Toward a better insulin analog: improving product yield enables scientific study of potential new diabetes therapy.
Daily injections of the pancreatic peptide-hormone insulin are essential to life for many people living with type 1 or advanced type 2 diabetes. While therapeutic insulin was originally available only by purifying it from animal sources, in 1982 a recombinant or biosynthetic “human” form became available as the first recombinant protein licensed by the FDA for therapeutic use.
Produced by Genentech and marketed under the brand name Humalog, that first recombinant human insulin product was biomanufactured by introducing the relevant human gene into the bacteria E. coli, growing industrial-sized cultures in bioreactors, and purifying the resulting peptide from the resulting bacterial soup. Other approaches to producing biosynthetic human insulin have included using yeast or other unicellular organisms as background hosts. Because the insulin peptide is readily broken down and rendered inactive in the human digestive tract, it cannot be consumed orally and therefore must be administered by subcutaneous injection.
For reasons that are still to be understood, but that likely involve complex issues of supply, demand, pharmacoeconomics, policy, and regulation, the price for recombinant human insulin has risen sharply since 2003,1,2 to the point that it is now threatening the health, lives, and financial wellbeing of patients who are uninsured, underinsured, or whose resources cannot support the necessary level of medical spending. More cost-effective insulin-therapy options are urgently needed.
Research into a promising novel, orally available insulin analog has been stymied by low expression yields
Researchers at the University of Southern California (USC) School of Pharmacy, led by investigator Wei-Chiang Shen PhD, had previously designed and expressed a proposed insulin analog comprised of the pro-insulin peptide fused to the human protein transferrin (ProINS-Tf), in the human cell line HEK293.3 Their subsequent research found that ProINS-Tf can act as an long-acting insulin analog with liver-specific activity in a streptozotocin-induced mouse model of type 1 diabetes.3-5 Because transferrin fusion proteins have previously been shown to improve oral bioavailability of other protein-based drugs, the investigators also speculated that the presence of the transferrin moiety could potentially protect the pro-insulin peptide from degradation in the gut and act as a carrier to deliver the pro-drug to the liver. There, it would be converted to its active form, thus hypothetically creating an orally bioavailable form of recombinant insulin. However, low expression yields in HEK293 presented an obstacle to testing this intriguing hypothesis.
ExpressTec improves yields of biologically active ProINS-Tf, enabling bioavailability studies and future development.
Recently, scientists from Dr. Shen’s group, West Coast University, Ventria Bioscience worked together to adapt their drug candidate for high-yield, cost-effective expression in ExpressTec rice. In a study published last year in the International Journal of Molecular Sciences, they showed that in vivo, ExpressTec-ProINS-Tf was a more potent agent for blood-glucose control than ProINS-Tf isolated from HEK293 cells.6 Furthermore, they found that oral administration of the ExpressTec-ProINS-Tf in the mouse model of type 1 diabetes was nearly as effective for prolonged control of blood glucose as administration by injection. The authors concluded that the potency and cost-effective expression of ExpressTec-ProINS-Tf makes a promising potential candidate for further study as an orally bioavailable, long-acting insulin analog.
- Hua X, Carvalho N, Tew M, Huang ES, Herman WH, Clarke P. Expenditures and Prices of Antihyperglycemic Medications in the United States: 2002-2013. JAMA. 2016;315(13):1400-1402.
- Sable-Smith B. ‘We’re Fighting for Our Lives’: Patients Protest Sky-High Insulin Prices. NPR website. Published: 2018. Accessed: February 10, 2019
- Wang Y, Chen YS, Zaro JL, Shen WC. Receptor-mediated activation of a proinsulin-transferrin fusion protein in hepatoma cells. J Control Release. 2011;155(3):386-392.
- Shao J, Zaro JL, Shen WC. Proinsulin-Transferrin Fusion Protein Exhibits a Prolonged and Selective Effect on the Control of Hepatic Glucose Production in an Experimental Model of Type 1 Diabetes. Mol Pharm. 2016;13(8):2641-2646.
- Wang Y, Shao J, Zaro JL, Shen WC. Proinsulin-transferrin fusion protein as a novel long-acting insulin analog for the inhibition of hepatic glucose production. Diabetes. 2014;63(5):1779-1788.
- Chen YS, Zaro JL, Zhang D, Huang N, Simon A, Shen WC. Characterization and Oral Delivery of Proinsulin-Transferrin Fusion Protein Expressed Using ExpressTec. Int J Mol Sci. 2018;19(2)