Objective Cobimetinib, a MEK1/2 inhibitor, was administered to patients with advanced solid tumors to assess safety, pharmacokinetics, pharmacodynamics, and anti-tumor activity. Methods For dose-escalation, a 3 + 3 design was used. Oral cobimetinib was administered once daily on a 21-day on/7-day off (21/7) or a 14-day on/14-day off (14/14) schedule. Serial plasma samples were collected for pharmacokinetic (PK) analysis on Day 1 and at steady state. In expansion stages, patients with RAS or RAF mutant tumors were treated at the maximum tolerated dose (MTD) of the 21/7 or 14/14 schedule. Results Ninety-seven patients received cobimetinib. In the 21/7 dose escalation, 36 patients enrolled in 8 cohorts (0.05 mg/kg–80 mg). Dose-limiting toxicities (DLTs) were Grade 4 hepatic encephalopathy, Grade 3 diarrhea, and Grade 3 rash. In the 14/14 dose escalation, 20 patients enrolled in 4 cohorts (60–125 mg). DLTs were Grade 3 rash and Grade 3 blurred vision associated with presence of reversible subretinal fluid. The MTD was 60 mg on 21/7 schedule and 100 mg on 14/14 schedule. Cobimetinib PK showed dose-proportional increases in exposure. The most frequent adverse events attributed to cobimetinib were diarrhea, rash, fatigue, edema, nausea, and vomiting. In patients treated at the 60-mg (21/7) or 100-mg (14/14) dose, one unconfirmed complete response and 6 confirmed partial responses were observed. All responses occurred in melanoma patients; 6 harbored the BRAFV600E mutation. Conclusions Cobimetinib is generally well tolerated and durable responses were observed in BRAFV600E mutant melanoma patients. Evaluation of cobimetinib in combination with other therapies is ongoing.

Background XL281 is a potent and selective inhibitor of wild-type and mutant RAF kinases with anti-tumor activity in multiple xenograft models. Mutations in KRAS or BRAF can activate the RAF/MEK/ERK pathway in human tumors and may confer sensitivity to RAF kinase inhibitors. Methods We performed a phase I study of XL281 in patients with advanced solid tumors. Patients were enrolled in successive cohorts of XL281 orally once daily in 28-day cycles. Twice daily dosing, different formulations, and the effect of food and famotidine were also studied. At the MTD expanded cohorts with defined mutations were treated. Results In total, 160 patients were treated. The MTD on the QD schedule was 150 mg. The most common toxicities were diarrhea, nausea, and fatigue. Plasma C-max and AUC increased with dose. Famotidine resulted in lower AUC while food had no effect. Two patients had partial responses by RECIST: One with papillary thyroid cancer with NRAS mutation and one with uveal melanoma. Another nine patients had tumor decrease of > 10 % but did not meet RECIST criteria for PR. Matched tumors pairs from 33 patients showed evidence of RAF inhibition with significant decreases in pERK, pMEK and pAKT. Conclusions XL281 was generally well tolerated and the MTD was established at 150 mg/day. Partial responses and clinical benefit were observed in several patients. Tumor biopsies demonstrated effective target inhibition.

The ERK/MAP kinase cascade is a key mechanism subject to dysregulation in cancer and is constitutively activated or highly upregulated in many tumor types. Mutations associated with upstream pathway components RAS and Raf occur frequently and contribute to the oncogenic phenotype through activation of MEK and then ERK. Inhibitors of MEK have been shown to effectively block upregulated ERK/MAPK signaling in a range of cancer cell lines and have further demonstrated early evidence of efficacy in the clinic for the treatment of cancer. Guided by structural insight, a strategy aimed at the identification of an optimal diphenylamine-based MEK inhibitor with an improved metabolism and safety profile versus PD-0325901 led to the discovery of development candidate 1-({3,4-difluoro-2-[(2-fluoro-4-iodophenyl)amino]phenyl}carbonyl)-3-[(2S)-piperidin-2-yl]azetidin-3-ol (XL518, GDC-0973) (1). XL518 exhibits robust in vitro and in vivo potency and efficacy in preclinical models with sustained duration of action and is currently in early stage clinical trials.

