- Email: [email protected]
Thermoresponsive polymer for local chemoradiotherapy with doxorubicin bound via a newly developed hydrolytically labile bond
e40
Abstracts/Journal of Controlled Release 132 (2008) e37– e53
higher concentration resulting in a less efficient UV polymerisation and thus a lower crosslink density. To investigate the functional and structural integrity of the released protein, biological activity tests and CD measurements were performed. The Micrococcus lysodeikticus lysis assay on released lysozyme demonstrated that its enzymatic activity was fully preserved. The CD spectra of lysozyme released and the freshly prepared control protein were identical, indicating that the secondary structure of lysozyme was retained during encapsulation and release. Conclusion UV photopolymerisable pHPMAmlac-PEG-pHPMAmlac hydrogels are suitable delivery systems for controlled release of pharmaceutical proteins. The full preservation of protein structural and functional integrity emphasizes the protein-friendly nature of the hydrogel preparation method. The release rate is to some extent dependent on the polymer content of the gel and might also be tailored by the degree of methacrylation of the polymers, which is the topic of further investigation. References [1] W.E. Hennink, C.F. van Nostrum, Adv. Drug Deliv. Rev. 54 (2002) 13–36. [2] T. Vermonden, N.A.M. Besseling, M.J. van Steenbergen, W.E. Hennink, Langmuir 22 (2006) 10180–10184. [3] T. Vermonden, N.E. Fedorovich, D. van Geemen, J. Alblas, C.F. van Nostrum, W.J.A. Dhert, W.E. Hennink, Biomacromolecules In Press.
doi:10.1016/j.jconrel.2008.09.025
Thermoresponsive polymer for local chemoradiotherapy with doxorubicin bound via a newly developed hydrolytically labile bond M. Hrubýa,⁎, J. Kučkab, Č. Koňáka, M. Větříkb, O. Lebedab, K. Ulbricha Institute of Macromolecular Chemistry, Academy of Sciences of the Czech Republic, Heyrovský Sq. 2, 162 06 Prague 6, Czech Republic b Nuclear Physics Institute, Academy of Sciences of the Czech Republic, 250 68 Řež near Prague, Czech Republic E-mail: [email protected]. a
Abstract summary A new polymeric drug delivery system designed for possible local chemoradiotherapy using injectable thermoresponsive polymer with radionuclide and doxorubicin, which serves as an antiproliferative agent and hydrophobic moiety controlling bioerosion in the same time, was synthesized and characterized. Doxorubicin is bound to the polymer carrier by a newly developed N-glycosylamine bond.
potent cancerostatic with known synergy with ionization radiation [3] and is sufficiently soluble in water to readily diffuse from the degrading polymer and sufficiently hydrophobic to efficiently control CPT in the same time. The bond by which DOX is attached to the polymer should be cleavable at proper rate corresponding to the half-life of the radionuclide used, which is in the order of days for the common therapeutic radionuclides (e.g., 8.040 days for 131 I, 1.117 days for 166Ho, 2.67 days for 90Y or 6.71 days for 177Lu). The bond also should not have strong pH dependence of the drug release rate, because inflammated or cancer tissue have often lower pH than blood (pH 7.4) and high pH dependence of the degradation rate may thus lead to uncertainty in degradation rate of such polymer, because pH of the application site is caseto-case different and also changes in time. We have developed a new type of DOX attachment to the polymer for this purpose, which is described in this paper, the N-glycosylamine bond. The N-glycosylamine bond readily formed from a reducing saccharide and a primary amine, is hydrolytically labile under neutral and slightly acidic pH and up to our knowledge was not yet used to attach any drug to a polymer carrier. We thus describe a new type of such system in this paper that uses DOX bound by a newly developed Nglycosylamine hydrolytically labile bond to the polymer support to provide both solubilization control and potentially additional chemotherapeutic action to the polymer-bound therapeutic radionuclide. Results and discussion Acetal-protected carbohydrate monomers 6-O-methacryloyl-1,2:3,4-diO-isopropylidene-α-D-galactopyranose and 3-O-methacryloyl-1,2:5,6-di-Oisopropylidene-α-D-glucofuranose were synthesized by methacryloylation of the particular commercially available protected carbohydrates. A set of thermoresponsive copolymers of methacryloylated carbohydrate monomers with N-isopropylmethacrylamide (NIPMA) with different monomer ratio was synthesized in yields ca 65 % and an excellent linear correlation between the composition of the polymerization mixture and monomer ratio in the copolymers was found (R2 > 0.999), which enables fine-tuning of the saccharide monomeric unit content in the copolymers. Deprotection of acetal groups was tested using the two methods described for lowmolecular-weight analogies, i.e. by heating with diluted hydrochloric acid and by stirring in 80% aqueous trifluoroacetic acid. Heating with diluted hydrochloric acid led to extensive crosslinking, but trifluoroacetic acid deprotected the acetals smoothly without any crosslinking. Conjugation of saccharide monomeric units with DOX hydrochloride was first studied in methanol, but due to unsatisfactory conjugation yields another method was developed. This method uses non-aqueous (a mixture dimethyl sulfoxide–methanol) acetate buffer in which the N-glycosylamine is formed in yields above 66% even at high DOX contents in the case of the 6-Omethacryloyl-D-galactose (MAGA) monomeric unit. In the case of 3-Omethacryloyl-D-glucose monomeric unit the conjugation with DOX proceeds
