Can the Efficacy of [18F]FDG-PET/CT in Clinical Oncology Be Enhanced by Screening Biomolecular Profiles?

Advances in PET/CT Imaging for Breast Cancer

One out of eight women will be affected by breast cancer during her lifetime. Imaging plays a key role in breast cancer detection and management, providing physicians with information about tumor location, heterogeneity, and dissemination. In this review, we describe the latest advances in PET/CT imaging of breast cancer, including novel applications of 18F-FDG PET/CT and the development and testing of new agents for primary and metastatic breast tumor imaging and therapy. Ultimately, these radiopharmaceuticals may guide personalized approaches to optimize treatment based on the patient's specific tumor profile, and may become a new standard of care. In addition, they may enhance the assessment of treatment efficacy and lead to improved outcomes for patients with a breast cancer diagnosis.

Recent Development of Radiofluorination of Boron Agents for Boron Neutron Capture Therapy of Tumor: Creation of 18F-Labeled C-F and B-F Linkages

Boron neutron capture therapy (BNCT) is a binary therapeutic technique employing a boron agent to be delivered to the tumor site followed by the irradiation of neutrons. Biofunctional molecules/nanoparticles labeled with F-18 can provide an initial pharmacokinetic profile of patients to guide the subsequent treatment planning procedure of BNCT. Borono phenylalanine (BPA), recognized by the l-type amino acid transporter, can cross the blood-brain barrier and be accumulated in gliomas. The radiofluoro BNCT agents are reviewed by considering (1) less cytotoxicity, (2) diagnosing and therapeutic purposes, (3) aqueous solubility and extraction route, as well as (4), the trifluoroborate effect. A trifluoroborate-containing amino acid such as fluoroboronotyrosine (FBY) represents an example with both functionalities of imaging and therapeutics. Comparing with the insignificant cytotoxicity of clinical BPA with IC50 > 500 μM, FBY also shows minute toxicity with IC50 > 500 μM. [18F]FBY is a potential diagnostic agent for its tumor to normal accumulation (T/N) ratio, which ranges from 2.3 to 24.5 from positron emission tomography, whereas the T/N ratio of FBPA is greater than 2.5. Additionally, in serving as a BNCT therapeutic agent, the boron concentration of FBY accumulated in gliomas remains uncertain. The solubility of 3-BPA is better than that of BPA, as evidenced by the cerebral dose of 3.4%ID/g vs. 2.2%ID/g, respectively. While the extraction route of d-BPA differs from that of BPA, an impressive T/N ratio of 6.9 vs. 1.5 is noted. [18F]FBPA, the most common clinical boron agent, facilitates the application of BPA in clinical BNCT. In addition to [18F]FBY, [18F] trifluoroborated nucleoside analog obtained through 1,3-dipolar cycloaddition shows marked tumoral uptake of 1.5%ID/g. Other examples using electrophilic and nucleophilic fluorination on the boron compounds are also reviewed, including diboronopinacolone phenylalanine and nonsteroidal anti-inflammatory agents.

Skin Cancer Pathobiology at a Glance: A Focus on Imaging Techniques and Their Potential for Improved Diagnosis and Surveillance in Clinical Cohorts

Early diagnosis is essential for completely eradicating skin cancer and maximizing patients' clinical benefits. Emerging optical imaging modalities such as reflectance confocal microscopy (RCM), optical coherence tomography (OCT), magnetic resonance imaging (MRI), near-infrared (NIR) bioimaging, positron emission tomography (PET), and their combinations provide non-invasive imaging data that may help in the early detection of cutaneous tumors and surgical planning. Hence, they seem appropriate for observing dynamic processes such as blood flow, immune cell activation, and tumor energy metabolism, which may be relevant for disease evolution. This review discusses the latest technological and methodological advances in imaging techniques that may be applied for skin cancer detection and monitoring. In the first instance, we will describe the principle and prospective clinical applications of the most commonly used imaging techniques, highlighting the challenges and opportunities of their implementation in the clinical setting. We will also highlight how imaging techniques may complement the molecular and histological approaches in sharpening the non-invasive skin characterization, laying the ground for more personalized approaches in skin cancer patients.