[3,4-Difluoro-2-(2-fluoro-4-iodo-phenylamino)-phenyl]-((S)-3-hydroxy-3-piperidin-2-yl-azetidin-1-yl)-methanone (GDC-0973) is a potent and highly selective inhibitor of mitogen-activated protein kinase(MAPK)/extracellular signal-regulated kinase (ERK) 1/2 (MEK1/2), a MAPK kinase that activates ERK1/2. The objectives of these studies were to characterize the disposition of GDC-0973 in preclinical species and to determine the relationship of GDC-0973 plasma concentrations to efficacy in Colo205 mouse xenograft models. The clearance (CL) of GDC-0973 was moderate in mouse (33.5 ml · min(-1) · kg(-1)), rat (37.9 ± 7.2 ml · min(-1) · kg(-1)), and monkey (29.6 ± 8.5 ml · min(-1) · kg(-1)). CL in dog was low (5.5 ± 0.3 ml · min(-1) · kg(-1)). The volume of distribution across species was large, 6-fold to 15-fold body water; half-lives ranged from 4 to 13 h. Protein binding in mouse, rat, dog, monkey, and human was high, with percentage unbound, 1 to 6%. GDC-0973-related radioactivity was rapidly and extensively distributed to tissues; however, low concentrations were observed in the brain. In rats and dogs, [(14)C]GDC-0973 was well absorbed (fraction absorbed, 70-80%). The majority of [(14)C]GDC-0973-related radioactivity was recovered in the bile of rat (74-81%) and dog (65%). The CL and volume of distribution of GDC-0973 in human, predicted by allometry, was 2.9 ml · min(-1) · kg(-1) and 9.9 l/kg, respectively. The predicted half-life was 39 h. To characterize the relationship between plasma concentration of GDC-0973 and tumor growth inhibition, pharmacokinetic-pharmacodynamic modeling was applied using an indirect response model. The KC(50) value for tumor growth inhibition in Colo205 xenografts was estimated to be 0.389 μM, and the predicted clinical efficacious dose was ∼10 mg. Taken together, these data are useful in assessing the disposition of GDC-0973, and where available, comparisons with human data were made.

Abstract Combinations of MAP/ERK kinase (MEK) and phosphoinositide 3-kinase (PI3K) inhibitors have shown promise in preclinical cancer models, leading to the initiation of clinical trials cotargeting these two key cancer signaling pathways. GDC-0973, a novel selective MEK inhibitor, and GDC-0941, a class I PI3K inhibitor, are in early stage clinical trials as both single agents and in combination. The discovery of these selective inhibitors has allowed investigation into the precise effects of combining inhibitors of two major signaling branches downstream of RAS. Here, we investigated multiple biomarkers in the mitogen-activated protein kinase (MAPK) and PI3K pathway to search for points of convergence that explain the increased apoptosis seen in combination. Using washout studies in vitro and alternate dosing schedules in mice, we showed that intermittent inhibition of the PI3K and MAPK pathway is sufficient for efficacy in BRAF and KRAS mutant cancer cells. The combination of GDC-0973 with the PI3K inhibitor GDC-0941 resulted in combination efficacy in vitro and in vivo via induction of biomarkers associated with apoptosis, including Bcl-2 family proapoptotic regulators. Therefore, these data suggest that continuous exposure of MEK and PI3K inhibitors in combination is not required for efficacy in preclinical cancer models and that sustained effects on downstream apoptosis biomarkers can be observed in response to intermittent dosing. Cancer Res; 72(1); 210–9. ©2011 AACR.

A series of substituted benzofuropyrimidinones with pan-PIM activities and excellent selectivity against a panel of diverse kinases is described. Initial exploration identified aryl benzofuropyrimidinones that were potent, but had cell permeability limitation. Using X-ray crystal structures of the bound PIM-1 complexes with 3, 5m, and 6d, we were able to guide the SAR and identify the alkyl benzofuropyrimidinone (6l) with good PIM potencies, permeability, and oral exposure.

