Systematic pharmacological analysis of agonistic and antagonistic fibroblast growth factor receptor 1 MAbs reveals a similar unique mode of action.

Fibroblast growth factor receptor 1 (FGFR1) is a receptor tyrosine kinase that plays a major role in developmental processes and metabolism. The dysregulation of FGFR1 through genetic aberrations leads to skeletal and metabolic diseases as well as cancer. For this reason, FGFR1 is a promising therapeutic target, yet a very challenging one due to potential on-target toxicity. More puzzling is that both agonistic and antagonistic FGFR1 antibodies are reported to exhibit similar toxicity profiles in vivo, namely weight loss. In this study, we aimed to assess and compare the mechanism of action of these molecules to better understand this apparent contradiction. By systematically comparing the binding of these antibodies and the activation or the inhibition of the major FGFR1 signaling events, we demonstrated that the molecules displayed similar properties and can behave either as an agonist or antagonist depending on the presence or the absence of the endogenous ligand. We further demonstrated that these findings translated in xenografts mice models. In addition, using time-resolved FRET and mass spectrometry analysis, we showed a functionally distinct FGFR1 active conformation in the presence of an antibody that preferentially activates the FGFR substrate 2 (FRS2)-dependent signaling pathway, demonstrating that modulating the geometry of a FGFR1 dimer can effectively change the signaling outputs and ultimately the activity of the molecule in preclinical studies. Altogether, our results highlighted how bivalent antibodies can exhibit both agonistic and antagonistic activities and have implications for targeting other receptor tyrosine kinases with antibodies.

Primary results and characterization of patients with exceptional outcomes in a phase 1b study combining PARP and MEK inhibition, with or without anti-PD-L1, for BRCA wild-type, platinum-sensitive, recurrent ovarian cancer.

BACKGROUND: This phase 1b study (ClinicalTrials.gov identifier NCT03695380) evaluated regimens combining PARP and MEK inhibition, with or without PD-L1 inhibition, for BRCA wild-type, platinum-sensitive, recurrent ovarian cancer (PSROC). METHODS: Patients with PSROC who had received one or two prior treatment lines were treated with 28-day cycles of cobimetinib 60 mg daily (days 1-21) plus niraparib 200 mg daily (days 1-28) with or without atezolizumab 840 mg (days 1 and 15). Stage 1 assessed safety before expansion to stage 2, which randomized patients who had BRCA wild-type PSROC to receive either doublet or triplet therapy, stratified by genome-wide loss of heterozygosity status (<16% vs. ≥16%; FoundationOne CDx assay) and platinum-free interval (≥6 to <12 vs. ≥12 months). Coprimary end points were safety and the investigator-determined objective response rate (ORR) according to Response Evaluation Criteria in Solid Tumors (RECIST). Potential associations between genetic parameters and efficacy were explored, and biomarker profiles of super-responders (complete response or those with progression-free survival [PFS] >15 months) and progressors (disease progression as the best response) were characterized. RESULTS: The ORR in patients who had BRCA wild-type PSROC was 35% (95% confidence interval, 20%-53%) with the doublet regimen (n = 37) and 27% (95% confidence interval, 14%-44%) with the triplet regimen (n = 37), and the median PFS was 6.0 and 7.4 months, respectively. Post-hoc analyses indicated more favorable ORR and PFS in the homologous recombination-deficiency-signature (HRDsig)-positive subgroup than in the HRDsig-negative subgroup. Tolerability was consistent with the known profiles of individual agents. NF1 and MKNK1 mutations were associated with sustained benefit from the doublet and triplet regimens, respectively. CONCLUSIONS: Chemotherapy-free doublet and triplet therapy demonstrated encouraging activity, including among patients who had BRCA wild-type, HRDsig-positive or HRDsig-negative PSROC harboring NF1 or MKNK1 mutations.

4-Aminoindazolyl-dihydrofuro[3,4-d]pyrimidines as non-covalent inhibitors of mutant epidermal growth factor receptor tyrosine kinase.

The treatment of epidermal growth factor receptor (EGFR)-driven non-small cell lung cancers with the T790M resistance mutation remains a significant unmet medical need. We report the identification of 4-aminoindazolyl-dihydrofuro[3,4-d]pyrimidines as non-covalent inhibitors of EGFR, with excellent activity against the T790M resistance double mutants and initial single activating mutants. Using an optimization strategy focused on structure-based design and improving PK properties through metabolite identification, we obtained advanced leads with high oral exposure.

LUZ-Y, a novel platform for the mammalian cell production of full-length IgG-bispecific antibodies.

