Norman Kong

Characterization of a Novel Mitogen-Activated Protein Kinase Kinase 1/2 Inhibitor with a Unique Mechanism of Action for Cancer Therapy

The mitogen-activated protein kinase (MAPK) signal transduction pathway plays a central role in regulating tumor cell growth, survival, differentiation, and angiogenesis. The key components of the Ras/Raf/MEK/ERK signal module are frequently altered in human cancers. Targeting this pathway represents a promising anticancer strategy. Small molecule inhibitors targeting MEK1/2 have shown promise in the clinic; however, ultimate clinical proof-of-concept remains elusive. Here, we report a potent and highly selective non-ATP-competitive MEK1/2 inhibitor, RO4927350, with a novel chemical structure and unique mechanism of action. It selectively blocks the MAPK pathway signaling both in vitro and in vivo, which results in significant antitumor efficacy in a broad spectrum of tumor models. Compared with previously reported MEK inhibitors, RO4927350 inhibits not only ERK1/2 but also MEK1/2 phosphorylation. In cancer cells, high basal levels of phospho-MEK1/2 rather than phospho-ERK1/2 seem to correlate with greater sensitivity to RO4927350. Furthermore, RO4927350 prevents a feedback increase in MEK phosphorylation, which has been observed with other MEK inhibitors. We show that B-Raf rather than C-Raf plays a critical role in the feedback regulation. The unique MAPK signaling blockade mediated by RO4927350 in cancer may reduce the risk of developing drug resistance. Thus, RO4927350 represents a novel therapeutic modality in cancers with aberrant MAPK pathway activation.

Benzazepinones and benzoxazepinones as antagonists of inhibitor of apoptosis proteins (IAPs) selective for the second baculovirus IAP repeat (BIR2) domain.

XIAP is a key regulator of apoptosis, and its overexpression in cancer cells may contribute to their survival. The antiapoptotic function of XIAP derives from its BIR domains, which bind to and inhibit pro-apoptotic caspases. Most known IAP inhibitors are selective for the BIR3 domain and bind to cIAP1 and cIAP2 as well as XIAP. Pathways activated upon cIAP binding contribute to the function of these compounds. Inhibitors selective for XIAP should exert pro-apoptotic effects through competition with the terminal caspases. This paper details our synthetic explorations of a novel XIAP BIR2-selective benzazepinone screening hit with a focus on increasing BIR2 potency and overcoming high in vivo clearance. These efforts led to the discovery of benzoxazepinone 40, a potent BIR2-selective inhibitor with good in vivo pharmacokinetic properties which potentiates apoptotic signaling in a manner mechanistically distinct from that of known pan-IAP inhibitors.

Abstract 3655: Discovery of SC10914: a highly potent, selective and orally active PARP inhibitor for the treatment of BRCA1/2 deficient cancer

Proceedings: AACR 106th Annual Meeting 2015; April 18-22, 2015; Philadelphia, PA Poly(ADP ribose) polymerase (PARP) inhibitors are a class of anticancer agents that target DNA base excision repair and radio-sensitize cells through impaired DNA repair. When PARP function was impaired, double-stranded DNA breaks accumulated in the absence of effective BER. In cells deficient in homologous recombination (HR), especially in the setting of BRCA-deficiency, these breaks cannot be accurately repaired, resulting in synthetic lethality. Here, we described the identification and characterization of SC10914- a novel, highly potent oral active PARP inhibitor with favorable pharmacokinetic properties. SC10914 is a highly potent PARP inhibitor (PARP1 IC50 = 7.87 nM) with potent anti-proliferative activity against human BRCA deficient tumor cells (MDA-MB-436, BRCA1 deficient, IC50 = 4.03 nM, Capan-1 BRCA2 deficient, IC50 = 11.66 nM) and PTEN deficient tumor cells (HGC-27,PTEN deficient, IC50 = 0.35 μM). Methods and Results: MDA-MB-436 xenograft was derived from human breast cancer cells. Fragments of MDA-MB-436 tumor (approximately 1.5mm3) were implanted into the flank of female BALB/cA nude-mice which were randomized into four groups. Oral treatment with vehicle only, AZD2281 (75 mg/kg qd), SC10914 (25 mg/kg qd) or SC10914 (75 mg/kg qd) were carried out for 21 days. Vc8 xenograft was derived from Chinese hamster Vc8 (BRCA2 deficient) cells, fragments of Vc8 tumor (approximately 1.5mm3) were implanted into the flank of female BALB/cA nude-mice which were randomized into four groups; oral treatment with vehicle only, SC10914 (75 mg/kg qd), SC10914 (25 mg/kg qd) or SC10914 (5 mg/kg qd) were carried out for 21 days. SC10914 showed convincing in vivo efficacy at tolerated doses and resulted in robust dose-dependent anti-tumor efficacy in two xenograft models in nude-mice. Once daily oral treatment of SC10914 led to completed tumor stasis in established MDA-MB-436 xenografts and Vc-8 xenografts. In MDA-MB-436 xenografts, the low dose group (25mg/Kg) had the same efficacy with AZD2281 control group (75mg/Kg). SC10914 displayed a better pharmacokinetics profile compared with AZD2281 on SD rats with a single dosage of 15mg/Kg (oral bioavailability (%): 45.6% vs 26.2%, AUCinf (ng/mL/h): 3123 vs 1721, T1/2 (min): 160 vs 63.6). The pharmacokinetics profile displayed a positive correlation between the dosage of SC10914, drug plasma exposure (AUC0-t) and peak concentration (Cmax) when the dosages were in the range of 40-400mg/Kg. SC10914 has no hERG inhibition (IC50 > 30 μM). Ames tests suggested SC10914 has no mutagenic effects which were carried out in Salmonella typhimurium strains TA98 and TA100. In conclusion, our data indicated that SC10914, a potent inhibitor of PARP with potent anti-tumor activity in BRCA1/2 mutant tumor models and better pharmacokinetics profile has the potential to be selected as the clinical candidate for the treatment of treatment of BRCA1/2 deficient cancers. Citation Format: Daxin Gao, Heping Yang, Yajun Yu, Norman Kong. Discovery of SC10914: a highly potent, selective and orally active PARP inhibitor for the treatment of BRCA1/2 deficient cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3655. doi:10.1158/1538-7445.AM2015-3655

