The oncogenic transcription factor MYC is a key driver of the development and progression of various types of cancer, but its intrinsically disordered structure and dependence on protein-protein interactions make it a difficult therapeutic target. Proteolysis-targeting chimeras (PROTACs) are bifunctional molecules that can induce the selective degradation of disease-relevant proteins. In this study, we report the synthesis and biological testing of a series of novel MYC-targeted PROTACs derived from the MYC inhibitor EN4. These ligands were conjugated to cereblon (CRBN) or von Hippel-Lindau (VHL) E3 ligase recruiters using different linker architectures and connection sites. The resulting PROTACs were synthesized in high purity and characterized analytically. Cellular evaluation in HEK293T, Panc-1 and HCT-116 cancer cells revealed only moderate reductions in cell viability. Unfortunately, none of the synthesized PROTACs showed detectable MYC degradation at biologically relevant concentrations. Testing the stability of the PROTACs in microsomes showed rapid degradation, which may be a reason for the observed inactivity in cells. These results underscore the significant challenges associated with the targeted protein degradation of intrinsically disordered transcription factors such as MYC. Further studies are necessary to identify additional causes for the lack of MYC degradation and to optimize the chemical structures accordingly.

Background/Objectives: Acute myeloid leukemia (AML) is a hematological malignancy frequently driven by mutations in the FLT3 gene, particularly internal tandem duplications (FLT3-ITD), which contribute to aberrant cell proliferation and resistance to tyrosine kinase inhibitors (FLT3i). The limitations of current FLT3i therapies, including drug resistance, off-target effects, and poor selectivity, necessitate the development of novel therapeutic strategies. Proteolysis-targeting chimeras (PROTACs) represent a promising approach to achieving degradation of oncogenic proteins. Methods: We developed FLT3-targeting PROTACs based on the previously described compound MA49, with a focus on linker modifications to improve degradation efficiency and pharmacokinetic properties. Results: Among these, compounds MA190 and MA191, containing rigid cyclohexyl-piperidine/piperazine linkers, demonstrate superior degradation of FLT3-ITD in MV4-11 AML cells at nanomolar concentrations, achieving >95% reduction in FLT3-ITD levels, outperforming MA49. In addition to improved kinase selectivity, good solubility, and plasma stability, MA190 and MA191 also exhibit excellent metabolic stability, whereas the predecessor PROTAC MA49 was unstable in microsomal assays. In cellular assays, MA190 and MA191 induce potent apoptosis in FLT3-ITD+ AML cells but have minimal effects on cells with wild-type FLT3. Proteomics reveal that MA191 also degrades MAPK14 (p38α), a kinase upregulated in leukemia, in addition to FLT3. Conclusions: Dual targeting of FLT3-ITD and MAPK14 enhances proapoptotic signaling without any cytotoxic effect on normal human HEK293 cells. The co-inhibition using MA191 or a combination of doramapimod (a MAPK14 inhibitor) with a non-degrading FLT3 inhibitor result in greater caspase-3 activation than either treatment alone. This synergistic effect can be a therapeutic advantage, as several oncogenic drivers are switched off simultaneously by MA191.

Targeted protein degradation has emerged as a promising therapeutic strategy, yet rational degrader design remains challenged by the dynamic nature of protein of interest (POI)–E3 ligase interactions. While X-ray crystallography and cryo-EM provide valuable structural snapshots, they are insufficient for capturing the conformational heterogeneity underpinning efficient ubiquitination and degradation. Here, we present a unified computational workflow to systematically generate and evaluate POI–E3 ligase conformational states for CRBN- and VHL-mediated proteolysis-targeting chimeras (PROTACs). The workflow integrates warhead connectivity analysis, conformational clustering, ubiquitination accessibility assessment and molecular dynamics simulations to identify productive POI–E3 ligase geometries. Analysis of experimental structures revealed that PROTAC linkers do not exceed 15 Å, providing a practical attachment-atom distance based filter for docking-derived models. Furthermore, POI–E3 ligase conformations differing by more than 7.5 Å Cα RMSD exhibited distinct ubiquitination profiles, offering quantitative guidance for defining structurally and functionally divergent states. Experimental ternary complexes consistently positioned one or more solvent-exposed POI lysine residues within 50 Å of the E2 catalytic Cys111, establishing a mechanistically grounded criterion for ubiquitination competence. Validation against 34 experimentally determined PROTAC ternary complexes achieved a 97

