Macrocyclic Carbon-Linked Pyrazoles As Novel Inhibitors of MCL-1

Myeloid cell leukemia-1 (MCL-1) is a member of the antiapoptotic BCL-2 proteins family and a key regulator of mitochondrial homeostasis. Overexpression of MCL-1 is found in many cancer cells and contributes to tumor progression, which makes it an attractive therapeutic target. Pursuing our previous study of macrocyclic indoles for the inhibition of MCL-1, we report herein the impact of both pyrazole and indole isomerism on the potency and overall properties of this family of compounds. We demonstrated that the incorporation of a fluorine atom on the naphthalene moiety was a necessary step to improve cellular potency and that, combined with the introduction of various side chains on the pyrazole, it enhanced solubility significantly. This exploration culminated in the discovery of compounds (R_a)-10 and (R_a)-15, possessing remarkable cellular potency and properties.

Discovery of an Oral, Beyond-Rule-of-Five Mcl-1 Protein-Protein Interaction Modulator with the Potential of Treating Hematological Malignancies

Avoidance of apoptosis is critical for the development and sustained growth of tumors. The pro-survival protein myeloid cell leukemia 1 (Mcl-1) is an anti-apoptotic member of the Bcl-2 family of proteins which is overexpressed in many cancers. Upregulation of Mcl-1 in human cancers is associated with high tumor grade, poor survival, and resistance to chemotherapy. Therefore, pharmacological inhibition of Mcl-1 is regarded as an attractive approach to treating relapsed or refractory malignancies. Herein, we disclose the design, synthesis, optimization, and early preclinical evaluation of a potent and selective small-molecule inhibitor of Mcl-1. Our exploratory design tactics focused on structural modifications which improve the potency and physicochemical properties of the inhibitor while minimizing the risk of functional cardiotoxicity. Despite being in the "non-Lipinski" beyond-Rule-of-Five property space, the developed compound benefits from exquisite oral bioavailability in vivo and induces potent pharmacodynamic inhibition of Mcl-1 in a mouse xenograft model.

Abstract A28: BCL10 mutations define distinct dependencies guiding precision therapy for DLBCL

Diffuse large B-cell lymphoma (DLBCL) is the most common lymphoid malignancy and the activated B cell-like subtype (ABC-DLBCL) is the most aggressive form and harbors frequent mutations of immune signaling pathways that culminate in constitutive activation of CARD11-MALT1-BCL10 (CBM) complex and downstream NF-κB pathway. CBM complexes form large macromolecular structures due to signal-induced polymerization of the BCL10 subunit, which is affected by recurrent somatic mutations in ABC-DLBCLs. Through biochemical, structural and functional dissection of these mutations, we find that BCL10 mutations fall into two functionally distinct classes: missense mutations of the BCL10 CARD domain (hotspot R58Q) and truncation of its C-terminal tail (hotspot E140X). To explore the functional consequences of BCL10 mutations, we established reporter systems to evaluate their impact on MALT1 and NF-𝜅B activities which are BCL10 downstream signaling cascades. We found that almost all mutants induced aberrantly strong NF-𝜅B and MALT1 activities in lymphoma cells as compared to WT BCL10, indicating the gain-of-function effect of BCL10 mutations. By performing immunohistochemistry staining of p65 in a set of tumor tissue microarray from DLBCL patients (n=298), we revealed that BCL10 mutant tumors have significantly (Mann-Whitney p<0.0001) increased p65 nuclear staining score compared to BCL10 WT tumors, suggesting enhanced NF-𝜅B activity. To investigate the biochemical impact of BCL10 mutants on CBM complex formation, we performed fluorescence polarization and filamentation formation assays with purified WT and mutant BCL10 proteins and found that both BCL10R58Q and BCL10E140X manifested faster and more spontaneous polarization compared to BCL10WT. Surprisingly, through mapping the BCL10-MALT1 interaction, we found that truncating mutation (E140X) abrogated a novel protein interaction motif through which MALT1 inhibits BCL10 polymerization, thus unleashing spontaneous CBM filament formation and inducing addiction to MALT1 activity. In marked contrast, the CARD missense mutation (R58Q) on BCL10 filament interface not only does not disrupt but enhances filament formation and it also alters CBM complex kinetics forming glutamine network structures that stabilize BCL10 filaments, but this still may require the upstream signal to activate MALT1. Importantly, we found that BCL10 mutant cells were less dependent on upstream CARD11 activation in MALT1 activation, NF-𝜅B signaling and cell growth assays performed in ABC-DLBCL lines. Furthermore, in vitro and in vivo xenograft studies revealed that BCL10 mutant lymphomas are resistant to BTK inhibitors, whereas BCL10 truncating (E140X) but not missense CARD (R58Q) mutants were hypersensitive to MALT1 protease inhibitors. Therefore, BCL10 mutations are potential biomarkers for BTK inhibitor resistance in ABC-DLBCL and further precision can be achieved by tailoring therapy (e.g. MALT1 inhibitors that are currently being tested in clinical trials) according to specific biochemical effects of distinct mutation classes.

Citation Format: Min Xia, Liron David, Matthew R Teater, Johana Gutierrez, Xiang Wang, Cem Meydan, Andrew Lytle, Graham Slack, David Scott, Ozlem Onder, Kojo Elenitoba-Johnson, Nahuel Zamponi, Leandro Cerchietti, Tianbao Lu, Ulrike Philippar, Lorena Fontan, Hao Wu, Ari Melnick. BCL10 mutations define distinct dependencies guiding precision therapy for DLBCL [abstract]. In: Proceedings of the Third AACR International Meeting: Advances in Malignant Lymphoma: Maximizing the Basic-Translational Interface for Clinical Application; 2022 Jun 23-26; Boston, MA. Philadelphia (PA): AACR; Blood Cancer Discov 2022;3(5_Suppl):Abstract nr A28.

BCL10 Mutations Define Distinct Dependencies Guiding Precision Therapy for DLBCL

Activated B cell-like diffuse large B-cell lymphomas (ABC-DLBCL) have unfavorable outcomes and chronic activation of CARD11-BCL10-MALT1 (CBM) signal amplification complexes that form due to polymerization of BCL10 subunits, which is affected by recurrent somatic mutations in ABC-DLBCLs. Herein, we show that BCL10 mutants fall into at least two functionally distinct classes: missense mutations of the BCL10 CARD domain and truncation of its C-terminal tail. Truncating mutations abrogated a motif through which MALT1 inhibits BCL10 polymerization, trapping MALT1 in its activated filament-bound state. CARD missense mutations enhanced BCL10 filament formation, forming glutamine network structures that stabilize BCL10 filaments. Mutant forms of BCL10 were less dependent on upstream CARD11 activation and thus manifested resistance to BTK inhibitors, whereas BCL10 truncating but not CARD mutants were hypersensitive to MALT1 inhibitors. Therefore, BCL10 mutations are potential biomarkers for BTK inhibitor resistance in ABC-DLBCL, and further precision can be achieved by selecting therapy based on specific biochemical effects of distinct mutation classes.

