Discovery of GBT440, an Orally Bioavailable R-State Stabilizer of Sickle Cell Hemoglobin

Brian Metcalf, Chihyuan Chuang, Kobina Dufu, Mira P Patel, Abel Silva-Garcia, Carl Johnson, Qing Lu, James R Partridge, Larysa Patskovska, Yury Patskovsky, Steven C Almo, Matthew P Jacobson, Lan Hua, Qing Xu, Stephen L Gwaltney 2nd, Calvin Yee, Jason Harris, Bradley P Morgan, Joyce James, Donghong Xu, Athiwat Hutchaleelaha, Kumar Paulvannan, Donna Oksenberg, Zhe Li, Brian Metcalf, Chihyuan Chuang, Kobina Dufu, Mira P Patel, Abel Silva-Garcia, Carl Johnson, Qing Lu, James R Partridge, Larysa Patskovska, Yury Patskovsky, Steven C Almo, Matthew P Jacobson, Lan Hua, Qing Xu, Stephen L Gwaltney 2nd, Calvin Yee, Jason Harris, Bradley P Morgan, Joyce James, Donghong Xu, Athiwat Hutchaleelaha, Kumar Paulvannan, Donna Oksenberg, Zhe Li

Abstract

We report the discovery of a new potent allosteric effector of sickle cell hemoglobin, GBT440 (36), that increases the affinity of hemoglobin for oxygen and consequently inhibits its polymerization when subjected to hypoxic conditions. Unlike earlier allosteric activators that bind covalently to hemoglobin in a 2:1 stoichiometry, 36 binds with a 1:1 stoichiometry. Compound 36 is orally bioavailable and partitions highly and favorably into the red blood cell with a RBC/plasma ratio of ∼150. This partitioning onto the target protein is anticipated to allow therapeutic concentrations to be achieved in the red blood cell at low plasma concentrations. GBT440 (36) is in Phase 3 clinical trials for the treatment of sickle cell disease (NCT03036813).

Keywords: Schiff-base formation; Sickle cell disease; aldehyde; allosteric modulator; oxygen affinity; red blood cell partitioning; sickle cell hemoglobin.

Conflict of interest statement

The authors declare the following competing financial interest(s): B.M., K.D., M.P., A.S., C.J., J.P., Q.X., S.G., C.Y., J.H., A.H., D.O., and Z.L. are employees of Global Blood Therapeutics, which has a commercial interest in hemoglobin modulators; M.P.J. owns GBT stock.

Figures

Figure 1
Figure 1
(a) Literature Hb binding aldehydes. (b) Structures of compounds 4, 5, and 6.
Figure 2
Figure 2
Time-dependent change in hemoglobin-oxygen affinity for 1, 4, and 5. Measurement was taken after a 20 min oxygenation/deoxygenation cycle in the Hemox Analyzer.
Figure 3
Figure 3
Cocrystal structure of 6 (in stick) with CO-ligand HbS.
Figure 4
Figure 4
Zoomed image of the binding pocket for 31. The H-bond with Ser131 from the neighboring α chain appears to be a key interaction for maintaining the R-state of HbS.
Figure 5
Figure 5
Overlay of compounds 6, 31, and 36. All compounds bind with Val1 (green). Compound 6 binds 2:1 per Hb tetramer, and both compounds 31 and 36 bind 1:1 per tetramer. This difference in stoichiometry is further demonstrated with the omit maps included in Figures S1 and S2.
Scheme 1. Synthesis of 36
Scheme 1. Synthesis of 36
Reagents and conditions: (a) MOMCl, DIEPA, DCM, 0 °C to rt 2 h, 90%; (b) nBuLi, DMF, THF, −78 to 0 °C, 94%; (c) 12 N HCl, THF, rt, 1.5 h, 81%; (d) Pd(dppf)Cl2, NaHCO3, H2O/dioxane, 100 °C, 12 h, 40%; (e) SOCl2, DCM, rt, 100%; (f) Na2CO3, DMF, 65 °C, 1.5 h, 81%; (g) 12 N HCl, THF, rt, 3 h, 96%.

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