Alberto J. Schuhmacher

Tumour biology: Senescence in premalignant tumours

Oncogene-induced senescence is a cellular response that may be crucial for protection against cancer development, but its investigation has so far been restricted to cultured cells that have been manipulated to overexpress an oncogene. Here we analyse tumours initiated by an endogenous oncogene, ras, and show that senescent cells exist in premalignant tumours but not in malignant ones. Senescence is therefore a defining feature of premalignant tumours that could prove valuable in the diagnosis and prognosis of cancer.

CSF-1R inhibition alters macrophage polarization and blocks glioma progression

Glioblastoma multiforme (GBM) comprises several molecular subtypes, including proneural GBM. Most therapeutic approaches targeting glioma cells have failed. An alternative strategy is to target cells in the glioma microenvironment, such as tumor-associated macrophages and microglia (TAMs). Macrophages depend on colony stimulating factor-1 (CSF-1) for differentiation and survival. We used an inhibitor of the CSF-1 receptor (CSF-1R) to target TAMs in a mouse proneural GBM model, which significantly increased survival and regressed established tumors. CSF-1R blockade additionally slowed intracranial growth of patient-derived glioma xenografts. Surprisingly, TAMs were not depleted in treated mice. Instead, glioma-secreted factors, including granulocyte-macrophage CSF (GM-CSF) and interferon-γ (IFN-γ), facilitated TAM survival in the context of CSF-1R inhibition. Expression of alternatively activated M2 markers decreased in surviving TAMs, which is consistent with impaired tumor-promoting functions. These gene signatures were associated with enhanced survival in patients with proneural GBM. Our results identify TAMs as a promising therapeutic target for proneural gliomas and establish the translational potential of CSF-1R inhibition for GBM.

Pancreatitis-Induced Inflammation Contributes to Pancreatic Cancer by Inhibiting Oncogene-Induced Senescence

Pancreatic acinar cells of adult mice (≥P60) are resistant to transformation by some of the most robust oncogenic insults including expression of K-Ras oncogenes and loss of p16Ink4a/p19Arf or Trp53 tumor suppressors. Yet, these acinar cells yield pancreatic intraepithelial neoplasias (mPanIN) and ductal adenocarcinomas (mPDAC) if exposed to limited bouts of non-acute pancreatitis, providing they harbor K-Ras oncogenes. Pancreatitis contributes to tumor progression by abrogating the senescence barrier characteristic of low-grade mPanINs. Attenuation of pancreatitis-induced inflammation also accelerates tissue repair and thwarts mPanIN expansion. Patients with chronic pancreatitis display senescent PanINs, providing they have received antiinflammatory drugs. These results support the concept that antiinflammatory treatment of people diagnosed with pancreatitis may reduce their risk of developing PDAC.

The tumor microenvironment underlies acquired resistance to CSF-1R inhibition in gliomas

