Caisson’s patented HEPtune system has numerous inherent advantages over competing linker and half-life extension technologies:
- Ease of Manufacturing and Conjugation
- Favorable Safety Profile
- Lack of Immunogenicity
- Superior Conjugate Biological Activity and Efficacy
- Efficient Downstream Processing and Purification
- Solubility and Stability
- Precisely Controlled Molecular Weights
In the bloodstream, heparosan is stable and unchanged thus yielding predictable half-life. If heparosan is internalized by the cell, then it is transported to the lysosome and degraded by resident glucuronidase and hexosaminidase enzymes. Studies have shown both lysosomal extracts and human exoglycosidases enzymatically cut heparosan. Degradation of heparosan in macrophages is also much faster than PEG. Primate studies have also demonstrated degradation of high molecular weight heparosan resulting in excretion of very small saccharides (1-4 sugars in length).
Overall, this behavior allows virtually any size heparosan polymer to be utilized in drug delivery, unlike PEG and other competing technologies that have some size limitations for in vivo use.
Another key advantage for modifying therapeutics with heparosan is that its degradation products, N-acetylglucosamine and glucuronic acid, are pre-existing monosaccharides in the human body and can be recycled by cells. On the other hand, PEG metabolites are known to be cytotoxic.
Ease of Manufacturing & Conjugation
Using patented processes, Caisson leverages the heparosan synthase, PmHS1, for the production of heparosan polymers. This enzyme serves as a catalyst for the chemoenzymatic synthesis of heparosan, resulting in pre-determined uniform molecular weight polymers. These patented methods are also amenable to defined and reproducible site-specific chemical activation of heparosan to facilitate coupling of drugs and tuning of therapeutic dosing profiles and potency.
Favorable Safety Profile
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 than its expected use in humans) have shown no adverse effects as measured by blood and urine chemistry, hematology or histopathology.
Lack of Immunogenicity
No immunogenic responses have been attributed to heparosan to date.
Because heparosan is a naturally occurring sugar polymer in the human body, the body does not recognize heparosan as foreign. As a result, molecules such as heparosan are regarded as “self ” and therefore are not subjected to attack by the body’s antibodies, phagocytes, or complement system. Repeated dose studies with drug conjugate have not shown a heparosan-specific IgG or IgM response.
It is known that certain pathogenic bacteria camouflage themselves with heparosan molecules in order to hide from host defenses. Caisson uses this ‘stealth’ strategy to its advantage by using heparosan to decorate certain types of delivery systems, such as nanocarriers, in order to disguise them from the body.
Solubility and Stability
The heparosan polymer is both heat tolerant and pH stable. No chain breakage has been observed at pH 5-9 at 40°C for extended periods. The polymer is amenable to freezing and thawing and is also easy to ship (either as a lyophilized powder or a frozen solution).
Downstream Processing and Purification
The anionic nature of HEPtune polymers facilitate easy purification of HEPtune-drug conjugates. Most biologics have different charge densities than heparosan, which can allow for easy separation of an uncoupled drug from the formed HEPtune-drug conjugate. For example, strong anion/cation exchange chromatography or reversed phase chromatography may facilitate separation.
Heparosan and heparosan-drug conjugates are compatible with common chromatographic methods and downstream processing procedures.
Superior biological activity and efficacy of HEP-drug conjugates
Plasma analysis demonstrates that heparosan-conjugated FVIIa analogues have similar or better activity than PEG-FVIIa reference molecules.
Proteolytic activity of heparosan-conjugated FVIIa analogues were demonstrated to be more active than PEG-FVIIa controls in FX activation assays. For some analogs (e.g., 40kDaHEP-FVIIa407c), activity is nearly 2-fold higher than for corresponding 40kDa-PEG analogues.
In vivo studies, using a breast cancer model in mice, indicated the efficacy of heparosan-coated liposomes containing doxorubicin, were comparable to the efficacy of polyethylene glycol-coated liposomes containing doxorubicin.
Single dosing of heparosan-G-CSF (granulocyte-colony stimulating factor) in normal rats exhibited similar potency for increasing neutrophil count in blood as PEG-G-CSF.