Detection of Hypoxia in Cancer Models: Significance, Challenges, and Advances

The rapid proliferation of cancer cells combined with deficient vessels cause regions of nutrient and O₂ deprivation in solid tumors. Some cancer cells can adapt to these extreme hypoxic conditions and persist to promote cancer progression. Intratumoral hypoxia has been consistently associated with a worse patient prognosis. In vitro, 3D models of spheroids or organoids can recapitulate spontaneous O₂ gradients in solid tumors. Likewise, in vivo murine models of cancer reproduce the physiological levels of hypoxia that have been measured in human tumors. Given the potential clinical importance of hypoxia in cancer progression, there is an increasing need to design methods to measure O₂ concentrations. O₂ levels can be directly measured with needle-type probes, both optical and electrochemical. Alternatively, indirect, noninvasive approaches have been optimized, and include immunolabeling endogenous or exogenous markers. Fluorescent, phosphorescent, and luminescent reporters have also been employed experimentally to provide dynamic measurements of O₂ in live cells or tumors. In medical imaging, modalities such as MRI and PET are often the method of choice. This review provides a comparative overview of the main methods utilized to detect hypoxia in cell culture and preclinical models of cancer.

Linking Metabolic Reprogramming, Plasticity and Tumor Progression

Simple Summary

In the present review, we discuss the role of metabolic reprogramming which occurs in malignant cells. The process of metabolic reprogramming is also known as one of the “hallmarks of cancer”. Due to several reasons, including the origin of cancer, tumor microenvironment, and the tumor progression stage, metabolic reprogramming can be heterogeneous and dynamic. In this review, we provide evidence that the usage of metabolic drugs is a promising approach to treat cancer. However, because these drugs can damage not only malignant cells but also normal rapidly dividing cells, it is important to understand the exact metabolic changes which are elicited by particular drivers in concrete tissue and are specific for each stage of cancer development, including metastases. Finally, the review highlights new promising targets for the development of new metabolic drugs.

Abstract

The specific molecular features of cancer cells that distinguish them from the normal ones are denoted as “hallmarks of cancer”. One of the critical hallmarks of cancer is an altered metabolism which provides tumor cells with energy and structural resources necessary for rapid proliferation. The key feature of a cancer-reprogrammed metabolism is its plasticity, allowing cancer cells to better adapt to various conditions and to oppose different therapies. Furthermore, the alterations of metabolic pathways in malignant cells are heterogeneous and are defined by several factors including the tissue of origin, driving mutations, and microenvironment. In the present review, we discuss the key features of metabolic reprogramming and plasticity associated with different stages of tumor, from primary tumors to metastases. We also provide evidence of the successful usage of metabolic drugs in anticancer therapy. Finally, we highlight new promising targets for the development of new metabolic drugs.

Development of Novel Analogs of the Monocarboxylate Transporter Ligand FACH and Biological Validation of One Potential Radiotracer for Positron Emission Tomography (PET) Imaging

Monocarboxylate transporters 1-4 (MCT1-4) are involved in several metabolism-related diseases, especially cancer, providing the chance to be considered as relevant targets for diagnosis and therapy. [¹⁸F]FACH was recently developed and showed very promising preclinical results as a potential positron emission tomography (PET) radiotracer for imaging of MCTs. Given that [¹⁸F]FACH did not show high blood-brain barrier permeability, the current work is aimed to investigate whether more lipophilic analogs of FACH could improve brain uptake for imaging of gliomas, while retaining binding to MCTs. The 2-fluoropyridinyl-substituted analogs 1 and 2 were synthesized and their MCT1 inhibition was estimated by [¹⁴C]lactate uptake assay on rat brain endothelial-4 (RBE4) cells. While compounds 1 and 2 showed lower MCT1 inhibitory potencies than FACH (IC₅₀ = 11 nM) by factors of 11 and 25, respectively, 1 (IC₅₀ = 118 nM) could still be a suitable PET candidate. Therefore, 1 was selected for radiosynthesis of [¹⁸F]1 and subsequent biological evaluation for imaging of the MCT expression in mouse brain. Regarding lipophilicity, the experimental log D_7.4 result for [¹⁸F]1 agrees pretty well with its predicted value. In vivo and in vitro studies revealed high uptake of the new radiotracer in kidney and other peripheral MCT-expressing organs together with significant reduction by using specific MCT1 inhibitor α-cyano-4-hydroxycinnamic acid. Despite a higher lipophilicity of [¹⁸F]1 compared to [¹⁸F]FACH, the in vivo brain uptake of [¹⁸F]1 was in a similar range, which is reflected by calculated BBB permeabilities as well through similar transport rates by MCTs on RBE4 cells. Further investigation is needed to clarify the MCT-mediated transport mechanism of these radiotracers in brain.