The ability of bispecific antibodies to simultaneously bind two unique antigens has great clinical potential. However, most approaches utilized to generate bispecific antibodies yield antibody-like structures that diverge significantly from the structure of archetype human IgG, and those that do approach structural similarity to native antibodies are often challenging to engineer and manufacture. Here, we present a novel platform for the mammalian cell production of bispecific antibodies that differ from their parental mAbs by only a single point mutation per heavy chain. Central to this platform is the addition of a leucine zipper to the C terminus of the C(H)3 domain of the antibody that is sufficient to drive the heterodimeric assembly of antibody heavy chains and can be readily removed post-purification. Using this approach, we developed various antibody constructs including one-armed Abs, bispecific antibodies that utilize a common light chain, and bispecific antibodies that pair light chains to their cognate heavy chains via peptide tethers. We have applied this technology to various antibody pairings and will demonstrate the engineering, purification, and biological activity of these antibodies herein.

Engineering upper hinge improves stability and effector function of a human IgG1.

Upper hinge is vulnerable to radical attacks that result in breakage of the heavy-light chain linkage and cleavage of the hinge of an IgG1. To further explore mechanisms responsible for the radical induced hinge degradation, nine mutants were designed to determine the roles that the upper hinge Asp and His play in the radical reactions. The observation that none of these substitutions could inhibit the breakage of the heavy-light chain linkage suggests that the breakage may result from electron transfer from Cys(231) directly to the heavy-light chain linkage upon radical attacks, and implies a pathway separate from His(229)-mediated hinge cleavage. On the other hand, the substitution of His(229) with Tyr showed promising advantages over the native antibody and other substitutions in improving the stability and function of the IgG1. This substitution inhibited the hinge cleavage by 98% and suggests that the redox active nature of Tyr did not enable it to replicate the ability of His to facilitate radical induced degradation. We propose that the lower redox potential of Tyr, a residue that may be the ultimate sink for oxidizing equivalents in proteins, is responsible for the inhibition. More importantly, the substitution increased the antibody's binding to FcγRIII receptors by 2-3-fold, and improved ADCC activity by 2-fold, while maintaining a similar pharmacokinetic profile with respect to the wild type. Implications of these observations for antibody engineering and development are discussed.

Hepatitis C virus induces epidermal growth factor receptor activation via CD81 binding for viral internalization and entry.

While epidermal growth factor receptor (EGFR) has been shown to be important in the entry process for multiple viruses, including hepatitis C virus (HCV), the molecular mechanisms by which EGFR facilitates HCV entry are not well understood. Using the infectious cell culture HCV model (HCVcc), we demonstrate that the binding of HCVcc particles to human hepatocyte cells induces EGFR activation that is dependent on interactions between HCV and CD81 but not claudin 1. EGFR activation can also be induced by antibody mediated cross-linking of CD81. In addition, EGFR ligands that enhance the kinetics of HCV entry induce EGFR internalization and colocalization with CD81. While EGFR kinase inhibitors inhibit HCV infection primarily by preventing EGFR endocytosis, antibodies that block EGFR ligand binding or inhibitors of EGFR downstream signaling have no effect on HCV entry. These data demonstrate that EGFR internalization is critical for HCV entry and identify a hitherto-unknown association between CD81 and EGFR.

Erlotinib directly inhibits HER2 kinase activation and downstream signaling events in intact cells lacking epidermal growth factor receptor expression.

Erlotinib (Tarceva), is an orally available, reversible inhibitor of epidermal growth factor receptor (EGFR; HER1) that exhibits inhibitory activity on purified HER2 kinase at much higher concentrations. Despite the minimal activity on purified protein in vitro, in vivo studies show that erlotinib inhibits the growth of HER2-driven systems effectively. Several hypotheses have been put forward to explain this discrepancy. In particular, it has been suggested that erlotinib might indirectly suppress the activity of HER2 by blocking the ability of EGFR to transactivate it when the two receptors are part of a heterodimer complex. However, an alternative possibility that has not been adequately addressed is whether the direct inhibitory action of erlotinib on the HER2 kinase might account for the observed biological responses. To distinguish between a direct effect of erlotinib on HER2 kinase in intact cells or an indirect effect of erlotinib on HER2 activity that is mediated through EGFR, we generated cell lines that express either EGFR-H2 chimeric receptor or HER2 and HER3 receptors in an EGFR-negative background. We show that dose-dependent inhibition of HER2 was achieved at the receptor level, on downstream signaling molecules, and more importantly was also translated into inhibition of cell growth. Our findings imply that the inhibitory effect of erlotinib in HER2-expressing cells may in part be mediated through direct interaction with HER2 rather than indirectly through a process that requires the presence of EGFR.

