Nam Song Choi

Identification of CKD-516: A Potent Tubulin Polymerization Inhibitor with Marked Antitumor Activity against Murine and Human Solid Tumors

Tubulin polymerization inhibitors had emerged as one of promising anticancer therapeutics because of their dual mechanism of action, i.e. apoptosis by cell-cycle arrest and VDA, vascular disrupting agent. VDAs are believed to be more efficient, less toxic, and several of them are currently undergoing clinical trials. To identify novel tubulin inhibitors that possess potent cytotoxicity and strong inhibition of tubulin polymerization as well as potent in vivo antitumor efficacy, we have utilized benzophenone scaffold. Complete SAR analysis of newly synthesized analogues that were prepared by incorporation of small heterocycles (C2, C4, and C5 position) into B-ring along with the evaluation of their in vitro cytotoxicity, tubulin polymerization inhibition, and in vivo antitumor activity allowed us to identify 22 (S516). Compound 22 was found to have potent cytotoxicity against several cancer cells including P-gp overexpressing MDR positive cell line (HCT15). It also induced cell cycle arrest at G(2)/M phase, which is associated with strong inhibition of tubulin polymerization. Its in vivo efficacy was improved by preparing its (l)-valine prodrug, 65 (CKD-516), which together with greatly improved aqueous solubility has shown marked antitumor efficacy against both murine tumors (CT26 and 3LL) and human xenogratfs (HCT116 and HCT15) in mice.

Discovery of a potent tubulin polymerization inhibitor: Synthesis and evaluation of water-soluble prodrugs of benzophenone analog

Prodrugs have proven to be very useful in enhancing aqueous solubility of sparingly water-soluble drugs, thereby increasing in vivo efficacy without a need of special excipients. In vitro and in vivo evaluations of a number of amino acid prodrugs of 1, a previously identified potent tubulin polymerization inhibitor and cytotoxic against various cancer cell lines led to the discovery of 3·HCl (l-valine attached) which is highly efficacious in mouse xenografts bearing human cancer. Pharmacokinetic analysis in rats revealed that compound 1 was released immediately upon administration of 3·HCl intravenously, with rapid clearance of 3·HCl indicating the effective cleavage of prodrug. Compound 3·HCl (CKD-516) has now been progressed to phase 1 clinical trial.

Quinazolines as potent and highly selective PDE5 inhibitors as potential therapeutics for male erectile dysfunction

In an effort to minimize side effects associated with low selectivity against PDE isozymes, we have successfully identified a series of 6,7,8-substituted quinzaolines as potent inhibitors of PDE5 with high level of isozyme selectivity, especially against PDE6 and PDE11. PDE5 potency and isozyme selectivity of quinazolines were greatly improved with substitutions both at 6- and 8-position. The synthesis, structure-activity relationships and in vivo efficacy of this novel series of potent PDE5 inhibitors are described.

Discovery of potent, selective, and orally bioavailable PDE5 inhibitor: Methyl-4-(3-chloro-4-methoxybenzylamino)-8-(2-hydroxyethyl)-7-methoxyquinazolin-6-ylmethylcarbamate (CKD 533)

In a continuing effort to discover novel PDE5 inhibitors, we have successfully found quinazolines with 4-benzylamino substitution as potent and selective PDE5 inhibitors. Initial lead compound (1) was found to be easily metabolized when incubated with human liver microsomes mainly through C6 amide hydrolysis. Blocking of this metabolic hot spot led to discovery of 10 (CKD533) which is highly potent, selective and orally efficacious in conscious rabbit model for erectile dysfunction and now is undergoing preclinical toxicology study.

Functional divergency oriented synthesis of azoninones as the key intermediates for bioactive indolizidine alkaloids analogs

A functional divergency oriented synthetic approach to the azoninone (9-membered lactams), key intermediate for the indolizidine alkaloids library, using amide enolate induced aza-Claisen rearrangement has been achieved.

