Drug Discovery
• Unlike small molecule drugs (pharmaceuticals), large molecule drugs (biopharmaceuticals) are mainly protein-based
o These protein-base... [Show More] d drugs are similar to natural biological compounds found in human body or they're fragments that mimic active part of natural compounds
Discovery of Pharmaceuticals
commences w/ scanning hundreds of compounds, whether w/ actual materials (irrational approach) or virtual simulations (rational approach)
• Pharmaceuticals are new chemical entities (NCE) and are produced (synthesized) in manufacturing plants using techniques based on chemical reactions of reactants
Discovery of Biopharmaceuticals
researchers have to examine compounds w/in humans
o Ex. Hormones or other biological response modifiers and how they affect biological processes
o In some cases, study pathogens such as influenza virus or bacteria to derive vaccines
o In other cases, researchers copy these biological response modifiers and use them as replacement therapy
o Protein-based drugs are manufactured in biological systems, such as living cells, producing desired protein molecules in large reaction vessels or by extraction from animal serum
o Becoming increasingly important
• More potent and specific—more similar to proteins w/in body therefore more effective in treating our diseases
Areas of Biopharmaceuticals
• Prophylactic→ preventive as in vaccines
• Therapeutic→ antibodies
• Replacement therapy→ hormones, growth factors
Biologics
FDA definition is:
o Biological product subject to licensure under Public Health Service Act is any virus, therapeutic serum, toxin, antitoxin, vaccine, blood, a blood component or derivative, allergenic produce, or analogous product, applicable to prevention, treatment or cure of diseases or injuries to humans. Biological products include, but are not limited to, bacterial and viral vaccines, human blood and plasma and their derivatives, and certain products produced by biotechnology, such as interferons and erythropoietins. Biologics encompass many different protein-based drugs, and include blood products such as clotting factors extracted from blood.
Vaccines
• Basis of vaccination is that administering small quantity of a vaccine (antigen that has been treated) stimulates our immune system and causes antibodies to be secreted to react against foreign antigen
• Later in life, when we encounter another exposure to same antigen, our immune system will evoke a memory response and activate defense mechanisms by generating antibodies to combat invading antigen
• Contains antigenic components that are obtained from or derived from pathogen
o Include mainly viruses, bacteria, parasites and fungi
o Research has shown that part of pathogen that causes disease (virulence) can be decoupled from protective part (immunity)
• Development focuses on means to reduce virulence factor while retaining immunity stimulation
• Oral or parenteral
Vaccine Preparations
Attenuated Vaccines
Killed or Inactivated Vaccines
Toxoids
Attenuated Vaccines
• Virulence of pathogen that can be reduced in number of ways
• By chemical treatment, by temperature adaptation, or by growing pathogen in specified other than natural host (passaging)
• Advantages are low cost preparation, elicit desired immunological response, and normally single dose is sufficient
• Disadvantages are potential to revert to virulence and limited shelf life
Killed or Inactivated Vaccines
• Chemical and temperature treatment are normally used to kill or inactivate pathogen
• Formaldehyde treatment most common method
• Other chemicals used are phenol and acetone
• Another method is to irradiate pathogen to render it inactive
• Advantages are non-reversal to virulence and relatively stable shelf life
• Disadvantages are higher cost of production, more control is required for production to ensure reliable processes for complete inactivation and there is possibility of reduced immunological response due to treatment processes so multiple booster vaccinations may be required
Toxoids
• Derived from toxins secreted by pathogen
• Advantages and disadvantages similar to killed or inactivated vaccines(advantages: non-reversal to virulence and relatively stable shelf life; disadvantages: higher cost of production, more control is required for production to ensure reliable processes for complete inactivation and there is possiblity of reduced immunological response due to treatment processes so multiple booster vaccinations may be required)
New Vaccines
• Advances in genomics, molecular biology and recombinant technology has provided new directions for discovery, development and manufacture of vaccines
• Current approach is minimalist strategy to decouple virulence and immunity functions
• Aim is to use only immunity part to confer protection, so vaccine is safe to be administered
• Approach can be divided into subunit, vector-based, DNA and peptide vaccines
Subunit Vaccines
• Use only part of bacteria or virus instead of entire pathogen
• Part is derived from outside envelope protein of pathogen
• Requires knowledge of genome sequence of pathogen by identifying open reading frames (ORF) that potentially encode novel antigenic surface proteins known as epitopes, which bind to antibodies
• When identified, ORFs are cloned to express protein epitopes using self-replicating plasmids
• Binding properties of epitopes can be studied using enzyme linked immunosorbent assay (ELISA) or fluorescent activated cell sorter (FACS)
• Leading candidates of epitopes are injected into animals to determine whether they elicit any antibody response
