Chemical Probes Research Articles

Spiro-Substituted Dioxetane-Based Chemical Probes with Enhanced Detection and Sensitivity Limits

Spiro-Substituted Dioxetane-Based Chemical Probes with Enhanced Detection and Sensitivity Limits

Synthesis of α,α-Difluoro-β-amino Ketones from N-Boc-α-Amidosulfones and Pentafluoro-gem-diols.

To circumvent the synthesis and isolation of imines, a method was devised to construct α,α-difluoro-β-amino ketones from N-Boc-α-amidosulfones. The reactive nucleophiles, difluoroenolates, are generated in situ from the pentafluoro-gem-diols using cesium fluoride in pyridine. NMR studies confirm the role of the α-amidosulfones in this process. Incubation of the α,α-difluoro-β-amino ketones in rat serum demonstrates the relative stability of this structure as well as its value as a chemical probe or lead.

Soluble Zinc Phthalocyanines as chemical probes for Δ-9-tetrahydrocannabinol in different solvents

The detection of Δ-9-tetrahydrocannabinol (THC) is important for several applications from agriculture and pharmaceuticals to law enforcement. Two novel soluble zinc phthalocyanines were synthesized and their interaction with THC was studied. We report the change in the electrochemical and spectroelectrochemical response of the two zinc derivatives in the presence of THC using different organic solvents (DCM, THF, and DMF). The greatest change in spectroelectrochemical response was found when DCM was employed, whereas when THF was used an increase in higher energy π−π∗ transitions within the Pc cores was observed. Using DMF on the other hand demonstrated little change in response. We also found that the functional group used to solubilize the ZnPc played a significant role in the observed spectrochemical response to THC. These results demonstrate the potential for ZnPc-based chemical probes for the use in detection of THC.

Unraveling the enigma: housekeeping gene Ugt1a7c as a universal biomarker for microglia

BackgroundMicroglia, brain resident macrophages, play multiple roles in maintaining homeostasis, including immunity, surveillance, and protecting the central nervous system through their distinct activation processes. Identifying all types of microglia-driven populations is crucial due to the presence of various phenotypes that differ based on developmental stages or activation states. During embryonic development, the E8.5 yolk sac contains erythromyeloid progenitors that go through different growth phases, eventually resulting in the formation of microglia. In addition, microglia are present in neurological diseases as a diverse population. So far, no individual biomarker for microglia has been discovered that can accurately identify and monitor their development and attributes.SummaryHere, we highlight the newly defined biomarker of mouse microglia, UGT1A7C, which exhibits superior stability in expression during microglia development and activation compared to other known microglia biomarkers. The UGT1A7C sensing chemical probe labels all microglia in the 3xTG AD mouse model. The expression of Ugt1a7c is stable during development, with only a 4-fold variation, while other microglia biomarkers, such as Csf1r and Cx3cr1, exhibit at least a 10-fold difference. The UGT1A7C expression remains constant throughout its lifespan. In addition, the expression and activity of UGT1A7C are the same in response to different types of inflammatory activators’ treatment in vitro.ConclusionWe propose employing UGT1A7C as the representative biomarker for microglia, irrespective of their developmental state, age, or activation status. Using UGT1A7C can reduce the requirement for using multiple biomarkers, enhance the precision of microglia analysis, and even be utilized as a standard for gene/protein expression.

Functionalizing tandem mass tags for streamlining click-based quantitative chemoproteomics

Mapping the ligandability or potential druggability of all proteins in the human proteome is a central goal of mass spectrometry-based covalent chemoproteomics. Achieving this ambitious objective requires high throughput and high coverage sample preparation and liquid chromatography-tandem mass spectrometry analysis for hundreds to thousands of reactive compounds and chemical probes. Conducting chemoproteomic screens at this scale benefits from technical innovations that achieve increased sample throughput. Here we realize this vision by establishing the silane-based cleavable linkers for isotopically-labeled proteomics-tandem mass tag (sCIP-TMT) proteomic platform, which is distinguished by early sample pooling that increases sample preparation throughput. sCIP-TMT pairs a custom click-compatible sCIP capture reagent that is readily functionalized in high yield with commercially available TMT reagents. Synthesis and benchmarking of a 10-plex set of sCIP-TMT reveal a substantial decrease in sample preparation time together with high coverage and high accuracy quantification. By screening a focused set of four cysteine-reactive electrophiles, we demonstrate the utility of sCIP-TMT for chemoproteomic target hunting, identifying 789 total liganded cysteines. Distinguished by its compatibility with established enrichment and quantification protocols, we expect sCIP-TMT will readily translate to a wide range of covalent chemoproteomic applications.