Concise Synthesis of Broussonone A

A concise and expeditious approach to the total synthesis of broussonone A, a p-quinol natural compound, has been developed. The key features of the synthesis include the Grubbs II catalyst mediated cross metathesis of two aromatic subunits, and a chemoselective oxidative dearomatizationin the presence of two phenol moieties. Especially, optimization associated with the CM reaction of ortho-alkoxystyrenes was also studied, which are known to be ineffective for Ru-catalyzed metathesis reactions under conventional reaction conditions because ortho-alkoxy group could coordinate to the ruthenium center, resulting in the potential complication of catalyst inhibition.

Synthesis and anti-platelet activity of obovatol derivatives

Obovatol derivatives were synthesized and evaluated for anti-platelet activity. Three derivatives (1, 2, 4i) displayed equipotent activity to obovatol in arachidonic acid-induced platelet aggregation. An initial SAR study revealed that the introduction of alkoxy group in B ring could enhance inhibitory activity.

Identification of chalcones as potent and selective PDE5A1 inhibitors.

Chalcones have an affinity for many receptors, enzymes, and transcription factors as flavonoid analogues. Their most studied pharmacological action is that of vasodilatation due to inhibition of phosphodiesterase 5A1 (PDE5A1). To this end, we have established a recursive partitioning model with 3 chemical descriptors for the prediction of compounds that can inhibit PDE5A1. This model was able to predict active compounds with an accuracy of 82.8%. Compound 4 was found to be a potent and selective inhibitor, with a relatively low IC(50) value. The binding mechanism of this compound was also investigated through molecular docking studies.

Abstract 941: Discovery of novel VEGFR2 and Raf-1 kinase inhibitorsuppressing MAPK signaling pathway in K-Ras mutant cancer cell-lines.

Proceedings: AACR 104th Annual Meeting 2013; Apr 6-10, 2013; Washington, DC Introduction: Signal transduction in the Ras-Raf-MEK-ERK (MAPK) pathway plays a key role in cell survival, growth and proliferation. The pathway is controlled by extracellular signals through receptor tyrosine kinases (RTK) and is activated by oncogenic mutations in many types of cancer. The B-Raf mutants are found in various cancers, such as melanoma, colorectal, ovarian, and prostate cancer. The Ras mutants are also found in various carcinomas including colon cancer, pancreatic cancer, non-small-cell lung cancer, and liver cancer. The mutated K-Ras gene sends continuous signals to the colorectal cancer cells, telling them to grow independent of the way ERBITUX blocks the EGFR growth signals. Especially, over 90% of detected mutations in B-Raf are a V600E which leads to constitutive kinase activity 500-fold greater than B-Raf wild type and correlates with increased malignancy. Vascular endothelial growth factor (VEGF) and its receptors have been implicated in the angiogenesis that is essential for growth and metastasis of solid tumors. Since formation of solid tumors are angiogenesis dependent, several strategies have been developed to inhibit VEGF signal transduction as part of anticancer therapy. The first VEGFR2 and Raf-1 inhibitor to enter clinical development was the multikinase inhibitor SORAFENIB, which is now approved for the treatment of patients with advanced renal cell carcinoma. More potent dual inhibitors against VEGFR2 and Raf-1 may be beneficial for patients suffering from various tumors. In this study, some of rational-designed compounds were synthesized and carried out the in vitro and in vivo studies to find more efficient VEGFR2 and Raf-1 inhibitors. Methods: About two hundreds of compounds were designed and synthesized. in vitro assays and in vivo studies were performed to characterize the potential of VEGFR2 and Raf-1 inhibitors for solid tumors. Results: Compound UI-162 showed strong kinase inhibition against VEGFR2 (12 nM), B-Raf V600E mutant (0.2 nM), B-Raf wildtype (2.0 nM) and Raf-1(0.6 nM). The compound showed good inhibitory effect in against malignant cells expressing K-Ras or B-Raf V600E mutant type of cell-line (SK-MEL-2 GI50: 133 nM / HCT-116 GI50: 229 nM / MDA-MB231 GI50: 278 nM / A375P GI50: 51 nM / HT29 GI50: 40 nM / COLO 205 GI50: 12 nM, respectively). In mechanism studies, the phosphorylation of MEK and ERK were suppressed by the UI-162 compound in HCT-116 cell-line. In addition, paradoxical effects were not detected compared with VEMURAFENIB. The compound had also a good anti-proliferative activity against HUVEC and showed a good oral bioavailability. Conclusions: The results of in vitro and in vivo studies suggests that dual inhibition of VEGFR2 and Raf-1 may provide strong antitumor efficacy and that UI-162 is a promising candidate for the treatment of various human cancers harboring the K-Ras and B-Raf V600E mutation. Citation Format: Seung Yong Kim, Younho Lee, Hyungtae Bang, Kihwan Eum, Sungpyo Hong, Ky-Youb Nam, Nam Song Choi, Ju Hee Kang, Hara Kang, Kil Won Kim, Michael Lee, Soon Kil Ahn. Discovery of novel VEGFR2 and Raf-1 kinase inhibitorsuppressing MAPK signaling pathway in K-Ras mutant cancer cell-lines. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 941. doi:10.1158/1538-7445.AM2013-941

