Interface-Engineered Amphiphilic Block Copolymers with Tuned

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Chapter 9

Interface-Engineered Amphiphilic Block Copolymers with Tuned Enzymatic Resistance for Controlled Delivery of Chemotherapeutic Drugs Uttam Satyal,1 Vishnu Dutt Sharma,1 Jennifer A. Shif,2 and Marc A. Ilies*,1 1Department

of Pharmaceutical Sciences and Moulder Center of Drug Discovery Research, Temple University School of Pharmacy, Philadelphia, Pennsylvania 19140, United States 2College of Science and Technology, Temple University, 1803 N. Broad Street, Philadelphia, Pennsylvania 19122, United States *E-mail: [email protected].

Amphiphilic block copolymers combining polyethylene glycol with hydrophobic biodegradable polyesters, such as PEG-PLA or PEG-PCL, can act in self-assembled form as drug delivery systems (DDSs) with proved clinical efficiency. However, circulation time and biodistribution of these polymeric DDSs can be further improved by understanding the factors affecting their dynamic stability and degradation. We are presenting data revealing that micelles generated from interface-engineered PEG-PBO-PCL triblock copolymers can resist esterases present in blood better than micelles made out of standard PEGPCL congeners, but can be degraded faster than these ones by specific esterases over-expressed in tumors, thus showing selective stability blood/tumor.

© 2017 American Chemical Society Ilies; Control of Amphiphile Self-Assembling at the Molecular Level: Supra-Molecular Assemblies with Tuned ... ACS Symposium Series; American Chemical Society: Washington, DC, 2017.


Introduction Cancer is currently the second most common cause of death in the US and worldwide (1). Chemotherapeutic drugs used in the treatment of various forms of cancer generally lack selectivity between normal and malignant cells and consequently are associated with significant adverse effects, many of them life-threatening. On the other hand, drug delivery systems (DDSs) can change the pharmacokinetics of chemotherapeutic drugs, focusing their action on the tumor site (2, 3). These engineered systems can also improve the solubility of many poorly water-soluble anticancer drugs (e.g. paclitaxel, docetaxel), can prevent their premature inactivation, and can control the amount and rate of drug delivered to the affected site (4–12). Consequently, the therapeutic index of chemotherapeutic drugs can be significantly improved and the side effects associated with the use of these highly toxic agents can be substantially reduced, allowing efficient treatment of late-stage cases of cancer (13). Amphiphilic copolymers based on polyethylene glycol (PEG) and biodegradable lipophilic polymers such as polylactic acid (PLA), and polycaprolactone (PCL) (14–21) can self-assemble in water generating nanosystems extremely attractive as drug and gene delivery systems (10, 22–35). Depending on the packing parameter (36–38) and other thermodynamic factors (39, 40) one may observe micelles, filomicelles, or polymerosomes, displaying a wide range of hydrodynamic properties and drug loading capacities (21, 41–44). The dense PEG brush on the surface of these nanosystems reduces the interaction with proteins and figurative elements of the blood, conferring “stealth” properties and increases the circulation time of the delivery system. Other important advantages include the relative ease of synthesis and formulation, excellent biocompatibility, large cargo loading capacity, good control of supra-molecular shape and stiffness, a favorable drug release, toxicity and translational profile. They also allow many derivatization strategies for practically endless targeting possibilities (31, 32, 42, 43, 45–49). These major advantages propelled polymeric DDSs into clinic. Notably, PEG-PLA micelles with diameter around 25 nm encapsulating paclitaxel (Genexol-PM) were approved in Korea and are under advanced clinical trials in the U.S. for the management of metastatic non-small-cell lung cancer, breast cancer and in combination with carboplatin for the treatment of ovarian cancer (48, 50). The hydrophilic/hydrophobic interface structure and chemical stability is critical for formation, stability, drug loading and drug release profile of self-assembled DDSs (51–53). An important premise for successful drug delivery focused to the tumor is a good circulation time of the DDS when administered IV, in the range of several days (28) for efficient and selective targeting or accumulation at tumor sites via EPR effect, via enhanced uptake, or via selective degradation at the tumor site (9, 10, 28, 54, 55). Currently, circulation time of biocompatible PEG-based DDSs is in the range of hours to 1-2 days at best (43, 56). This is due to a large extent to the premature inactivation of DDSs through substantial modification of their physicochemical properties (size, shape, zeta potential, PEG chain density) via absorption of opsonins and other amphiphilic blood proteins at the hydrophilic/hydrophobic interface. Some 212 Ilies; Control of Amphiphile Self-Assembling at the Molecular Level: Supra-Molecular Assemblies with Tuned ... ACS Symposium Series; American Chemical Society: Washington, DC, 2017.