SIGNIFICANCE

ABC-DLBCLs feature frequent mutations of signaling mediators that converge on the CBM complex. We use structure-function approaches to reveal that BCL10 mutations fall into two distinct biochemical classes. Both classes confer resistance to BTK inhibitors, whereas BCL10 truncations confer hyperresponsiveness to MALT1 inhibitors, providing a road map for precision therapies in ABC-DLBCLs. See related commentary by Phelan and Oellerich, p. 1844. This article is highlighted in the In This Issue feature, p. 1825.

Discovery and Pharmacological Characterization of JNJ-64619178, a Novel Small-Molecule Inhibitor of PRMT5 with Potent Antitumor Activity

The protein arginine methyltransferase 5 (PRMT5) methylates a variety of proteins involved in splicing, multiple signal transduction pathways, epigenetic control of gene expression, and mechanisms leading to protein expression required for cellular proliferation. Dysregulation of PRMT5 is associated with clinical features of several cancers, including lymphomas, lung cancer, and breast cancer. Here, we describe the characterization of JNJ-64619178, a novel, selective, and potent PRMT5 inhibitor, currently in clinical trials for patients with advanced solid tumors, non-Hodgkin's lymphoma, and lower-risk myelodysplastic syndrome. JNJ-64619178 demonstrated a prolonged inhibition of PRMT5 and potent antiproliferative activity in subsets of cancer cell lines derived from various histologies, including lung, breast, pancreatic, and hematological malignancies. In primary acute myelogenous leukemia samples, the presence of splicing factor mutations correlated with a higher ex vivo sensitivity to JNJ-64619178. Furthermore, the potent and unique mechanism of inhibition of JNJ-64619178, combined with highly optimized pharmacological properties, led to efficient tumor growth inhibition and regression in several xenograft models in vivo, with once-daily or intermittent oral-dosing schedules. An increase in splicing burden was observed upon JNJ-64619178 treatment. Overall, these observations support the continued clinical evaluation of JNJ-64619178 in patients with aberrant PRMT5 activity-driven tumors.

Discovery of Highly Potent and Selective IRAK1 Degraders to Probe Scaffolding Functions of IRAK1 in ABC DLBCL

MyD88 gene mutation has been identified as one of the most prevalent driver mutations in the activated B-cell-like diffuse large B-cell lymphoma (ABC DLBCL). The published literature suggests that interleukin-1 receptor-associated kinase 1 (IRAK1) is an essential gene for ABC DLBCL harboring MyD88 mutation. Importantly, the scaffolding function of IRAK1, rather than its kinase activity, is required for tumor cell survival. Herein, we present our design, synthesis, and biological evaluation of a novel series of potent and selective IRAK1 degraders. One of the most potent compounds, Degrader-3 (JNJ-1013), effectively degraded cellular IRAK1 protein with a DC₅₀ of 3 nM in HBL-1 cells. Furthermore, JNJ-1013 potently inhibited IRAK1 downstream signaling pathways and demonstrated strong anti-proliferative effects in ABC DLBCL cells with MyD88 mutation. This work suggests that IRAK1 degraders have the potential for treating cancers that are dependent on the IRAK1 scaffolding function.

Abstract 1267: Combination therapy of JNJ-67856633, a novel, first-in-class MALT1 protease inhibitor, and JNJ-64264681, a novel BTK inhibitor, for the treatment of B-cell lymphomas

Background: Constitutive activation of the classical nuclear factor kappa-light-chain-enhancer of activated B-cells (NF-κB) pathway is a clear driver of B-cell non-Hodgkin lymphomas (NHL). Bruton's Tyrosine Kinase (BTK) and Mucosa-associated lymphoid tissue lymphoma translocation protein 1 (MALT1), which lies downstream of BTK, are key mediators of the classical NF-κB signaling pathway activated by BCR and TCR receptors. JNJ-67856633 is a first-in-class MALT1 protease inhibitor. JNJ-64264681 is a BTK inhibitor with improved selectivity against BTK. Blocking the BCR pathway at multiple points using these two orally bioavailable compounds could enhance clinical activity in B-cell lymphoma patients.

Methods: JNJ-67856633 and JNJ-64264681 are currently being evaluated in phase 1 clinical trials designed to establish safety, PK, PD and the Recommended Phase 2 Dose (RP2D) of each agent.

Results: JNJ-67856633 is a potent, selective, orally bioavailable, allosteric inhibitor of MALT1 protease activity. The compound inhibits proliferation of activated B-cell diffuse large B-cell lymphoma (ABC-DLBCL) cell lines bearing CD79b or CARD11 mutations as well as models mimicking resistance to covalent BTK inhibitors. JNJ-67856633 exhibits potent tumor growth inhibition in two human DLBCL xenograft models, OCI-Ly3 and OCI-Ly10, and mutation selected patient derived DLBCL xenografts. Furthermore, treatment with JNJ-67856633 leads to dose dependent inhibition of the generation of Tregs (CD4+CD25+FoxP3+) following CD3/28 stimulation in vitro, suggesting a potential immune modulatory role of MALT1 inhibition. JNJ-64264681 is an orally active small molecule that is a potent, selective, and irreversible covalent BTK inhibitor. JNJ-64264681 inhibits the growth of CD79b-mutant DLBCL cell lines in vitro and potently inhibits tumor growth in xenograft- or patient-derived DLBCL models in vivo. Treatment with JNJ-64264681 and JNJ-67856633 administered together demonstrated statistically significant tumor growth inhibition compared with vehicle control in two CD79b mutant mouse lymphoma models, one based on a DLBCL cell line (OCI-Ly10) and one based on a patient-derived DLBCL model (LY2298). In both models, the combination showed increased growth inhibition compared with single agents and tumor regression in the combination arm. Synergistic anti-proliferative activity was observed in three DLBCL cell lines carrying CD79b mutations and one MCL cell line.

Conclusions: Taken together, the in vitro and in vivo data for JNJ-67856633 and JNJ-64264681 suggest that combination therapy can increase the anti-tumor effect of the monotherapies and provide a more sustained response, offering strong support for clinical investigation of the combination of these two novel agents. A phase 1b combination study is scheduled to initiate.

Citation Format: Ulrike Philippar, Lorena Fontan, Ivo Cornelissen, Haopeng Rui, Sriram Balasubramanian, Marcello Gaudiano, Mariette Bekkers, Luc Van Nuffel, Tianbao Lu, Tianbao Lu, John Wiener, Mark Tichenor, Tony Greway, Kathryn Packman, Bie Verbist, Yusri Elsayed, Ricardo Attar, Jacqueline Bussolari, John Gerecitano. Combination therapy of JNJ-67856633, a novel, first-in-class MALT1 protease inhibitor, and JNJ-64264681, a novel BTK inhibitor, for the treatment of B-cell lymphomas [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1267.