Another pathway to cancer resistance Therapies targeting the tumor microenvironment show promise for treating cancer. For example, antibodies targeting colony-stimulating factor-1 receptor (CSF-1R) inhibit protumorigenic macrophages and regress tumors in mouse models of glioblastoma multiforme (GBM), a deadly form of brain cancer. Quail et al. found that although CSR-1R blockade prolonged survival in mouse models of GBM, more than 50% of tumors eventually recurred. Recurrence was correlated with elevated PI3-K activity in tumors, driven by macrophage-secreted IGF-1. Blocking PI3-K and IGF-1 signaling in rebounding tumors prolonged survival. Thus, tumors can acquire resistance to therapy through intrinsic changes and through changes in their microenvironment. Science, this issue p. 10.1126/science.aad3018 Brain tumors can acquire resistance to therapy through changes to their microenvironment. INTRODUCTION Therapies targeted against the tumor microenvironment (TME) represent a promising approach for treating cancer. This appeal arises in part from the decreased likelihood of acquired resistance through mutations in target TME cells, as is frequently observed with cancer cell–targeted therapies. Although classical mechanisms of tumor cell–intrinsic resistance to cytotoxic and targeted agents have been well-defined—including aberrant drug metabolism and transport, drug target mutation, and activation of alternative survival pathways—it still remains unclear whether resistance to TME-directed therapies follows similar principles. Given that TME-targeted agents are increasingly being evaluated in the clinic, it is becoming critical to mechanistically define how resistance may evolve in response to these therapies in order to provide long-term disease management for patients. RATIONALE Macrophages and microglia are of the most abundant noncancerous cell types in glioblastoma multiforme (GBM), in some cases accounting for up to 30% of the total tumor composition. Macrophages accumulate with GBM progression and can be acutely targeted via inhibition of colony-stimulating factor–1 receptor (CSF-1R) to regress high-grade gliomas in animal models. However, it is currently unknown whether and how resistance emerges in response to sustained CSF-1R blockade in GBM. Despite this, multiple clinical trials are currently underway testing the efficacy of CSF-1R inhibition in glioma patients. Therefore, determining whether long-term CSF-1R inhibition can stably regress GBM by using animal models is an important and timely question to address. RESULTS Using genetic mouse models of GBM, we show that although overall survival is significantly prolonged in response to CSF-1R inhibition, tumors recur eventually in >50% of mice. Upon isolation and transplantation of recurrent tumor cells into naïve animals, gliomas reestablish sensitivity to CSF-1R inhibition, indicating that resistance is microenvironment-driven. Through RNA-sequencing of glioma cells and macrophages purified from treated tumors and ex vivo cell culture assays, we found elevated phosphatidylinositol 3-kinase (PI3K) pathway activity in recurrent GBM after CSF-1R inhibition, driven by macrophage-derived insulin-like growth factor–1 (IGF-1) and tumor cell IGF-1 receptor (IGF-1R). Consequently, combining IGF-1R or PI3K blockade with continuous CSF-1R inhibition in recurrent tumors significantly prolonged overall survival. In contrast, monotherapy with IGF-1R or PI3K inhibitors in rebound or treatment-naïve tumors was less effective, indicating the necessity of combination therapy to expose PI3K signaling dependency in recurrent disease. Mechanistically, we found that activation of macrophages in recurrent tumors by IL4 led to elevated Stat6 and nuclear factor of activated T cells (NFAT) signaling upstream of Igf1, and inhibition of either of these pathways in vivo was sufficient to significantly extend survival. CONCLUSION We have identified a mechanism of drug resistance that can circumvent therapeutic response to a TME-targeted therapy and promote disease recurrence in the absence of tumor cell–intrinsic alterations. Specifically, we have uncovered a heterotypic paracrine signaling interaction that is initiated by the TME and drives resistance to CSF-1R inhibition through IGF-1R/PI3K signaling. Given that PI3K signaling is aberrantly activated in a substantial proportion of GBM patients, and that recent clinical trial results show limited efficacy in recurrent (albeit very advanced) GBM, it is possible that this pathway could similarly contribute to intrinsic resistance to CSF-1R inhibition. Our findings underscore the importance of bidirectional feedback between cancer cells and their microenvironment and support the notion that although stromal cells are less susceptible to genetic mutation than are cancer cells, a tumor can nonetheless acquire a resistant phenotype by exploiting its extracellular environment. Resistance to CSF-1R inhibition in glioma. (A) Macrophages contribute to GBM progression by creating a protumorigenic niche associated with M2-like gene expression. CSF-1R is a critical receptor for macrophage biology and is under clinical evaluation as a therapeutic target in glioma . (B) Targeting CSF-1R early in gliomagenesis significantly prolongs survival in mouse models. CSF-1R inhibition reprograms macrophages to become antitumorigenic by down-regulating M2-like genes and enhancing phagocytosis. Tumor-derived survival factors sustain macrophage viability despite CSF-1R blockade

A mouse model for Costello syndrome reveals an Ang II–mediated hypertensive condition

Germline activation of H-RAS oncogenes is the primary cause of Costello syndrome (CS), a neuro-cardio-facio-cutaneous developmental syndrome. Here we describe the generation of a mouse model of CS by introduction of an oncogenic Gly12Val mutation in the mouse H-Ras locus using homologous recombination in ES cells. Germline expression of the endogenous H-RasG12V oncogene, even in homozygosis, resulted in hyperplasia of the mammary gland. However, development of tumors in these mice was rare. H-RasG12V mutant mice closely phenocopied some of the abnormalities observed in patients with CS, including facial dysmorphia and cardiomyopathies. These mice also displayed alterations in the homeostasis of the cardiovascular system, including development of systemic hypertension, extensive vascular remodeling, and fibrosis in both the heart and the kidneys. This phenotype was age dependent and was a consequence of the abnormal upregulation of the renin-Ang II system. Treatment with captopril, an inhibitor of Ang II biosynthesis, prevented development of the hypertension condition, vascular remodeling, and heart and kidney fibrosis. In addition, it partially alleviated the observed cardiomyopathies. These mice should help in elucidating the etiology of CS symptoms, identifying additional defects, and evaluating potential therapeutic strategies.

