Abstract 3976: Recurrent BCL10 mutations drive BTK inhibitor resistance in BN2-subtype diffuse large B-cell lymphomas by constitutively activating NF-kB and the MALT1 protease

Diffuse large B cell lymphoma (DLBCL), the most common lymphoma diagnosis, is a heterogeneous group of sub-entities with differing biology and prognosis. Frontline R-CHOP (rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisone), used regardless of subtype, cures 60-70%. Patients failed by this combination have poor prognosis. Extensive efforts to improve on R-CHOP in the frontline have failed, but recent post-hoc analysis of one negative trial suggested younger patients with specific DLBCL biologic subtypes may benefit from addition of a Bruton’s Tyrosine Kinase inhibitor (BTKi). These results could inform prospective studies in a small subset of DLBCL cases, but the rest lack biomarker-driven frontline optimizations. Newer classification systems define the BN2 (LymphGen) or Cluster 1 (Chapuy consensus clusters) subtype, characterized by BCL6 translocations and/or NOTCH2 truncations. BN2 cases specifically saw no benefit from adding BTKi to R-CHOP regardless of patient age. BCL10, encoding a key protein promoting NF-kB activation through formation of a signaling complex with CARD11 and MALT1, is recurrently mutated in DLBCL (~5%), clustering strongly in BN2 (30-40%). We hypothesize that activation of NF-kB downstream of BTK due to BCL10 gain of function promotes BTKi resistant lymphomagenesis. Recurrent BCL10 mutations include the R58Q missense mutation in the oncogenic N-terminal CARD domain and frequent truncations of the regulatory C-terminal S/T-rich domain. Overexpression of BCL10 with either mutation type in DLBCL cells promoted strong activation of NF-kB assessed by immunoblotting and EGFP NF-kB reporters. Truncated BCL10 also increased MALT1 protease activity, measured by increased substrate cleavage. BCL10 mutations drove resistance to BTKis as hypothesized, but there was no difference in sensitivity to MALT1 inhibition, revealing that downstream targets overcome drug resistance by BCL10 mutant-mediated activation. Combining MALT1i with BTKi synergistically killed cells, identifying a promising therapeutic strategy for BN2 cases. Delving into the mechanism of BCL10-mutant lymphomagenesis, gene ontology analysis of transcriptome data showed cross-activation of ERK1/2 signaling, confirmed by immunoblotting, and strong induction of cytokine production and related signaling. To fuel future studies, we have established a cre-inducible conditional BCL10-truncation mouse model at the ROSA26 locus in C57BL/6J mice. After crossing into the Mb1-Cre background, these animals showed expansion of the B-cell compartment by three months of age and remain under observation for onset of lymphoma. We therefore define mechanisms and therapeutic consequences of recurrent BCL10 mutations in DLBCL and provide new drug combinations aimed at overcoming them.

Citation Format: Caroline A. Coughlin, Preet Kumar, Evan R. Roberts, Horacio Gonzalez Lopez, Marianna Lekakis, Lingxio Li, Daniel Bilbao, Jonathan H. Schatz. Recurrent BCL10 mutations drive BTK inhibitor resistance in BN2-subtype diffuse large B-cell lymphomas by constitutively activating NF-kB and the MALT1 protease [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3976.

Aminopyridine analogs selectively target metastatic pancreatic cancer

Metastatic outgrowth is supported by metabolic adaptations that may differ from the primary tumor of origin. However, it is unknown if such adaptations are therapeutically actionable. Here we report a novel aminopyridine compound that targets a unique Phosphogluconate Dehydrogenase (PGD)-dependent metabolic adaptation in distant metastases from pancreatic cancer patients. Compared to structurally similar analogs, 6-aminopicolamine (6AP) potently and selectively reversed PGD-dependent metastatic properties, including intrinsic tumorigenic capacity, excess glucose consumption, and global histone hyperacetylation. 6AP acted as a water-soluble prodrug that was converted into intracellular bioactive metabolites that inhibited PGD in vitro, and 6AP monotherapy demonstrated anti-metastatic efficacy with minimal toxicity in vivo. Collectively, these studies identify 6AP and possibly other 6-aminopyridines as well-tolerated prodrugs with selectivity for metastatic pancreatic cancers. If unique metabolic adaptations are a common feature of metastatic or otherwise aggressive human malignancies, then such dependencies could provide a largely untapped pool of druggable targets for patients with advanced cancers.