The ataxia telangiectasia and RAD3-related (ATR) kinase is a central regulator of DNA damage responses. Its pharmacological degradation by proteolysis-targeting chimeras (PROTACs) represents a promising strategy to sensitize cancer cells to DNA-damaging chemotherapy. It is currently unknown if ATR PROTACs can be pharmacologically designed to target a second cancer-relevant kinase. In this study, we report the design, synthesis, and biological evaluation of novel cereblon (CRBN)-based PROTACs for ATR. Structure-guided design and chemical synthesis enabled the development of a focused library of degraders based on selective ATR inhibitors and optimized CRBN ligands. Among the synthesized compounds, Abd141 turns out as the most promising degrader, showing potent ATR degradation in human leukemia cells, without affecting ATM, WEE1 or DNA-PKcs. Consistently, the developed PROTACs prove activity in an in vitro ATR/ATRIP binding assay. Abd141 exhibits high chemical, microsomal, and plasma stability, and no cytotoxicity in non-cancerous HEK293 cells. Proteomic studies and immunoblot experiments identify aurora kinase A (AURKA) as additional target of CRBN-induced proteasomal degradation by Abd141. Dose-degradation studies of Abd141 in the MOLT-4 cell line yielded a DC50 of 97.7 nM for ATR and 6.7 nM for AURKA. These findings disclose Abd141 as effective dual ATR/AURKA degrader and innovative chemo-sensitizer that encourages preclinical development.

Leishmania braziliensis is the primary causative agent of American tegumentary leishmaniasis (ATL), a critical parasitic tropical neglected disease. The chemotherapeutic arsenal has limited efficacy and significant toxic effects that lead to an urgent need to develop new medicines. Using the "drug repurposing" approach, histone-modifying enzyme inhibitors have been the subject of developing new drugs against neglected parasitic diseases. In this work, furamidine, a known diphenyl furan inhibitor of human Protein Arginine Methyltransferase (PRMT), along with a library of 31 developed analogues, was tested for leishmanicidal activity against L. braziliensis in the in vitro infection of macrophage assay. The most active and selective leishmanicidal analogue, BSF2 (EC50 of 0.64 μM (95% CI: 0.56-0.72), SI of 17.36), was further investigated by dual RNA-seq at 0.16 μM BSF2. The dual-transcriptome detected only 10 genes with significant differential expression (FDR ≤10%) in L. braziliensis related to ubiquitination, chromatin remodeling, and peroxisomal membrane transport pathways, following BSF2 treatment of infected macrophages. In addition, BSF2 had a significant effect (FDR ≤5%) on the expression of 577 genes in the infected macrophages, including the downregulation of TNF, IL-17, NF-κB, and Toll-like receptor pathways. This work opens new venues for developing new chemotherapy for leishmaniasis based on BSF2 or derivatives and highlights the dual transcriptome as a valuable phenotypic assay tool to investigate host-parasite interactions for antileishmanial drug discovery.

The goal of this project is to design, synthesize, and test compounds that combine fragments derived from natural products (NPs) for their HIV-1 latency-reversal properties, particularly those that act by histone deacetylase inhibition. A fragment library was created by implementing the Retrosynthetic Combinatorial Analysis Procedure (RECAP) on a collection of NPs isolated from different regions in Africa. The top-scoring docked fragments within the histone deacetylase (HDAC1) binding site were reconstructed to design and synthesize chemical scaffolds that have not been previously described as HDAC inhibitors. Synthesized compounds were then tested for the ability to reverse HIV latency in J-Lat 10.6 cells and/or inhibit cellular histone deacetylases. The synthesized scaffolds include indole-chalcones and aminobenzamides. Of fifty-one synthesized compounds, compound S2-13 was the most active with HIV latency reversal 20.2% ± 6.2% of J-Lat 10.6 cells at 10 μg/mL (25.1 μM), which was comparable to the HIV latency-reversing agent Prostratin. S2-13 also inhibited HDAC activity with a half-maximal inhibitory concentration (IC50) of 17.0 μM. We demonstrate that the use of pseudo-NPs can identify novel chemical scaffolds that can reverse HIV latency and inhibit HDACs in vitro.

