Discovery of a novel dipeptidyl boronic acid proteasome inhibitor for the treatment of multiple myeloma and triple-negative breast cancer

Proteasome inhibitors FHND6091 enhance the ability of NK cells to kill tumor cells through multiple mechanisms

The immune system has a strong connection to tumors. When a tumor cell is recognized as an abnormal cell by the immune system, the immune system may initiate an immune response to kill the tumor cell. In this study, RNA sequencing was performed on multiple myeloma (MM) cells treated with the proteasome inhibitor FHND6091. The transcriptional changes induced by FHND6091 in RPMI8226 cells aligned notably with immune response activation and results indicated upregulation of cGAS-STING pathway-related genes in the FHND6091-treated group. In vivo and in vitro experiments had demonstrated that FHND6091 stimulated the immunoreaction of MM cells via activation of the cyclic guanosine monophosphate-adenosine synthase/stimulator of interferon genes (cGAS-STING) pathway. This activation resulted in the generation of type-I interferons and the mobilization of natural killer (NK) cells. Notably, FHND6091 upregulated the levels of calreticulin and the protein ligands UL16-binding protein 2/5/6, MHC class I chain-related A (MICA), and MICB on the surface of MM cells. Subsequently, upon engaging with the surface activation receptors of NK cells, these ligands triggered NK cell activation, leading to the subsequent elimination of tumor cells. Thus, our findings elucidated the mechanism whereby FHND6091 exerted its immunotherapeutic activity as a STING agonist, enhancing the killing ability of NK cells against tumor cells.

The Rise of Boron-Containing Compounds: Advancements in Synthesis, Medicinal Chemistry, and Emerging Pharmacology

Boron-containing compounds (BCC) have emerged as important pharmacophores. To date, five BCC drugs (including boronic acids and boroles) have been approved by the FDA for the treatment of cancer, infections, and atopic dermatitis, while some natural BCC are included in dietary supplements. Boron's Lewis acidity facilitates a mechanism of action via formation of reversible covalent bonds within the active site of target proteins. Boron has also been employed in the development of fluorophores, such as BODIPY for imaging, and in carboranes that are potential neutron capture therapy agents as well as novel agents in diagnostics and therapy. The utility of natural and synthetic BCC has become multifaceted, and the breadth of their applications continues to expand. This review covers the many uses and targets of boron in medicinal chemistry.

Conjugated Polyelectrolyte Containing a High Density of Pendant Phenylboronic Acid Groups for Dopamine Detection

A fluorescent sensing system based on a conjugated polyelectrolyte was constructed to detect dopamine (DA) in complex samples. The conjugated polymer PFPE-PBA with poly[fluorenyl-alt-p-phenyleneethynylene] (PFPE) as the backbone and carrying four pendant phenylboronic acid (PBA) groups in each repeat unit was synthesized. PFPE-PBA was found to have good solubility in polar solvents. After optimization, glycine-NaOH at pH 10 was selected as the buffer, and the solvent composition of the system was set to methanol/water (9/1 by volume). Titration experiments showed that DA could effectively quench the fluorescence of the polymer solution with a response time within 60 s and a limit of detection of 23 nM. Polyols, cations, and other possible interfering substances do not significantly affect the fluorescence of the polymer, thereby allowing for the highly selective detection of DA. Furthermore, quantitative determination of DA in spiked serum and artificial urine samples was successfully demonstrated, with recoveries ranging from 96.7 to 104%. Preliminary mechanism studies suggest that the pedant PBAs capture DA via reaction with the catechol group, and the fluorescence quenching is most likely due to the photoinduced electron transfer between the aromatic part of DA and the conjugated backbone. This study provides a general strategy for the future design of conjugated polyelectrolyte-based sensing systems.

