Radioiodinated Small-Molecule Tyrosine Kinase Inhibitor for HER2-Selective SPECT Imaging

Achieving theranostic probes targeting BRD3/BRD4 for imaging and therapy of tumor

The BET family proteins play pleiotropic roles in the tumorigenesis and growth of various human malignancies that have aroused great interests as the cancer therapeutic targets. Therefore, it's significant to develop labeling toolkits for the dynamic monitoring of BET family proteins in living tumor cells and tissue slices. In particular, there are few small-molecule fluorescent probes based on BET family proteins developed for real-time imaging of these proteins in tumor cells and tissues and treatment of breast cancer. In general, antibodies of BET family proteins are chosen for imaging of these proteins. However, the cost of these antibodies is more expensive than small molecules and the operation is relatively complicated. Moreover, the antibodies for imaging are not capable of the therapy for breast cancer. Thus, it's essential to exploit a novel imaging system for BET family proteins which is easy-operating and economical, with achieving therapeutic effects simultaneously. Therefore, a series of fluorescent probes (17-21) targeting BET family proteins were developed. Through the evaluation studies, probe 17 showed advantages in docking studies, analysis of cell viability, and imaging studies. Importantly, probe 17 was capable of distinguishing tumor cells and tissue slices and made a distinction between them by labeling BRD3 and BRD4 proteins. Importantly, probe 17 showed higher resolution in mouse tumor and human tumor slice imaging than BRD3 and BRD4 antibodies. Moreover, compared with these antibodies, probe 17 was more stable, more economical and easier to operate in the imaging assays. In addition, it also played an anti-tumor role by inducing cell apoptosis, proliferation inhibition, and cycle arrest in tumor cells. All these features render probe 17 to perform as an effective labeling toolkit compatible for imaging studies of BRD3/BRD4, as well as an approach to diagnosis and treatment of breast cancer.

Hypoxia-Inducible Factor-1α-Activated Protein Switch Based on Allosteric Self-Splicing Reduces Nonspecific Cytotoxicity of Pharmaceutical Drugs

Protein-based therapeutic agents currently used for targeted tumor therapy exhibit limited penetrability, nonspecific toxicity, and a short circulation half-life. Although targeting cell surface receptors improves cancer selectivity, the receptors are also slightly expressed in normal cells; consequently, the nonspecific toxicity of recombinant protein-based therapeutic agents has not been eliminated. In this study, an allosteric-regulated protein switch was designed that achieved cytoplasmic reorganization of engineered immunotoxins in tumor cells via interactions between allosteric self-splicing elements and cancer markers. It can target the accumulated HIF-1α in hypoxic cancer cells and undergo allosteric activation, and the splicing products were present in hypoxic cancer cells but were absent in normoxic cells, selectively killing tumor cells and reducing nonspecific toxicity to normal cells. The engineered pro-protein provides a platform for targeted therapy of tumors while offering a novel universal strategy for combining the activation of therapeutic functions with specific cancer markers. The allosteric self-splicing element is a powerful tool that significantly reduces the nonspecific cytotoxicity of therapeutic proteins.

Synthesis and initial in vitro evaluation of olmutinib derivatives as prospective imaging probe for non-small cell lung cancer

Introduction

Imaging a non-small cell lung cancer (NSCLC) using radiolabeled tyrosine kinase inhibitors (TKIs) has attracted attention due to their unique interaction with the target epidermal growth factor receptor (EGFR). Olmutinib (OTB) is one of the third-generation EGFR TKIs, which selectively inhibit EGFR L858R/T790M mutation. In this study, we aim to estimate the interaction of the iodinated OTB (I-OTB)-receptor complex by molecular docking. Furthermore, we will synthesize the I-OTB and evaluate its activity toward EGFR L858R/T790M by in vitro cytotoxicity assay.

Methods

A molecular docking simulation was carried out using an AutoDock Vina program package to estimate the interaction of the ligand-receptor complex. The I-OTB, N-{3-iodo-5-[(2-{[4-(4-methylpiperazin-1-yl)phenyl]aminothieno{3,2-d}pyrimidin-4-yl)oxy]phenyl} acrylamide, was synthesized by introducing an iodine atom in the phenyl group in the 3-aryloxyanilide structure. The half inhibitory concentration (IC50) was determined by employing a 2-(2-methoxy-4-nitrophenyl)-3-(4-nitrophenyl)-5-(2,4-disulfophenyl)-2H tetrazolium monosodium salt (WST-8) assay to evaluate the activity of I-OTB.