Introduction Local brachytherapy using surgically implanted radioactive emitters is a very widely used method for the treatment of localized cancer lesions [1], especially in the case of prostate, but also of breast, ovarian and other cancer types. Local application largely eliminates radiation burden of healthy tissues while deploying high radiation doses to the site of implantation. Radiolabeled thermoresponsive polymers with cloud point temperature (CPT) between room and body temperatures may have an advantage for such applications that thermoresponsive polymers may be isotopically labelled in solution at room temperature, injected as solution and in the site of application the polymer forms a depo due to precipitation at body temperature [2]. If such a polymer is bioerodable and readily eliminable from the body after solubilization, then such depo may dissolve after decay of the radionuclide and both surgeries during implantation and removal may be avoided. Numerous anticancer drugs show synergic cytotoxic effects with ionizing radiation [3], which gives a special advantage to the connection of local chemotherapy and local radiotherapy using injectable thermoresponsive polymer as carrier for radionuclide and anticancer drug, which serves as an antiproliferative agent and hydrophobic moiety controlling bioerosion at the same time. We have chosen DOX as a drug for this study, because it is a
Fig. 1. The effect of copolymer composition on the cloud point temperature of the copolymers; ● poly(NIPMA-co-NIPAA), the content of NIPAA monomeric units is the variable; ■ poly(NIPMA-co-MAGA), the content of MAGA monomeric units is the variable; ▲ the effect of DOX loading on poly(NIPMA-co-MAGA) with 10 mol% saccharide monomeric unit, the content of DOX-modified monomeric units is the variable.
Abstracts/Journal of Controlled Release 132 (2008) e37– e53
e41
for possible radiotherapeutic applications, J. Controlled Release 119 (1) (2007) 25–33. [3] Y.G. Zhang, J.R. Williams, Time-targeted therapy (TTT): proof of principle using doxorubicin and radiation in a cultured cell system, Acta Oncol. 46 (5) (2007) 621–627.
doi:10.1016/j.jconrel.2008.09.026
Ultrasound-triggered local release of lipophilic drugs from a novel polymeric ultrasound contrast agent
Fig. 2. The in vitro release of DOX from the N-glycosylamine conjugate into the PBS buffer: ▲ pH 5.0; ● pH 6.5; ■ pH 7.4.
with low conversion only. This is why the copolymer with 10 mol% of MAGA monomeric unit was chosen for further studies. As expected, the highly hydrophilic saccharide monomeric unit increases the CPT of its copolymers with NIPMA, but the dependence is nonlinear (Fig. 1) probably due to steric reasons. Conjugation of such copolymers with DOX strongly decreases the CPT (Fig. 1) due to hydrophobicity of the anthracycline part of the DOX molecule. Copolymerization of NIPMA with Nisopropyl acrylamide (NIPAA; CPT of homopolymer 29 °C in 0.15 M NaCl) was used to further decrease the CPT of the carrier system below body temperature before degradation. The dependence of CPT on the content of the NIPAA monomeric unit in the polymer was linear (R2 > 0.99; see Fig. 1) as proven by the preparation and characterization of the set of copolymers NIPMA / NIPAA. The final optimization of the copolymer composition was done by interpolation of the dependencies of the CPT on the copolymer composition under presumption that the effect of the monomeric unit content increments is additive. The CPT of the prepared optimized copolymer was in good agreement with the theoretically predicted value [CPT before degradation calculated 33 °C, measured 34 °C; CPT after degradation both calculated and measured 40 °C; copolymer composition: 45.5 mol% NIPMA, 44 mol% NIPAA, 10 mol% MAGA, 0.5 mol% N-methacryloyl tyrosinamide (radioiodinable monomer) and 11.1 wt.% DOX]. The in vitro release study had proven that the release of DOX has a suitable rate in relation to the half-life of the radionuclides used in medicine (in the order of days, see Fig. 2) and is only slightly pH-dependent in the physiologically relevant pH range 5.0–7.4. The polymer completely dissolves during 2 weeks of incubation. A 125I and 131I-labelable phenolic moiety was introduced in the polymers to introduce the radionuclide, the radiochemical studies are underway and will be presented. Conclusion A new polymeric drug delivery system designed for possible local chemoradiotherapy using injectable thermoresponsive polymer with radionuclide and DOX that serves as an antiproliferative agent and hydrophobic moiety controlling bioerosion in the same time, was synthesized and characterized. DOX was bound to the polymer carrier by a newly developed N-glycosylamine bond enabling hydrolytically controlled drug release. Acknowledgments Financial support of the Grant Agency of the Academy of Sciences of the Czech Republic (grant # IAA400480616) and of the Academy of Sciences of the Czech Republic (grant # KAN200200651) is gratefully acknowledged.
