Novel Protein Design Offers Hope for Less Frequent Anemia Treatment

www.nature.com reported that a recent study has unveiled a new approach to treating anemia, focusing on extending the effective life of erythropoietin (EPO) products in the body. The goal of this research is to allow for less frequent drug administration, which could improve both the effectiveness of treatment and patient compliance.

The study involved genetically linking EPO, a product that stimulates the creation of red blood cells in patients with anemia, to an engineered variant of albumin called QMP. Albumin is a protein known for its long presence in the bloodstream. This new fusion protein, named EPO-QMP, demonstrated favorable binding to the neonatal Fc receptor (FcRn), a key regulator of albumin's plasma half-life.

Upon intravenous administration, EPO-QMP showed a 5.2-fold prolonged plasma half-life in human FcRn expressing mice when compared to EPO fused to wild-type albumin. A similar extended half-life was observed following subcutaneous administration. Notably, the fusion protein's ability to bind to the EPO receptor was equal to that of darbepoetin alfa, a commercially available EPO product. Mice receiving EPO-QMP after intravenous administration experienced a slower decline in EPO levels and a prolonged increase in red blood cells compared to those given darbepoetin alfa.

Further demonstrating its potential, intranasal administration of EPO-QMP resulted in circulating amounts that were five times higher than darbepoetin alfa, along with a sustained increase in red blood cells. These findings suggest that long-acting EPO-QMP could be an attractive design for exploring both traditional invasive and novel non-invasive delivery methods for patients suffering from anemia.

Currently, EPO products are widely used to boost red blood cell production in patients with anemia caused by conditions such as chronic kidney disease, cancer chemotherapy, or human immunodeficiency virus infection. These products are typically delivered intravenously or subcutaneously, often several times a week, because of their relatively short plasma half-life, which can range from 4 to 11 hours after intravenous administration. Some studies also indicate EPO may offer benefits in neurological conditions like neurodegenerative diseases, schizophrenia, and stroke, making it relevant for both short-term and lifelong treatments.

To address the short half-life of existing EPO products, various engineering strategies have been explored. For instance, darbepoetin alfa was designed with amino acid substitutions to introduce additional N-glycan sites, extending its plasma half-life in humans to 26.3 hours after intravenous administration. Another example, methoxy polyethylene glycol (PEG)-epoetin beta, uses a chemically conjugated PEG moiety to achieve a plasma half-life of 134 hours.

An alternative strategy, which this study pursued, involves fusing EPO to a protein carrier like human albumin or immunoglobulin G (IgG). Both albumin and IgG have an unusually long plasma half-life, about three weeks in humans, due to their interaction with FcRn. This receptor rescues these proteins from degradation by recycling them within cells. FcRn also facilitates the transport of these proteins across mucosal barriers, such as those in the lungs, after intranasal delivery. Previous research has shown albumin is transcytosed more efficiently than IgG after intranasal delivery in human FcRn transgenic mice, making FcRn an appealing target for delivering albumin-fused therapeutic proteins across mucosal surfaces.

Prior attempts to fuse EPO with other proteins included genetic fusion to the N-terminal end of human IgG1 fragment crystallizable (Fc), resulting in an EPO-Fc fusion with a plasma half-life of 25 hours in cynomolgus monkeys, compared to 6.5 hours for epoetin alfa. An aerosolized version also showed more EPO in the serum after lung delivery, and healthy adults receiving pulmonary EPO-Fc showed increased red blood cells. However, fusing EPO to wild-type human albumin in rats yielded a plasma half-life similar to darbepoetin alfa, which was not unexpected given that human albumin binds poorly to mouse and rat FcRn. This meant the full potential of human albumin as an EPO carrier had not been thoroughly explored until this current study.

The present research designed recombinant EPO-albumin fusions by attaching human EPO to the N-terminal end of human albumin variants. This included wild-type albumin (EPO-WT), the engineered QMP variant (EPO-QMP) which was specifically improved for 180-fold stronger pH-dependent binding to human FcRn, and a variant designed for reduced binding (EPO-AQ). These findings demonstrate that an albumin variant engineered for improved FcRn binding can lead to a significantly extended plasma half-life and enhanced transport across mucosal barriers, offering a promising new path for anemia treatment.