PTEN Loss Research Articles

EXTH-82. THE ROLE OF PTEN AND EPIGENETIC KINOME PROGRAMMING IN EGFR TKI RESPONSE IN GLIOBLASTOMA

Abstract Glioblastoma (GBM) is the most common brain tumor and standard therapy only extends survival from 12 to 15 months. The receptor tyrosine kinase EGFR is altered in ~60% of GBM, resulting in aberrant activation of downstream pathways, including PI3K, that potentiate tumorigenesis. Though EGFR targeting has been successful in other cancers, clinical trials with EGFR tyrosine kinase inhibitors (TKI) have failed in GBM, in part due to resistance. Trial results suggested that the most common oncogenic EGFR variant, EGFRvIII (vIII), and negative regulator of PI3K signaling, PTEN, were biomarkers of response. To dissect the role of PTEN in GBM tumorigenesis and EGFR TKI response, we utilized vIII-expressing mouse astrocytes with and without functional Pten. Pten loss potentiated tumorigenesis in vitro and in vivo, as proliferation and stemness were significantly increased, and mouse survival was decreased upon implantation as orthoptic allografts. Both RNA-seq and proteomic analysis using multiplex inhibitor beads with mass spectrometry (MIB-MS) showed significantly altered kinome profiles. Pten deleted cells were 5-fold more sensitive to the EGFR TKI neratinib, a drug that induced Pten-dependent modulation of the kinase transcriptome over 48h. This acute transcriptional adaptation implies alteration of the epigenetic landscape. We hypothesized that disruption of enhancer dynamics via BET bromodomain inhibition would improve EGFR TKI durability. We found that cells expressing Pten were 10-fold more sensitive to multiple BET inhibitors, including JQ1, birabresib, and molibresib, and these inhibitors synergized with neratinib to reduce proliferation only in the Pten wild type model. Ongoing work is focused on defining the role of PTEN in maintenance of differential transcriptional and epigenetic programs. We will explore potential mechanistic roles of both the enzymatic and non-enzymatic functions of Pten and characterize its effect on hallmark cancer phenotypes such as proliferation, stemness/self-renewal, and tumorigenesis in the presence and absence of EGFR ± BET inhibitors.

A Dual Role of SOX11 Expression in the Formation of T-Cell Acute Lymphoblastic Leukemia in Mouse Models

