Organic Nanoparticle-Based Drug-Delivery Systems as Alternatives to Lipid Nanoparticles

Magnified View of Lipid Nanoparticles | Image Credit: ©Aniwat - stock.adobe.com

Addressing the challenges posed by the limited bioavailability of many small-molecule APIs and the instability and inability of nucleic acids to pass through cell membranes has become an important goal within drug development. Most efforts have focused on finding delivery systems that enhance stability and solubility, facilitate cellular entry, and ideally allow effective targeting of specific cells, tissues, and/or organs. Nanoparticle systems, with their small size, high surface areas, and adjustable functionality have attracted significant attention (1).

Most prominent systems to date have been lipid nanoparticles (LNPs), which have been shown to be effective for the delivery of RNA and DNA. LNPs have their own limitations, however, which is driving interest in the development of other nanoparticle delivery systems, including both inorganic and organic alternatives. Three organic options with real potential include exosomes, polymeric nanoparticles, and DNA-based nanoscale frameworks.

Limitations of LNPs

While LNPs are currently the go-to solution for delivery of nucleic acids, there is significant room for higher-performing alternatives, as LNPs face several limitations that impact their effectiveness as drug-delivery systems, according to Grant Boldt, chief operating officer at CPTx and gxstrands.

These issues include poor stability, a limited loading capacity for drug substances, manufacturing process scale-up challenges, and the small number of approved lipid excipients available for LNP formulation, notes Tom Tice, senior director global strategic and technical marketing for parenteral drug delivery with Evonik Health Care.

LNP instability is of particular concern. “LNPs can potentially be unstable during storage, leading to drug leakage,” Boldt observes. They are also subject to rapid clearance from circulation, reducing their bioavailability.

In addition, LNPs suffer from challenging extrahepatic delivery, says Davide Zocco, head of exosomes development at Lonza. Specifically, intravenously injected LNPs are mostly absorbed by the liver, with limited exposure to other tissues. “While new lipid chemistries have been developed to facilitate extrahepatic delivery, no (successful) clinical data have been reported yet,” he says. Furthermore, achieving effective endosomal escape and intracellular delivery remains a significant challenge, limiting the successful release of therapeutic cargo into target cells, Boldt adds.

Other challenges highlighted by Zocco include limited activation of mucosal immunity required for successful intranasal administration of vaccines, risk of unwanted immunogenic reactions, and limited evidence of the ability of LNPs to deliver other drug substances such as proteins.

Alternative nanoscale technologies

The advantages of nanoscale delivery systems have led to significant efforts to identify other forms of nanoparticles without the limitations associated with LNPs. FDA guidance (2) considers nanomaterials, such as nanoparticles, as materials with dimensions within the nanoscale range of approximately 1nm to 100nm or outside the nanoscale range (up to < 1000 nm) if they exhibit properties or phenomena that are attributable to their dimensions, Tice observes. Alternative inorganic and organic solutions are under investigation. Leading inorganic nanoparticle technologies include those based on gold, iron oxide, and mesoporous silica nanoparticles, as well as quantum dots.

Organic options include extracellular vesicles such as exosomes; polymeric nanoparticles such as dendrimers, polyplexes, and polymersomes; DNA nanostructures; self-assembling peptides; and virus-like particles (VLPs).

While polymeric and inorganic NPs are synthetic, exosomes are produced by cells, and their molecular composition varies depending on the cell source, according to Zocco. Their potential as delivery vehicles is, adds Tice, primarily based on their ability to mimic important cellular interactions and signaling. Exosomes also, notes Boldt, leverage their natural origin and tissue tropism for targeted and biocompatible delivery. DNA origami and other DNA nanostructures, meanwhile, provide precise structural control, programmability, and multifunctionality for advanced therapeutic payloads, Boldt says.

Polymeric nanoparticles are, says Tice, among the leading organic technologies with demonstrated utility in the clinic. Most notable are those based on polymers already used as excipients in drug formulations, particularly bioabsorbable, biocompatible poly(lactide-co-glycolide) polymers (LG polymers), and poly(ethylene glycol) (PEG)/LG polymer copolymers (diblock polymers). Typically, polymeric nanoparticles are designed for drug targeting and to be taken up by cells such as T-cells or the spleen for immunotherapy, Tice adds. In addition, they can provide immediate release or extended release of their active ingredients.

Dendrimers, with their highly branched architecture, enable efficient drug encapsulation and controlled release, Boldt comments. He also notes that self-assembling peptides are gaining attention for their ability to form stable and versatile nanostructures, and VLPs are of interest because they mimic the efficiency of viral delivery while avoiding infectious risks.