Evaluation of the NRF1-proteasome axis as a therapeutic target in breast cancer

Proteasomes are multi-subunit complexes that specialize in protein degradation. Cancer cells exhibit a heightened dependence on proteasome activity, presumably to support their enhanced proliferation and other cancer-related characteristics. Here, a systematic analysis of TCGA breast cancer datasets revealed that proteasome subunit transcript levels are elevated in all intrinsic subtypes (luminal, HER2-enriched, and basal-like/triple-negative) when compared to normal breast tissue. Although these observations suggest a pan-breast cancer utility for proteasome inhibitors, our further experiments with breast cancer cell lines and patient-derived xenografts (PDX) pointed to triple-negative breast cancer (TNBC) as the most sensitive subtype to proteasome inhibition. Finally, using TNBC cells, we extended our studies to in vivo xenograft experiments. Our previous work has firmly established a cytoprotective role for the transcription factor NRF1 via its ability to upregulate proteasome genes in response to proteasome inhibition. In further support of this notion, we show here that NRF1 depletion significantly reduced tumor burden in an MDA-MB-231 TNBC xenograft mouse model treated with carfilzomib. Taken together, our results point to TNBC as a particularly vulnerable breast cancer subtype to proteasome inhibition and provide a proof-of-principle for targeting NRF1 as a viable means to increase the efficacy of proteasome inhibitors in TNBC tumors.

New trends in synthetic drugs and natural products targeting 20S proteasomes in cancers

Cancer is a global health challenge that remains to be a field of extensive research aiming to find new anticancer therapeutics. The 20S proteasome complex is one of the targets of anticancerdrugs, as it is correlated with several cancer types. Herein, we aim to discuss the 20S proteasome subunits and investigatethe currently studied proteasome inhibitors targeting the catalytically active proteasome subunits. In this review, we summarize the proteindegradation mechanism of the 20S proteasome complex and compareit with the 26S proteasome complex. Afterwards, the localization of the 20S proteasome is summarized as well as its use as a diagnosticandprognostic marker. The FDA-approved proteasome inhibitors (PIs) under clinical trials are summarized and their current limited use in solid tumors is also reviewed in addition to the expression of theβ5 subunit in differentcell lines. The review discusses in-silico analysis of the active subunit of the 20S proteasome complex. For development of new proteasome inhibitor drugs, the natural products inhibiting the 20S proteasome are summarized, as well as novel methodologies and challenges for the natural product discovery and current information about the biosynthetic gene clusters encoding them. We herein briefly summarize some resistancemechanismsto the proteasomeinhibitors. Additionally, we focus on the three main classes of proteasome inhibitors: 1] boronic acid, 2] beta-lactone and 3] epoxide inhibitor classes, as well as other PI classes, and their IC₅₀ values and their structure-activity relationship (SAR). Lastly,we summarize several future prospects of developing new proteasome inhibitors towards the treatment of tumors, especially solid tumors.

KPT-330 and Y219 exert a synergistic antitumor effect in triple-negative breast cancer through inhibiting NF-κB signaling

Triple-negative breast cancer (TNBC) is an aggressive breast cancer subtype, which has poor prognosis due to the lack of effective targeted drugs. KPT-330, an inhibitor of the nuclear export protein CRM-1, has been widely used in clinical medicine. Y219, a novel proteasome inhibitor designed by our group, shows superior efficacy, reduced toxicity, and reduced off-target effects as compared to the proteasome inhibitor bortezomib. In this study, we investigated the synergistic effect of KPT-330 and Y219 against TNBC cells, as well as the underlying mechanisms. We report that combination treatment with KPT-330 and Y219 synergistically inhibited the viability of TNBC cells in vitro and in vivo. Further analysis revealed that the combined use of KPT-330 and Y219 induced G2-M phase arrest and apoptosis in TNBC cells, and attenuated nuclear factor kappa B (NF-κB) signaling by facilitating nuclear localization of IκB-α. Collectively, these results suggest that the combined use of KPT-330 and Y219 may be an effective therapeutic strategy for the treatment of TNBC.

Design, synthesis, and biological evaluation of some novel naphthoquinone-glycine/β-alanine anilide derivatives as noncovalent proteasome inhibitors