Introduction: T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive hematological malignancy that accounts for 10%-15% of pediatric and 25% of adult ALL cases. Intensified chemotherapy and bone marrow transplants have improved the survival of T-ALL patients. However, around 20% of patients still suffer from primary resistant or relapsed T-ALL. Therefore, improving our knowledge of T-ALL biology and developing precision oncology therapeutics is essential for further progress in T-ALL treatment. SRY-related HMG-box 11 (SOX11) is a transcription factor that regulates the development and survival of multiple embryonic tissues and is crucial for the nervous system. SOX11 is expressed in a multitude of tumor types, where it has been associated with either increased or decreased cell proliferation, metastatic potential, and with either good or bad prognosis, depending on cancer type. Despite being absent in the T-cell lineage, SOX11 is expressed in a subset of T-ALLs, where it plays an unknown role. Based on having a malignantly restricted expression, we hypothesize that SOX11 might be oncogenic in T-ALL. Aim: Identify the role of aberrant SOX11 expression in (pre)leukemic T-cells. Methods: Using a conditional Rosa26-SOX11 overexpression mouse model, we generated mice with T-cell specific (using Lck-cre) SOX11 expression (SOX11 Lck). To assess the self-renewal potential of SOX11 Lck thymocytes, we performed thymic transplantations on sublethally irradiated mice expressing a different allele of CD45. To study SOX11 in a leukemic context, we crossed the SOX11 Lck mice with two established T-ALL mouse models that are either driven by the overexpression of Lmo2 (SOX11 Lck-Lmo2 CD2) or by the loss of the tumor suppressor Pten (SOX11/Pten Lck). An aging cohort of these T-ALL models was followed, and tumor samples were collected. Thymi of 8-weeks old mice were used to study the impact of SOX11 in a pre-leukemic context, and T-cell tumors arising in these models were also used for RNA-sequencing. Using a retroviral strategy, we overexpressed SOX11 in human cord blood stem cells, which we differentiated towards the T-cell lineage ex vivo by co-culturing them on OP9 stromal cells expressing Delta-like Notch ligand 4. Furthermore, we transduced Jurkat cells with a SOX11 expression vector, or with an empty vector, and injected the cells into immunocompromised mice to assess the effect of SOX11 on tumor growth in vivo. Results: In SOX11 Lck mice, we found a significant increase in the immature double-negative 3 (DN3) thymic fraction, with a concomitant decrease in the amount of more mature double-positive CD4 +CD8 + (DP) thymocytes (Fig. A). A possible explanation for this phenotype would be the establishment of a stem-like self-renewal program similar to the one driven by Lmo2. However, by performing thymic transplantations into sublethally irradiated mice, we concluded that SOX11 does not confer self-renewal properties to thymocytes. Additionally, we aged a cohort of SOX11 Lck mice and did not observe formation of T-cell malignancies up to 500 days of age. Given that the expression of SOX11 does not suffice to produce T-cell tumors, we generated the SOX11 Lck-Lmo2 CD2 and SOX11/Pten Lck T-ALL mouse models. In SOX11 Lck-Lmo2 CD2 mice, we found a synergistic effect of the co-expression of both genes on the expansion of DN3 thymocytes (Fig. A), which led to accelerated leukemia formation (Fig. B). By sequencing the RNA of pre-leukemic and leukemic DN3 cells, we observed that SOX11 is mostly regulating cell adhesion, morphology, and cell-cell interactions to promote this oncogenic phenotype in Lmo2-driven T-ALL. On the other hand, SOX11/Pten Lck mice suffered from delayed leukemogenesis (Fig. B), and this tumor suppressor role might be associated with the decrease in DP cells observed in the pre-leukemic stage. Lastly, we set out to validate these findings in a human context. The ex vivo differentiation of human hematopoietic stem cells toward the T-cell lineage showed that SOX11 strongly accelerates early commitment to double-negative T-cell precursors. Also, we observed that Jurkat T-ALL cells engraft faster in immunocompromised mice when expressing SOX11. Conclusions: By generating multiple models of SOX11 expression in the T-cell lineage, we showed that SOX11 impacts T-cell differentiation, both in mice and humans, and that it can promote or hinder T-ALL formation depending on the oncogenic driver.

Mechanistic Insights on Localized to Metastatic Prostate Cancer Transition and Therapeutic Opportunities.

Prostate cancer is the most common non-cutaneous cancer among American men. Multiple mechanisms are involved in tumorigenesis and progression to metastases. While androgen deprivation therapy remains the cornerstone of treatment, progression to castration-resistant disease becomes inevitable. Aberrant pathway activations of PI3K/AKT due to PTEN loss, epithelial-mesenchymal transition pathways, homologous recombination repair, and DNA repair pathway mechanisms of resistance and cross-talk lead to opportunities for therapeutic targeting in metastatic castration-resistant prostate cancer. This review focuses on mechanisms of progression and key trials that evaluate the drugs and combinations that exploit these pathways.

TAS0612, a Novel RSK, AKT, and S6K Inhibitor, Exhibits Antitumor Effects in Preclinical Tumor Models.

The MAPK and PI3K pathways are involved in cancer growth and survival; however, the clinical efficacy of single inhibitors of each pathway is limited or transient owing to resistance mechanisms, such as feedback signaling and/or reexpression of receptor-type tyrosine kinases (RTK). This study identified a potent and novel kinase inhibitor, TAS0612, and characterized its properties. We found that TAS0612 is a potent, orally available compound that can inhibit p90RSK (RSK), AKT, and p70S6K (S6K) as a single agent and showed a strong correlation with the growth inhibition of cancer cells with PTEN loss or mutations, regardless of the presence of KRAS and BRAF mutations. Additional RSK inhibitory activity may differentiate the sensitivity profile of TAS0612 from that of signaling inhibitors that target only the PI3K pathway. Moreover, TAS0612 demonstrated broad-spectrum activity against tumor models wherein inhibition of MAPK or PI3K pathways was insufficient to exert antitumor effects. TAS0612 exhibited a stronger growth-inhibitory activity against the cancer cell lines and tumor models with dysregulated signaling with the genetic abnormalities described above than treatment with inhibitors against AKT, PI3K, MEK, BRAF, and EGFR/HER2. In addition, TAS0612 demonstrated the persistence of blockade of downstream growth and antiapoptotic signals, despite activation of upstream effectors in the signaling pathway and FoxO-dependent reexpression of HER3. In conclusion, TAS0612 with RSK/AKT/S6K inhibitory activity may provide a novel therapeutic strategy for patients with cancer to improve clinical responses and overcome resistance mechanisms.