Abstract 1256: JNJ-74856665, a novel DHODH inhibitor, mediates potent anti-leukemic activity and differentiation in vitro and in vivo

Acute myeloid leukemia (AML) is a heterogeneous disease characterized by uncontrolled clonal expansion of hematopoietic progenitor cells (myeloid blasts). Disease remission can be achieved with standard induction chemotherapy, but refractory and relapsed disease remains a challenge with a 5-year overall survival rate of approximately 25%. Induction of differentiation is an alternative approach to AML therapy. Dihydroorotate dehydrogenase (DHODH) catalyzes the ubiquinone-mediated oxidation of dihydroorotate (DHO) to orotate in the de novo pyrimidine synthesis pathway. Pre-clinical findings demonstrated that DHODH is a metabolic vulnerability in AML and a new target for differentiation therapy. Given the genetic complexity of myeloid malignancies, future use of DHODH inhibitors in combination with selected antineoplastic agents (e.g., azacitidine) with nonoverlapping mechanisms of action may address specific aspects of the complex pathogenesis of AML and MDS (myelodysplastic syndrome), ultimately improving patients' outcomes.JNJ74856665 is an orally available, potent and selective DHODH inhibitor. JNJ-74856665 inhibited the biochemical activity of human DHODH with a 50% inhibitory concentration (IC50) in the subnanomolar range and in vitro inhibited proliferation of MOLM-13, OCI-AML3, HL60 and THP-1 AML cell lines with low nanomolar IC50 values. Mechanism of action studies using these four cell lines demonstrated induction of CD11b and CD14 differentiation marker mRNA levels. Differentiation was accompanied by cell cycle arrest and apoptosis induction. Importantly, addition of excess uridine to the tissue culture conditions abrogated the anti-proliferative, differentiation and apoptosis inducing activity of JNJ-74856665, indicating on target activity. In vivo, JNJ-74856665 mediated significant activity in decreasing leukemic burden and increasing life span across subcutaneous (MOLM-13 and OCI-AML3) and disseminated (MOLM-13) xenografts, respectively. Pharmacodynamic investigations demonstrated target engagement as evidenced by upregulation of the DHODH substrate dihydroorotate in plasma and induction of differentiation markers in tumor. Combination of JNJ-74856665 with azacitidine in vivo demonstrated lack of antagonism in the anti-leukemic activity.The results described herein demonstrate that JNJ-74856665 exerts potent anti-leukemic activity in vitro and in vivo and warrant further investigation. To that end, a phase 1 clinical trial assessing the safety and efficacy of JNJ-74856665 in patients with AML and MDS is planned to initiate shortly.

Citation Format: Christine Pietsch, Scott Kuduk, Xiaochun Zhang, Tammy Bush, Faraz Kazmi, Edgar Jacoby, Zhuming Zhang, Lindsey DeRatt, Weixue Wang, Aaron Patrick, Andrew Steele, Friedericke Pastore, Tony Greway, Nikki Daskalakis, Kathryn Bradford, Kathryn Packman, Gilles Bignan, James Edwards, Ricardo Attar, Yusri Elsayed, Jacqueline Bussolari, Ulrike Philippar. JNJ-74856665, a novel DHODH inhibitor, mediates potent anti-leukemic activity and differentiation in vitro and in vivo [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1256.

Abstract PO-49: Discovery of JNJ-67856633: A novel, first-in-class MALT1 protease inhibitor for the treatment of B-cell lymphomas

Introduction: Constitutive activation of the classical nuclear factor kappa-light-chain-enhancer of activated B cells (NF κB) pathway is a clear driver of B-cell lymphomas, especially the aggressive activated B-cell (ABC) subtype of diffuse large B-cell lymphoma (DLBCL). Mucosa-associated lymphoid tissue lymphoma translocation protein 1 (MALT1) is a key mediator of the classical NF-κB signaling pathway downstream of B-cell receptor and T-cell receptor. MALT1 possesses two functions: a scaffolding function to recruit NF-κB signaling proteins and a protease function to cleave and inactivate inhibitors of the NF-κB signaling pathway.

Methods: Using a high-throughput screen followed by iterative structure-activity relationship (SAR) analyses, the MALT1 inhibitor JNJ-67856633 was identified. JNJ-67856633 was evaluated using biochemical, cellular in vitro, in vivo tumor efficacy and safety models.

Results: JNJ-67856633 is a potent, selective, allosteric inhibitor of MALT1 protease activity as measured by biochemical assays or downstream cellular cytokine readouts (IL6/10) or direct MALT1 substrate cleavage (RelB, BCL10). The compound inhibits proliferation of activated B-cell diffuse large B-cell lymphoma (ABC-DLBCL) cell lines bearing CD79b or CARD11 mutations as well as models mimicking resistance to covalent Bruton's tyrosine kinase (BTK) inhibitors. Furthermore, combination effects were observed in CD79b cellular ABC-DLBCL models when JNJ-67856633 was combined with a BTK inhibitor. JNJ-67856633 showed activity in organoid cultures derived from ABC-DLBCL patients. JNJ-67856633 leads to potent in vivo pharmacodynamic shutdown in CD79b- as well as CARD11-mutant ABC-DLBCL models as measured by serum IL10 or uncleaved BCL10 levels in tumors. JNJ-67856633 exhibits potent tumor growth inhibition in two human DLBCL xenograft models, OCI Ly3 and OCI Ly10. In addition, >5 patient-derived DLBCL xenografts were evaluated and activity in mutation selected models was observed. To address the role of MALT1 inhibition in T cells, primary human T cells derived from normal healthy volunteers were treated with JNJ-67856633 in vitro. Dose-dependent inhibition of the generation of Tregs (CD4+CD25+FoxP3+) following CD3/28 stimulation was observed upon treatment with JNJ-67856633, suggesting a potential immune-modulatory role of MALT1 inhibition.

Conclusions: Phase 1 clinical trials assessing the safety and efficacy of JNJ-67856633 initiated in 2019. JNJ-67856633 is a combination partner for BTK inhibitors and a promising treatment option for BTKi-resistant tumors, with demonstrated preclinical activity in CARD11 mutant tumors. In addition to ABC-DLBCL, a MALT1 inhibitor is a promising treatment option for patients with CLL, MCL, WM, and FL whose tumors have been shown to be sensitive to inhibition of BTK. MALT lymphomas, characterized by MALT1 and BCL10 translocation, represent another attractive target for MALT1 inhibition.

Citation Format: Ulrike Philippar, Tianbao Lu, Lorena Fontan, Nele Vloemans, Mariette Bekkers, Luc van Nuffel, Marcello Gaudiano, Katarzyna Wnuk-Lipinska, Bas-Jan Van Der Leede, Katie Amssoms, Kristof Kimpe, Bart Medaer, Tony Greway, Yann Abraham, Max Cummings, Emanuele Trella, Greet Vanhoof, Weimei Sun, Jan Willem Thuring, Peter Connolly, Haopeng Rui, Sriram Balasubramanian, John Gerecitano, Ari Melnick, Ricardo Attar. Discovery of JNJ-67856633: A novel, first-in-class MALT1 protease inhibitor for the treatment of B-cell lymphomas [abstract]. In: Proceedings of the AACR Virtual Meeting: Advances in Malignant Lymphoma; 2020 Aug 17-19. Philadelphia (PA): AACR; Blood Cancer Discov 2020;1(3_Suppl):Abstract nr PO-49.

