Nanotechnology in Pharmaceutics and Drug Delivery Systems
Eleni Samaridou, Head of Early-stage Formulation Development & Process Design team, Merck KGaA
Nanotechnology has had a transformative impact on drug delivery and pharmaceutics over the past few decades. The unique properties of the nanotechnology-based delivery systems allow them to overcome traditional constraints, and to address longstanding challenges in the field, related to the efficacy, bioavailability, tissue-specific targeting, safety, and stability of pharmaceutics. The success of these systems is reflected by the outstanding applications in the treatment of various diseases and the number of ongoing clinical studies. However, there are still certain challenges that need to be addressed to ensure the development and clinical translation of these promising approaches.
1. How do you assess the current state of nanotechnology in drug delivery, particularly for RNA therapeutics?
Nucleic acid pharmaceuticals have proven their potential to successfully treat or prevent intractable diseases over the last years. However, their rapid degradation profile and poor cellular uptake dictate the use of rationally designed delivery vehicles to safely transfer them to the desired site. The range of emerging systems and approaches that can be used to deliver such therapeutics is growing and advancing at an incredible rate. With this extraordinary progress in nano-engineered lipid-, polymeric-and hybrid-based delivery systems, the scope of therapeutic targets has significantly broadened. Still, lipid nanoparticles (LNPs) are the most clinically advanced delivery system for RNA therapeutics and vaccines. The approval of the first siRNA drug i.e. ONPATTRO™, based on LNP delivery, for the management of transthyretin-regulated amyloidosis in 2018 was a legendary breakthrough. Followed by the now established role of these delivery vehicles in the success of mRNA vaccines against infectious diseases (i.e., SARS-CoV-2 and respiratory syncytial virus). Inspired from these success stories, the scientific community is motivated to further explore and advance the LNP delivery technology, with several studies focusing on addressing potential challenges around these systems (target specificity, safety, stability, scalability etc.), and with numerous ongoing clinical studies, with particular focus on infectious diseases, oncology and genetic disorders.
2. What are the key design principles for engineering high-performing lipid nanoparticles (LNPs) for RNA delivery, and how do they impact stability and efficacy?
The LNPs provide a protective wrapper for the delicate RNA molecules and enable their safe and efficient delivery into cells. While the concept itself sounds simple, engineering high-performing LNPs for RNA delivery is not straightforward. Thousands of promising LNPs have been explored in the preclinical phase so far, yet only a handful of them manage to reach the clinic. Designing the right delivery vehicle for RNA delivery and clinical translation requires a high level of expertise and strong technical capabilities to ensure the rational design and assembly of a scalable, reproducible LNP formulation with high target specificity, safety and long-term stability.
Key design principles to ensure a smooth journey from formulation discovery all the way to market approval, is (i) the meticulous and rational design of the LNP composition to ensure high biological performance, tolerability and target specificity, (ii) the deep understanding of the critical process parameters for its manufacturing and purification to ensure its scalability and batch-to-batch reproducibility, and finally (iii) the selection of the proper conditions to ensure its long shelf life, all while maintaining the cost of this approach as low as possible.
3. From an industrial perspective, what are the primary bottlenecks in scaling up the manufacturing of nanomedicines while ensuring batch-to-batch reproducibility?
One of the primary bottlenecks in the clinical development of nanomedicines is the fact that the scaling up of the manufacturing of nanomedicines is not considered early enough in formulation development, leading eventually to failure of translating any preparative method from a laboratory scale to an industrial scale. This is mainly due to the lack of manufacturing expertise, capabilities and material limitations. The scale-up of nanomedicines includes the integration of methods as well as the transfer of technology for their large-scale industrial production. A well-designed scale-up process is crucial to ensure the quality, cost-effectiveness and batch-to-batch reproducibility of the formulation.
4. How have recent advances in nanomedicine influenced the development of vaccines, and what innovations do you foresee shaping the future of RNA-based vaccine delivery?
