Brain biocompatibility of a biodegradable controlled release polymer consisting of anhydride copolymer of fatty acid dimer and sebacic acid

Stimuli-Responsive Polymeric Nanovaccines Toward Next-Generation Immunotherapy

The development of nanovaccines that employ polymeric delivery carriers has garnered substantial interest in therapeutic treatment of cancer and a variety of infectious diseases due to their superior biocompatibility, lower toxicity and reduced immunogenicity. Particularly, stimuli-responsive polymeric nanocarriers show great promise for delivering antigens and adjuvants to targeted immune cells, preventing antigen degradation and clearance, and increasing the uptake of specific antigen-presenting cells, thereby sustaining adaptive immune responses and improving immunotherapy for certain diseases. In this review, the most recent advances in the utilization of stimulus-responsive polymer-based nanovaccines for immunotherapeutic applications are presented. These sophisticated polymeric nanovaccines with diverse functions, aimed at therapeutic administration for disease prevention and immunotherapy, are further classified into several active domains, including pH, temperature, redox, light and ultrasound-sensitive intelligent nanodelivery systems. Finally, the potential strategies for the future design of multifunctional next-generation polymeric nanovaccines by integrating materials science with biological interface are proposed.

"Just right" combinations of adjuvants with nanoscale carriers activate aged dendritic cells without overt inflammation

BACKGROUND

The loss in age-related immunological markers, known as immunosenescence, is caused by a combination of factors, one of which is inflammaging. Inflammaging is associated with the continuous basal generation of proinflammatory cytokines. Studies have demonstrated that inflammaging reduces the effectiveness of vaccines. Strategies aimed at modifying baseline inflammation are being developed to improve vaccination responses in older adults. Dendritic cells have attracted attention as an age-specific target because of their significance in immunization as antigen presenting cells that stimulate T lymphocytes.

RESULTS

In this study, bone marrow derived dendritic cells (BMDCs) were generated from aged mice and used to investigate the effects of combinations of adjuvants, including Toll-like receptor, NOD2, and STING agonists with polyanhydride nanoparticles and pentablock copolymer micelles under in vitro conditions. Cellular stimulation was characterized via expression of costimulatory molecules, T cell-activating cytokines, proinflammatory cytokines, and chemokines. Our results indicate that multiple TLR agonists substantially increase costimulatory molecule expression and cytokines associated with T cell activation and inflammation in culture. In contrast, NOD2 and STING agonists had only a moderate effect on BMDC activation, while nanoparticles and micelles had no effect by themselves. However, when nanoparticles and micelles were combined with a TLR9 agonist, a reduction in the production of proinflammatory cytokines was observed while maintaining increased production of T cell activating cytokines and enhancing cell surface marker expression. Additionally, combining nanoparticles and micelles with a STING agonist resulted in a synergistic impact on the upregulation of costimulatory molecules and an increase in cytokine secretion from BMDCs linked with T cell activation without excessive secretion of proinflammatory cytokines.

CONCLUSIONS

These studies provide new insights into rational adjuvant selection for vaccines for older adults. Combining appropriate adjuvants with nanoparticles and micelles may lead to balanced immune activation characterized by low inflammation, setting the stage for designing next generation vaccines that can induce mucosal immunity in older adults.

