Chulho Lee

Structure and property based design, synthesis and biological evaluation of γ-lactam based HDAC inhibitors.

Histone deacetylases (HDACs) are involved in post-translational modification and gene expression. Cancer cells recruited amounts of HDACs for their survival by epi-genetic down regulation of tumor suppressor genes. HDACs have been the promising targets for treatment of cancer, and many HDAC inhibitors have been investigated nowadays. In previous study, we synthesized δ-lactam core HDAC inhibitors which showed potent HDAC inhibitory activities as well as cancer cell growth inhibitory activities. Through QSAR study of the δ-lactam based inhibitors, the smaller core is suggested as more active than larger one because it fits better in narrow hydrophobic tunnel of the active pocket of HDAC enzyme. The smaller γ-lactam core HDAC inhibitors were designed and synthesized for biological and property optimization. Phenyl, naphthyl and thiophenyl groups were introduced as the cap groups. Hydrophobic and bulky cap groups increase potency of HDAC inhibition because of hydrophobic interaction between HDAC and inhibitors. In overall, γ-lactam based HDAC inhibitors showed more potent than δ-lactam analogues.

Property-based optimization of hydroxamate-based γ-lactam HDAC inhibitors to improve their metabolic stability and pharmacokinetic profiles.

Hydroxamate-based HDAC inhibitors have promising anticancer activities but metabolic instability and poor pharmacokinetics leading to poor in vivo results. QSAR and PK studies of HDAC inhibitors showed that a γ-lactam core and a modified cap group, including halo, alkyl, and alkoxy groups with various carbon chain linkers, improved HDAC inhibition and metabolic stability. The biological properties of the γ-lactam HDAC inhibitors were evaluated; the compound designated 8f had potent anticancer activity and high oral bioavailability.

Discovery of thienopyrimidine-based FLT3 inhibitors from the structural modification of known IKKβ inhibitors

Inactivation of the NF-κB signaling pathway by inhibition of IKKβ is a well-known approach to treat inflammatory diseases such as rheumatoid arthritis and cancer. Thienopyrimidine-based analogues were designed through modification of the known IKKβ inhibitor, SPC-839, and then biologically evaluated. The resulting analogues had good inhibitory activity against both nitric oxide and TNF-α, which are well-known inflammatory responses generated by activated NF-κB. However, no inhibitory activity against IKKβ was observed with these compounds. The thienopyrimidine-based analogues were subsequently screened for a target kinase, and FLT3, which is a potential target for acute myeloid leukemia (AML), was identified. Thienopyrimidine-based FLT3 inhibitors showed good inhibition profiles against FLT3 under 1μM. Overall, these compounds represent a promising family of inhibitors for future development of a treatment for AML.

Synthesis and biological evaluation of novel thieno(2,3-d)pyrimidine- based FLT3 inhibitors as anti-leukemic agents

The most common mutations in acute myeloid leukemia (AML) are those that cause the activation of FMS-like tyrosine kinase 3 (FLT3). Therefore, FLT3 is regarded as a potential target for the treatment of AML. A novel series of thieno[2,3-d]pyrimidine-based analogs was designed and synthesized as FLT3 inhibitors. All synthesized compounds were assayed for the tyrosine kinase activity of FLT3 and growth inhibitory activity in four human leukemia cell lines (THP1, MV4-11, K562, and HL-60). Among these compounds, compound 17a, which possesses relatively short and simple substituents at the C6 position of thieno[2,3-d]pyrimidine, emerged as the most promising anti-leukemic agent. Compound 17a exhibited potent inhibition of FLT3-positive leukemic cell growth and of the FLT3 D835Y kinase; such inhibition is required for the successful treatment of AML. The data supports the further investigation of this class of compounds as potential anti-leukemic agents.

