Protein: A gateway to better medicine, better life

The number one benefit of information technology is that it empowers people to do what they want to do. It lets people be creative. It lets people be productive. It lets people learn things they did n't think they could learn before, and so in a sense it is all about potential.

The quote above provides a better perceptive to consider the advantages of the upcoming advancements in technology in every field. In medicine, therapeutic proteins and peptides have emerged as new drug entities for various elements. Proteins being small are the popular category that is haunted as new therapeutic entities because they are easy to synthesize and make available in large quantities which can be used for treating various diseases, amongst the huge population all across the world. Further the techniques for manufacturing and quality control is improved and practiced due to the change in circumstances like emergence of resistance, not only to infectious conditions but also to several other segments like epilepsy, Parkinsonism, cancer, etc. have necessitated inventing new molecules with normal strategies. The theme of new drug discovery had paradigm shift from a molecule entity to the proteins and peptides. The literature accounts for large number of therapeutic proteins with excellent efficacy and safety. The major drawback to us is the ornamentum of new therapies which are limited to the fact that they cannot be administered orally as they are going to get digested in the stomach; they need to be administered by subcutaneous route through injection. There are other risks and challenges in adopting proteins as therapeutic agents involved in vitro and in vivo instability and homogeneity as well as shorter half-life.

Proteins were recognized in the 18th Century by Antoine Fourcroy and others. They are able to come together in distinct condition e.g. Albumin from egg whites, blood serum albumin, fibrin and wheat gluten. The elemental analysis of protein was demonstrated by Gerhardus Johannes Mulder. The therapeutic protein drug delivery development has been growing since 1953 when the first accurate model of DNA was suggested followed by 1982 when the human insulin was created using recombinant DNA technology to 2006 when an inhaled form of insulin (Exubera) was approved, expanding protein products into a new dosage form. Protein therapeutics can be dealt in different aspects such as

• protein therapeutics with enzymatic or regulatory activity which includes ways like replacing a protein that's deficient or abnormal
• protein therapeutics with special targeting activity including interfering with a molecule or organism,
• Protein vaccine that helps in targeting cancer and the last area is the protein diagnostics.

The deliveries of therapeutic proteins have to be specific and they should be well distributed. Therefore, targeted protein delivery includes protein polymer conjugate like

• Most commonly employed polymer: Polyethylene glycol (PEG) & Poly (N-isopropylacrylamide) (PNIPAM)
• These polymers that alter their solubility for self-assembly when exposed to changes in pH or temperature allow their responsive nature to be conferred to the protein to which they are attached.
• Combined with active esters and hence can be conjugated with protein amine.

As experiments for therapeutic drug deliveries progressed, new processes also emerged. Therapeutic protein drugs can be delivered by various processes such as:

1. PEGylation is the covalent attachment of PEG (poly ethylene glycol) moieties to a protein, thereby, enhancing the stability, pharmacokinetics and the therapeutic utility of the protein molecule.
2. Hyperglycosylationmainly refers in particular to the enzymatic process that attaches glycosyl groups to proteins, lipids or other organic molecules. Addition of extra carbohydrates to the protein, serve to reduce interactions with the clearance mechanism and antigen presenting cells in an effort to prolong circulation and reduce immunogenicity. Immunogenicity is the ability of a particular substance to induce a humoral or cell mediated immune response.
3. PLGA microspheres and nano particulate drug delivery. PLGA is polymer of lactic acid and glycolic acid joined my ester bonds. They are biodegradable and biocompatible.
4. Lipid drug delivery involves Liposomes which are spherical, self-closed structures formed by one or more concentric lipid bilayers with an encapsulated aqueous phase in the center and between the bilayers. Incorporation of proteins and peptides into the liposomal formulation helps to circumvent limitations such as their surface charge distribution and large size, have a limited ability to cross the cell membranes; repeated injections of protein drugs over the long therapeutic periods are one factor that contributes to immunogenicity.

Well now a question arises, Why proteins against small drug molecules?
The diversity of functional groups in proteins such as free thiols in cysteine residue or amine on the N terminal which leads to scope for functionality by Micheal addition They have highly specific function which cannot be mimicked by other chemical compounds They are highly specific in action resulting in decreasing the risk of adverse effects. Body produces many of the proteins that are used as therapeutic and hence are often well tolerated and are less likely to elicit responses. There is comparatively faster clinical development and the far-reaching patent protection for protein therapeutic is easily obtained.
Challenges faced by protein polymer conjugate are:

• Mixing ratio,
• Protein loading capacity,
• Study of uptake efficiency with different inhibitors for different cellular entry mechanism for maximum delivery efficiency.
• Cost & storage.

Drug-delivery systems are designed to lower toxicity and improve pharmacokinetic/pharmacodynamic profiles of therapeutic drugs, cytotoxicity, low water solubility, rapid clearance from circulation, and side-effects are common drawbacks of therapeutically important small-molecule drugs. To overcome these shortcomings, many multifunctional nanocarriers have been proposed to enhance the drug delivery. An emerging solution to improve control over these particles is genetic engineering. Genetically engineered nanocarriers precisely control the size and structure and can provide specific control over sites for chemical attachment of drugs. Genetically engineered drug carriers that assemble nanostructures including nanoparticles and nanofibres can be polymeric or non-polymeric. Unlike chemically synthesized carriers, proteins provide unique opportunities to form nanostructures based on the well-established secondary, tertiary, and quaternary structures commonly found in natural proteins. Protein polymers are consisted of natural or unnatural repetitive amino-acid sequences and are generally biosynthesized in cells, either prokaryotes or eukaryotes. Because protein polymers can be engineered at the genetic level, their sequences can be controlled. Compared with conventional polymers, protein polymers may cause lower cytotoxicity, which may be due to the fact that they have biologically relevant mechanisms for proteolysis into relatively inert amino acids such as ELPs. Protein polymers such as ELPs, SLPs, and SELPs can form nanoparticle structures under certain conditions. In the last few years, multiple articles have been published focusing on these nanocarriers in the delivery of genes and drugs due to the burgeoning advancements shown by the results of these nanocarriers.

The advantages of genetically engineered carriers over chemically synthesized carriers are related to both, the precise control of the chain length and monodispersity, due to the ability to seamlessly introduce precise modifications to their structures and biosynthesis at the genetic level. Genetically engineered polymeric drug carriers can be designed to assemble into nanoparticles or nanofibres. These nanostructures can be modified with multiple functional groups such as targeting moieties, imaging agents, or attachment sites for the purpose of drug and gene delivery. Similar to polymeric genetically engineered drug carriers, non-polymeric genetically engineered drug carriers such as vault proteins and viral proteins also form nanostructures, which are being explored for the delivery of genes and drugs. Delivery using these genetically engineered nanocarriers has yet to be translated aggressively to use in humans. At the current time, the understanding of these materials remains in its infancy. New ideas and perspectives are needed to advance genetically engineered nanocarriers into the clinic; however, their numerous preclinical applications suggest that they may provide a powerful new approach for creating nanomedicines. Many technologies have successfully made to market, but the delivery of required therapeutic concentration of protein or peptide product to its site of actions without any substantial adverse reactions is still a challenge to overcome. As the research progresses, there will always be a new and better strategy towards protein drug delivery.