amphiphilic proteins present in blood such as albumin and especially endothelial lipases (57–59) have esterase activity and thus can catalyze the hydrolysis of the ester junction between the PEG block and the polyester hydrophobic core (60–62). The result is PEG shedding and a loss of stealth properties (63, 64), with subsequent binding of other blood proteins (65, 66), uptake by macrophages of the mononuclear phagocyte system, or removal by Kupffer cells (28). The loaded drug is either prematurely released in the bloodstream or is ending in scavenging cells, causing systemic toxicity. The use of longer PEG segments (MW>5000 Da) (65) can partially alleviate the problem, at the expense of increasing the size and immunogenicity of the nanoparticles and of decreasing the availability of any targeting moiety present. In collaboration with the groups of Drs. Bradford Wayland and Michael Fryd, we proposed a new chemical way to selectively stabilize PEG-based self-assembled amphiphilic copolymers via interfacial engineering (51, 67). Thus, in DDSs based on self-assembled PEG-based amphiphilic diblock copolymers such as PEG-PLA, PEG-PLGA, PEG-PCL, the boundary between the biodegradable block and the hydrolytically stable block coincides with the hydrophilic/hydrophobic self-assembling interface (Figure 1). Water has access to the interface between the stable (PEG) and the hydrolysable block (PLA, PCL), therefore adsorption at this double interface of amphiphilic proteins with esterase activity can dramatically accelerate hydrolysis and can cause fast and complete degradation of the nanosystems within hours, as shown by literature studies (51, 56, 60, 61, 63, 68, 69). The hydrolytic degradation at the hydrophilic/hydrophobic interface can also be further self-catalyzed by small amounts of acid monomer (lactic, 6-hydroxycaproic acids) released when these (loaded) nanosystems are stored before use, reducing shelf life and batch-to-batch consistency of these formulations. The negative impact is augmented when encapsulated drugs are also hydrolytically vulnerable. On the other hand, the DDSs should degrade as fast as possible once the delivery site is reached. This degradation should occur either in the immediate vicinity of the membrane of the cancer cells or inside the cancer cells, if the DDSs were internalized. In both cases the degradation should be ensured by esterases present in these environments. The selective stability against esterases encountered by the DDS en-route versus those encountered at the delivery site is essential for the success of the delivery process and hence for enhancing the therapeutic index of chemotherapeutic drugs. As mentioned above, we have separated the hydrophilic/hydrophobic interface of PEG-PCL diblock copolymers from the hydrolysable interface between PEGand PCL blocks through the insertion of a short, non-degradable, oligomeric PBO hydrophobic linking segment between the non-degradable hydrophilic PEG block and the biodegradable hydrophobic PCL block, thus synthesizing novel PEG-PBO-PCL polymers (Figure 1) (51). We have selected PEG-PCL as model for implementing our interfacial inactivation strategy because the semi-crystalline nature of the PCL block allows a better evaluation of consequences associated with interfacial engineering of amphiphilic block copolymers as compared with other models (20, 70). 213 Ilies; Control of Amphiphile Self-Assembling at the Molecular Level: Supra-Molecular Assemblies with Tuned ... ACS Symposium Series; American Chemical Society: Washington, DC, 2017.


Figure 1. Interfacial engineering strategy of diblock copolymers and its consequences: separation of the hydrophilic/hydrophobic interface of PEG-PCL diblock copolymers from the nonhydrolysable/hydrolysable boundary between PEG and PCL blocks, through the insertion of a non-hydrolysable hydrophobic PBO block, modulates the enzymatic degradation of the corresponding micelles by amphiphilic esterases. Interfacial engineering can be tuned to allow hydrolysis by selected esterases that are over-expressed in tumors and to resist blood esterases, conferring selective stability of the polymeric DDS. Adapted from reference (51). Copyright 2012 American Chemical Society.

We have previously shown that this interfacial engineering of PEG-PCL diblock copolymers confers stability against acid and esterases typically encountered in the GI tract, aiming to develop new oral DDSs (51, 67). In the current study, we are extending these enzymatic stability studies to esterases typically encountered in the blood and at tumor sites, for assessing the usefulness of the concept towards the development of DDSs suitable to be administered IV for the delivery of chemotherapeutic drugs to tumors.