The ataxia telangiectasia and RAD3-related (ATR) kinase is a central regulator of DNA damage responses. Its pharmacological degradation by proteolysis-targeting chimeras (PROTACs) represents a promising strategy to sensitize cancer cells to DNA-damaging chemotherapy. It is currently unknown if ATR PROTACs can be pharmacologically designed to target a second cancer-relevant kinase. In this study, we report the design, synthesis, and biological evaluation of novel cereblon (CRBN)-based PROTACs for ATR. Structure-guided design and chemical synthesis enabled the development of a focused library of degraders based on selective ATR inhibitors and optimized CRBN ligands. Among the synthesized compounds, Abd141 turns out as the most promising degrader, showing robust ATR degradation in human leukemia cells, without affecting ATM, WEE1 or DNA-PKcs. Consistently, the developed PROTACs prove activity in an in vitro ATR/ATRIP binding assay. Abd141 exhibits high chemical, microsomal, and plasma stability, and no cytotoxicity in non-cancerous HEK293 cells. Proteomic studies and experiments identify aurora kinase A (AURKA) as additional target of CRBN-induced proteasomal degradation by Abd141. These findings disclose Abd141 as innovative chemo-sensitizer that encourages preclinical development.

Indole-chalcone hybrids are a large group of compounds known for their excellent biological properties against diverse pathogens. The current research describes a rapid synthetic pathway for the synthesis of ten (10) indole-chalcone hybrids 3(a-j), from 1-Boc-3-formylindole (1) and acetophenone derivatives (2), in a one-pot approach. The Boc was deprotected during the reaction and occurred automatically at the end of the reaction. 1H-NMR, 13C-NMR, and MS were used to elucidate the structures of the compounds. Contrary to previous methods for the synthesis of indole-chalcone hybrids, this novel synthetic method, which involves using a Boc-protected indole via microwave-assisted synthesis, is advantageous because it is a one-pot approach making it facile, and rapid.

Indole–chalcone hybrids are a large group of compounds known for their excellent biological properties the help combat diverse pathogens. This study describes a rapid synthetic pathway for the synthesis of ten indole–chalcone hybrids, namely, 3(a–j), from 1-Boc-3-formylindole (1) and acetophenone derivatives (2), in a one-pot approach. This synthesis involved an initial condensation reaction and subsequent deprotection of the Boc group. 1H-NMR, 13C-NMR, and MS were used to elucidate the structures of the final compounds. Contrary to previous methods for the synthesis of indole–chalcone hybrids, this novel synthetic method, which involves using a Boc-protected indole via microwave-assisted synthesis, is advantageous because it is a one-pot approach, making it facile and rapid.

Checkpoint kinase-1 (CHK1) controls DNA replication and repair. Tumor cells depend on CHK1, whose high levels are associated with worse patient prognosis. We define a bona fide proteolysis-targeting-chimera (PROTAC) for CHK1. PROTAC MA203 contains the type I kinase inhibitor rabusertib, which preferentially inhibits activated CHK1, and the cereblon (CRBN) ligand pomalidomide. MA203 accelerates CRBN-dependent proteasomal degradation of CHK1 in solid tumor-derived cells and acute leukemia cells. Chemotherapy-induced DNA replication stress and a consequent activation of CHK1 accelerate this event-driven process which promotes DNA damage and tumor cell apoptosis. Biochemical and cellular target engagement studies confirm the potency and selectivity of MA203. MA203 does not damage healthy differentiated and primitive hematopoietic cells, stromal cells, and retinal epithelial cells. MA203 is superior to its corresponding kinase inhibitor concerning DNA damage, dysregulation of BCL2 proteins, and apoptosis induction. These processes occur independently of the tumor-suppressive transcription factor p53. Elimination of CHK1 protein as structural element, but not its inhibition per se, triggers a proteasomal degradation of key DNA replication and repair proteins. Genetic CHK1 elimination confirms that such newly recognized functions of CHK1 rely on functions beyond its well-known catalytic activity. Thus, kinase-independent functions of CHK1 can be exploited with innovative pharmacological agents.

