Alessandro Carugo

Oncogene ablation-resistant pancreatic cancer cells depend on mitochondrial function

Pancreatic ductal adenocarcinoma (PDAC) is one of the deadliest cancers in western countries, with a median survival of 6 months and an extremely low percentage of long-term surviving patients. KRAS mutations are known to be a driver event of PDAC, but targeting mutant KRAS has proved challenging. Targeting oncogene-driven signalling pathways is a clinically validated approach for several devastating diseases. Still, despite marked tumour shrinkage, the frequency of relapse indicates that a fraction of tumour cells survives shut down of oncogenic signalling. Here we explore the role of mutant KRAS in PDAC maintenance using a recently developed inducible mouse model of mutated Kras (KrasG12D, herein KRas) in a p53LoxP/WT background. We demonstrate that a subpopulation of dormant tumour cells surviving oncogene ablation (surviving cells) and responsible for tumour relapse has features of cancer stem cells and relies on oxidative phosphorylation for survival. Transcriptomic and metabolic analyses of surviving cells reveal prominent expression of genes governing mitochondrial function, autophagy and lysosome activity, as well as a strong reliance on mitochondrial respiration and a decreased dependence on glycolysis for cellular energetics. Accordingly, surviving cells show high sensitivity to oxidative phosphorylation inhibitors, which can inhibit tumour recurrence. Our integrated analyses illuminate a therapeutic strategy of combined targeting of the KRAS pathway and mitochondrial respiration to manage pancreatic cancer.

Telomere Dysfunction Drives Aberrant Hematopoietic Differentiation and Myelodysplastic Syndrome

Myelodysplastic syndrome (MDS) risk correlates with advancing age, therapy-induced DNA damage, and/or shorter telomeres, but whether telomere erosion directly induces MDS is unknown. Here, we provide the genetic evidence that telomere dysfunction-induced DNA damage drives classical MDS phenotypes and alters common myeloid progenitor (CMP) differentiation by repressing the expression of mRNA splicing/processing genes, including SRSF2. RNA-seq analyses of telomere dysfunctional CMP identified aberrantly spliced transcripts linked to pathways relevant to MDS pathogenesis such as genome stability, DNA repair, chromatin remodeling, and histone modification, which are also enriched in mouse CMP haploinsufficient for SRSF2 and in CD34(+) CMML patient cells harboring SRSF2 mutation. Together, our studies establish an intimate link across telomere biology, aberrant RNA splicing, and myeloid progenitor differentiation.

Genetic Events That Limit the Efficacy of MEK and RTK Inhibitor Therapies in a Mouse Model of KRAS-Driven Pancreatic Cancer

Mutated KRAS (KRAS*) is a fundamental driver in the majority of pancreatic ductal adenocarcinomas (PDAC). Using an inducible mouse model of KRAS*-driven PDAC, we compared KRAS* genetic extinction with pharmacologic inhibition of MEK1 in tumor spheres and in vivo. KRAS* ablation blocked proliferation and induced apoptosis, whereas MEK1 inhibition exerted cytostatic effects. Proteomic analysis evidenced that MEK1 inhibition was accompanied by a sustained activation of the PI3K-AKT-MTOR pathway and by the activation of AXL, PDGFRa, and HER1-2 receptor tyrosine kinases (RTK) expressed in a large proportion of human PDAC samples analyzed. Although single inhibition of each RTK alone or plus MEK1 inhibitors was ineffective, a combination of inhibitors targeting all three coactivated RTKs and MEK1 was needed to inhibit proliferation and induce apoptosis in both mouse and human low-passage PDAC cultures. Importantly, constitutive AKT activation, which may mimic the fraction of AKT2-amplified PDAC, was able to bypass the induction of apoptosis caused by KRAS* ablation, highlighting a potential inherent resistance mechanism that may inform the clinical application of MEK inhibitor therapy. This study suggests that combinatorial-targeted therapies for pancreatic cancer must be informed by the activation state of each putative driver in a given treatment context. In addition, our work may offer explanative and predictive power in understanding why inhibitors of EGFR signaling fail in PDAC treatment and how drug resistance mechanisms may arise in strategies to directly target KRAS.

In Vivo Genetic Screens of Patient-Derived Tumors Revealed Unexpected Frailty of the Transformed Phenotype

UNLABELLED The identification of genes maintaining cancer growth is critical to our understanding of tumorigenesis. We report the first in vivo genetic screen of patient-derived tumors, using metastatic melanomas and targeting 236 chromatin genes by expression of specific shRNA libraries. Our screens revealed unprecedented numerosity of genes indispensable for tumor growth (∼50% of tested genes) and unexpected functional heterogeneity among patients (<15% in common). Notably, these genes were not activated by somatic mutations in the same patients and are therefore distinguished from mutated cancer driver genes. We analyzed underlying molecular mechanisms of one of the identified genes, the Histone-lysine N-methyltransferase KMT2D, and showed that it promotes tumorigenesis by dysregulating a subset of transcriptional enhancers and target genes involved in cell migration. The assembly of enhancer genomic patterns by activated KMT2D was highly patient-specific, regardless of the identity of transcriptional targets, suggesting that KMT2D might be activated by distinct upstream signaling pathways. SIGNIFICANCE Drug targeting of biologically relevant cancer-associated mutations is considered a critical strategy to control cancer growth. Our functional in vivo genetic screens of patient-derived tumors showed unprecedented numerosity and interpatient heterogeneity of genes that are essential for tumor growth, but not mutated, suggesting that multiple, patient-specific signaling pathways are activated in tumors. Cancer Discov; 6(6); 650-63. ©2016 AACR.This article is highlighted in the In This Issue feature, p. 561.