The application of nanotechnology to vaccine development revolutionised the field, something that we all witnessed firsthand with the extraordinary success of the mRNA LNP-based Moderna and Pfizer/BioNTech COVID-19 vaccines. Thanks to decades of research and innovation, mRNA vaccine nanotechnology was ready when needed. The approval of these mRNA-LNP vaccines have already paved the way for new vaccines, like the mRNA vaccine against respiratory syncytial virus (RSV) by Moderna (now approved in the US & Canada), or other advanced-stage mRNA vaccines against other respiratory viruses such as the flu or protection against diseases like tuberculosis and HIV. In parallel, we see the employment of novel nucleic acid modalities, like self-amplifying mRNA (saRNA) and circular RNA (circRNA) vaccines, which offer promising possibilities for disease prevention and treatment, including potential applications in cancer, apart from infectious diseases.
5. Given the complex nature of biological barriers such as the blood-brain barrier, how are nanocarriers being optimised for effective central nervous system (CNS) drug delivery?
One of the big advantages of nanocarriers is their design versatility that allows them to address some of the most complex biological barriers and reach tissues and cellular targets with high specificity. Having said that, drug delivery to the CNS is particularly challenging, although crucial for the treatment of debilitating neurological disorders. Nanomedicine can enhance the pharmacokinetics and activity of drugs to the CNS, either via invasive (disruption of the BBB or local injection (intracranial)) or non-invasive routes of administration, thus improving patient comfort. Examples of non-invasive/alternative administration routes are the employment of surface characteristics that can give the nanocarriers active targeting properties to the CNS through BBB receptors (via intravenous injection) or the employment of alternative administration routes, like intranasal and intrathecal administration.
6. How do the physicochemical properties of LNPs influence cellular uptake and endosomal escape, and what novel strategies are being explored to enhance these processes?
Based on what we know around the LNP technology so far, their cellular uptake and, subsequently, their endosomal escape is governed primarily by the selection and molar ratio of the ionisable lipid in the LNP composition, and the molar ratio between lipid and RNA nucleotides. The top strategies to further enhance the LNP cellular uptake and endosomal escape focus around the design of novel and more potent ionisable lipids, the optimisation of other lipid molecules in the LNP composition, or the incorporation of auxiliary materials.
7. How does your team approach the early formulation screening process to ensure the identification of the most promising nanocarrier candidates?
As part of the Early Formulation Screening Service (EFSS) team at Merck KGaA, Darmstadt, Germany, we have gathered best-in-class expertise dedicated to the preclinical development of LNP solutions, while simplifying the “go-to-market”, by supporting in-house transfer to clinical GMP manufacturing at our site in Indianapolis, US.
It is our ambition to develop precisely engineered LNPs that are tailored to the requirements of each project and application. For this, we follow three basic steps: the formulation screening, formulation optimisation and early-stage process development to ensure the scalability of the identified top-performing formulation. In the screening phase, we secure the identification of lead ionisable lipid (the key to successful LNP formulation development), by testing a carefully selected panel (per application) of structurally diverse ionisable lipids from multiple libraries. In the second step, the formulation optimisation phase, we tailor the LNP properties to obtain the perfect composition for maximal efficacy and target specificity. And in the last step, the up-scaling phase, we transition from small scale to large scale manufacturing process to prepare the LNP in larger scale and ensure a smooth technology transfer for further clinical development. We have expertise in LNP development across multiple nucleic acid modalities, IP access to top-of-the-art ionisable lipids from multiple libraries, wide variety of scalable mixing technology platforms, strong expertise in-house technology transfer to GMP manufacturing, offer a large panel of analytical methods (including expertise in lipid metabolism and clearance, in-house in vitro capabilities, in vivo support) and support dedicated stability studies (including state-of-art lyophilisation capabilities).
8. What role do artificial intelligence and computational modeling play in the rational design and optimisation of nanoparticle-based delivery platforms?
