Inhibition of mTOR signaling and clinical activity of metformin in oral premalignant lesions

BACKGROUND

The aberrant activation of the PI3K/mTOR signaling circuitry is one of the most frequently dysregulated signaling events in head and neck squamous cell carcinoma (HNSCC). Here, we conducted a single-arm, open-label phase IIa clinical trial in individuals with oral premalignant lesions (OPLs) to explore the potential of metformin to target PI3K/mTOR signaling for HNSCC prevention.

METHODS

Individuals with OPLs, but who were otherwise healthy and without diabetes, underwent pretreatment and posttreatment clinical exam and biopsy. Participants received metformin for 12 weeks (week 1, 500 mg; week 2, 1000 mg; weeks 3–12, 2000 mg daily). Pretreatment and posttreatment biopsies, saliva, and blood were obtained for biomarker analysis, including IHC assessment of mTOR signaling and exome sequencing.

RESULTS

Twenty-three participants were evaluable for response. The clinical response rate (defined as a ≥50% reduction in lesion size) was 17%. Although lower than the proposed threshold for favorable clinical response, the histological response rate (improvement in histological grade) was 60%, including 17% complete responses and 43% partial responses. Logistic regression analysis revealed that when compared with never smokers, current and former smokers had statistically significantly increased histological responses (P = 0.016). Remarkably, a significant correlation existed between decreased mTOR activity (pS6 IHC staining) in the basal epithelial layers of OPLs and the histological (P = 0.04) and clinical (P = 0.01) responses.

CONCLUSION

To our knowledge this is the first phase II trial of metformin in individuals with OPLs, providing evidence that metformin administration results in encouraging histological responses and mTOR pathway modulation, thus supporting its further investigation as a chemopreventive agent.

TRIAL REGISTRATION

NCT02581137

FUNDING

NIH contract HHSN261201200031I, grants R01DE026644 and R01DE026870

Abstract 1610: Local delivery of anti CTLA4 mediates cDC1 dependent eradication of HNSCC with limited IRAEs in a preclinical model of oral squamous cell carcinoma

Head and neck squamous cell carcinoma (HNSCC) ranks 6th in cancer incidence worldwide and has a five-year survival rate of only 63%. Despite advances in curative-intent therapies over the past three decades, rates of recurrence exceed 50% and long-term toxicities remain unacceptably morbid. Immunotherapies - principally immune checkpoint inhibitors (ICI) such as αPD-1 and αCTLA-41 antibodies which restore endogenous antitumor T cell immunity - offer the greatest promise for achieving durable response in HNSCC. However, the clinical application of ICI has been limited by immune-related adverse events (irAEs), which is a consequence of compromised peripheral immune tolerance after ICI therapy. Although irAEs are often reversible they can become severe, at best prompting premature termination of therapy or at worst becoming life-threatening. To address the off-target irAEs inherent to systemic ICI therapy, we developed a novel, local delivery strategy based upon an array of soluble microneedles (MN). Leveraging our recently reported syngeneic, tobacco-signature murine HNSCC model, we characterized the αCTLA-41 anti-tumor response as both CD8 T cell- and conventional dendritic cell type 1-dependent. When comparing αCTLA-4 therapy delivered in the traditional systemic format or with our local-MN delivery system, we found that while both routes of delivery led to >90% tumor responses, local-MN delivery achieved responses with lower total dosing while also limiting distribution of αCTLA-41 antibody from areas distal to draining lymphatic basins. Employing the previously described Foxp3-GFP-DTR GEMM developed for interrogation of murine irAEs, we found that local-MN protected animals from irAEs observed with systemic therapy. Taken together, our findings support the exploration of the microneedle array as a viable delivery strategy for ICI treatment in HNSCC.

Citation Format: Mara Gilardi, Zhiyong Wang, Victoria H. Wu, Miguel Angel Lopez-Ramirez, Fernando Soto-Alvarez, Robert Saddawi-Konefka, Dana Steffen, Marco Proietto, Zbigniew Mikulski, Haruka Miki, Jayanth Shankara Narayanan, Alfredo Molinolo, Joseph Wang, J. Silvio Gutkind. Local delivery of anti CTLA4 mediates cDC1 dependent eradication of HNSCC with limited IRAEs in a preclinical model of oral squamous cell carcinoma [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 1610.

Abstract 1425: Synergistic antitumor efficacy of the dual RAF/MEK inhibitor VS-6766 with FAK inhibition for treatment of RAS-dependent solid tumors