Proteomics reveal cap-dependent translation inhibitors remodel the translation machinery and translatome

Tactical disruption of protein synthesis is an attractive therapeutic strategy, with the first-in-class eIF4A-targeting compound zotatifin in clinical evaluation for cancer and COVID-19. The full cellular impact and mechanisms of these potent molecules are undefined at a proteomic level. Here, we report mass spectrometry analysis of translational reprogramming by rocaglates, cap-dependent initiation disruptors that include zotatifin. We find effects to be far more complex than simple “translational inhibition” as currently defined. Translatome analysis by TMT-pSILAC (tandem mass tag-pulse stable isotope labeling with amino acids in cell culture mass spectrometry) reveals myriad upregulated proteins that drive hitherto unrecognized cytotoxic mechanisms, including GEF-H1-mediated anti-survival RHOA/JNK activation. Surprisingly, these responses are not replicated by eIF4A silencing, indicating a broader translational adaptation than currently understood. Translation machinery analysis by MATRIX (mass spectrometry analysis of active translation factors using ribosome density fractionation and isotopic labeling experiments) identifies rocaglate-specific dependence on specific translation factors including eEF1ε1 that drive translatome remodeling. Our proteome-level interrogation reveals that the complete cellular response to these historical “translation inhibitors” is mediated by comprehensive translational landscape remodeling.

Tactical protein synthesis inhibition is actively pursued as a cancer therapy that bypasses signaling redundancies limiting current strategies. Ho et al. show that rocaglates, first identified as inhibitors of eIF4A activity, globally reprogram cellular translation at both protein synthesis machinery and translatome levels, inducing cytotoxicity through anti-survival GEF-H1/RHOA/JNK signaling.

Abstract 1031: Translatome and protein synthesis machinery remodeling by rocaglates drives antitumor activity

Rocaglates are under active development for cancer therapy, with the first-in-class member zotatifin recently entering Phase I/II clinical trial for advanced solid tumor malignancies (NCT04092673). Initiation of this trial was based purely on rocaglates' inhibitory activity against translation initiation factor and RNA helicase eIF4A. Rapid development of these compounds towards clinical use urgently requires a complete understanding of their mechanisms. Critically, however, the full effects of rocaglates on protein synthesis are unknown, especially with regards to up-regulated proteins and rocaglate-activated translation factors that mediate their potent anticancer activity. Past rocaglate studies focused exclusively on mechanisms and targets of translational inhibition, relying exclusively on indirect RNA-based approaches that do not reliably capture proteome-level changes, a caveat proven in cancer cells responding to drugs. Formal proteomic investigations of rocaglate effects are non-existent in the literature. We addressed these vital knowledge gaps in this study. An original proteome-level analysis using metabolic pulse-labeling and TMT-mass spectrometry revealed extensive rocaglate-induced changes in protein output (translatome), including myriad rocaglate-up-regulated proteins that drive cytotoxicity through currently uncharacterized mechanisms. Specifically, we find in vitro and in vivo that rocaglates, including zotatifin, induce GEF-H1, activating anti-survival RHOA/JNK signaling. Intriguingly, these responses occur regardless of eIF4A expression. Beyond translatome remodeling, mass spectrometry-based MATRIX interrogation of the protein synthesis machinery revealed widespread rocaglate-dependent changes. As a prime example, rocaglate-augmented eEF1ϵ1 activity mediates initiator methionine-tRNAiMet delivery to drive synthesis of rocaglate-inducible proteins and phenotypes. Overall, this study transforms the current definition of rocaglates from one-dimensional eIF4A inhibitors to translation remodelers that globally reprogram protein output and the translation machinery. As human patients begin treatment with these compounds, our discovery of rocaglate-inducible proteins and rocaglate-activated translation factors that drive drug-specific responses highlights an entirely uncharacterized yet critical aspect of rocaglate potency. These timely findings emphasize systemic translational modeling as a newer concept for cancer therapy, and advocate for a systematic overhaul in our understanding of drugs traditionally defined as translation inhibitors.

Citation Format: Jyun David Ho, Jr, Tyler A. Cunningham, Caroline A. Coughlin, Artavazd Arumov, Evan R. Roberts, Daniel Bilbao, Jonathan R. Krieger, Stephen Lee, Jonathan H. Schatz. Translatome and protein synthesis machinery remodeling by rocaglates drives antitumor activity [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 1031.

