Marcian E. Van Dort

Targeted Imaging and Therapy of Brain Cancer Using Theranostic Nanoparticles

The past decade has seen momentous development in brain cancer research in terms of novel imaging-assisted surgeries, molecularly targeted drug-based treatment regimens or adjuvant therapies and in our understanding of molecular footprints of initiation and progression of malignancy. However, mortality due to brain cancer has essentially remained unchanged in the last three decades. Thus, paradigm-changing diagnostic and therapeutic reagents are urgently needed. Nanotheranostic platforms are powerful tools for imaging and treatment of cancer. Multifunctionality of these nanovehicles offers a number of advantages over conventional agents. These include targeting to a diseased site thereby minimizing systemic toxicity, the ability to solubilize hydrophobic or labile drugs leading to improved pharmacokinetics and their potential to image, treat and predict therapeutic response. In this article, we will discuss the application of newer theranostic nanoparticles in targeted brain cancer imaging and treatment.

Inhibition of Furin/Proprotein Convertase-catalyzed Surface and Intracellular Processing by Small Molecules

Furin is a ubiquitously expressed proprotein convertase (PC) that plays a vital role in numerous disease processes including cancer metastasis, bacterial toxin activation (e.g. anthrax and Pseudomonas), and viral propagation (e.g. avian influenza and human immunodeficiency virus). To identify small molecule inhibitors of furin and related processing enzymes, we performed high-throughput screens of chemical diversity libraries utilizing both enzyme-based and cell-based assays. The screens identified partially overlapping sets of compounds that were further characterized for affinity, mechanism, and efficacy in additional cellular processing assays. Dicoumarols were identified as a class of compounds that inhibited furin non-competitively and reversibly with Ki values in the micromolar range. These compounds inhibited furin/furin-like activity both at the cell surface (protecting against anthrax toxin) and in the secretory pathway (blocking processing of the metastasis factor membrane-type 1 matrix metalloproteinase/MT1-MMP) at concentrations close to Ki values. Compounds tested exhibited distinct patterns of inhibition of other furin-family PCs (rat PACE4, human PC5/6 and human PC7), showing that dicoumarol derivatives might be developed as either generic or selective inhibitors of the PCs. The extensive clinical use, high bioavailability and relatively low toxicity of dicoumarols suggests that the dicoumarol structure will be a good starting point for development of drug-like inhibitors of furin and other PCs that can act both intracellularly and at the cell surface.

Synthesis of 11C-labeled desipramine and its metabolite 2-hydroxydesipramine: Potential radiotracers for pet studies of the norepinephrine transporter☆☆☆

The antidepressant desipramine (DMI) and its principal metabolite 2-hydroxydesipramine (HDMI) have been radiolabeled with 11C for PET studies. The normethyl precursors of DMI and HDMI were synthesized from iminodibenzyl in 35% and 11% overall yield, respectively. Direct methylation of the normethyl precursor with [11C]CH3I, followed by HPLC purification, provided [11C]DMI and [11C]HDMI in 18-30% and 15-23% decay-corrected radiochemical yields, respectively, in a 45 min synthesis time from end of bombardment. The specific activities of the two radiotracers were >1459 Ci/mmol at the end of synthesis. [11C]DMI and [11C]HDMI have potential utility as PET radiotracers for the norepinephrine transporter.

Radioiodination via isotope exchange in pivalic acid

A variety of benzoic and aryl aliphatic mono and polyiodinated acids and esters (sterol, triglyceride) were radioiodinated in 55–99% radiochemical yield by isotope exchange with Na 125I in a melt of pivalic acid. In general, the reaction was complete in 1 h at 155°C with little or no substrate decompostion. High specific activity studies afforded 125I-labeled iopanoic acid with a specific activity of over 700 Ci/mmol.

Synthesis and evaluation of [123I]-Iodo-PK11195 for mapping peripheral-type benzodiazepine receptors (ω3) in heart

Abstract An iodinated analog of PK11195, 1-(2-chlorophenyl)- N -methyl- N -(1-methylpropyl)isoquinoline-3-carboxamide, a specific antagonist of the peripheral-type benzodiazepine receptor (ω 3 ), has been synthesized in three steps with an overall chemical yield of 40%. Both [ 123 I]- and [ 125 I]-Iodo-PK11195 have been synthesized by solid-state isotopic exchange in >60% isolated radiochemical yield and specific activity of 233–348 mCi/mmol. Tissue distribution studies in rats indicate a high uptake of radioactivity in adrenal glands, heart, lung and kidneys, which was blocked 63–87% by preadministration of cold PK11195. Single photon emission computer tomography (SPECT) imaging of the canine heart has been accomplished with [ 123 I]PK11195. These results suggest that [ 123 I]PK11195 has potential as a SPECT radiotracer for studying the ω 3 receptor in humans.

