Dr Jason Bellia, Senior Patent Examiner at the
UK Intellectual Property Office (IPO)
I will look at just two of a vast number of routes – one to deliver nucleic acids across cell membranes and another looking to harness paracellular absorption to deliver biologics, for example across the GI tract. These solutions representing different ways to reap some of these rewards and illustrate a little about the patent system along the way.
Of the inventions that pass through our hands at the IPO many represent incremental improvements. In these cases we are often left with the question “is the increment enough to be new and inventive?” – not merely a modification that would be obvious to someone working in that field. Truly disruptive technology is often only really clear in hindsight, but a clear idea of the problem to be solved and the context provided by the present, presumably imperfect solutions, is always necessary whatever the invention.
The challenge of getting biologics across membranes doesn’t even start with the polar phospholipid groups – “Cells are not simple lipid bilayers, everyone draws these, but mother nature never gets the memo!” so said Prof Mrsny from the University of Bath – I have drawn on heavily his lecture for this article. The classical picture of the passive, stationary lipid bilayer with the odd receptor is far from the truth. The so called “glycocalyx” for example as found lining luminal endothelial cells in vascular tissues, comprises a complex array of anionic molecules which are variously recruited as coreceptors and involved in cell to cell interactions. These molecules present a challenge for avoiding off-target effects, even before biologics reach the lipid bi-layer.
Cell penetrating peptides especially those displaying highly basic sequences often come with problems of permanently disrupting the cell membrane, the classic alternative is the use of viral particles, or indirectly influencing the cell via cell surface receptors.
Nucleic acid-based drugs acutely illustrate these problems. While gene therapy has for decades held out the prospect of treating a vast number of diseases the challenge of delivery has inhibited the growth of this field. At present approximately 70% of gene therapy trials employ viral vectors, even though they generally suffer from the limitations of immune response activation, tropism (or selectivity of viruses for particular tissues/hosts), limited capacity and complexity of production, and even the risk of carcinogenesis.
Non-viral vectors don’t generally suffer from these problems but are yet to achieve anything like the efficiency of transfection achieved by viruses. One proposed solution has been the system developed by Alnylam Pharmaceuticals, concerning the delivery of RNA interference molecules using a delivery mechanism targeted for hepatocytes wherein the nucleic acid is conjugated to a N-acetyl-D-Galactosylamine (GalNac) molecule. In vivo GalNac binds to the sialoglycoprotein receptor ASGP-R targeted for its high capacity and abundance on hepatocytes. The affinity of the receptor for the GalNac bound nucleic acid is further enhanced to the nM range by providing a conjugate with a trivalent cluster of GalNac sugars, with subsequent degradation of the trivalent cluster in the low pH of the endosome. Liberation of the siRNA intact from the endosome may however require the separate use of fusogenic agents to disrupt the endosome, enabling liberation of the conjugate to the cytoplasm, where it can suppress transcription.
Fusogenic agents come with associated problems. Indeed “endosome escape” – liberating active agents from the endocytic pathway before the endosome matures into an ultimately destructive lysosome, is a perennial problem of drug delivery to cells. One proposed method provides biomolecules with an early exit from the endosomal pathway by the use of endosomal escape domains, initial studies on GFP internalisation by carcinoma cells have shown that conjugating a bioactive with an “endosomal escape domain” comprising a combination of indole and phenyl groups a fixed distance of 6 PEG units from the cargo can favour delivering the cargo to the cytoplasm before destroying its contents.
An alternative to the passage of compounds into (and through) cells when seeking intestinal absorption, is the paracellular route, as has been investigated by Professor Mrsny at Bath University. Navigating the paracellular route, between the cells of the intestinal epithelium can accommodate the passage of materials as large as 100nm in diameter and provides a very large potential surface area for absorption. One method developed has been to trigger an endogenous mechanism for enhancing tight junction permeability of intestinal epithelia. This operates by promoting cytoskeletal contraction triggered in the presence of inert macromolecule nutrients, this route has the benefit of being readily reversible. The phosphorylation of Myosin light chain (MLC) by its kinase results in a conformational change in the structure of myosin II in enterocytes increasing tight junction permeability, whilst an endogenous MLC phosphatase in due course reverses the effect, closing the tight junction. Rationally designed peptides termed permeant inhibitor of phosphatases (PIPs) block this dephosphorylation step to keep the tight junctions open for longer in the presence of macromolecular nutrients, and so when administered with the biomolecular drug of choice enable a temporary passage between enterocytes in the gut.
All in all, biologics face challenges at every interface within the patient, but this protective complexity is probably just what mother nature intended.
Comparing the journal references and the patents for the papers on endosome escape and paracellular absorption it is notable that they illustrate a number of differences of patents vs journal publications that underlie their different purposes. The journals, as we would expect, focus on testing the optimised molecules to illustrate the particular effects they produce in vivo and demonstrate the validity of the conclusions drawn. The patents, on the other hand, use largely the same experimental data but extrapolate from the optimised molecules from the literature references to propose alternative molecules that demonstrate the same effects, and it is this class of molecules that are defined in the patent claims. The inventors are seeking to maximise the commercial benefit of their invention by casting the scope of the protection afforded by the patent widely. This difference can be a useful adjunct in literature research to see where the proposed boundaries of the effects may lie, and what elements of the molecule the inventors see as crucial.
It is also worth noting that the patents have a priority date (when the first version of the disclosure was submitted to a patent office) several years before the journal publication date and as such the patents were presumably submitted long before of the journal articles. The above inventors have wisely submitted their patent applications before the journal article to avoid making an invention publicly available and, as such, preventing its protection by a patent. It is disappointing for patent examiners to see that this basic message hasn’t always got through to the research community.