BRCA2 Germline Mutations Identify Gastric Cancers Responsive to PARP Inhibitors

Despite negative results of clinical trials conducted on the overall population of patients with gastric cancer, PARP inhibitor (PARPi) therapeutic strategy still might represent a window of opportunity for a subpopulation of patients with gastric cancer. An estimated 7% to 12% of gastric cancers exhibit a mutational signature associated with homologous recombination (HR) failure, suggesting that these patients could potentially benefit from PARPis. To analyze responsiveness of gastric cancer to PARPi, we exploited a gastroesophageal adenocarcinoma (GEA) platform of patient-derived xenografts (PDX) and PDX-derived primary cells and selected 10 PDXs with loss-of-function mutations in HR pathway genes. Cell viability assays and preclinical trials showed that olaparib treatment was effective in PDXs harboring BRCA2 germline mutations and somatic inactivation of the second allele. Olaparib responsive tumors were sensitive to oxaliplatin as well. Evaluation of HR deficiency (HRD) and mutational signatures efficiently stratified responder and nonresponder PDXs. A retrospective analysis on 57 patients with GEA showed that BRCA2 inactivating variants were associated with longer progression-free survival upon platinum-based regimens. Five of 7 patients with BRCA2 germline mutations carried the p.K3326* variant, classified as "benign." However, familial history of cancer, the absence of RAD51 foci in tumor cells, and a high HRD score suggest a deleterious effect of this mutation in gastric cancer. In conclusion, PARPis could represent an effective therapeutic option for BRCA2-mutated and/or high HRD score patients with GEA, including patients with familial intestinal gastric cancer.

SIGNIFICANCE

PARP inhibition is a potential strategy for treating patients with gastric cancer with mutated BRCA2 or homologous repair deficiency, including patients with familial intestinal gastric cancer, for whom BRCA2 germline testing should be recommended.

SEMA6C: a novel adhesion-independent FAK and YAP activator, required for cancer cell viability and growth

Transmembrane semaphorins are signaling molecules, controlling axonal wiring and embryo development, which are increasingly implicated in human diseases. Semaphorin 6C (Sema6C) is a poorly understood family member and its functional role is still unclear. Upon targeting Sema6C expression in a range of cancer cells, we observed dramatic growth suppression, decreased ERK phosphorylation, upregulation of cell cycle inhibitor proteins p21, p27 and p53, and the onset of cell senescence, associated with activation of autophagy. These data are consistent with a fundamental requirement for Sema6C to support viability and growth in cancer cells. Mechanistically, we unveiled a novel signaling pathway elicited by Sema6C, and dependent on its intracellular domain, mediated by tyrosine kinases c-Abl and Focal Adhesion Kinase (FAK). Sema6C was found in complex with c-Abl, and induced its phosphorylation, which in turn led to FAK activation, independent of cell-matrix adhesion. Sema6C-induced FAK activity was furthermore responsible for increased nuclear localization of YAP transcriptional regulator. Moreover, Sema6C conferred YAP signaling-dependent long-term cancer cell survival upon nutrient deprivation. In conclusion, our findings demonstrate that Sema6C elicits a cancer promoting-signaling pathway sustaining cell viability and self-renewal, independent of growth factors and nutrients availability.

Identification of a subpopulation of patients with gastric cancer responsive to PARP inhibitors

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Background: Treatment with PARP inhibitors (PARPi) has been approved in some tumors bearing a deficient Homologous Recombination (HR) system. Despite negative results of clinical trials conducted on the overall population of gastric cancer (GC) patients, we wondered whether a PARPi therapeutic strategy might represent a window of opportunity for a subpopulation of these patients. 7-12% of gastric cancers exhibit a mutational signature associated with HR failure, suggesting that these patients might benefit from PARPi. Methods: To analyze responsiveness to PARPi we exploited a proprietary human Gastro-Esophageal Adenocarcinoma (GEA) annotated platform of Patient-Derived Xenografts (PDXs) and PDX-derived primary cells on which we performed in vivo and in vitro experiments. Results: We selected 10 PDXs with loss-of-function mutations in HR pathway genes. Cell viability assays and preclinical trials showed that treatment with PARPi was effective in PDXs harbouring BRCA2 germline mutations and somatic inactivation of the second allele in a microsatellite stable background. PARPi responsive tumors were sensitive to oxaliplatin as well. Evaluation of HR deficiency and mutational signatures efficiently stratified responder vs non-responder PDXs. A retrospective analysis on 57 GEA patients showed that those carrying BRCA2 inactivating variants had longer PFS upon platinum-based regimens (used as proxy). In 5 out of 7 BRCA2 germline mutated patients we identified the p.K3326* variant, currently classified as “benign”. However, familial history of cancer, the absence of RAD51 foci in the tumor cells and a high HR deficiency score suggest a deleterious effect for this mutation in gastric cancer. Conclusions: PARP inhibition could represent a new therapeutic perspective for BRCA2 mutated and/or high HRD score GEA patients, including familial intestinal gastric cancer patients.