Artificial intelligence (AI) and computational modeling (CM) are being increasingly applied, over the last years, to improve the efficiency of research activities. As you can imagine, development of AI/CM methodologies have become particularly relevant to the LNP community, as they allow the acceleration of the LNP formulation and process optimisation while reducing the time, resources and costs of the experiments required. Examples of how AI/CM tools can be applied in the development of novel and more potent RNA-LNP are (i) the identification of lipidic components (novel ionisable lipid structures or alternative lipid components) and (ii) the amounts of each component (formulation composition) required to achieve a particular physicochemical property, stability or biological activity, enabling a deeper structure/ composition activity relationship based approach, or, (iii) even, process optimisation by predicting the effect of critical process parameters on selected physicochemical properties and stability of the LNP formulations, among others. Having said that, we need to be cautious that these approaches are still emerging and face significant limitations, driven mainly by the requirement for large datasets, potential biases (due to data scarcity and low data quality), and lack of interpretability. Data curation and preprocessing for accurate prediction requires a significant portion of time and effort. Mitigating these challenges is an active research topic.
9. What are the current gaps in understanding the in vivo fate of nanocarriers, and what methodologies are being developed to better track their biodistribution and clearance?
Thorough understanding of the in vivo fate of nanomedicines is crucial — without it, the development of such approaches would be a hit-or-miss game. To avoid this and to accelerate the clinical translation of nanocarrierbased delivery systems, it is important to perform rational studies to fully unravel where a nanocarrier traverses in the body, and what pharmacological effects it elicits, as early as possible. The prediction of the in vivo fate of nanocarriers based solely upon their physicochemical properties and in vitro assessment is insufficient, and in most cases misleading, since these approaches cannot mimic or take into consideration complex biological interactions that occur in vivo. On the other hand, animal studies should be designed in a rational and ethical manner. Rodents are currently the main model for early evaluation of the in vivo fate of the nanocarriers, although there has been shown that there might be lower correlation to human data. Larger animal models, like non-human primates, are considered the most predictive models, but also come with important considerations in terms of accessibility and cost. In terms of available methodologies, the field has advanced, and several in vivo/ex vivo imaging techniques are available to monitor the in vivo fate of nanocarriers. The utility of reporter genes, environment-responsive fluorophores, radioactive labelling, gamma scintigraphy, magnetic resonance imaging, single photon computed tomography, positron emission tomography, mass spectrometry and magnetic marker monitoring are only some examples.
10. How do you address the challenge of targeted delivery while minimising off-target effects in the clinical translation of RNA-based nanomedicines?
The specific delivery of therapeutic molecules (e.g., RNA therapies and vaccines) to target sites in the body, while minimising off-target effects, represents an active area of research. For this, the rational selection of suitable materials is a critical first step in the design of organ-targeted delivery systems. To date, most developed nanocarrier-based technologies largely target at the organ level — with LNP exhibiting an inherent tendency to target the liver (especially when administered intravenously). Huge scientific effort is currently dedicated to tune the biodistribution of these systems and to achieve cell-specific delivery (with particular focus on extrahepatic delivery). For this, three different approaches are mainly employed: (i) passive, (ii) endogenous and (iii) active targeting. In the case of the passive targeting, the nanocarriers’ physical properties are the main driver of their distribution (e.g., circulation time and organ accumulation). For endogenous targeting, the nanocarriers’ composition is the main driver, as the selection of materials (e.g., lipids) governs the formation of a specific protein corona in vivo, which in turn gives the nanoparticles distinct organ-targeting properties.
Lastly, active targeting relies on the identification of suitable targeting ligands (e.g., antibodies, nanobodies, small molecules, sugar moieties etc.) that are used to decorate the surface of the nanocarriers in order to avidly target a specific cell type. Interestingly, nanoparticles that use active targeting have not advanced beyond clinical trials; this may be due to various reasons such as added complexity of the formulations, lack/complexity of scalability, or limited targeting efficacy and translation of this efficacy from animal models to human.
