Cell Engineering and Molecular Pharming for Biopharmaceuticals M.A
Total Page：16
File Type：pdf, Size：1020Kb
The Open Medicinal Chemistry Journal, 2008, 2, 49-61 49 Open Access Cell Engineering and Molecular Pharming for Biopharmaceuticals M.A. Abdullah*,1, Anisa ur Rahmah1, A.J. Sinskey2 and C.K. Rha3 1Department of Chemical Engineering, Universiti Teknologi Petronas, Tronoh, Perak, Malaysia 2Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA 3Biomaterials Science and Engineering Laboratory, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA Abstract: Biopharmaceuticals are often produced by recombinant E. coli or mammalian cell lines. This is usually achieved by the introduction of a gene or cDNA coding for the protein of interest into a well-characterized strain of pro- ducer cells. Naturally, each recombinant production system has its own unique advantages and disadvantages. This paper examines the current practices, developments, and future trends in the production of biopharmaceuticals. Platform tech- nologies for rapid screening and analyses of biosystems are reviewed. Strategies to improve productivity via metabolic and integrated engineering are also highlighted. INTRODUCTION production of hundreds of therapeutic proteins such as insu- lin, monoclonal antibodies, interferons or interleukins, have Findings in the 1950s that DNA is the molecule that en- been developed [1,2,4]. codes proteins, which in turn control all the cellular proc- esses inside the organism, have provided the impetus for the The world wide pharmaceutical market is estimated to biotechnology era [1]. This has led to the advent of recombi- grow to $1.3 trillion by the year 2020 [5]. While chemical- nant DNA technology and hybridoma technology in the based drug continues to be the major source of drugs, the 1970s, which marks the birth of modern biopharmaceutical world-wide biopharmaceutical market in 2003 is estimated development. As far as drug discovery and development is in the region of $30-35 billion, accounting for 15% of the concerned, this is a significant milestone as some molecules overall world pharmaceutical market [6]. Of these, plant- are too complex and far too difficult to be extracted and puri- derived drugs and intermediates account for approximately fied from living materials, or synthesized chemically [2]. $9-11 billion annually in the USA [2,5]. It was the scientific Genetic engineering provides an alternative means for the and technological innovation in drug discovery and devel- production of therapeutic proteins through the use of bacte- opment that had led to the creation of hundreds of start-up ria, yeasts, insect, animal and plant cells. The compounds biopharmaceutical companies in the 1970s and 80s. With the produced provide alternative therapies for serious life threat- basic research done in the universities and research institu- ening diseases such as cancer, viral infection or hereditary tions, the synergies between industrial players and academia deficiencies, and other untreatable conditions [1]. over the years have resulted in the new technologies and tools to find new molecules to combat diseases; development Various technologies have since emerged ranging from of methods and biomarkers for clinical phenotyping; and the innovations in broad-based, rapid screening and mac- validation of biochemical hypothesis of a drug candidate roscale analyses, to the sophistication in the imaging, control [1,2,4]. The growing confidence and interest in biopharma- and automation technologies. Also contributing to the rapid ceuticals has pushed big pharma companies to acquire tech- progress are the innovations in gene therapies, antisense, cell nologies or invest in manufacturing facilities. Merck has surface engineering and molecular diagnostics. The produc- bought RNAi developer, Sirna Therapeutics for $1.1 billion tion of biopharmaceuticals via recombinant technologies has (RNAi being short interfering molecules to inhibit any gene led to new, innovative products, as well as significant im- of interest in any cells) [7]. Genentech has invested $140 provements in quality and yield of existing products. They million to set-up microbial-based manufacturing operations are better defined scientifically, with consistent quality and for biotherapeutics in Asia [8]. Despite high expenses in are free from infectious agents due to stringent cGMP guide- R&D, Merck and Genentech earn $32.8 and $1.4 billion in lines [2]. The industrial scale manufacturing of penicillin G revenue, respectively, in the year 2000 [4]. This review arti- by the fermentation of mould Penicillium notatum in the cle examines the practices, developments, and future trends early 1940s is the early success story of the use of living in the production of