The importance of being CAFs (in cancer resistance to targeted therapies)

In the last two decades, clinical oncology has been revolutionized by the advent of targeted drugs. However, the efficacy of these therapies is significantly limited by primary and acquired resistance, that relies not only on cell-autonomous mechanisms but also on tumor microenvironment cues. Cancer-associated fibroblasts (CAFs) are extremely plastic cells of the tumor microenvironment. They not only produce extracellular matrix components that build up the structure of tumor stroma, but they also release growth factors, chemokines, exosomes, and metabolites that affect all tumor properties, including response to drug treatment. The contribution of CAFs to tumor progression has been deeply investigated and reviewed in several works. However, their role in resistance to anticancer therapies, and in particular to molecular therapies, has been largely overlooked. This review specifically dissects the role of CAFs in driving resistance to targeted therapies and discusses novel CAF targeted therapeutic strategies to improve patient survival.

Targeting Neuropilin-1 with Nanobodies Reduces Colorectal Carcinoma Development

Simple Summary

Neuropilin-1 is a co-receptor for semaphorins and vascular endothelial growth factor family members. Neuropilin-1 can be expressed on tumor cells, tumor-infiltrating myeloid and lymphoid cells and has been linked to a tumor-promoting environment. We investigated nanobodies (Nbs) targeting neuropilin-1 for their potential to hamper colorectal carcinoma development in mice. Our data suggest that targeting neuropilin-1 in cancer using neuropilin-1 blocking Nbs delays tumor growth and extends the survival through a shift in the anti-tumor macrophage/pro-tumor macrophage ratio and activation of colorectal cancer-specific CD8⁺ T cells. These findings provide a rationale for the further development of Nbs targeting human neuropilin-1 and bringing them from the bench to the bedside.

Abstract

Neuropilin-1 (NRP-1) is a co-receptor for semaphorins and vascular endothelial growth factor (VEGF) family members that can be expressed on cancer cells and tumor-infiltrating myeloid, endothelial and lymphoid cells. It has been linked to a tumor-promoting environment upon interaction with semaphorin 3A (Sema3A). Nanobodies (Nbs) targeting NRP-1 were generated for their potential to hamper the NRP-1/Sema3A interaction and their impact on colorectal carcinoma (CRC) development was evaluated in vivo through the generation of anti-NRP-1-producing CRC cells. We observed that tumor growth was significantly delayed and survival prolonged when the anti-NRP-1 Nbs were produced in vivo. We further analyzed the tumor microenvironment and observed that the pro-inflammatory MHC-II^high/trophic MHC-II^low macrophage ratio was increased in tumors that produce anti-NRP-1 Nbs. This finding was corroborated by an increase in the expression of genes associated with MHC-II^high macrophages and a decrease in the expression of MHC-II^low macrophage-associated genes in the macrophage pool sorted from anti-NRP-1 Nb-producing tumors. Moreover, we observed a significantly higher percentage of tumor-associated antigen-specific CD8⁺ T cells in tumors producing anti-NRP-1 Nbs. These data demonstrate that an intratumoral expression of NRP-1/Sema3A blocking biologicals increases anti-tumor immunity.

Distinct Mechanisms Are Responsible for Nrf2-Keap1 Pathway Activation at Different Stages of Rat Hepatocarcinogenesis

Activation of the Nrf2-Keap1 pathway, the main intracellular defense against environmental stress, has been observed in several human cancers, including hepatocellular carcinoma (HCC). Here, we assessed whether distinct mechanisms of activation may be involved at different stages of hepatocarcinogenesis. We adopted an experimental model consisting of treatment with diethylnitrosamine (DENA) followed by a choline-devoid methionine-deficient (CMD) diet for 4 months. The CMD diet was then replaced with a basal diet, and the animals were killed at 6, 10 or 13 months after DENA injection. Nrf2 activation occurred at early steps of hepatocarcinogenesis and persisted throughout the tumorigenic process. While Nrf2 mutations were extremely frequent at early steps (90%), their incidence diminished with the progression to malignancy (25%). Conversely, while p62 was almost undetectable in early nodules, its accumulation occurred in HCCs, suggesting that Nrf2 pathway activation at late stages is mainly due to Keap1 sequestration by p62. We demonstrate that, in a model of hepatocarcinogenesis resembling human non-alcoholic fatty liver disease, Nrf2 mutations are the earliest molecular changes responsible for the activation of the Nrf2-Keap1 pathway. The progressive loss of mutations associated with a concomitant p62 accumulation implies that distinct mechanisms are responsible for Nrf2-Keap1 pathway activation at different stages of hepatocarcinogenesis.

