Gadolinium-conjugated TiO2-DNA oligonucleotide nanoconjugates show prolonged intracellular retention period and T1-weighted contrast enhancement in magnetic resonance images.

Nanoconjugates composed of titanium dioxide (TiO2) nanoparticles, DNA oligonucleotides, and a gadolinium (Gd) contrast agent were synthesized for use in magnetic resonance imaging. Transfection of cultured cancer cells with these nanoconjugates showed them to be superior to the free contrast agent of the same formulation with regard to intracellular accumulation, retention, and subcellular localization. Our results have shown that 48 hours after treatment, the concentration of Gd in nanoconjugate-treated cells was 1000-fold higher than in cells treated with contrast agent alone. Consequently, T1-weighted contrast enhancements were observed in cells treated with nanoconjugates but not in cells treated by the contrast agent alone. This type of nanoconjugate with increased retention time, Gd accumulation, and intracellular delivery may find its use in Gd neutron-capture cancer therapy.

RGD targeted poly(L-glutamic acid)-cystamine-(Gd-DO3A) conjugate for detecting angiogenesis biomarker alpha(v) beta3 integrin with MRT, mapping.

Cyclic Arg-Gly-Asp-D-Phe-Lys [c(RGDfK)] targeted poly(L-glutamic acid) (PGA)-(Gd-DO3A) conjugate with a biodegradable cystamine spacer was prepared and evaluated for in vivo detection of an angiogenesis biomarker, alpha(v)beta3 integrin, in neoplastic tissues with T1 mapping, a quantitative magnetic resonance imaging (MRI) technique. The binding activity of the c(RGDfK) containing conjugate was investigated using in vitro vitronectin assay with human prostate carcinoma DU145 cell line and Kaposi's sarcoma SLK cell line. The peptide c(RGDfK) and PGA-cystamine-(Gd-DO3A) conjugate were used as controls. The binding affinity of polymer bound c(RGDfK) was slightly lower than free c(RGDfK) peptide. The RGD targeted conjugate had higher binding affinity to the DU145 cells than the SLK cells, which was consistent to free c(RGDfK). The imaging of alpha(v)beta3 integrin with targeted PGA-cystamine-(Gd-DO3A) was evaluated in nude mice bearing DU145 and SLK xenografts at a dose of 5 micromol-Gd/kg. The targeted conjugate demonstrated higher in vivo binding affinity to the DU145 xenografts than the SLK xenografts, resulting in a significant decrease of T1 values of water protons in the periphery of the DU145 tumors as shown in the MR T1 maps. No significant decrease of T1 values was observed in the SLK tumor with the targeted conjugate and in both tumors with the non-targeted conjugate. The targeted polymeric Gd(III) chelate conjugate with a degradable spacer has the potential to be a new paradigm for safe and effective probes in molecular imaging with quantitative MR T1 mapping.

Noninvasive visualization of in vivo drug delivery of poly(L-glutamic acid) using contrast-enhanced MRI.

Biomedical imaging is valuable for noninvasive investigation of in vivo drug delivery with polymer conjugates. It can provide real-time information on pharmacokinetics, biodistribution, and drug delivery efficiency of the conjugates. Noninvasive visualization of in vivo drug delivery of polymer conjugates with contrast-enhanced magnetic resonance imaging (MRI) was studied with paramagnetically labeled poly(L-glutamic acid) in an animal tumor model. Poly(L-glutamic acid) is a biocompatible and biodegradable drug carrier for diagnostics and therapeutics. Poly(L-glutamic acid)-1,6-hexanediamine--(Gd-DO3A) conjugates with molecular weights of 87, 50, and 28 kDa and narrow molecular weight distributions were prepared and studied in mice bearing MDA-MB-231 human breast cancer xenografts. Contrast-enhanced MRI resulted in real-time and three-dimensional visualization of blood circulation, pharmacokinetics, biodistribution, and tumor accumulation of the conjugates, and the size effect on these pharmaceutics properties. The conjugate of 28 kDa rapidly cleared from the circulation and had a relatively lower tumor accumulation. The conjugates with higher molecular weights exhibited a more prolonged blood circulation and higher tumor accumulation. The difference between the conjugates of 87 and 50 kDa was not significant. Contrast-enhanced MRI is effective for noninvasive real-time visualization of in vivo drug delivery of paramagnetically labeled polymer conjugates.

