HEPtune, the use of heparosan for drug delivery, has superior attributes including:
1) new intellectual property,
2) inertness in the bloodstream,
3) biodegradation in cells,
4) polymer size control,
5) lack of immunogenicity,
6) lack of toxicity,
7) lack of anticoagulant bioactivity,
8) stable polymer and drug conjugate,
9) downstream processing and purification,
10) superior biological activity and efficacy of HEP-drug conjugates.
New intellectual property
Caisson offers its partners access to a broad patent portfolio, encompassing both US and international patents. The novel HEPtune system can be used in combination with new active pharmaceutical ingredients and existing actives, providing life cycle management opportunities.
Caisson’s IP landscape covers the heparosan polymer, its methods and use within drug delivery, composition of the heparosan with actives and applications, the enzymes/catalysts used to produce the heparosan and production/methods of select sizes of monodisperse heparosan polymers.
Inert in the bloodstream / Extended half-life
The body produces no extracellular degradation enzymes for heparosan and additionally, no binding proteins or receptors have been identified for the polymer. These qualities make heparosan a prime drug delivery candidate and allow for long circulation time in the blood.
Additional glycosaminoglycans (GAGs) exist within the body and are known to have receptors and binding proteins. Structural differences between heparosan and other GAGs attribute to heparosan’ s resistance to cleavage by enzymes and systems designed to clear traditional GAGs from the bloodstream.
As an example, extracellular stability studies in rats (both intramuscular and intraperitoneal) and monkeys (subcutaneous) show stability ofheparosan within the bloodstream (observed out to 120 hours and 168 hours, respectively). No degradation products were seen in either model.
Biodegradable in cells
Heparosan is made and turned-over in the body.
Once heparosan is internalized by cells, most likely through pinocytosis, it is degraded naturally by resident lysosomal glucuronidase and hexosaminidase enzymes, in a fashion similar to heparin or hyaluronan. Heparosan’ s degradation products, GlcNAc and GlcUA, are normal monosaccharides, which are non-toxic and can be recycled by cells.
Rat IV and primate SC models have shown residual oligosaccharides (~1-3 sugars in length) are excreted in the urine and feces; this process mimics the natural glucuronidation elimination pathway used for excretion of many drugs and endogenous substances.
Polymer size control
Caisson’s HEPtune polymers are uniform and monodisperse, produced using a chemoenzymatic synthese that allows for pharmacokinetic customization and tailoring for each drug conjugate.
Caisson discovered and patented bacterial enzymes, which can be utilized for the chemoenzymatic synthesis of heparosan polymers in vitro with (i) a very narrow size distribution, termed ‘quasi-monodisperse’, and (ii) virtually all heparosan chains activated for drug coupling.
The proprietary processes developed by Caisson enable production of high purity, quasi-monodisperse heparosan polymers (<1.05), in a reproducible manner with molecular weights in the range of ~10-300 kDa. Caisson’ s processes have been proven internally, both at small and large scales, and externally at commercial scales by multiple sites, and facilities.
Lack of immunogenicity
Because heparosan is a naturally occurring sugar polymer, as expected, no immunogenic responses have yet been attributed to heparosan.
Molecules that normally exist in the body are regarded as “self ” and therefore are not subjected to attack by antibodies, phagocytes, or the complement system. Because heparosan is a naturally occurring sugar polymer in the human body, the body does not recognize heparosan as foreign. Heparosan has not induced an immunologic response in any heparosan conjugates to date. Drug conjugate repeated dose studies have not shown heparosan specific IgG or IgM.
Certain pathogenic bacteria camouflage themselves with heparosan molecules to hide themselves from host defenses. Caisson uses this to its advantage by using heparosan to decorate certain types of delivery systems, such as nanocarriers, disguising them from the body.
Lack of toxicity
No adverse HEP-specific toxicity events have been identified in any drug formulations to date.
Studies using high and repeated dosing of heparosan and heparosan drug conjugates (intravenous and subcutaneous injections, translating to ~100-fold to 2,000-fold higher levels that its expected use in humans) have shown no adverse effects as measured by blood and urine chemistry and hematology. Histopathology examinations also indicate that neither vacuoles nor inclusion bodies were present in either the kidneys or the choroid plexus of any of the treatment groups. Major organs have normal appearance and weights.
Lack of anticoagulant bioactivity
One function of heparin/heparan sulfate is to inhibit blood clotting. Since heparosan and heparin/heparan sulfate are structurally similar to heparosan, studies were conducted to test if heparosan was an anti-coagulant. Heparosan does not affect clotting of human plasma, even when used at 15,000 times the human heparin dose. The lack of O-sulfation on the heparosan polymer is most likely attributed to the lack of this activity.
Stable polymer and drug conjugate
The heparosan polymer is both heat tolerant and pH stable. No chain breakage has been observed at pH 5-9 at 40C (> ~1 week). The polymer is amenable to freezing and thawing and is easy to ship (either as a lyophilized powder or a frozen solution).
Downstream processing and purification
The anionic nature of the HEPtune polymer can often facilitate purification of HEPtune-drug conjugates. Most biologics will have different charge densities than heparosan. This can allow for easy separation of uncoupled drug from the formed HEPtune-drug conjugate by, for example, strong anion/cation exchange chromatography or reversed phase chromatography.
Heparosan and heparosan drug conjugates are compatible with common chromatographic methods and down stream processing procedures.
Superior biological activity and efficacy of HEP-drug conjugates
Plasma Analysis: Plasma analysis demonstrates that heparosan conjugated FVIIa analogues have similar or better activity than PEG-FVIIa reference molecules.
Proteolytic Activity: Heparosan conjugated FVIIa analogues all are more active than PEG-FVIIa controls in FX activation assay. For some analogues (e.g., 40kDaHEP-FVIIa407c), activity is nearly 2 fold higher than for corresponding 40kDa-PEG analogues.
An in-vivo study, using a breast cancer model in mice, indicated the efficacy of HEP-liposomes containing doxorubicin, was comparable to the efficacy of Doxil-like liposome (PEGylated version).
Single dosing of HEP-G-CSF in normal rats exhibited similar potency for increasing neutrophil count in blood as PEG-G-CSF (Neulasta®).
Potential avoidance of the hand-foot syndrome (HFS)
Doxorubicin contained in PEGylated liposomes has been linked to HFS in 51% of the patients receiving Doxil, due to the increase circulation time. In an in-vivo study using a breast cancer model in mice, it was found that HEP-liposomes containing doxorubicin, were more rapidly transferred from the blood to the tumor than the PEGylated version.
This finding demonstrates the potential of HEP-liposomes to avoid the painful HFS observed with Doxil.