Mechanism of antagonist ligand binding to REV-ERBα.

REV-ERBα, a therapeutically promising nuclear hormone receptor, plays a crucial role in regulating various physiological processes such as the circadian clock, inflammation, and metabolism. However, the availability of chemical probes to investigate the pharmacology of this receptor is limited, with SR8278 being the only identified synthetic antagonist. Moreover, no X-ray crystal structures are currently available that demonstrate the binding of REV-ERBα to antagonist ligands. This lack of structural information impedes the development of targeted therapeutics. To address this issue, we employed Gaussian accelerated molecular dynamics (GaMD) simulations to investigate the binding pathway of SR8278 to REV-ERBα. For comparison, we also used GaMD to observe the ligand binding process of STL1267, for which an X-ray structure is available. GaMD simulations successfully captured the binding of both ligands to the receptor's orthosteric site and predicted the ligand binding pathway and important amino acid residues involved in the antagonist SR8278 binding. This study highlights the effectiveness of GaMD in investigating protein-ligand interactions, particularly in the context of drug recognition for nuclear hormone receptors.

Fluorogenic Chemical Probes for Wash-free Imaging of Cell Membrane Damage in Ferroptosis, Necrosis, and Axon Injury.

Selectively labeling cells with damaged membranes is needed not only for identifying dead cells in culture, but also for imaging membrane barrier dysfunction in pathologies in vivo. Most membrane permeability stains are permanently colored or fluorescent dyes that need washing to remove their non-uptaken extracellular background and reach good image contrast. Others are DNA-binding environment-dependent fluorophores, which lack design modularity, have potential toxicity, and can only detect permeabilization of cell volumes containing a nucleus (i.e., cannot delineate damaged volumes in vivo nor image non-nucleated cell types or compartments). Here, we develop modular fluorogenic probes that reveal the whole cytosolic volume of damaged cells, with near-zero background fluorescence so that no washing is needed. We identify a specific disulfonated fluorogenic probe type that only enters cells with damaged membranes, then is enzymatically activated and marks them. The esterase probe MDG1 is a reliable tool to reveal live cells that have been permeabilized by biological, biochemical, or physical membrane damage, and it can be used in multicolor microscopy. We confirm the modularity of this approach by also adapting it for improved hydrolytic stability, as the redox probe MDG2. We conclude by showing the unique performance of MDG probes in revealing axonal membrane damage (which DNA fluorogens cannot achieve) and in discriminating damage on a cell-by-cell basis in embryos in vivo. The MDG design thus provides powerful modular tools for wash-free in vivo imaging of membrane damage, and indicates how designs may be adapted for selective delivery of drug cargoes to these damaged cells: offering an outlook from selective diagnosis toward therapy of membrane-compromised cells in disease.

A chemical proteomics approach for global mapping of functional lysines on cell surface of living cell.

Cell surface proteins are responsible for many crucial physiological roles, and they are also the major category of drug targets as the majority of therapeutics target membrane proteins on the surface of cells to alter cellular signaling. Despite its great significance, ligand discovery against membrane proteins has posed a great challenge mainly due to the special property of their natural habitat. Here, we design a new chemical proteomic probe OPA-S-S-alkyne that can efficiently and selectively target the lysines exposed on the cell surface and develop a chemical proteomics strategy for global analysis of surface functionality (GASF) in living cells. In total, we quantified 2639 cell surface lysines in Hela cell and several hundred residues with high reactivity were discovered, which represents the largest dataset of surface functional lysine sites to date. We discovered and validated that hyper-reactive lysine residues K382 on tyrosine kinase-like orphan receptor 2 (ROR2) and K285 on Endoglin (ENG/CD105) are at the protein interaction interface in co-crystal structures of protein complexes, emphasizing the broad potential functional consequences of cell surface lysines and GASF strategy is highly desirable for discovering new active and ligandable sites that can be functionally interrogated for drug discovery.