Allosteric PI3Kα Inhibition Overcomes On-target Resistance to Orthosteric Inhibitors Mediated by Secondary PIK3CA Mutations.

In one of the largest patient cohorts analyzed to date, this study defines the clinical landscape of acquired resistance to PI3Kα inhibitors. Genomic alterations within the PI3K pathway represent a major mode of resistance and identify a novel class of secondary PIK3CA resistance mutations that can be overcome by an allosteric PI3Kα inhibitor. See related commentary by Gong and Vanhaesebroeck, p. 204 . See related article by Varkaris et al., p. 240 . This article is featured in Selected Articles from This Issue, p. 201.

PTEN-regulated PI3K-p110 and AKT isoform plasticity controls metastatic prostate cancer progression

PTEN loss, one of the most frequent mutations in prostate cancer (PC), is presumed to drive disease progression through AKT activation. However, two transgenic PC models with Akt activation plus Rb loss exhibited different metastatic development: Pten/RbPE:−/− mice produced systemic metastatic adenocarcinomas with high AKT2 activation, whereas RbPE:−/− mice deficient for the Src-scaffolding protein, Akap12, induced high-grade prostatic intraepithelial neoplasias and indolent lymph node dissemination, correlating with upregulated phosphotyrosyl PI3K-p85α. Using PC cells isogenic for PTEN, we show that PTEN-deficiency correlated with dependence on both p110β and AKT2 for in vitro and in vivo parameters of metastatic growth or motility, and with downregulation of SMAD4, a known PC metastasis suppressor. In contrast, PTEN expression, which dampened these oncogenic behaviors, correlated with greater dependence on p110α plus AKT1. Our data suggest that metastatic PC aggressiveness is controlled by specific PI3K/AKT isoform combinations influenced by divergent Src activation or PTEN-loss pathways.

AKT2 Loss Impairs BRAF-Mutant Melanoma Metastasis.

Despite recent advances in treatment, melanoma remains the deadliest form of skin cancer due to its highly metastatic nature. Melanomas harboring oncogenic BRAFV600E mutations combined with PTEN loss exhibit unrestrained PI3K/AKT signaling and increased invasiveness. However, the contribution of different AKT isoforms to melanoma initiation, progression, and metastasis has not been comprehensively explored, and questions remain about whether individual isoforms play distinct or redundant roles in each step. We investigate the contribution of individual AKT isoforms to melanoma initiation using a novel mouse model of AKT isoform-specific loss in a murine melanoma model, and we investigate tumor progression, maintenance, and metastasis among a panel of human metastatic melanoma cell lines using AKT isoform-specific knockdown studies. We elucidate that AKT2 is dispensable for primary tumor formation but promotes migration and invasion in vitro and metastatic seeding in vivo, whereas AKT1 is uniquely important for melanoma initiation and cell proliferation. We propose a mechanism whereby the inhibition of AKT2 impairs glycolysis and reduces an EMT-related gene expression signature in PTEN-null BRAF-mutant human melanoma cells to limit metastatic spread. Our data suggest that the elucidation of AKT2-specific functions in metastasis might inform therapeutic strategies to improve treatment options for melanoma patients.

Immunohistochemistry-Based Biomarkers and Impact on Outcomes Following Salvage Radiotherapy for Prostate Cancer.