Room Temperature Stable PspA-Based Nanovaccine Induces Protective Immunity

Streptococcus pneumoniae is a major causative agent of pneumonia, a debilitating disease particularly in young and elderly populations, and is the leading worldwide cause of death in children under the age of five. While there are existing vaccines against S. pneumoniae, none are protective across all serotypes. Pneumococcal surface protein A (PspA), a key virulence factor of S. pneumoniae, is an antigen that may be incorporated into future vaccines to address the immunological challenges presented by the diversity of capsular antigens. PspA has been shown to be immunogenic and capable of initiating a humoral immune response that is reactive across approximately 94% of pneumococcal strains. Biodegradable polyanhydrides have been studied as a nanoparticle-based vaccine (i.e., nanovaccine) platform to stabilize labile proteins, to provide adjuvanticity, and enhance patient compliance by providing protective immunity in a single dose. In this study, we designed a room temperature stable PspA-based polyanhydride nanovaccine that eliminated the need for a free protein component (i.e., 100% encapsulated within the nanoparticles). Mice were immunized once with the lead nanovaccine and upon challenge, presented significantly higher survival rates than animals immunized with soluble protein alone, even with a 25-fold reduction in protein dose. This lead nanovaccine formulation performed similarly to protein adjuvanted with Alum, however, with much less tissue reactogenicity at the site of immunization. By eliminating the free PspA from the nanovaccine formulation, the lead nanovaccine was efficacious after being stored dry for 60 days at room temperature, breaking the need for maintaining the cold chain. Altogether, this study demonstrated that a single dose PspA-based nanovaccine against S. pneumoniae induced protective immunity and provided thermal stability when stored at room temperature for at least 60 days.

The brain tissue response to biodegradable poly(methylidene malonate 2.1.2)-based microspheres in the rat

The aim of this study was to follow the in vivo biodegradation as well as to appreciate the brain tissue response to poly(methylidene malonate 2.1.2) (PMM 2.1.2)-based microspheres implanted into the rat brain. Ninety-three adult Sprague-Dawley female rats were engaged in the study in which 54 underwent stereotactic implantation of blank gamma-sterilized PMM 2.1.2-based microspheres, prepared by an emulsion-extraction method. Twelve rats were implanted with the same 5-fluorouracil (5-FU)-loaded microspheres. Seventeen controls received the suspension medium alone (carboxymethylcellulose aqueous solution). The animals were sacrificed on post-operative days 1, 2, 8 and months 1, 2, 3, 6, 9, 12, 15 and 18. The brains were dissected, frozen, cut in a freezing microtome, and the slides were processed for immunohistological evaluation and scanning electron microscopy. During the first few days, the moderate inflammatory response to blank or loaded PMM 2.1.2 microspheres was largely a consequence of the mechanical trauma that occurs during surgery. The macrophagous-microglial reaction was similar to the one typically found following any damage in the CNS. There were also no differences in GFAP reactivity between the implanted animals and the controls. Blank microspheres began to degrade between 3 and 6 months, while 5-FU microspheres degraded between 8 days and 1 month. The polymer degradation generated in both cases a pronounced inflammatory and immunological reaction, leading to an important cell loss, a cerebral atrophy and to the death of several animals. PMM 2.1.2 was thus shown to be inadequate for intracerebral drug delivery.

Single dose vaccine based on biodegradable polyanhydride microspheres can modulate immune response mechanism

This study focuses on the development of single dose vaccines based on biodegradable polyanhydride microspheres that have the unique capability to modulate the immune response mechanism. The polymer system employed consists of copolymers of 1,6-bis(p-carboxyphenoxy)hexane and sebacic acid. Two copolymer formulations that have been shown to provide extended release kinetics and protein stability were investigated. Using tetanus toxoid (TT) as a model antigen, in vivo studies in C3H/HeOuJ mice demonstrated that the encapsulation procedure preserves the immunogenicity of the TT. The polymer itself exhibited an adjuvant effect, enhancing the immune response to a small dose of TT. The microspheres provided a prolonged exposure to TT sufficient to induce both a primary and a secondary immune response (i.e., high antibody titers) with high-avidity antibody production, without requiring an additional administration. Antigen-specific proliferation 28 weeks after a single immunization indicated that immunization with the polyanhydride microspheres generated long-lived memory cells and plasma cells (antibody-secreting B cells) that generally do not occur without maturation signals from T helper cells. Furthermore, by altering the vaccine formulation, the overall strength of the T helper type 2 immune response was selectively diminished, resulting in a balanced immune response, without reducing the overall titer. This result is striking, considering free TT induces a T helper type 2 immune response, and has important implications for developing vaccines to intracellular pathogens. The ability to selectively tune the immune response without the administration of additional cytokines or noxious adjuvants is a unique feature of this delivery vehicle that may make it an excellent candidate for vaccine development.