Assessing IRAK4 Functions in ABC DLBCL by IRAK4 Kinase Inhibition and Protein Degradation

The interleukin-1 receptor-activated kinase 4 (IRAK4) belongs to the IRAK family of serine/threonine kinases and plays a central role in the innate immune response. However, the function of IRAK4 in tumor growth and progression remains elusive. Here we sought to determine the enzymatic and scaffolding functions of IRAK4 in activated B-cell-like diffuse large B cell lymphoma (ABC DLBCL). We chose a highly selective IRAK4 kinase inhibitor to probe the biological effects of kinase inhibition and developed a series of IRAK4 degraders to evaluate the effects of protein degradation in ABC DLBCL cells. Interestingly, the results demonstrated that neither IRAK4 kinase inhibition nor protein degradation led to cell death or growth inhibition, suggesting a redundant role for IRAK4 in ABC DLBCL cell survival. IRAK4 degraders characterized in this study provide useful tools for understanding IRAK4 protein scaffolding function, which was previously unachievable using pharmacological perturbation.

Abstract 5690: Discovery of JNJ-67856633: A novel, first-in-class MALT1 protease inhibitor for the treatment of B cell lymphomas

Introduction: Constitutive activation of the classical nuclear factor kappa-light-chain-enhancer of activated B-cells (NF-κB) pathway is a clear driver of B-cell lymphomas, especially the aggressive activated B-cell (ABC) subtype of diffuse large B-cell lymphoma (DLBCL). Mucosa-associated lymphoid tissue lymphoma translocation protein 1 (MALT1) is a key mediator of the classical NF-κB signaling pathway downstream of B-cell receptor and T-cell receptor. MALT1 possesses 2 functions: a scaffolding function to recruit NF-κB signaling proteins and a protease function to cleave and inactivate inhibitors of the NF-κB signaling pathway.

Methods: Using a high-throughput screen followed by iterative structure-activity relationship (SAR) analyses, the MALT1 inhibitor JNJ-67856633 was identified. The lead compound was evaluated using biochemical, in vitro cellular and in vivo tumor efficacy and safety models.

Results: JNJ-67856633 is a potent, selective, allosteric inhibitor of MALT1 protease activity as measured by biochemical assays or downstream cellular cytokine readouts (IL 6/10) or direct MALT1 substrate cleavage (RelB, BCL10). The compound inhibits proliferation of activated B-cell diffuse large B-cell lymphoma (ABC-DLBCL) cell lines bearing CD79b or CARD11 mutations as well as models mimicking resistance to covalent Bruton's Tyrosine Kinase (BTK) inhibitors. Furthermore, combination effects were observed in CD79b cellular ABC-DLBCL models when JNJ-67856633 was combined with a BTK inhibitor. JNJ-67856633 leads to potent in vivo pharmacodynamic shutdown in CD79b- as well as CARD11-mutant ABC-DLBCL models as measured by serum IL10 or uncleaved BCL10 levels in tumors. JNJ-67856633 exhibits potent tumor growth inhibition in two human DLBCL xenograft models, OCI Ly3 and OCI Ly10, and mutation selection patient derived DLBCL xenografts. To address the role of MALT1 inhibition in T cells, primary human T cells derived from normal healthy volunteers were treated with JNJ-67856633 in vitro. Dose dependent inhibition of the generation of Tregs (CD4+CD25+FoxP3+) following CD3/28 stimulation was observed upon treatment with JNJ-67856633 suggesting a potential immune modulatory role of MALT1 inhibition.

Conclusions: Phase 1 clinical trials assessing the safety and efficacy of JNJ-67856633 initiated in 2019. JNJ-67856633 is a combination partner for BTK inhibitors and a promising treatment option for BTKi-resistant tumors, with demonstrated preclinical activity in CARD11 mutant tumors. In addition to ABC-DLBCL, a MALT1 inhibitor is a promising treatment option for patients with CLL, MCL, WM, and FL whose tumors have been shown to be sensitive to inhibition of BTK. MALT lymphomas, characterized by MALT1 and BCL10 translocation, represent another attractive target for MALT1 inhibition.

Citation Format: Ulrike Philippar, Tianbao Lu, Nele Vloemans, Mariette Bekkers, Luc Van Nuffel, Marcello Gaudiano, Katarzyna Wnuk-Lipinska, Bas-jan Van Der Leede, Katie Amssoms, Kristof Kimpe, Bart Medaer, Tony Greway, Yann Abraham, Max Cummings, Emanuele Trella, Greet Vanhoof, Weimei Sun, Jan Willem Thuring, Peter Connolly, Jan Linders, Haopeng Rui, Sriram Balasubramanian, Amy Johnson, John Gerecitano, Jenna Goldberg, James P. Edwards, Yusri Elsayed, Jennifer Smit, Jaqueline Bussolari, Jaqueline Bussolari, Ricardo Attar. Discovery of JNJ-67856633: A novel, first-in-class MALT1 protease inhibitor for the treatment of B cell lymphomas [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 5690.

Influence of the bispecific antibody IgG subclass on T cell redirection

T cell redirection mediated by bispecific antibodies (BsAbs) is a promising cancer therapy. Dual antigen binding is necessary for potent T cell redirection and is influenced by the structural characteristics of a BsAb, which are dependent on its IgG subclass. In this study, model BsAbs targeting CD19xCD3 were generated in variants of IgG1, IgG2, and IgG4 carrying Fc mutations that reduce FcγR interaction, and two chimeric IgG subclasses termed IgG1:2 and IgG4:2, in which the IgG1- or IgG4-F(ab)2 are grafted on an IgG2 Fc. Molecules containing an IgG2 or IgG4-F(ab)2 domain were confirmed to be the most structurally compact molecules. All BsAbs were shown to bind both of their target proteins (and corresponding cells) equally well. However, CD19xCD3 IgG2 did not bind both antigens simultaneously as measured by the absence of cellular clustering of T cells with target cells. This translated to a reduced potency of IgG2 BsAbs in T-cell redirection assays. The activity of IgG2 BsAbs was fully restored in the chimeric subclasses IgG4:2 and IgG1:2. This confirmed the major contribution of the F(ab)2 region to the BsAb's functional activity and demonstrated that function of BsAbs can be modulated by engineering molecules combining different Fc and F(ab)2 domains. Abbreviations: ADCC: Antibody-dependent cellular cytotoxicity; AlphaScreenTM: Amplified Luminescent Proximity Homogeneous Assay Screening; ANOVA: Analysis of variance; BiTE: bispecific T-cell engager; BSA: bovine serum albumin; BsAb: bispecific antibody; cFAE: controlled Fab-arm exchange; CDC: complement-dependent cellular cytotoxicity; CIEX: cation-exchange; CIR: chimeric immune receptor; DPBS: Dulbecco's phosphate-buffered saline; EC50 value: effective concentration to reach half-maximum effect; EGFR: epidermal growth factor receptor; EI: expansion index (RAt=x/RAt=0); FACS: fluorescence-activated cell sorting; FVD: fixable viability dye; HI-HPLC: hydrophobic interaction HPLC; HI-FBS: heat-inactivated fetal bovine serum; HPLC: high-pressure liquid chromatography; IC50 value: effective concentration to reach half-maximum inhibition; IQ: Inhibition Quotient; IS: immunological synapse; MES: 2-(N-morpholino)ethanesulfonic acid; R-PE: recombinant phycoerythrin; RA: red area in μm2/well; RD: receptor density; RFP: red fluorescent protein; Rg: radius of gyration; RSV: respiratory syncytial virus; SAXS: small-angle x-ray scattering; scFv: single-chain variable fragment; SD: standard deviation; SPR: surface plasmon resonance; WT: wild-type.

