Ultrasmall superparamagnetic iron oxide nanoparticles (uSPIOs) are attractive platforms for the development of smart contrast agents for magnetic resonance imaging (MRI). Oleic acid-capped uSPIOs are commercially available yet hydrophobic, hindering in vivo applications. A hydrophilic ligand with high affinity toward uSPIO surfaces can render uSPIOs water-soluble, biocompatible, and highly stable under physiological conditions. A small overall hydrodynamic diameter ensures optimal pharmacokinetics, tumor delivery profiles, and, of particular interest, enhanced T 1 MR contrasts. In this study, for the first time, we synthesized a ligand that not only fulfills the as-proposed properties but also provides multiple reactive groups for further modifications. The synthesis delivers a facile approach using commercially available reactants, with resultant uSPIO–ligand constructs assembled through a single-step ligand exchange process. Structural and molecular size analyses confirmed size uniformity and small hydrodynamic diameter of the constructs. On average, 43 reactive amine groups were present per uSPIO nanoparticle. Its r 1 relaxivity has been tested on a 7 Tesla MR instrument and is comparable to that of the clinically available T 1 gadolinium-based contrast agent GBCA (1 vs 3 mM–1 s–1, respectively). A significant decrease in tumor T 1 (15%) within 1 h of injection and complete signal recovery after 2 h were detected with a dose of 7 μg Fe/g mouse. The agent also has high r 2 relaxivity and can be used for T 2 contrast-enhanced MRI. Taken together, good relaxation and delivery properties and the presence of multiple surface reactive groups can facilitate its application as a universal MRI-compatible nanocarrier platform.

Pretargeted drug delivery has been explored for decades as a promising approach in cancer therapy. An image-guided pretargeting strategy significantly enhances the intrinsic advantages of this approach since imaging the pretargeting step can be used for diagnostic purposes, while imaging of the drug delivery step can be utilized to evaluate drug distribution and assess therapeutic response. A trastuzumab (Tz)-based HER2 pretargeting component (Tz-TCO-[89Zr-DFO]) was developed by conjugating with trans-cyclooctene (TCO) bioorthogonal click chemistry functional groups and deferoxamine (DFO) to enable radiolabeling with a 89Zr PET tracer. The drug delivery component (HSA-DM1-Tt-[99mTc-HyNic]) was developed by conjugating human serum albumin (HSA) with mertansine (DM1), tetrazine (Tt) functional groups, and a HyNic chelator and radiolabeling with 99mTc. For ex vivo biodistribution studies, pretargeting and delivery components (without drug) were administered subsequently to mice bearing human HER2­(+) breast cancer xenografts, and a high tumor uptake of Tz-TCO-[89Zr-DFO] (26.4% ID/g) and HSA-Tt-[99mTc-HyNic] (4.6% ID/g) was detected at 24 h postinjection. In vivo treatment studies were performed in the same HER2­(+) breast cancer model using PET–SPECT image guidance. The increased tumor uptake of the pretargeting and drug delivery components was detected by PET-CT and SPECT-CT, respectively. The study showed a significant 92% reduction of the relative tumor volume in treated mice (RTV = 0.08 in 26 days), compared to the untreated control mice (RTV = 1.78 in 11 days) and to mice treated with only HSA-DM1-Tt-[99mTc-HyNic] (RTV = 1.88 in 16 days). Multimodality PET–SPECT image-guided and pretargeted drug delivery can be utilized to maximize efficacy, predict therapeutic response, and minimize systemic toxicity.

The availability of nanoparticles (NPs) to deliver small interfering RNA (siRNA) has significantly expanded the specificity and range of ‘druggable’ targets for precision medicine in cancer. This is especially important for cancers such as triple negative breast cancer (TNBC) for which there are no targeted treatments. Our purpose here was to understand the role of tumor vasculature and vascular endothelial growth factor (VEGF) overexpression in a TNBC xenograft in improving the delivery and function of siRNA NPs using in vivo as well as ex vivo imaging. We used triple negative MDA-MB-231 human breast cancer xenografts derived from cells engineered to overexpress VEGF to understand the role of VEGF and vascularization in NP delivery and function. We used polyethylene glycol (PEG) conjugated polyethylenimine (PEI) NPs to deliver siRNA that downregulates choline kinase alpha (Chkα), an enzyme that is associated with malignant transformation and tumor progression. Because Chkα converts choline to phosphocholine, effective delivery of Chkα siRNA NPs resulted in functional changes of a significant decrease in phosphocholine and total choline that was detected with 1H magnetic resonance spectroscopy (MRS). We observed a significant increase in NP delivery and a significant decrease in Chkα and phosphocholine in VEGF overexpressing xenografts. Our results demonstrated the importance of tumor vascularization in achieving effective siRNA delivery and downregulation of the target gene Chkα and its function.

Prostate-specific membrane antigen (PSMA) is overexpressed in prostate cancers (PC) compared to normal tissues. Hence, PSMA can be used as a diagnostic biomarker and biological target to deliver drugs in PC therapy. In this study, we have conjugated ultra-small superparamagnetic iron oxide nanoparticles with mertansine (DM1), a chemotherapeutic drug, novel anti-PSMA 5D3 antibody, and NIR CF-750 fluorophore. This multimodality image-guided drug delivery system was evaluated in PC mouse models using in vivo fluorescent imaging and MRI at 9.4T. Promising results encourage further development of targeted image-guided drug delivery platforms for PC therapy.