Carbonic Anhydrase IX-Targeted Near-Infrared Dye for Fluorescence Imaging of Hypoxic Tumors

Carbonic Anhydrase IX Targeting Mn(II)-Based Magnetic Resonance Molecular Imaging Probe for Hypoxia Tumors

Physiological hypoxic conditions in the tumor microenvironment and consequential overexpression of carbonic anhydrase IX (CA IX) are two characteristics shared by numerous types of solid malignant tumors. Early detection with hypoxia assessment is crucial to improve the prognosis and therapy outcomes of hypoxia tumors. Herein, using acetazolamide (AZA) as a CA IX-targeting moiety, we design and synthesize an Mn(II)-based MR imaging probe (named AZA-TA-Mn) incorporating AZA and two Mn(II) chelates of Mn-TyEDTA on a rigid triazine (TA) scaffold. The per Mn relaxivity of AZA-TA-Mn is 2-fold higher than its monomeric Mn-TyEDTA, which allows it for low-dose imaging of hypoxic tumors. In a xenograft mice model of esophageal squamous cell carcinoma (ESCC), a low dosage of AZA-TA-Mn (0.05 mmol/kg) can selectively produce prolonged and stronger contrast enhancement in the tumor compared to the non-specific Gd-DTPA (0.1 mmol/kg). A competition study of co-injection of free AZA and Mn(II) probes confirms the in vivo tumor selectivity of AZA-TA-Mn, resulting in a more than 2.5-fold decreased tumor-to-muscle contrast-to-noise ratio (ΔCNR) at 60 min post-injection. MR imaging results were further supported by the quantitative analysis of Mn tissue levels, as the co-injection of free AZA resulted in significantly reduced Mn accumulation in tumor tissues. Finally, immunofluorescence staining of tissue sections confirms the positive correlation between the tumor accumulation of AZA-TA-Mn and CA IX overexpression. Hence, using CA IX as the hypoxia biomarker, our results illustrate a practical strategy for the development of novel imaging probes for hypoxic tumors.

PET radiotracers and fluorescent probes for imaging human carbonic anhydrase IX and XII in hypoxic tumors

Positron emission tomography (PET) and fluorescent imaging play a pivotal role in medical diagnosis, biomedical oncologic research, and drug development process, which include identification of target location, target engagement, but also prove on mechanism of action or pharmacokinetics of new drug candidates. PET estimates physiological changes at the molecular level using specific radiotracers containing a short-lived positron emitting radionuclide such as fluorine-18 or carbon-11, whereas fluorescent imaging techniques use fluorescent probes labeled with suitable drug candidates for detection at the molecular level. The human carbonic anhydrase (hCA) isoforms IX and XII are overexpressed in hypoxic cancer cells, promoting tumor growth by regulating extra/intracellular pH, ferroptosis, and metabolism, being recognized as promising targets for anticancer theranostic agents. In this review, we have focused on PET radiotracers as well as fluorescent probes for diagnosis and treatment of tumors expressing hCA IX and hCA XII.

Aza-BODIPY based carbonic anhydrase IX: Strategy to overcome hypoxia limitation in photodynamic therapy

Hypoxia caused by photodynamic therapy (PDT) is a major hurdle to cancer treatment since it can promote recurrence and progression by activating angiogenic factors, lowering therapeutic efficacy dramatically. In this work, AZB-I-CAIX₂ was developed as a carbonic anhydrase IX (CAIX)-targeting NIR photosensitizer that can overcome the challenge by utilizing a combination of CAIX knockdown and PDT. AZB-I-CAIX₂ showed a specific affinity to CAIX-expressed cancer cells and enhanced photocytotoxicity compared to AZB-I-control (the molecule without acetazolamide). Moreover, selective detection and effective cell cytotoxicity of AZB-I-CAIX₂ by PDT in hypoxic CAIX-expressed murine cancer cells were achieved. Essentially, AZB-I-CAIX₂ could minimize tumor size in the tumor-bearing mice compared to that in the control groups. The results suggested that AZB-I-CAIX₂ can improve therapeutic efficiency by preventing PDT-induced hypoxia through CAIX inhibition.

Picomolar fluorescent probes for compound affinity determination to carbonic anhydrase IX expressed in live cancer cells

Numerous human cancers, especially hypoxic solid tumors, express carbonic anhydrase IX (CAIX), a transmembrane protein with its catalytic domain located in the extracellular space. CAIX acidifies the tumor microenvironment, promotes metastases and invasiveness, and is therefore considered a promising anticancer target. We have designed a series of high affinity and high selectivity fluorescein-labeled compounds targeting CAIX to visualize and quantify CAIX expression in cancer cells. The competitive binding model enabled the determination of common CA inhibitors' dissociation constants for CAIX expressed in exponentially growing cancer cells. All tested sulfonamide compounds bound the proliferating cells with similar affinity as to recombinantly purified CAIX. The probes are applicable for the design of selective drug-like compounds for CAIX and the competition strategy could be applied to other drug targets.