Biocompatibility of implantable synthetic polymeric drug carriers: focus on brain biocompatibility

Numerous polymeric biomaterials are implanted each year in human bodies. Among them, drug delivery devices are potent novel powerful therapeutics for diseases which lack efficient treatments. Controlled release systems are in direct and sustained contact with the tissues, and some of them degrade in situ. Thus, both the material itself and its degradation products must be devoid of toxicity. The knowledge and understanding of the criteria and mechanisms determining the biocompatibility of biomaterials are therefore of great importance. The classical tissue response to a foreign material leads to the encapsulation of the implant, which may impair the drug diffusion in the surrounding tissue and/or cause implant failure. This tissue response depends on different factors, especially on the implantation site. Indeed, several organs possess a particular immunological status, which may reduce the inflammatory and immune reactions. Among them, the central nervous system is of particular interest, since many pathologies still need curative treatments. This review describes the classical foreign body reaction and exposes the particularities of the central nervous system response. The recent in vivo biocompatibility studies of implanted synthetic polymeric drug carriers are summarized in order to illustrate the behavior of different classes of polymers and the methodologies used to evaluate their tolerance.

Therapeutic effectiveness of novel 5-fluorouracil-loaded poly(methylidene malonate 2.1.2)-based microspheres on F98 glioma-bearing rats

BACKGROUND

Drug delivery to the central nervous system (CNS) remains a real challenge for neurosurgeons and neurologists, because many molecules cannot cross the blood-brain barrier (BBB). In recent years, solid polymeric materials have been implanted into animal and human brains either by surgery or using stereotactic methods to assure the controlled release of a drug over a determined period, thus circumventing the difficulties posed by the BBB. Poly(methylidene malonate 2.1.2) (PMM 2.1.2) is a new polymer that was described a few years ago and that allows the fabrication of novel, 5-fluorouracil (5-FU)-loaded PMM 2.1.2 microspheres. The objective of the current study was to assess the therapeutic effectiveness of those particles in a rat brain tumor model, the F98 glioma.

METHODS

Forty-three rats were used in this study. First, a histologic evaluation of the F98 tumor model was performed on Fischer female rats. Thereafter, different groups of rats were injected and were treated with 5-FU microspheres in 2 different suspension media: carboxymethylcellulose (CMC) aqueous solution with or without 5-FU.

RESULTS

The tumor was confirmed as extremely aggressive and invasive, even in early development. The 5-FU-loaded microspheres improved rat median survival significantly compared with untreated animals, CMC-treated animals, and 5-FU solution-treated animals when injected in CMC without 5-FU, demonstrating the interest of a sustained release and the efficacy of intratumoral chemotherapy against an established tumor.

CONCLUSIONS

PMM 2.1.2 microspheres appeared to be a promising system, because their degradation rate in vivo was longer compared with many polymers, and they may be capable of long-term delivery.

Polyanhydrides: an overview

Polyanhydrides have been considered to be useful biomaterials as carriers of drugs to various organs of the human body such as brain, bone, blood vessels, and eyes. They can be prepared easily from available, low cost resources and can be manipulated to meet desirable characteristics. Polyanhydrides are biocompatible and degrade in vivo into non-toxic diacid counterparts that are eliminated from the body as metabolites. Owing to their usefulness, this review focuses on the development, synthesis methods, structures and characterization of polyanhydrides, which will provide an overview for the researchers in the field. Their in vitro and in vivo degradability, toxicity, biocompatibility and applications are discussed in the subsequent chapters of this special issue on polyanhydrides and poly(ortho esters).

Toxicity, biodegradation and elimination of polyanhydrides

Although originally developed for the textile industry, polyanhydrides have found extensive use in biomedical applications due to their biodegradability and excellent biocompatibility. Polyanhydrides are most commonly synthesized from diacid monomers by polycondensation. Efficient control over various physicochemical properties, such as biodegradability and biocompatibility, can be achieved for this class of polymers, due to the availability of a wide variety of diacid monomers as well as by copolymerization of these monomers. Biodegradation of these polymers takes place by the hydrolysis of the anhydride bonds and the polymer undergoes predominantly surface erosion, a desired property to attain near zero-order drug release profile. This review examines the mode of degradation and elimination of these polyanhydrides in vivo as well as the biocompatibility and toxicological aspects of various polyanhydrides.