NRG1 is a critical regulator of differentiation in TP63-driven squamous cell carcinoma.

Squamous cell carcinomas (SCCs) account for the majority of cancer mortalities. Although TP63 is an established lineage-survival oncogene in SCCs, therapeutic strategies have not been developed to target TP63 or it's downstream effectors. In this study we demonstrate that TP63 directly regulates NRG1 expression in human SCC cell lines and that NRG1 is a critical component of the TP63 transcriptional program. Notably, we show that squamous tumors are dependent NRG1 signaling in vivo, in both genetically engineered mouse models and human xenograft models, and demonstrate that inhibition of NRG1 induces keratinization and terminal squamous differentiation of tumor cells, blocking proliferation and inhibiting tumor growth. Together, our findings identify a lineage-specific function of NRG1 in SCCs of diverse anatomic origin.

ERBB3 and IGF1R Signaling Are Required for Nrf2-Dependent Growth in KEAP1-Mutant Lung Cancer.

Mutations in KEAP1 and NFE2L2 (encoding the protein Nrf2) are prevalent in both adeno and squamous subtypes of non-small cell lung cancer, as well as additional tumor indications. The consequence of these mutations is stabilized Nrf2 and chronic induction of a battery of Nrf2 target genes. We show that knockdown of Nrf2 caused modest growth inhibition of cells growing in two-dimension, which was more pronounced in cell lines expressing mutant KEAP1. In contrast, Nrf2 knockdown caused almost complete regression of established KEAP1-mutant tumors in mice, with little effect on wild-type (WT) KEAP1 tumors. The strong dependency on Nrf2 could be recapitulated in certain anchorage-independent growth environments and was not prevented by excess extracellular glutathione. A CRISPR screen was used to investigate the mechanism(s) underlying this dependence. We identified alternative pathways critical for Nrf2-dependent growth in KEAP1-mutant cell lines, including the redox proteins thioredoxin and peroxiredoxin, as well as the growth factor receptors IGF1R and ERBB3. IGF1R inhibition was effective in KEAP1-mutant cells compared with WT, especially under conditions of anchorage-independent growth. These results point to addiction of KEAP1-mutant tumor cells to Nrf2 and suggest that inhibition of Nrf2 or discrete druggable Nrf2 target genes such as IGF1R could be an effective therapeutic strategy for disabling these tumors. SIGNIFICANCE: This study identifies pathways activated by Nrf2 that are important for the proliferation and tumorigenicity of KEAP1-mutant non-small cell lung cancer.

Correction: Combined MEK and ERK inhibition overcomes therapy-mediated pathway reactivation in RAS mutant tumors.

[This corrects the article DOI: 10.1371/journal.pone.0185862.].

"Two-in-One" approach for bioassay selection for dual specificity antibodies.

Dual specific antibodies and bispecific antibodies that recognize two different antigen targets are currently being regarded as very effective therapeutics for complex human diseases. While effective, designing and developing a bioassay strategy for dual specific antibodies that is reflective of the mechanism of action (MoA) and also measures the dual activities of antibodies pose unique and exciting challenges. An important question asked while developing a bioassay for dual specific antibodies is, "How many bioassays will be needed, one bioassay or two separate bioassays?" Here we present an approach of using one bioassay for a dual specific antibody that targets two receptors in signaling pathways. The presented assay is able to measure the antibody effects on both target bindings, which would not be achievable using two separate assays. Furthermore, this assay can detect changes in the binding of either target, which impact overall efficacy of the antibody. Its improved sensitivity enables substituting two binding assays with this one bioassay for lot release and stability testing to measure any changes on either target binding, ensuring consistency between lots. This is a single-bioassay approach for a dual specific antibody that is MoA reflective of the intended therapeutic indication. The demonstrated assay development and bridging study strategy for this bioassay for a dual specific mAb1 could be applicable to the other dual specific, bispecific antibodies, and antibodies used for combination therapy.

Erratum: Clinical responses to ERK inhibition in BRAFV600E-mutant colorectal cancer predicted using a computational model.

[This corrects the article DOI: 10.1038/s41540-017-0016-1.].

Clinical responses to ERK inhibition in BRAFV600E-mutant colorectal cancer predicted using a computational model.