Size-dependent intranasal administration of magnetoelectric nanoparticles for targeted brain localization

The brain is a massive network of neurons which are interconnected through chemical and electrical field oscillations. It is hard to overestimate the significance of the ability to control chemical and physical properties of the network at both the collective and single-cell levels. Most psychiatric and neurodegenerative diseases are typically characterized by certain aberrations of these oscillations. Recently, magnetoelectric nanoparticles (MENs) have been introduced to achieve the desired control. MENs effectively enable wirelessly controlled nanoelectrodes deep in the brain. Although MENs have been shown to cross the blood-brain barrier via intravenous (IV) administration, achieving adequate efficacy of the delivery remains an open question. Herein, through in vivo studies on a mouse model, we demonstrate at least a 4-fold improved efficacy of the targeted delivery of MENs across BBB via intranasal administration compared to an equivalent IV administration.

Optimized Doxorubicin Chemotherapy for Diffuse Large B-cell Lymphoma Exploits Nanocarrier Delivery to Transferrin Receptors

New treatments are needed to address persistent unmet clinical needs for diffuse large B-cell lymphoma (DLBCL). Overexpression of transferrin receptor 1 (TFR1) is common across cancer and permits cell-surface targeting of specific therapies in preclinical and clinical studies of various solid tumors. Here, we developed novel nanocarrier delivery of chemotherapy via TFR1-mediated endocytosis, assessing this target for the first time in DLBCL. Analysis of published datasets showed novel association of increased TFR1 expression with high-risk DLBCL cases. Carbon-nitride dots (CND) are emerging nanoparticles with excellent in vivo stability and distribution and are adaptable to covalent conjugation with multiple substrates. In vitro, linking doxorubicin (Dox) and transferrin (TF) to CND (CND-Dox-TF, CDT) was 10-100 times more potent than Dox against DLBCL cell lines. Gain- and loss-of-function studies and fluorescent confocal microscopy confirmed dependence of these effects on TFR1-mediated endocytosis. In contrast with previous therapeutics directly linking Dox and TF, cytotoxicity of CDT resulted from nuclear entry by Dox, promoting double-stranded DNA breaks and apoptosis. CDT proved safe to administer in vivo, and when incorporated into standard frontline chemoimmunotherapy in place of Dox, it improved overall survival by controlling patient-derived xenograft tumors with greatly reduced host toxicities. Nanocarrier-mediated Dox delivery to cell-surface TFR1, therefore, warrants optimization as a potential new therapeutic option in DLBCL. SIGNIFICANCE: Targeted nanoparticle delivery of doxorubicin chemotherapy via the TRF1 receptor presents a new opportunity against high-risk DLBCL tumors using potency and precision.

Abstract PO-48: Cytotoxic mechanism of a novel transferrin receptor-targeting chemotherapeutic nanocarrier for use in diffuse large B-cell lymphoma