Specific covalent inhibition of MALT1 paracaspase suppresses B cell lymphoma growth

The paracaspase MALT1 plays an essential role in activated B cell-like diffuse large B cell lymphoma (ABC DLBCL) downstream of B cell and TLR pathway genes mutated in these tumors. Although MALT1 is considered a compelling therapeutic target, the development of tractable and specific MALT1 protease inhibitors has thus far been elusive. Here, we developed a target engagement assay that provides a quantitative readout for specific MALT1-inhibitory effects in living cells. This enabled a structure-guided medicinal chemistry effort culminating in the discovery of pharmacologically tractable, irreversible substrate-mimetic compounds that bind the MALT1 active site. We confirmed that MALT1 targeting with compound 3 is effective at suppressing ABC DLBCL cells in vitro and in vivo. We show that a reduction in serum IL-10 levels exquisitely correlates with the drug pharmacokinetics and degree of MALT1 inhibition in vitro and in vivo and could constitute a useful pharmacodynamic biomarker to evaluate these compounds in clinical trials. Compound 3 revealed insights into the biology of MALT1 in ABC DLBCL, such as the role of MALT1 in driving JAK/STAT signaling and suppressing the type I IFN response and MHC class II expression, suggesting that MALT1 inhibition could prime lymphomas for immune recognition by cytotoxic immune cells.

Abstract 1383: A CRISPR-Cas9 tiling screen to identify functional domains within DNMT1 and/or DNMT3B that can be targeted for therapeutic intervention in AML

DNA methylation is an epigenetic mechanism that regulates gene expression during many stages of development, including genomic imprinting, stem cell regulation, and X-chromosome inactivation. Moreover, aberrant DNA methylation patterns, characterized by genome-wide hypomethylation and promoter-specific hypermethylation, are a prominent feature of cancer. Methylation of DNA at the 5-position of cytosines is mediated by the DNA methyltransferase (DNMT) protein family, which regulates both maintenance methylation (DNMT1) and de novo methylation (DNMT3A and DNMT3B). Loss-of-function mutations of DNMT3A have been identified in hematological malignancies including acute myeloid leukemia (AML), where DNMT3A is mutated in approximately 25% of known cases.

Published reports suggest the existence of a synthetic lethal interaction between DNMT3A and DNMT1/3B. To further study this potential genetic interaction, we are performing a CRISPR-Cas9 tiling screen to identify functional domains within DNMT1 and/or DNMT3B that are synthetic lethal with DNMT3A. We generated a lentiviral library containing 777 and 421 single guide RNAs (sgRNAs) that tile the coding region of DNMT1 and DNMT3B, respectively and performed viability screens in AML cell lines that are either wild-type or mutant for DNMT3A. This screen was designed to identify in-frame alterations within functional domains that lead to effects on cell viability. Next generation sequencing of sgRNAs identified three functional domains of DNMT1 which, when mutated, leads to decreases in cell viability. Current efforts are focused on verifying the essentiality of these functional domains using CRISPR-Cas9-based approaches as well as mutagenesis by integrated tiles (MITE)-seq analyses.

Citation Format: Balpreet Bhogal, Barbara Weir, Ramona Crescenzo, Min Chul Kwon, Ulrike Philippar, Ricardo Attar, Glenn Cowley, David Pocalyko. A CRISPR-Cas9 tiling screen to identify functional domains within DNMT1 and/or DNMT3B that can be targeted for therapeutic intervention in AML [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1383.

Abstract LB-303: Substrate-mimetic covalent inhibitor of MALT1 is most effective against CARD11 mutant ABC-DLBCL

Diffuse Large B-cell lymphoma is the most common subtype of B-cell non Hodgkin Lymphoma (B-NHL) representing 30% of all B-NHL. There are three molecular subtypes: germinal center B cell-like (GCB) DLBCL, activated B cell-like (ABC) DLBCL, and primary mediastinal B cell lymphoma (PMBL). Of those, Activated B-cell like Diffuse Large B-cell Lymphoma (ABC-DLBCL) represents a third of the patients and is characterized by constitutive NF-κB activity due to mutations in various proteins of the B-cell receptor (BCR) as well as Toll-like receptor (TLR) pathways. Mutations in the BCR pathway include: activating mutations of CD79A/B (20% of ABC-DLBCLs) and CARD11 (10%) and deletion or inactivating mutation of A20 (20-30%). In the TLR pathway, MYD88 is mutated in 37% of ABC-DLBCL patients. Given this scenario, numerous therapeutic strategies targeting proteins signaling downstream of the BCR pathway have been proposed for ABC-DLBCL -including inhibitors targeting kinases SYK, BTK, PI3K, PKC, MAPKs and AKT or the protease MALT1. MALT1 inhibition provides advantages to other targets because it is downstream of most of the BCR pathway mutations present in patients, including CARD11. Patients with CARD11 mutations do not respond to BTK inhibitors. However, none of the MALT1 inhibitors reported to date are good candidates for clinical use.

Here we report a new class of substrate mimetic MALT1 inhibitors based on Z-VRPR-fmk. Our lead compound, SCM-02-138 displayed nanomolar potency in biochemical and cellular MALT1 protease reporter assays. Crystallography shows covalent binding of the compound to MALT1 active site Cys residue. SCM-02-138 was highly selective for MALT1 and showed over 100-fold differential killing in sensitive vs resistant cell lines. MALT1 inhibition was most effective in CARD11 mutant cells. SCM-02-138 was active in vivo, as assessed by hIL10 inhibition in xenografted models of ABC-DLBCL cell lines. Moreover it was effective against ABC-DLBCL xenografts and PDX DLBCL ex vivo. Combination of SCM-02-138 with other BCR inhibitors revealed PI3K delta inhibition as the most synergistic combination. Combination of SCM-02-138 and CAL-101 potentiated both proliferation inhibition and apoptosis.

In summary, we have developed a new class of MALT1 peptidic inhibitor characterized by nanomolar potency, irreversibility and high specificity. This inhibitor will be particularly useful against CARD11 mutant ABC-DLBCL, which are resistant to BTK inhibitors.

Citation Format: Lorena Fontan, David Scott, John Hatcher, Qi Qiao, Ilkay Us, Gabriella Casalena, Mariette Bekkers, Ulrike Philippar, Matthew Durant, Spandan Chennamadhavuni, Hao Wu, Nathaniel Gray, Ari Melnick. Substrate-mimetic covalent inhibitor of MALT1 is most effective against CARD11 mutant ABC-DLBCL [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr LB-303. doi:10.1158/1538-7445.AM2017-LB-303

Discovery of 1-(1H-Pyrazolo[4,3-c]pyridin-6-yl)urea Inhibitors of Extracellular Signal-Regulated Kinase (ERK) for the Treatment of Cancers

The ERK/MAPK pathway plays a central role in the regulation of critical cellular processes and is activated in more than 30% of human cancers. Specific BRAF and MEK inhibitors have shown clinical efficacy in patients for the treatment of BRAF-mutant melanoma. However, the majority of responses are transient, and resistance is often associated with pathway reactivation of the ERK signal pathway. Acquired resistance to these agents has led to greater interest in ERK, a downstream target of the MAPK pathway. De novo design efforts of a novel scaffold derived from SCH772984 by employing hydrogen bond interactions specific for ERK in the binding pocket identified 1-(1H-pyrazolo[4,3-c]pyridin-6-yl)ureas as a viable lead series. Sequential SAR studies led to the identification of highly potent and selective ERK inhibitors with low molecular weight and high LE. Compound 21 exhibited potent target engagement and strong tumor regression in the BRAF(V600E) xenograft model.