Background Feline McDonough sarcoma (FMS)-related receptor tyrosine kinase 3 with activating internal tandem duplications (FLT3-ITD) causes acute myeloid leukemia (AML). Targeted protein degraders for FLT3 have evolved as drugs against leukemia. Methods We synthesized and characterized MA191 as novel von Hippel-Lindau (VHL)-based proteolysis targeting chimera (PROTAC) for FLT3. We analyzed protein expression, protein degradation mechanisms, and posttranslational modifications by immunoblot. Selective proteasome modulation, an inactive stereoisomer of MA191, and siRNA confirmed the event-driven degradation of FLT3-ITD. Hematopoietic cell survival and differentiation were determined by flow cytometry using apoptosis and cell surface markers. As models, we used cultured and primary human AML cells, FLT3 inhibitor-resistant AML cells, mature blood cells, and hematopoietic stem cells. We scrutinized the databases DepMap, GEPIA2, Hemap, and HPA to assess FLT3 expression and patient survival. Experiments with Danio rerio larvae verified in vivo anti-leukemic activity of MA191. ANOVA and Bonferroni correction were used for statistics. Results MA191 is a rapid nanomolar apoptosis inducer in AML cells harboring FLT3-ITD (IC50=10.16-11.6 nM; EC50=0.015-0.883 µM). A stereoisomer of MA191 that cannot recruit VHL demonstrates that elimination of FLT3-ITD is superior to its inhibition. MA191 abrogates FLT3 inhibitor resistance from rebound activation of mitogen-activated kinases. Rapid depletion of FLT3-ITD by MA191 (DC50=10 nM) requires VHL, neddylation, and the pro-apoptotic BH3-only protein BIM. Reduction of FLT3-ITD by MA191 precedes apoptosis. This reveals an apoptosis-independent function of BIM on protein stability. Leukemia cells express more FLT3 than healthy cells (n=3675/n=1249) and FLT3 expression is associated with worse AML patient survival (p=0.0099). MA191 does not harm blood cells and bone marrow progenitor cells and does not disturb myeloid blood cell differentiation. In Danio rerio , MA191 halts AML cell proliferation without significant toxicity. Anti-leukemic effects of MA191 are not susceptible to anti-apoptotic effects of human stromal cells and mutations in the tyrosine kinase of FLT3-ITD that confer resistance to selective FLT3 inhibitors. Conclusions these insights and the disclosure of the structure of MA191 provide a framework for an improved design of PROTACs that target mutant FLT3 and are not vulnerable to extrinsic and intrinsic resistance mechanisms. Degradation kinetics appear as determinant of such resistance breakers. ![Figure][1] ### Competing Interest Statement O.H.K. declares the patents WO2019/034538, WO2016020369A1, and WO/2004/027418, and paid advisory work for the BASF Ludwigshafen, Germany. WO2019/034538 (Synthesis, Pharmacology and use of New and Selective FMS-like tyrosine kinase 3 (FLT3) FLT3 Inhibitors) covers substance classes that are discussed in this work. The substances that are covered in these patents are not the same that are shown in the submitted manuscript. The BASF has not influenced our study, and its products are not discussed in the manuscript. Thus, there are no direct competing interests. All other authors declare that they have no conflict of interest. Deutsche Forschungsgemeinschaft, https://ror.org/018mejw64, KR2291/SI868 [1]: pending:yes

Acute myeloid leukemia (AML) is a hematological malignancy frequently driven by mutations in the FLT3 gene, particularly internal tandem duplications (FLT3-ITD), which contribute to aberrant cell proliferation and resistance to tyrosine kinase inhibitors (FLT3i). The limitations of current FLT3i therapies, including drug resistance, off-target effects, and poor selectivity, necessitate the development of novel therapeutic strategies. Proteolysis-targeting chimeras (PROTACs) represent a promising approach to achieve selective degradation of oncogenic proteins. We developed and characterized an optimized series of FLT3-targeting PROTACs based on our previously described compound MA49, with a focus on linker modifications and pharmacophore optimization to improve degradation efficiency and pharmacokinetic properties. Among these, compounds MA190 and MA191,containing rigid cyclohexyl-piperidine/piperazine linkers, demonstrate superior degradation of FLT3-ITD in MV4-11 AML cells at nanomolar concentrations, achieving >95% reduction in FLT3-ITD levels, outperforming MA49. These compounds exhibit good solubility, high chemical and plasma stability, and improved kinase selectivity. In cellular assays, MA190 and MA191 induce potent apoptosis in FLT3-ITD+ AML cells but have minimal effects on cells with wild-type FLT3. Proteomic analysis reveal that MA191 also degrades MAPK14 (p38α), a kinase upregulated in leukemia, in addition to FLT3. Dual targeting of FLT3-ITD and MAPK14 enhances pro-apoptotic signaling. The co-inhibition using MA191 or a combination of doramapimod (a MAPK14 inhibitor) with a non-degrading FLT3 inhibitor results in greater caspase-3 activation than either treatment alone. This synergistic effect underscores the therapeutic advantage of degrading multiple oncogenic drivers simultaneously.