K. Kooimana,⁎, M.R. Böhmerb, M. Emmera, H.J. Vosa, C. Chlonb, M. FoppenHartevelda, M. Versluisd, N. de Jonga,c,d, A. van Wamela a Department of Biomedical Engineering, Thoraxcenter, Erasmus MC, P.O. Box 2040, 3000 CA Rotterdam, The Netherlands b Philips Research Laboratories Eindhoven, Biomolecular Engineering, HTC11, 5656 AE Eindhoven, The Netherlands c Interuniversity Cardiology Institute of the Netherlands, P.O. Box 19258, 3501 DG Utrecht, The Netherlands d Institute for Biomedical Technology (BMTI), Department of Physics of Fluids, Faculty of Science and Technology, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands E-mail: [email protected]. Abstract summary The advantage of ultrasound contrast agents (UCAs) as drug delivery systems is the ability to non-invasively control the local and triggered release of a drug or gene. In this study we designed and characterized a novel UCAbased drug delivery system, based on polymer-shelled microcapsules filled with a mixture of gas and oil, for the local delivery of lipophilic drugs. Introduction Ultrasound contrast agents (UCAs) are routinely used in perfusion imaging in cardiology as well as radiology. UCAs consist of a gas core that is surrounded by a shell made from lipid, protein, sugar or polymer. The diameter of the microbubbles is in the range of 1 to 10 μm [1]. Although UCAs were initially developed to enhance diagnostic imaging, their potential as local drug delivery systems is now widely recognized and their use continues to expand. A unique feature of ultrasound is local insonification which can be used to trigger drug release from an UCA-based drug delivery system only at a region of interest. In addition, ultrasound imaging will aid the guidance and monitoring of therapy. Given the presence of microvascular networks in nearly all tissues, local drug delivery using an UCA-based drug delivery system provides extensive possibilities for treating pathological tissues, including the treatment of vascular structures themselves [1,2,3]. This study focuses on the production and characterization of novel nearmicrometer polymer-shelled microcapsules that were designed for the local delivery of lipophilic drugs. In principal there are several ways to incorporate a drug into ultrasound contrast agents. In this study we dissolved the lipophilic drug in oil, i.e. hexadecane, and loaded this within the microcapsules. Experimental methods The polymer poly(l-lactic acid) terminated with 1H-1H perfluoro-octan1-ol (Philips, 1659 WN495-3), abbreviated as pLA-pFO, formed the shell of the microcapsules [4]. A solution of the shell-forming polymer and an alkane in dichloromethane was prepared and emulsified in water containing polyvinyl alcohol. This solution was shaken manually to prepare a premix and then repeatedly pressed through a glass filter. Microcapsules were prepared Table 1 Composition of microcapsules
References
Sample label
Cyclodecane to hexadecane ratio
Calculated fill of microcapsules with hexadecane (= oil)a
[1] A. Sahgal, M. Roach, Permanent prostate seed brachytherapy: a current perspective on the evolution of the technique and its application, Nat. Clin. Pract. Urol. 4 (12) (2007) 658–670. [2] M. Hruby, J. Kucka, O. Lebeda, H. Mackova, M. Babic, C. Konak, M. Studenovsky, A. Sikora, J. Kozempel, K. Ulbrich, New bioerodable thermoresponsive polymers
S0 S40 S97
1:0 1:1 0:1
0% oil 40–42% oil 97–100% oil
a
determined with GC/MS.
