Katherine M. Galvin

A role for Smad6 in development and homeostasis of the cardiovascular system

Smad proteins are intracellular mediators of signalling initiated by Tgf-βsuperfamily ligands (Tgf-βs, activins and bone morphogenetic proteins (Bmps)). Smads 1, 2, 3, 5 and 8 are activated upon phosphorylation by specific type I receptors, and associate with the common partner Smad4 to trigger transcriptional responses. The inhibitory Smads (6 and 7) are transcriptionally induced in cultured cells treated with Tgf-β superfamily ligands, and downregulate signalling in in vitro assays. Gene disruption in mice has begun to reveal specific developmental and physiological functions of the signal-transducing Smads. Here we explore the role of an inhibitory Smad in vivo by targeted mutation of Madh6 (which encodes the Smad6 protein). Targeted insertion of a LacZ reporter demonstrated that Smad6 expression is largely restricted to the heart and blood vessels, and that Madh6 mutants have multiple cardiovascular abnormalities. Hyperplasia of the cardiac valves and outflow tract septation defects indicate a function for Smad6 in the regulation of endocardial cushion transformation. The role of Smad6 in the homeostasis of the adult cardiovascular system is indicated by the development of aortic ossification and elevated blood pressure in viable mutants. These defects highlight the importance of Smad6 in the tissue-specific modulation of Tgf-β superfamily signalling pathways in vivo.

Antitumor activity of MLN8054, an orally active small-molecule inhibitor of Aurora A kinase

Increased Aurora A expression occurs in a variety of human cancers and induces chromosomal abnormalities during mitosis associated with tumor initiation and progression. MLN8054 is a selective small-molecule Aurora A kinase inhibitor that has entered Phase I clinical trials for advanced solid tumors. MLN8054 inhibits recombinant Aurora A kinase activity in vitro and is selective for Aurora A over the family member Aurora B in cultured cells. MLN8054 treatment results in G2/M accumulation and spindle defects and inhibits proliferation in multiple cultured human tumor cells lines. Growth of human tumor xenografts in nude mice was dramatically inhibited after oral administration of MLN8054 at well tolerated doses. Moreover, the tumor growth inhibition was sustained after discontinuing MLN8054 treatment. In human tumor xenografts, MLN8054 induced mitotic accumulation and apoptosis, phenotypes consistent with inhibition of Aurora A. MLN8054 is a selective inhibitor of Aurora A kinase that robustly inhibits growth of human tumor xenografts and represents an attractive modality for therapeutic intervention of human cancers.

Localization of human TACC3 to mitotic spindles is mediated by phosphorylation on Ser558 by Aurora A: a novel pharmacodynamic method for measuring Aurora A activity.

Aurora A is a serine/threonine protein kinase essential for normal mitotic progression. Aberrant increased expression of Aurora A, which occurs frequently in human cancers, results in abnormal mitoses leading to chromosome instability and possibly tumorigenesis. Consequently, Aurora A has received considerable attention as a potential target for anticancer therapeutic intervention. Aurora A coordinates several essential mitotic activities through phosphorylation of a variety of proteins, including TACC3, which modulates microtubule stabilization of the mitotic spindle. Recent studies identified a conserved serine in Xenopus (Ser(626)) and Drosophila (Ser(863)) TACC3 orthologues that is phosphorylated by Aurora A. We show that this conserved serine on human TACC3 (Ser(558)) is also phosphorylated by Aurora A. Moreover, phosphorylation of TACC3 by Aurora A in human cells is essential for its proper localization to centrosomes and proximal mitotic spindles. Inhibition of Aurora A with the selective small molecule inhibitor MLN8054 in cultured human tumor cells resulted in mislocalization of TACC3 away from mitotic spindles in a concentration-dependent manner. Furthermore, oral administration of MLN8054 to nude mice bearing HCT-116 human tumor xenografts caused a dose-dependent mislocalization of TACC3 away from spindle poles that correlated with tumor growth inhibition. As TACC3 localization to mitotic spindles depends on Aurora A-mediated phosphorylation, quantifying TACC3 mislocalization represents a novel pharmacodynamic approach for measuring Aurora A activity in cancer patients treated with inhibitors of Aurora A kinase.