The RAS/RAF/MEK/ERK pathway is the most mutated oncogenic pathway in cancer, and RAS pathway mutations often present with an overall worse prognosis. Although RAF and MEK have been validated as anticancer targets and several BRAF and MEK inhibitors (MEKi) are FDA approved, acquired resistance develops in most patients. Preclinically, inhibition of RAF or MEK has been found to activate focal adhesion kinase (FAK) signaling which may bypass RAS pathway blockade by driving tumor growth through activation of downstream pathways such as RhoA and YAP. VS-6766 is a unique dual RAF/MEK inhibitor which allows VS-6766 to block MEK signaling without the compensatory MEK activation that limits the efficacy of other MEK inhibitors. Defactinib is a selective FAK inhibitor (FAKi). Clinical studies are ongoing evaluating VS-6766 and defactinib for the treatment of various solid tumors. In 3D proliferation assays in vitro, defactinib was synergistic with VS-6766 or trametinib (MEKi) in reducing viability of several human tumor cell lines, including KRAS mutant (mt) ovarian cancer (TOV-21G) and KRAS-G12V mt non-small cell lung cancer (NSCLC; H441). We next investigated whether FAKi augments the efficacy of VS-6766 in solid tumor models. Combination of a FAKi with VS-6766 in a KRAS mt ovarian xenograft model (TOV21G) induced >30% tumor regression in 9/10 mice, whereas each agent alone induced mainly tumor stasis (>30% tumor regression with FAKi monotherapy or VS-6766 monotherapy in 1/10 and 3/10 mice, respectively) following 11 days of treatment. Similar results were observed in KRAS mt NSCLC (H2122) and GNAQ mt uveal melanoma (92.1) models in which the combination of FAKi with VS-6766 or trametinib induced tumor regression. In several patients with KRAS mt tumors, sequential biopsies showed that treatment with VS-6766 induced FAK activation (pY397) as a potential resistance mechanism, and this increased FAK activation was reversed in the presence of the defactinib/VS-6766 combination. Accordingly, the combination of VS-6766 with defactinib showed clinical activity in low grade serous ovarian cancer (LGSOC; ORR = 56% in KRAS-G12 mt and ORR = 41% in all 17 LGSOC patients; 8/17/20 data cut off). Importantly, the combination of defactinib with VS-6766 also induced responses in patients who had progressed on previous MEK inhibitor regimens. VS-6766 with defactinib also showed clinical activity in KRAS-G12V mt NSCLC. Furthermore, this combination regimen of VS-6766 with defactinib exhibited a manageable safety profile with no patients discontinuing for adverse events (NCT03875820). These preclinical and clinical data support the recent initiation of two registration-directed studies evaluating VS-6766 ± defactinib for the treatment of recurrent LGSOC with or without a KRAS mutation (NCT04625270) and recurrent NSCLC with KRAS-G12V or other KRAS mutation (NCT04620330).

Citation Format: Silvia Coma, Justine S. Paradis, J Silvio Gutkind, Jonathan A. Pachter. Synergistic antitumor efficacy of the dual RAF/MEK inhibitor VS-6766 with FAK inhibition for treatment of RAS-dependent solid tumors [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 1425.

G Protein-Coupled receptors and heterotrimeric G proteins as cancer drivers

G protein-coupled receptors (GPCRs) and heterotrimeric G proteins play central roles in a diverse array of cellular processes. As such, dysregulation of GPCRs and their coupled heterotrimeric G proteins can dramatically alter the signalling landscape and functional state of a cell. Consistent with their fundamental physiological functions, GPCRs and their effector heterotrimeric G proteins are implicated in some of the most prevalent human diseases, including a complex disease such as cancer that causes significant morbidity and mortality worldwide. GPCR/G protein-mediated signalling impacts oncogenesis at multiple levels by regulating tumour angiogenesis, immune evasion, metastasis, and drug resistance. Here, we summarize the growing body of research on GPCRs and their effector heterotrimeric G proteins as drivers of cancer initiation and progression, and as emerging antitumoural therapeutic targets.

Synthetic Lethal Screens Reveal Cotargeting FAK and MEK as a Multimodal Precision Therapy for GNAQ-Driven Uveal Melanoma

PURPOSE

Uveal melanoma is the most common eye cancer in adults. Approximately 50% of patients with uveal melanoma develop metastatic uveal melanoma (mUM) in the liver, even after successful treatment of the primary lesions. mUM is refractory to current chemo- and immune-therapies, and most mUM patients die within a year. Uveal melanoma is characterized by gain-of-function mutations in GNAQ/GNA11, encoding Gαq proteins. We have recently shown that the Gαq-oncogenic signaling circuitry involves a noncanonical pathway distinct from the classical activation of PLCβ and MEK-ERK. GNAQ promotes the activation of YAP1, a key oncogenic driver, through focal adhesion kinase (FAK), thereby identifying FAK as a druggable signaling hub downstream from GNAQ. However, targeted therapies often activate compensatory resistance mechanisms leading to cancer relapse and treatment failure.

EXPERIMENTAL DESIGN

We performed a kinome-wide CRISPR-Cas9 sgRNA screen to identify synthetic lethal gene interactions that can be exploited therapeutically. Candidate adaptive resistance mechanisms were investigated by cotargeting strategies in uveal melanoma and mUM in vitro and in vivo experimental systems.

RESULTS

sgRNAs targeting the PKC and MEK-ERK signaling pathways were significantly depleted after FAK inhibition, with ERK activation representing a predominant resistance mechanism. Pharmacologic inhibition of MEK and FAK showed remarkable synergistic growth-inhibitory effects in uveal melanoma cells and exerted cytotoxic effects, leading to tumor collapse in uveal melanoma xenograft and liver mUM models in vivo.

CONCLUSIONS

Coupling the unique genetic landscape of uveal melanoma with the power of unbiased genetic screens, our studies reveal that FAK and MEK-ERK cotargeting may provide a new network-based precision therapeutic strategy for mUM treatment.See related commentary by Harbour, p. 2967.

