Noninvasive Monitoring of HPMA Copolymer–RGDfK Conjugates by Magnetic Resonance Imaging
To evaluate the tumor targeting potential of N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer–gadolinium(Gd)–RGDfK conjugates by magnetic resonance (MR) T1-mapping.
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 r1 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 αvβ3 targeting was assessed by using non-paramagnetic targetable polymer to block αvβ3 integrins followed by injection of paramagnetic targetable polymers after 2 h.
The polymer conjugates showed relaxivities higher than Gd-DOTA. Endothelial cell binding studies showed that IC50 values for the copolymer with RGDfK binding to αvβ3 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.
These results demonstrate the potential of this conjugate as an effective targetable MR contrast agent for tumor imaging and therapy monitoring.
KEY WORDScontrast agents HPMA copolymers MRI targeted delivery tumor targeting
American type culture collection
Field of view
Fast protein liquid chromatography
High pressure liquid chromatography
Human umbilical vein endothelial cell
Inductively coupled plasma optical emission spectroscopy
Interactive data language
Magnetic resonance imaging
Molecular weight cut off
Phosphate buffered saline
Region of interest
Severe combined immunodeficient
Size exclusion chromatography
Longitudinal relaxation time
This study received financial support from the Department of Defense Breast Cancer Research Program pre-doctoral fellowship to Bahar Zarabi (W81XWH0410341) and a grant from the National Institute of Biomedical Imaging and Bioengineering (R01-EB007171). The authors acknowledge Mrudulla Pullambhatla and Wenlian Zhu at Johns Hopkins University School of Medicine Molecular Imaging Center for their assistance with in vivo MR imaging and facilitated by a grant from the National Cancer Institute (U24 CA92871).
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