Effective Degradation of Metronidazole through Electrochemical Activation of Peroxymonosulfate: Mechanistic Insights and Implications

The investigation into the degradation of metronidazole (MNZ), a frequently employed antibiotic, through the electrochemical activation of peroxymonosulfate (PMS) utilizing either boron-doped diamond (BDD) or dimensional stable anode (DSA) as the anode, was conducted in a systematic manner. The enhancement of MNZ removal was observed with increasing current density, PMS dosage, and initial pH. Response surface methodology (RSM), based on a Box–Benken design, was utilized to evaluate the efficiency of MNZ elimination concerning current density (ranging from 11.1 to 33.3 mA/cm2), initial pH (ranging from 3 to 9), PMS dosage (ranging from 1 to 5 mmol·L−1), and reaction time (ranging from 25 to 45 min). The optimal operational conditions for MNZ removal were determined as follows: a current density of 13.3 mA/cm2, a pH of 3.7, a PMS dosage of 2.4 mmol·L−1, and a reaction time of 40 min. Electron paramagnetic resonance (EPR), quenching experiments, and chemical probe experiments confirmed the involvement of •OH, SO4•− and 1O2 radicals as the primary reactive species in MNZ degradation. The presence of HCO3− and H2PO4− hindered MNZ removal, whereas the presence of Cl− accelerated it. The degradation pathways of MNZ were elucidated by identifying intermediates and assessing their toxicity. Additionally, the removal efficiencies of other organic pollutants, such as sulfamethoxazole (SMX), carbamazepine (CBZ), and nitrobenzene (NB), were compared. This study contributes to a comprehensive understanding of MNZ degradation efficiency, mechanisms, and pathways through electrochemical activation of PMS employing BDD or DSA anodes, thereby offering valuable insights for the selection of wastewater treatment systems.

Investigating impacts of the mycothiazole chemotype as a chemical probe for the study of mitochondrial function and aging.

Small molecule inhibitors of the mitochondrial electron transport chain (ETC) hold significant promise to provide valuable insights to the field of mitochondrial research and aging biology. In this study, we investigated two molecules: mycothiazole (MTZ) - from the marine sponge C. mycofijiensis and its more stable semisynthetic analog 8-O-acetylmycothiazole (8-OAc) as potent and selective chemical probes based on their high efficiency to inhibit ETC complex I function. Similar to rotenone (Rote), MTZ, a newly employed ETC complex I inhibitor, exhibited higher cytotoxicity against cancer cell lines compared to certain non-cancer cell lines. Interestingly, 8-OAc demonstrated greater selectivity for cancer cells when compared to both MTZ and Rote, which has promising potential for anticancer therapeutic development. Furthermore, in vivo experiments with these small molecules utilizing a C. elegans model demonstrate their unexplored potential to investigate aging studies. We observed that both molecules have the ability to induce a mitochondria-specific unfolded protein response (UPRMT) pathway, that extends lifespan of worms when applied in their adult stage. We also found that these two molecules employ different pathways to extend lifespan in worms. Whereas MTZ utilizes the transcription factors ATFS-1 and HSF1, which are involved in the UPRMT and heat shock response (HSR) pathways respectively, 8-OAc only required HSF1 and not ATFS-1 to mediate its effects. This observation underscores the value of applying stable, potent, and selective next generation chemical probes to elucidate an important insight into the functional roles of various protein subunits of ETC complexes and their regulatory mechanisms associated with aging.

Identification and structural characterization of small molecule inhibitors of PINK1

Mutations in PINK1 and Parkin cause early-onset Parkinson’s Disease (PD). PINK1 is a kinase which functions as a mitochondrial damage sensor and initiates mitochondrial quality control by accumulating on the damaged organelle. There, it phosphorylates ubiquitin, which in turn recruits and activates Parkin, an E3 ubiquitin ligase. Ubiquitylation of mitochondrial proteins leads to the autophagic degradation of the damaged organelle. Pharmacological modulation of PINK1 constitutes an appealing avenue to study its physiological function and develop therapeutics. In this study, we used a thermal shift assay with insect PINK1 to identify small molecules that inhibit ATP hydrolysis and ubiquitin phosphorylation. PRT062607, an SYK inhibitor, is the most potent inhibitor in our screen and inhibits both insect and human PINK1, with an IC50 in the 0.5–3 µM range in HeLa cells and dopaminergic neurons. The crystal structures of insect PINK1 bound to PRT062607 or CYC116 reveal how the compounds interact with the ATP-binding pocket. PRT062607 notably engages with the catalytic aspartate and causes a destabilization of insert-2 at the autophosphorylation dimer interface. While PRT062607 is not selective for PINK1, it provides a scaffold for the development of more selective and potent inhibitors of PINK1 that could be used as chemical probes.