Discovery of Pyridone‐Based Histone Deacetylase Inhibitors: Approaches for Metabolic Stability

Histone deacetylases (HDACs) are important enzymes in epigenetic regulation and are therapeutic targets for cancer. Most zinc‐dependent HDACs induce proliferation, dedifferentiation, and anti‐apoptotic effects in cancer cells. We designed and synthesized a new series of pyridone‐based HDAC inhibitors that have a pyridone ring in the core structure and a conjugated system with an olefin connecting the hydroxamic acid moiety. Consequently, most of the selected pyridone‐based HDAC inhibitors showed similar or higher inhibition profiles in addition to remarkable metabolic stability against hydrolysis relative to the corresponding lactam‐based HDAC inhibitors. Furthermore, the selectivity of the novel pyridine‐based compounds was evaluated across all of the HDAC isoforms. One of these compounds, (E)‐N‐hydroxy‐3‐{1‐[3‐(naphthalen‐2‐yl)propyl]‐2‐oxo‐1,2‐dihydropyridin‐3‐yl}acrylamide, exhibited the highest level of HDAC inhibition (IC50=0.07 μM), highly selective inhibition of class I HDAC1 and class II HDAC6 enzymes, metabolic stability in mouse liver microsomal studies, and effective growth inhibition of various cancer cell lines. Docking studies indicated that a long alkyl linker and bulky hydrophobic cap groups affect in vitro activities. Overall, the findings reported herein regarding pyridone‐based HDAC inhibitors can be used to guide future research efforts to develop new and effective anticancer therapeutics.

Secreted tryptophanyl-tRNA synthetase as a primary defence system against infection.

The N-terminal truncated form of a protein synthesis enzyme, tryptophanyl-tRNA synthetase (mini-WRS), is secreted as an angiostatic ligand. However, the secretion and function of the full-length WRS (FL-WRS) remain unknown. Here, we report that the FL-WRS, but not mini-WRS, is rapidly secreted upon pathogen infection to prime innate immunity. Blood levels of FL-WRS were increased in sepsis patients, but not in those with sterile inflammation. FL-WRS was secreted from monocytes and directly bound to macrophages via a toll-like receptor 4 (TLR4)–myeloid differentiation factor 2 (MD2) complex to induce phagocytosis and chemokine production. Administration of FL-WRS into Salmonella typhimurium-infected mice reduced the levels of bacteria and improved mouse survival, whereas its titration with the specific antibody aggravated the infection. The N-terminal 154-amino-acid eukaryote-specific peptide of WRS was sufficient to recapitulate FL-WRS activity and its interaction mode with TLR4–MD2 is now suggested. Based on these results, secretion of FL-WRS appears to work as a primary defence system against infection, acting before full activation of innate immunity.

Structural modifications at the 6-position of thieno[2,3-d]pyrimidines and their effects on potency at FLT3 for treatment of acute myeloid leukemia.

Fms-like tyrosine kinase 3 (FLT3) is a well-known and important target for the treatment of acute myeloid leukemia (AML). A series of thieno[2,3-d]pyrimidine derivatives from a modification at the 6-position were synthesized to identify effective FLT3 inhibitors. Although compounds 1 and 2 emerged as promising FLT3 inhibitors among the synthesized compounds, both compounds exhibited poor metabolic stability in human and rat liver microsomes. Hence, further optimization was required for the discovery of FLT3 inhibitors, with a focus on improving metabolic stability. Compound 16d, which had structural modifications of the methyl group at the 5-position and the 4-(2-methylaminoethoxy) phenyl group at the 6-position, exhibited good inhibitory activity against FLT3 and showed effective antiproliferative activity against four leukemia cell lines, including MV4-11. Moreover, compound 16d displayed enhanced metabolic stability. The results of this study indicated that 16d could be a promising compound for further optimization and development as a potent FLT3 inhibitor.