Abstract 1803: Discovery of novel B-Raf kinase inhibitor with potent orally anticancer activity

Introduction: The B-Raf, one of serine/threonine kinase, is related to the Ras-Raf-MEK-ERK (MAPK) signal transduction. The signaling pathway plays a key role in cell survival, growth and proliferation. The B-Raf mutants are found in various cancer patients, such as melanoma, papillary thyroid, cisplatin-refractory testicular cancer, colorectal, ovarian, and prostate cancer. Especially, over 90% of detected mutations in B-Raf are a V600E which leads to constitutive kinase activity 500-fold greater than B-Raf wild type and correlates with increased malignancy and decreased response the chemotherapy. There are currently numerous efforts to develop therapeutic agents to target B-Raf or its downstream kinases. The first Raf inhibitor to enter clinical development was the multi-kinase inhibitor Nexavar (sorafenib tosylate), which is now approved for the treatment of patients with advanced renal cell carcinoma. However, the broad selectivity profile of this inhibitor makes it unsuitable for proof of concept evaluation of Raf kinase inhibition in tumors. Recently, more selective Raf inhibitors have been disclosed, and chemical inhibition of B-Raf enzymatic activity using these compounds can result in diminished proliferation and survival of tumor cells. However, very limited drug candidates with in vivo data have been published for B-Raf V600E . In this study, some of rational-designed compounds were synthesized and carried out the in vitro and in vivo studies to investigate more efficient B-Raf V600E inhibitors. Methods: About two hundreds of compounds were designed and synthesized. The in vitro assays and in vivo studies were performed to characterize the potential of B-Raf V600E inhibitors for solid tumors. Results: Compound UAI-201 had good inhibition effect in malignant cells expressing B-Raf V600E mutant type of cell-line (A375P GI 50 : 6nM / HT29 GI 50 : 5nM / COLO 205 GI 50 : 1nM), selectively. And the compound showed better tumor growth inhibition in xenograft mouse models (TGI(%): 61.87, 10mg/kg, PO, BID x 2weeks) compared with known inhibitors. In mechanism studies, the phosphorylation levels of MEK and ERK were effectively decreased by the UAI-201 compound in A375P cell-line. In addition, paradoxical effects were not detected compared with known compound. The compound had no toxicity in normal cell-line(HS-27 cell) and did not inhibit several CYP P450s. And also, UAI-201 showed good oral bioavailability with an acceptable clearance and half-life pharmacokinetic properties. Conclusions: The in vitro and in vivo studies of UAI-201 indicate that it is safe and efficacious, and suggests that it may good drug candidate for the preclinical study. Preclinical study our candidate, UAI-201, was started and the results will be disclosed in the near future. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1803. doi:1538-7445.AM2012-1803