Biodegradable cystamine spacer facilitates the clearance of Gd(III) chelates in poly(glutamic acid) Gd-DO3A conjugates for contrast-enhanced MR imaging.

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.

Contrast enhanced MRI-guided photodynamic therapy for site-specific cancer treatment.

Photodynamic therapy (PDT) is a minimally invasive and effective approach for cancer treatment. It is potentially useful for treating tumors that are not accessible to surgery, radiation, or destructive ablations, and are resistant to chemotherapy. Efficacious treatment of interstitial tumors with PDT requires efficient delivery of photosensitizers and accurate location of tumor tissues for effective light irradiations. In this study we performed contrast-enhanced (CE) MRI-guided PDT with a bifunctional polymer conjugate containing both a magnetic resonance imaging (MRI) contrast agent and a photosensitizer, poly(L-glutamic acid) (PGA)-(Gd-DO3A)-mesochlorin e(6) (Mce(6)). The efficacy of the bifunctional conjugate in cancer CE-MRI and cancer treatment was evaluated in athymic nude mice bearing MDA-MB-231 human breast carcinoma xenografts, with PGA-(Gd-DO3A) used as a control. The polymer conjugates preferentially accumulated in the solid tumor due to the hyperpermeability of the tumor vasculature, resulting in significant tumor enhancement for accurate tumor detection and localization by MRI. Significant therapeutic response was observed for PDT with the bifunctional conjugate as compared to the control. CE-MRI-guided PDT with the bifunctional conjugate is effective for tumor detection and minimally invasive cancer treatment.

Pharmacokinetics, biodistribution and contrast enhanced MR blood pool imaging of Gd-DTPA cystine copolymers and Gd-DTPA cystine diethyl ester copolymers in a rat model.

PURPOSE: To investigate plasma pharmacokinetics and biodistribution of biodegradable polydisulfide Gd(III) complexes, Gd-DTPA cystine copolymers (GDCP) and Gd-DTPA cystine diethyl ester copolymers (GDCEP) and their efficacy as blood pool MRI contrast agents in comparison with a nondegradable macromolecular agent, Gd-DTPA 1,6-hexanediamine copolymers (GDHC). METHODS: The pharmacokinetics and biodistribution of GDCP and GDCEP with molecular weight of 35 KDa were investigated in Sprague-Dawley rats after intravenous administration at a dose of 0.1 mmol Gd/kg. GDHC with the same molecular weight was used as a control. The Gd content in the plasma and various tissues and organs were determined by the ICP-OES. Plasma pharmacokinetic parameters were calculated by using a two-compartment model. The contrast enhanced blood pool MR imaging of the agents was evaluated in Sprague-Dawley rats on a Siemens Trio 3T MR scanner. RESULTS: The biodegradable macromolecular agents, GDCP and GDCEP, had faster blood pool clearance than the nondegradable GDHC. The long-term Gd(III) tissue retention of the biodegradable polydisulfide agents was substantially lower than the nondegradable macromolecular agent. Both GDCP and GDCEP resulted in significant blood pool enhancement for the first 2 min post-injection and more rapid disappearance of the enhancement over time than GDHC. The negatively charged GDCP had prolonged enhancement duration as compared to GDCEP. The structure and biodegradability of the macromolecular contrast agents significantly affected their pharmacokinetics and blood pool contrast enhancement. CONCLUSION: Both GDCP and GDCEP provided effective contrast enhancement for MR imaging of the blood pool. The accumulation of toxic Gd(III) ions in the body was greatly reduced with GDCP and GDCEP as compared to the nondegradable control.

Gd-DTPA L-cystine bisamide copolymers as novel biodegradable macromolecular contrast agents for MR blood pool imaging.