Results

The docking study exhibited that I-OTB could take an interaction similar to that of the parent compound. We successfully synthesized I-OTB and confirmed its structure by instrumental analysis. The binding energy of OTB and I-OTB in complex with EGFR T790M are -8.7 and -7.9 kcal/mol, respectively. The cytotoxicity assay showed that I-OTB also has an affinity towards the EGFR L858R/T790M mutation with the IC50 10.49 ± 5.64 𝜇M compared to the EGFR wild type with the IC50 over than 10 𝜇M.

Conclusion

The cytotoxicity effect of I-OTB was comparable to that of OTB. This result indicates that the iodine substituent in OTB did not alter the parent compound selectivity toward double mutations EGFR L858R/T790M. Therefore, I-OTB is prominent for radioiodination, and [123/124I] I-OTB may be a promising candidate for EGFR L858R/T790M mutation imaging.

Pyrazole derivatives as potent EGFR inhibitors: synthesis, biological evaluation and in silico and biodistribution study

Aim: Synthesis of pyrazole derivatives as EGFR inhibitors. Materials & methods: Cytotoxicity and EGFR inhibitory effect were evaluated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide and EGFR kits, respectively. The biodistribution of radioiodinated compound nanoparticles in tumor-bearing mice was studied. Results: The IC₅₀ values of compound 4a against HepG2 cells and EGFR were 0.15 ± 0.03 and 0.31 ± 0.008 μM, respectively, while those of erlotinib were 0.73 ± 0.04 and 0.11 ± 0.008 μM, respectively. The binding scores of compound 4a and erlotinib to EGFR were -9.52 and -10.23 Kcal/mol, respectively. The maximum tumor uptake of radioiodinated compound after intravenous nanoparticle injection was 6.7 ± 0.3% radioactivity/g. Conclusion: Compound 4a is a promising antitumor agent with a potential EGFR inhibitory effect.

Affinity probes based on small-molecule inhibitors for tumor imaging

Methods for molecular imaging of target areas, including optical imaging, radionuclide imaging, magnetic resonance imaging and other imaging technologies, are helpful for the early diagnosis and precise treatment of cancers. In addition to cancer management, small-molecule inhibitors are also used for developing cancer target probes since they act as the tight-binding ligands of overexpressed proteins in cancer cells. This review aims to summarize the structural designs of affinity probes based on small-molecule inhibitors from the aspects of the inhibitor, linker, dye and radionuclide, and discusses the influence of the modification of these structures on affinity and pharmacokinetics. We also present examples of inhibitor affinity probes in clinical applications, and these summaries will provide insights for future research and clinical translations.

China’s radiopharmaceuticals on expressway: 2014–2021

This review provides an essential overview on the progress of rapidly-developing China’s radiopharmaceuticals in recent years (2014–2021). Our discussion reflects on efforts to develop potential, preclinical, and in-clinical radiopharmaceuticals including the following areas: (1) brain imaging agents, (2) cardiovascular imaging agents, (3) infection and inflammation imaging agents, (4) tumor radiopharmaceuticals, and (5) boron delivery agents (a class of radiopharmaceutical prodrug) for neutron capture therapy. Especially, the progress in basic research, including new radiolabeling methodology, is highlighted from a standpoint of radiopharmaceutical chemistry. Meanwhile, we briefly reflect on the recent major events related to radiopharmaceuticals along with the distribution of major R&D forces (universities, institutions, facilities, and companies), clinical study status, and national regulatory supports. We conclude with a brief commentary on remaining limitations and emerging opportunities for China’s radiopharmaceuticals.

Development and Preclinical Evaluation of Radiolabeled Covalent G12C-Specific Inhibitors for Direct Imaging of the Oncogenic KRAS Mutant

Although KRAS has been an important target for many cancers, direct inhibition of oncogenic RAS remains challenging. Until recently, covalent KRAS G12C-specific inhibitors have been developed and progressed to the clinics. Nevertheless, not all patients benefit from these covalent inhibitors. At present, identification of candidates for this treatment requires tissue biopsies and gene sequencing, which are invasive, time-consuming, and could be of insufficient quality and limited predictive value owing to tumor heterogeneity. The use of noninvasive molecular imaging techniques such as PET and SPECT for spying KRAS G12C mutation in tumors provide a promising strategy for circumventing these hurdles. In the present study, based on the covalent G12C-specific inhibitor ARS-1620, we sought to develop radiolabeled small molecules for direct imaging of the KRAS mutation status in tumors. [¹³¹I]I-ARS-1620 and [¹⁸F]F-ARS-1620 were successfully prepared with high radiochemical yield, radiochemical purity, and molar activity. In vitro and in vivo studies have demonstrated the affinity, specificity, and capacity of [¹³¹I]I-ARS-1620 for direct imaging of the oncogenic KRAS G12C mutant. This initial attempt allows us to directly screen the KRAS G12C mutant for the first time in vivo.