Clinical trial in progress: Phase II trial of defactinib (VS-6063) combined with VS-6766 (CH5126766) in patients with metastatic uveal melanoma

TPS9588

Background: Despite successful treatment of primary uveal melanomas (UM), up to 50% of patients subsequently develop systemic metastasis, with the liver involved in up to 90% of patients. Currently there is no US FDA-approved treatment for metastatic uveal melanoma (MUM). Activating mutations in genes encoding alpha subunits of the heterotrimeric G proteins, GNAQ and GNA11, are found in 80-90% of UM. Recent information suggests that GNAQ/GNA11-oncogenic signaling involves a non-canonical pathway conferring the activation of YAP1, distinct from the activation of PLCβ and PKC-MEK-ERK, which may explain the failure of MEK inhibitors in MUM patients. Focal Adhesion Kinase (FAK) is a tyrosine kinase that provides a direct link between Gαq and tyrosine phosphorylation networks controlling YAP and UM growth. Interestingly, UM represents the human cancer harboring the highest level of FAK overexpression. Recent kinome-wide CRISPR-Cas9 screens revealed that FAK and RAF/MEK co-targeting may provide a new network-based precision therapeutic strategy for MUM treatment. Methods: This is an investigator-initiated, prospective, single arm, single-institution, phase II trial evaluating the combination of a FAK inhibitor (defactinib, VS-6063) with a RAF/MEK inhibitor (VS-6766, CH5126766) for the treatment of patients with metastatic uveal melanoma [NCT04720417]. The primary endpoint of the study is disease control rate (DCR) of 50% including complete response (CR), partial response (PR), and stable disease (SD) as determined by RECIST criteria version 1.1. Secondary endpoints include progression free survival, overall survival, and causality of adverse events. Exploratory endpoints include analysis of the pharmacodynamic profile, mechanism of resistance to the combination, and investigation of circulating free DNA as a biomarker. The efficacy of this combination treatment will be assessed using the Simon’s two stage design. In stage I, a total number of 8 patients are accrued and if there are 2 or fewer overall responses among these 8 patients, further enrollment of patients may be stopped with the conclusion that DCR cannot be 50% or greater. Otherwise, an additional 10 patients will be accrued in stage II, resulting in a total sample size of 18 patients. Patients at 18 years or older with metastases from uveal melanoma will be eligible (any line of therapy). Defactinib (200 mg) will be administered orally twice a day in combination with VS-6766 (3.2 mg) administered orally twice a week for 3 weeks, in 28-day cycles. Dose modification will be considered based on toxicity. Treatment will be continued until maximum clinical benefit is obtained; disease progression or the development of intolerable side effects. Enrollment to stage 1 began in February 2021. Clinical trial information: NCT04720417.

Disruption of the HER3-PI3K-mTOR oncogenic signaling axis and PD-1 blockade as a multimodal precision immunotherapy in head and neck cancer

Immune checkpoint blockade (ICB) therapy has revolutionized head and neck squamous cell carcinoma (HNSCC) treatment, but <20% of patients achieve durable responses. Persistent activation of the PI3K/AKT/mTOR signaling circuitry represents a key oncogenic driver in HNSCC; however, the potential immunosuppressive effects of PI3K/AKT/mTOR inhibitors may limit the benefit of their combination with ICB. Here we employ an unbiased kinome-wide siRNA screen to reveal that HER3, is essential for the proliferation of most HNSCC cells that do not harbor PIK3CA mutations. Indeed, we find that persistent tyrosine phosphorylation of HER3 and PI3K recruitment underlies aberrant PI3K/AKT/mTOR signaling in PIK3CA wild type HNSCCs. Remarkably, antibody-mediated HER3 blockade exerts a potent anti-tumor effect by suppressing HER3-PI3K-AKT-mTOR oncogenic signaling and concomitantly reversing the immune suppressive tumor microenvironment. Ultimately, we show that HER3 inhibition and PD-1 blockade may provide a multimodal precision immunotherapeutic approach for PIK3CA wild type HNSCC, aimed at achieving durable cancer remission.

The anti-tumour activity of DNA methylation inhibitor 5-aza-2'-deoxycytidine is enhanced by the common analgesic paracetamol through induction of oxidative stress

The DNA demethylating agent 5-aza-2'-deoxycytidine (DAC, decitabine) has anti-cancer therapeutic potential, but its clinical efficacy is hindered by DNA damage-related side effects and its use in solid tumours is debated. Here we describe how paracetamol augments the effects of DAC on cancer cell proliferation and differentiation, without enhancing DNA damage. Firstly, DAC specifically upregulates cyclooxygenase-2-prostaglandin E2 pathway, inadvertently providing cancer cells with survival potential, while the addition of paracetamol offsets this effect. Secondly, in the presence of paracetamol, DAC treatment leads to glutathione depletion and finally to accumulation of ROS and/or mitochondrial superoxide, both of which have the potential to restrict tumour growth. The benefits of combined treatment are demonstrated here in head and neck squamous cell carcinoma (HNSCC) and acute myeloid leukaemia cell lines, further corroborated in a HNSCC xenograft mouse model and through mining of publicly available DAC and paracetamol responses. The sensitizing effect of paracetamol supplementation is specific to DAC but not its analogue 5-azacitidine. In summary, the addition of paracetamol could allow for DAC dose reduction, widening its clinical usability and providing a strong rationale for consideration in cancer therapy.