A series of novel noncovalent glycine/β-alanine anilide derivatives possessing 2-chloronaphthoquinone structure as a pharmacophoric unit were designed, synthesized, and evaluated for their antiproliferative and antiproteasomal activities against MCF-7 cell line, in vitro. According to biological activity results, all the target compounds showed antiproliferative activity in the range of IC₅₀  = 7.10 ± 0.10-41.08 ± 0.14 μM and most of them exhibited inhibitory efficacy with varying ratios against the three catalytic subunits (β1, β2, and β5) presenting caspase-like (C-L), trypsin-like (T-L) and chymotrypsin-like (ChT-L) activities of proteasome. The antiproteasomal activity evaluations revealed that compounds preferentially inhibited the β5 subunit compared with β1 and β2 subunits of the proteasome. Among the compounds, compounds 7 and 9 showed the highest antiproliferative activity with an IC₅₀ value of 7.10 ± 0.10 and 7.43 ± 0.25 μM, respectively. Additionally, compound 7 displayed comparable potency to PI-083 lead compound in terms of β5 antiproteasomal activity with an inhibition percentage of 34.67 at 10 μM. This compound showed an IC₅₀ value of 32.30 ± 0.45 μM against β5 subunit. Furthermore, molecular modeling studies of the most active compound 7 revealed key interactions with β5 subunit. The results suggest that this class of compounds may be beneficial for the development of new potent proteasome inhibitors.

Preclinical Pharmacokinetics, Tissue Distribution and in vitro Metabolism of FHND6091, a Novel Oral Proteasome Inhibitor

Introduction

Methods

Results

Conclusion

Boron-Containing heterocycles as promising pharmacological agents

The incorporation of the "magic" boron atom has been established as an important new strategy in the field of medicinal chemistry as boron compounds have been shown to form various bonds with their biological targets. Currently, a number of boron-based drugs (e.g. bortezomib, crisaborole, and tavaborole) have been FDA approved and are in the clinic, and several other boron-containing compounds are in clinical trials. Boron-based heterocycles have an incredible potential in the ongoing quest for new therapeutic agents owing to their plethora of biological activities and useful pharmacokinetic profiles. The present perspective is intended to review the pharmacological applications of boron-based heterocycles that have been published. We have classified these compounds into groups exhibiting shared pharmacological activities and discussed their corresponding biological targets focusing mainly on the most potent therapeutic compounds.

Borax Pentahydrate and Disodium Pentaborate Decahydrate Are Candidates as Anti-leukemic Drug Components by Inducing Apoptosis and Changing Bax/Bcl-2 Ratio in HL-60 Cell Line

Acute myeloid leukemia (AML) is the most common form of acute leukemia and has the lowest 5-year survival rates. Current treatment strategies do not meet the expectations also. Therefore, there is a need to improve therapeutic approaches still. Boron, which is a natural trace element in human diet, is gaining attention with its important roles in cellular processes for the development of new anti-cancer drug candidates. For instance, bortezomib, a dipeptidyl boronic acid, has encouraging results in the treatment of multiple myeloma and mantle cell lymphoma. However, severe toxic effects and resistance development are the limitations to its application for AML treatment. Hence, the development of alternative boron-derived anti-AML agents is unmet need. Therefore, we aimed to evaluate anti-leukemic effect of two promising boron compounds, borax pentahydrate (BP) and disodium pentaborate decahydrate (DPD), and comparison of each other in terms of the capacity to trigger apoptosis on acute promyelocytic leukemia cells (HL-60). Cell viability was assessed by MTT assay. Apoptotic effects of the boron compounds on HL-60 cells were evaluated by annexin V/propidium iodide dyes and caspase 3/7 activity assay by flow cytometry. In addition, Bax/Bcl-2 and cleaved PARP levels were detected by western blotting. Although BP showed greater apoptosis-inducing capacity, we observed that both DPD (6 mM) and BP (24 mM) treatment showed anti-leukemic effect by triggering apoptotic pathway through increasing Bax/Bcl-2 ratio for the first time. Our study suggests that BP and DPD are the promising candidates for anti-AML drug development research, which may be confirmed by further wide-spectrum studies.

The Boron Advantage: The Evolution and Diversification of Boron’s Applications in Medicinal Chemistry

In this review, the history of boron’s early use in drugs, and the history of the use of boron functional groups in medicinal chemistry applications are discussed. This includes diazaborines, boronic acids, benzoxaboroles, boron clusters, and carboranes. Furthermore, critical developments from these functional groups are highlighted along with recent developments, which exemplify potential prospects. Lastly, the application of boron in the form of a prodrug, softdrug, and as a nanocarrier are discussed to showcase boron’s emergence into new and exciting fields. Overall, we emphasize the evolution of organoboron therapeutic agents as privileged structures in medicinal chemistry and outline the impact that boron has had on drug discovery and development.