Germline expression of H-RasG12V causes neurological deficits associated to Costello syndrome

Costello syndrome (CS) is a rare congenital disorder caused by germline activation of H‐Ras oncogenes. A mouse model of CS generated by introduction of an oncogenic Gly12Val mutation in the mouse H‐Ras locus using homologous recombination in embryonic stem (ES) cells has been recently described. These mice phenocopied some of the abnormalities observed in patients with CS, including facial dysmorphia and cardiomyopathies. We investigated here their neurological and behavioral phenotype. The analysis of H‐RasG12V mice revealed phenotypes that resembled the hyperemotivity, hypersensibility and cognitive impairments observed in children with CS. Stronger neurological deficits were found in the analysis of mice homozygous for this mutation than in the analysis of heterozygous mice, suggesting the existence of a gene dose effect. These mice represent the first mouse model for CS, offering an experimental tool to study the molecular and physiological alterations underlying the neurological manifestations of CS and to test new therapies aimed at preventing or ameliorating the cognitive and emotional impairments associated to this condition.

K-RasV14I recapitulates Noonan syndrome in mice

Significance Noonan syndrome (NS) is a developmental disorder caused by germ-line mutations in various components of the RAS signaling pathway. The pathophysiological mechanisms underlying the clinical manifestations in NS patients and the basis for the observed phenotypic variability are poorly understood. To date, mouse models carrying mutations in Protein Tyrosine Phosphatase Non-Receptor type 11 (Ptpn11), Son of Sevenless homolog 1 (Sos1), and Raf1 loci have been described. The new model described here, induced by K-RasV14I expression, recapitulates most of the NS features including small size, craniofacial dysmorphism, cardiac defects, and myeloproliferative disorders, highly reminiscent of juvenile myelomonocytic leukemia. These mice should help us understand better the phenotypic variations of NS and serve as a preclinical tool to test forthcoming therapies based on the design of novel inhibitors of the RAS pathway. Noonan syndrome (NS) is an autosomal dominant genetic disorder characterized by short stature, craniofacial dysmorphism, and congenital heart defects. NS also is associated with a risk for developing myeloproliferative disorders (MPD), including juvenile myelomonocytic leukemia (JMML). Mutations responsible for NS occur in at least 11 different loci including KRAS. Here we describe a mouse model for NS induced by K-RasV14I, a recurrent KRAS mutation in NS patients. K-RasV14I–mutant mice displayed multiple NS-associated developmental defects such as growth delay, craniofacial dysmorphia, cardiac defects, and hematologic abnormalities including a severe form of MPD that resembles human JMML. Homozygous animals had perinatal lethality whose penetrance varied with genetic background. Exposure of pregnant mothers to a MEK inhibitor rescued perinatal lethality and prevented craniofacial dysmorphia and cardiac defects. However, Mek inhibition was not sufficient to correct these defects when mice were treated after weaning. Interestingly, Mek inhibition did not correct the neoplastic MPD characteristic of these mutant mice, regardless of the timing at which the mice were treated, thus suggesting that MPD is driven by additional signaling pathways. These genetically engineered K-RasV14I–mutant mice offer an experimental tool for studying the molecular mechanisms underlying the clinical manifestations of NS. Perhaps more importantly, they should be useful as a preclinical model to test new therapies aimed at preventing or ameliorating those deficits associated with this syndrome.

Inhibition of colony stimulating factor-1 receptor abrogates microenvironment-mediated therapeutic resistance in gliomas

Glioblastomas represent the most aggressive glioma grade and are associated with a poor patient prognosis. The current standard of care, consisting of surgery, radiation and chemotherapy, only results in a median survival of 14 months, underscoring the importance of developing effective new therapeutic strategies. Among the challenges in treating glioblastomas are primary resistance and the rapid emergence of recurrent disease, which can result from tumor cell-intrinsic mechanisms in addition to tumor microenvironment (TME)-mediated extrinsic resistance. Using a PDGF-B-driven proneural glioma mouse model, we assessed a panel of tyrosine kinase inhibitors with different selectivity profiles. We found that PLX3397, an inhibitor of colony stimulating factor-1 receptor (CSF-1R), blocks glioma progression, markedly suppresses tumor cell proliferation and reduces tumor grade. By contrast, the multi-targeted tyrosine kinase inhibitors dovitinib and vatalanib, which directly target tumor cells, exert minimal anti-tumoral effects in vivo, despite killing glioma cells in vitro, suggesting a TME-mediated resistance mechanism may be involved. Interestingly, PLX3397 interferes with tumor-mediated education of macrophages and consequently restores the sensitivity of glioma cells to tyrosine kinase inhibitors in vivo in preclinical combination trials. Our findings thus demonstrate that microenvironmental alteration by CSF-1R blockade renders tumor cells more susceptible to receptor tyrosine kinase inhibition in a preclinical glioblastoma model, which may have important translational relevance.