Abstracts/Journal of Controlled Release 132 (2008) e37– e53
higher concentration resulting in a less efficient UV polymerisation and thus a lower crosslink density. To investigate the functional and structural integrity of the released protein, biological activity tests and CD measurements were performed. The Micrococcus lysodeikticus lysis assay on released lysozyme demonstrated that its enzymatic activity was fully preserved. The CD spectra of lysozyme released and the freshly prepared control protein were identical, indicating that the secondary structure of lysozyme was retained during encapsulation and release. Conclusion UV photopolymerisable pHPMAmlac-PEG-pHPMAmlac hydrogels are suitable delivery systems for controlled release of pharmaceutical proteins. The full preservation of protein structural and functional integrity emphasizes the protein-friendly nature of the hydrogel preparation method. The release rate is to some extent dependent on the polymer content of the gel and might also be tailored by the degree of methacrylation of the polymers, which is the topic of further investigation. References [1] W.E. Hennink, C.F. van Nostrum, Adv. Drug Deliv. Rev. 54 (2002) 13–36. [2] T. Vermonden, N.A.M. Besseling, M.J. van Steenbergen, W.E. Hennink, Langmuir 22 (2006) 10180–10184. [3] T. Vermonden, N.E. Fedorovich, D. van Geemen, J. Alblas, C.F. van Nostrum, W.J.A. Dhert, W.E. Hennink, Biomacromolecules In Press.
doi:10.1016/j.jconrel.2008.09.025
Thermoresponsive polymer for local chemoradiotherapy with doxorubicin bound via a newly developed hydrolytically labile bond M. Hrubýa,⁎, J. Kučkab, Č. Koňáka, M. Větříkb, O. Lebedab, K. Ulbricha Institute of Macromolecular Chemistry, Academy of Sciences of the Czech Republic, Heyrovský Sq. 2, 162 06 Prague 6, Czech Republic b Nuclear Physics Institute, Academy of Sciences of the Czech Republic, 250 68 Řež near Prague, Czech Republic E-mail: [email protected]. a
Abstract summary A new polymeric drug delivery system designed for possible local chemoradiotherapy using injectable thermoresponsive polymer with radionuclide and doxorubicin, which serves as an antiproliferative agent and hydrophobic moiety controlling bioerosion in the same time, was synthesized and characterized. Doxorubicin is bound to the polymer carrier by a newly developed N-glycosylamine bond.
potent cancerostatic with known synergy with ionization radiation [3] and is sufficiently soluble in water to readily diffuse from the degrading polymer and sufficiently hydrophobic to efficiently control CPT in the same time. The bond by which DOX is attached to the polymer should be cleavable at proper rate corresponding to the half-life of the radionuclide used, which is in the order of days for the common therapeutic radionuclides (e.g., 8.040 days for 131 I, 1.117 days for 166Ho, 2.67 days for 90Y or 6.71 days for 177Lu). The bond also should not have strong pH dependence of the drug release rate, because inflammated or cancer tissue have often lower pH than blood (pH 7.4) and high pH dependence of the degradation rate may thus lead to uncertainty in degradation rate of such polymer, because pH of the application site is caseto-case different and also changes in time. We have developed a new type of DOX attachment to the polymer for this purpose, which is described in this paper, the N-glycosylamine bond. The N-glycosylamine bond readily formed from a reducing saccharide and a primary amine, is hydrolytically labile under neutral and slightly acidic pH and up to our knowledge was not yet used to attach any drug to a polymer carrier. We thus describe a new type of such system in this paper that uses DOX bound by a newly developed Nglycosylamine hydrolytically labile bond to the polymer support to provide both solubilization control and potentially additional chemotherapeutic action to the polymer-bound therapeutic radionuclide. Results and discussion Acetal-protected carbohydrate monomers 6-O-methacryloyl-1,2:3,4-diO-isopropylidene-α-D-galactopyranose and 3-O-methacryloyl-1,2:5,6-di-Oisopropylidene-α-D-glucofuranose were synthesized by methacryloylation of the particular commercially available protected carbohydrates. A set of thermoresponsive copolymers of methacryloylated carbohydrate monomers with N-isopropylmethacrylamide (NIPMA) with different monomer ratio was synthesized in yields ca 65 % and an excellent linear correlation between the composition of the polymerization mixture and monomer ratio in the copolymers was found (R2 > 0.999), which enables fine-tuning of the saccharide monomeric unit content in the copolymers. Deprotection of acetal groups was tested using the two methods described for lowmolecular-weight analogies, i.e. by heating with diluted hydrochloric acid and by stirring in 80% aqueous trifluoroacetic acid. Heating with diluted hydrochloric acid led to extensive crosslinking, but trifluoroacetic acid deprotected the acetals smoothly without any crosslinking. Conjugation of saccharide monomeric units with DOX hydrochloride was first studied in methanol, but due to unsatisfactory conjugation yields another method was developed. This method uses non-aqueous (a mixture dimethyl sulfoxide–methanol) acetate buffer in which the N-glycosylamine is formed in yields above 66% even at high DOX contents in the case of the 6-Omethacryloyl-D-galactose (MAGA) monomeric unit. In the case of 3-Omethacryloyl-D-glucose monomeric unit the conjugation with DOX proceeds