Neuropilin-1 upregulation elicits adaptive resistance to oncogene-targeted therapies

Cancer cell dependence on activated oncogenes is therapeutically targeted, but acquired resistance is virtually unavoidable. Here we show that the treatment of addicted melanoma cells with BRAF inhibitors, and of breast cancer cells with HER2-targeted drugs, led to an adaptive rise in neuropilin-1 (NRP1) expression, which is crucial for the onset of acquired resistance to therapy. Moreover, NRP1 levels dictated the efficacy of MET oncogene inhibitors in addicted stomach and lung carcinoma cells. Mechanistically, NRP1 induced a JNK-dependent signaling cascade leading to the upregulation of alternative effector kinases EGFR or IGF1R, which in turn sustained cancer cell growth and mediated acquired resistance to BRAF, HER2, or MET inhibitors. Notably, the combination with NRP1-interfering molecules improved the efficacy of oncogene-targeted drugs and prevented or even reversed the onset of resistance in cancer cells and tumor models. Our study provides the rationale for targeting the NRP1-dependent upregulation of tyrosine kinases, which are responsible for loss of responsiveness to oncogene-targeted therapies.

Downregulating Neuropilin-2 Triggers a Novel Mechanism Enabling EGFR-Dependent Resistance to Oncogene-Targeted Therapies

Neuropilins are a class of cell surface proteins implicated in cell migration and angiogenesis, with aberrant expression in human tumors. Here, we show that the expression of Neuropilin-2 (NRP2) controls EGFR protein levels, thereby impinging on intracellular signaling, viability, and response to targeted therapies of oncogene-addicted cells. Notably, increased NRP2 expression in EGFR-addicted tumor cells led to downregulation of EGFR protein and tumor cell growth inhibition. NRP2 also blunted upregulation of an EGFR "rescue" pathway induced by targeted therapy in Met-addicted carcinoma cells. Cancer cells acquiring resistance to MET oncogene-targeted drugs invariably underwent NRP2 loss, a step required for EGFR upregulation. Mechanistic investigations revealed that NRP2 loss activated NFkB and upregulated the EGFR-associated protein KIAA1199/CEMIP, which is known to oppose the degradation of activated EGFR kinase. Notably, KIAA1199 silencing in oncogene-addicted tumor cells improved therapeutic responses and counteracted acquired drug resistance. Our findings define NRP2 as the pivotal switch of a novel broad-acting and actionable pathway controlling EGFR signaling, and driving resistance to therapies targeting oncogene-addiction.Significance: These important findings identify the cell surface molecule Nrp2 as the pivotal switch of a novel, actionable pathway driving EGFR upregulation and resistance to oncogene- targeted therapies. Cancer Res; 78(4); 1058-68. ©2017 AACR.

Antibody-Feeding Assay: A Method to Track the Internalization of Neuropilin-1 and Other Cell Surface Receptors

Ligand-induced endocytosis of receptors exposed on the plasma membrane is a fundamental regulatory step for their functional activation and interaction with intracellular signal transducers. Thus, elucidating the timing of endocytosis and tracing the intracellular fate of receptors is instrumental to understand their signaling cascade in different conditions. Here we describe an assay for the study of endocytosis and intracellular trafficking of individual surface receptors, in living cells subject to different experimental challenges. We applied this method for studying the functional interaction between semaphorin coreceptor Neuropilin-1 and a tyrosine kinase receptor exposed on the cell surface.

Impeding macrophage entry into hypoxic tumor areas by Sema3A/Nrp1 signaling blockade inhibits angiogenesis and restores antitumor immunity

Recruitment of tumor-associated macrophages (TAMs) into avascular areas sustains tumor progression; however, the underlying guidance mechanisms are unknown. Here, we report that hypoxia-induced Semaphorin 3A (Sema3A) acts as an attractant for TAMs by triggering vascular endothelial growth factor receptor 1 phosphorylation through the associated holoreceptor, composed of Neuropilin-1 (Nrp1) and PlexinA1/PlexinA4. Importantly, whereas Nrp1 levels are downregulated in the hypoxic environment, Sema3A continues to regulate TAMs in an Nrp1-independent manner by eliciting PlexinA1/PlexinA4-mediated stop signals, which retain them inside the hypoxic niche. Consistently, gene deletion of Nrp1 in macrophages favors TAMs' entrapment in normoxic tumor regions, which abates their pro-angiogenic and immunosuppressive functions, hence inhibiting tumor growth and metastasis. This study shows that TAMs' heterogeneity depends on their localization, which is tightly controlled by Sema3A/Nrp1 signaling.