Cancer-associated fibroblast secretion of PDGFC promotes gastrointestinal stromal tumor growth and metastasis

Targeted therapies for gastrointestinal stromal tumor (GIST) are modestly effective, but GIST cannot be cured with single agent tyrosine kinase inhibitors. In this study, we sought to identify new therapeutic targets in GIST by investigating the tumor microenvironment. Here, we identified a paracrine signaling network by which cancer-associated fibroblasts (CAFs) drive GIST growth and metastasis. Specifically, CAFs isolated from human tumors were found to produce high levels of platelet-derived growth factor C (PDGFC), which activated PDGFC-PDGFRA signal transduction in GIST cells that regulated the expression of SLUG, an epithelial-mesenchymal transition (EMT) transcription factor and downstream target of PDGFRA signaling. Together, this paracrine induce signal transduction cascade promoted tumor growth and metastasis in vivo. Moreover, in metastatic GIST patients, SLUG expression positively correlated with tumor size and mitotic index. Given that CAF paracrine signaling modulated GIST biology, we directly targeted CAFs with a dual PI3K/mTOR inhibitor, which synergized with imatinib to increase tumor cell killing and in vivo disease response. Taken together, we identified a previously unappreciated cellular target for GIST therapy in order to improve disease control and cure rates.

Insights into epithelial cell senescence from transcriptome and secretome analysis of human oral keratinocytes

Senescent cells produce chronic inflammation that contributes to the diseases and debilities of aging. How this process is orchestrated in epithelial cells, the origin of human carcinomas, is poorly understood. We used human normal oral keratinocytes (NOKs) to elucidate senescence programs in a prototype primary mucosal epithelial cell that senesces spontaneously. While NOKs exhibit several typical facets of senescence, they also display distinct characteristics. These include expression of p21WAF1/CIP1 at early passages, making this common marker of senescence unreliable in NOKs. Transcriptome analysis by RNA-seq revealed specific commonalities with and differences from cancer cells, explicating the tumor avoidance role of senescence. Repression of DNA repair genes that correlated with downregulation of E2F1 mRNA and protein was observed for two donors; a divergent result was seen for the third. Using proteomic profiling of soluble (non-vesicular) and extracellular vesicle (EV) associated secretions, we propose additions to the senescence associated secretory phenotype, including HSP60, which localizes to the surface of EVs. Finally, EVs from senescent NOKs activate interferon pathway signaling in THP-1 monocytes in a STING-dependent manner and associate with mitochondrial and nuclear DNA. Our results highlight senescence changes in epithelial cells and how they might contribute to chronic inflammation and age-related diseases.

Detecting cancer metastasis and accompanying protein biomarkers at single cell levels using a 3D-printed microfluidic immunoarray

A low-cost microfluidic microarray capable of lysing cells and quantifying proteins released after lysis was designed and 3D-printed. The array lyses cells on-chip in lysis buffer augmented with a 2s pulse of a sonic cell disruptor. Detection of desmoglein 3 (DSG3), a metastatic biomarker for head and neck squamous cell carcinoma (HNSCC), along with two accompanying HNSCC biomarkers from a single cell lysate of oral cancer cell cultures was demonstrated. A lysis chamber and reagent compartments deliver sample and reagents into detection chambers decorated with capture antibodies immobilized onto inner walls coated with a highly swollen 3D chitosan hydrogel film. Sandwich immunoassays are achieved when captured analytes labeled with biotinylated secondary antibodies, which then capture streptavidin-poly [horse radish peroxidase] (Poly-HRP). Subsequent delivery of super-bright femto-luminol with H2O2 generates chemiluminescence captured with a CCD camera. DSG3 is membrane-bound protein in HNSCC cells of invaded lymph nodes, vascular endothelial growth factor-A (VEGF-A), vascular endothelial growth factor-C (VEGF-C) were positive controls overexpressed into the HNSCC culture medium. Beta-tubulin (β-Tub) was used as a loading control to estimate the number of cells in analyzed samples. Limits of detection (LOD) were 0.10 fg/mL for DSG3, and 0.20 fg/mL for VEGF-A, VEGF-C and β-Tub. Three orders of magnitude semilogarithmic dynamic ranges were achieved. VEGF-A showed high in-cell expression, but VEGF-C had low levels inside cells. The very low LODs enabled quantifying these proteins released from single cells. Strong correlation between results from on-chip cell lysis, conventional off-line lysis and ELISA confirmed accuracy.

