A phase Ib study of GSK3052230, an FGF ligand trap in combination with pemetrexed and cisplatin in patients with malignant pleural mesothelioma.

Background Fibroblast growth factors (FGFs) have a fundamental role in cancer. Sequestering FGFs with GSK3052230 (FP-1039) blocks their ability to activate FGFRs while avoiding toxicities associated with small molecule inhibitors of FGFR, including hyperphosphatemia and retinal, nail, and skin toxicities. Methods A multicenter, open-label, phase Ib study evaluated weekly GSK3052230 added to pemetrexed/cisplatin in patients with treatment-naive, unresectable malignant pleural mesothelioma. Doses were escalated according to a 3 + 3 design, followed by cohort expansion at the maximum tolerated dose (MTD). Endpoints included safety, overall response rate, progression-free survival, and pharmacokinetics. Results 36 patients were dosed at 10, 15, and 20 mg/kg doses of GSK3052230. Three dose-limiting toxicities were observed at 20 mg/kg and one at 15 mg/kg. The MTD was defined as 15 mg/kg and used for cohort expansion. The most common treatment-related adverse events (AEs) were nausea (56%), decreased appetite (36%), infusion reactions (36%), decreased neutrophil counts (36%), and fatigue (33%). The confirmed ORR was 39% (95% CI: 23.1-56.5) (14/36 PRs) and 47% had stable disease (17/36), giving a disease control rate of 86%. At 15 mg/kg GSK3052230 (n = 25), the ORR was 44% (95% CI: 24.4-65.1), and the median PFS was 7.4 months (95% CI: 6.7-13.4). Four patients had disease control for over 1 year, and three were still ongoing. Conclusion At 15 mg/kg weekly, GSK3052230 was well tolerated in combination with pemetrexed/cisplatin and durable responses were observed. Importantly, AEs associated with small molecule inhibitors of FGFR were not observed, as predicted by the unique mechanism of action of this drug.

Long-Range Inhibitor-Induced Conformational Regulation of Human IRE1α Endoribonuclease Activity.

Activation of the inositol-requiring enzyme-1 alpha (IRE1α) protein caused by endoplasmic reticulum stress results in the homodimerization of the N-terminal endoplasmic reticulum luminal domains, autophosphorylation of the cytoplasmic kinase domains, and conformational changes to the cytoplasmic endoribonuclease (RNase) domains, which render them functional and can lead to the splicing of X-box binding protein 1 (XBP 1) mRNA. Herein, we report the first crystal structures of the cytoplasmic portion of a human phosphorylated IRE1α dimer in complex with (R)-2-(3,4-dichlorobenzyl)-N-(4-methylbenzyl)-2,7-diazaspiro(4.5)decane-7-carboxamide, a novel, IRE1α-selective kinase inhibitor, and staurosporine, a broad spectrum kinase inhibitor. (R)-2-(3,4-dichlorobenzyl)-N-(4-methylbenzyl)-2,7-diazaspiro(4.5)decane-7-carboxamide inhibits both the kinase and RNase activities of IRE1α. The inhibitor interacts with the catalytic residues Lys599 and Glu612 and displaces the kinase activation loop to the DFG-out conformation. Inactivation of IRE1α RNase activity appears to be caused by a conformational change, whereby the αC helix is displaced, resulting in the rearrangement of the kinase domain-dimer interface and a rotation of the RNase domains away from each other. In contrast, staurosporine binds at the ATP-binding site of IRE1α, resulting in a dimer consistent with RNase active yeast Ire1 dimers. Activation of IRE1α RNase activity appears to be promoted by a network of hydrogen bond interactions between highly conserved residues across the RNase dimer interface that place key catalytic residues poised for reaction. These data implicate that the intermolecular interactions between conserved residues in the RNase domain are required for activity, and that the disruption of these interactions can be achieved pharmacologically by small molecule kinase domain inhibitors.

Negative feedback control of HIF-1 through REDD1-regulated ROS suppresses tumorigenesis.

The HIF family of hypoxia-inducible transcription factors are key mediators of the physiologic response to hypoxia, whose dysregulation promotes tumorigenesis. One important HIF-1 effector is the REDD1 protein, which is induced by HIF-1 and which functions as an essential regulator of TOR complex 1 (TORC1) activity in Drosophila and mammalian cells. Here we demonstrate a negative feedback loop for regulation of HIF-1 by REDD1, which plays a key role in tumor suppression. Genetic loss of REDD1 dramatically increases HIF-1 levels and HIF-regulated target gene expression in vitro and confers tumorigenicity in vivo. Increased HIF-1 in REDD1(-/-) cells induces a shift to glycolytic metabolism and provides a growth advantage under hypoxic conditions, and HIF-1 knockdown abrogates this advantage and suppresses tumorigenesis. Surprisingly, however, HIF-1 up-regulation in REDD1(-/-) cells is largely independent of mTORC1 activity. Instead, loss of REDD1 induces HIF-1 stabilization and tumorigenesis through a reactive oxygen species (ROS) -dependent mechanism. REDD1(-/-) cells demonstrate a substantial elevation of mitochondrial ROS, and antioxidant treatment is sufficient to normalize HIF-1 levels and inhibit REDD1-dependent tumor formation. REDD1 likely functions as a direct regulator of mitochondrial metabolism, as endogenous REDD1 localizes to the mitochondria, and this localization is required for REDD1 to reduce ROS production. Finally, human primary breast cancers that have silenced REDD1 exhibit evidence of HIF activation. Together, these findings uncover a specific genetic mechanism for HIF induction through loss of REDD1. Furthermore, they define REDD1 as a key metabolic regulator that suppresses tumorigenesis through distinct effects on mTORC1 activity and mitochondrial function.