PURPOSE: The purpose of this study was to synthesize biodegradable Gd-DTPA L-cystine bisamide copolymers (GCAC) as safe and effective, macromolecular contrast agents for magnetic resonance imaging (MRI) and to evaluate their biodegradability and efficacy in MR blood pool imaging in an animal model. METHODS: Three new biodegradable GCAC with different substituents at the cystine bisamide [R = H (GCAC), CH2CH2CH3 (Gd-DTPA L-cystine bispropyl amide copolymers, GCPC), and CH(CH3)2 (Gd-DTPA cystine bisisopropyl copolymers, GCIC)] were prepared by the condensation copolymerization of diethylenetriamine pentaacetic acid (DTPA) dianhydride with cystine bisamide or bisalkyl amides, followed by complexation with gadolinium triacetate. The degradability of the agents was studied in vitro by incubation in 15 microM cysteine and in vivo with Sprague-Dawley rats. The kinetics of in vivo contrast enhancement was investigated in Sprague-Dawley rats on a Siemens Trio 3 T scanner. RESULTS: The apparent molecular weight of the polydisulfide Gd(III) chelates ranged from 22 to 25 kDa. The longitudinal (T1) relaxivities of GCAC, GCPC, and GCIC were 4.37, 5.28, and 5.56 mM(-1) s(-1) at 3 T, respectively. The polymeric ligands and polymeric Gd(III) chelates readily degraded into smaller molecules in incubation with 15 microM cysteine via disulfide-thiol exchange reactions. The in vitro degradation rates of both the polymeric ligands and macromolecular Gd(III) chelates decreased as the steric effect around the disulfide bonds increased. The agents readily degraded in vivo, and the catabolic degradation products were detected in rat urine samples collected after intravenous injection. The agents showed strong contrast enhancement in the blood pool, major organs, and tissues at a dose of 0.1 mmol Gd/kg. The difference of their in vitro degradability did not significantly alter the kinetics of in vivo contrast enhancement of the agents. CONCLUSION: These novel GCAC are promising contrast agents for cardiovascular and tumor MRI, which are later cleaved into low molecular weight Gd(III) chelates and rapidly cleared from the body.

Effect of size and charge on pharmacokinetics and in vivo MRI contrast enhancement of biodegradable polydisulfide Gd(III) complexes.

The purpose of this study is to investigate how the structures of polydisulfide Gd(III) complexes affect their pharmacokinetics and in vivo contrast enhancement as biodegradable macromolecular MRI contrast agents. A negatively charged polydisulfide Gd(III) complex, (Gd-DTPA)-cystine copolymers (GDCP), and a neutral agent, (Gd-DTPA)-cystine diethyl ester copolymers (GDCEP), with different molecular weights were prepared and characterized. The MRI contrast enhancement of the agents was studied in mice. Neutral GDCEP showed more rapid degradation than negatively charged GDCP in the blood plasma. Consequently, GDCP resulted in more significant and prolonged contrast enhancement in the blood pool and liver than GDCEP. The size of GDCEP did not significantly affect its in vivo contrast enhancement due to rapid degradation and clearance from the blood circulation. The increase in the molecular weight of GDCP resulted in prolonged in vivo contrast enhancement in the blood pool. The structural modification of polydisulfide Gd(III) complexes resulted in biodegradable macromolecular MRI contrast agents with different degradability and in vivo contrast enhancement.

Pharmacokinetics and tissue retention of (Gd-DTPA)-cystamine copolymers, a biodegradable macromolecular magnetic resonance imaging contrast agent.

PURPOSE: To investigate the pharmacokinetics, long-term tissue retention of Gd(III) ions, and magnetic resonance imaging (MRI) contrast enhancement of extracellular biodegradable macromolecular Gd(III) complexes, (Gd-DTPA)-cystamine copolymers (GDCC), of different molecular weights. METHODS: The pharmacokinetics of blood clearance and long-term Gd(III) retention of GDCC were investigated in Sprague-Dawley rats. Pharmacokinetic parameters were calculated by using a two-compartment model. The blood pool contrast enhancement of GDCC was evaluated in Sprague-Dawley rats on a Siemens Trio 3T MR scanner. Gd-(DTPA-BMA) was used as a control. RESULTS: The alpha phase half-life of Gd-(DTPA-BMA) and GDCC with molecular weights of 18,000 (GDCC-18) and 60,000 Da (GDCC-60) was 0.48 +/- 0.16 min, 1.08 +/- 0.24 min, and 1.74 +/- 0.57 min, and the beta phase half-life was 21.2 +/- 5.5 min, 26.5 +/- 5.9 min, and 53.7 +/- 15.9 min, respectively. GDCC had minimal long-term Gd tissue retention comparable to that of Gd-(DTPA-BMA). GDCC resulted in more significant contrast enhancement in the blood pool than Gd-(DTPA-BMA). CONCLUSIONS: GDCC provides a prolonged blood pool retention time for effective MRI contrast enhancement and then clears rapidly with minimal accumulation of Gd (III) ions. It is promising for further development as a blood pool MRI contrast agent.