Approximately 10% of colorectal cancers harbor BRAFV600E mutations, which constitutively activate the MAPK signaling pathway. We sought to determine whether ERK inhibitor (GDC-0994)-containing regimens may be of clinical benefit to these patients based on data from in vitro (cell line) and in vivo (cell- and patient-derived xenograft) studies of cetuximab (EGFR), vemurafenib (BRAF), cobimetinib (MEK), and GDC-0994 (ERK) combinations. Preclinical data was used to develop a mechanism-based computational model linking cell surface receptor (EGFR) activation, the MAPK signaling pathway, and tumor growth. Clinical predictions of anti-tumor activity were enabled by the use of tumor response data from three Phase 1 clinical trials testing combinations of EGFR, BRAF, and MEK inhibitors. Simulated responses to GDC-0994 monotherapy (overall response rate = 17%) accurately predicted results from a Phase 1 clinical trial regarding the number of responding patients (2/18) and the distribution of tumor size changes ("waterfall plot"). Prospective simulations were then used to evaluate potential drug combinations and predictive biomarkers for increasing responsiveness to MEK/ERK inhibitors in these patients.

Combined MEK and ERK inhibition overcomes therapy-mediated pathway reactivation in RAS mutant tumors.

Mitogen-activated protein kinase (MAPK) pathway dysregulation is implicated in >30% of all cancers, rationalizing the development of RAF, MEK and ERK inhibitors. While BRAF and MEK inhibitors improve BRAF mutant melanoma patient outcomes, these inhibitors had limited success in other MAPK dysregulated tumors, with insufficient pathway suppression and likely pathway reactivation. In this study we show that inhibition of either MEK or ERK alone only transiently inhibits the MAPK pathway due to feedback reactivation. Simultaneous targeting of both MEK and ERK nodes results in deeper and more durable suppression of MAPK signaling that is not achievable with any dose of single agent, in tumors where feedback reactivation occurs. Strikingly, combined MEK and ERK inhibition is synergistic in RAS mutant models but only additive in BRAF mutant models where the RAF complex is dissociated from RAS and thus feedback productivity is disabled. We discovered that pathway reactivation in RAS mutant models occurs at the level of CRAF with combination treatment resulting in a markedly more active pool of CRAF. However, distinct from single node targeting, combining MEK and ERK inhibitor treatment effectively blocks the downstream signaling as assessed by transcriptional signatures and phospho-p90RSK. Importantly, these data reveal that MAPK pathway inhibitors whose activity is attenuated due to feedback reactivation can be rescued with sufficient inhibition by using a combination of MEK and ERK inhibitors. The MEK and ERK combination significantly suppresses MAPK pathway output and tumor growth in vivo to a greater extent than the maximum tolerated doses of single agents, and results in improved anti-tumor activity in multiple xenografts as well as in two Kras mutant genetically engineered mouse (GEM) models. Collectively, these data demonstrate that combined MEK and ERK inhibition is functionally unique, yielding greater than additive anti-tumor effects and elucidates a highly effective combination strategy in MAPK-dependent cancer, such as KRAS mutant tumors.

High cell-surface density of HER2 deforms cell membranes.

Breast cancers (BC) with HER2 overexpression (referred to as HER2 positive) progress more aggressively than those with normal expression. Targeted therapies against HER2 can successfully delay the progression of HER2-positive BC, but details of how this overexpression drives the disease are not fully understood. Using single-molecule biophysical approaches, we discovered a new effect of HER2 overexpression on disease-relevant cell biological changes in these BC. We found HER2 overexpression causes deformation of the cell membranes, and this in turn disrupts epithelial features by perturbing cell-substrate and cell-cell contacts. This membrane deformation does not require receptor signalling activities, but results from the high levels of HER2 on the cell surface. Our finding suggests that early-stage morphological alterations of HER2-positive BC cells during cancer progression can occur in a physical and signalling-independent manner.

Activation Mechanism of Oncogenic Deletion Mutations in BRAF, EGFR, and HER2.

Activating mutations in protein kinases drive many cancers. While how recurring point mutations affect kinase activity has been described, the effect of in-frame deletions is not well understood. We show that oncogenic deletions within the ß3-αC loop of HER2 and BRAF are analogous to the recurrent EGFR exon 19 deletions. We identify pancreatic carcinomas with BRAF deletions mutually exclusive with KRAS mutations. Crystal structures of BRAF deletions reveal the truncated loop restrains αC in an active "in" conformation, imparting resistance to inhibitors like vemurafenib that bind the αC "out" conformation. Characterization of loop length explains the prevalence of five amino acid deletions in BRAF, EGFR, and HER2 and highlights the importance of this region for kinase activity and inhibitor efficacy.

Pyridones as Highly Selective, Noncovalent Inhibitors of T790M Double Mutants of EGFR.

