Sawako Ozawa

Synthesis and biological activities of a pH-dependently activated water-soluble prodrug of a novel hexacyclic camptothecin analog.

CH0793076 (1) is a novel hexacyclic camptothecin analog showing potent antitumor activity in various human caner xenograft models. To improve the water solubility of 1, water-soluble prodrugs were designed to generate an active drug 1 nonenzymatically, thus expected to show less interpatient PK variability than CPT-11. Among the prodrugs synthesized, 4c (TP300, hydrochloride) having a glycylsarcosyl ester at the C-20 position of 1 is highly water-soluble (>10mg/ml), stable below pH 4 and rapidly generates 1 at physiological pH in vitro. The rapid (ca. <1min) generation of 1 after incubation of TP300 with plasma (mouse, rat, dog and monkey) was also demonstrated. TP300 showed a broader antitumor spectrum and more potent antitumor activity than CPT-11 in various human cancer xenograft models.

Fluorine Scanning by Nonselective Fluorination: Enhancing Raf/MEK Inhibition while Keeping Physicochemical Properties

A facile methodology effective in obtaining a set of compounds monofluorinated at various positions (fluorine scan) by chemical synthesis is reported. Direct and nonselective fluorination reactions of our lead compound 1a and key intermediate 2a worked efficiently to afford a total of six monofluorinated derivatives. All of the derivatives kept their physicochemical properties compared with the lead 1a and one of them had enhanced Raf/MEK inhibitory activity. Keeping physicochemical properties could be considered a benefit of monofluorinated derivatives compared with chlorinated derivatives, iodinated derivatives, methylated derivatives, etc. This key finding led to the identification of compound 14d, which had potent tumor growth inhibition in a xenograft model, excellent PK profiles in three animal species, and no critical toxicity.

Synthesis of new camptothecin analogs with improved antitumor activities

Novel hexacyclic camptothecin analogs containing cyclic amidine, urea, or thiourea moiety were designed and synthesized based on the proposed 3D-structure of the topoisomerase I (Topo I)/DNA/camptothecin ternary complex. The analogs were prepared from 9-nitrocamptothecin via 7,9-diaminocamptothecin derivatives as a key intermediate. Among them, 7c exhibited in vivo antitumor activities superior to CPT-11 in human cancer xenograft models in mice at their maximum tolerated doses though its in vitro antiproliferative activity was comparable to SN-38 against corresponding cell lines.

A water soluble prodrug of a novel camptothecin analog is efficacious against breast cancer resistance protein-expressing tumor xenografts

PurposeIdentification of a novel topoisomerase I inhibitor which shows superior efficacy and less individual variation than irinotecan hydrochloride (CPT-11).MethodsA novel camptothecin analog that is effective against breast cancer resistance protein (BCRP)-positive cells was screened, and a water soluble prodrug was generated. Antitumor activity of the prodrug was examined in BCRP-positive and -negative xenografts both as a single agent and in combination with other anti-cancer drugs.ResultsA novel camptothecin analog, CH0793076, was discovered. Because CH0793076 was found to be highly lipophilic, a water soluble prodrug (TP300) was generated. TP300 is stable in an acidic solution but is rapidly converted to CH0793076 under physiological pH conditions such as in sera. This efficient prodrug activation would minimize interpatient differences in pharmacokinetic and toxicity profiles. Unlike CPT-11, TP300 does not exhibit cholinergic interaction or cause acute diarrhea at effective doses. In mouse xenograft models, TP300 showed antitumor activity against both BCRP-positive and -negative xenografts, whereas CPT-11 was less active against BCRP-positive xenografts. In addition, the effective dose range (MTD/ED50) for TP300 was wider than for CPT-11 and TP300 showed additive or synergistic antitumor effects in combination with other anti-cancer drugs such as capecitabine, oxaliplatin, cisplatin, bevacizumab and cetuximab.ConclusionIt is therefore expected that TP300 will provide an additional treatment option for patients who will undergo chemotherapy with camptothecins.

The sulfamide moiety affords higher inhibitory activity and oral bioavailability to a series of coumarin dual selective RAF/MEK inhibitors.

Introducing a sulfamide moiety to our coumarin derivatives afforded enhanced Raf/MEK inhibitory activity concomitantly with an acceptable PK profile. Novel sulfamide 17 showed potent HCT116 cell growth inhibition (IC50=8 nM) and good PK profile (bioavailability of 51% in mouse), resulting in high in vivo antitumor efficacy in the HCT116 xenograft (ED50=4.8 mg/kg). We confirmed the sulfamide moiety showed no negative impact on tests run on the compound to evaluate DMPK (PK profiles in three animal species, CYP inhibition and CYP induction) and the safety profile (hERG and AMES tests). Sulfamide 17 had favorable properties that warranted further preclinical assessment.

Optimizing the Physicochemical Properties of Raf/MEK Inhibitors by Nitrogen Scanning

Substituting a carbon atom with a nitrogen atom (nitrogen substitution) on an aromatic ring in our leads 11a and 13g by applying nitrogen scanning afforded a set of compounds that improved not only the solubility but also the metabolic stability. The impact after nitrogen substitution on interactions between a derivative and its on- and off-target proteins (Raf/MEK, CYPs, and hERG channel) was also detected, most of them contributing to weaker interactions. After identifying the positions that kept inhibitory activity on HCT116 cell growth and Raf/MEK, compound 1 (CH5126766/RO5126766) was selected as a clinical compound. A phase I clinical trial is ongoing for solid cancers.

Abstract 2789: Discovery of a novel specific MEK and Raf inhibitor, CH5126766 (RO5126766), hit to lead study of a unique scaffold for kinase inhibitor to a clinical compound

Background: Among tumor signaling pathways, the most frequently dysregulated in human cancer is Ras-Raf-MEK axis, and therefore allosteric MEK inhibitors and ATP competitive Raf inhibitors are being tested in clinical trials. However, these inhibitors result in marked activation of upstream signal of MEK in tumor cells, especially with mutant K-ras. This feedback activation or activation of Raf would attenuate the anticancer effects of these inhibitors. One of the strategies to prevent this attenuation will be blocking upstream signal concurrent with MEK inhibition. To validate the hypothesis, we executed a hit to lead study of our HTS hit showing MEK/Raf dual inhibition. Methods and Results: To increase direct MEK inhibitory activity (by binding to MEK) of the HTS hit coumarin compound and indirect Raf inhibitory activity (by enhancement of the binding between B-Raf /C-Raf and MEK1), introduction of a sulfamide group afforded the best result, compared with similar functional groups such as urea, amide and sulfonamide. Fluorine-scan (C-H/C-F substitutions) and nitrogen-scan (CH/N substitutions) worked efficient to increase both MEK and Raf inhibitory activities and optimize physicochemical properties (water solubility, hERG inhibition, CYP inhibitions etc). These three key transformations afforded CH5126766, which has MEK1 (IC50 = 160 nM) and B-Raf (IC50 = 19 nM) inhibitions and excellent PK profiles (mouse BA 93%, CL 1.1 mL/min/kg, rat BA 66%, CL 0.7 mL/min/kg, monkey BA 82%, CL 0.1 mL/min/kg). The compound showed potent antitumor activity in human cancer xenograft model (HCT116) by once daily oral administration (128% of tumor growth inhibition at a 1 mg/kg dose). Conclusion: SAR study of our novel type molecule (MEK and Raf dual inhibitor) affords identification of CH5126766. It showed strong antitumor efficacy in vivo, good PK in three animal species and good safety profiles. Thus, CH5126766 is now under clinical investigation with solid tumor patients. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2789. doi:10.1158/1538-7445.AM2011-2789