Regioselective covalent modification of hemoglobin in search of antisickling agents.
Although the molecular defect in sickle hemoglobin that produces sickle cell disease has been known for decades, there is still no effective drug treatment that acts on hemoglobin itself. In this work, a series of diversely substituted isothiocyanates (R-NCS) were examined for their regioselective reaction with hemoglobin in an attempt to alter the solubility properties of sickle hemoglobin. Electrospray mass spectrometry, molecular modeling, X-ray crystallography, and conventional protein chemistry were used to study this regioselectivity and the resulting increase in solubility of the modified hemoglobin. Depending on the attached R-group, the isothiocyanates were found to react either with the Cysbeta93 or the N-terminal amine of the alpha-chain. One of the most effective compounds in the series, 2-(N,N-dimethylamino)ethyl isothiocyanate, selectively reacts with the thiol of Cysbeta93 which, in conjunction with the cationic group, was seen to perturb the local hemoglobin structure. This modified HbS shows an approximately 30% increase in solubility for the fully deoxygenated state, along with a significant increase in oxygen affinity. This compound and a related analogue appear to readily traverse the erythrocyte membrane. A discussion of the relation of these structural changes to inhibition of gelation is presented. The dual activities of increasing HbS oxygen affinity and directly inhibiting deoxy HbS polymerization, in conjunction with facile membrane traversal, suggest that these cationic isothiocyanates show substantial promise as lead compounds for development of therapeutic agents for sickle cell disease.
Park
Soobong
S
Department of Medicinal Chemistry and Pharmacognosy and Center for Pharmaceutical Biotechnology, College of Pharmacy, University of Illinois at Chicago, 833 S. Wood Street, Chicago, Illinois 60612, USA.
Hayes
Brittany L
BL
Marankan
Fatima
F
Mulhearn
Debbie C
DC
Wanna
Linda
L
Mesecar
Andrew D
AD
Santarsiero
Bernard D
BD
Johnson
Michael E
ME
Venton
Duane L
DL
D000755:Anemia, Sickle Cell / Q000188:drug therapy; D002463:Cell Membrane Permeability; D018360:Crystallography, X-Ray; D004910:Erythrocyte Membrane / Q000378:metabolism; D006441:Hemoglobin A / Q000737:chemistry; D006451:Hemoglobin, Sickle / Q000737:chemistry; D006454:Hemoglobins / Q000737:chemistry*; D006801:Humans; D066298:In Vitro Techniques; D017879:Isothiocyanates / Q000138:chemical synthesis* / Q000737:chemistry / Q000493:pharmacokinetics; D008958:Models, Molecular; D011108:Polymers; D012995:Solubility; D021241:Spectrometry, Mass, Electrospray Ionization; D013056:Spectrophotometry, Ultraviolet; D055672:Static Electricity; D013237:Stereoisomerism; D013329:Structure-Activity Relationship
D006451:Hemoglobin, Sickle; D006454:Hemoglobins; D017879:Isothiocyanates; D011108:Polymers; D006441:Hemoglobin A