To simulate doxorubicin transport in non-ablated and ablated liver tumors, a one-dimensional, cylindrically symmetric transport model was generated using a finite element method (FEM). Parameters of this model, the diffusion (D) and elimination (gamma) coefficients for doxorubicin, were estimated using drug distributions measured 4 and 8 days after placing biodegradable implants in non-ablated and ablated rabbit VX2 liver carcinomas. In non-ablated tumor, values of diffusion and elimination parameters were 25% and 94% lower than normal liver tissue, respectively. In ablated tumor, diffusion near the ablation center was 75% higher than non-ablated tumor but decreased to the non-ablated tumor value at the ablation periphery. Drug elimination in ablated tumor was zero for the first four days, but by day 8 returned to 98% of the value for non-ablated tumor. Three-dimensional (3-D) simulations of drug delivery from implants with and without RF thermal ablation underscore the benefit of using RF ablation to facilitate local drug distribution. This study demonstrates the use of computational modeling and optimal parameter estimation to predict local drug pharmacokinetics from intratumoral implants after ablation.

Injectable polymer depot combined with radiofrequency ablation for treatment of experimental carcinoma in rat

OBJECTIVE

The purpose of this study was to investigate whether an intralesional chemotherapy depot with or without a chemosensitizer could improve the efficacy of radiofrequency (RF) ablation in treatment of experimental carcinoma in rats.

MATERIALS AND METHODS

Eighteen BD-IX rats were inoculated with bilateral subcutaneous tumors via injection of DHD/K12TRb rat colorectal carcinoma cells in suspension. Four weeks after inoculation, one tumor in each rat was treated with RF ablation at 80 degrees C for 2 minutes and the other with RF ablation followed by intralesional chemotherapy with carboplatin. The drug was administered via 2 different in situ-forming poly(D,L-lactide-coglycolide) (PLGA) depot formulations either with or without a chemosensitizer. Treatment efficacy was assessed by comparing the change in tumor diameter compared with control, percent of coagulation necrosis and a rating of treatment completeness.

RESULTS

Tumors treated with ablation and carboplatin + sensitizer (n = 9) showed a diameter decrease of 49.4 +/- 24.5% at the end point relative to ablation control, while those treated with ablation and carboplatin only (n = 8) showed a 7.1 +/- 12.6% decrease. Use of sensitizer also showed increased tissue necrosis (81.9 +/- 9.7% compared with 68.7 +/- 26.7% for ablation only) and double the number of complete treatments (6/9 or 66.7%) compared with ablation control (3/9 or 33.3%).

CONCLUSIONS

From these results, we conclude that intralesional administration of a carboplatin and sensitizer-loaded polymer depot after RF ablation has the potential to improve the outcome of ablation by increasing effectiveness of local adjuvant chemotherapy in preventing progression of tumor unaffected by the ablation treatment.

Antitumor efficacy and local distribution of doxorubicin via intratumoral delivery from polymer millirods

The purpose of this study was to evaluate the antitumor efficacy and local drug distribution from doxorubicin-containing poly(D,L-lactide-co-glycolide) (PLGA) implants for intratumoral treatment of liver cancer in a rabbit model. Cylindrical polymer millirods (length 8 mm, diameter 1.5 mm) were produced using 65% PLGA, 21.5% NaCl, and 13.5% doxorubicin. These implants were placed in the center of VX2 liver tumors (n = 16, 8 mm in diameter) in rabbits. Tumors were removed 4 and 8 days after millirod implantation, and antitumor efficacy was assessed using tumor size measurements, tumor histology, and fluorescent measurement of drug distribution. The treated tumors were smaller than the untreated controls on both day 4 (0.17 +/- 0.06 vs. 0.31 +/- 0.08 cm(2), p = 0.048) and day 8 (0.14 +/- 0.04 vs. 1.8 +/- 0.8 cm(2), p = 0.025). Drug distribution profiles demonstrated high doxorubicin concentrations (>1000 microg/g) at the tumor core at both time points and drug penetration distances of 2.8 and 1.3 mm on day 4 and 8, respectively. Histological examination confirmed necrosis throughout the tumor tissue. Biodegradable polymer millirods successfully treated the primary tumor mass by providing high doxorubicin concentrations to the tumor tissue over an eight day period.

Combined radiofrequency ablation and doxorubicin-eluting polymer implants for liver cancer treatment

Previously, biodegradable polymer implants (polymer millirods) to release chemotherapeutic agents directly into tumors have been developed. The purpose of this study is to evaluate local drug distribution from these implants in liver tumors treated with radiofrequency (RF) ablation and determine if the implants provide a therapeutic improvement over RF ablation alone. Cylindrical implants were fabricated using 65% poly(D,L-lactide-co-glycolide) (PLGA), 21.5% NaCl, and 13.5% doxorubicin. Control or drug-containing millirods were implanted inside VX2 liver tumors (11 mm diameter) in rabbits after RF ablation. Therapeutic efficacy was assessed 4 and 8 days after treatment using tumor size, histology, and fluorescence measurement of drug distribution. Tumors in both test groups recurred at the boundary of the ablated region. Therapeutic doxorubicin concentrations were found in more than 80% of the ablated area, but concentrations declined rapidly at the boundary between normal and ablated tissue. This region was characterized by a developing fibrous capsule with resolving inflammation, which restricted drug transport out of the ablated zone. The intratumoral doxorubicin implants delivered high concentrations of drug within the ablated region but only limited amounts outside the ablation zone. Future studies will focus on overcoming the fibrotic transport barrier and enhancing drug delivery to the periphery of the ablation region to prevent tumor progression.