“These technologies offer unique and complementary properties, enabling tailored solutions for specific therapeutic applications and enhancing the potential for effective and targeted drug delivery,” Boldt concludes.

Focus on exosomes

Exosomes, observes Zocco, are nanoparticles naturally produced by cells to maintain cell homeostasis (e.g., disposal of molecules) and communicate with other cells through material transfer or surface receptor-mediated signaling (kiss and run mechanism). “As a result,” he says, “they can be exploited to deliver drugs to specific tissues across biological barriers and, given their physiological role, with a lower risk of triggering adverse immune reactions as compared to other organic or inorganic nanoparticles.”

Development of exosomes as drug delivery vehicles does present some challenges, though. Given the high heterogeneity of exosomes, critical quality attributes (CQAs) of exosome-based drugs are not clearly defined, and companies need to proactively engage with regulatory bodies to define their path toward clinical development and commercialization, according to Zocco.

In addition, the development of analytical technologies to characterize exosome-based drugs is an ongoing effort (e.g., single-particle analysis), and as yet no single technology has been generally adopted to address CQAs. “As a consequence,” Zocco notes, “acceptance criteria ranges may change depending on the chosen technology. Furthermore, most analytical technologies have been developed for exosome characterization, with only a handful of them supporting qualified assays for quality control in good manufacturing practice (GMP) manufacturing.”

There is also a lack of expertise in, and scalable processes for, the scalable manufacture of exosomes, according to Zocco. This issue is further exacerbated by the fact that most developers establish their own exosome manufacturing processes using specific cell sources (and media), and no exosome manufacturing platform (and cell source) has been widely accepted yet.

Finally, unlike LNPs for which delivery of nucleic acids has been effectively demonstrated, loading of exosomes with this type of drug substance has proven challenging. “While surface linking with antiSense oligonucleotides and small-interfering RNAs has been demonstrated, luminal loading via electroporation or other means has been largely unsuccessful. Cell engineering strategies or alternative technologies for post-production loading are required to advance the field further,” Zocco concludes.

Despite the challenges, exosomes are still an exciting and innovative drug delivery system, Zocco believes. “While it’s likely that exosomes will not replace LNPs or other nanoparticles any time soon, they may provide a valid alternative to developers that are willing to solve the challenges and benefit from their natural ability to deliver molecules designed to improve health and treat disease,” he concludes.

Lonza’s EngX drug delivery system, which achieves surface and luminal loading of therapeutic molecules into exosomes via linkage to the expressed proteins prostaglandin F2 receptor inhibitor in the EWI (glutamine-tryptophan-isoleucine) immunoglobulin superfamily and brain-abundant membrane-attached signal protein 1 in the myristoylated alanine-rich C-kinase substrate protein family, respectively, is one example of an exosome technology being investigated in clinical trials. Other companies employ similar approaches with exosome shuttle proteins mediating active loading into exosomes, according to Zocco. “Using these systems, efficient loading of large proteins (e.g., gene-editing elements), nucleic acids (e.g., messenger RNA), and even viruses (e.g., adeno-associated viral vectors) has been demonstrated.”

Exploring polymeric nanoparticles

Lipid nanoparticles can include liposomes (lipid vesicles that have at least one lipid bilayer with or without a PEG lipid) and lipid vesicles without a lipid bilayer and comprising multiple lipids, including a PEG lipid and an ionizable lipid designed to deliver messenger RNA. Compared to these LNPs, LG polymer nanoparticles, which have a wide range of tunable properties and performance qualities, can better meet the needs of today’s new modalities, according to Tice.

LG polymer tuning includes manipulation of polymer molecular weight, lactide/glycolide ratio for hydrophobicity tailoring, and end-group structures, says Tice. Nanoparticles made with PEG/LG polymers, meanwhile, have PEG molecules oriented on their surfaces to which various molecules can be attached to increase targeting properties and/or active ingredients.

Compared to LNPs, LG polymeric nanoparticles can support higher drug loading levels and release drugs over longer periods, Tice observes. In addition, they do not require self-assembly and can be produced using more controlled and scalable processes, such as emulsion-based continuous nanoencapsulation. They are also simpler than LNPs, requiring a single polymer excipient, and can be lyophilized and stored at refrigerator temperatures.

As with other technologies, there are some challenges to using polymeric nanoparticles for drug delivery. Tice highlights encapsulation of water-soluble drug substances with high encapsulation efficiencies as potentially presenting difficulties. However, the tunability of polymeric nanoparticles often makes it possible to overcome this issue by modifying the polymer properties and developing an appropriate and optimized manufacturing process. He also notes that optimal processes often help address any scaling challenges, with typical batch sizes for clinical trial materials ranging from 1 to 10 kg.