Design and Optimization of Potent and Orally Bioavailable Tetrahydronaphthalene Raf Inhibitors

Inhibition of mutant B-Raf signaling, through either direct inhibition of the enzyme or inhibition of MEK, the direct substrate of Raf, has been demonstrated preclinically to inhibit tumor growth. Very recently, treatment of B-Raf mutant melanoma patients with a selective B-Raf inhibitor has resulted in promising preliminary evidence of antitumor activity. This article describes the design and optimization of tetrahydronaphthalene-derived compounds as potent inhibitors of the Raf pathway in vitro and in vivo. These compounds possess good pharmacokinetic properties in rodents and inhibit B-Raf mutant tumor growth in mouse xenograft models.

Discovery and optimization of pyrazoline compounds as B-Raf inhibitors.

The discovery of novel pyrazoline derivatives as B-Raf (V600E) inhibitors is described in this report. Chemical modification of the pyrazoline scaffold led to the development of SAR and identified potent and selective inhibitors of B-Raf (V600E). Determination of the pharmacokinetic properties of selected inhibitors is also reported.

A small-molecule inhibitor of the ubiquitin activating enzyme for cancer treatment

The ubiquitin–proteasome system (UPS) comprises a network of enzymes that is responsible for maintaining cellular protein homeostasis. The therapeutic potential of this pathway has been validated by the clinical successes of a number of UPS modulators, including proteasome inhibitors and immunomodulatory imide drugs (IMiDs). Here we identified TAK-243 (formerly known as MLN7243) as a potent, mechanism-based small-molecule inhibitor of the ubiquitin activating enzyme (UAE), the primary mammalian E1 enzyme that regulates the ubiquitin conjugation cascade. TAK-243 treatment caused depletion of cellular ubiquitin conjugates, resulting in disruption of signaling events, induction of proteotoxic stress, and impairment of cell cycle progression and DNA damage repair pathways. TAK-243 treatment caused death of cancer cells and, in primary human xenograft studies, demonstrated antitumor activity at tolerated doses. Due to its specificity and potency, TAK-243 allows for interrogation of ubiquitin biology and for assessment of UAE inhibition as a new approach for cancer treatment.

Abstract C146: Combination treatment with the investigational RAF kinase inhibitor MLN2480 and the investigational MEK kinase inhibitor TAK-733 inhibits the growth of BRAF mutant and RAS mutant preclinical models of melanoma and CRC.

Background: RAS mutant melanoma and colorectal cancer represent areas of significant unmet medical need. MLN2480 is an investigational class II RAF kinase inhibitor and TAK-733 is an investigational allosteric MEK kinase inhibitor; each of which is the subject of a single agent phase I clinical trial. The present studies have characterized the combination activity of these agents in BRAF mutant and RAS mutant preclinical models of melanoma and colorectal cancer. Methods: Combination effects of MLN2480 and TAK-733 on cell viability were studied using an ATP-based cell viability assay across a panel of BRAF and RAS mutant melanoma and CRC cell lines. Western blot analysis was used to compare effects on MAPK pathway signaling and response markers in cell lines showing a range of sensitivity to this combination. Pharmacodynamic responses and growth inhibitory effects of the combination were studied in xenografts of the same cell lines, as well as in primary human tumor xenografts, of RAS mutant melanoma and CRC. Results: MLN2480 inhibits MAPK pathway signaling in BRAF mutant and some RAS mutant preclinical cancer models at concentrations that are tolerated in vivo. MLN2480 is most potent in BRAF mutant melanoma models but also has single agent activity in some RAS mutant models. The combination of MLN2480 with TAK-733 inhibits the growth of a broader range of RAS mutant tumor models than single agent MLN2480, including primary human tumor xenograft models of melanoma and CRC. In vitro analysis of this drug combination in cell proliferation assays demonstrates synergistic activity. Western blot analysis demonstrated the effect of MLN2480 in reversing feedback activation of MEK in response to TAK-733, leading to more concerted MAPK pathway inhibition. Conclusions: The activity of the RAF kinase inhibitor MLN2480 in preclinical models of BRAF and RAS mutant melanoma and CRC provides a rationale for clinical testing. The combination of MLN2480 with the MEK inhibitor TAK-733 represents an additional strategy for clinical research within these tumor types. Citation Information: Mol Cancer Ther 2013;12(11 Suppl):C146. Citation Format: Elizabeth Grace Carideo Cunniff, Julie Zhang, Jouhara Chouitar, Jerome Mettetal, Kazuhide Nakamura, Takeo Arita, Akito Nakamura, Masanori Okaniwa, Tomoyasu Ishikawa, Sei Yoshida, Robyn Fabrey, Patrick Vincent, Kurt Eng, Khristofer Garcia, Deanna Borelli, Teena Vagrhese, Steve Stroud, Saurabh Menon, Mike Kuranda, Katherine Galvin. Combination treatment with the investigational RAF kinase inhibitor MLN2480 and the investigational MEK kinase inhibitor TAK-733 inhibits the growth of BRAF mutant and RAS mutant preclinical models of melanoma and CRC. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr C146.

