Successful Drug Development with Synthetic Lipids: Critical Aspects and Strategies

Lipid-based drug delivery systems offer several advantages, including improving the stability, solubility, bioavailability, and toxicity profiles of active pharmaceutical ingredients (APIs). It is essential to select the optimal lipid excipients with the appropriate characteristics for each specific API and application and to ensure that they can be produced using high-quality production methods that are scalable for GMP manufacturing. Working with the right supplier that offers consistent, high-quality products and has expertise in the drug development process and the regulatory environment is essential for the successful development and commercialization of lipid-based drug products.

Why Lipid-Based Drug Delivery?

Lipid-based formulations have shown significant promise in drug development and delivery. In addition to enhancing the stability of the API in vivo, they boost the bioavailability of both hydrophilic and hydrophobic drugs.^1,2 Lipid-based formulations also improve the toxicity profile of the entrapped API via passively targeting inflamed or tumor tissues or certain organs and enable the delivery of difficult APIs, such as RNA, that are prone to instability, nuclease-mediated lysis, strong immune responses, and an inability to reach the site of action.¹ They also facilitate patient compliance by reducing dosing frequency and/or increasing tolerability.³

These benefits can be realized for patients with a wide range of disease indications. In addition, lipid-based drug-delivery systems (LBDDSs) can be used to formulate drugs in the most common dosage forms, including topical, oral, pulmonary, or parenteral administration.

Several Approvals and Many Lipid-Based Drugs in Development

The first lipid-based drug, Doxil®, comprising liposome-encapsulated doxorubicin, was approved by the U.S. Food and Drug Administration (FDA) in 1995. Figure 1 shows the marketed liposomal formulations in six therapeutic categories, with the most lipid-based drugs indicated for the treatment of cancer.⁵  

Currently, 18 lipid-based drugs have received marketing approval, and hundreds more are in clinical trials for a wide range of ailments. There is active work in developing generics of off-patent lipid-based drugs, and the FDA has issued product-specific guidances to aid in the development of a range of generic lipid-based products.

The latest developments in lipid-based drug delivery have been in the field of nucleic acid delivery involving APIs such as short RNAs for gene silencing or activation (short interfering (siRNA), micro (miRNA), short activating (saRNA)) and long RNA (messenger RNA (mRNA)) for applications in cancer therapy, enzyme replacement therapy, vaccines, and others.

In 2018, the first lipid-based drug for gene therapy encapsulating siRNA, Onpattro^®, was approved by the FDA for the treatment of hereditary transthyretin amyloidosis (hATTR). Lipid-based RNA formulations are also finding their use as vaccines for infectious diseases. There is rapid development of mRNA-based COVID-19 vaccines, where an mRNA encoding a SARS-COV-2 virus protein is encapsulated in a lipid nanoparticle. The success of an RNA vaccine for COVID-19 will catalyze this field, leading to the approval of many more gene therapy drugs using lipids in the next few years.

Advantages of Synthetic Lipids

Lipid type, source, and quality/purity have a direct impact on the impurity profile and properties of final liposome formulations, such as the particle characteristics, bilayer structure, stability, and drug-release profile. For reproducible results, it is essential to synthesize lipids using only high-quality raw materials with optimal material characteristics and consistent quality.

Chemically synthesized lipids are advantageous over natural lipids, because they consist of a single lipid of known quality, whereas tissue-derived lipids are usually a mixture of egg-derived or bovine-derived lipids. Unlike tissue-derived lipids, synthetic lipids do not show batch-to-batch variability or risk of viral or protein contamination.

The purity of synthetic lipids can be optimized by selecting high-quality starting materials and optimizing the manufacturing processes and purification techniques. Raw materials should have a low level of by-products, defined stereochemistry (D/L) and isomeric purity (cis/trans), low bioburden and endotoxin levels, and be plant derived with bovine spongiform encephalopathy (BSE)/transmissible spongiform encephalopathy (TSE) and non-genetically modified organism (GMO) certificates and produced using only class II or III solvents. Class I solvents should be avoided based on guidelines from the International Council for Harmonization of Technical Requirements for Pharmaceuticals for Human Use (ICH) in ICH Q3C.

Material Characteristics and Scalability 

GMP manufacturing of lipid-based drug products requires consistent, high-quality raw materials, and characteristics, including solubility, crystallinity, stability, and flowability, play important roles in the manufacturing process. Lipids, the key raw materials for producing liposomes, are waxy by nature, which can result in slow dissolution rates and lead to challenges when handling them in large quantities. 

Four methods can be used to enhance the surface characteristics of lipids to achieve fast and complete dissolution and enable reproducible liposome manufacturing processes: cryo-milling, spray drying, crystallization, and lyophilization. In addition to solubility improvements, these processing methods provide liposomes with higher purity, enhanced stability, and easier handling characteristics, all of which enable easier formulation. Spray drying and lyophilization result in materials with very high surface areas, high homogeneity, and good handling characteristics. Crystallization is one of the most commonly used methods to enhance the surface of lipids. 