Salvage radiation therapy (SRT) is a mainstay of treatment for prostate cancer patients who experience biochemical relapse following radical prostatectomy. We sought to characterize the prognostic impact of previously identified deleterious molecular phenotypes-loss of PTEN, ERG expression, and p53 mutation- upon survival in patients undergoing SRT. We analyzed an institutional database of 320 patients treated with SRT for whom prostatectomy tissue was available; tissue microarrays (TMAs) were constructed and used for genetically validated immunohistochemistry assays for PTEN, ERG, and p53. Chi-squared and Mann-Whitney's tests were used to assess association between molecular expression and clinical risk factors for adverse survival. Uni- and multivariate Cox-proportional hazards models were constructed to determine effects on biochemical (bRFS) and metastasis-free survival (MFS), calculated from end of SRT to event. Loss of PTEN (n = 123, 50%) and ERG expression (n = 118, 39.1%) were common, while p53 overexpression (signifying TP53 missense mutation) was less common (n = 21, 6.6%). On univariate Cox regression, loss of PTEN portended worse bRFS [HR 1.86; 95% CI 1.36-2.57] and MFS [HR 1.89; 1.21-2.94], with homogeneous loss associated with particularly worse MFS [HR 2.47; 1.54-3.95]. Similarly, p53 overexpression predicted worse bRFS [HR 1.95; 1.14-3.32] and MFS [HR 2.79; 1.50-5.19]. ERG expression was associated with only worse MFS [HR 1.6; 1.03-2.48]. On multivariate analysis adjusting for known prognostic features (grade, nodal involvement, pathologic stage, androgen deprivation therapy (ADT), and PSA velocity), homogeneous PTEN loss remained predictive of adverse bRFS [HR 1.73; 1.06-2.82] and MFS [HR 2.35; 1.04-5.34]. PTEN loss identified by immunohistochemistry is an independent adverse prognostic factor for both biochemical and metastasis-free survival in prostate cancer patients treated with SRT. Although clinically validated RNA expression assays also exist which are prognostic for outcomes following SRT, stromal contamination in bulk RNA could mask "loss" signals specific to tumor cells, such as PTEN. Further work is necessary to determine the optimal approach to treating patients with poor molecular prognostic features in a salvage setting.

Efficient genetic editing of human intestinal organoids using ribonucleoprotein-based CRISPR.

Organoids, combined with genetic editing strategies, have the potential to offer rapid and efficient investigation of gene function in many models of human disease. However, to date, the editing efficiency of organoids with the use of non-viral electroporation methods has only been up to 30%, with implications for the subsequent need for selection, including turnaround time and exhaustion or adaptation of the organoid population. Here, we describe an efficient method for intestinal organoid editing using a ribonucleoprotein-based CRISPR approach. Editing efficiencies of up to 98% in target genes were robustly achieved across different gut anatomical locations and developmental timepoints from multiple patient samples with no observed off-target editing. The method allowed us to study the effect of loss of the tumour suppressor gene PTEN in normal human intestinal cells. Analysis of PTEN-deficient organoids defined phenotypes that likely relate to its tumour suppressive function in vivo, such as a proliferative advantage and increased organoid budding. Transcriptional profiling revealed differential expression of genes in pathways commonly known to be associated with PTEN loss, including mTORC1 activation.

Circumvention of Gefitinib Resistance by Repurposing Flunarizine via Histone Deacetylase Inhibition.

Gefitinib is an epidermal growth factor receptor tyrosine kinase inhibitor (EGFR TKI) for treating advanced non-small cell lung cancer (NSCLC). However, drug resistance seriously impedes the clinical efficacy of gefitinib. This study investigated the repositioning of the non-oncology drug capable of inhibiting histone deacetylases (HDACs) to overcome gefitinib resistance. A few drug candidates were identified using the in silico repurposing tool "DRUGSURV" and tested for HDAC inhibition. Flunarizine, originally indicated for migraine prophylaxis and vertigo treatment, was selected for detailed investigation in NSCLC cell lines harboring a range of different gefitinib resistance mechanisms (EGFR T790M, KRAS G12S, MET amplification, or PTEN loss). The circumvention of gefitinib resistance by flunarizine was further demonstrated in an EGFR TKI (erlotinib)-refractory patient-derived tumor xenograft (PDX) model in vivo. The acetylation level of cellular histone protein was increased by flunarizine in a concentration- and time-dependent manner. Among the NSCLC cell lines evaluated, the extent of gefitinib resistance circumvention by flunarizine was found to be the most pronounced in EGFR T790M-bearing H1975 cells. The gefitinib-flunarizine combination was shown to induce the apoptotic protein Bim but reduce the antiapoptotic protein Bcl-2, which apparently circumvented gefitinib resistance. The induction of Bim by flunarizine was accompanied by an increase in the histone acetylation and E2F1 interaction with the BIM gene promoter. Flunarizine was also found to upregulate E-cadherin but downregulate the vimentin expression, which subsequently inhibited cancer cell migration and invasion. Importantly, flunarizine was also shown to significantly potentiate the tumor growth suppressive effect of gefitinib in EGFR TKI-refractory PDX in vivo. The findings advocate for the translational application of flunarizine to circumvent gefitinib resistance in the clinic.