Materials and Methods Materials Diblock and triblock copolymers used in this study were synthesized as previously described (51). Nile Red dye, phosphate buffer saline tablets, HEPES buffer saline (HBS), albumin from human serum, butyryl cholinesterase from equine serum, lipases from Pseudomonas fluorescens, and Pseudomonas cepacia, carbonic anhydrase (isozyme II from human erythrocytes), phospholipase A2 (PLA2) from porcine pancreas, and papain from papaya latex were bought from Sigma Aldrich (St Louis, MO). Fetal bovine serum (FBS) was purchased from Rocky Mountain Biologicals (Missoula, MT). Methods Esterase Activity Assay through 4-Nitrophenyl Acetate Hydrolysis A 0.01 M solution of 4-nitrophenyl acetate was prepared in DME. Enzymatic solution stocks of 1 mg/mL were prepared for each of lipase (from P. fluorescens or from P. cepacia) and carbonic anhydrase II enzymes in HBS. Similarly stock solutions of butyryl cholinesterase (2 mg/mL), and albumin (250 mg/mL) were also prepared in HBS. Phospholipase A2 solution was used at nominal 214 Ilies; Control of Amphiphile Self-Assembling at the Molecular Level: Supra-Molecular Assemblies with Tuned ... ACS Symposium Series; American Chemical Society: Washington, DC, 2017.


concentration received. These concentrations were based on the estimated esterase activity provided by the manufacturer. Note that the activities were estimated using different substrates for different enzymes. In a clean glass/quartz cuvette, 10 μL of an enzyme stock was mixed with 890 μL of HBS. To the buffered enzyme solution, 100 μL of 4-nitrophenyl acetate solution was added and the absorption was measured at 400 nm at pre-designated time intervals, at 25 °C. For estimation of autohydrolysis reaction, 900 μL of HBS was taken in a cuvette and mixed with 100 μL of 4-nitrophenyl acetate and the absorption measured at 400 nm, at 25 °C. The absorption value obtained from autohydrolysis reaction was deducted from the absorption value obtained for enzymatic hydrolysis study to obtain the corrected esterase activity of various enzymes against 4-nitrophenyl acetate.

Preparation of Polymeric Micelles Stock solutions of polymers (PEG45-PCL61, PEG45-PBO6-PCL58, PEG45-PBO9-PCL53) were prepared in acetone at a concentration of 20 mg/mL. A Nile red dye stock solution of 1 mg/mL was also prepared in acetone. Polymeric micelles were prepared by treating 500 µL of polymer stock solution in acetone with 0.5 mL of water added dropwise at the rate of 0.5 mL/min under continuous stirring and allowing the amphiphile to self-assemble into nano-sized micelles. The size of the micelles thus prepared was determined using a Zetasizer Nano (Malvern Instruments, Malvern, UK). The micelle suspension was then dialyzed through 3500 MWCO dialysis membrane overnight to remove acetone from the suspension. Acetone removal was confirmed via UV-Vis absorption measurement at 266 nm. These micelles were filtered through 0.2 μm filters, followed by 0.1 μm filters and their size was re-determined. While preparing the micelles containing Nile Red dye, the dye stock solution was added to polymer solution before nanoprecipitation at the concentration of 5 μL dye per 10 mg polymer, following the same nanoprecipitation technique described above. A PEG assay was performed to determine the concentration of the polymers in final polymeric micelle suspension.

Micelle Degradation Studies Using Fluorescent Decay Polymeric micelles containing Nile Red dye were used in this experiment. In a fluorescent cuvette, a micellar solution containing 2 mg polymer (typically around 1.3 mg/mL) was diluted with 200 μL of 10x PBS and the final volume adjusted to 1.98 mL with DI water. The cuvette was thermostatted at 37 °C and 20 μL of 1 mg/mL lipase enzyme stock (from P. cepacia) was added and the fluorescence of Nile Red was measured at λEx: 535 nm, λEm: 592 nm with a cutoff at 550 nm, at predefined time intervals. The cuvettes were incubated at 37°C for the whole study.

215 Ilies; Control of Amphiphile Self-Assembling at the Molecular Level: Supra-Molecular Assemblies with Tuned ... ACS Symposium Series; American Chemical Society: Washington, DC, 2017.