Activating Inducible T-cell Costimulator Yields Antitumor Activity Alone and in Combination with Anti-PD-1 Checkpoint Blockade.

In recent years, there has been considerable interest in mAb-based induction of costimulatory receptor signaling as an approach to combat cancer. However, promising nonclinical data have yet to translate to a meaningful clinical benefit. Inducible T-cell costimulator (ICOS) is a costimulatory receptor important for immune responses. Using a novel clinical-stage anti-ICOS immunoglobulin G4 mAb (feladilimab), which induces but does not deplete ICOS+ T cells and their rodent analogs, we provide an end-to-end evaluation of the antitumor potential of antibody-mediated ICOS costimulation alone and in combination with programmed cell death protein 1 (PD-1) blockade. We demonstrate, consistently, that ICOS is expressed in a range of cancers, and its induction can stimulate growth of antitumor reactive T cells. Furthermore, feladilimab, alone and with a PD-1 inhibitor, induced antitumor activity in mouse and humanized tumor models. In addition to nonclinical evaluation, we present three patient case studies from a first-time-in-human, phase I, open-label, dose-escalation and dose-expansion clinical trial (INDUCE-1; ClinicalTrials.gov: NCT02723955), evaluating feladilimab alone and in combination with pembrolizumab in patients with advanced solid tumors. Preliminary data showing clinical benefit in patients with cancer treated with feladilimab alone or in combination with pembrolizumab was reported previously; with example cases described here. Additional work is needed to further validate the translation to the clinic, which includes identifying select patient populations that will benefit from this therapeutic approach, and randomized data with survival endpoints to illustrate its potential, similar to that shown with CTLA-4 and PD-1 blocking antibodies. Significance: Stimulation of the T-cell activation marker ICOS with the anti-ICOS agonist mAb feladilimab, alone and in combination with PD-1 inhibition, induces antitumor activity across nonclinical models as well as select patients with advanced solid tumors.

Characterization of GSK2334470, a novel and highly specific inhibitor of PDK1.

PDK1 (3-phosphoinositide-dependent protein kinase 1) activates a group of protein kinases belonging to the AGC [PKA (protein kinase A)/PKG (protein kinase G)/PKC (protein kinase C)]-kinase family that play important roles in mediating diverse biological processes. Many cancer-driving mutations induce activation of PDK1 targets including Akt, S6K (p70 ribosomal S6 kinase) and SGK (serum- and glucocorticoid-induced protein kinase). In the present paper, we describe the small molecule GSK2334470, which inhibits PDK1 with an IC50 of ~10 nM, but does not suppress the activity of 93 other protein kinases including 13 AGC-kinases most related to PDK1 at 500-fold higher concentrations. Addition of GSK2334470 to HEK (human embryonic kidney)-293, U87 or MEF (mouse embryonic fibroblast) cells ablated T-loop residue phosphorylation and activation of SGK isoforms and S6K1 induced by serum or IGF1 (insulin-like growth factor 1). GSK2334470 also inhibited T-loop phosphorylation and activation of Akt, but was more efficient at inhibiting Akt in response to stimuli such as serum that activated the PI3K (phosphoinositide 3-kinase) pathway weakly. GSK2334470 inhibited activation of an Akt1 mutant lacking the PH domain (pleckstrin homology domain) more potently than full-length Akt1, suggesting that GSK2334470 is more effective at inhibiting PDK1 substrates that are activated in the cytosol rather than at the plasma membrane. Consistent with this, GSK2334470 inhibited Akt activation in knock-in embryonic stem cells expressing a mutant of PDK1 that is unable to interact with phosphoinositides more potently than in wild-type cells. GSK2334470 also suppressed T-loop phosphorylation and activation of RSK2 (p90 ribosomal S6 kinase 2), another PDK1 target activated by the ERK (extracellular-signal-regulated kinase) pathway. However, prolonged treatment of cells with inhibitor was required to observe inhibition of RSK2, indicating that PDK1 substrates possess distinct T-loop dephosphorylation kinetics. Our data define how PDK1 inhibitors affect AGC signalling pathways and suggest that GSK2334470 will be a useful tool for delineating the roles of PDK1 in biological processes.

An open-label phase IB study to evaluate GSK3052230 in combination with paclitaxel and carboplatin, or docetaxel, in FGFR1-amplified non-small cell lung cancer.