Introduction Local brachytherapy using surgically implanted radioactive emitters is a very widely used method for the treatment of localized cancer lesions [1], especially in the case of prostate, but also of breast, ovarian and other cancer types. Local application largely eliminates radiation burden of healthy tissues while deploying high radiation doses to the site of implantation. Radiolabeled thermoresponsive polymers with cloud point temperature (CPT) between room and body temperatures may have an advantage for such applications that thermoresponsive polymers may be isotopically labelled in solution at room temperature, injected as solution and in the site of application the polymer forms a depo due to precipitation at body temperature [2]. If such a polymer is bioerodable and readily eliminable from the body after solubilization, then such depo may dissolve after decay of the radionuclide and both surgeries during implantation and removal may be avoided. Numerous anticancer drugs show synergic cytotoxic effects with ionizing radiation [3], which gives a special advantage to the connection of local chemotherapy and local radiotherapy using injectable thermoresponsive polymer as carrier for radionuclide and anticancer drug, which serves as an antiproliferative agent and hydrophobic moiety controlling bioerosion at the same time. We have chosen DOX as a drug for this study, because it is a
Fig. 1. The effect of copolymer composition on the cloud point temperature of the copolymers; ● poly(NIPMA-co-NIPAA), the content of NIPAA monomeric units is the variable; ■ poly(NIPMA-co-MAGA), the content of MAGA monomeric units is the variable; ▲ the effect of DOX loading on poly(NIPMA-co-MAGA) with 10 mol% saccharide monomeric unit, the content of DOX-modified monomeric units is the variable.
Abstracts/Journal of Controlled Release 132 (2008) e37– e53
e41
for possible radiotherapeutic applications, J. Controlled Release 119 (1) (2007) 25–33. [3] Y.G. Zhang, J.R. Williams, Time-targeted therapy (TTT): proof of principle using doxorubicin and radiation in a cultured cell system, Acta Oncol. 46 (5) (2007) 621–627.
doi:10.1016/j.jconrel.2008.09.026
Ultrasound-triggered local release of lipophilic drugs from a novel polymeric ultrasound contrast agent
Fig. 2. The in vitro release of DOX from the N-glycosylamine conjugate into the PBS buffer: ▲ pH 5.0; ● pH 6.5; ■ pH 7.4.
with low conversion only. This is why the copolymer with 10 mol% of MAGA monomeric unit was chosen for further studies. As expected, the highly hydrophilic saccharide monomeric unit increases the CPT of its copolymers with NIPMA, but the dependence is nonlinear (Fig. 1) probably due to steric reasons. Conjugation of such copolymers with DOX strongly decreases the CPT (Fig. 1) due to hydrophobicity of the anthracycline part of the DOX molecule. Copolymerization of NIPMA with Nisopropyl acrylamide (NIPAA; CPT of homopolymer 29 °C in 0.15 M NaCl) was used to further decrease the CPT of the carrier system below body temperature before degradation. The dependence of CPT on the content of the NIPAA monomeric unit in the polymer was linear (R2 > 0.99; see Fig. 1) as proven by the preparation and characterization of the set of copolymers NIPMA / NIPAA. The final optimization of the copolymer composition was done by interpolation of the dependencies of the CPT on the copolymer composition under presumption that the effect of the monomeric unit content increments is additive. The CPT of the prepared optimized copolymer was in good agreement with the theoretically predicted value [CPT before degradation calculated 33 °C, measured 34 °C; CPT after degradation both calculated and measured 40 °C; copolymer composition: 45.5 mol% NIPMA, 44 mol% NIPAA, 10 mol% MAGA, 0.5 mol% N-methacryloyl tyrosinamide (radioiodinable monomer) and 11.1 wt.% DOX]. The in vitro release study had proven that the release of DOX has a suitable rate in relation to the half-life of the radionuclides used in medicine (in the order of days, see Fig. 2) and is only slightly pH-dependent in the physiologically relevant pH range 5.0–7.4. The polymer completely dissolves during 2 weeks of incubation. A 125I and 131I-labelable phenolic moiety was introduced in the polymers to introduce the radionuclide, the radiochemical studies are underway and will be presented. Conclusion A new polymeric drug delivery system designed for possible local chemoradiotherapy using injectable thermoresponsive polymer with radionuclide and DOX that serves as an antiproliferative agent and hydrophobic moiety controlling bioerosion in the same time, was synthesized and characterized. DOX was bound to the polymer carrier by a newly developed N-glycosylamine bond enabling hydrolytically controlled drug release. Acknowledgments Financial support of the Grant Agency of the Academy of Sciences of the Czech Republic (grant # IAA400480616) and of the Academy of Sciences of the Czech Republic (grant # KAN200200651) is gratefully acknowledged.