Micelle Degradation Studies Using DLS


Micelle degradation via DLS was studied by adding an amount of 50 μL of enzyme stock solution to the fixed amount of polymer at a final concentration of 1 mg/mL polymer in the solution. Thus, a micellar suspension containing 500 μg of polymer (typically around 1.3 mg/mL) was diluted with 50 μL of 10x PBS in a new cuvette, and the final volume adjusted to 450 μL with DI water. The cuvette was thermostatted at 37 °C, and 50 μL of enzyme stock was added and the size of the micelles was measured at various time intervals at 37°C. For albumin degradation study, a final concentration of 1 mg/mL albumin was used, while for FBS degradation study, 50% FBS by volume (250 μL) was used.

Results and Discussion The kinetic studies of micelles degradation in the presence of acid or lipase, as typical degradation elements encountered in the GI tract, revealed a higher stability of the triblock PEG-PBO-PCL nano micelles as compared to standard diblock PEG-PCL ones. The degradation kinetics was followed using 1H-NMR, GPC and DLS as major techniques (Figure 2) (51, 67). These techniques are sensitive but rather cumbersome, and require substantial resources. For fast screening of many enzymes and polymeric formulations we were interested in exploring other inexpensive, fast and sensitive methods. An analysis of literature evidenced fluorescence methods as adequate for this purpose (71, 72). They rely on the use of solvatochromy of hydrophobic dyes such as Nile Red or DiI to follow the degradation process (73–75). We have selected the Nile Red method as this dye is very lipophilic and disperses well into the hydrophobic core of the amphiphilic block copolymer micelles. We compared the lipase catalyzed degradation of interfacial engineered PEG45-PBO9-PCL53 based micelles with size-matched PEG45-PCL61 diblock copolymer based micelles via Nile Red fluorescence method (Figure 2). An analysis of Figure 2, clearly reveals that the Nile Red-based solvatochromy fluorescence method yielded similar results with NMR and GPC. Another method that we explored was the DLS method (76–78). If the size of the polymeric micelle nano-DDSs is monitored while incubated with acid or lipase, one can observe that the main peak of the nanoformulation remains constant in time. This is due to the fact that the rate limiting step in the degradation is the docking of the enzyme to the micelle. The enzyme docking is followed by hydrolysis of the interfacial ester bond, loss of PEG corona and coalescence of remaining core with other similarly degraded entities (Figure 3), generating larger aggregates that can be seen in DLS as additional peaks at higher size values (Figure 2f). As a consequence, the polydispersity of the system increases and the Zav (the average size of the particle size distribution) also increases (Figure 2g). Consequently, an even easier way to follow the polymeric micelle hydrolysis kinetics is to plot the ratio between the Zav (Zav at a given time) and the initial Zav0 as a function of time (Figure 2g). We found that the DLS method is as fast and sensitive as the fluorescence method and other spectroscopic methods used 216 Ilies; Control of Amphiphile Self-Assembling at the Molecular Level: Supra-Molecular Assemblies with Tuned ... ACS Symposium Series; American Chemical Society: Washington, DC, 2017.


previously (51, 67, 79). We adopted this method for our study, as it does not require any additives (dyes, etc) that could affect the degradation kinetics. To prove our hypothesis, we assessed the esterase hydrolysis pattern of the two polymeric micelle DDSs using various esterases associated with the IV route of administration. A plethora of enzymes have been shown to have esterase activity in the blood and tissues (80–82).

Figure 2. Comparative acid- or esterase-mediated hydrolytic degradation of PEG45PCL62 diblock copolymer micelles versus PEG45PBO6PCL58 and PEG45PBO9PCL61 triblock copolymer micelles, in PBS buffer pH = 7.4, at 37°C, with either HCl or with Pseudomonas cepacia lipase (2.86 U/mL), at different incubation times, monitored by 1H-NMR (a, b), GPC (c, d), fluorescence (e) or DLS (f, g). Adapted in part with permission from reference (51). Copyright 2012 American Chemical Society; and reference (67). Copyright 2013 Elsevier.



