The safety and efficacy of protein therapeutics are limited by three interrelated pharmaceutical issues, in vitro and in vivo instability, immunogenicity and shorter half-lives. Novel drug modifications for overcoming these issues are under investigation and include covalent attachment of poly(ethylene glycol) (PEG), polysialic acid, or glycolic acid, as well as developing new formulations containing nanoparticulate or colloidal systems (e.g. liposomes, polymeric microspheres, polymeric nanoparticles). Such strategies have the potential to develop as next generation protein therapeutics. This review includes a general discussion on these delivery approaches. KeywordsProtein delivery; PEGylation; Liposomes; hyperglycosylation; Poly(lactic/glycolic) acid INTRODUCTIONSince the late 20 th century numerous therapeutic proteins and peptides have emerged in the market. PHARMA 2010 reported that biotech products accounted for more than 35% of the 37 new active substances launched in 2001.1 In 2007, global biotech drug sales grew at twice the rate of traditional small molecule drugs (12.5% vs 6.4%) with total revenues of $75 billion US. Biotech drugs accounted for one fifth of all blockbuster drugs in the market as of 2008.2 From a therapeutic perspective, proteins offer the distinct advantage of specific mechanisms of action and are highly potent. Despite these advantages, biotech products must overcome the hurdles posed by high molecular weight, short half-lives, instability, and immunogenicity. Several strategies have been evaluated in an effort to improve the current limitations of therapeutic peptides and proteins in the creation of so called "second generation" protein therapeutics. Most efforts center around one of two approaches-either a change in the agent itself (e.g. mutations in protein structure or covalent attachment of moieties) or by a change in formulation.3 In contrast to modifying the protein structure, covalent chemical attachment of compounds such as poly(ethylene glycol) (PEG) or polysialic acid (PSA) to therapeutic protein represent a relatively new approach. Drug formulation systems, such as liposomes, polymeric microspheres, and polymeric nanoparticles, are another means to help overcome the current limitations of protein therapeutics.4 , 5The intent of this review is to provide a general discussion of approaches being applied to improve safety and efficacy of protein therapeutics. This includes the areas of PEGylation, PEGYLATIONThe conjugation of polymers to proteins had been in practice since the 1950s, but it was the development of PEGylation that provided the real breakthrough in enhancing the pharmaceutical properties of proteins and peptides in a viable manner 6 PEGylation, the covalent attachment of PEG moieties to a therapeutic agent, was first reported in the 1970s. 7,8 Experiments attempting to improve delivery aspects via PEGylation found not only the intended benefits, but overall enhancement of stability, pharmacokinetics, and therapeutic utility of molecules. [9][10][11][1...

The identification of immunosuppressive factors within human tumor microenvironments, and the ability to block these factors, would be expected to enhance patients’ anti-tumor immune responses. We previously established that an unidentified factor, or factors, present in ovarian tumor ascites fluids reversibly inhibited the activation of T cells by arresting the T cell signaling cascade. Ultracentrifugation of the tumor ascites fluid has now revealed a pellet that contains small extracellular vesicles (EV) with an average diameter of 80nm. The T cell arrest was determined to be causally linked to phosphatidylserine (PS) that is present on the outer leaflet of the vesicle bilayer, as a depletion of PS expressing EV or a blockade of PS with anti-PS antibody significantly inhibits the vesicle induced signaling arrest. The inhibitory EV were also isolated from solid tumor tissues. The presence of immune suppressive vesicles in the microenvironments of ovarian tumors and our ability to block their inhibition of T cell function represent a potential therapeutic target for patients with ovarian cancer.

The anatomical site of subcutaneous injection influences the rate of absorption and bioavailability of rituximab in rats. Saturable binding may be a major determinant of the nonlinear absorptive transport of monoclonal antibodies.

Biotherapeutics is a rapidly growing drug class, and over 200 biotherapeutics have already obtained approval, with about 50 of these being approved in 2015 and 2016 alone. Several hundred protein therapeutic products are still in the pipeline, including interesting new approaches to treatment. Owing to patients' convenience of at home administration and reduced number of hospital visits as well as the reduction in treatment costs, subcutaneous (SC) administration of biologics is of increasing interest. Although several avenues for treatment using biotherapeutics are being explored, there is still a sufficient gap in knowledge regarding the interplay of formulation conditions, immunogenicity, and pharmacokinetics (PK) of the absorption of these compounds when they are given SC. This review seeks to highlight the major concerns and important factors governing this route of administration and suggest a holistic approach for effective SC delivery.

Protein therapeutics have drastically changed the landscape of treatment for many diseases by providing a regimen that is highly specific and lacks many off target toxicities. The clinical utility of many therapeutic proteins has been undermined by the potential development of unwanted immune responses against the protein, limiting their efficacy and negatively impacting its safety profile. This review attempts to provide an overview of immunogenicity of therapeutic proteins, including immune mechanisms and factors influencing immunogenicity, impact of immunogenicity, pre-clinical screening methods, and strategies to mitigate immunogenicity.