Gαs directly drives PDZ-RhoGEF signaling to Cdc42

Gα proteins promote dynamic adjustments of cell shape directed by actin-cytoskeleton reorganization via their respective RhoGEF effectors. For example, Gα13 binding to the RGS-homology (RH) domains of several RH-RhoGEFs allosterically activates these proteins, causing them to expose their catalytic Dbl-homology (DH)/pleckstrin-homology (PH) regions, which triggers downstream signals. However, whether additional Gα proteins might directly regulate the RH-RhoGEFs was not known. To explore this question, we first examined the morphological effects of expressing shortened RH-RhoGEF DH/PH constructs of p115RhoGEF/ARHGEF1, PDZ-RhoGEF (PRG)/ARHGEF11, and LARG/ARHGEF12. As expected, the three constructs promoted cell contraction and activated RhoA, known to be downstream of Gα13 Intriguingly, PRG DH/PH also induced filopodia-like cell protrusions and activated Cdc42. This pathway was stimulated by constitutively active Gαs (GαsQ227L), which enabled endogenous PRG to gain affinity for Cdc42. A chemogenetic approach revealed that signaling by Gs-coupled receptors, but not by those coupled to Gi or Gq, enabled PRG to bind Cdc42. This receptor-dependent effect, as well as CREB phosphorylation, was blocked by a construct derived from the PRG:Gαs-binding region, PRG-linker. Active Gαs interacted with isolated PRG DH and PH domains and their linker. In addition, this construct interfered with GαsQ227L's ability to guide PRG's interaction with Cdc42. Endogenous Gs-coupled prostaglandin receptors stimulated PRG binding to membrane fractions and activated signaling to PKA, and this canonical endogenous pathway was attenuated by PRG-linker. Altogether, our results demonstrate that active Gαs can recognize PRG as a novel effector directing its DH/PH catalytic module to gain affinity for Cdc42.

Correction: Rigiracciolo, D.C., et al., IGF-1/IGF-1R/FAK/YAP Transduction Signaling Prompts Growth Effects in Triple-Negative Breast Cancer (TNBC) Cells. Cells 2020, 9, 1010

The authors wish to make the following changes to their paper [...].

Tipifarnib as a Precision Therapy for HRAS-Mutant Head and Neck Squamous Cell Carcinomas

Tipifarnib is a potent and highly selective inhibitor of farnesyltransferase (FTase). FTase catalyzes the posttranslational attachment of farnesyl groups to signaling proteins that are required for localization to cell membranes. Although all RAS isoforms are FTase substrates, only HRAS is exclusively dependent upon farnesylation, raising the possibility that HRAS-mutant tumors might be susceptible to tipifarnib-mediated inhibition of FTase. Here, we report the characterization of tipifarnib activity in a wide panel of HRAS-mutant and wild-type head and neck squamous cell carcinoma (HNSCC) xenograft models. Tipifarnib treatment displaced both mutant and wild-type HRAS from membranes but only inhibited proliferation, survival, and spheroid formation of HRAS-mutant cells. In vivo, tipifarnib treatment induced tumor stasis or regression in all six HRAS-mutant xenografts tested but displayed no activity in six HRAS wild-type patient-derived xenograft (PDX) models. Mechanistically, drug treatment resulted in the reduction of MAPK pathway signaling, inhibition of proliferation, induction of apoptosis, and robust abrogation of neovascularization, apparently via effects on both tumor cells and endothelial cells. Bioinformatics and quantitative image analysis further revealed that FTase inhibition induces progressive squamous cell differentiation in tipifarnib-treated HNSCC PDXs. These preclinical findings support that HRAS represents a druggable oncogene in HNSCC through FTase inhibition by tipifarnib, thereby identifying a precision therapeutic option for HNSCCs harboring HRAS mutations.

HPV E2, E4, E5 drive alternative carcinogenic pathways in HPV positive cancers

The dominant paradigm for HPV carcinogenesis includes integration into the host genome followed by expression of E6 and E7 (E6/E7). We explored an alternative carcinogenic pathway characterized by episomal E2, E4, and E5 (E2/E4/E5) expression. Half of HPV positive cervical and pharyngeal cancers comprised a subtype with increase in expression of E2/E4/E5, as well as association with lack of integration into the host genome. Models of the E2/E4/E5 carcinogenesis show p53 dependent enhanced proliferation in vitro, as well as increased susceptibility to induction of cancer in vivo. Whole genomic expression analysis of the E2/E4/E5 pharyngeal cancer subtype is defined by activation of the fibroblast growth factor receptor (FGFR) pathway and this subtype is susceptible to combination FGFR and mTOR inhibition, with implications for targeted therapy.

Abstract LB-386: Novel multimodal precision immunotherapy by co-targeting the HER3 oncogenic signaling circuitry and PD-1 for head and neck squamous cell carcinoma