Abstract 2631: Discovery of SC110237, a highly potent, selective and orally active FLT3 inhibitor for the treatment of acute myeloid leukemia

FLT3 (Fms-like tyrosine kinase 3) is the most frequently mutated gene in acute myeloid leukemia (AML). Activating Flt3 mutations occur in about 30% of patients with AML, often as internal tandem duplication(ITD) mutations. These mutations are associated with the poor prognosis. Here, we report the Denovo preclinical candidate SC110237, a novel, selective, highly potent, and orally active FLT3 inhibitor which has very similar antitumor efficacy in MV4-11 xenograft models, but has better cardiac safety, and more favorable pharmacokinetic profiles compared with AC220, the first-in-class FLT3 inhibitor in clinical trial. SC110237 showed potent activity against FLT3 enzyme (IC 50 = 91 nM) and anti-proliferative activity against MV4-11 tumor cells (SC110237 IC 50 = 0.09 nM, AC220 IC 50 = 0.56 nM). Unlike most FLT3 inhibitors in clinical trials, SC110237 showed good selectivity within the Class III RTK family. In vivo, SC110237showed excellent efficacy in the subcutaneous models of AML and CEL (Chronic Eosinophilic Leukemia): MV4-11, MOLM-13 and EOL-1 model. MV4-11, MOLM-13 human AML cells have FLT3-ITD mutations, EOL-1 human CEL (Chronic Eosinophilic Leukemia) cells have FIP1L1-PDGFRA and over-expression of wild-type FLT3 receptor. In s.c. MV4-11 AML model, SC110237-2 (2, 6, 18 mg/kg) demonstrated potent activity. Tumor is completely eradicated in all groups even at the lowest dose of 2 mg/kg, with prolonged inhibition effect on tumor growth after drug withdrawal. At the lowest dose of 2 mg/kg for SC110237-2, there is 1 tumor re-growth until day 55 (12 days post last dose) compared to 3 tumors re-growth (one of the mice died) on the day 55 (12 days post dose) for AC220 at the same dose of 2 mg/kg. At higher dose of 6 mg/kg for SC110237-2, there is no sign of tumor re-growth until day 82 (39 days post last dose) comparing with 1 tumor re-growth on the day 76 (33 days post dose) for AC220 at the same dose of 6 mg/kg. In s.c. MOLM-13 and EOL-1 models, Tumor is completely eradicated in 4/8 mg/kg groups after 5 or 8 days dosing. SC110237-2 has no inhibition on CYP450 2C9, 2D6, 3A4 (Midazolam). Exposure of SC110237 is similar to that of AC220 which has the best PK profile among FLT3 inhibitors, while C max of SC110237 is lower than that of AC220. SC110237-2 exhibits linear dose-proportional exposure in mice and dog, and easier to adjust the dosage. Bioavailability of SC110237-2 in dog is 35%. To evaluate the effects of SC110237-2 and AC220 on the cardiovascular system, real time ECG was observed in conscious monkeys by a telemetry system. No abnormal phenomena have been observed in the 20 and 40 mg/kg SC110237 group, only with faster heart rate in the 80 mg/kg SC110237-2. On the other hand, 40 mg/kg AC220 can obviously prolong the QTcB interval. In conclusion, SC110237 exhibited a remarkable anti-tumor activity with favorable pharmacokinetic profiles and showed promise as a novel oral drug for the treatment of acute myeloid leukemia. Citation Format: Norman Kong, Daxin Gao, Heping Yang, Yajun Yu. Discovery of SC110237, a highly potent, selective and orally active FLT3 inhibitor for the treatment of acute myeloid leukemia. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2631. doi:10.1158/1538-7445.AM2015-2631