PANEL DISCUSSION ON OLIGONUCLEOTIDES AND THERAPEUTICS

TRENDS, CHALLENGES, AND FUTURE DIRECTIONS

As I thaw out of nearly three years of pandemic-induced disruption of daily life, I reflect on the journey that oligonucleotide therapeutics have taken us.  Pre-pandemic, my thoughts of nucleic acid therapeutics were limited to anti-sense oligonucleotides (ASO) and siRNA, although considerable interest existed in mRNA-therapeutics, my exposure to mRNA vaccines was for rabies, Zika, and Chikungunya viruses.

This all changed at the end of 2019 when the global explosion of COVID-19 forced the pharmaceutical industry to rapidly develop a vaccine.  Traditional vaccine development relied on either attenuated virus or protein antigens to induce an immune response.  Sequencing of SARS-CoV2, the virus that causes COVID-19 allowed for a new class of mRNA vaccine.  But this is only part of the story as mRNA is chemically unstable.  The parallel development of lipid nanoparticles (LNP), starting around 2001 for the delivery of DNA was the second piece of the puzzle.  The ability to scale manufacturing of LNPs in the mid-2010s allowed for approval of the siRNA patisiran to treat polyneuropathy in 2018. It is this winning combination of two key technologies, a way to rapidly and to deliver it, developed over decades of research in oligonucleotide therapeutics that led to these COVID-19 mRNA vaccines.

Oligonucleotide therapeutics have made incredible strides.  On the chemistry side, modifications of the phosphodiester or sugar structure like phosphorothioate (PS), phosphorodiamidate morpholino (PMO), peptide nucleic acid (PNA), locked nucleic acid (LNA), 2’-O-methyl, and 2’-O-methoxyethyl have led to molecules with enhanced stability, potency and reduced off-target toxicity and immune response.  On the delivery side, enhanced stability by conjugation to N-acetyl galactosamine (GalNAc) and lipid-based delivery have been successful.  Nano-formulations of various polymers like PLGA and PBAE, have been unsuccessful due to toxicity.

Central Neural System (CNS) indications are well represented in approved oligonucleotide therapeutics (ASO and siRNA).  Spinal muscular atrophy and the very recent approval of tofersen for SOD1-ALS are both intrathecal administered.  Although functional, there are challenges with either frequent administration or administration in large populations.  This begs the question as to whether this class of CNS therapeutic is most appropriate for rare or genetic diseases.  Oligonucleotide therapeutics are well positioned in personalized medicine.  Genetic mutations leading to a particular disease could potentially be treated with an oligonucleotide designed to that particular mutation.  Of course, there are limitations to the types of mutations that can be corrected with this approach.  Currently, RNA cleavage by RNase H, RNA interference or steric hinderance result in less protein production, ideally suited for dominant-negative mutations.  Exon skipping is another approach which can restore proper protein expression.

As an example of more personalized medicine, the non-profit n-Lorem Foundation, headed by Dr Stanley Crooke, founder of Ionis Pharmaceuticals, is working to develop ASO treatments for nano-rare diseases (defined as less than 30 patients) and even the n-of-one patient.  The foundation works closely with FDA, which published regulatory guidance for manufacturing, nonclinical and clinical testing of individualized oligonucleotide treatments.  This is an excellent example of how the power of oligonucleotide therapeutics can serve the high unmet medical need of the individual.

Recent history showed us what is possible when there is collective cooperation on a global scale.  There is tremendous strength in working together and our challenge is to replicate this daily and not wait until the next global crisis. The partnership between industry, manufacturers and regulators is a key part of this collaboration.

As the number of approved oligonucleotide therapeutics increases, the question becomes what’s next?  What are our current challenges and opportunities?  A world class panel of experts were invited to share their perspectives on the four topics and questions listed below about the future of oligonucleotide therapeutics.

A common response by several panelists is the critical nature of a robust supply chain.  Dedicated suppliers and redundancies will be important to establish a secure supply chain.  An additional lesson learned from the pandemic is how when focused on a common goal, effective cooperation and collaboration can lead to success.

ABOUT THE AUTHOR
Dr Morimoto has over 25 years of industry experience in leading project teams in the development of innovative medicines, providing guidance in the design and execution of preclinical, manufacturing, clinical and regulatory activities with a therapeutic focus in neurodegenerative diseases including Parkinson’s, Alzheimer’s, ALS and frontotemporal dementias.  Previously, Bruce held leadership roles at Alkahest, Celerion, Cerecin and Allon Therapeutics, and works closely with the Michael J Fox Foundation, chairing one of their scientific review panels. He is an advisor to several biotech companies helping to move their programs into clinical development and drug registration.
Bruce started his career on the faculty in the Chemistry Department at Purdue University where his independent research focused on neuronal signal transduction.  Bruce earned his doctorate in biochemistry from UCLA and completed a postdoctoral fellowship at the University of California Berkeley.

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COVADONGA PANEDA
Chief Operating Officer, Altamira Therapeutics/Auris Medical AG

What challenges remain in the delivery of oligo therapeutics?
One of the main roles of cellular membranes is to exert a strict control of interchange of materials with the extracellular surroundings. While small lipophilic molecules are typically able to cross biological membranes, the size and charge of oligonucleotides precludes them from entering the cytoplasm. On the other hand, extracellular fluids are commonly rich in nucleases and naked oligonucleotides are rapidly cleared by the kidney once they reach circulation. This combination of features makes oligonucleotides poor drugs; they are rapidly degraded and cleared after administration and they are unable to enter the cell, a requirement for exercising their biological action. Improving the pharmacological properties of these molecules is therefore essential to turn this promising class of molecules into effective drugs.

 

In the last decade, advances towards improving the properties of oligonucleotides as drugs have been significant. Chemical modification of the sugar and/or nucleobase moieties, modification to the phosphodiester backbone and protection from nucleases using different microencapsulation techniques have significantly contributed to enhance biological stability of therapeutic oligonucleotides. Chemically increasing the stability of oligonucleotides has allowed the field to move towards delivery approaches that do not necessarily entail encapsulation of the compound, such as conjugation. Both encapsulation and conjugation have been successfully applied to deliver oligonucleotides to the liver; conjugation to N-acetylgalactosamine (GalNac) promotes interaction with the asialoglycoprotein receptor (ASGPR) present on the hepatocyte cell membrane leading to receptor mediated endocytosis and effective delivery of oligonucleotide into the cytoplasm. The first FDA approved siRNA drug, Onpattro, is encapsulated in lipid nanoparticles (LNP). This drug reduces production of transthyretin in the liver avoiding toxic tissue accumulation of the mutant form of the protein. However, while delivery of oligonucleotides to hepatocytes has been successfully achieved, effective extrahepatic delivery remains elusive. In addition, using LNPs to deliver oligonucleotide results in massive degradation of the active molecule in endosomes due to ineffective release from these cellular compartments and activation of immune response. While the former reduces the efficacy of therapeutic oligonucleotides the latter results infusion related side effects and other toxicities. In summary, identification of effective delivery vehicles for extrahepatic delivery, solutions to increase endosomal release and identification of non-immunogenic encapsulation materials are the main challenges the field faces to extrapolate the success of these oligonucleotide modalities in the treatment of hepatocyte-driven diseases.