In prior studies, we have shown that persistent activation of the PI3K/mTOR signaling circuitry is the most frequently dysregulated signaling pathway in HNSCC (&gt;80% of all HPV- and HPV+ cases), and that mTOR inhibitors (mTORi) exert potent antitumor activity in multiple experimental HNSCC model systems and in a recent Phase 2 clinical trial. In this regard, the overreliance on PI3K/mTOR signaling for tumor growth may in turn expose a cancer vulnerability that can be exploited therapeutically. However, the immunosuppressive effects of mTORi limit the potential benefits of their combination with new immune oncology (IO) agents. These include immune check point blockade with pembrolizumab and nivolumab (anti-PD-1), which have recently demonstrated anti-tumor activity in HNSCC, albeit only &lt;20% of the patients show durable responses. There is urgent need to search for alternative approaches for HNSCC treatment. We conducted a kinome-wide siRNA screen to identify new therapeutic targets for HNSCC. This revealed that the ERBB3 gene, encoding HER3, is among the top 20 kinases whose knockdown (KD) decreases HNSCC cell proliferation. A counter screen analysis revealed that ERBB3 was the gene whose KD results in the highest reduction of mTOR pathway activation (indicated by pS6). Remarkably, HER3 KD specifically reduced activation of mTOR but not ERK in cells that do not harbor PIK3CA mutations, and immunoprecipitation of HER3 showed direct binding between HER3 and PI3K. Furthermore, a blocking antibody targeting HER3 (CDX-3379) potently inhibited the tumor growth of PIK3CA wild type but not PIK3CA mutant HNSCC cells. CDX-3379 also showed anti-tumor activity in 4MOSC1, our recently reported tobacco-associated syngeneic HNSCC model. Of importance, we found that HER3 is not expressed in immune cells, but CDX-3379 treatment led to a rapid increase in the accumulation of pro-immunogenic IL-2 and IL-7, concomitant with a reduction in multiple pro-tumorigenic and immune suppressive cytokines (e.g., IL-10, VEGF, G-CSF, GM-CSF, IL-6). This provided a rationale to combine HER3i with IO agents. Indeed, the combination of HER3 and PD-1 blockade elicited a remarkable beneficial effect, with an increase of tumor-infiltrating CD8+ T cells and ~70% of the mice exhibiting complete and durable (&gt;6 months) responses and consequently a significant increase in overall survival. Overall, our findings suggest that persistent tyrosine phosphorylation of HER3 underlies aberrant PI3K/mTOR signaling in HNSCC harboring wild type PIK3CA, and that targeting HER3 may exert its anti-tumor effect by both reducing cancer-driving mTOR activity and reversing an immune evasive tumor microenvironment. These findings also support that co-targeting the HER3 signaling circuitry combined with PD-1 blockade may represent a novel multimodal precision therapeutic approach for HNSCC aimed at achieving durable responses and cancer remission.

Citation Format: Zhiyong Wang, Yusuke Goto, Mara Gilardi, Michael Allevato, Victoria Wu, Robert Saddawi-konefka, Diego Alvarado, Alfredo Molinolo, J. Silvio Gutkind. Novel multimodal precision immunotherapy by co-targeting the HER3 oncogenic signaling circuitry and PD-1 for head and neck squamous cell carcinoma [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 LB-386.

Abstract 6406: FAK and MEK co-targeting: A new multimodal precision therapy for GNAQ-driven uveal melanoma

Uveal melanoma (UM) is characterized by gain-of-function mutations in GNAQ or GNA11, encoding Gα proteins from the Gq/11 family. UM is the most common eye malignancy in adults. Approximately 50% of UM patients develop liver metastasis (mUM) within 5-10 years after diagnosis, independently of the successful treatment of the primary lesions. mUM is refractory to cytotoxic, targeted, and immunotherapies, with most mUM patients dying within a year. Recent information suggests that GNAQ-oncogenic signaling involves a non-canonical pathway distinct from the activation of PLCβ and PKC-MEK-ERK, which may explain the failure of MEK inhibitors (MEKi) in increasing mUM patient survival. Instead, we found that GNAQ promotes the activation of YAP1, a key oncogenic driver, by a mechanism involving the activation of RhoA by the direct association of Gαq to TRIO, a Rho-GEF (Cancer Cell, 2014). In turn, YAP1 is essential for uveal melanoma cell growth, however no effective and safe YAP1 inhibitors are currently available. Using a novel bioinformatics pipeline, we recently found that PTK2, encoding Focal Adhesion Kinase (FAK), is a synthetic lethal gene with GNAQ activation, and uncovered that GNAQ controls YAP1 through FAK (Cancer Cell, 2019). This study identified FAK as a druggable signaling hub downstream from GNAQ in UM. However, activation of compensatory pathways often results in resistance to targeted agents. Here, we combined the use of CRISPR-Cas9 sgRNA screens with a recently described Cancer Signaling Toolkit approach to identify synthetic lethal interactions enhancing the response to FAKi and signaling networks mediating drug resistance, respectively. Remarkably, both approaches converged to reveal that co-targeting FAK and the MEK-ERK pathway would be a promising combination for treatment of UM. Indeed, MEK-ERK pathway inhibition by multiple approved MEKis (e.g., trametinib), combined with FAK inhibition (VS-4718 or defactinib), showed remarkable synergistic growth inhibitory effects in UM cells. Additionally, the novel RAF/MEK inhibitor RO5126766 also showed synergistic anti-proliferative effects with defactinib. Accordingly, FAKi combination with MEKi exerted cytotoxic effects (apoptotic death) leading to rapid tumor shrinkage in UM xenografts, whereas single drugs were primarily cytostatic. Furthermore, the FAKi/MEKi combination was successful at reducing tumor burden in recently developed liver metastasis UM models. By coupling the unique genetic landscape of UM with the power of unbiased computational pipelines and systems biology genetic screens, our studies revealed that FAK and MEK-ERK co-targeting may provide a new network-based precision therapeutic strategy for mUM treatment. Indeed, the combination of defactinib and RO5126766 is currently being evaluated in patients with various solid tumors (NCT03875820), and could be explored in mUM based on these preclinical findings.

Citation Format: Justine S. Paradis, Monica Acosta, Nadia Arang, Robert Saddawi-Konefka, Ayush Kishore, Takahito Sugase, Xiaodong Feng, Kris C. Wood, Silvia Coma, Mizue Terai, Takami Sato, Jonathan A. Pachter, J. Silvio Gutkind. FAK and MEK co-targeting: A new multimodal precision therapy for GNAQ-driven uveal melanoma [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 6406.