Preclinical Incorporation Dosimetry of [18F]FACH-A Novel 18F-Labeled MCT1/MCT4 Lactate Transporter Inhibitor for Imaging Cancer Metabolism with PET

Overexpression of monocarboxylate transporters (MCTs) has been shown for a variety of human cancers (e.g., colon, brain, breast, and kidney) and inhibition resulted in intracellular lactate accumulation, acidosis, and cell death. Thus, MCTs are promising targets to investigate tumor cancer metabolism with positron emission tomography (PET). Here, the organ doses (ODs) and the effective dose (ED) of the first 18F-labeled MCT1/MCT4 inhibitor were estimated in juvenile pigs. Whole-body dosimetry was performed in three piglets (age: ~6 weeks, weight: ~13-15 kg). The animals were anesthetized and subjected to sequential hybrid Positron Emission Tomography and Computed Tomography (PET/CT) up to 5 h after an intravenous (iv) injection of 156 ± 54 MBq [18F]FACH. All relevant organs were defined by volumes of interest. Exponential curves were fitted to the time-activity data. Time and mass scales were adapted to the human order of magnitude and the ODs calculated using the ICRP 89 adult male phantom with OLINDA 2.1. The ED was calculated using tissue weighting factors as published in Publication 103 of the International Commission of Radiation Protection (ICRP103). The highest organ dose was received by the urinary bladder (62.6 ± 28.9 µSv/MBq), followed by the gall bladder (50.4 ± 37.5 µSv/MBq) and the pancreas (30.5 ± 27.3 µSv/MBq). The highest contribution to the ED was by the urinary bladder (2.5 ± 1.1 µSv/MBq), followed by the red marrow (1.7 ± 0.3 µSv/MBq) and the stomach (1.3 ± 0.4 µSv/MBq). According to this preclinical analysis, the ED to humans is 12.4 µSv/MBq when applying the ICRP103 tissue weighting factors. Taking into account that preclinical dosimetry underestimates the dose to humans by up to 40%, the conversion factor applied for estimation of the ED to humans would rise to 20.6 µSv/MBq. In this case, the ED to humans upon an iv application of ~300 MBq [18F]FACH would be about 6.2 mSv. This risk assessment encourages the translation of [18F]FACH into clinical study phases and the further investigation of its potential as a clinical tool for cancer imaging with PET.

Special Issue "Anticancer Drugs"

The focus of this Special Issue of Pharmaceuticals is on the design, synthesis, and molecular mechanism of action of novel antitumor, drugs with a special emphasis on the relationship between the chemical structure and the biological activity of the molecules. This Special Issue also provides an understanding of the biologic and genotypic context in which targets are selected for oncology drug discovery, thus providing a rationalization for the biological activity of these drugs and guiding the design of more effective agents. In this Special Issue of Pharmaceuticals dedicated to anticancer drugs, we present a selection of preclinical research papers including both traditional chemotherapeutic agents and newer more targeted therapies and biological agents. We have included articles that report the design of small molecules with promising anticancer activity as tubulin inhibitors, vascular targeting agents, and topoisomerase targeting agents, alongside a comprehensive review of clinically successful antibody-drug conjugates used in cancer treatment.

Al18 F labeled sulfonamide-conjugated positron emission tomography tracer in vivo tumor-targeted imaging

An ideal positron emission tomography (PET) tracer should be highly extractable by the tumor tissue or organ that contains low toxicity and can provide high-resolution images in vivo. In this work, the aim was to evaluate the application of Al¹⁸ F-labeled 1,4,7-triazacyclononane-1,4,7-triacetic acid containing sulfonamide group (¹⁸ F-Al-NOTA-SN) as a potential tumor-targeting signal-enhanced radioactive tracer in PET. SN as a tumor-targeting group was incorporated to NOTA to make a ligand. Subsequently, this ligand reacted with Na¹⁸ F and AlCl₃ to produce a compound ¹⁸ F-Al-NOTA-SN. This compound was further characterized and its property in regard to cell cytotoxicity assay, microPET imaging, biodistribution, cell uptake assay, and tumor selectivity in vitro and in vivo, was also investigated. ¹⁸ F-Al-NOTA-SN possessed low cell cytotoxicity and uptake to COS-7 and 293T healthy cells and high cell cytotoxicity and uptake to MDA-MB-231, HepG2, and HeLa tumor cells in vitro. Moreover, ¹⁸ F-Al-NOTA-SN showed good tumor-targeting property and high PET signal enhancement of HeLa tumors, liver, and kidneys in mice, as well as the uptake ratios of tumor to blood and tumor to muscle, were 4.98 and 3.87, respectively. ¹⁸ F-Al-NOTA-SN can be accepted to be kidney and liver eliminated earlier and show a potential tumor-targeting signal-enhanced radioactive tracer in PET.