Noninvasive monitoring of HPMA copolymer-RGDfK conjugates by magnetic resonance imaging.
OBJECTIVE
To evaluate the tumor targeting potential of N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer-gadolinium(Gd)-RGDfK conjugates by magnetic resonance (MR) T1-mapping.


METHODS
HPMA copolymers with and without RGDfK were synthesized to incorporate side chains for Gd chelation. The conjugates were characterized by their side-chain contents and r(1) relaxivity. In vitro integrin-binding affinities of polymeric conjugates were assessed via competitive cell binding assays on HUVEC endothelial cells and MDA-MB-231 breast cancer cells. In vivo MR imaging was performed on MDA-MB-231 tumor-bearing SCID mice at different time points using non-targetable and targetable polymers. The specificity of alphavbeta3 targeting was assessed by using non-paramagnetic targetable polymer to block alphavbeta3 integrins followed by injection of paramagnetic targetable polymers after 2 h.


RESULTS
The polymer conjugates showed relaxivities higher than Gd-DOTA. Endothelial cell binding studies showed that IC(50) values for the copolymer with RGDfK binding to alphavbeta3 integrin-positive HUVEC and MDA-MB-231 cells were similar to that of free peptide. Significantly lower T1 values were observed at the tumor site after 2 h using targetable conjugate (p < 0.012). In vivo blocking study showed significantly higher T1 values (p < 0.045) compared to targetable conjugate.


CONCLUSIONS
These results demonstrate the potential of this conjugate as an effective targetable MR contrast agent for tumor imaging and therapy monitoring.
Zarabi
Bahar
B
Department of Pharmaceutical Sciences, University of Maryland, Baltimore, Baltimore, Maryland, USA.
Borgman
Mark P
MP
Zhuo
Jiachen
J
Gullapalli
Rao
R
Ghandehari
Hamidreza
H
D000818:Animals; D001943:Breast Neoplasms / Q000175:diagnosis*; D045744:Cell Line, Tumor; D002478:Cells, Cultured; D003287:Contrast Media / Q000008:administration & dosage / Q000032:analysis* / Q000138:chemical synthesis / Q000378:metabolism*; D005260:Female; D006492:Hempa / Q000008:administration & dosage / Q000032:analysis* / Q000737:chemistry / Q000378:metabolism*; D006801:Humans; D016023:Integrins / Q000378:metabolism; D008279:Magnetic Resonance Imaging / Q000379:methods*; D051379:Mice; D016513:Mice, SCID; D009368:Neoplasm Transplantation; D009942:Organometallic Compounds / Q000008:administration & dosage / Q000032:analysis* / Q000737:chemistry / Q000378:metabolism*; D010456:Peptides, Cyclic / Q000008:administration & dosage / Q000032:analysis* / Q000737:chemistry / Q000378:metabolism*; D011485:Protein Binding; D014018:Tissue Distribution
D003287:Contrast Media; D016023:Integrins; D009942:Organometallic Compounds; D010456:Peptides, Cyclic; D006492:Hempa