11. What advancements in lipid formulation strategies are being pursued to enhance RNA stability, particularly under real-world storage and transport conditions?
Long-term storage stability is a driving factor for the clinical translation of nanoparticles for RNA delivery. Maintaining LNP stability during storage requires careful control of several factors, including optimising lipid composition, concentration, storage matrix used, and ensuring the use of appropriate storage conditions (including proper temperature control). For RNA-loaded LNP, the current standard, in order to minimise degradation of both the LNPs and their cargo, is to store them at ultra-low temperatures, ranging from -60 to -90°C. However, ultracold storage comes with great restrictions for global distribution — something that we all witnessed during the recent pandemic. For this reason, researchers are now dedicating efforts to enable the storage of LNP formulations at higher storage temperatures (such as -20 °C, 2-8°C or even at room temperature), to significantly ease the logistical challenges of distributing these therapies and vaccines. In this regard, several advancements have been already made either in the field of generating novel thermostable lipid components, or in acquiring deeper understanding of the interactions of specific lipidic components with the RNA payload, or by optimising the storage matrix used, or, finally, by developing efficient lyophilisation processes to enable the storage of these formulations in powder form at higher storage temperatures.
12. How do you see the role of personalised medicine evolving with nanotechnology, and what are the key challenges in adapting RNA-based nanomedicine for individualised treatments?
Nanomedicine is expected to be a very important instrument for personalized, targeted, and regenerative medicine. This is a very exciting and emerging field. As example, several key players in the field (such as BioNTech and Moderna among others) are focusing on the use of the mRNA vaccine technology as fully individualised immunotherapies that aim to address each patient’s unique tumor (using genetic sequencing information). Such personalized mRNA vaccines are already showing impressive results in ongoing clinical evaluations in various solid tumor indications, including first-line melanoma, adjuvant colorectal cancer, and adjuvant pancreatic ductal adenocarcinoma. Despite the tremendous potential, there are still significant challenges. The advanced techniques in genomics and bioinformatics required for personalised vaccines are particularly time-consuming and costly, raising significantly the cost of such personalized approaches. Moreover, manufacturing and scalability of personalized mRNA vaccines with adequate speed, flexibility and in accordance with stringent regulatory standards pose practical challenges. Ensuring the readiness and education of expert CDMOs to support developers with personalized mRNA products is essential for clinical success.
13. What are the biggest challenges in achieving regulatory approval for novel nano-technology based drug delivery systems, and how can these be addressed?
The regulatory framework for RNA-loaded nanotechnology-based delivery systems is still an evolving field. Rapid and combined efforts are being made by regulatory agencies, academia, and industry to cover any gaps. Still, drug developers face significant challenges in having to navigate through complex and diverse regulatory requirements, depending on the indication or the diversity of the compositions used for RNA delivery. One strategy to streamline both the clinical trial regulatory process and the drug approval is to establish the level of information needed by regulators as early as possible in preclinical development. Therefore, it is crucial for the drug developers to have expert regulatory support as early as possible to design an optimised regulatory strategy and ensure a faster and less complex time to market.
Author Bio
Dr. Eleni Samaridou heads the Early-stage Formulation Development & Process Design team, at Merck KGaA, Darmstadt, Germany. She is a chemical engineer by training and holds a MSc in Biochemistry and a PhD on Nanomedicine, followed by 3-year postdoctoral research experience on advanced drug delivery. She brings over a decade of experience on the development of polymer- and lipidbased delivery systems for therapeutic protein and RNA delivery, and more than 6 years of industrial experience, having served previously as Scientist at BioNTech SE, Mainz, Germany, and, at Genevant Sciences, Vancouver, Canada. The focus of her research currently is the preclinical development of high-performing lipid nanoparticles (LNP) to enable the development and clinical translation of RNA therapies and vaccines.