biopharmaceuticals. cells for drug production to combat infection by Staphylo- coccus and other bacteria [3]. Since mid-1970s, large scale HOST SYSTEMS FOR MOLECULAR PHARMING The triggering factor behind the revolution in biopharma- *Address correspondence to this author at the Department of Chemical ceutical industries can largely be attributed to the develop- Engineering, Universiti Teknologi Petronas, Tronoh, Perak, Malaysia; Tel.: ment of advanced methods in the field of recombinant DNA +605-3687636; Fax: +605-3656176; E-mail: [email protected] 1874-1045/08 2008 Bentham Science Publishers Ltd. 50 The Open Medicinal Chemistry Journal, 2008, Volume 2 Abdullah et al. technology. Cell engineering and transgenic technology bor- transferred and expressed in its native Bacillus amylolique- der on several enabling techniques in such diverse fields as faciens, or antibiotic biosynthetic genes in Streptomycetes cell biology, embryology, molecular genetics, bioprocesses species [2]. and metabolic engineering. A more directed approach to Many therapeutically useful proteins, when naturally improve the cells or a given pathway of interest have become produced in the body are glycosylated. The limitation in bio- possible with specific genetic perturbations through modifi- logical activities of some expressed proteins from prokaryo- cation of the promoter strength of a given gene, or by gene tes has been attributed to their limited capability to carry out deletions, or by introducing whole new genes or pathways post-translational modifications (PTMs) [2,21]. Vast major- into the cells [9-12]. This means that the alteration effects ity of therapeutic proteins undergo several PTMs, which are can be determined and the amount directly-probed and pro- the final steps in which genetic information from a gene di- duced at a specified quantity. rects the formation of a functional gene product. PTMs in- Scientific advances gained by transgenic capabilities also clude covalent modifications of individual amino acids resi- enable further understanding of basic biological pathways dues such as glycosylation, phosphorylation, methylation, and yield insights into how changes in fundamental proc- ADP-ribosylation, oxidation and glycation; proteolytic proc- esses can perturb programmed development or culminate in essing and non-enzymatic modifications such as deamidation disease pathogenesis [13]. Primary step behind recombinant and racemisation. Most therapeutic proteins require at least DNA technology is the introduction of heterologous gene(s) proteolytic cleavages, oligomerization and glycosylation for in a non-native genetic background, and the sufficient ex- their bioactivity, pharmacokinetics, stability and solubility pression of a cloned gene in the new host system. Two types [22,23]. Polyglutamylation is an example of PTM that gener- of gene library are known, namely the genomic library which ates lateral acidic side chains on proteins by sequential addi- includes all the total chromosomal DNA of an organism; and tion of glutamate amino acids. This modification is first dis- cDNA library which corresponds to the mRNA fraction from covered on tubulins, and is important for several microtubule a cell or tissue at specific point and time [14]. functions [24]. As complex therapeutic proteins produced in prokaryotes are not always properly folded to confer the de- Recombinant Microorganisms sired biological activity, microbial expression system is suit- Biopharmaceuticals produced from microorganisms that able mainly for the expression of relatively simple proteins have gained marketing approval are invariably produced in which do not require folding or PTMs to be biologically ac- the recombinant E. coli cell systems such as E. coli K12. The tive. Table 1 shows the comparison between different trans- species are well-studied, documented and optimized as hosts genic systems for the production of recombinant proteins. for gene cloning [15-17]. These biopharmaceutical products Eukaryotic Cell Systems include tissue plasminogen activator, insulin, ,-interferons, interleukin-2, granulocyte colony stimulating factor and hu- Major advantage of eukaryotic expression systems such man growth hormone [1,2,18]. The advantages that are nor- as yeast, Chinese hamster ovary strain K1 (CHO-K1) or mally associated with E. coli as the source of biopharmaceu- Baby hamster kidney cells (BHK), is their ability to carry out ticals include the well-characterized molecular biology and PTMs of protein product. While bacteria and yeasts may the ease of genetic manipulation; high levels of heterologous only be suitable for the synthesis of antibody fragments, in- protein expression (as high as 25% of total cellular protein in sect cells infected by baculovirus and CHO cells can be the the