Diffuse large B-cell lymphoma (DLBCL), the most common hematologic malignancy, is an aggressive form of non-Hodgkin lymphoma. Approximately 60% of DLBCL patients achieve long-term disease-free survival from frontline R-CHOP (rituximab, cyclophosphamide, doxorubicin, vincristine, prednisone), but patients with relapsed or refractory disease have poor prognosis. Doxorubicin (Dox) remains the most active anti-lymphoma agent, but its use is limited by well-characterized toxicities, including potentially irreversible cardiac damage. Targeted and specific delivery of Dox to tumors to overcome these limitations has been an area of active research. Targeted delivery of Dox via the transferrin receptor (TFR1) has preclinical efficacy in solid malignancies but has yet to be explored in lymphoma. We have uncovered for the first time a significant association between TFR1 expression and poor prognosis in DLBCL. Carbon-nitride dots (CNDs) are third-generation nanocarriers with inherent photoluminescence, which are easily conjugated with a wide variety of substrates. We conjugated Dox and transferrin (TF), the ligand for TFR1, to CNDs to develop CND-Dox-TF (CDT). CDT is uniquely designed to enhance Dox delivery to TFR1-expressing DLBCL tumors while limiting effects on nonmalignant tissues. BJAB and Farage cell lines treated with CDT for 24 hours underwent apoptosis at a significantly lower concentration when compared to Dox (50 nM vs. 1000 nM). Overall, CDT was 1-2 Log10 more potent than Dox against DLBCL cell lines. Co-incubation with 250 uM of antagonist holo-transferrin significantly decreased BJAB and Farage sensitivity to CDT, confirming activity through TFR1. Confocal microscopy of BJAB cells incubated up to 24 hours with 250 nM Dox and 30 nM CDT reveled enhanced nuclear colocalization of Dox at a significantly lower concentration. Prior dose-finding experiments in non-tumor bearing mice identified a CDT safe working dose of 33.0 mg/kg containing 16% moles of Dox in comparison to Dox maximum-tolerated dose (MTD) 3.3 mg/kg. We engrafted 2 groups of 10 NSG mice with a Dox-sensitive high-TFR1 expressing patient-derived xenograft (PDX) tumor. Mice were dosed with CDT and Dox on day 0, 14, and 24. CDT demonstrated similar anti-lymphoma efficacy with reduced toxicity: CDT-treated mice displayed no significant decline in body weight, which is characteristic and was observed following each single-agent Dox treatment. Histology analyses revealed little to no obvious damage to CDT-treated nonmalignant tissues, including myocardium. With a working dose of CDT identified, we now have under way clinically relevant R-CHOP vs. R-nanoCHOP (CDT substituted for Dox) assessments in our PDX mouse model. Capitalizing on the unique design, we expect to observe improved anti-lymphoma efficacy, with decreased toxicities and an improvement in overall survival. In sum, we provide mechanistic insight for novel DLBCL nano-chemotherapy and illustrate preclinical efficacy for a promising new therapeutic approach.

Citation Format: Artavazd Arumov, Piumi Y. Liyanage, Asaad Trabolsi, Evan R. Roberts, Braulio Ferreira, Daniel Bilbao, Roger M. LeBlanc, Jonathan H. Schatz. Cytotoxic mechanism of a novel transferrin receptor-targeting chemotherapeutic nanocarrier for use in diffuse large B-cell lymphoma [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-48.

Dual Screen for Efficacy and Toxicity Identifies HDAC Inhibitor with Distinctive Activity Spectrum for BAP1-Mutant Uveal Melanoma

Drug screens leading to successful targeted therapies in cancer have been mainly based on cell viability assays identifying inhibitors of dominantly acting oncogenes. In contrast, there has been little success in discovering targeted therapies that reverse the effects of inactivating mutations in tumor-suppressor genes. BAP1 is one such tumor suppressor that is frequently inactivated in a variety of cancers, including uveal melanoma, renal cell carcinoma, and mesothelioma. Because BAP1 is an epigenetic transcriptional regulator of developmental genes, we designed a two-phase drug screen involving a cell-based rescue screen of transcriptional repression caused by BAP1 loss, followed by an in vivo screen of lead compounds for rescue of a BAP1-deficient phenotype with minimal toxicity in Xenopus embryos. The first screen identified 9 compounds, 8 of which were HDAC inhibitors. The second screen eliminated all except one compound due to inefficacy or toxicity. The resulting lead compound, quisinostat, has a distinctive activity spectrum, including high potency against HDAC4, which was recently shown to be a key target of BAP1. Quisinostat was further validated in a mouse model and found to prevent the growth of BAP1-mutant uveal melanomas. This innovative strategy demonstrates the potential for identifying therapeutic compounds that target tumor-suppressor mutations in cancer. IMPLICATIONS: Few drugs have been identified that target mutations in tumor suppressors. Using a novel 2-step screening approach, strategy, we identified quisinostat as a candidate for therapy in BAP1-mutant uveal melanoma. HDAC4 is implicated as a key target in uveal melanoma and perhaps other BAP1-mutant cancers.