Diversity of effects induced by boron-containing compounds on immune response cells and on antibodies in basal state

BACKGROUND

It has been reported that boron induces changes in the immune response, including in inflammatory processes. Recently, the effect of boric acid has been documented on the differentiation of lymphocyte clusters in mice and rats. However, the differences among boron-containing compounds (BCC) have been poorly explored.

METHODS

In this study, we analyzed the effects after oral administration of boric acid (BOR), methylboronic (MET), 3-thyenylboronic (3TB), 4-hydroxymethyl-phenylboronic (4MP) and 4-methanesulfonyl-phenylboronic (4SP) acids on the populations of lymphocytes from spleen and Peyer's patch (PP) as well as on antibodies. Groups of six male BALB/c were orally treated with 4.6 mg/kg of body weight with BOR, MET, 3TB, 4MP, and 4SP/daily for 10 days or vehicle (VEH) as a control group. After euthanasia, the spleen and small intestine were dissected. We conducted flow cytometry assays to assess B, CD3⁺ T, CD4⁺ T, and CD8⁺ T cells. Levels of IgG and IgM in serum, and IgA in intestinal fluid samples were analyzed by enzyme immunoassay.

RESULTS

In particular, we observed the effects of the administration of boronic acids on the number of lymphocytes; these changes were more notable in spleen than in PP. We found different profiles for each boron-containing compound, that is BOR induced an increase in the percentage of CD8⁺ T and CD19⁺/IgA⁺ cells in spleen, but a decrease in CD8⁺ T and B220⁺/CD19⁺ cells in PP. Meanwhile MET induced a decrease of CD4⁺ T in spleen, but induced an increase of CD4⁺ T cells and a decrease in the number of CD8⁺ T cells in PP. Boronic acids with an aromatic ring moiety induced changes in serum immunoglobulins levels, while 3TB acid induced a notable increase in S-IgA.

CONCLUSIONS

Effects in lymphocyte populations and antibodies are different for each tested compound. These results highlight the establishment of the necessary structure-activity relationship for BCC as immunomodulatory drugs. This is relevant in the biomedical field due to their attractiveness for selecting compounds to develop therapeutic tools.

Merging the Versatile Functionalities of Boronic Acid with Peptides

Peptides inherently feature the favorable properties of being easily synthesized, water-soluble, biocompatible, and typically non-toxic. Thus, boronic acid has been widely integrated with peptides with the goal of discovering peptide ligands with novel biological activities, and this effort has led to broad applications. Taking the integration between boronic acid and peptide as a starting point, we provide an overview of the latest research advances and highlight the versatile and robust functionalities of boronic acid. In this review, we summarize the diverse applications of peptide boronic acids in medicinal chemistry and chemical biology, including the identification of covalent reversible enzyme inhibitors, recognition, and detection of glycans on proteins or cancer cell surface, delivery of siRNAs, development of pH responsive devices, and recognition of RNA or bacterial surfaces. Additionally, we discuss boronic acid-mediated peptide cyclization and peptide modifications, as well as the facile chemical synthesis of peptide boronic acids, which paved the way for developing a growing number of peptide boronic acids.

Discovery of novel tripeptide propylene oxide proteasome inhibitors for the treatment of multiple myeloma

The ubiquitin proteasome pathway (UPP) plays a critical role in the maintenance of cell homeostasis and the development of diseases, such as cancer and neurodegenerative disease. A series of novel tripeptide propylene oxide compounds as proteasome inhibitors were designed, synthesized and biologically investigated in this manuscript. The enzymatic activities of final compounds against 20S human proteasome were investigated and structure-activity relationship (SAR) was summarized. Some potent compounds were further evaluated to inhibit the proliferation of multiple myeloma (MM) cancer cell lines RPMI8226 and U266B. The results showed that some compounds were active against MM cancer cell lines with IC₅₀ values of less than 50 nM. The microsomal metabolic stabilities in human, rat and mice species were carried out and the results showed that compounds 30 and 31 were stable enough to be in vivo investigated. The in vivo pharmacokinetic results showed that compounds 30 and 31 had acceptable biological parameters for both ig and iv administrations. In vivo antitumor activities of compounds 30 and 31 with the doses of 100 mg/kg and 50 mg/kg BIW were performed by using RPMI8226 xenograft nude mouse model. Toxicities of compounds 30 and 31 were not observed during the experiment and dose dependent effect was obvious and the tumor volume was greatly inhibited.

