Oligonucleotide therapeutics make up a small but rapidly growing segment of the overall global drug pipeline, with 245 programs currently in development today. While only one approved oligo therapeutic is currently on the market (Pfizer’s Macugen®), there are currently nearly 250 programs under development. Direct investment in this space was nearly $400 million in 2011, and it is projected that this class of drugs could represent up to 10% of total approvals in the next two years in the U.S. and EU, according to Gary Carter, director of strategy and marketing at Agilent Technologies' Nucleic Acid Solutions Division (NASD).
Oligo therapeutics include siRNAs, antisense oligos, miRNA inhibitors, and mimics, with cancer, infectious diseases, ocular conditions, and cardiovascular, CNS, and renal conditions being the primary targets among a diverse pipeline.
With increasing numbers of oligo therapeutics nearing the market, the manufacturing process for these drugs is assuming increased importance, with considerations of raw material availability, product yield and purity, cost effectiveness, reproducibility, validation, and product consistency during process scaling being critical parameters.
The forthcoming IBC Life Sciences “TIDES: Oligonucleotide and Peptide Research, Technology and Product Development” conference will feature several speakers from key players in the oligo therapeutic arena providing a variety of perspectives on the oligonucleotide manufacturing process.
Topics that will be addressed range from chemical strategies to improve oligonucleotide delivery, uptake, and targeting, to logistical issues associated with maintaining the worldwide oligonucleotide supply chain. The supply chain encompasses companies that specialize in sourcing raw materials required for the production of oligonucleotide synthesis reagents, as well as companies that focus on the logistics of commercial scale-up of the actual oligo production process.
Agilent is investing in its oligonucleotide manufacturing in anticipation of continued growth in this area. “NASD’s three-year plan includes further expansion of our state-of-the-art kilo manufacturing facilities to support a projected 10-fold increase in demand for a broad portfolio of oligo APIs,” says Skip Thune, general manger of Agilent’s NASD.
A critical hurdle for oligonucleotide therapeutics is efficient drug delivery. Selectively targeting the oligo to desired tissues and ensuring its efficient uptake at the cellular level and release within the cytosol requires specific design strategies for each oligo.
“One strategy for drug delivery is to chemically conjugate oligonucleotides to a delivery vehicle, which can include polyethylene glycol polymers, cholesterol, vitamins, sugars, and peptides,” says Kenneth Hill, Ph.D., principal investigator in Agilent’s NASD.
“An important consideration is whether or not the oligonucleotide can be modified while on the solid support,” he adds. If the modification group is not amenable or is unstable to the synthesis or deprotection conditions, then a post synthetic means of conjugation is required.
“Thiol-, amine-, or aldehyde-compatible chemistries originating from protein modification have been used for oligonucleotides,” says Dr. Hill. More recently, pericyclic reactions for conjugation have grown in popularity, since the reagents and conditions are very mild, with high yields and little to no side products.
At the opposite end of the drug pipeline to drug delivery, another key consideration in the manufacturing process is management of change and impact of raw material impurities on drug quality.
“A well-documented supply chain risk assessment is not only prudent but is expected by regulatory authorities as part of the development process,” observes Paul Metz, senior director of operations at Agilent.
Nucleoside phosphoramidites are highly reactive 3´-O-(N,N-diisopropyl phosphoramidite) derivatives of nucleosides that are the basic starting material in the oligo manufacturing process. DNA and RNA phosphoramidites are typically manufactured in reactors before purification by preparative column chromatography on silica gel with medium- to high-pressure chromatography equipment.
The presence of critical impurities in chemical preparations of phosphoramidites is an important regulatory and safety consideration during the manufacturing process. “Monitoring and testing for critical impurities in phosphoramidites starts as soon as we receive the raw material,” adds Metz. The industry is beginning to harmonize the testing methods and specifications for these key oligonucleotide building blocks.