Local drug delivery to the brain

The controlled local delivery of antineoplastic agents by biodegradable polymers is a technique that allows for exposure of tumor cells to therapeutic doses of an active agent for prolonged periods of time while avoiding high systemic doses associated with debilitating toxicities. The use of polymers for chemotherapy delivery expands the spectrum of available treatment of neoplasms in the central nervous system, and facilitates new approaches for the treatment of malignant gliomas. In this article, we discuss the rationale and history of the development and use of these polymers, and review the various agents that have used this technology to treat malignant brain tumors.

Ricinoleic acid-based biopolymers

Polyanhydrides synthesized from pure ricinoleic acid half-esters with maleic and succinic anhydrides possess desired physicochemical and mechanical properties for use as drug carriers. Ricinoleic acid maleate or succinate diacid half-esters were prepared from the reaction of crude ricinoleic acid (85% content) with succinic or maleic anhydride. The pure diacid monomers were obtained by chromatography purification through silica gel using petroleum ether/ethyl acetate/acetic acid (80/30/1 v/v/v) mixture as eluent. The pure diacid monomers (>99%) were polymerized by melt condensation to yield film-forming polymers with molecular weights exceeding 40,000 with a polydispersity of 2. Extensive biocompatibility study demonstrated their toxicological inertness and biodegradability. Their rate of elimination from rats in the course of about 4-6 weeks was faster than that found for similar fatty acid-based polyanhydrides previously tested. In vitro studies showed that these polymers underwent rapid hydrolytic degradation in 10 days. Methotrexate release from the polymers was not affected by the initial polymer molecular weight in the range of 10,000-35,000. The in vitro drug release correlated with the degradation of the polymers. The fatty acid ester monomers were further degraded to its counterparts, ricinoleic acid and succinic or maleic acid.

Peptide drug delivery into the central nervous system

The microvasculature of the central nervous system (CNS) is characterized by tight junctions between the endothelial cells and, thus, behaves as a continuous lipid bilayer that prevents the passage of polar and lipid-insoluble substances such as peptides. Highly active enzymes expressed in the morphological components of the microcirculation also represent a metabolic component that contributes to the homeostatic balance of the CNS. Peptides generally cannot enter the brain and spinal cord from the circulating blood because they are highly polar and lipid insoluble, metabolically unstable, and active transport systems only exist for very few of them in this membraneous barrier separating the systemic circulation from the interstitial fluid of the CNS. This blood-brain barrier is, therefore, the major obstacle to peptide-based drugs that are potentially useful for combating diseases affecting the brain and spinal cord. This review discusses and critically evaluates invasive, chemical-enzymatic (prodrug and chemical delivery/targeting system) and biological carrier-based approaches to overcome the blood-brain barrier for these highly active and versatile molecules that are very attractive as a future generation of neuropharmaceuticals.

Polymeric implants for cancer chemotherapy

Cancer chemotherapy is not always effective. Difficulties in drug delivery to the tumor, drug toxicity to normal tissues, and drug stability in the body contribute to this problem. Polymeric materials provide an alternate means for delivering chemotherapeutic agents. When anticancer drugs are encapsulated in polymers, they can be protected from degradation. Implanted polymeric pellets or injected microspheres localize therapy to specific anatomic sites, providing a continuous sustained release of anticancer drugs while minimizing systemic exposure. In certain cases, polymeric microspheres delivered intravascularly can be targeted to specific organs or tumors. This article reviews the principles of chemotherapy using polymer implants and injectable microspheres, and summarizes recent preclinical and clinical studies of this new technology for treating cancer.

Intralesionally implanted cisplatin cures primary brain tumor in rats

BACKGROUND AND OBJECTIVES

Chemotherapy has added little to the overall survival of the patients with primary malignant brain tumors, primarily due to its difficulty penetrating the blood-brain barrier. Use of polymers, releasing high doses of chemotherapy locally over time, is a promising new treatment strategy. Three experiments were conducted to test the effect of cisplatin, released from biodegradable polymer, on rats with 1 week established brain tumor.