Abstract PR13: PTPN11 plays oncogenic roles and is a therapeutic target for BRAF wild-type melanomas

Melanoma is one of the most highly mutated cancer types, harboring numerous alterations with unknown significance. To identify functional drivers of melanoma, we searched for cross-species conserved mutations utilizing a mouse melanoma model driven by loss of PTEN and CDKN2A, and identified mutations in Kras, Erbb3, and Ptpn11. PTPN11 encodes the SHP2 protein tyrosine phosphatase (PTP) that activates the RAS/RAF/MAPK pathway. Although PTPN11 is an oncogene in leukemia, lung, and breast cancers, its roles in melanoma are not clear. In this study, we found that PTPN11 is frequently activated in human melanoma specimens and cell lines and is required for full RAS/RAF/MAPK signaling activation in BRAF wild-type (either NRAS mutant or wild-type) melanoma cells. PTPN11 played oncogenic roles in melanoma by driving anchorage-independent colony formation and tumor growth. In Pten and Cdkn2a null mice, tet-inducible and melanocyte-specific PTPN11E76K expression significantly enhanced melanoma tumorigenesis. Melanoma cells derived from this mouse model showed doxycycline-dependent tumor growth in nude mice. Silencing PTPN11E76K expression by doxycycline withdrawal caused regression of established tumors by induction of apoptosis and senescence and suppression of proliferation. Moreover, the PTPN11 inhibitor (SHP099) also caused regression of NRASQ61K-mutant melanoma. Using a quantitative tyrosine phospho-proteomics approach, we identified GSK3α/β as one of the key substrates that were differentially tyrosine-phosphorylated in these experiments modulating PTPN11. This study demonstrates that PTPN11 plays oncogenic roles in melanoma and regulates RAS and GSK3α/β signaling pathways. This study also identifies PTPN11 as a novel and actionable therapeutic target for BRAF wild-type melanoma.

This abstract is also being presented as Poster A14.

Citation Format: Kristen S. Hill, Evan R. Roberts, Xue Wang, John M. Koomen, Jane L. Messina, Jamie K. Teer, Youngchul Kim, Jie Wu, Charles E. Chalfant, Minjung Kim. PTPN11 plays oncogenic roles and is a therapeutic target for BRAF wild-type melanomas [abstract]. In: Proceedings of the AACR Special Conference on Melanoma: From Biology to Target; 2019 Jan 15-18; Houston, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(19 Suppl):Abstract nr PR13.

Abstract 4025: New candidate therapy for BAP1-mutant cancer identified using novel screen

Inactivation of the oncogene BAP1 is associated with poor prognosis in many cancers, including uveal melanoma (UM). Therapies for mediating the detrimental effects of BAP1 mutations have yet to be developed. Previously, we found that BAP1 depletion in Xenopus causes a striking developmental phenotype and a global dysregulation of differentiation markers across the genetic landscape. This was caused by impaired promoter assembly at commitment genes, marked by decreased H3K27ac levels. Inhibition of HDAC4 protein rescues the affected BAP1-depleted phenotype and genetic regulations, further emphasizing the role of H3K27ac in BAP1 function. Pairing these findings with a lab-devised multitiered screening process, we identified an epigenetic compound that successfully reverses the detrimental effects of the BAP1 deficient phenotype back to phenotypically normal conditions. This multitiered screening process tests prospective compounds for the ability to mediate transcriptional aberrations caused by BAP1 loss in UM cells (phase 1), rescue the BAP1 loss phenotype in Xenopus (phase 2), and provide significant inhibition of UM tumor growth in a mouse model (phase 3). These findings reveal a new application for a promising epigenetic compound as a therapeutic and reversing agent for BAP1 mutant UM. Furthermore, our streamlined process for the testing of promising therapeutic agents can accelerate the testing of such agents and getting them to clinical trials in a timely manner.

Citation Format: DAWN A. OWENS, Jeffim N. Kuznetsov, Andy Lopez, Stefan Kurtenbach, Daniel Bilbao, Evan R. Roberts, Claude-Henry Volmar, Claes R. Wahlestedt, Shaun P. Brothers, J. William Harbour. New candidate therapy for BAP1-mutant cancer identified using novel screen [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 4025.

K27-linked ubiquitination of BRAF by ITCH engages cytokine response to maintain MEK-ERK signaling

BRAF plays an indispensable role in activating the MEK/ERK pathway to drive tumorigenesis. Receptor tyrosine kinase and RAS-mediated BRAF activation have been extensively characterized, however, it remains undefined how BRAF function is fine-tuned by stimuli other than growth factors. Here, we report that in response to proinflammatory cytokines, BRAF is subjected to lysine 27-linked poly-ubiquitination in melanoma cells by the ITCH ubiquitin E3 ligase. Lysine 27-linked ubiquitination of BRAF recruits PP2A to antagonize the S365 phosphorylation and disrupts the inhibitory interaction with 14-3-3, leading to sustained BRAF activation and subsequent elevation of the MEK/ERK signaling. Physiologically, proinflammatory cytokines activate ITCH to maintain BRAF activity and to promote proliferation and invasion of melanoma cells, whereas the ubiquitination-deficient BRAF mutant displays compromised kinase activity and reduced tumorigenicity. Collectively, our study reveals a pivotal role for ITCH-mediated BRAF ubiquitination in coordinating the signals between cytokines and the MAPK pathway activation in melanoma cells.

