title: Biodegradable cystamine spacer facilitates the clearance of Gd(III) chelates in poly(glutamic acid) Gd-DO3A conjugates for contrast-enhanced MR imaging.
abstract: Poly(L-glutamic acid) (PGA)-cystamine-[gadolinium (Gd)-DO3A] was prepared in high yield with a high Gd-DO3A conjugation efficiency. Approximately 55% of the carboxylic groups in PGA were loaded with Gd-DO3A via cystamine as the spacer. Cystamine can be readily cleaved by endogenous thiols to release the Gd(III) chelates from the conjugate facilitating Gd(III) excretion after the magnetic resonance imaging (MRI). The contrast-enhanced MRI with PGA-cystamine-(Gd-DO3A) was investigated in mice bearing MDA-MB-231 breast carcinoma xenografts. PGA-1,6-hexanediamine-(Gd-DO3A), a paramagnetic polymer conjugate of a nondegradable spacer, was used as a control. Both conjugates resulted in similar contrast enhancement in the heart, vasculature, liver and kidneys in the first hour post injection. More substantial signal intensity reduction was observed for PGA-cystamine-(Gd-DO3A) in these organs than PGA-1,6-hexanediamine-(Gd-DO3A) due to release of the Gd chelates from PGA-cystamine-(Gd-DO3A) after the cleavage of the disulfide spacer by the endogenous thiols. Both conjugates resulted in similar tumor enhancement with approximately 70% increased signal intensity in the tumor periphery and 10-40% increased signal intensity in tumor interstitium. No cross-reaction was observed between PGA-cystamine-(Gd-DO3A) and human serum albumin, a plasma protein containing a cysteine residue. PGA-cystamine-(Gd-DO3A) resulted in significantly lower Gd(III) tissue retention than PGA-1,6-hexanediamine-(Gd-DO3A) 10 days after the injection in the mice (P<.05). The conjugation of Gd(III) chelates to biomedical copolymers via the degradable disulfide spacer resulted in significant contrast enhancement in the blood pool and tumor tissue but minimal long-term Gd(III) tissue retention.
authors.affiliation: Department of Pharmaceutics and Pharmaceutical Chemistry, University of Utah, Salt Lake City, UT 84108, USA.
authors.forename: Tianyi
authors.initials: T
authors.lastname: Ke
authors.forename: Yi
authors.initials: Y
authors.lastname: Feng
authors.forename: Junyu
authors.initials: J
authors.lastname: Guo
authors.forename: Dennis L
authors.initials: DL
authors.lastname: Parker
authors.forename: Zheng-Rong
authors.initials: ZR
authors.lastname: Lu
mesh_terms: D020341:Absorbable Implants; D000818:Animals; D003538:Cystamine / Q000737:chemistry* / Q000493:pharmacokinetics; D004220:Disulfides / Q000737:chemistry / Q000378:metabolism; D005260:Female; D006571:Heterocyclic Compounds / Q000138:chemical synthesis / Q000737:chemistry / Q000493:pharmacokinetics*; D008279:Magnetic Resonance Imaging; D008325:Mammary Neoplasms, Experimental / Q000378:metabolism; D051379:Mice; D008819:Mice, Nude; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000737:chemistry* / Q000493:pharmacokinetics; D011099:Polyglutamic Acid / Q000138:chemical synthesis / Q000737:chemistry* / Q000493:pharmacokinetics; D011897:Random Allocation; D013329:Structure-Activity Relationship
chemical_list: D004220:Disulfides; D006571:Heterocyclic Compounds; D009942:Organometallic Compounds; C090600:gadobutrol; D011099:Polyglutamic Acid; C050823:gadolinium 1,4,7,10-tetraazacyclododecane-N,N',N'',N'''-tetraacetate; D003538:Cystamine