Recent advances on the role of high-valent metals formed during persulfate activation

Over the past years, persulfate-based advanced oxidation processes have been widely employed in scientific research and practical application because of their outstanding oxidizing capability for decontamination and sterilization. In contrast to SO4•− and •OH radicals that are commonly considered to be the primary reactive oxidants, high-valent metals, such as Fe(IV), Co(IV), Cu(III), and Mn(V), formed during persulfate activation have only been observed in recent years. The advantages of high-valent metals over radicals lie in the better tolerance of background ions and the selective reaction towards compounds containing electron-rich groups. In this review, current research progress on high-valent metals generated during persulfate activation is outlined, and the formation mechanism, oxidation performance, and practical application are discussed. Specifically, the formation of high-valent metals has been observed via 18O-labeled water combined with chemical probes and in situ spectroscopy; compared to radicals, the formation of these metals was more thermodynamically favorable. Unlike •OH and SO4•−, which exhibit strong and nonselective reactivity, high-valent metals possess moderate oxidation power and selectively react with compounds containing electron-rich groups; these reactions are affected by several parameters, such as pH, temperature, activator/persulfate dosage, and ligand. The applications of high-valent metal-mediated oxidation processes and challenges encountered are discussed. Overall, potential applications of high-valent metal-mediated oxidation based on persulfate could be extended for practical wastewater treatment.

Underestimated role of hydroxyl radicals for bromate formation in persulfate-based advanced oxidation processes

In persulfate-based advanced oxidation processes (PS-AOPs), sulfate radicals (SO4•-) have been recognized to play more important roles in inducing bromate (BrO3−) formation rather than hydroxyl radicals (HO•) because of the stronger oxidation capacity of the former. However, this study reported an opposite result that HO• indeed dominated the formation of bromate instead of SO4•-. Quenching experiments were coupled with electron paramagnetic resonance (EPR) detection and chemical probe identification to elucidate the contributions of each radical species. The comparison of different thermal activated persulfates (PDS and PMS) demonstrated that the significant higher bromate formation in HEAT/PMS ([BrO3−]/[Br−]0 = 0.8), as compared to HEAT/PDS ([BrO3−]/[Br−]0 = 0.2), was attributable to the higher concentration of HO• radicals in HEAT/PMS. Similarly, the bromate formation in UV/PDS ([BrO3−]/[Br−]0 = 1.0), with a high concentration of HO•, further underscored the dominant role of HO•. As a result, we quantified that HO• and SO4•- radicals accounted 66.7% and 33.3% for bromate formation. This controversial result can be reconciled by considering the critical intermediate, hypobromic acid/hypobromate (HOBr/BrO−), involved in the transformation of Br− to BrO3−. HO• have the chemical preference to induce the formation of HOBr/BrO− intermediates (contributing ∼ 60%) relative to SO4•- radicals (contributing ∼ 40%). This study highlighted the dominant role of HO• in the formation of bromate rather than SO4•- in PS-AOPs and potentially offered novel insights for reducing disinfection byproduct formation by controlling the radical species in AOPs.

Enhanced activation of sulfite by the iron-citrate complexes under NUV irradiation for metronidazole degradation: Kinetic, degradation mechanism and efficiency in real water

In the present study, a novel approach for the elimination of emerging pollutants through an advanced oxidation process has been developed by combining near ultraviolet (NUV) irradiation with an iron-citrate complex (Fe(III)-Cit) to overcome the defects of the traditional Fe(III)/sulfite system and enhance the activation of sulfite in a neutral aqueous solution. The performance of this system was studied using metronidazole (MTZ) as the target pollutant, and the impact of operational conditions such as initial pH, Fe(III)-Cit complex concentration, sulfite dose, metronidazole concentration and dissolved oxygen were studied. The rate constant of MTZ degradation at natural pH (7.0 ± 0.2) by the Fe(III)-Cit/sulfite/NUV system is over 12.72-times and 13.25-times higher than the sulfite/NUV and Fe(III)-Cit/NUV individual binary systems. The effectiveness of the system was further examined in various real water matrices. The latter proved to be effective in the following order: groundwater > ultra-pure water > > seawater, revealing that it was very effective in the former. Chemical probe experiments indicated that sulfate radicals and hydroxyl radicals were the principal reactive oxygen species involved in the photodegradation of MTZ. Additionally, dissolved oxygen played a crucial role in the reaction. MTZ degradation products were determined by HPLC/MS, leading to the identification of nine different by-products and the proposal of possible degradation pathways. Although further studies are required to better understand this system, this work paves the way for the application of activated sulfite-based processes for environmental remediation without pH adjustment, offering an alternative to the use of conventional oxidants.