Scalability, reproducibility, and optimization of the manufacturing process with respect to appropriate GMP principles, liposome yield, concentration, and isomeric purity and other quality aspects, as well as reaction and work-up times, are also paramount for ensuring the greatest efficiency and lowest cost possible. Figure 2 illustrates the impurities in a commercially available sample of dioleoyl-rac-glycerol (GDO) as contrasted with a high-purity sample offered by MilliporeSigma. Scalability for both the synthesis and purification operations should be considered from the very beginning to ensure an economy of scale with increasing batch size, with the aim of minimizing the number of synthetic steps and clearly defining the GMP steps. Ideally, crystallization or liquid/liquid extraction methods should be used for purification, with filtration over silica gel used as an alternative to chromatography whenever possible.

Methods of Liposome Manufacturing

Liposomes or lipid nanoparticles can be manufactured using several different methods,⁶ but the challenge is to ensure scalable, robust, and efficient processes. One method for producing multilamellar vesicles (MLVs) (Figure 5A) is to dissolve the lipid in an organic solvent followed by solvent removal (drying) and hydration with water under agitation. If unilamellar vesicles (ULVs) are desired, they can be generated by adding a sonification or extrusion step to downsize the vesicles. Hydrophobic APIs are added to the solvent during the dissolution step, while hydrophilic drug substances are added to the aqueous solution in the hydration step. Purification is typically the final step in the process. 

Ethanol injection, in which the lipids are dissolved in ethanol and rapidly mixed with an aqueous medium containing the API, is a prominent alternative method for the production of small ULVs¹ containing hydrophilic compounds (Figure 5B).

The choice of manufacturing method often depends on the final application.⁶ The ethanol injection method is suitable for the production of small ULVs and stable nucleic acid lipid particles but not for creating large liposomes, such as the larger MLVs and multivesicular vesicles used for vaccines administered by subcutaneous injection or intramuscular injection. In this case, the rehydration method is used.

Developing Lipid-based Drug Products

In the preclinical stages of liposome-based drug development, the optimum, cost-effective synthetic route should be identified, feasibility studies completed, and lab-scale production runs performed. Process optimization should be the focus during the late preclinical stage and phase I clinical trials, including identification of key raw materials and the development of required analytical methods for the lipid. 

Process scale-up as appropriate should be performed during clinical trials, including implementation of analytical methods and determination of in-process controls, with stability studies also underway. Critical parameters for the process must be defined, process validation of the lipids planned, raw material suppliers qualified, and rigorous risk analysis and intermediates testing completed during late-stage clinical trials. Selecting the wrong raw materials and material suppliers can lead to negative financial implications and delays.

Regulatory Aspects of Lipid-Based Drug Formulations

Currently, there is no clear path to regulatory approval of liposome drug products, due to the absence of globally harmonized regulatory requirements for lipid excipients. Since the purity and quality of the lipid components can affect the quality of lipid-based formulations, detailed information on chemistry, manufacturing, and controls (CMC) is requested by regulatory authorities, often at a level of detail comparable to that for a drug substance.

An FDA guidance on liposomes finalized in April 2018 addresses what information should be submitted to the FDA by the drug sponsor in new drug applications or abbreviated new drug applications.⁸ The guidance refers to several ICH guidelines, including ICH Q11: Development and Manufacture of Drug Substances.⁹ 

The European Medicines Agency published a revised reflection paper in March 2013 on the data requirements for intravenous lipid-based products developed with reference to an innovator lipid-based product.¹⁰ The paper highlights the link between quality material and drug product, demonstrating that the characterization and specification of the lipid is vital. The level of information to be provided with the submission depends on the complexity of the excipients.

Guidelines published in March 2016 by Japan’s Ministry of Health, Labor, and Welfare note that the quality of liposome components should be evaluated and controlled to a greater extent than general excipients, because they have a significant impact on the drug product.¹¹

There are no specific ICH guidelines on lipid-based drugs, but in addition to ICH Q11, several ICH guidelines are applicable, including ICH Q7 (API GMP),¹² ICH Q1A(R2),¹³ ICH Q2(R1),¹⁴ and ICH Q6A.¹⁵ Several guidelines published by the IPEC Federation on good manufacturing and distribution practices, excipient stability and composition, and management of change, among other topics, are also relevant.^16–22 The IPEC guidelines have been accepted globally by many companies and regulatory authorities to develop appropriate standards for excipient control.

The submission of the excipient information to regulatory authorities presents another challenge. In some countries, excipient information can be submitted in the form of a drug master file. In Europe, this regulatory procedure does not exist for excipients. The excipient information must be submitted by the finished drug product manufacturer as part of its application. 

Due to the challenging regulatory environments, it is recommended that the drug manufacturer works closely with a supplier that provides regulatory expertise and counsel through all phases of clinical development and commercialization, covering all aspects of quality assurance and documentation.