K. Kooimana,⁎, M.R. Böhmerb, M. Emmera, H.J. Vosa, C. Chlonb, M. FoppenHartevelda, M. Versluisd, N. de Jonga,c,d, A. van Wamela a Department of Biomedical Engineering, Thoraxcenter, Erasmus MC, P.O. Box 2040, 3000 CA Rotterdam, The Netherlands b Philips Research Laboratories Eindhoven, Biomolecular Engineering, HTC11, 5656 AE Eindhoven, The Netherlands c Interuniversity Cardiology Institute of the Netherlands, P.O. Box 19258, 3501 DG Utrecht, The Netherlands d Institute for Biomedical Technology (BMTI), Department of Physics of Fluids, Faculty of Science and Technology, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands E-mail: [email protected]. Abstract summary The advantage of ultrasound contrast agents (UCAs) as drug delivery systems is the ability to non-invasively control the local and triggered release of a drug or gene. In this study we designed and characterized a novel UCAbased drug delivery system, based on polymer-shelled microcapsules filled with a mixture of gas and oil, for the local delivery of lipophilic drugs. Introduction Ultrasound contrast agents (UCAs) are routinely used in perfusion imaging in cardiology as well as radiology. UCAs consist of a gas core that is surrounded by a shell made from lipid, protein, sugar or polymer. The diameter of the microbubbles is in the range of 1 to 10 μm [1]. Although UCAs were initially developed to enhance diagnostic imaging, their potential as local drug delivery systems is now widely recognized and their use continues to expand. A unique feature of ultrasound is local insonification which can be used to trigger drug release from an UCA-based drug delivery system only at a region of interest. In addition, ultrasound imaging will aid the guidance and monitoring of therapy. Given the presence of microvascular networks in nearly all tissues, local drug delivery using an UCA-based drug delivery system provides extensive possibilities for treating pathological tissues, including the treatment of vascular structures themselves [1,2,3]. This study focuses on the production and characterization of novel nearmicrometer polymer-shelled microcapsules that were designed for the local delivery of lipophilic drugs. In principal there are several ways to incorporate a drug into ultrasound contrast agents. In this study we dissolved the lipophilic drug in oil, i.e. hexadecane, and loaded this within the microcapsules. Experimental methods The polymer poly(l-lactic acid) terminated with 1H-1H perfluoro-octan1-ol (Philips, 1659 WN495-3), abbreviated as pLA-pFO, formed the shell of the microcapsules [4]. A solution of the shell-forming polymer and an alkane in dichloromethane was prepared and emulsified in water containing polyvinyl alcohol. This solution was shaken manually to prepare a premix and then repeatedly pressed through a glass filter. Microcapsules were prepared Table 1 Composition of microcapsules
References
Sample label
Cyclodecane to hexadecane ratio
Calculated fill of microcapsules with hexadecane (= oil)a
[1] A. Sahgal, M. Roach, Permanent prostate seed brachytherapy: a current perspective on the evolution of the technique and its application, Nat. Clin. Pract. Urol. 4 (12) (2007) 658–670. [2] M. Hruby, J. Kucka, O. Lebeda, H. Mackova, M. Babic, C. Konak, M. Studenovsky, A. Sikora, J. Kozempel, K. Ulbrich, New bioerodable thermoresponsive polymers
S0 S40 S97
1:0 1:1 0:1
0% oil 40–42% oil 97–100% oil
a
determined with GC/MS.