Ongoing research is also leading to further progress with polymeric systems designed to mimic the biological compatibility and complexity of therapeutic mechanisms of action, and particularly those that can serve as alternatives to lipid-based drug delivery systems, according to Tice. “The goal is to combine the biological performance advantages of lipid-based systems with the process and manufacturing advantages of polymer-based drug delivery systems,” he states.

A new solution: DNA-based nanostructures

One of the newest organic nanoparticle technologies in development involves the use of DNA-based nanostructures, which Boldt believes offer distinct advantages for drug delivery due to their highly programmable and customizable structures. “DNA-based nanoparticles are biocompatible, biodegradable, and allow precise control over size, shape, and ligand display, enabling targeted and efficient delivery,” he states.

As importantly, DNA-based nanoparticles can carry multiple therapeutic payloads and demonstrate improved cellular uptake and endosomal escape capabilities, according to Boldt. In fact, DNA nanostructures provide superior structural control and multifunctionality compared to other organic options, offering enhanced adaptability for complex therapeutic needs, he says. “Furthermore, compared to alternatives, they exhibit very low immunogenicity and can be easily modified chemically for targeting or payload attachment,” Boldt notes.

Boldt concludes that given their high biocompatibility, minimal toxicity, and biodegradability, DNA-based systems represent a promising platform for the delivery of advanced, personalized, and genetic medicines. In particular, CPTx believes DNA nanostructures are ideally positioned to serve as a versatile and effective next-generation solution in genetic medicines.

Given the nascent nature of this technology, DNA-based nanoparticle delivery systems not only offer exciting opportunities for innovation and progress, but also present many hurdles to commercial development that require specialized expertise in DNA manufacturing and manipulation as well as drug development in general.

For instance, Boldt notes that nuclease degradation in biological fluids and rapid clearance from circulation presents initial challenges that are being addressed with ongoing advancements in stabilization techniques and delivery strategies. Efforts underway to development enhanced cellular uptake and overcome endosomal entrapment are also proving to be promising. Potential immunogenicity issues, meanwhile, are being overcome through sophisticated design approaches, ensuring safer therapeutic use. Regulatory validation is also a necessary step, but one that represents an opportunity to establish robust standards that will facilitate broader adoption across the industry, according to Boldt.

“By overcoming these challenges, the immense potential of DNA-based nanoparticles as a transformative platform for drug delivery can be fully realized, opening doors to more precise, effective, and personalized medical treatments,” Boldt states.

CPTx is one of only a few companies at the forefront of DNA-nanoparticle-based drug development and working to realize its potential. The company is focused initially on the development of DNA nanostructures for targeted self-gene delivery to specific cell and tissue types. “Our innovative approach leverages the delivery of genes as single-stranded DNA (ssDNA) vectors, offering remarkably low immunogenicity and enabling the potential for repeat dosing—an exciting leap forward for applications like in vivo chimeric antigen receptor T-cell therapies,” Boldt explains.

Proprietary technologies needed to achieve successful scale-up and meet rigorous regulatory requirements for clinical and commercial therapies have already been established, according to Boldt. In particular, CPTx’s processes for production of ssDNA strands and nanoscale DNA frameworks for drug delivery applications allow for efficient, economically viable manufacturing at the large scales needed to meet the demands of several high-impact unmet medical needs. Advanced analytical methods have also been developed to ensure safety, efficacy, and compliance throughout the regulatory process and address the challenges associated with introduction of novel modalities.

Big expectations for nanoscale organic delivery technologies

In the near term, LNPs are expected to remain a preferred option for nanoparticle-based drug delivery. The unique properties of alternative systems, including exosomes, polymeric nanoparticles, and DNA-based nanoscale frameworks, offer the potential for improved performance over LNPs for many drug substances and therapeutic applications, including cancer, autoimmune and infectious diseases, inflammatory conditions, and genetic disorders (1).

References

1. Rumiana Tenchov. Nano-sized Drug Delivery Systems Can Treat Cancer, HIV, and More. Chemical Abstracts Service Insights, August 30, 2024.
2. FDA. Guidance for Industry: Drug Products, Including Biological Products, that Contain Nanomaterials (Rockville, MD, Nov. 2022).

About the author

Cynthia A. Challener, PhD, is a contributing editor to Pharmaceutical Technology®.

Article details

Pharmaceutical Technology®
Vol. 49, No 2
March 2025
Pages: 14–17

Citation

When referring to this article, please cite it as Challener, C.A. Organic Nanoparticle-Based Drug-Delivery Systems as Alternatives to Lipid Nanoparticles. Pharmaceutical Technology 2025 49 (2).