Abstract A215: Integrated analysis of clinical pharmacokinetics (PK), nonclinical PK/efficacy (E) and pharmacodynamic (PD)/E relationships, and translational PK/PD simulations to guide clinical dose and schedule of MLN2480, an oral investigational pan-RAF kinase inhibitor.

Background: MLN2480 is an oral investigational pan-RAF kinase inhibitor currently in Phase I of clinical development. An integrated analysis of clinical PK, nonclinical PK/E and PD/E relationships, and translational PK/PD simulations was performed to help inform selection of dose and schedule for future clinical studies. Methods: Nonclinical PK/E, PK/PD, and PD/E relationships were evaluated at doses of 2 to 37.5 mg/kg QD in the A375 (BRAF mutant) melanoma xenograft model. Tumor PD was characterized by decrease in phosphorylated ERK (pERK) from baseline. A sigmoidal Emax model was fitted to the PK/E data and an inhibitory Emax model to PK/PD data. The PK/E and PK/PD models were used to generate a PD/E relationship, which was characterized by a sigmoidal inhibitory Emax model. Clinical PK was characterized in an ongoing first-in-human (FIH) study and a base population PK model was developed (NONMEM version 7.2). The time course of decrease in tumor pERK was simulated at the clinical maximum tolerated dose (200 mg Q2D) using human population PK parameters and nonclinical PK/PD model parameters corrected for inter-species differences in free fraction. The clinical exposures and simulated PD at 200 mg Q2D were used to provide translational estimates of antitumor activity based on nonclinical PK/E and PD/E relationships. Results: The nonclinical PK/E and PK/PD relationships were characterized by unbound EC50 or IC50 (coefficient of variation [CV]) of 62 ng/mL (20%) and 66 ng/mL (12%), respectively. PD/E analysis indicated that half-maximal tumor growth inhibition (TGI) was associated with a 44% decrease in pERK (CV 7.5%). Clinical PK (n=24) was characterized by rapid absorption (median Tmax 2 hr), low fluctuation at steady-state (mean peak to trough ratio 2.2), and 2.5-fold accumulation after Q2D dosing. Steady-state exposures (AUC0-tau) increased approximately dose-proportionally over 20 to 280 mg Q2D. A one-compartment PK model with first order absorption and elimination adequately described the data (n=26); parameter estimates and interindividual variability (CV%) were 0.73 hr−1 (65%) for Ka, 128 L (35%) for V/F, and 1.6 L/hr (41%) for CL/F. At 200 mg Q2D, time-averaged unbound exposure and predicted decrease in pERK levels were 62 ng/mL and 48%, respectively, translating to 86% and 101% TGI based on the respective nonclinical PK/E and PD/E relationships in the A375 xenograft model. Conclusions: Steady-state exposures at 200 mg Q2D are predicted to result in pERK decreases and antitumor activity associated with tumor stasis in nonclinial models of BRAF mutant melanoma. In ongoing expansion cohorts of an FIH study, tumor PD and antitumor activity are being evaluated in treatment-naive or relapsed/refractory patients with locally advanced or metastatic melanoma, including those with BRAF mutations. Citation Information: Mol Cancer Ther 2013;12(11 Suppl):A215. Citation Format: Stephanie Faucette, Jerome Mettetal, Xiaofei Zhou, Jouhara Chouitar, Mayank Patel, Michael Bargfrede, Katherine Galvin, Viviana Bozon, Karthik Venkatakrishnan. Integrated analysis of clinical pharmacokinetics (PK), nonclinical PK/efficacy (E) and pharmacodynamic (PD)/E relationships, and translational PK/PD simulations to guide clinical dose and schedule of MLN2480, an oral investigational pan-RAF kinase inhibitor. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr A215.