PTPN11 Plays Oncogenic Roles and Is a Therapeutic Target for BRAF Wild-Type Melanomas

Melanoma is one of the most highly mutated cancer types. To identify functional drivers of melanoma, we searched for cross-species conserved mutations utilizing a mouse melanoma model driven by loss of PTEN and CDKN2A, and identified mutations in Kras, Erbb3, and Ptpn11. PTPN11 encodes the SHP2 protein tyrosine phosphatase that activates the RAS/RAF/MAPK pathway. Although PTPN11 is an oncogene in leukemia, lung, and breast cancers, its roles in melanoma are not clear. In this study, we found that PTPN11 is frequently activated in human melanoma specimens and cell lines and is required for full RAS/RAF/MAPK signaling activation in BRAF wild-type (either NRAS mutant or wild-type) melanoma cells. PTPN11 played oncogenic roles in melanoma by driving anchorage-independent colony formation and tumor growth. In Pten- and Cdkn2a-null mice, tet-inducible and melanocyte-specific PTPN11^E76K expression significantly enhanced melanoma tumorigenesis. Melanoma cells derived from this mouse model showed doxycycline-dependent tumor growth in nude mice. Silencing PTPN11^E76K expression by doxycycline withdrawal caused regression of established tumors by induction of apoptosis and senescence, and suppression of proliferation. Moreover, the PTPN11 inhibitor (SHP099) also caused regression of NRAS^Q61K -mutant melanoma. Using a quantitative tyrosine phosphoproteomics approach, we identified GSK3α/β as one of the key substrates that were differentially tyrosine-phosphorylated in these experiments modulating PTPN11. This study demonstrates that PTPN11 plays oncogenic roles in melanoma and regulates RAS and GSK3β signaling pathways. IMPLICATIONS: This study identifies PTPN11 as an oncogenic driver and a novel and actionable therapeutic target for BRAF wild-type melanoma.

Abstract 4364: R-Ras activation cooperates with BRAF mutation in melanoma tumorigenesis

The Ras family of small GTP binding proteins are tightly regulated through a complex network of proteins. In melanoma the Ras signaling pathway is frequently activated by mutations in NRAS (20%), KRAS (2%) and HRAS (1%); alternatively, Ras can also be activated by the inactivation of Ras GTPase activating proteins (RasGAPs) such as NF1, RASA1, and RASA2. Recently, we observed that inactivation of RASA1 (RAS p21 protein activator 1, also called p120RasGAP) suppressed melanoma via its RasGAP activity toward the R-Ras (related RAS viral (r-ras) oncogene homolog) isoform and that R-Ras was required to promote anchorage-independent growth driven by RASA1 inactivation. Moreover, a low level of RASA1 mRNA expression is associated with decreased overall survival in melanoma patients with BRAF mutations. Based on these observations, we hypothesized that, although not mutated, R-Ras is activated in melanoma by inactivation of RasGAPs and that BRAF activation cooperates with this RasGAP/R-Ras pathway activation in melanoma tumorigenesis.

In this study, we addressed the importance of R-Ras, a previously less appreciated member of the Ras small GTPases family, in melanoma tumorigenesis. We observed frequent activation of R-Ras in BRAF mutant human melanoma cell lines and human melanoma specimens. In addition, RNAi-mediated knockdown of R-Ras suppressed anchorage-independent colony growth and tumor growth. Of the 3 major RAS effector pathways, specifically MEK/ERK, AKT and Ral-A, reduced R-Ras expression suppressed Ral-A activation, which may explain the mechanism of Ral-A activation in BRAF mutant melanoma. Interestingly, anchorage-independent growth driven by R-Ras activation downstream of RASA1 inactivation was suppressed by both genetic (siRNA targeting Ral-A) and pharmacological (Ral inhibitor BQU57) inhibition of Ral-A. To further investigate the impact of RASA1 loss, and thus R-Ras activation, on BRAF mutant melanoma development in vivo, we generated a Rasa1L/L; BRAFCA/CA; Tyr-CreERT2 mouse model in which treatment with 4OHT results in expression of constitutively activated mutant BRAF and deletion of Rasa1 in melanocytic lineage cells. Preliminary analysis shows hyperpigmentation of the ear, tail, and foot pad in Rasa1L/L BRAFCA/CA mice compared to Rasa1+/+ BRAFCA/CA littermates; as well as, the development of cutaneous melanoma in Rasa1 deficient mice. Tumors generated in this animal model will be analyzed to determine the extent of R-Ras and Ral-A activity in vivo. This study demonstrates the importance of the RASA1/R-Ras/Ral-A signaling pathway in BRAF mutant melanoma and supports the possible combinatorial treatment strategy targeting both the BRAF/MAPK and Ral signaling pathways.