Figure 3. Proposed mechanism for esterase-mediated enzymatic degradation of polymeric micelles: once the enzyme docks on the surface of a diblock/triblock copolymer micelle, interfacial hydrolysis occurs, generating a partially PEGunshielded micelle, which can stabilize through coalescence with similar (partially-degraded) micelles and form a larger assembly. Eventually the PCL block in all micelles will be entirely hydrolyzed, yielding water-soluble products and the initial enzyme, which can start a new degradation cycle. 4-Nitrophenyl Acetate Hydrolysis by Different Esterases Present in Blood/Vasculature or in Tumor Sites The various esterases we acquired had their activities determined against different substrates and the esterase activity values provided by the vendors had different units. Therefore, in order to compare the activity of these enzymes within the same framework, we assessed the esterase activity of each enzyme used in this study for the hydrolysis of amphiphilic 4-nitrophenyl acetate (Figure 4). An analysis of the data from Figure 4 revealed that lipase from P. fluorescens had the highest hydrolysis rate of the substrate after 30 minutes. Esterases from serum (50% FBS, non-heat-treated) also showed comparable activity with P. fluorescens lipase, followed by butyryl cholinesterase, carbonic anhydrase. Albumin also showed some esterase activity, as previously reported (83–85). This clearly shows that enzymes present in the serum, in addition to albumin, have important contributions to the total esterase activity of the blood. Assessment of En-Route Stability of the Block Copolymer Micelles The first barrier that an injectable DDS encounters is the blood environment, rich in various enzymes that have esterase activity. Therefore, before assessing individual enzymes, we looked into the esterase activity of fresh serum. Thus, 50% FBS v/v was mixed into micelles formulated using either diblock PEG45PCL61 or our novel interface-engineered triblock copolymer PEG45PBO9PCL53 at 37 °C and the size dynamics of the polymeric micelles was measured using DLS (Figure 5). We found that FBS has very high esterase activity and it could degrade both polymers, but the micelles generated using surface-engineered triblock copolymer PEG45PBO9PCL53 were much resistant to the degradation than corresponding ones generated from diblock PEG45PCL61, which were substantially degraded within 1h (Figure 5). 218 Ilies; Control of Amphiphile Self-Assembling at the Molecular Level: Supra-Molecular Assemblies with Tuned ... ACS Symposium Series; American Chemical Society: Washington, DC, 2017.


Figure 4. 4-Nitrophenyl acetate hydrolysis catalyzed by different esterases relevant to drug delivery. The enzymes included here are either present in blood, on the surface of blood vessels, or are present near or inside the tumor cells targeted by polymeric DDSs.

Figure 5. Average size dynamics and size distribution of polymeric micelles generated from diblock PEGPCL copolymers and interface-engineered triblock PEGPBOPCL triblock copolymers after treatment with 50% FBS v/v for 1h. Lipase was used as a representative esterase structurally related with lipoprotein lipase, hepatic lipase and endothelial lipases present abundantly on the luminal surface of the endothelium lining the arteries and capillaries in liver, lungs, kidneys, and placenta, where they play a key role in metabolism of triglycerides and of natural transporters (delivery systems) of cholesterol and cholesterol esters HDL, LDL and chylomicrons (58, 86–89) Lipases and related amphiphilic esterases possess a specialized amphiphilic interface comprising a mobile hydrophobic flap that helps them dock and lock into the natural and synthetic amphiphilic nanocarriers and hydrolyze them (58, 90, 91). We used readily available lipase from P. fluorescens was to assess the degradation pattern of our novel polymeric micelles by this enzyme. The micelles formulated using 219 Ilies; Control of Amphiphile Self-Assembling at the Molecular Level: Supra-Molecular Assemblies with Tuned ... ACS Symposium Series; American Chemical Society: Washington, DC, 2017.


either PEG45PCL61 or PEG45PBO9PCL53 were incubated with lipase at 37 °C and size dynamics of the system was assessed using DLS, at various time intervals within 1 h. The results (Figure 6a) showed that the interface-engineered polymeric micelles are more resistant to esterase activity of lipase than diblock ones (Figure 6A). Another esterase present in blood plasma in large amounts is butyryl cholinesterase (81). Therefore, we assessed the degradation pattern of our novel polymeric micelles with this enzyme in the same conditions. The size dynamics of the nanosystem showed that both micelle types were relatively unstable, with the diblock micelles significantly more unstable as compared to our triblock polymeric micelles (Figure 6B). We subsequently assessed the degradation of micelles with one of the most abundant plasma protein, albumin, known to have non-selective esterase activity (83, 84). The experiment was performed at a final concentration of 1 mg/mL albumin, which was mixed with the polymeric micelles and incubated at 37 °C.