Preclinical SPECT and SPECT-CT in Oncology

Molecular imaging enables both spatial and temporal understanding of the complex biologic systems underlying carcinogenesis and malignant spread. Single-photon emission tomography (SPECT) is a versatile nuclear imaging-based technique with ideal properties to study these processes in vivo in small animal models, as well as to identify potential drug candidates and characterize their antitumor action and potential adverse effects. Small animal SPECT and SPECT-CT (single-photon emission tomography combined with computer tomography) systems continue to evolve, as do the numerous SPECT radiopharmaceutical agents, allowing unprecedented sensitivity and quantitative molecular imaging capabilities. Several of these advances, their specific applications in oncology as well as new areas of exploration are highlighted in this chapter.

18F-labeled ethisterone derivative for progesterone receptor targeted PET imaging of breast cancer

PURPOSE

A novel radiolabeled probe 1‑(17‑[¹⁸F]fluoro‑3,6,9,12,15‑pentaoxaheptadecyl‑1H‑1,2,3‑triazole testosterone ([¹⁸F]FPTT) was synthesized and evaluated for PET imaging of progesterone receptor (PR)-positive breast cancer.

METHODS

The ethinyl group of ethisterone, a PR targeting pharmacophore, was coupled with azide modified PEG-OTs by click chemistry to obtain the labeling precursor. The final [¹⁸F]FPTT was synthesized by a one-step nucleophilic substitution reaction with ¹⁸F. The in vitro stabilities of [¹⁸F]FPTT in saline or rat serum were determined after 2 h incubation. Then the in vitro cell binding, ex vivo biodistribution and in vivo imaging of [¹⁸F]FPTT were further investigated to evaluate the PR targeting ability and feasibility for the diagnosis of PR-positive breast cancer with PET imaging.

RESULTS

[¹⁸F]FPTT was obtained in high decay-corrected radiochemical yield (78 ± 9%) at the end of synthesis. It had high radiochemical purity (>98%) after HPLC purification and good in vitro stability. The molar activity of [¹⁸F]FPTT was calculated as 17 GBq/μmol. The microPET imaging of [¹⁸F]FPTT in tumor-bearing mice showed much higher tumor uptake in PR-positive MCF-7 tumor (3.9 ± 0.20%ID/g) than that of PR-negative MDA-MB-231 tumor (1.3 ± 0.08%ID/g). The high MCF-7 tumor uptake could be specifically inhibited by blocking with ethisterone (1.3 ± 0.11%ID/g) or [¹⁹F]FPTT (2.20 ± 0.17%ID/g), respectively. The biodistribution in estrogen-primed female SD rats of [¹⁸F]FPTT showed high uterus and ovary uptakes (8.31 ± 1.74%ID/g and 3.79 ± 0.82%ID/g at 1 h post-injection). The specific uptakes of uterus and ovary in normal rats were 3.52 ± 0.29%ID/g and 3.22 ± 0.50%ID/g respectively and could be inhibited by co-injecting of ethisterone.

CONCLUSION

A novel [¹⁸F]FPTT probe based on ethisterone modification could be a potential diagnostic agent for PR-positive breast cancer.

Radioiodinated progesterone derivative for progesterone receptor targeting with enhanced nucleus uptake via phenylboronic acid conjugation

A novel ¹³¹ I-radiolabeled probe with aromatic boronate motif (¹³¹ I-EIPBA) was designed to target progesterone receptor (PR)-positive breast cancer with enhanced nucleus uptake. Acetylene progesterone was conjugated with pegylated phenylboronic acid via click reaction and radiolabeled with ¹³¹ I to afford ¹³¹ I-EIPBA. Meanwhile, ¹³¹ I-EIPB without boronate was prepared as control agent. After determination of the lipophilicity and stability of these tracers, in vitro cell uptake studies and in vivo biodistribution in rats were performed to verify the enhanced nucleus uptake and PR targeting ability of ¹³¹ I-EIPBA. ¹³¹ I-EIPBA was obtained with moderate radiochemical yield (40.35 ± 3.52%) and high radiochemical purity (>98%). As expected, the high binding affinity (39.58 nM) of ¹³¹ I-EIPBA for PR was determined by cell binding assay. The internalization ratio of ¹³¹ I-EIPBA was remarkably higher than that of ¹³¹ I-EIPB in PR-positive MCF-7 cells. Furthermore, the enhanced nucleus uptake of ¹³¹ I-EIPBA (0.59 ± 0.02%) was found to be significantly higher than that of ¹³¹ I-EIPB (0.13 ± 0.01%) in MCF-7 cells. A novel ¹³¹ I-EIPBA compound was developed for PR targeting with improved cellular nucleus uptake. Furthermore, the introduction of aromatic boronate motif provides a worthwhile strategy for enhancing the nuclear receptor targeting of tracers.