Abstract IA08: Regulation of YAP by tyrosine phosphorylation of core Hippo pathway components: Lessons learned from the GNAQ oncogene and FAK

Dysregulation of the Hippo signaling pathway and the consequent YAP1 activation is a frequent event in human malignancies, yet the underlying molecular mechanisms are still poorly understood. In prior studies we have focused on uveal melanoma, the most frequent eye malignancy in adults that is caused by constitutively active mutations in the GNAQ oncogenes, which encode Gαq and Gα11 heterotrimeric G protein α subunits. We found that GNAQ promotes the activation of YAP1 by a mechanism involving the activation of RhoA by the direct association of Gαq to TRIO, a Rho-GEF, and the consequent stimulation of acting polymerization and the release of YAP from its complex with AMOT. We also showed that YAP1 is essential for uveal melanoma cell growth, thus representing a potential therapeutic target for this malignancy. However, no effective and safe YAP1 inhibitors are currently available. Using a novel integrated bioinformatics pipeline, we recently found that PTK2, encoding Focal Adhesion Kinase (FAK), represents a candidate synthetic lethal gene with GNAQ activation (Feng et al., Cancer Cell 2019). We found that Gαq activates FAK through the TRIO-RhoA noncanonical Gαq-signaling, and that genetic ablation or pharmacologic inhibition of FAK inhibits uveal melanoma growth. Surprisingly, analysis of the FAK-regulated transcriptome indicated that GNAQ stimulates YAP1 through FAK. Dissection of the underlying mechanism revealed that FAK regulates YAP1 by tyrosine phosphorylation of MOB1, thereby disrupting MOB1/LATS association and core Hippo pathway signaling. By coupling the power of an unbiased computational pipeline to the unique genetic landscape of uveal melanoma, we uncovered a molecular framework regulating YAP1 and identified FAK as a druggable signaling hub downstream from GNAQ in uveal melanoma. Our findings established FAK as a potential therapeutic target for uveal melanoma and other diseases that may involve FAK activation and unrestrained YAP1 function. Further studies on how multiple growth promoting and oncogenic tyrosine kinase signaling networks may converge to phosphorylate core Hippo pathway components to activate YAP1 in cancer will be also discussed.

Citation Format: J. Silvio Gutkind. Regulation of YAP by tyrosine phosphorylation of core Hippo pathway components: Lessons learned from the GNAQ oncogene and FAK [abstract]. In: Proceedings of the AACR Special Conference on the Hippo Pathway: Signaling, Cancer, and Beyond; 2019 May 8-11; San Diego, CA. Philadelphia (PA): AACR; Mol Cancer Res 2020;18(8_Suppl):Abstract nr IA08.

Pathway-Specific Genome Editing of PI3K/mTOR Tumor Suppressor Genes Reveals that PTEN Loss Contributes to Cetuximab Resistance in Head and Neck Cancer

Cetuximab, an mAb targeting EGFR, is a standard of care for the treatment for locally advanced or metastatic head and neck squamous cell carcinoma (HNSCC). However, despite overexpression of EGFR in more than 90% of HNSCC lesions, most patients with HNSCC fail to respond to cetuximab treatment. In addition, there are no available biomarkers to predict sensitivity or resistance to cetuximab in the clinic. Here, we sought to advance precision medicine approaches for HNSCC by identifying PI3K/mTOR signaling network-specific cetuximab resistance mechanisms. We first analyzed the frequency of genomic alterations in genes involved in the PI3K/mTOR signaling circuitry in the HNSCC TCGA dataset. Experimentally, we took advantage of CRISPR/Cas9 genome editing approaches to systematically explore the contribution of genomic alterations in each tumor suppressor gene (TSG) controlling the PI3K-mTOR pathway to cetuximab resistance in HNSCC cases that do not exhibit PIK3CA mutations. Remarkably, we found that many HNSCC cases exhibit pathway-specific gene copy number loss of multiple TSGs that normally restrain PI3K/mTOR signaling. Among them, we found that both engineered and endogenous PTEN gene deletions can mediate resistance to cetuximab. Our findings suggest that PTEN gene copy number loss, which is highly prevalent in HNSCC, may result in sustained PI3K/mTOR signaling independent of EGFR, thereby representing a promising mechanistic biomarker predictive of cetuximab resistance in this cancer type. Further prospective studies are needed to investigate the impact of PTEN loss on cetuximab efficacy in the clinic.

Nonmuscle myosin 2 regulates cortical stability during sprouting angiogenesis

Among the three nonmuscle myosin 2 (NM2) paralogs, NM 2A and 2B, but not 2C, are detected in endothelial cells. To study the role of NM2 in vascular formation, we ablate NM2 in endothelial cells in mice. Ablating NM2A, but not NM2B, results in reduced blood vessel coverage and increased vascular branching in the developing mouse skin and coronary vasculature. NM2B becomes essential for vascular formation when NM2A expression is limited. Mice ablated for NM2B and one allele of NM2A develop vascular abnormalities similar to those in NM2A ablated mice. Using the embryoid body angiogenic sprouting assay in collagen gels reveals that NM2A is required for persistent angiogenic sprouting by stabilizing the endothelial cell cortex, and thereby preventing excessive branching and ensuring persistent migration of the endothelial sprouts. Mechanistically, NM2 promotes focal adhesion formation and cortical protrusion retraction during angiogenic sprouting. Further studies demonstrate the critical role of Rho kinase–activated NM2 signaling in the regulation of angiogenic sprouting in vitro and in vivo.