Citation Format: Kristen S. Hill, Evan R. Roberts, Xue Wang, Youngchul Kim, Jane Messina, Minjung Kim. R-Ras activation cooperates with BRAF mutation in melanoma tumorigenesis [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 4364.

Abstract B12: The importance of the RASA1/R-Ras/Ral-A signaling axis in melanoma tumorigenesis

The Ras family of small GTP-binding proteins is frequently activated by mutations, including NRAS (20%), KRAS (2%), and HRAS (1%), in melanoma. In addition to mutations, Ras isoforms can also be activated by the inactivation of Ras GTPase activating proteins (RasGAPs), such as NF1, RASA1, and RASA2. In our recent study, we observed that the inactivation of RASA1 (RAS p21 protein activator 1, also called p120RasGAP) suppressed melanoma via its RasGAP activity toward the R-Ras (related RAS viral (r-ras) oncogene homolog) isoform. We hypothesized that, although not mutated, R-Ras is activated in melanoma through the inactivation of RasGAPs and that RasGAP/R-Ras pathway activation cooperates with BRAF activation in melanoma tumorigenesis.

In this study, we addressed the importance of R-Ras, a previously less-appreciated member of the Ras family, in melanoma tumorigenesis and investigated the molecular mechanisms underlying R-Ras signaling in BRAF mutant melanoma. We observed frequent activation of R-Ras in BRAF mutant human melanoma cell lines. In addition, RNAi-mediated reduced expression of R-Ras suppressed anchorage-independent colony growth and tumor growth. Moreover, among the three major RAS effector pathways, reduced R-Ras expression suppressed Ral-A activation, which may explain the mechanism of Ral-A activation in BRAF mutant melanoma. Interestingly, anchorage-independent growth driven by RASA1 inactivation and subsequent R-Ras activation was suppressed by both genetic (siRNA targeting Ral-A) and pharmacologic (Ral inhibitor BQU57) inhibition of Ral-A. To further investigate the impact of RASA1 loss, and thus R-Ras activation, on BRAF mutant melanoma development in vivo, we generated a RASA1 L/L; BRAF CA/CA; Tyr-CreERT2 mouse model in which treatment with 4OHT results in the expression of constitutively activated mutant BRAF and the deletion of RASA1 in melanocytic lineage cells. Preliminary analysis shows hyperpigmentation of the ear, tail, and foot pad in RASA1 L/L BRAF CA/CA mice compared to RASA1 +/+ BRAF CA/CA littermates and the development of melanoma in RASA1 mutant mice. This study demonstrates the importance of the RASA1/R-Ras/Ral-A signaling pathway in BRAF mutant melanoma and supports the possible combinatorial treatment strategy targeting both the BRAF/MAPK and Ral signaling pathways.

Citation Format: Kristen S. Hill, Xue Wang, Evan R. Roberts, Youngchul Kim, Jane Messina, Minjung Kim. The importance of the RASA1/R-Ras/Ral-A signaling axis in melanoma tumorigenesis [abstract]. In: Proceedings of the AACR Special Conference: Advances in Modeling Cancer in Mice: Technology, Biology, and Beyond; 2017 Sep 24-27; Orlando, Florida. Philadelphia (PA): AACR; Cancer Res 2018;78(10 Suppl):Abstract nr B12.