METHODS

9L gliosarcoma cells and drug-free or cisplatin-loaded polymer were administered through a right frontal lobe cannula in male Fischer 344 rats. Tumor cells were infused on day 0 and polymer on day 7. Animals were monitored for 60 days.

RESULTS

In experiment one, 0.5 mg/m2 of cisplatin loaded in polymer resulted in a mean survival time (MST) of 51 +/- 14 days with 63% (10/16) rats surviving to day 60. MST for the control group was 24 +/- 4 days (p = 2.5 x 10(-9)). Evidence of clinical or histologic brain toxicity was minimal. In a second experiment, using drug-free polymer (n = 7), MST was 24 +/- 3 days. This was compared against an MST of 24 +/- 4 days in the tumor control group (n = 7) and 49 +/- 7 days in a cisplatin-polymer treated group (n = 6). In a third experiment, two doses of drug-free polymer and three doses of cisplatin-loaded polymer were tested in normal nontumor-bearing rats and found to be well tolerated.

CONCLUSIONS

Intralesional sustained release of cisplatin from biodegradable polymer is safe and effective for the treatment of brain 9L gliosarcoma in rats.

Efficacy of intralesionally administered cisplatin-impregnated biodegradable polymer for the treatment of 9L gliosarcoma in the rat

OBJECTIVE

Use of biodegradable polymers for the local delivery of chemotherapy is a promising new strategy in the treatment of high-grade gliomas. We examine the benefit of local delivery of cisplatin, via biodegradable polymer, in the treatment of intracranial glioma in rats. This treatment is compared against intralesionally administered free cisplatin and systemic cisplatin.

METHODS

The Fischer 344 9L gliosarcoma rat model was used with a cannula placed in the right frontal lobe. On Day 0, 5 x 10(3) 9L gliosarcoma cells were infused. Treatment was initiated on Day 7. In Experiment 1, polymer alone was infused intralesionally to rule out any inherent toxic or tumoricidal properties. In Experiment 2, polymer impregnated with 0.5, 5.0, and 25 mg/m2 cisplatin was infused intralesionally. In Experiment 3, the most effective dose of drug containing polymer was compared against a similar dose of intralesionally administered free cisplatin and the systemic administration of cisplatin.

RESULTS

In Experiment 1, polymer alone demonstrated no inherent toxic or tumoricidal properties. In Experiment 2, polymer impregnated with 0.5 mg/m2 was 100% effective in eradicating intracranial tumor with minimal histological evidence of toxicity. At the 5.0 and 25 mg/m2 doses, local brain toxicity was significant. In Experiment 3, at Day 60, 8 of 12 animals treated with polymer containing 0.5 mg/m2 cisplatin were alive and tumor free. This compared with 3 of 13 tumor-free survivors for the group treated with intralesionally administered free cisplatin, and 0 of 13 and 0 of 11 survivors for the 50 and 100 mg/m2 intraperitoneally administered doses, respectively.

CONCLUSION

The local instillation of cisplatin-impregnated biodegradable polymer, allowing the sustained release of high-dose chemotherapy locally, seems to be effective treatment for intracranial 9L gliosarcoma in the rat. Treatment was superior to intralesionally administered free or systemic cisplatin.

Prevention of venous thrombosis in microvascular surgery by transmural release of heparin from a polyanhydride polymer

BACKGROUND

The effects of transmurally released heparin on the patency of microvenous anastomoses were studied by using a bioerodible polymer delivery system in a rat microvascular thrombosis model.

METHODS

A polyanhydride carrier with heparin was wrapped around the outside of a highly thrombogenic venous inversion graft in 14 animals, and patency rates were compared with those of 17 control animals.

RESULTS

Anastomotic patency was significantly greater in the groups treated with transmurally released heparin, measured both at 24 hours (86% versus 16%; p < 0.02) and at 7 days (86% versus 36%; p < 0.05) after operation. No significant complications occurred.

