No abstract

This communication demonstrates that yeast cell wall particles (YCWPs) are a promising class of nature-inspired biocompatible microcarriers for the delivery of amphipathic/lipophilic imaging reporters. When a paramagnetic MRI agent is loaded, the longitudinal relaxivity per particle at 0.5 T is the highest ever reported for Gd-based systems.

The work aimed at developing a novel MRI-based theranostic protocol for improving the anticancer efficacy of a Doxil-like liposomal formulation. The goal was achieved stimulating the intratumor release of the drug from the nanocarrier and favoring its diffusion in the lesion by the sequential application of low-intensity pulsed ultrasound. The protocol was tested on mice bearing a syngeneic breast cancer model. The combination of acoustic waves with different characteristics allowed for: i) the release of the drug and the co-encapsulated MRI agent (Gadoteridol) from the liposomes in the vessels of the tumor region, and ii) the extravasation of the released material, as well as intact liposomes, in the tumor stroma. The MR-T1 contrast enhancement measured in the tumor reported on the delivery and US-triggered release of Doxorubicin. The developed protocol resulted in a marked increase in the intratumor drug concentration that, in turn, led to the complete regression of the lesion. The protocol has a good clinical translatability because all the components of the theranostic agent (Doxorubicin, liposomes, Gadoteridol) are approved for human use. MRIJbased% procedure% for% the% in$ vivo% visualization% of% the% release% of% an% anticancer% drug% (Doxorubicin)% from% liposomes% stimulated% by% the% local% application% of% pulsed% lowJintensity% planar% ultrasound.% First,% we% investigated% the% in% vitro% release% properties% of% several% nanovesicular% carriers% under% US% application% and% demonstrated% that% the% release% was% i)% caused% by% the% mechanical% characteristics% of% the% US% stimulus,% ii)% very% sensitive% to% the% composition% of% the% particle% membrane,% and% iii)% MRI% detectable% (Giustetto% et$ al.,% J.$ Med.$ Imaging$Health$Inf.%3,%356J366%(2013)).%Next,%the%MRI%potential%of%the%method%was%demonstrated%in$vivo%on%a% mouse%model%of%melanoma% (Rizzitelli%et$al.,%Nanomedicine%10,%901J904%(2014)).%More%recently,%the%theranostic% protocol% was% implemented% by% the% encapsulation% of% Doxorubicin,% and% both% the% MRI% performance% and% the% therapeutic% benefits% associated% with% the% USJtriggered% intratumor% release% of% the% drug% on% a% mouse% model% of% breast%cancer%were%reported%(Rizzitelli%et$al.,%J.$Control.$Release%202,%21J30% (2015)).% In%the%submitted%paper,%we%further%improved%the%performance%of%the%method%through%the%sequential% application%of%two%different%low%intensity%US%stimuli,%one%inducing%a%permeabilization%of%the%tumor%vascular% endothelium,%and%the%other%stimulating%the%release%of%the%drug%from%the%nanocarrier.%The%synergy%between% the%two%short%stimuli%(only%3%minutes%in%total)%allowed%for%a%complete%tumor%regression%in%a%mouse%model%of% breast%cancer.%Furthermore,%also%the%MRI%detectability%of%the%process%was%improved.%% Though% several% examples% dealing% with% the% use% of% US% (but% mostly% focused% with% highJintensity)% for% triggering% drug% release% can% be% found% in% literature,% this% is,% to% our% knowledge,% the% case% with% the% highest% therap...

The preparation of ultrasmall and rigid platforms (USRPs) that are covalently coupled to macrocycle-based, calcium-responsive/smart contrast agents (SCAs), and the initial in vitro and in vivo validation of the resulting nanosized probes (SCA-USRPs) by means of magnetic resonance imaging (MRI) is reported. The synthetic procedure is robust, allowing preparation of the SCA-USRPs on a multigram scale. The resulting platforms display the desired MRI activity—i.e., longitudinal relaxivity increases almost twice at 7 T magnetic field strength upon saturation with Ca(2+). Cell viability is probed with the MTT assay using HEK-293 cells, which show good tolerance for lower contrast agent concentrations over longer periods of time. On intravenous administration of SCA-USRPs in living mice, MRI studies indicate their rapid accumulation in the renal pelvis and parenchyma. Importantly, the MRI signal increases in both kidney compartments when CaCl2 is also administrated. Laser-induced breakdown spectroscopy experiments confirm accumulation of SCA-USRPs in the renal cortex. To the best of our knowledge, these are the first studies which demonstrate calcium-sensitive MRI signal changes in vivo. Continuing contrast agent and MRI protocol optimizations should lead to wider application of these responsive probes and development of superior functional methods for monitoring calcium-dependent physiological and pathological processes in a dynamic manner.

Two novel Gd-based contrast agents (CAs) for the molecular imaging of matrix metalloproteinases (MMPs) were synthetized and characterized in vitro and in vivo. These probes were based on the PLG*LWAR peptide sequence, known to be hydrolyzed between Gly and Leu by a broad panel of MMPs. A Gd-DOTA chelate was conjugated to the N-terminal position through an amide bond, either directly to proline (compd Gd-K11) or through a hydrophilic spacer (compd Gd-K11N). Both CA were made strongly amphiphilic by conjugating an alkyl chain at the C-terminus of the peptide sequence. Gd-K11 and Gd-K11N have a good affinity for β-cyclodextrins (K(D) 310 and 670 µ m respectively) and for serum albumin (K(D) 350 and 90 µ m respectively), and can be efficiently cleaved in vitro at the expected site by MMP-2 and MMP-12. Upon MMP-dependent cleavage, the CAs lose the C-terminal tetrapeptide and the alkyl chain, thus undergoing to an amphiphilic-to-hydrophilic transformation that is expected to alter tissue pharmacokinetics. To prove this, Gd-K11 was systemically administered to mice bearing a subcutaneous B16.F10 melanoma, either pre-treated or not with the broad spectrum MMP inhibitor GM6001 (Ilomastat). The washout of the Gd-contrast enhancement in MR images was significantly faster for untreated subjects (displaying MMP activity) with respect to treated ones (MMP activity inhibited). The washout kinetics of Gd-contrast enhancement from the tumor microenvironment could be then interpreted in terms of the local activity of MMPs.