Background: The RAS/RAF/MEK/ERK signaling pathway, which is deregulated in a variety of tumor types, plays a major role in mediating cell growth and differentiation. GDC-0973 is a potent, selective, orally bioavailable MEK1/2 inhibitor which has shown antitumor activity in preclinical models. Methods: A phase I dose-escalation study using a 3+3 design was initiated in patients (pts) with solid tumors to evaluate the safety and pharmacokinetic (PK) characteristics of GDC-0973. FDG-PET was evaluated as a pharmacodynamic (PD) marker. Pts were treated QD with oral GDC-0973 on a 21-day on/7-day off (21/7) or a 14-day on/14-day off (14/14) dosing schedule. Serial plasma samples for GDC-0973 pharmacokinetic (PK) analysis were collected following first dose (Day 1) and last dose (Day 21 or Day 14, respectively) in Cycle 1. At expansion stages, pts with RAS or RAF mutant tumors were treated at the maximum tolerated dose (MTD) of the 21/7 or 14/14 schedule, and underwent serial FDG-PET scans (baseline, C1D10-14 (steady state) and C1D26-28 (trough). Results: In the 21/7 dose escalation, 36 pts enrolled in eight successive cohorts (0.05 mg/kg-80 mg). Dose-limiting toxicities (DLTs) reported were Grade 4 hepatic encephalopathy (40 mg), Grade 3 diarrhea (80 mg) and Grade 3 rash (60 mg and 80 mg). On a 21/7 dosing schedule, the MTD was 60 mg, and the most frequent adverse events (AE) attributed to GDC-0973 by the investigator were diarrhea, rash, nausea, fatigue, dry skin, and edema. In the 14/14 dose escalation, 16 pts enrolled in four successive cohorts (60-125 mg). The DLTs reported were Grade 3 rash (125 mg) and Grade 3 blurred vision associated with presence of reversible subretinal fluid (125 mg). On a 14/14 dosing schedule, the MTD was 100 mg, and the most frequent AEs attributed to GDC-0973 by the investigator were diarrhea, rash, pruritus, nausea, vomiting, blurred and impaired vision, fatigue, and abdominal pain. Preliminary GDC-0973 PK data showed dose-proportional increases in Cmax and AUC, and a mean elimination half-life of approximately 40 hours. With daily oral dosing, there was approximately 2.5-fold accumulation, consistent with the GDC-0973 half-life and dosing interval. Of 17 patients in the 21/7 cohort with PET scans read to date, 9 (53%) had a partial metabolic response (> 20% decrease in mean SUVmax from baseline) in at least one timepoint. Of 6 patients in the 14/14 cohort with PET scans read to date, 5 (83%) had a partial metabolic response in at least one timepoint. Confirmed partial responses were observed in 3 melanoma patients, of which two had BRAFV600E mutation. Six pts with prolonged stable disease (≥ 5 mo) were observed to date. Conclusion: GDC-0973 is generally well tolerated and has signs of antitumor activity. Preliminary analysis indicates GDC-0973 has linear PK with a half-life that allows once daily dosing. Updated data will be presented. 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 4716. doi:10.1158/1538-7445.AM2011-4716

C209 Activation of the Ras/Raf/MEK/Erk pathway is a frequent occurrence in human tumors and often results from mutational activation of K-Ras or B-Raf. Activating B-Raf mutations are prevalent in malignant melanomas (66%) and are also found in colon cancer (15%) and papillary thyroid carcinoma (27%). Eighty percent of the constitutive activating B-Raf mutations result in a single substitution (V600E) in the activation loop of the kinase. Cancer cells transformed by B-RafV600E are exquisitely sensitive to MEK1 inhibition; therefore, MEK1 inhibitors may have particular clinical utility in melanoma and other tumors harboring this B-Raf mutation. XL518 is a potent, selective, orally bioavailable inhibitor of MEK1, with an IC50