Discovery of Orally Available Runt-Related Transcription Factor 3 (RUNX3) Modulators for Anticancer Chemotherapy by Epigenetic Activation and Protein Stabilization

Recently, we identified a novel strategy for anticancer chemotherapy by restoring runt-related transcription factor 3 (RUNX3) levels via lactam-based histone deacetylase (HDAC) inhibitors that stabilize RUNX3. Described here are the synthesis, biological evaluation, and pharmacokinetic evaluation of new synthetic small molecules based on pyridone-based HDAC inhibitors that specifically stabilize RUNX3 by acetylation and regulate its function. Many of the newly synthesized compounds showed favorable RUNX activities, HDAC inhibitory activities, and inhibitory activities on the growth of human cancer cell lines. Notably, one of these new derivatives, (E)-N-hydroxy-3-(2-oxo-1-(quinolin-2-ylmethyl)-1,2-dihydropyridin-3-yl)acrylamide (4l), significantly restored RUNX3 in a dose-dependent manner and showed high metabolic stability, a good pharmacokinetic profile with high oral bioavailability and long half-life, and strong antitumor activity. This study suggests that pyridone-based analogues modulate RUNX3 activity through epigenetic regulation as well as strong transcriptional and post-translational regulation of RUNX3 and could be potential clinical candidates as orally available RUNX3 modulators for the treatment of cancer.

Potential therapeutic application of small molecule with sulfonamide for chondrogenic differentiation and articular cartilage repair

The restoration of damaged articular cartilage is a long-pursued goal in regenerative medicine. Chondrocyte-specific differentiation of mesenchymal stem cells (MSCs) may be an effective means of repairing damaged cartilage. We identified small molecule 6 with sulfonamide as an agent that promotes specific chondrogenic differentiation of human adipose-derived MSCs (hASCs). Unlike other chondrogenic differentiation media composed of various defined components, simply adding compound 6 into culture medium was sufficient to induce chondrogenesis in this study. In an animal osteoarthritis model, both the small molecule 6 and the 6-treated hASCs exhibited enhanced recovery of injured articular cartilage. This work provides new insight into MSC differentiation induced by small molecules and potential new therapeutic approaches for articular cartilage injury.

Coordination of the leucine-sensing Rag GTPase cycle by leucyl-tRNA synthetase in the mTORC1 signaling pathway

Significance LRS, an enzyme involved in protein synthesis, and Sestrin2, a stress-induced metabolic protein, are suggested to function as leucine sensors for the mTORC1 pathway, a central regulator of cell metabolism, growth, proliferation, and survival. The Rag GTPase cycle regulates mTORC1; however, regulators of the Rag GTPase cycle and their coordination remain unknown. We show the dynamics of the RagD–RagB GTPase cycle during leucine signaling and describe contrasting yet complementary roles for LRS and Sestrin2 in the Rag GTPase–mTORC1 pathway, functioning as “ON” and “OFF” switches, respectively. Our results extend the current view of amino acid sensing by mTORC1 and will be invaluable for the development of novel approaches to combat mTORC1-related human diseases such as cancer. A protein synthesis enzyme, leucyl-tRNA synthetase (LRS), serves as a leucine sensor for the mechanistic target of rapamycin complex 1 (mTORC1), which is a central effector for protein synthesis, metabolism, autophagy, and cell growth. However, its significance in mTORC1 signaling and cancer growth and its functional relationship with other suggested leucine signal mediators are not well-understood. Here we show the kinetics of the Rag GTPase cycle during leucine signaling and that LRS serves as an initiating “ON” switch via GTP hydrolysis of RagD that drives the entire Rag GTPase cycle, whereas Sestrin2 functions as an “OFF” switch by controlling GTP hydrolysis of RagB in the Rag GTPase–mTORC1 axis. The LRS–RagD axis showed a positive correlation with mTORC1 activity in cancer tissues and cells. The GTP–GDP cycle of the RagD–RagB pair, rather than the RagC–RagA pair, is critical for leucine-induced mTORC1 activation. The active RagD–RagB pair can overcome the absence of the RagC–RagA pair, but the opposite is not the case. This work suggests that the GTPase cycle of RagD–RagB coordinated by LRS and Sestrin2 is critical for controlling mTORC1 activation, and thus will extend the current understanding of the amino acid-sensing mechanism.