OBJECTIVES: GSK3052230 (FP-1039) is a soluble fusion protein that acts as ligand trap sequestering fibroblast growth factors (FGFs) involved in tumor growth and angiogenesis, while sparing the hormonal FGFs. Because of this selectivity, the molecule is predicted to avoid toxicities associated with small molecule inhibitors of FGFR, including hyperphosphatemia and retinal, nail, and skin toxicities. Herein we report the results of a phase 1b study where GSK3052330 was administered with standard of care chemotherapy in FGFR1-amplified squamous non-small cell lung cancer (sqNSCLC) patients. METHODS AND METHODS: Eligible patients with stage IV or recurrent metastatic sqNSCLC harboring FGFR1 gene amplification received escalating doses of GSK3052230 in combination with paclitaxel and carboplatin at the starting doses 200 mg/m2 and AUC of 6, respectively, in the first line setting (Arm A) or docetaxel 75 mg/m2 in second line (Arm B). The primary endpoints of the study were safety and tolerability, to identify a maximum tolerated dose (MTD), and to assess overall response rate (ORR) based on investigator assessment. RESULTS: Twenty-nine patients were enrolled into the study, including 20 patients on Arm A and 9 patients on Arm B. There were no dose limiting toxicities in either Arm and the MTD was not reached. The most common adverse events (AEs) were compatible with the chemotherapy backbone used in each Arm, including neutropenia, alopecia, nausea, arthralgia, asthenia, diarrhea and peripheral neuropathy. The overall response rate and median progression-free survival were 47% and 5.5 months, respectively, for Arm A and 0% and 4.6 months, respectively, for Arm B. CONCLUSION: GSK3052230 is a novel FGFR pathway inhibitor, which is well tolerated in combination with chemotherapy. Importantly, AEs associated with small molecule inhibitors of FGFR were not observed, as predicted by the unique mechanism of action of this drug.

A First-Time-in-Human Study of GSK2636771, a Phosphoinositide 3 Kinase Beta-Selective Inhibitor, in Patients with Advanced Solid Tumors.

Background: The PI3K/protein kinase B (AKT) pathway is commonly activated in several tumor types. Selective targeting of p110ß could result in successful pathway inhibition while avoiding the on- and off-target effects of pan-PI3K inhibitors. GSK2636771 is a potent, orally bioavailable, adenosine triphosphate-competitive, selective inhibitor of PI3Kß.Methods: We evaluated the safety, pharmacokinetics, pharmacodynamics and antitumor activity of GSK2636771 to define the recommended phase II dose (RP2D). During the dose-selection and dose-escalation stages (parts 1 and 2), patients with PTEN-deficient advanced solid tumors received escalating doses of GSK2636771 (25-500 mg once daily) using a modified 3+3 design to determine the RP2D; tumor type-specific expansion cohorts (part 3) were implemented to further assess tumor responses at the RP2D.Results: A total of 65 patients were enrolled; dose-limiting toxicities were hypophosphatemia and hypocalcemia. Adverse events included diarrhea (48%), nausea (40%), and vomiting (31%). Single- and repeat-dose exposure increased generally dose proportionally. GSK2636771 400 mg once daily was the RP2D. Phospho/total AKT ratio decreased with GSK2636771 in tumor and surrogate tissue. A castrate-resistant prostate cancer (CRPC) patient harboring PIK3CB amplification had a partial response for over a year; an additional 10 patients derived durable (≥24 weeks) clinical benefit, including two other patients with CRPC with PIK3CB alterations (≥34 weeks). GSK2636771 400 mg once daily orally induced sufficient exposure and target inhibition with a manageable safety profile.Conclusions: Genomic aberrations of PIK3CB may be associated with clinical benefit from GSK2636771. Clin Cancer Res; 23(19); 5981-92. ©2017 AACR.

Inhibition of FGF/FGFR autocrine signaling in mesothelioma with the FGF ligand trap, FP-1039/GSK3052230.

Fibroblast growth factor (FGF) ligand-dependent signaling has a fundamental role in cancer development and tumor maintenance. GSK3052230 (also known as FP-1039) is a soluble decoy receptor that sequesters FGFs and inhibits FGFR signaling. Herein, the efficacy of this molecule was tested in models of mesothelioma, a tumor type shown to express high levels of FGF2 and FGFR1. GSK3052230 demonstrated antiproliferative activity across a panel of mesothelioma cell lines and inhibited growth of tumor xenografts in mice. High expression of FGF2 and FGFR1 correlated well with response to FGF pathway inhibition. GSK3052230 inhibited MAPK signaling as evidenced by decreased phospho-ERK and phospho-S6 levels in vitro and in vivo. Additionally, dose-dependent and statistically-significant reductions in tumor vessel density were observed in GSK3052230-treated tumors compared to vehicle-treated tumors. These data support the role of GSK3052230 in effectively targeting FGF-FGFR autocrine signaling in mesothelioma, demonstrate its impact on tumor growth and angiogenesis, and provide a rationale for the current clinical evaluation of this molecule in mesothelioma patients.