Synthetic vulnerabilities of mesenchymal subpopulations in pancreatic cancer

Malignant neoplasms evolve in response to changes in oncogenic signalling. Cancer cell plasticity in response to evolutionary pressures is fundamental to tumour progression and the development of therapeutic resistance. Here we determine the molecular and cellular mechanisms of cancer cell plasticity in a conditional oncogenic Kras mouse model of pancreatic ductal adenocarcinoma (PDAC), a malignancy that displays considerable phenotypic diversity and morphological heterogeneity. In this model, stochastic extinction of oncogenic Kras signalling and emergence of Kras-independent escaper populations (cells that acquire oncogenic properties) are associated with de-differentiation and aggressive biological behaviour. Transcriptomic and functional analyses of Kras-independent escapers reveal the presence of Smarcb1–Myc-network-driven mesenchymal reprogramming and independence from MAPK signalling. A somatic mosaic model of PDAC, which allows time-restricted perturbation of cell fate, shows that depletion of Smarcb1 activates the Myc network, driving an anabolic switch that increases protein metabolism and adaptive activation of endoplasmic-reticulum-stress-induced survival pathways. Increased protein turnover renders mesenchymal sub-populations highly susceptible to pharmacological and genetic perturbation of the cellular proteostatic machinery and the IRE1-α–MKK4 arm of the endoplasmic-reticulum-stress-response pathway. Specifically, combination regimens that impair the unfolded protein responses block the emergence of aggressive mesenchymal subpopulations in mouse and patient-derived PDAC models. These molecular and biological insights inform a potential therapeutic strategy for targeting aggressive mesenchymal features of PDAC.

RNAi screens identify CHD4 as an essential gene in breast cancer growth

Epigenetic regulation plays an essential role in tumor development and epigenetic modifiers are considered optimal potential druggable candidates. In order to identify new breast cancer vulnerabilities and improve therapeutic chances for patients, we performed in vivo and in vitro shRNA screens in a human breast cancer cell model (MCF10DCIS.com cell line) using epigenetic libraries. Among the genes identified in our screening, we deeply investigated the role of Chromodomain Helicase DNA binding Protein 4 (CHD4) in breast cancer tumorigenesis. CHD4 silencing significantly reduced tumor growth in vivo and proliferation in vitro of MCF10DCIS.com cells. Similarly, in vivo breast cancer growth was decreased in a spontaneous mouse model of breast carcinoma (MMTV-NeuT system) and in metastatic patient-derived xenograft models. Conversely, no reduction in proliferative ability of non-transformed mammary epithelial cells (MCF10A) was detected. Moreover, we showed that CHD4 depletion arrests proliferation by inducing a G0/G1 block of cell cycle associated with up-regulation of CDKN1A (p21). These results highlight the relevance of genetic screens in the identification of tumor frailties and the role of CHD4 as a potential pharmacological target to inhibit breast cancer growth.

WDR5 regulates epithelial-to-mesenchymal transition in breast cancer cells via TGFB

Even if the mortality rate in breast cancer (BC) has recently decreased, development of metastases and drug resistance are still challenges to successful systemic treatment. The epithelial-to-mesenchymal transition (EMT), as well as epigenetic dynamic modifications, plays a pivotal role in invasion, metastasis, and drug resistance. Here, we report that WDR5, the core subunit of histone H3 K4 methyltransferase complexes, is crucial in coordinating EMT and regulating epigenetic changes that drive metastasis. We show that silencing of WDR5 in BC up-regulates an epithelial signature in triple negative and luminal B like patients by transcriptional repression of mesenchymal genes and reduction of the metastatic properties of these cells. Moreover, we demonstrate that this regulation is mediated by inhibition of the TGFβ signaling both at the transcriptional and post-translational level, suggesting an active role of WDR5 in guiding tumor plasticity upon oncogenic insults, regardless of the pathological BC subtypes. We therefore suggest that WDR5 inhibition could be a successful pharmacologic approach to inhibit EMT and sensitize breast cancer cells to chemotherapy.