New Developments in Carbonic Anhydrase IX-Targeted Fluorescence and Nuclear Imaging Agents

Carbonic anhydrase IX (CAIX) is a tumor-specific and hypoxia-induced biomarker for the molecular imaging of solid malignancies. The nuclear- and optical-imaging of CAIX-expressing tumors have received great attention due to their potential for clinical applications. Nuclear imaging is a powerful tool for the non-invasive diagnosis of primary and metastatic CAIX-positive tumors and for the assessment of responses to antineoplastic treatment. Intraoperative optical fluorescence imaging provides improved visualization for surgeons to increase the discrimination of tumor lesions, allowing for safer surgical treatment. Over the past decades, many CAIX-targeted molecular imaging probes, based on monoclonal antibodies, antibody fragments, peptides, and small molecules, have been reported. In this review, we outline the recent development of CAIX-targeted probes for single-photon emission computerized tomography (SPECT), positron emission tomography (PET), and near-infrared fluorescence imaging (NIRF), and we discuss issues yet to be addressed.

Efficient capture of circulating tumor cells with low molecular weight folate receptor-specific ligands

Retrieval of circulating tumor cells (CTC) has proven valuable for assessing a patient's cancer burden, evaluating response to therapy, and analyzing which drug might treat a cancer best. Although most isolation methods retrieve CTCs based on size, shape, or capture by tumor-specific antibodies, we explore here the use of small molecule tumor-specific ligands linked to magnetic beads for CTC capture. We have designed folic acid-biotin conjugates with different linkers for the capture of folate receptor (FR) + tumor cells spiked into whole blood, and application of the same technology to isolate FR + CTCs from the peripheral blood of both tumor-bearing mice and non-small cell lung patients. We demonstrate that folic acid linked via a rigid linker to a flexible PEG spacer that is in turn tethered to a magnetic bead enables optimal CTC retrieval, reaching nearly 100% capture when 100 cancer cells are spiked into 1 mL of aqueous buffer and ~ 90% capture when the same quantity of cells is diluted into whole blood. In a live animal model, the same methodology is shown to efficiently retrieve CTCs from tumor-bearing mice, yielding cancer cell counts that are proportional to total tumor burden. More importantly, the same method is shown to collect ~ 29 CTCs/8 mL peripheral blood from patients with non-small cell lung cancer. Since the ligand-presentation strategy optimized here should also prove useful in targeting other nanoparticles to other cells, the methods described below should have general applicability in the design of nanoparticles for cell-specific targeting.

Design and Characterization of Fibroblast Activation Protein Targeted Pan-Cancer Imaging Agent for Fluorescence-Guided Surgery of Solid Tumors

Tumor-targeted fluorescent dyes have been shown to significantly improve a surgeon's ability to locate and resect occult malignant lesions, thereby enhancing a patient’s chances of long term survival. Although several...

In vivo noninvasive preclinical tumor hypoxia imaging methods: a review

Tumors exhibit areas of decreased oxygenation due to malformed blood vessels. This low oxygen concentration decreases the effectiveness of radiation therapy, and the resulting poor perfusion can prevent drugs from reaching areas of the tumor. Tumor hypoxia is associated with poorer prognosis and disease progression, and is therefore of interest to preclinical researchers. Although there are multiple different ways to measure tumor hypoxia and related factors, there is no standard for quantifying spatial and temporal tumor hypoxia distributions in preclinical research or in the clinic. This review compares imaging methods utilized for the purpose of assessing spatio-temporal patterns of hypoxia in the preclinical setting. Imaging methods provide varying levels of spatial and temporal resolution regarding different aspects of hypoxia, and with varying advantages and disadvantages. The choice of modality requires consideration of the specific experimental model, the nature of the required characterization and the availability of complementary modalities as well as immunohistochemistry.

Nano versus Molecular: Optical Imaging Approaches to Detect and Monitor Tumor Hypoxia

Hypoxia is a ubiquitous feature of solid tumors, which plays a key role in tumor angiogenesis and resistance development. Conventional hypoxia detection methods lack continuous functional detection and are generally less suitable for dynamic hypoxia measurement. Optical sensors hereby provide a unique opportunity to noninvasively image hypoxia with high spatiotemporal resolution and enable real-time detection. Therefore, these approaches can provide a valuable tool for personalized treatment planning against this hallmark of aggressive cancers. Many small optical molecular probes can enable analyte triggered response and their photophysical properties can also be fine-tuned through structural modification. On the other hand, optical nanoprobes can acquire unique intrinsic optical properties through nanoconfinement as well as enable simultaneous multimodal imaging and drug delivery. Furthermore, nanoprobes provide biological advantages such as improving bioavailability and systemic delivery of the sensor to enhance bioavailability. This review provides a comprehensive overview of the physical, chemical, and biological analytes for cancer hypoxia detection and focuses on discussing the latest nano- and molecular developments in various optical imaging approaches (fluorescence, phosphorescence, and photoacoustic) in vivo. Finally, this review concludes with a perspective toward the potentials of these optical imaging approaches in hypoxia detection and the challenges with molecular and nanotechnology design strategies.