Hypoxia in tumors contributes to chemotherapy resistance, worsened by acidosis driven by carbonic anhydrases (hCA IX and XII). Targeting these enzymes can mitigate acidosis, thus enhancing tumor sensitivity to cytotoxic drugs. Herein, novel 4-(pyrazolyl)benzenesulfonamide ureas (SH7a-t) were developed and evaluated for their inhibitory activity against hCA IX and XII. They showed promising results (hCA IX: KI = 15.9-67.6 nM, hCA XII: KI = 16.7-65.7 nM). Particularly, SH7s demonstrated outstanding activity (KIs = 15.9 nM for hCA IX and 55.2 nM for hCA XII) and minimal off-target kinase inhibition over a panel of 258 kinases. In NCI anticancer screening, SH7s exhibited broad-spectrum activity with an effective growth inhibition full panel GI50 (MG-MID) value of 3.5 μM and a subpanel GI50 (MG-MID) range of 2.4-6.3 μM. Furthermore, SH7s enhanced the efficacy of Taxol and 5-fluorouracil in cotreatment regimens under hypoxic conditions in HCT-116 colorectal cancer cells, indicating its potential as a promising anticancer agent.

Class I histone deacetylases (HDACs) are considered promising targets in current cancer research. To obtain subtype-selective and potent HDAC inhibitors, we used the aminobenzamide scaffold as the zinc-binding group and prepared new derivatives with a pyrazole ring as the linking group. The synthesized compounds were analyzed in vitro using an enzymatic assay against HDAC1, -2, and -3. Compounds 12b, 15b, and 15i were found to be potent HDAC1 inhibitors, also in comparison to the reference compounds entinostat and tacedinaline, with IC50 values of 0.93, 0.22, and 0.68 μM, respectively. The best compounds were measured for their cellular effect and target engagement in acute myeloid leukemia (AML) cells. In addition, we studied the interaction of the compounds with HDAC subtypes using docking and molecular dynamic simulations. In summary, we have developed a new chemotype of HDAC1 inhibitors that can be used for further structure-based optimization.

Class I HDACs are considered promising targets for cancer due to their role in epigenetic modifications. The main challenges in developing a new, potent and non-toxic class I HDAC inhibitor are selectivity and appropriate pharmacokinetics. The PROTAC technique (Proteolysis Targeting Chimera) is a new method in drug development for the production of active substances that can degrade a protein of interest (POI) instead of inhibiting it. This technique will open the era to produce selective and potent drugs with a high margin of safety. Previously, we reported different inhibitors targeting class I HDACs functionalized with aminobenzamide or hydroxamate groups. In the current research work, we will employ PROTAC technique to develop class I HDAC degraders based on our previously reported inhibitors. We synthesized two series of aminobenzamide-based PROTACs and hydroxamate-based PROTACs and tested them in vitro against class I HDACs. To ensure their degradation, all of them were screened against HDAC2 as representative example of class I. The best candidates were evaluated at different concentrations at various HDAC subtypes. This resulted in the PROTAC (32a) (HI31.1) that degrades HDAC8 with a DC50 of 8.9 nM with a proper margin of selectivity against other isozymes. Moreover, PROTAC 32a is able to degrade HDAC6 with DC50 = 14.3 nM. Apoptotic study on leukemic cells (MV-4-11) displayed more than 50 % apoptosis took place at 100 nM. PROTAC 32a (HI31.1) showed a good margin of safety against normal cell line and proper chemical stability.

The Ataxia telangiectasia and RAD3-related (ATR) kinase is a key regulator of DNA replication stress responses and DNA-damage checkpoints. Several potent and selective ATR inhibitors are reported and four of them are currently in clinical trials in combination with radio- or chemotherapy. Based on the idea of degrading target proteins rather than inhibiting them, we designed, synthesized and biologically characterized a library of ATR-targeted proteolysis targeting chimera (PROTACs). Among the synthesized compounds, the lenalidomide-based PROTAC 42i was the most promising. In pancreatic and cervix cancer cells cancer cells (MIA PaCa-2), it reduced ATR to 40% of the levels in untreated cells. 42i selectively degraded ATR through the proteasome, dependent on the E3 ubiquitin ligase component cereblon, and without affecting the associated kinases ATM and DNA-PKcs. 42i may be a promising candidate for further optimization and biological characterization in various cancer cells.