Progress in the medicinal chemistry of organoboron compounds

The review aims to draw attention to the latest advances in the organoboron chemistry and therapeutic use of organoboron compounds. The synthetic strategies towards boron-containing compounds with proven in vitro and/or in vivo biological activities, including derivatives of boronic acids, benzoxaboroles, benzoxaborines and benzodiazaborines, are summarized. Approaches to the synthesis of hybrid structures containing an organoboron moiety as one of the pharmacophores are considered, and the effect of this modification on the pharmacological activity of the initial molecules is analyzed. On the basis of analysis of the published data, the most promising areas of research in the field of organoboron compounds are identified, including the latest methods of synthesis, modification and design of effective therapeutic agents.

The bibliography includes 246 references.

A theoretical and experimental case study of the hydrogen bonding predilection of S-methylcysteine

S-containing amino acids can lead to two types of local NH···S interactions which bridge backbone NH sites to the side chain to form either intra- or inter-residue H-bonds. The present work reports on the conformational preferences of S-methyl-L-cysteine, Cys(Me), using a variety of investigating tools, ranging from quantum chemistry simulations, gas-phase UV and IR laser spectroscopy, and solution state IR and NMR spectroscopies, on model compounds comprising one or two Cys(Me) residues. We demonstrate that in gas phase and in low polarity solution, the C- and N-capped model compound for one Cys(Me) residue adopts a preferred C5-C6γ conformation which combines an intra-residue N-H···O=C backbone interaction (C5) and an inter-residue N-H···S interaction implicating the side-chain sulfur atom (C6γ). In contrast, the dominant conformation of the C- and N-capped model compound featuring two consecutive Cys(Me) residues is a regular type I β-turn. This structure is incompatible with concomitant C6γ interactions, which are no longer in evidence. Instead, C5γ interactions occur, that are fully consistent with the turn geometry and additionally stabilize the structure. Comparison with the thietane amino acid Attc, which exhibits a rigid cyclic side chain, pinpoints the significance of side chain flexibility for the specific conformational behavior of Cys(Me).

From cow manure to bioactive carbon dots: a light-up probe for bioimaging investigations, glucose detection and potential immunotherapy agent for melanoma skin cancer

Bioactive carbon dots (C-dots) with ca. 4 nm were successfully produced with singular photophysical properties, low-toxicity and interesting immunological response. The optical properties of the C-dots were investigated and the "light-up" behaviour enabled them to be explored in glucose detection and bioimaging experiments (mitochondrial selective probe). C-dots were not selective to the tumour region and several fluorescent spots were visualized spread on animal bodies. The histology investigations showed that cancer-bearing mice treated with C-dots presented a large number of regions with necrosis and inflammatory infiltrates, which were not identified for cancer-bearing mice without the treatment. These results suggested that C-dots have the potential to be explored as an immune therapy agent for melanoma skin cancer.

In vitro and in vivo efficacy of the novel oral proteasome inhibitor NNU546 in multiple myeloma

Proteasome inhibition demonstrates highly effective impact on multiple myeloma (MM) treatment. Here, we aimed to examine anti-tumor efficiency and underlying mechanisms of a novel well tolerated orally applicable proteasome inhibitor NNU546 and its hydrolyzed pharmacologically active form NNU219. NNU219 showed more selective inhibition to proteasome catalytic subunits and less off-target effect than bortezomib ex vivo. Moreover, intravenous and oral administration of either NNU219 or NNU546 led to more sustained pharmacodynamic inhibitions of proteasome activities compared with bortezomib. Importantly, NNU219 exhibited potential anti-MM activity in both MM cell lines and primary samples in vitro. The anti-MM activity of NNU219 was associated with induction of G2/M-phase arrest and apoptosis via activation of the caspase cascade and endoplasmic reticulum stress response. Significant growth-inhibitory effects of NNU219 and NNU546 were observed in 3 different human MM xenograft mouse models. Furthermore, such observation was even found in the presence of a bone marrow microenvironment. Taken together, these findings provided the basis for clinical trial of NNU546 to determine its potential as a candidate for MM treatment.