Neuropilin-1-dependent regulation of EGF-receptor signaling

Neuropilin-1 (NRP1) is a coreceptor for multiple extracellular ligands. NRP1 is widely expressed in cancer cells and in advanced human tumors; however, its functional relevance and signaling mechanisms are unclear. Here, we show that NRP1 expression controls viability and proliferation of different cancer cells, independent of its short intracellular tail. We found that the extracellular domain of NRP1 interacts with the EGF receptor (EGFR) and promotes its signaling cascade elicited upon EGF or TGF-α stimulation. Upon NRP1 silencing, the ability of ligand-bound EGFR to cluster on the cell surface, internalize, and activate the downstream AKT pathway is severely impaired. EGFR is frequently activated in human tumors due to overexpression, mutation, or sustained autocrine/paracrine stimulation. Here we show that NRP1-blocking antibodies and NRP1 silencing can counteract ligand-induced EGFR activation in cancer cells. Thus our findings unveil a novel molecular mechanism by which NRP1 can control EGFR signaling and tumor growth.

Multifaceted role of neuropilins in cancer

Neuropilins comprise two homologous widely-expressed single-pass plasma membrane receptors (Nrp1 and Nrp2), originally identified for binding secreted Semaphorins and Vascular Endothelial Growth Factors (in association with Plexins and VEGF-Receptors). Semaphorins have been implicated with opposite functions in cancer: either as putative tumor suppressors and anti-angiogenic factors, or mediating tumour angiogenesis, invasion and metastasis. Moreover, due to their implication in VEGF signaling, neuropilins regulate vascular development and tumor angiogenesis. Recent evidence further suggests a role of neuropilins in cancer progression due to their interaction with receptor tyrosine kinases, adhesion molecules, and integrins. Furthermore, neuropilins have been implicated in response to additional growth factors, such as Hepatocyte Growth Factor, Fibroblast Growth Factor, Transforming Growth Factor beta, Galectin, etc. Altogether, these data seem to qualify neuropilins as signaling platforms on the cell surface, potentially capable of regulating cancer cells, as well as cells of the tumor microenvironment. Intriguingly, clinical-pathological data often indicate a correlation between increased expression of neuropilins and advanced stage tumors with poor prognosis. In this article, we will review the current experimental evidence about the functional role of neuropilins in cancer and the underlying molecular mechanisms.

Sema3E-Plexin D1 signaling drives human cancer cell invasiveness and metastatic spreading in mice

Semaphorin 3E (Sema3E) is a secreted molecule implicated in axonal path finding and inhibition of developmental and postischemic angiogenesis. Sema3E is also highly expressed in metastatic cancer cells, but its mechanistic role in tumor progression was not understood. Here we show that expression of Sema3E and its receptor Plexin D1 correlates with the metastatic progression of human tumors. Consistent with the clinical data, knocking down endogenous expression of either Sema3E or Plexin D1 in human metastatic carcinoma cells hampered their metastatic potential when injected into mice, while tumor growth was not markedly affected. Conversely, overexpression of exogenous Sema3E in cancer cells increased their invasiveness, transendothelial migration, and metastatic spreading, although it inhibited tumor vessel formation, resulting in reduced tumor growth in mice. The proinvasive and metastatic activity of Sema3E in tumor cells was dependent on transactivation of the Plexin D1-associated ErbB2/Neu oncogenic kinase. In sum, Sema3E-Plexin D1 signaling in cancer cells is crucially implicated in their metastatic behavior and may therefore be a promising target for strategies aimed at blocking tumor metastasis.

Semaphorin signals on the road to cancer invasion and metastasis

Semaphorins are a large family of secreted and membrane-bound molecules initially implicated in the development of the nervous system and in axon guidance. More recently, they have been found to regulate cell adhesion and cell motility, angiogenesis, immune function and tumour progression. Notably, Semaphorins have been implicated with opposite functions in cancer: either as putative tumor suppressors and anti-angiogenic factors, or as mediating tumour angiogenesis, invasion and metastasis. Interestingly, Semaphorins may display divergent activities in different cell types. These multifaceted functions may be explained by the involvement of different kinds of semaphorin receptor complexes, and by the consequent activation of multiple signaling pathways, in different cells or different functional stages. Semaphorin signaling is largely mediated by the Plexins. However, semaphorin receptor complexes may also include Neuropilins and tyrosine kinases implicated in cancer. In this review, we will focus on major open questions concerning the potential role of Semaphorin signals in cancer.