An efficient MRI agent targeting extracellular markers in prostate adenocarcinoma

Abstract

Purpose Prostate cancer (PCa) is the most widespread tumor affecting males in Western countries. We propose a novel MRI molecular tetrameric probe based on the heptadentate gadolinium (Gd)‐AAZTA (6‐amino‐6‐methylperhydro‐1,4‐diazepinetetraacetic acid) that is able to in vivo detect PCa through the recognition of the fibrin–fibronectin (FB–FN) complex. Methods The peptide CREKA (Cys‐Arg‐Glu‐Lys‐Ala), targeting the FB–FN complex in the reactive stroma of the tumor, was synthesized by solid phase peptide synthesis (SPPS) and conjugated to the tetramer dL‐(Gd‐AAZTA)4. The resulting probe was characterized by 1H relaxometry, tested in vitro on FB clots and in vivo on an orthotopic mouse model of PCa. Results CREKA‐dL‐(Gd‐AAZTA)4 showed a remarkable relaxivity of 18.2 mMGd-1s−1 (0.47 T, 25°C) because of the presence of 2 water molecules (q = 2) in the inner coordination sphere of each Gd3+ ion, whose rotational motion (τR) is lengthened as the result of the relatively high molecular weight. The probe displayed a detectable affinity for plasma‐derived FB clots. On intravenous injection of the probe in an orthotopic mouse model of PCa, a significant increase in the prostate T1 contrast (~40%) was observed. The MRI signal appears statistically higher either with respect to the one observed for the control probes and to the one detected when CREKA‐dL‐(Gd‐AAZTA)4 was administered to healthy animals. Conclusions This study demonstrated the ability of the CREKA‐dL‐(Gd‐AAZTA)4 probe to specifically localize in prostate tumor after injection. The high relaxivity of the probe allows the reduction of the injected dose to 20 µmolGd/kg, yielding a good in vivo contrast enhancement in the region of prostate tumor.

Extracellular Matrix Targeted MRI Probes

“…[58] Finally, the high relaxivity CREKA-dL-(Gd-AAZTA) 4 tetrameric probe based on the AAZTA chelator (6-amino-6-methylperhydro-1,4-diazepinetetraacetic acid) [59] enabled detection of prostate cancer with a reduced dose of injected gadolinium. [60] The Fibronectin Extra-Domain B (EDB) based-probe (MT218) showed tumour enhancement that lasted for 30 minutes postinjection in a breast cancer model and in small pancreatic tumours allowing for accurate tumour delineation (even at low 0.02 mmol Gd/kg dose). [61,62] Importantly, detection of pancreatic ductal adenocarcinoma metastasis was possible at low doses.…”

“…The shorter pentapeptide tetrameric‐agent based on DOTA‐monoamide like chelate, CREKA‐dL‐(Gd‐DOTA) 4 , revealed strong enhancement in prostate tumours within 5 minutes post‐injection [57] and its tripod analogue enabled robust contrast enhancement of metastatic breast tumours and detection of micro‐metastases (<0.5 mm), extending the detection limit of the current clinical imaging modalities despite having a slightly lower r 1 relaxivity (Figure 3). [58] Finally, the high relaxivity CREKA‐dL‐(Gd‐AAZTA) 4 tetrameric probe based on the AAZTA chelator (6‐amino‐6‐methylperhydro‐1,4‐diazepinetetraacetic acid) [59] enabled detection of prostate cancer with a reduced dose of injected gadolinium [60] …”

Solid phase synthesis in the development of magnetic resonance imaging probes

“…(a) A binary targeting CA consisting of both RGD and NGR binding sequences; 80 (b) a multimeric DOTA-based CA with a CREKA peptide for prostate cancer imaging; 93 (c) a prostate cancer targeted multimeric AAZTA-based CA. 99 for coupling with an AAZTA derivative (Fig. 4c).…”

“…97 In a follow-up study, the maleimide derivative was synthesised and combined with the CREKA peptide for prostate cancer detection in a similar method to that described previously. 93,99 The authors hypothesised that an improvement in contrast could be achieved by using their AAZTA-derived tetramer due to the favourable relaxometric properties of AAZTA (compared to DOTA monoamide). High molecular relaxivity was observed for the targeted probe (18.2 mM −1 s −1 per Gd 3+ or 72.8 mM −1 s −1 per molecule, 0.5 T, 25°C), allowing for higher contrast to be achieved in vivo with a lower dose of the compound relative to current clinically approved CAs.…”

Derivatives of GdAAZTA Conjugated to Amino Acids: A Multinuclear and Multifrequency NMR Study

“…In addition, GdAAZTA has also been conjugated with a wide range of targeting vectors capable of specific interactions with biomolecules other than HSA, with the aim of developing contrast agents for molecular imaging applications. Such biochemically targeted probes include GdAAZTA coupled with lipids targeting the liver fatty acid binding protein (L-FABP), with peptidomimetics interacting with integrin α ν β 3 expressed in cancers cells, and with fibrin targeting peptides, , as pathological biomarkers.…”