Cyanine Conjugate-Based Biomedical Imaging Probes

Cyanine is a class of fluorescent dye with meritorious fluorescence properties and has motivated numerous researchers to explore its imaging capabilities by miscellaneous structural modification and functionalization strategies. The covalent conjugation with other functional molecules represents a distinctive design strategy and has shown immense potential in both basic and clinical research. This review article summarizes recent achievements in cyanine conjugate-based probes for biomedical imaging. Particular attention is paid to the conjugation with targeting warheads and other contrast agents for targeted fluorescence imaging and multimodal imaging, respectively. Additionally, their clinical potential in cancer diagnostics is highlighted and some concurrent impediments for clinical translation are discussed.

Near-IR emissive rare-earth nanoparticles for guided surgery

Intraoperative image-guided surgery (IGS) has attracted extensive research interests in determination of tumor margins from surrounding normal tissues. Introduction of near infrared (NIR) fluorophores into IGS could significantly improve the in vivo imaging quality thus benefit IGS. Among the reported NIR fluorophores, rare-earth nanoparticles exhibit unparalleled advantages in disease theranostics by taking advantages such as large Stokes shift, sharp emission spectra, and high chemical/photochemical stability. The recent advances in elements doping and morphologies controlling endow the rare-earth nanoparticles with intriguing optical properties, including emission span to NIR-II region and long life-time photoluminescence. Particularly, NIR emissive rare earth nanoparticles hold advantages in reduction of light scattering, photon absorption and autofluorescence, largely improve the performance of nanoparticles in biological and pre-clinical applications. In this review, we systematically compared the benefits of RE nanoparticles with other NIR probes, and summarized the recent advances of NIR emissive RE nanoparticles in bioimaging, photodynamic therapy, drug delivery and NIR fluorescent IGS. The future challenges and promises of NIR emissive RE nanoparticles for IGS were also discussed.

Emerging Fluorescent Molecular Tracers to Guide Intra-Operative Surgical Decision-Making

Fluorescence imaging is an emerging technology that can provide real-time information about the operating field during cancer surgery. Non-specific fluorescent agents, used for the assessment of blood flow and sentinel lymph node detection, have so far dominated this field. However, over the last decade, several clinical studies have demonstrated the great potential of targeted fluorescent tracers to visualize tumor lesions in a more specific way. This has led to an exponential growth in the development of novel molecular fluorescent contrast agents. In this review, the design of fluorescent molecular tracers will be discussed, with particular attention for agents and approaches that are of interest for clinical translation.

Diagnostic performance of receptor-specific surgical specimen staining correlates with receptor expression level

Intraoperative margin assessment is imperative to cancer cure but is a continued challenge to successful surgery. Breast conserving surgery is a relevant example, where a cosmetically improved outcome is gained over mastectomy, but re-excision is required in >25  %   of cases due to positive or closely involved margins. Clinical translation of margin assessment modalities that must directly contact the patient or required administered contrast agents are time consuming and costly to move from bench to bedside. Tumor resections provide a unique surgical opportunity to deploy margin assessment technologies including contrast agents on the resected tissues, substantially shortening the path to the clinic. However, staining of resected tissues is plagued by nonspecific uptake. A ratiometric imaging approach where matched targeted and untargeted probes are used for staining has demonstrated substantially improved biomarker quantification over staining with conventional targeted contrast agents alone. Our group has developed an antibody-based ratiometric imaging technology using fluorescently labeled, spectrally distinct targeted and untargeted antibody probes termed dual-stain difference specimen imaging (DDSI). Herein, the targeted biomarker expression level and pattern are evaluated for their effects on DDSI diagnostic potential. Epidermal growth factor receptor expression level was correlated to DDSI diagnostic potential, which was found to be robust to spatial pattern expression variation. These results highlight the utility of DDSI for accurate margin assessment of freshly resected tumor specimens.

Novel approaches for designing drugs that interfere with pH regulation

INTRODUCTION

In all living species, pH regulation is a tightly controlled process, with a plethora of proteins involved in its regulation. These include sodium-proton exchangers, carbonic anhydrases, anion exchangers, bicarbonate transporters/cotransporters, H⁺-ATPases, and monocarboxylate transporters. All of them play crucial roles in acid-base balancing, both in eukaryotic as well as in prokaryotic organisms, making them interesting drug targets for the management of pathological events (in)directly involved in pH regulation. Areas covered: Interfering with pH regulation for the treatment of tumors and microbial infections is the main focus of this review, with particular attention paid to inhibitors targeting the above-mentioned proteins. The latest advances in each field id reviewed. Expert opinion: Interfering with the pH regulation of tumor cells is a validated approach to tackle primary tumors and metastases growth. Carbonic anhydrases are the most investigated proteins of those aforementioned, with several inhibitors in clinical development. Recent advances in the characterization of proteins involved in pH homeostasis of various pathogens evidenced their crucial role in the survival and virulence of bacterial, fungal, and protozoan microorganisms. Some encouraging results shed light on the possibility to target such proteins for obtaining new anti-infectives, overcoming the extensive drug resistance problems of clinically used drugs.