Targeting MT1-MMP as an ImmunoPET-Based Strategy for Imaging Gliomas.

Background A critical challenge in the management of Glioblastoma Multiforme (GBM) tumors is the accurate diagnosis and assessment of tumor progression in a noninvasive manner. We have identified Membrane-type 1 matrix metalloproteinase (MT1-MMP) as an attractive biomarker for GBM imaging since this protein is actively involved in tumor growth and progression, correlates with tumor grade and is closely associated with poor prognosis in GBM patients. Here, we report the development of an immunoPET tracer for effective detection of MT1-MMP in GBM models. Methods An anti-human MT1-MMP monoclonal antibody (mAb), LEM2/15, was conjugated to p-isothiocyanatobenzyl-desferrioxamine (DFO-NCS) for 89Zr labeling. Biodistribution and PET imaging studies were performed in xenograft mice bearing human GBM cells (U251) expressing MT1-MMP and non-expressing breast carcinoma cells (MCF-7) as negative control. Two orthotopic brain GBM models, patient-derived neurospheres (TS543) and U251 cells, with different degrees of blood-brain barrier (BBB) disruption were also used for PET imaging experiments. Results 89Zr labeling of DFO-LEM2/15 was achieved with high yield (>90%) and specific activity (78.5 MBq/mg). Biodistribution experiments indicated that 89Zr-DFO-LEM2/15 showed excellent potential as a radiotracer for detection of MT1-MMP positive GBM tumors. PET imaging also indicated a specific and prominent 89Zr-DFO-LEM2/15 uptake in MT1-MMP+ U251 GBM tumors compared to MT1-MMP- MCF-7 breast tumors. Results obtained in orthotopic brain GBM models revealed a high dependence of a disrupted BBB for tracer penetrance into tumors. 89Zr-DFO-LEM2/15 showed much higher accumulation in TS543 tumors with a highly disrupted BBB than in U251 orthotopic model in which the BBB permeability was only partially increased. Histological analysis confirmed the specificity of the immunoconjugate in all GBM models. Conclusion A new anti MT1-MMP-mAb tracer, 89Zr-DFO-LEM2/15, was synthesized efficiently. In vivo validation showed high-specific-contrast imaging of MT1-MMP positive GBM tumors and provided strong evidence for utility of MT1-MMP-targeted immunoPET as an alternate to nonspecific imaging of GBM.

Mechanisms underlying cognitive deficits in a mouse model for Costello Syndrome are distinct from other RASopathy mouse models

RASopathies, characterized by germline mutations in genes encoding proteins of the RAS-ERK signaling pathway, show overlapping phenotypes, which manifest themselves with a varying severity of intellectual disability. However, it is unclear to what extent they share the same downstream pathophysiology that underlies the cognitive deficits. Costello syndrome (CS) is a rare RASopathy caused by activating mutations in the HRAS gene. Here we investigated the mechanisms underlying the cognitive deficits of HRasG12V/G12V mice. HRasG12V/G12V mice showed robust upregulation of ERK signaling, neuronal hypertrophy, increased brain volume, spatial learning deficits, and impaired mGluR-dependent long-term depression (LTD). In contrast, long-term potentiation (LTP), which is affected in other RASopathy mouse models was unaffected. Treatment with lovastatin, a HMG-CoA-Reductase inhibitor which has been shown to rescue the behavioral phenotypes of mouse models of NF1 and Noonan syndrome, was unable to restore ERK signaling and the cognitive deficits of HRasG12V/G12V mice. Administration of a potent mitogen-activated protein kinase (MEK) inhibitor rescued the ERK upregulation and the mGluR-LTD deficit of HRasG12V/G12V mice, but failed to rescue the cognitive deficits. Taken together, this study indicates that the fundamental molecular and cellular mechanisms underlying the cognitive aspects of different RASopathies are remarkably distinct, and may require disease specific treatments.