Figure 6. Average size dynamics of diblock and triblock polymeric micelles after treatment with lipase (A), butyryl cholinesterase (B), albumin (C), and carbonic anhydrase II (D), measured by DLS at different incubation times. The size dynamics determined by DLS clearly showed that diblock micelles were highly unstable in the presence of albumin, while our interface-engineered polymeric micelles were much more resilient (Figure 6C). Other blood enzymes with known esterase activity present in blood are carbonic anhydrases (92–94). Carbonic anhydrase II is ubiquitously present in all tissues and in red blood cells (RBCs). RBC lysis is a common side effect 220 Ilies; Control of Amphiphile Self-Assembling at the Molecular Level: Supra-Molecular Assemblies with Tuned ... ACS Symposium Series; American Chemical Society: Washington, DC, 2017.


following administration of DDSs based on self-assembled amphiphiles, which can release CA II into the bloodstream (92). The triblock copolymer micelles were found to be essentially unaffected by incubation with CA II, while diblock ones were clearly destabilized by this esterase (Figure 6D). Since lipase and butyryl cholinesterase were found to significantly catalyze the degradation of our polymeric micelles, we reassessed these enzymes in presence of 1 mg/mL albumin (Figure 7) in order to mimic the conditions encountered in the vasculature by the DDSs. Thus, in the presence of albumin, lipase showed an enhanced degradation effect on the micelles generated using the diblock copolymer, while the micelles generated form the triblock copolymer were significantly less affected (Figure 7A). On the other hand, addition of albumin to butyryl cholinesterase didn’t change the degradation pattern of both micelle types, with diblock-based nanoformulations being quickly degraded and triblock-based formulation showing resistance to hydrolysis (Figure 7B).

Figure 7. Diblock and triblock polymeric micelle degradation kinetics with lipase (A) and butyryl cholinesterase (B) in the presence of 1 mg/mL albumin: average size dynamics of diblock and triblock polymeric micelles measured by DLS at different incubation times. Assessment of Micelle Stability in Conditions Mimicking the Tumor Site When DDS reaches the target tissue it will interact first with proteins, including esterases, secreted by these (malignant) tissues. One of the most abundant esterase secreted by various tumor cell is Phospholipase A2 (PLA2) (95). It is quite plausible to imagine that the DDS will encounter PLA2 at the target site. Therefore, we assessed the degradation activity of our polymeric micelles in the presence of this enzyme (Figure 8A). We found that PLA2 is quite effective in degrading micelles prepared from our triblock copolymer, while the micelles prepared from the standard diblock were not significantly affected (Figure 8A). This remarkable finding implies a selective degradation of triblock copolymer micelles and release of the drug load in the vicinity of tumor cells. Part of the DDSs are usually uptaken via endocytosis, ending up into endosomes. Endosomal maturation involves loading of these vesicles with various enzymes that can degrade the materials inside it (96). One of the major 221 Ilies; Control of Amphiphile Self-Assembling at the Molecular Level: Supra-Molecular Assemblies with Tuned ... ACS Symposium Series; American Chemical Society: Washington, DC, 2017.


enzymes produced inside the endosome is Cathepsin B, a cysteine protease with esterase activity (97, 98). Papain is another cysteine protease with esterase activity, readily available, and provides a cheaper option to cathepsin B. Thus we used papain as a model of degradation of our polymeric micelles by cathepsin B and related proteases with esterase activity in the endosome. We found that the micelles prepared using diblock copolymer were relatively stable throughout the length of the study against papain activity, similarly to the micelles generated using triblock copolymers (Figure 8B).

Figure 8. Average size dynamics and size distribution of diblock/triblock polymeric micelles after treatment with PLA2 (A) or papain (B) for 1h.

Conclusions In this study we revealed how interfacial engineering of PEG-PCL diblock copolymers into PEG-PBO-PCL triblock ones can increase the resilience of the polymeric material and its self-assemblies in blood following systemic delivery, with potential benefic effects towards circulation time of these DDSs. Moreover, we presented data indicating that the micelles made of interface-engineered PEG-PBO-PCL block copolymers can be degraded faster than the ones generated from parent PEG-PCL by enzymes over-expressed in tumors, thus showing selective stability blood/tumor. Therefore, more efficient drug delivery systems are expected to be generated based on our proposed technology that has the potential to focus the effect of chemotherapeutic drugs on the tumor, increasing the 222 Ilies; Control of Amphiphile Self-Assembling at the Molecular Level: Supra-Molecular Assemblies with Tuned ... ACS Symposium Series; American Chemical Society: Washington, DC, 2017.

therapeutic index of the drug, and the effective dose delivered to the malignancy, reducing tumor resistance and systemic side effects.

Acknowledgments


Financial support from Temple University School of Pharmacy – Dean’s Office and from Temple Undergraduate Research Program is gratefully acknowledged. The authors wish to thank Drs. Bradford B. Wayland, Michael Fryd and Xiaobo Zhu for their contributions towards the synthesis and degradation studies of the polymers presented in this chapter in conditions mimicking the GI tract environment.

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