cRGD-decorated biodegradable polytyrosine nanoparticles for robust encapsulation and targeted delivery of doxorubicin to colorectal cancer in vivo

The clinical success of nanomedicines demands on the development of simple biodegradable nanocarriers that can efficiently and stably encapsulate chemotherapeutics while quickly release the payloads into target cancer cells. Herein, we report that cRGD-decorated biodegradable polytyrosine nanoparticles (cRGD-PTN) boost encapsulation and targeted delivery of doxorubicin (DOX) to colorectal cancer in vivo. The co-assembly of poly(ethylene glycol)-poly(L-tyrosine) (PEG-PTyr) and cRGD-functionalized PEG-PTyr (mol/mol, 80/20) yielded small-sized cRGD-PTN of 70 nm. Interestingly, cRGD-PTN exhibited an ultra-high DOX encapsulation with drug loading contents ranging from 18.5 to 54.1 wt%. DOX-loaded cRGD-PTN (cRGD-PTN-DOX) was highly stable against dilution, serum, and Triton X-100 surfactant, while quickly released DOX in HCT-116 cancer cells, likely resulting from enzymatic degradation of PTyr. Flow cytometry, confocal microscopy and MTT assays displayed that cRGD-PTN-DOX was efficiently internalized into α_vβ₅ overexpressing HCT-116 colorectal cancer cells, rapidly released DOX into the nuclei, and induced several folds better antitumor activity than non-targeted PTN-DOX and clinically used liposomal DOX (Lipo-DOX). SPECT/CT imaging revealed strong tumor accumulation of ¹²⁵I-labeled cRGD-PTN, which was 2.8-fold higher than ¹²⁵I-labeled PTN. Notably, cRGD-PTN-DOX exhibited over 5 times better toleration than Lipo-DOX and significantly more effective inhibition of HCT-116 colorectal tumor than non-targeted PTN-DOX control, affording markedly improved survival rate in HCT-116 tumor-bearing mice with depleting side effects at 6 or 12 mg DOX equiv./kg. cRGD-PTN-DOX with great simplicity, robust drug encapsulation and efficient nucleic drug release appears promising for targeted chemotherapy of colorectal tumor.

Radioiodinated Portable Albumin Binder as a Versatile Agent for in Vivo Imaging with Single-Photon Emission Computed Tomography

In this study, radioiodinated 4-( p-iodophenyl)butyric acid ([¹³¹I]IBA) was synthesized and evaluated as a portable albumin-binder for potential applications in single photon emission computed tomography imaging of blood pool, tumor, and lymph node with significantly improved pharmacokinetic properties. The [¹³¹I]IBA was prepared under the catalyst of Cu₂O/1,10-phenanthroline. After that, the albumin-binding capability of [¹³¹I]IBA was tested in vitro, ex vivo, and in vivo, respectively. [¹³¹I]IBA was obtained with very high radiolabeling yield (>99%) and good radiochemical purity (>98%) within 10 min. It binds to albumin effectively with high affinity (IC₅₀= 46.5 μM) and has good stability. The results of biodistribution indicated that the [¹³¹I]IBA was mainly accumulated in blood with good retention (10.51 ± 2.58%ID/g at 30 min p.i. and 4.63 ± 0.17%ID/g at 4 h p.i.). In the SPECT imaging of mice models with [¹³¹I]IBA, blood pool, lymph node, and tumors could be imaged clearly with high target-to-background ratio. Overall, the radioiodinated albumin binder of [¹³¹I]IBA with long blood half-life and excellent stability could be used to decorate diversified albumin-binding radioligands and developed as a versatile theranostic agent.

Multimodal Molecular Imaging: Current Status and Future Directions

Molecular imaging has emerged at the end of the last century as an interdisciplinary method involving in vivo imaging and molecular biology aiming at identifying living biological processes at a cellular and molecular level in a noninvasive manner. It has a profound role in determining disease changes and facilitating drug research and development, thus creating new medical modalities to monitor human health. At present, a variety of different molecular imaging techniques have their advantages, disadvantages, and limitations. In order to overcome these shortcomings, researchers combine two or more detection techniques to create a new imaging mode, such as multimodal molecular imaging, to obtain a better result and more information regarding monitoring, diagnosis, and treatment. In this review, we first describe the classic molecular imaging technology and its key advantages, and then, we offer some of the latest multimodal molecular imaging modes. Finally, we summarize the great challenges, the future development, and the great potential in this field.