Abstract A03: Perturbation of proteostasis is lethal in SMARCB1-deficient tumors

Alterations in chromatin remodeling genes have been increasingly implicated in human oncogenesis. The SWI/SNF complex, specifically, is involved in a plethora of biologic functions including cell cycle regulation, terminal differentiation, and regulation of cell metabolism. The crucial chromatin-remodeling function of the SWI/SNF complex during organogenesis and tissue specification is further supported by clinical data showing that the biallelic inactivation of the core subunits SMARCB1 and SMARCA4 results in the emergence of extremely aggressive pediatric malignancies characterized by a dramatic impairment of cell cycle regulation and cellular differentiation programs, resulting in highly lethal diseases characterized by early onset, widespread metastatic dissemination, and resistance to chemotherapy. So far the lack of conditional genetic models of malignant rhabdoid tumors (MRTs) made difficult to investigate the molecular bases of malignant transformation as well as the existence of dependencies associated with SMARCB1 loss. In order to identify the functional vulnerabilities of SMARCB1-deficient cancers, we developed an embryonic mosaic model of malignant rhabdoid tumors (MRTs) that faithfully recapitulates the clinicopathologic features of human disease. By using this novel experimental system we discovered that, upon SMARCB1 ablation, embryonic epithelial progenitors undergo a profound anabolic reprogramming resulting in a global increase in protein biosynthesis and in the adaptive activation of UPR and ER stress response. As a consequence, murine and human SMARCB1-deficient malignancies display an exquisite sensitivity to agents inducing proteotoxic stress and to the pharmacologic and genetic perturbation of autophagy. Our findings, therefore, have immediate clinical implications, paving the way for drug repositioning trials investigating combinations of agents with already known safety profiles targeting simultaneously UPR and the authopagic catabolic machinery in a class of orphan diseases affecting children with limited therapeutic options. Note: This abstract was not presented at the conference. Citation Format: Giannicola Genovese, Alessandro Carugo, Rosalba Minelli, Frederick, Scott Robinson, Pavlos Msaouel, Tim Heffernan, Andrea Viale, Nizar Tannir, Giulio Draetta. Perturbation of proteostasis is lethal in SMARCB1-deficient tumors [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 A03.

Collapsing the tumor ecosystem: Preventing adaptive response to treatment by inhibiting transcription

Adaptation and resistance to treatment are the results of a multitude of (epi)genetic events unmasked or directly triggered by therapies targeting the genetic driver(s) of a dominant cell population within a tumor mass. Rusan and colleagues report that drug-tolerant cells are sensitive to THZ1, a dual CDK7/12 inhibitor, which, by impairing the transcriptional machinery, can prevent cellular rewiring to survive therapeutic attack. Cancer Discov; 8(1); 17-9. ©2018 AACRSee related article by Rusan et al., p. 59.

Abstract 3016: Identification of protein arginine methyltransferase 1 as novel epigenetic vulnerability in KRAS/p53 mutant PDAC primary patient models

Pancreatic ductal adenocarcinoma (PDAC) is a rapidly progressing disease associated with less than 10% 5-year survival rate. Various treatment regimens failed to improve survival of PDAC patients, thus a critical need exists to identify druggable targets essential for tumor maintenance. We developed a powerful in vivo platform that enables the identification of new molecular drivers in the PDAC context where activating mutation of KRAS gene and loss of p53 dominate the genetic landscape. Through an in vivo loss of function screen performed in KRAS/p53 mutant PDAC primary patient models, we identify protein arginine methyltransferase 1 (PRMT1) as top scoring hit. This novel dependency in PDAC was subsequently validated in multiple PDAC models using both shRNA mediated as well as CRISPR base genetic inhibition and we demonstrated that PRMT1 knockdown induces a significant growth inhibition in vitro. Methylation of arginine 3 on histone H4 (H4R3me2a) as well as global arginine methylation was also evaluated and showed a dramatic reduction upon PRMT1 knockdown, correlating observed phenotype with target engagement. To further confirm a role for PRMT1 in tumor maintenance, we developed inducible PRMT1 knockdown in a primary patient model and showed a dramatic tumor growth inhibition (TGI) in vivo upon PRMT1 knockdown. PRMT1 is the primary enzyme responsible for arginine asymmetric demethylation, however other members of the Type I family are also involved in this process and we evaluated the role of protein arginine methyltransferase 4 (PRMT4) and 6 (PRMT6) in our workhorse model. Surprisingly, no significant phenotypic response was observed upon genetic inhibition of PRMT4 or PRMT6 suggesting no redundancy between different PRMT type I and a unique dependency on PRMT1. To strengthen and complement the genetic validation, we leveraged a PRMT Type I inhibitor and confirmed in vitro results as well as in vivo efficacy at tolerated doses (xenograft vs allograft). Key models have been prioritized in order to inform on PRMT1 dependency and to refine responder population. Our research has identified and validated for the first time an arginine methyltransferase as a novel genetic vulnerability in PDAC and strongly suggest PRMT1 as a new therapeutic opportunity in PDAC cancers. Citation Format: Virginia Giuliani, Bhavatarini Vangamudi, Erika Suzuki, Meredith Miller, Chiu-Yi Liu, Alessandro Carugo, Christopher Bristow, Guang Gao, Jing Han, Yuting Sun, Ningping Feng, Edward Chang, Joseph Marszalek, Jeffrey Kovacs, Maria Emilia Di Francesco, Carlo Toniatti, Timothy Heffernan, Philip Jones, Giulio Draetta. Identification of protein arginine methyltransferase 1 as novel epigenetic vulnerability in KRAS/p53 mutant PDAC primary patient models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3016. doi:10.1158/1538-7445.AM2017-3016