Mercury‐Group 13 Metal Covalent Bonds: A Systematic Comparison of Aluminyl, Gallyl and Indyl Metallo‐ligands

Bimetallic compounds containing direct metal‐group 13 element bonds have been shown to display unprecedented patterns of cooperative reactivity towards small molecules, which can be influenced by the identity of the group 13 element. In this context, we present here a systematic appraisal of group 13 metallo‐ligands of the type [(NON)E]‐ (NON = 4,5‐bis(2,6‐diisopropylanilido)‐2,7‐di‐tert‐butyl‐9,9‐dimethylxanthene) for E = Al, Ga and In, through a comparison of structural and spectroscopic parameters associated with the trans L or X ligands in linear d10 complexes of the types LM{E(NON)} and XM'{E(NON)}. These studies are facilitated by convenient syntheses (from the In(I) precursor, InCp) of the potassium indyl species [{K(NON)In}·KCp]n (1) and [(18‐crown‐6)2K2Cp] [(NON)In] (1'), and lead to the first structural characterisation of Ag–In and Hg–E (E = Al, In) covalent bonds. The resulting structural, spectroscopic and quantum chemical probes of Ag/Hg complexes are consistent with markedly stronger sigma‐donor capabilities of the aluminyl ligand, [(NON)Al]‐, over its gallium and indium counterparts.

Mercury-Group 13 Metal Covalent Bonds: A Systematic Comparison of Aluminyl, Gallyl and Indyl Metallo-ligands.

Bimetallic compounds containing direct metal-group 13 element bonds have been shown to display unprecedented patterns of cooperative reactivity towards small molecules, which can be influenced by the identity of the group 13 element. In this context, we present here a systematic appraisal of group 13 metallo-ligands of the type [(NON)E]-(NON =4,5-bis(2,6-diisopropylanilido)-2,7-di-tert-butyl-9,9-dimethylxanthene) for E = Al, Ga and In, through a comparison of structural and spectroscopic parameters associated with thetransL or X ligands in lineard10complexes of the types LM{E(NON)} and XM'{E(NON)}. These studies are facilitated by convenient syntheses (from the In(I) precursor, InCp) of the potassium indyl species [{K(NON)In}·KCp]n(1) and [(18-crown-6)2K2Cp] [(NON)In] (1'), and lead to the first structural characterisation of Ag-In and Hg-E (E = Al, In) covalent bonds. The resulting structural, spectroscopic and quantum chemical probes of Ag/Hg complexes are consistent with markedly strongersigma-donor capabilities of the aluminyl ligand, [(NON)Al]-, over its gallium and indium counterparts.

A genetically encoded fluorescent protein sensor for mitochondrial membrane damage detection

Mitochondria are essential cellular organelles; detecting mitochondrial damage is crucial in cellular biology and toxicology. Compared with existing chemical probe detection methods, genetically encoded fluorescent protein sensors can directly indicate cellular and molecular events without involving exogenous reagents. In this study, we introduced a molecular sensor system, MMD-Sensor, for monitoring mitochondrial membrane damage. The sensor consists of two molecular modules. Module I is a fusion structure of the mitochondrial localization sequence (MLS), AIF cleavage site sequence (CSS), nuclear localization sequence (NLS), N-terminus of mNeonGreen and mCherry. Module II is a fusion structure of the C-terminus of mNeonGreen, NLS sequence, and mtagBFP2. Under normal condition, Module I is constrained in the inner mitochondrial membrane anchored by MLS, while Module II is restricted to the nucleus by its NLS fusion component. If the mitochondrial membrane is damaged, CSS is cut from the inner membrane, causing Module I to shift into the nucleus guided by the NLS fusion component. After Module I enters the nucleus, the N- and C-terminus of mNeonGreen meet each other and rebuild its intact 3D structure through fragment complementation and thus generates green fluorescence in the nucleus. Dynamic migration of red fluorescence from mitochondria to the nucleus and generation of green fluorescence in the nucleus indicate mitochondrial membrane damage. Using the MMD-Sensor, mitochondrial membrane damage induced by various reagents, such as uncoupling agents, ATP synthase inhibitors, monovalent cationic carriers, and ROS, in HeLa and 293T cells are directly observed and evaluated.