The rapid advancement of a series of noncovalent inhibitors of T790M mutants of EGFR is discussed. The optimization of pyridone 1, a nonselective high-throughput screening hit, to potent molecules with high levels of selectivity over wtEGFR and the broader kinome is described herein.

Discovery of a Noncovalent, Mutant-Selective Epidermal Growth Factor Receptor Inhibitor.

Inhibitors targeting the activating mutants of the epidermal growth factor receptor (EGFR) have found success in the treatment of EGFR mutant positive non-small-cell lung cancer. A secondary point mutation (T790M) in the inhibitor binding site has been linked to the acquired resistance against those first generation therapeutics. Herein, we describe the lead optimization of a series of reversible, pan-mutant (L858R, del746-750, T790M/L858R, and T790M/del746-750) EGFR inhibitors. By use of a noncovalent double mutant (T790M/L858R and T790M/del746-750) selective EGFR inhibitor (2) as a starting point, activities against the single mutants (L858R and del746-750) were introduced through a series of structure-guided modifications. The in vitro ADME-PK properties of the lead molecules were further optimized through a number of rational structural changes. The resulting inhibitor (21) exhibited excellent cellular activity against both the single and double mutants of EGFR, demonstrating target engagement in vivo and ADME-PK properties that are suitable for further evaluation. The reversible, noncovalent inhibitors described complement the covalent pan-mutant EGFR inhibitors that have shown encouraging results in recent clinical trials.

Noncovalent Mutant Selective Epidermal Growth Factor Receptor Inhibitors: A Lead Optimization Case Study.

Because of their increased activity against activating mutants, first-generation epidermal growth factor receptor (EGFR) kinase inhibitors have had remarkable success in treating non-small-cell lung cancer (NSCLC) patients, but acquired resistance, through a secondary mutation of the gatekeeper residue, means that clinical responses only last for 8-14 months. Addressing this unmet medical need requires agents that can target both of the most common double mutants: T790M/L858R (TMLR) and T790M/del(746-750) (TMdel). Herein we describe how a noncovalent double mutant selective lead compound was optimized using a strategy focused on the structure-guided increase in potency without added lipophilicity or reduction of three-dimensional character. Following successive rounds of design and synthesis it was discovered that cis-fluoro substitution on 4-hydroxy- and 4-methoxypiperidinyl groups provided synergistic, substantial, and specific potency gain through direct interaction with the enzyme and/or effects on the proximal ligand oxygen atom. Further development of the fluorohydroxypiperidine series resulted in the identification of a pair of diastereomers that showed 50-fold enzyme and cell based selectivity for T790M mutants over wild-type EGFR (wtEGFR) in vitro and pathway knock-down in an in vivo xenograft model.

Dual targeting of HER2-positive cancer with trastuzumab emtansine and pertuzumab: critical role for neuregulin blockade in antitumor response to combination therapy.

PURPOSE: Targeting HER2 with multiple HER2-directed therapies represents a promising area of treatment for HER2-positive cancers. We investigated combining the HER2-directed antibody-drug conjugate trastuzumab emtansine (T-DM1) with the HER2 dimerization inhibitor pertuzumab (Perjeta). EXPERIMENTAL DESIGN: Drug combination studies with T-DM1 and pertuzumab were performed on cultured tumor cells and in mouse xenograft models of HER2-amplified cancer. In patients with HER2-positive locally advanced or metastatic breast cancer (mBC), T-DM1 was dose-escalated with a fixed standard pertuzumab dose in a 3+3 phase Ib/II study design. RESULTS: Treatment of HER2-overexpressing tumor cells in vitro with T-DM1 plus pertuzumab resulted in synergistic inhibition of cell proliferation and induction of apoptotic cell death. The presence of the HER3 ligand, heregulin (NRG-1ß), reduced the cytotoxic activity of T-DM1 in a subset of breast cancer lines; this effect was reversed by the addition of pertuzumab. Results from mouse xenograft models showed enhanced antitumor efficacy with T-DM1 and pertuzumab resulting from the unique antitumor activities of each agent. In patients with mBC previously treated with trastuzumab, lapatinib, and chemotherapy, T-DM1 could be dosed at the maximum tolerated dose (MTD; 3.6 mg/kg every 3 weeks) with standard dose pertuzumab. Adverse events were mostly grade 1 and 2, with indications of clinical activity. CONCLUSIONS: Dual targeting of HER2 with the combination of T-DM1 and pertuzumab in cell culture and mouse xenograft models resulted in enhanced antitumor activity. In patients, this combination showed an encouraging safety and tolerability profile with preliminary evidence of efficacy.