The kinase activity of the Ser/Thr kinase BUB1 promotes TGF-β signaling.

A kinase that controls cell division also promotes the activity of the transforming growth factor–β pathway. Placing BUB1 in the TGF-β Pathway The transforming growth factor–β (TGF-β) pathway regulates cell proliferation and migration, processes involved in development, regeneration, and tumorigenesis. The kinase BUB1, which promotes proper chromosome alignment as cells prepare to divide, also regulates cell proliferation. Nyati et al. connected BUB1 to TGF-β signaling. They found that knocking down BUB1 impaired TGF-β–mediated proliferation of tumor cells—but not by acting at chromosomes. Instead, cytoplasmic BUB1 interacted with TGF-β receptor subunits at the cell surface, promoting the interaction between receptor subunits and between the receptor and downstream signaling proteins. Inhibiting the kinase activity of BUB1 suppressed TGF-β pathway activity in cells in culture and in xenografts. The findings suggest a possible point of crosstalk between the mitotic checkpoint and TGF-β signaling. Transforming growth factor–β (TGF-β) signaling regulates cell proliferation and differentiation, which contributes to development and disease. Upon binding TGF-β, the type I receptor (TGFBRI) binds TGFBRII, leading to the activation of the transcription factors SMAD2 and SMAD3. Using an RNA interference screen of the human kinome and a live-cell reporter for TGFBR activity, we identified the kinase BUB1 (budding uninhibited by benzimidazoles-1) as a key mediator of TGF-β signaling. BUB1 interacted with TGFBRI in the presence of TGF-β and promoted the heterodimerization of TGFBRI and TGFBRII. Additionally, BUB1 interacted with TGFBRII, suggesting the formation of a ternary complex. Knocking down BUB1 prevented the recruitment of SMAD3 to the receptor complex, the phosphorylation of SMAD2 and SMAD3 and their interaction with SMAD4, SMAD-dependent transcription, and TGF-β–mediated changes in cellular phenotype including epithelial-mesenchymal transition (EMT), migration, and invasion. Knockdown of BUB1 also impaired noncanonical TGF-β signaling mediated by the kinases AKT and p38 MAPK (mitogen-activated protein kinase). The ability of BUB1 to promote TGF-β signaling depended on the kinase activity of BUB1. A small-molecule inhibitor of the kinase activity of BUB1 (2OH-BNPP1) and a kinase-deficient mutant of BUB1 suppressed TGF-β signaling and formation of the ternary complex in various normal and cancer cell lines. 2OH-BNPP1 administration to mice bearing lung carcinoma xenografts reduced the amount of phosphorylated SMAD2 in tumor tissue. These findings indicated that BUB1 functions as a kinase in the TGF-β pathway in a role beyond its established function in cell cycle regulation and chromosome cohesion.

Synthesis of the 123I- and 125I-labeled cholinergic nerve marker (-)-5-iodobenzovesamicol

The highly toxic curraremimetic and cholinergic neuron marker (-)-5-iodobenzovesamicol (IBVM) has been labeled with iodine-125 and iodine-123. [125I]IBVM, suitable for animal distribution and ex vivo autoradiographic studies, was synthesized by solid-state exchange; isolated yields were 65-89% with specific activities in the range of 130-200 Ci/mmol. The synthesis of no-carrier-added (-)-5-[125I]IBVM from the corresponding chiral (-)-5-(tri-n-butyltin) derivative using Na125I was evaluated using the oxidants H2O2, peracetic acid and chloramine-T. Both peracetic acid and chloramine-T gave good yields (70-95%). However, when Na123I was utilized, acceptable yields of [123I]IBVM were obtained only with chloramine-T. Use of the latter oxidant did produce 5-chlorobenzovesamicol which was eliminated during HPLC purification. After optimization of the reaction parameters, [123I]IBVM in batch sizes of 10-27 mCi, is routinely obtained with a specific activity of 30-70,000 Ci/mmol, radiochemical purity (> 97%) and chiral purity (> 98%). Isolated radiochemical yields have averaged 71% (N = 40). Distribution analyses of [125I]IBVM and [123I]IBVM in mice 4 h following intravenous administration show essentially equivalent concentrations of the two tracers in the four brain regions sampled. The exceptionally high specific activity of [123I]IBVM has made possible the evaluation of this radiotracer in humans.

