Issue link: https://www.e-digitaleditions.com/i/1497323
24 Pharmaceutical Technology ® The Real Message Behind Commercial mRNA Products April eBook 2023 PharmTech.com Development or phosphate-based together with salts such as so- dium chloride or potassium chloride to adjust the ionic strength, Bruno observes. Storage conditions (as aqueous solutions, frozen, or lyophilized) must also be carefully considered in the context of mRNA-LNP clinical translation, accord- ing to Bruno, because they can affect the long-term stability of mRNA-LNP formulations. "Sugar stabi- lizers (sucrose in particular, trehalose or mannitol as alternative options) are commonly used for this application," he says. Choosing the right non-lipid excipients important In addition to assuring long-term stability and in vivo performance, non-lipid excipients for mRNA-LNPs also play an important role in controlling manufac- turing processes, Jung comments. "The selection of t hese excipients must t herefore be done ca re- fully. Typically, they are initially chosen based on their chemical and physical properties (i.e., pKa and lyophilization characteristics, freezing point/state) because these attributes will determine compatibil- ity with the drug substance. Because these choices may also impact the mor pholog y of mRNA-LNPs, wh ic h ca n a f fec t overa l l ef f icac y a nd s t abi l it y, modifications may be required as determined [by] experimental testing," he says. The susceptibility of mRNA to degradation requires that formulation buffers be free of any ribonuclease contamination. Testing of excipients for the absence of nuclease activity is therefore the preferred approach, Bruno stresses. Other product-quality attributes should also be determined, including endotoxin content and bioburden, as they play an important role in controlling the risk of contamination by these materials. Beyond the product-quality attributes, Bruno em- phasizes the need to consider supplier related aspects for any excipients used in mRNA-LNPs, including non- lipid excipients. "Supply robustness and availability of supporting documentation are both essential if mRNA-LNP developers are to navigate regulator y challenges and ensure smooth manufacturing scale up and progression through clinical development to commercialization," he adds. Focus on improving stability Since the approval of the COVID-19 mRNA vaccines and demonstration of their effectiveness, interest in mRNA-LNP therapeutics and vaccines has risen dra- matically from all perspectives. In particular, the rise of the mRNA technology due to the COVID-19 pan- demic and the manufacturing scale needed to produce vaccines shifted the attention to mRNA manufactur- ing needs, according to Bruno. "The development of non-lipid excipients has primar- ily focused on the quality attributes based on the speci- ficity of the technology," Bruno notes. For instance, the need for endonuclease-free materials required estab- lishment of additional product-release testing methods and services to support drug manufacturers. There has also been a significant amount of effort placed on assessing non-lipid excipients that may im- prove the long-term stability of mRNA-LNP formula- tions, observes Jung. He points specifically to the use of different cryoprotectants to improve refrigerated storage stability. Lyophilization is also being explored as a means for eliminating cold-chain requirements, with several clinical-stage studies underway to assess the impact of lyophilization on the stability and in vivo efficacy of traditional mRNA-LNPs. Separate efforts are also underway to create novel delivery mechanisms for RNAs that are not dependent upon LNPs, Jung adds. Lipid advances A key focus in the mRNA field is on lipid excipients and that will continue to be true for some time, con- tends Aditi Mehta, head of mRNA process and de- liver y, MilliporeSigma, the Life Science business of Merck KGaA, Darmstadt, Germany. "Despite the success of the COVID-19 vaccines, we still have not reached the full potential of mRNA therapeutics, and there are several hurdles. Insufficient targeting of or- gans beyond the liver or vaccinations, an acute im- mune response against LNP administration, stability issues, and the need of extreme low temperature for storage are key bottlenecks in the development of LNP medicines," she says. These issues, Mehta obser ves, can be addressed through improvements in lipid and LNP design (e.g., optimization of linker chemistry, addition of degrad- able bonds, more optimal synthetic routes, better LNP components, etc.). "Strategies such as design of novel ionizable lipids based on large libraries produced with combinatorial synthesis have been aiding the under- standing of structure-function properties and enabling The susceptibility of mRNA to degradation requires that formulation buffers be free of any ribonuclease contamination.