PTP1B-dependent regulation of receptor tyrosine kinase signaling by the actin-binding protein Mena

The actin-binding protein Mena regulates RTK signaling after growth factor stimulation in tumor cells by a novel mechanism. The alternatively spliced MenaINV isoform disrupts this attenuation to drive sensitivity to growth factors, resistance to targeted inhibitors, and ultimately tumor invasion and metastasis.

During breast cancer progression, alternative mRNA splicing produces functionally distinct isoforms of Mena, an actin regulator with roles in cell migration and metastasis. Aggressive tumor cell subpopulations express Mena^INV, which promotes tumor cell invasion by potentiating EGF responses. However, the mechanism by which this occurs is unknown. Here we report that Mena associates constitutively with the tyrosine phosphatase PTP1B and mediates a novel negative feedback mechanism that attenuates receptor tyrosine kinase signaling. On EGF stimulation, complexes containing Mena and PTP1B are recruited to the EGFR, causing receptor dephosphorylation and leading to decreased motility responses. Mena also interacts with the 5′ inositol phosphatase SHIP2, which is important for the recruitment of the Mena-PTP1B complex to the EGFR. When Mena^INV is expressed, PTP1B recruitment to the EGFR is impaired, providing a mechanism for growth factor sensitization to EGF, as well as HGF and IGF, and increased resistance to EGFR and Met inhibitors in signaling and motility assays. In sum, we demonstrate that Mena plays an important role in regulating growth factor–induced signaling. Disruption of this attenuation by Mena^INV sensitizes tumor cells to low–growth factor concentrations, thereby increasing the migration and invasion responses that contribute to aggressive, malignant cell phenotypes.

Discovery of a novel ERK inhibitor with activity in models of acquired resistance to BRAF and MEK inhibitors

The high frequency of activating RAS or BRAF mutations in cancer provides strong rationale for targeting the mitogen-activated protein kinase (MAPK) pathway. Selective BRAF and MAP-ERK kinase (MEK) inhibitors have shown clinical efficacy in patients with melanoma. However, the majority of responses are transient, and resistance is often associated with pathway reactivation of the extracellular signal-regulated kinase (ERK) signaling pathway. Here, we describe the identification and characterization of SCH772984, a novel and selective inhibitor of ERK1/2 that displays behaviors of both type I and type II kinase inhibitors. SCH772984 has nanomolar cellular potency in tumor cells with mutations in BRAF, NRAS, or KRAS and induces tumor regressions in xenograft models at tolerated doses. Importantly, SCH772984 effectively inhibited MAPK signaling and cell proliferation in BRAF or MEK inhibitor-resistant models as well as in tumor cells resistant to concurrent treatment with BRAF and MEK inhibitors. These data support the clinical development of ERK inhibitors for tumors refractory to MAPK inhibitors.

Abstract 2343: A novel ERK inhibitor is active in models of acquired resistance to BRAF and MEK inhibitors

The high frequency of activating BRAFV600E mutations in melanoma (40-70%), thyroid (50%) and colorectal cancer (10%), or KRAS/NRAS mutations in melanoma (20%), pancreatic (90%), colorectal (50%) and non-small cell lung cancer (30%), provides strong rationale for targeting the MAPK pathway as a therapeutic strategy 1-6. Vemurafenib (PLX4032) and dabrafenib (GSK2118436), selective BRAF inhibitors, and trametinib (GSK1120212), an allosteric MEK inhibitor, have shown robust clinical efficacy in melanoma patients 7-10. However, the majority of responses are transient and cellular resistance is often associated with pathway reactivation involving the downstream extracellular-signal-regulated kinases 1 and 2 (ERK1/2) (reviewed in 11). We hypothesized that pathway blockade at ERK, the last signaling node prior to MAPK transcriptional programming, would not only be efficacious in MAPK-activated tumors but would also have utility in BRAF or MEK inhibitor resistant settings. We therefore sought to identify small molecule inhibitors of ERK. This report describes the identification and characterization of SCH772984, a potent and selective ATP competitive inhibitor of ERK1/2 which displays behaviors of both type I and type II kinase inhibitors. SCH772984 has nanomolar cellular potency on tumor cells with mutations in BRAF, NRAS, or KRAS and induces tumor regressions in xenograft models at tolerated doses. Importantly, SCH772984 effectively inhibited MAPK signaling and cell proliferation in BRAF or MEK inhibitor resistant models as well as in the context of BRAF/MEK combination resistance. Together these data support the clinical development of ERK inhibitors, not only in patients with MAPK activated tumors, but also in patients who have developed acquired resistance to BRAF or MEK inhibitors or resistance to the recently described combination of these agents.

Citation Format: Ahmed A. Samatar, Erick J. Morris, Sharda Jha, Restaino R. Clifford, Bart Luttrerbach, Marc Pelletier, Ulrike Philippar, Lata Jayaraman, Leigh Zawel, Steve Fawell, Gary Gilliland. A novel ERK inhibitor is active in models of acquired resistance to BRAF and MEK inhibitors. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2343. doi:10.1158/1538-7445.AM2013-2343

Gene signatures derived from a c-MET-driven liver cancer mouse model predict survival of patients with hepatocellular carcinoma

Biomarkers derived from gene expression profiling data may have a high false-positive rate and must be rigorously validated using independent clinical data sets, which are not always available. Although animal model systems could provide alternative data sets to formulate hypotheses and limit the number of signatures to be tested in clinical samples, the predictive power of such an approach is not yet proven. The present study aims to analyze the molecular signatures of liver cancer in a c-MET-transgenic mouse model and investigate its prognostic relevance to human hepatocellular carcinoma (HCC). Tissue samples were obtained from tumor (TU), adjacent non-tumor (AN) and distant normal (DN) liver in Tet-operator regulated (TRE) human c-MET transgenic mice (n = 21) as well as from a Chinese cohort of 272 HBV- and 9 HCV-associated HCC patients. Whole genome microarray expression profiling was conducted in Affymetrix gene expression chips, and prognostic significances of gene expression signatures were evaluated across the two species. Our data revealed parallels between mouse and human liver tumors, including down-regulation of metabolic pathways and up-regulation of cell cycle processes. The mouse tumors were most similar to a subset of patient samples characterized by activation of the Wnt pathway, but distinctive in the p53 pathway signals. Of potential clinical utility, we identified a set of genes that were down regulated in both mouse tumors and human HCC having significant predictive power on overall and disease-free survival, which were highly enriched for metabolic functions. In conclusions, this study provides evidence that a disease model can serve as a possible platform for generating hypotheses to be tested in human tissues and highlights an efficient method for generating biomarker signatures before extensive clinical trials have been initiated.