Combined Tumor Therapy by Using Radiofrequency Ablation and 5-FU–Laden Polymer Implants: Evaluation in Rats and Rabbits

PURPOSE

To evaluate the use of 5-fluorouracil (5-FU)-laden polymer implants as an adjunct to radiofrequency (RF) ablation for tumor treatment.

MATERIALS AND METHODS

All animal studies were performed in compliance with the Case Western Reserve University Institutional Animal Care and Use Committee guidelines. Three studies were performed to investigate (a) in vitro dissolution of 5-FU-laden polymer implants in saline and bovine serum, (b) tissue distribution of 5-FU and its metabolite, 5-fluorouridine (5-FUrd), in the ablated liver tissue of rats (n = 4), and (c) efficacy of combined approach (n = 4) compared with that of ablation alone (n = 6) for VX2 liver tumor model in rabbits. Characterization of 5-FU release in vitro and distribution of 5-FU in rat liver tissue were analyzed by using high performance liquid chromatography; in vivo efficacy was assessed by using computed tomography and pathologic examination.

RESULTS

Results of the in vitro dissolution study showed that a 75% release of 5-FU occurred in 2 days when exposed to bovine serum and in 9 days when exposed to phosphate-buffered saline. In the ablated rat liver, the 5-FU level was higher at the center and lower at the periphery of the tissue both at 24 hours (41.0 mg per kilogram tissue vs 15.0 mg per kilogram tissue, respectively) and at 48 hours (8.0 mg per kilogram tissue vs 2.0 mg per kilogram tissue, respectively). The 5-FUrd concentration was twofold higher peripherally than centrally and was higher at 48 hours than at 24 hours. In rabbits, local delivery of 5-FU immediately after RF ablation provided a significant (P < .05) reduction in tumor size compared with ablation alone (1.80 cm3 +/- 0.28 [standard error] vs 3.53 cm3 +/- 0.52, respectively; P = .034) and a more than 20-fold reduction in tumor size compared with the control (1.80 cm3 +/- 0.28 vs 41.95 cm3 +/- 11.58, respectively; P = .018).

CONCLUSION

Combined treatment by using 5-FU polymer implants and RF ablation shows uniform sustained release of 5-FU for 48 hours at least 8 mm from the edge of the ablation zone and appears to be successful at controlling the growth of an experimental tumor in rabbits appreciably better than does ablation alone.

Quantitative computed tomography analysis of local chemotherapy in liver tissue after radiofrequency ablation

RATIONALE AND OBJECTIVES

Computed tomography (CT) was used to noninvasively monitor local drug pharmacokinetics from polymer implants in rat livers before and following radiofrequency ablation.

MATERIALS AND METHODS

Polymer matrixes containing carboplatin (a platinum-containing chemotherapeutic agent) were implanted into rat livers either immediately after radiofrequency ablation (n = 15) or without prior treatment (n = 15). The animals were divided into five subgroups (n = 3 per group) and subjected to a terminal CT scan at 6, 24, 48, 96, or 144 hours. Carboplatin concentration in tissue and within the implant matrix was correlated with CT intensity, and standard curves were produced for each environment. This correlation was used to evaluate the differences in drug transport properties between normal and ablated rat livers. A quantitative image analysis method was developed and used to evaluate the release rate and tissue distribution of carboplatin in normal and ablated liver tissue. The CT data were validated by previously reported atomic absorption spectroscopy measurement of implant and tissue drug levels.

RESULTS

Correlation of carboplatin concentration and Hounsfield units results in a linear relationship with correlation coefficients (slopes) of 15 and 4 Hounsfield units/(mg/mL), for carboplatin in tissue and polymer, respectively. Noninvasive monitoring of local pharmacokinetics in normal and ablated tissues indicates that ablation before local carboplatin delivery increases the retention of carboplatin within the polymer matrix and drastically increases the drug retention in the ablated tissue volume (over 3-fold difference) resulting in a higher average dose to the surrounding tissue. At 1.6 mm from the implant boundary, carboplatin concentration is significantly higher in ablated tissue at 48, 96, and 144 hours (P <.05), and reaches 4.7 mg/mL in ablated tissue at 48 hours. In comparison, the concentration in normal liver at 1.6 mm reaches only 0.7 mg/mL at the same time point. The drug penetrates 3.1 mm in ablated liver compared with 2.3 mm in normal liver also at 48 hours. After 144 hours, the drug is still detected at 3.1 mm in ablated liver but not in normal liver. The differences are significant (P <.05) at both 48 and 144 hours. Correlation with chemical analysis suggests that CT data accurately predicts the drug pharmacokinetics in both ablated and normal livers.

CONCLUSION

This work shows that X-ray CT imaging is a useful and promising technique for in vivo monitoring of the release kinetics of locally delivered radiopaque agents.