Fluorescent Probes with Unnatural Amino Acids to Monitor Proteasome Activity in Real-Time

The proteasome is an essential protein complex that, when dysregulated, can result in various diseases in eukaryotic cells. As such, understanding the enzymatic activity of the proteasome and what can alter it is crucial to elucidating its roles in these diseases. This can be done effectively by using activity-based fluorescent substrate probes, of which there are many commercially available that target the individual protease-like subunits in the 20S CP of the proteasome. Unfortunately, these probes have not displayed appropriate characteristics for their use in live cell-based assays. In the work presented here, we have developed a set of probes which have shown improved fluorescence properties and selectivity toward the proteasome compared to other cellular proteases. By including unnatural amino acids, we have found probes which can be utilized in various applications, including monitoring the effects of small molecule stimulators of the proteasome in live cells and comparing the relative proteasome activity across different cancer cell types. In future studies, we expect the fluorescent probes presented here will serve as tools to support the discovery and characterization of small molecule modulators of proteasome activity.

PSMD12 promotes breast cancer growth via inhibiting the expression of pro-apoptotic genes

Breast cancer (BC), the most frequent cancer in women worldwide, is extremely heterogeneous. For effective and precise treatment and to cope with drug resistance in BC, we need to find more therapeutic molecular targets. In this study, we found that the Proteasome 26S Subunit, Non-ATPase 12 (PSMD12) was upregulated in BC samples, its expression was heterogeneous among different cell lines, and high levels of PSMD12 were related to poor prognosis of BC patients. Notably, the expression of PSMD12 increased in the nucleus. Cytological experiments revealed that PSMD12 knockdown inhibited cell growth and migration, and a genome-wide CRISPR-Cas9 knockout (GeCKO) screen also confirmed that PSMD12 is a crucial gene for the growth of BC cells. Flow cytometry showed that cell apoptosis increased in the PSMD12 knockdown, and RNA-seq indicated that the apoptosis pathway was activated, and the TXNIP, GADD45A, GADD45B, RHOB, and CDKN1A pro-apoptotic genes were highly expressed, a result that was validated by RT-qPCR and Western blot. Furthermore, restoration of PSMD12 expression decreased the expression of pro-apoptotic genes. A tumor-bearing mice assay demonstrated that BC growth was arrested by reduced PSMD12 levels in vivo. Taken together, PSMD12, a subunit of 19S regulator of 26S proteasome, was identified as a potential prognostic and therapeutic molecular target for BC, which provides a new insight for developing anticancer drugs that promote apoptosis based on the targeting of the 26S proteasome complex.

Boronic acid sensors with double recognition sites: a review

Boronic acids reversibly and covalently bind to Lewis bases and polyols, which facilitated the development of a large number of chemical sensors to recognize carbohydrates, catecholamines, ions, hydrogen peroxide, and so on. However, as the binding mechanism of boronic acids and analytes is not very clear, it is still a challenge to discover sensors with high affinity and selectivity. In this review, boronic acid sensors with two recognition sites, including diboronic acid sensors, and monoboronic acid sensors having another group or binding moiety, are summarized. Owing to double recognition sites working synergistically, the binding affinity and selectivity of sensors can be improved significantly. This review may help researchers to sort out the binding rules and develop ideal boronic acid-based sensors.

Boron in drug design: Recent advances in the development of new therapeutic agents

Advances in the field of boron chemistry have expanded the application of this element in Medicinal Chemistry. Boron-containing compounds represent a new class for medicinal chemists to use in their drug designs. Bortezomib (Velcade^®), a dipeptide boronic acid approved by the FDA in 2003 for treatment of multiple myeloma, paved the way for the discovery of new boron-containing compounds. After its approval, two other boron-containing compounds have been approved, tavaborole (Kerydin^®) for the treatment of onychomicosis and crisaborole (Eucrisa^®) for the treatment of mild to moderate atopic dermatitis. A number of boron-containing compounds have been described and evaluated for a plethora of therapeutic applications. The present review is intended to highlight the recent advances related to boron-containing compounds and their therapeutic applications. Here, we focused only in those most biologically active compounds with proven in vitro and/or in vivo efficacy in the therapeutic area published in the last years.