DLK1-DIO3 genomic imprinted microRNA cluster at 14q32.2 defines a stemlike subtype of hepatocellular carcinoma associated with poor survival

Hepatocellular carcinoma (HCC) is a heterogeneous and highly aggressive malignancy, for which there are no effective cures. Identification of a malignant stemlike subtype of HCC may offer patients with a dismal prognosis a potential targeted therapy using c-MET and Wnt pathway inhibitors. MicroRNAs (miRNAs) show promise as diagnostic and prognostic tools for cancer detection and stratification. Using a TRE-c-Met-driven transgenic HCC mouse model, we identified a cluster of 23 miRNAs that is encoded within the Dlk1-Gtl2 imprinted region on chromosome 12qF1 overexpressed in all of the isolated liver tumors. Interestingly, this region is conserved among mammalian species and maps to the human DLK1-DIO3 region on chromosome 14q32.2. We thus examined the expression of the DLK1-DIO3 miRNA cluster in a cohort of 97 hepatitis B virus-associated HCC patients and identified a subgroup (n = 18) of patients showing strong coordinate overexpression of miRNAs in this cluster but not in other cancer types (breast, lung, kidney, stomach, and colon) that were tested. Expression levels of imprinted gene transcripts from neighboring loci in this 14q32.2 region and from a subset of other imprinted sites were concomitantly elevated in human HCC. Interestingly, overexpression of the DLK1-DIO3 miRNA cluster was positively correlated with HCC stem cell markers (CD133, CD90, EpCAM, Nestin) and associated with a high level of serum α-fetoprotein, a conventional biomarker for liver cancer, and poor survival rate in HCC patients. In conclusion, our findings suggest that coordinate up-regulation of the DLK1-DIO3 miRNA cluster at 14q32.2 may define a novel molecular (stem cell-like) subtype of HCC associated with poor prognosis.

Degeneration of the mouse retina upon dysregulated activity of serum response factor

PURPOSE

Our aim was to generate and phenotypically characterize a transgenic mouse line expressing a constitutively active variant of the transcription regulatory protein serum response factor (SRF), namely the SRF-VP16 protein. This new mouse strain has been registered under the designation Gt(ROSA)26Sor(tm1(SRF-VP16)Antu). We found phenotypic changes upon ectopic expression of SRF-VP16, especially in the mouse retina.

METHODS

Using homologous recombination, we integrated an SRF-VP16 conditional (i.e., "flox-STOP" repressed) expression transgene into the Rosa26 locus of murine embryonic stem (ES) cells. These engineered ES cells were used to derive the Gt(ROSA)26Sor(tm1(SRF-VP16)Antu) mouse strain. Semiquantitative real-time PCR was used to determine expression of the SRF-VP16 transgene at the mRNA level, both in young (P20 and P30) and adult (six months old) Gt(ROSA)26Sor(tm1(SRF-VP16)Antu) mice. We also investigated the transcript levels of endogenous Srf and several SRF target genes. Retinal function was tested by electroretinography in both young and adult mice. Morphological abnormalities could be visualized by hematoxylin and eosin staining of sectioned, paraffin-embedded eye tissue samples. Scanning-laser ophthalmoscopy was used to investigate retinal vascularization and degeneration in adult mice.

RESULTS

We show that the SRF-VP16 mRNA is expressed to a low but significant degree in the retinas of young and adult animals of the Gt(ROSA)26Sor(tm1(SRF-VP16)Antu) mouse strain, even in the absence of Cre-mediated deletion of the "flox-STOP" cassette. In the retinas of these transgenic mice, endogenous Srf displays elevated transcript levels. Ectopic retinal expression of constitutively active SRF-VP16 is correlated with the malfunction of retinal neurons in both heterozygous and homozygous animals of both age groups (P20 and adult). Additionally, mislamination of retinal cell layers and cellular rosette formations are found in retinas of both heterozygous and homozygous animals of young age. In homozygous individuals, however, the cellular rosettes are more widespread over the fundus. At adult age, retinas both from animals that are heterozygous and homozygous for the floxSTOP/SRF-VP16 transgene display severe degeneration, mainly of the photoreceptor cell layer. Wild-type age-matched littermates, however, do not show any degeneration. The severity of the observed effects correlates with dosage of the transgene.

CONCLUSIONS

This is the first report suggesting an influence of the transcription factor SRF on the development and function of the murine retina. Ectopic SRF-VP16 mRNA expression in the retinas of young animals is correlated with photoreceptor layer mislamination and impaired retinal function. At an advanced age of six months, degenerative processes are detected in SRF-VP16 transgenic retinas accompanied by impaired retinal function. The Gt(ROSA)26Sor(tm1(SRF-VP16)Antu) mouse strain represents a genetic SRF gain-of-function mouse model that will complement the current SRF loss-of-function models. It promises to provide new insight into the hitherto poorly defined role of SRF in retinal development and function, including potential contributions to ophthalmologic disorders. Furthermore, using conditional Cre-mediated activation of SRF-VP16, the described mouse strain will enable assessment of the impact of dysregulated SRF activity on the physiologic functions of various other organs.

A Mena invasion isoform potentiates EGF-induced carcinoma cell invasion and metastasis

The spread of cancer during metastatic disease requires that tumor cells subvert normal regulatory networks governing cell motility to invade surrounding tissues and migrate toward blood and lymphatic vessels. Enabled (Ena)/vasodilator-stimulated phosphoprotein (VASP) proteins regulate cell motility by controlling the geometry of assembling actin networks. Mena, an Ena/VASP protein, is upregulated in the invasive subpopulation of breast cancer cells. In addition, Mena is alternately spliced to produce an invasion isoform, Mena(INV). Here we show that Mena and Mena(INV) promote carcinoma cell motility and invasiveness in vivo and in vitro, and increase lung metastasis. Mena and Mena(INV) potentiate epidermal growth factor (EGF)-induced membrane protrusion and increase the matrix degradation activity of tumor cells. Interestingly, Mena(INV) is significantly more effective than Mena in driving metastases and sensitizing cells to EGF-dependent invasion and protrusion. Upregulation of Mena(INV) could therefore enable tumor cells to invade in response to otherwise benign EGF stimulus levels.

Identification of invasion specific splice variants of the cytoskeletal protein Mena present in mammary tumor cells during invasion in vivo

We have studied the gene expression pattern of invasive primary mammary tumor cells using a unique in vivo invasion assay that isolates the invasive tumor cells by chemotaxis. One of the genes upregulated in the invasive tumor cells is Mena, an actin binding protein involved in the regulation of cell motility. There are multiple known splice variants of Mena accounted for by four alternatively included exons, +, ++, +++ and 11a. Using the in vivo invasion assay in rats and mice with mammary tumors we observed that two isoforms of Mena, ++ and +++, are upregulated in the invasive tumor cells and one isoform, 11a, is downregulated. The Mena isoform switching pattern described here may provide a new biomarker for the presence of metastatic cancer cells and for prognosis.