Partnering with the Right Suppliers

Despite the lack of harmony among regulatory authorities, there is a consensus that the quality of lipids used in drug development is critical. Partnering with the right synthetic lipid supplier therefore also ensures the development of a scalable, reproducible process following appropriate GMP principles that provides consistently high quality and yields. Knowledgeable suppliers can help select the optimal lipids with the best format, physical state, purity, and other characteristics for each specific application. 

Planning a product development strategy in advance with a supplier partner that offers consistent high-quality products, understands all steps of the drug development process and the regulatory environment, and provides a high level of customer support can ensure that excipients of the same quality are used throughout all stages of the project. A specialized life science supplier like MilliporeSigma, with over 25 years of experience in GMP lipid manufacture, can also help drug developers achieve consistent quality, avoiding variability in the formulation development process, as well as bridging toxicity studies, which also saves time and reduces costs. 

References

1. Yingchoncharoen, Phatsapong, Danuta S. Kalinowski and Des R. Richardson. “Lipid-Based Drug Delivery Systems in Cancer Therapy: What Is Available and What Is Yet to Come.” Pharmacological Reviews. 68 701-787 (2016). 

2. Danhier, F., O. Feron, and V. Préat. “To exploit the tumor microenvironment: passive and active tumor targeting of nanocarriers for anti-cancer drug delivery”. J. Control Release.148: 135–146 (2010).

3. “Lipid-Based Drug Delivery Systems— About.” American Association of Pharmaceutical Scientists. Accessed 28 Apr. 2017. Web.

4. Shrestha, Hina Rajni Bala and Sandeep Arora. “Lipid-Based Drug Delivery Systems.” Journal of Pharmaceutics. 19 May 2014. Web. 

5. Bulbake, U, et al. Liposomal Formulations in Clinical Use: An Updated Review. Pharmaceutics. 2017;9(2). Web.

6. Wagner, A. and K. Vorauer-Uhl. “Liposome technology for industrial purposes.” J. Drug Deliv. 2011: 591325 (2011).

7. Charcosset, C., et al. Preparation of liposomes at large scale using the ethanol injection method: Effect of scale-up and injection devices. Chemical Engineering Research and Design. 94: 508–515 (2015).

8. Food and Drug Administration (FDA) Liposome Drug Products: Chemistry, Manufacturing, and Controls; Human Pharmacokinetics and Bioavailability; and Labeling Documentation. Apr 2018. Web. 

9. ICH 11 Development and Manufacture of Drug Substances (Chemical Entities and Biotechnological/Biological Entities). International Council for Harmonisation of Technical Requirements for Pharmaceuticals for Human Use (ICH). 1 May 2012. Web. 

10. “Reflection paper on the data requirements for intravenous liposomal products developed with reference to an innovator liposomal product.” European Medicines Agency (EMA). Feb. 2013. Web. 

11. Guideline for the Development of Liposome Drug Products. Ministry of Health, Labour and Welfare (MHLW). Mar. 2016. Web. 

12. ICH Q7 (API GMP): Good Manufacturing Practice Guide for Active Pharmaceutical Ingredients Q7. International Council for Harmonisation of Technical Requirements for Pharmaceuticals for Human Use (ICH). 10 Nov. 2014. Web. 

13. ICH Q1A(R2): Stability Testing of New Drug Substances and Products. International Council for Harmonisation of Technical Requirements for Pharmaceuticals for Human Use (ICH). 6 Feb. 2003. Web. 

14. ICH Q2(R1): Validation of Analytical Procedures: Text and Methodology. International Council for Harmonisation of Technical Requirements for Pharmaceuticals for Human Use (ICH). Nov. 2005. Web. 

15. Q6A Specifications: Test Procedures and Acceptance Criteria for New Drug Substances and New Drug Products: Chemical Substances. International Council for Harmonisation of Technical Requirements for Pharmaceuticals for Human Use (ICH). 6 Oct. 1999. Web. 

16. “The Joint Good Manufacturing Practices Guide for Pharmaceutical Excipients.” International Pharmaceutical Excipients Council (IPEC) and Pharmaceutical Quality Group (PQG). 2017. Web. 

17. “The Good Distribution Practices Guide for Pharmaceutical Excipients.” International Pharmaceutical Excipients Council (IPEC). 2017. Web.

18. Qualification of Excipients for Use in Pharmaceuticals. International Pharmaceutical Excipients Council (IPEC). 2008. Web. 

19. “The IPEC Excipient Stability Program Guide.” International Pharmaceutical Excipients Council (IPEC). 2010. Web. 

20. “The IPEC Excipient Composition Guide.” International Pharmaceutical Excipients Council (IPEC).  2009. Web. 

21. “The IPEC Significant Change Guide for Pharmaceutical Excipients.” International Pharmaceutical Excipients Council (IPEC). 2014. Web. 

22. “IPEC-Americas Excipient Master File Guide.” International Pharmaceutical Excipients Council (IPEC).  2004. Web.