Abstract A04: Cross-species oncogenomics approach identifies PTPN11 as an oncogene and potential therapeutic target in melanoma

Melanoma is a deadly disease carrying many genetic mutations. A major challenge to the development of effective targeted therapies in melanoma is the identification of true “driver” mutations among numerous “passenger” alterations. Several previous studies support using cross-species comparative oncogenomic approaches for cancer gene discovery. Specifically, it has been shown that mice and humans share several genetic events in the development of cancer and that these events that are conserved across different species may point to functionally important and evolutionary conserved alterations targeting “driver” genes. Recently, we analyzed melanoma genomes from a mouse model driven by the loss of PTEN and CDKN2A (INK4A/ARF), commonly observed alterations in human melanoma patients, by whole-exome sequencing. This study identified several conserved cross-species orthologous mutations in Kras, Erbb3, and Ptpn11. In this study, we addressed the functional roles of PTPN11 in melanoma tumorigenesis and tumor maintenance, its effect on RAS/RAF/MEK/ERK signaling pathway, and its activation status in human melanoma.

Melanoma displays frequent activation of the RAS/RAF/MEK/ERK signaling pathway, which is intricately regulated by multiple proteins including PTPN11 (Tyrosine-Protein Phosphatase Non-Receptor Type 11, encoding SHP2). Although implicated as an oncogene in multiple cancer types, the oncogenic role of PTPN11 has not been fully established in melanoma. PTPN11 can be activated by receptor tyrosine kinases (RTKs) and/or by point mutations. Although the mutation rate is low (1~3%), we observed activating phosphorylation on Tyr 542 of PTPN11 in 40% (n=15/38) of melanoma specimens and the majority of human melanoma cell lines (n=14), indicating the potential frequent activation of PTPN11 in human melanoma. PTPN11 knock-down suppressed ERK activation in NRAS mutant (WM1361A, 1366, 1346) and BRAF/NRAS wt (WM3211, MeWo, CHL1) melanoma cells, but not in BRAF mutant (1205Lu, IGR1, 983C) cells. Moreover, we have shown that the expression of active PTPN11 E76K mutant drives soft-agar colony growth in vitro, tumor growth in nude mice, RAS/RAF/MEK/ERK activation, and resistance to MEK inhibition, whereas knock-down of Ptpn11 reduces colony growth and ERK activation. We generated a tet-inducible, melanocyte-specific, PTPN11 E76K transgenic mouse model in a Pten and Cdkn2a null background and observed melanoma formation. Implantation of melanoma cells derived from this model showed doxycycline-dependent tumor growth in nude mice; additionally, withdrawal of doxycycline and subsequent extinction of PTPN11 E76K caused regression of established tumors, supporting a tumor-maintenance role of PTPN11. These data support the oncogenic roles of PTPN11 in melanoma by regulating RAS/RAF/MAPK pathway activation and the value of PTPN11 as a novel and actionable therapeutic target.

Citation Format: Kristen S. Hill, Xue Wang, Evan R. Roberts, Ellen M. Marin, Jamie K. Teer, Youngchul Kim, Jane Messina, Jie Wu, Minjung Kim. Cross-species oncogenomics approach identifies PTPN11 as an oncogene and potential therapeutic target in melanoma [abstract]. In: Proceedings of the AACR Special Conference: Advances in Modeling Cancer in Mice: Technology, Biology, and Beyond; 2017 Sep 24-27; Orlando, Florida. Philadelphia (PA): AACR; Cancer Res 2018;78(10 Suppl):Abstract nr A04.

Adverse effects of homeopathy: a systematic review of published case reports and case series - comment by Tournier et al

Linked Comment: Jackson. Int J Clin Pract 2013; 67: 385. Linked Comment: Walach et al. Int J Clin Pract 2013; 67: 385–6. Linked Comment: Posadzki and Ernst. Int J Clin Pract 2013; 67: 386–7. Linked Comment: Grimes. Int J Clin Pract 2013; 67: 387. Linked Comment: Posadzki and Ernst. Int J Clin Pract 2013; 67: 389.

Mississippi public health nurses and midwives: a partnership that worked

At the turn of the century maternal and infant mortality rates were high in this southern state. Untrained midwives conducted many of the deliveries. Initial support for locating and training midwives by public health nurses was provided by the American Red Cross and the United States Public Health Services. Later, funding from a philanthropic organization (Rockefeller International Foundation) provided a mechanism that brought Mississippi public health nurses and midwives to a partnership that endured for over a half a century, and contributed to better maternal-infant health care outcomes for that state.