PET and SPECT Imaging of Tumor Biology: New Approaches Towards Oncology Drug Discovery and Development

Spiraling drug developmental costs and lengthy time-to-market introduction are two critical challenges facing the pharmaceutical industry. The clinical trials success rate for oncology drugs is reported to be 5% as compared to other therapeutic categories (11%) with most failures often encountered late in the clinical development process. PET and SPECT nuclear imaging technologies could play an important role in facilitating the drug development process improving the speed, efficiency and cost of drug development. This review will focus on recent studies of PET and SPECT radioligands in oncology and their application in the investigation of tumor biology. The use of clinically-validated radioligands as imaging-based biomarkers in oncology could significantly impact new cancer therapeutic development.

In Vivo Targeting and Positron Emission Tomography Imaging of Tumor with Intrinsically Radioactive Metal–Organic Frameworks Nanomaterials

Nanoscale metal-organic frameworks (nMOF) materials represent an attractive tool for various biomedical applications. Due to the chemical versatility, enormous porosity, and tunable degradability of nMOFs, they have been adopted as carriers for delivery of imaging and/or therapeutic cargos. However, the relatively low stability of most nMOFs has limited practical in vivo applications. Here we report the production and characterization of an intrinsically radioactive UiO-66 nMOF (89Zr-UiO-66) with incorporation of positron-emitting isotope zirconium-89 (89Zr). 89Zr-UiO-66 was further functionalized with pyrene-derived polyethylene glycol (Py-PGA-PEG) and conjugated with a peptide ligand (F3) to nucleolin for targeting of triple-negative breast tumors. Doxorubicin (DOX) was loaded onto UiO-66 with a relatively high loading capacity (1 mg DOX/mg UiO-66) and served as both a therapeutic cargo and a fluorescence visualizer in this study. Functionalized 89Zr-UiO-66 demonstrated strong radiochemical and material stability in different biological media. Based on the findings from cellular targeting and in vivo positron emission tomography (PET) imaging, we can conclude that 89Zr-UiO-66/Py-PGA-PEG-F3 can serve as an image-guidable, tumor-selective cargo delivery nanoplatform. In addition, toxicity evaluation confirmed that properly PEGylated UiO-66 did not impose acute or chronic toxicity to the test subjects. With selective targeting of nucleolin on both tumor vasculature and tumor cells, this intrinsically radioactive nMOF can find broad application in cancer theranostics.

Evaluation of Treatment-Associated Inflammatory Response on Diffusion-Weighted Magnetic Resonance Imaging and 2-[18F]-Fluoro-2-Deoxy-d-Glucose-Positron Emission Tomography Imaging Biomarkers

Purpose: Functional imaging biomarkers of cancer treatment response offer the potential for early determination of outcome through the assessment of biochemical, physiologic, and microenvironmental readouts. Cell death may result in an immunologic response, thus complicating the interpretation of biomarker readouts. This study evaluated the temporal effect of treatment-associated inflammatory activity on diffusion magnetic resonance imaging and 2-[18F]-fluoro-2-deoxy-d-glucose-positron emission tomography imaging (FDG-PET) biomarkers to delineate the effects of the inflammatory response on imaging readouts. Experimental Design: Rats with intracerebral 9L gliosarcomas were separated into four groups consisting of control, an immunosuppressive agent dexamethasone (Dex), 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU), and BCNU+Dex. Animals were imaged using diffusion-weighted magnetic resonance imaging and FDG-PET at 0, 3, and 7 days posttreatment. Results: In the BCNU- and BCNU+Dex-treated animal groups, diffusion values increased progressively over the 7-day study period to ∼23% over baseline. The FDG percentage change of standard uptake value decreased at day 3 (−30.9%) but increased over baseline levels at day 7 (+20.1%). FDG-PET of BCNU+Dex-treated animals were found to have percentage of standard uptake value reductions of −31.4% and −24.7% at days 3 and 7, respectively, following treatment. Activated macrophages were observed on day 7 in the BCNU treatment group with much fewer found in the BCNU+Dex group. Conclusions: Results revealed that treatment-associated inflammatory response following tumor therapy resulted in the accentuation of tumor diffusion response along with a corresponding increase in tumor FDG uptake due to the presence of glucose-consuming activated macrophages. The dynamics and magnitude of potential inflammatory response should be considered when interpreting imaging biomarker results. Clin Cancer Res; 16(5); 1542–52