G protein-regulated endocytic trafficking of adenylyl cyclase type 9

GPCRs are increasingly recognized to initiate signaling via heterotrimeric G proteins as they move through the endocytic network, but little is known about how relevant G protein effectors are localized. Here we report selective trafficking of adenylyl cyclase type 9 (AC9) from the plasma membrane to endosomes while adenylyl cyclase type 1 (AC1) remains in the plasma membrane, and stimulation of AC9 trafficking by ligand-induced activation of Gs-coupled GPCRs. AC9 transits a similar, dynamin-dependent early endocytic pathway as ligand-activated GPCRs. However, unlike GPCR traffic control which requires β-arrestin but not Gs, AC9 traffic control requires Gs but not β-arrestin. We also show that AC9, but not AC1, mediates cAMP production stimulated by endogenous receptor activation in endosomes. These results reveal dynamic and isoform-specific trafficking of adenylyl cyclase in the endocytic network, and a discrete role of a heterotrimeric G protein in regulating the subcellular distribution of a relevant effector.

Aberrant expression of CPSF1 promotes head and neck squamous cell carcinoma via regulating alternative splicing

Alternative mRNA splicing increases protein diversity, and alternative splicing events (ASEs) drive oncogenesis in multiple tumor types. However, the driving alterations that underlie the broad dysregulation of ASEs are incompletely defined. Using head and neck squamous cell carcinoma (HNSCC) as a model, we hypothesized that the genomic alteration of genes associated with the spliceosome may broadly induce ASEs across a broad range of target genes, driving an oncogenic phenotype. We identified 319 spliceosome genes and employed a discovery pipeline to identify 13 candidate spliceosome genes altered in HNSCC using The Cancer Genome Atlas (TCGA) HNSCC data. Phenotypic screens identified amplified and overexpressed CPSF1 as a target gene alteration that was validated in proliferation, colony formation, and apoptosis assays in cell line and xenograft systems as well as in primary HNSCC. We employed knockdown and overexpression assays followed by identification of ASEs regulated by CPSF1 overexpression to identify changes in ASEs, and the expression of these ASEs was validated using RNA from cell line models. Alterations in expression of spliceosome genes, including CPSF1, may contribute to HNSCC by mediating aberrant ASE expression.

Development and optimization of orthotopic liver metastasis xenograft mouse models in uveal melanoma

BACKGROUND

Patients with metastatic uveal melanoma (MUM) in the liver usually die within 1 year. The development of new treatments for MUM has been limited by the lack of diverse MUM cell lines and appropriate animal models. We previously reported that orthotopic xenograft mouse models established by direct injection of MUM cells into the liver were useful for the analysis associated with tumor microenvironment in the liver. However, considering that patients with UM metastasize to the liver hematogenously, direct liver injection model might not be suitable for investigation on various mechanisms of liver metastasis. Here, we aim to establish new orthotopic xenograft models via hematogenous dissemination of tumor cells to the liver, and to compare their characteristics with the hepatic injection model. We also determine if hepatic tumors could be effectively monitored with non-invasive live imaging.

METHODS

tdtTomate-labeled, patient-derived MUM cells were injected into the liver, spleen or tail vein of immunodeficient NSG mice. Tumor growth was serially assessed with In Vivo Imaging System (IVIS) images once every week. Established hepatic tumors were evaluated with CT scan and then analyzed histologically.

RESULTS

We found that splenic injection could consistently establish hepatic tumors. Non-invasive imaging showed that the splenic injection model had more consistent and stronger fluorescent intensity compared to the hepatic injection model. There were no significant differences in tumor growth between splenic injection with splenectomy and without splenectomy. The splenic injection established hepatic tumors diffusely throughout the liver, while the hepatic injection of tumor cells established a single localized tumor. Long-term monitoring of tumor development showed that tumor growth, tumor distribution in the liver, and overall survival depended on the number of tumor cells injected to the spleen.

CONCLUSION

We established a new orthotopic hepatic metastatic xenograft mouse model by splenic injection of MUM cells. The growth of orthotopic hepatic tumors could be monitored with non-invasive IVIS imaging. Moreover, we evaluated the therapeutic effect of a MEK inhibitor by using this model. Our findings suggest that our new orthotopic liver metastatic mouse model may be useful for preclinical drug screening experiments and for the analysis of liver metastasis mechanisms.

PRECOG: PREdicting COupling probabilities of G-protein coupled receptors

G-protein coupled receptors (GPCRs) control multiple physiological states by transducing a multitude of extracellular stimuli into the cell via coupling to intra-cellular heterotrimeric G-proteins. Deciphering which G-proteins couple to each of the hundreds of GPCRs present in a typical eukaryotic organism is therefore critical to understand signalling. Here, we present PRECOG (precog.russelllab.org): a web-server for predicting GPCR coupling, which allows users to: (i) predict coupling probabilities for GPCRs to individual G-proteins instead of subfamilies; (ii) visually inspect the protein sequence and structural features that are responsible for a particular coupling; (iii) suggest mutations to rationally design artificial GPCRs with new coupling properties based on predetermined coupling features.