Internal tandem duplications in the FMS-like tyrosine kinase-3 (FLT3-ITD) are common mutations in acute myeloid leukemia (AML). Proteolysis-targeting chimeras (PROTACs) that induce proteasomal degradation of mutated FLT3 emerge as innovative pharmacological approach. Molecular mechanisms that control targeted proteolysis beyond the ubiquitin-proteasome-system are undefined and PROTACs are the only known type of FLT3 degraders. We report that the von-Hippel-Lindau ubiquitin-ligase based FLT3 PROTAC MA49 (melotinib-49) and the FLT3 hydrophobic tagging molecule MA50 (halotinib-50) reduce endoplasmic reticulum-associated, oncogenic FLT3-ITD but spare FLT3. Nanomolar doses of MA49 and MA50 induce apoptosis of human leukemic cell lines and primary AML blasts with FLT3-ITD (p < 0.05-0.0001), but not of primary hematopoietic stem cells and differentiated immune cells, FLT3 wild-type cells, retinal cells, and c-KIT-dependent cells. In vivo activity of MA49 against FLT3-ITD-positive leukemia cells is verified in a Danio rerio model. The degrader-induced loss of FLT3-ITD involves the pro-apoptotic BH3-only protein BIM and a previously unidentified degrader-induced depletion of protein-folding chaperones. The expression levels of HSP90 and HSP110 correlate with reduced AML patient survival (p < 0.1) and HSP90, HSP110, and BIM are linked to the expression of FLT3 in primary AML cells (p < 0.01). HSP90 suppresses degrader-induced FLT3-ITD elimination and thereby establishes a mechanistically defined feed-back circuit.

Histone deacetylases are considered promising epigenetic targets for chemical protein degradation due to their diverse roles in physiological cellular functions and in the diseased state. Proteolysis-targeting chimeras (PROTACs) are bifunctional molecules that hijack the cell's ubiquitin-proteasome system (UPS). One of the promising targets for this approach is histone deacetylase 6 (HDAC6), which is highly expressed in several types of cancers and is linked to the aggressiveness of tumors. In the present work, we describe the synthesis of HDAC6 targeting PROTACs based on previously synthesized benzohydroxamates selectively inhibiting HDAC6 and how to assess their activities in different biochemical in vitro assays and in cellular assays. HDAC inhibition was determined using fluorometric assays, while the degradation ability of the PROTACs was assessed using western blot analysis.

Class I histone deacetylases (HDACs) are key regulators of cell proliferation and they are frequently dysregulated in cancer cells. We report here the synthesis of a novel series of class-I selective HDAC inhibitors (HDACi) containing a 2-aminobenzamide moiety as a zinc-binding group connected with a central (piperazin-1-yl)pyrazine or (piperazin-1-yl)pyrimidine moiety. Some of the compounds were additionally substituted with an aromatic capping group. Compounds were tested in vitro against human HDAC1, 2, 3, and 8 enzymes and compared to reference class I HDACi (Entinostat (MS-275), Mocetinostat, CI994 and RGFP-966). The most promising compounds were found to be highly selective against HDAC1, 2 and 3 over the remaining HDAC subtypes from other classes. Molecular docking studies and MD simulations were performed to rationalize the in vitro data and to deduce a complete structure activity relationship (SAR) analysis of this novel series of class-I HDACi. The most potent compounds, including 19f, which blocks HDAC1, HDAC2, and HDAC3, as well as the selective HDAC1/HDAC2 inhibitors 21a and 29b, were selected for further cellular testing against human acute myeloid leukemia (AML) and erythroleukemic cancer (HEL) cells, taking into consideration their low toxicity against human embryonic HEK293 cells. We found that 19f is superior to the clinically tested class-I HDACi Entinostat (MS-275). Thus, 19f is a new and specific HDACi with the potential to eliminate blood cancer cells of various origins.

Histone deacetylases (HDACs) are epigenetic regulators and additionally control the activity of non-histone substrates. We recently demonstrated that inhibition of HDAC8 overexpressed in various of cancers reduces hepatocellular carcinoma tumorigenicity in a T cell-dependent manner. Here, we present alkylated hydrazide-based class I HDAC inhibitors in which the n-hexyl side chain attached to the hydrazide moiety shows HDAC8 selectivity in vitro. Analysis of the mode of inhibition of the most promising compound 7d against HDAC8 revealed a substrate-competitive binding mode. 7d marked induced acetylation of the HDAC8 substrates H3K27 and SMC3 but not tubulin in CD4+ T lymphocytes, and significantly upregulated gene expressions for memory and effector functions. Furthermore, intraperitoneal injection of 7d (10 mg/kg) in C57BL/6 mice increased interleukin-2 expression in CD4+ T cells and CD8+ T cell proportion with no apparent toxicity. This study expands a novel chemotype of HDAC8 inhibitors with T cell modulatory properties for future therapeutic applications.