o Those that work are selected and optimized to become vaccine candidates w/ further tests before human clinical trials
o Also working on multiple epitope subunit vaccines which can provide different antigenic binding sites
Vector-based Vaccines
• Viruses and bacteria are detoxified and used as vehicles to carry vaccines
• Subunit vaccines are being delivered by carrier vehicles to elicit immune response
• Multiple types of envelope proteins can be delivered w/ this method
• Clinical trials w/ this type of vector-based vaccines are being investigated
DNA Vaccines
• Aka nucleic vaccines or genetic immunization
• Host (patient) is directly injected w/ selected viral genes which contain engineered DNA sequences that code for antigens
• Hosts own cells take up these genes and express antigens which are then presented to immune cells and activate immune response
Peptide Vaccines
• Chemically synthesized and normally consist of 8-24 amino acids
• Relatively small
• Aka peptidomimetic vaccines as they mimic epitopes
• Complex structures of cyclic components, branched chain or other configurations can be built into peptide chain
• They possess conformations similar to epitopes and can be recognized by immune cells
• An in silico vaccine design approach has been used to find potential epitopes
• Critical aspect of peptide vaccines is to produce 3D structures similar to native epitopes of pathogen
Adjuvant
• Vaccines formulated w/ certain substances to enhance immune response
• Latin adjuvare→ to help
• Most common adjuvants for humans are aluminum hydroxide, aluminum phosphate and calcium phosphate
• Others include bacteria and cholesterol
• Mineral oil emulsions normally adjuvants used in animal studies
• Adjuvant known as Freund's Complete Adjuvant consists of killed tubercle bacilli in water-in-mineral oil emulsion
• Freund's Incomplete Adjuvant is water-in-oil emulsion
• Both effective in stimulating immune response but cause unacceptable side effects in humans
3 Mechanisms Adjuvants Help Immune Response
• Adjuvants help immune response by forming reservoirs of antigens and providing sustained release of antigens over long period
• Adjuvants act as non-specific mediators of immune cell function by stimulating or modulating immune cells
• Adjuvants can serve as vehicles to deliver antigen to spleen and/or lymph nodes where immune response is initiated
Alzheimer's Disease
• Vaccine being tested contains small protein called B amyloid (AB)
o This protein forms abnormal deposits or "plaques" in the brains of individuals w/ Alzheimer's
o It's believed that AB deposition Causes loss of mental fxn by killing brain neurons
o AB vaccination stimulates immune system to clean up plaques and prevent further AB deposits
o Phase II clinical trial was halted because 15 of 360 patients developed severe brain inflammation
• Studies showed that AB did generate desired antibody response
• Acceptable vaccine may still be possible by modifying epitope to reduce inflammation effects
Pneumococcal
• In Oct 2006, FDA approved use of Prevnar for immunization of infants and toddlers against otitis media middle ear infection
o Prevnar is pneumococcal seven-valent conjugate vaccine
• Formulated w/ sterile solution of saccharides conjugated to antigen
Cancer
• In cancer, immune system doesn't recognize changes in cancer cells
• Cancer vaccines seek to mimic cancer-specific changes by using synthetic peptides to challenge immune system
o When these peptides are taken up by T cells, immune system is activated
o T cells search for cancer cells w/ specific markers and proceed to kill them
• Vaccines being tested are peptide called B-defensin 2 which activates immune system against tumor activity and outer coat protein of human papilloma virus act as vaccine against cervical cancer
AIDS
• Caused by HIV infection
• HIV belongs to large family of retroviruses, Lenti virus
• HIV genome is w/in RNA
• RNA genome of HIV is reverse-transcribed into DNA and integrated w/in human cell
• HIV undergoes frequent mutation and therefore highly variable
• Technique for producing AIDS vaccine is to reproduce, using recombinant technology, the surface proteins on HIV
o 2 particular envelope proteins being investigated
• gp120 and gp41
• trimeric protein and held together by 3 transmembrane gp41 proteins
• Vaccines based on these proteins can induce antibody responses to different strains of HIV
• Other AIDS treatments are use of antiviral (AZT, reverse transcriptase inhibitor) drugs, drugs (indinavir) that target and inhibit production of HIV protease, and enzyme required to assemble new virus particles and gene therapy—control of viral genome expression through use of synthetic oligonucleotides
Malaria
• Major disease in tropical countries
• According to WHO, 300-500million individuals are infected w/ malaria
o Death tolls are 1.5-3.5million people yearly
• 4 species of malaria parasites that infect humans
o plasmodium falciparum
• predominant malarial parasite found in Africa and most virulent
o P. vivax
o P. ovale
o P. malariae
• Vaccine strategies are of 3 types:
o Pre-erythrocytic
o Blood stage
o Transmission-blocking stage
Chicken Pox
• Highly contagious viral infection that causes rash-like blisters on skin surface and mucous membranes
• mild and not normally life-threatening
o can be deadly to pregnant women, people w/ leukemia, or immunosuppressed patients
• Varivax from Merck tested on about 11,000 children and adults and was approved by FDA as chicken pox vaccine [Show Less]