Human Mena+11a isoform serves as a marker of epithelial phenotype and sensitivity to epidermal growth factor receptor inhibition in human pancreatic cancer cell lines

PURPOSE

hMena, member of the enabled/vasodilator-stimulated phosphoprotein family, is a cytoskeletal protein that is involved in the regulation of cell motility and adhesion. The aim of this study was to determine whether or not the expression of hMena isoforms correlated with sensitivity to EGFR tyrosine kinase inhibitors and could serve as markers with potential clinical use.

EXPERIMENTAL DESIGN

Human pancreatic ductal adenocarcinoma cell lines were characterized for in vitro sensitivity to erlotinib, expression of HER family receptors, markers of epithelial to mesenchymal transition, and expression of hMena and its isoform hMena(+11a). The effects of epidermal growth factor (EGF) and erlotinib on hMena expression as well as the effect of hMena knockdown on cell proliferation were also evaluated.

RESULTS

hMena was detected in all of the pancreatic tumor cell lines tested as well as in the majority of the human tumor samples [primary (92%) and metastatic (86%)]. Intriguingly, in vitro hMena(+11a) isoform was specifically associated with an epithelial phenotype, EGFR dependency, and sensitivity to erlotinib. In epithelial BxPC3 cells, epidermal growth factor up-regulated hMena/hMena(+11a) and erlotinib down-regulated expression. hMena knockdown reduced cell proliferation and mitogen-activated protein kinase and AKT activation in BxPC3 cells, and promoted the growth inhibitory effects of erlotinib.

CONCLUSIONS

Collectively, our data indicate that the hMena(+11a) isoform is associated with an epithelial phenotype and identifies EGFR-dependent cell lines that are sensitive to the EGFR inhibitor erlotinib. The availability of anti-hMena(+11a)-specific probes may offer a new tool in pancreatic cancer management if these results can be verified prospectively in cancer patients.

Ena/VASP Is Required for neuritogenesis in the developing cortex

Mammalian cortical development involves neuronal migration and neuritogenesis; this latter process forms the structural precursors to axons and dendrites. Elucidating the pathways that regulate the cytoskeleton to drive these processes is fundamental to our understanding of cortical development. Here we show that loss of all three murine Ena/VASP proteins, a family of actin regulatory proteins, causes neuronal ectopias, alters intralayer positioning in the cortical plate, and, surprisingly, blocks axon fiber tract formation during corticogenesis. Cortical fiber tract defects in the absence of Ena/VASP arise from a failure in neurite initiation, a prerequisite for axon formation. Neurite initiation defects in Ena/VASP-deficient neurons are preceded by a failure to form bundled actin filaments and filopodia. These findings provide insight into the regulation of neurite formation and the role of the actin cytoskeleton during cortical development.

Neuronal migration in the murine rostral migratory stream requires serum response factor

The central nervous system is fundamentally dependent on guided cell migration, both during development and in adulthood. We report an absolute requirement of the transcription factor serum response factor (SRF) for neuronal migration in the mouse forebrain. Conditional, late-prenatal deletion of Srf causes neurons to accumulate ectopically at the subventricular zone (SVZ), a prime neurogenic region in the brain. SRF-deficient cells of the SVZ exhibit impaired tangential chain migration along the rostral migratory stream into the olfactory bulb. SVZ explants display retarded chain migration in vitro. Regarding target genes, SRF deficiency impairs expression of the beta-actin and gelsolin genes, accompanied by reduced cytoskeletal actin fiber density. At the posttranslational level, cofilin, a key regulator of actin dynamics, displays dramatically elevated inhibitory phosphorylation at Ser-3. Our studies indicate that SRF-controlled gene expression directs both the structure and dynamics of the actin microfilament, thereby determining cell-autonomous neuronal migration.

The SRF target gene Fhl2 antagonizes RhoA/MAL-dependent activation of SRF

RhoA signaling regulates the activity of the transcription factor SRF (serum response factor) during muscle differentiation. How RhoA signaling is integrated at SRF target promoters to achieve muscle-lineage-specific expression is largely unknown. Using large-scale expression profiling combined with bioinformatic and biochemical approaches, we identified several SRF target genes, including Fhl2, encoding a transcriptional cofactor that is highly expressed in the heart. SRF binds the Fhl2 promoter in vivo and regulates Fhl2 expression in response to RhoA activation. FHL2 protein and SRF interact physically, and FHL2 binds the promoters of SRF-responsive smooth muscle (SM) genes, but not the promoters of immediate-early genes (IEGs), in response to RhoA. FHL2 antagonizes induction of SM genes, but not IEGs or cardiac genes, by competing with the coactivator MAL/MRTF-A for SRF binding. Our findings identify an autoregulatory mechanism to selectively regulate subsets of RhoA-activated SRF target genes.

SRF regulates Bcl-2 expression and promotes cell survival during murine embryonic development

The transcription factor serum response factor (SRF) controls the expression of genes involved in cellular proliferation and differentiation. Interestingly, SRF also promotes cell survival by regulating the expression of antiapoptotic genes. In in vitro differentiating murine embryonic stem (ES) cells, SRF deficiency leads to increased apoptosis. Loss of SRF correlates with impaired expression of the antiapoptotic Bcl-2 and Bcl-xl genes. SRF binds the Bcl-2 promoter in vivo and activates Bcl-2 transcription. Reconstituting Bcl-2 in Srf-/- ES cells rescues these cells from apoptosis, demonstrating that SRF-dependent Bcl-2 expression is critical for ES cell survival. At the multicellular level, SRF deficiency leads to impaired cavitation and reduced Bcl-2 expression in embryoid bodies (EBs) and inappropriate apoptosis in both EBs and pregastrulation mouse embryos. Thus, our data from genetic and cellular studies uncover SRF-regulated Bcl-2 expression as a novel mechanism that is important for cell survival during early murine embryogenesis.

Serum response factor is crucial for actin cytoskeletal organization and focal adhesion assembly in embryonic stem cells

The activity of serum response factor (SRF), an essential transcription factor in mouse gastrulation, is regulated by changes in actin dynamics. Using Srf(-/-) embryonic stem (ES) cells, we demonstrate that SRF deficiency causes impairments in ES cell spreading, adhesion, and migration. These defects correlate with defective formation of cytoskeletal structures, namely actin stress fibers and focal adhesion (FA) plaques. The FA proteins FA kinase (FAK), beta1-integrin, talin, zyxin, and vinculin were downregulated and/or mislocalized in ES cells lacking SRF, leading to inefficient activation of the FA signaling kinase FAK. Reduced overall actin expression levels in Srf(-/-) ES cells were accompanied by an offset treadmilling equilibrium, resulting in lowered F-actin levels. Expression of active RhoA-V14 rescued F-actin synthesis but not stress fiber formation. Introduction of constitutively active SRF-VP16 into Srf(-/-) ES cells, on the other hand, strongly induced expression of FA components and F-actin synthesis, leading to a dramatic reorganization of actin filaments into stress fibers and lamellipodia. Thus, using ES cell genetics, we demonstrate for the first time the importance of SRF for the formation of actin-directed cytoskeletal structures that determine cell spreading, adhesion, and migration. Our findings suggest an involvement of SRF in cell migratory processes in multicellular organisms.