CK2 Inhibitors Targeting Inside and Outside the Catalytic Box

CK2 is a protein kinase that plays an important role in numerous cellular pathways involved in cell growth, differentiation, proliferation, and death. Consequently, upregulation of CK2 is implicated in many disease types, in particular cancer. As such, CK2 has gained significant attention as a potential therapeutic target in cancer, and over 40 chemical probes targeting CK2 have been developed in the past decade. In this review, we highlighted several chemical probes that target sites outside the conventional ATP-binding site. These chemical probes belong to different classes of molecules, from small molecules to peptides, and possess different mechanisms of action. Many of the chemical probes discussed in this review could serve as promising new candidates for drugs selectively targeting CK2.

An unusual highly sensitive dual-channel bis(salamo)-like chemical probe for recognizing B4O72−, sensing mechanism, theoretical calculations and practical applications

A bis(salamo)-like chemical sensor H3L ((1E,3E)-2-hydroxy-5-methylisophthalaldehyde O,O -di(3-((((E)-(2-hydroxynaphthalen-1-yl)methylene)amino)oxy)propyl) dioxime) was constructed. H3L is capable of recognizing B4O72- in H2O/DMF (1:9, v/v) solution by both fluorescent and colorimetric channels, bright green fluorescence was turned on when B4O72- was added to H3L and changed from colorless to yellow in natural light. The detection limit was 3.21 × 10−8 M. The identification has good anti-interfering ability, quickly responsive time (5 S) and broad pH detecting range (pH = 5–12). The mechanism of action was determined by 1H NMR titration, infrared spectrometry, HRMS spectra and further elucidated by theory calculations. The fluorescence imaging of bean sprouts and spiked recovery assays of actual water samples demonstrated the practical use of sensor H3L for the detection of B4O72−, which is expected to have applications for the detection of B4O72− in plants and the environment.

Abstract 3542: The Chemical Probes Portal: An essential resource providing expert advice on chemical tools for cancer research

Abstract Background: The Chemical Probes Portal (Portal) serves as a vital resource in the realm of cancer research and biomedical science generally - offering expert guidance on high-quality chemical tools, usually protein inhibitors, crucial for studying physiological and pathological processes and validating therapeutic targets. Researchers often grapple with selecting suitable chemical probes, inadvertently utilizing tools ill-suited for their purpose, and not following best practice, thereby contaminating the scientific literature and wasting valuable time and resources. To address this challenge, the Portal (https://www.chemicalprobes.org) was established as a non-profit, independent online platform, meticulously curating, annotating, and scoring the quality of chemical probes and providing associated information and advice. Results: The Portal stands apart as the sole expert-curated public resource evaluating the quality and utility of small-molecule chemical tool compounds for use in cancer research and wider biomedical research. More than 250 experts, comprising scientific leaders in chemical biology, medicinal chemistry, pharmacology, and related fields, contribute their experience and insights to assess featured chemical probes. Since 2021, a progressively updated and enhanced version of the Portal has been operational, housing over 1000 compounds targeting 500+ proteins across diverse families, now including PROTACs and molecular glues. We also flag 254 ‘Unsuitables’, which are compounds that should not be used to interrogate a specific protein target. Additionally, the Portal now offers informative pages, providing advice delineating guidelines for selecting well-validated compounds, including those suitable for rodent studies, necessitating specific pharmacokinetic and pharmacodynamic properties. Best practice use requires employing high-quality chemical probes from more than one distinct chemical class that target the same protein, incorporating an inactive control compound, and following the recommended concentration range - all aimed at mitigating off-target risks. Conclusion: The enhanced Chemical Probes Portal provides a vital platform for researchers to navigate and evaluate chemical probes, easily and effectively. It employs a rigorous expert review to ensure the quality of the probes listed. The resource not only aids high-quality probe selection but also provides advice through an Information Centre, offering guidelines, FAQs, and additional information on probe criteria and use. The continuous expansion and outreach efforts aim to make the Portal an indispensable tool for cancer researchers and the broader biomedical research community. Researchers are encouraged to participate in the Portal's development and contribute to the robustness of chemical probe use in scientific endeavors. Citation Format: Domenico Sanfelice, Albert Antolin, Alisa Crisp, Yi Chen, Paul Brennan, Susanne Müller, Bissan Al-Lazikani, Aled Edwards, Paul Workman. The Chemical Probes Portal: An essential resource providing expert advice on chemical tools for cancer research [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 3542.