CONCLUSIONS

Controlled release of heparin by transmural delivery is an effective and safe form of local antithrombotic therapy and may have applications both in microvascular and large vessel surgery.

Effectiveness of controlled release of a cyclophosphamide derivative with polymers against rat gliomas

Most malignant gliomas grow despite treatment by standard chemotherapeutic agents. The authors explored the use of an innovative drug, 4-hydroperoxycyclophosphamide (4HC), delivered via a controlled-release biodegradable polymer to determine whether local delivery would enhance efficacy. This drug is an alkylator-type chemotherapeutic agent derived from cyclophosphamide. Unlike the parent drug, which requires activation by hepatic microsomes, 4HC is active in vitro. Two rat glioma cell lines, 9L and F98, were treated in cell culture with medium containing 4HC. Both cell lines were more sensitive to 4HC than to a nitrosourea, BCNU, an agent of established value in the local therapy of gliomas. Ninety Fischer 344 rats implanted with 9L or F98 gliomas were treated with an intracranial polymer implant containing 0% to 50% loaded 4HC in the polymer, and it was found that 20% 4HC-loaded polymers caused minimum local brain toxicity and maximum survival. These polymers were then used to compare the in vivo efficacy of 4HC to BCNU in rats implanted with 9L glioma. Animals with brain tumors treated with 4HC had a median survival span of 77 days compared to the median survival of 21 days in BCNU-treated animals and median survival of 14 days in untreated animals. Long-term survival for more than 80 days was 40% in the 4HC-treated rats versus 30% in the BCNU-treated rats. The polymer carrier used in this study was a copolyanhydride of dimer erucic acid and sebacic acid 1:1, which was able to maintain the hydrolytically unstable 4HC in a stable state for local delivery. Thus, it is concluded that 4HC-impregnated polymers provide an effective and safe local treatment for rat glioma.

Erosion of a new family of biodegradable polyanhydrides

Studies investigating the erosion mechanism of the newly developed poly (fatty acid dimer: sebacic acid) polyanhydride (p:[FAD:SA]) are described. The overall erosion of different monomer compositions of p(FAD:SA) copolymers was examined to determine whether and to what extent copolymer properties affected polymer erosion. Increasing the hydrophobic monomer (FAD) content up to 50 wt% in the copolymer resulted in longer erosion, whereas further increases up to 70 wt% decreased the erosion period. Polymer crystallinity depended on copolymer FAD content. Copolymer degradation was studied by examining anhydride bond hydrolysis using infrared spectroscopy. Much faster hydrolysis was found in p(FAD:SA) 70:30 compared with more crystalline copolymers of higher SA content. Light microscopy indicates the presence of an erosion zone, a distinct area where mass loss occurs. This erosion zone moves from the outside toward the interior of the polymer matrix. It plays an important role in erosion because any water or monomer must diffuse through this eroded layer.

Metabolic disposition and elimination studies of a radiolabelled biodegradable polymeric implant in the rat brain

The metabolic disposition and elimination process of the anhydride co-polymer poly[1,3-bis(p-carboxy-phenoxypropane):sebacic acid] 20:80 [P(CPP:Sa)20:80] implanted in the rat brain was studied. Two polymers were prepared, one with [14C]SA and unlabelled CPP, and the other co-polymer with [14C]CPP and unlabelled SA. With these two polymers we were able to study the metabolic disposition of each monomer after polymer degradation. Polymer wafers loaded with N,N-bis(2-chloroethyl)-N-nitrosourea or without the drug were implanted in the rat brain. For the rats implanted with the [14C]SA-labelled polymer, approximately 40% of the radioactivity was found in the expired CO2, 10% in the urine, about 2% in the faeces and about 10% remained in the device 7 d after implantation. On the other hand, only 4% of the [14C]CPP monomer was eliminated by urine and faeces during this period. The drug-loaded polymer degraded faster than the blank polymer. This study supports the theory that the polymer is a biodegradable material that can be used for the direct and specific delivery of drugs into a targeted organ and can provide continued release of drugs over a period of time.