In Vivo Intra-Uterine Delivery of TAT-Fused Cre Recombinase and CRISPR/Cas9 Editing System in Mice Unveil Histopathology of Pten/p53-Deficient Endometrial Cancers.

Phosphatase and TENsin homolog (Pten) and p53 are two of the most frequently mutated tumor suppressor genes in endometrial cancer. However, the functional consequences and histopathological manifestation of concomitant p53 and Pten loss of function alterations in the development of endometrial cancer is still controversial. Here, it is demonstrated that simultaneous Pten and p53 deletion is sufficient to cause epithelial to mesenchymal transition phenotype in endometrial organoids. By a novel intravaginal delivery method using HIV1 trans-activator of transcription cell penetrating peptide fused with a Cre recombinase protein (TAT-Cre), local ablation of both p53 and Pten is achieved specifically in the uterus. These mice developed high-grade endometrial carcinomas and a high percentage of uterine carcinosarcomas resembling those found in humans. To further demonstrate that carcinosarcomas arise from epithelium, double Pten/p53 deficient epithelial cells are mixed with wild type stromal and myometrial cells and subcutaneously transplanted to Scid mice. All xenotransplants resulted in the development of uterine carcinosarcomas displaying high nuclear pleomorphism and metastatic potential. Accordingly, in vivo CRISPR/Cas9 disruption of Pten and p53 also triggered the development of metastatic carcinosarcomas. The results unfadingly demonstrate that simultaneous deletion of p53 and Pten in endometrial epithelial cells is enough to trigger epithelial to mesenchymal transition that is consistently translated to the formation of uterine carcinosarcomas in vivo.

Cholesterol biogenesis is a PTEN-dependent actionable node for the treatment of endocrine therapy-refractory cancers.

PTEN and PIK3CA mutations are the most prevalent PI3K pathway alterations in prostate, breast, colorectal, and endometrial cancers. p110β becomes the prominent PI3K isoform upon PTEN loss. In this study, we aimed to understand the molecular mechanisms of PI3K dependence in the absence of PTEN. Using online bioinformatical tools, we examined two publicly available microarray datasets with aberrant PI3K activation. We found that the rate-limiting enzyme of cholesterol biogenesis, SQLE, was significantly upregulated in p110β-hyperactivated or PTEN-deficient mouse prostate tumors. Concomitantly, the expression of cholesterol biosynthesis pathway enzymes was directly correlated with PI3K activation status in microarray datasets and diminished upon PTEN re-expression in PTEN-null prostate cancer cells. Particularly, PTEN re-expression decreased SQLE protein levels in PTEN-deficient prostate cancer cells. We performed targeted metabolomics and detected reduced levels of cholesteryl esters as well as free cholesterol upon PTEN re-expression. Notably, PTEN-null prostate and breast cancer cell lines were more sensitive to pharmacological intervention with the cholesterol pathway than PTEN-replete cancer cells. Since steroid hormones use sterols as structural precursors, we studied whether cholesterol biosynthesis may be a metabolic vulnerability that enhances antihormone therapy in PTEN-null castration-resistant prostate cancer cells. Coinhibition of cholesterol biosynthesis and the androgen receptor enhanced their sensitivity. Moreover, PTEN suppression in endocrine therapy-resistant luminal-A breast cancer cells leads to an increase in SQLE expression and a corresponding sensitization to the inhibition of cholesterol synthesis. According to our data, targeting cholesterol biosynthesis in combination with the hormone receptor signaling axis can potentially treat hormone-resistant prostate and breast cancers.

Oncogene-Induced Senescence Is a Crucial Antitumor Defense Mechanism of Human Endometrial Stromal Cells.

Being the major cellular component of highly dynamic tissue, endometrial stromal cells (EnSCs) are exposed to cycles of proliferation upon hormonal stimulation, which might pose risks for the accumulation of mutations and malignization. However, endometrial stromal tumors are rare and uncommon. The present study uncovered defense mechanisms that might underlie the resistance of EnSCs against oncogenic transformation. All experiments were performed in vitro using the following methods: FACS, WB, RT-PCR, IF, molecular cloning, lentiviral transduction, and CRISPR/Cas9 genome editing. We revealed that the expression of the mutant HRASG12V leads to EnSC senescence. We experimentally confirmed the inability of HRASG12V-expressing EnSCs to bypass senescence and resume proliferation, even upon estrogen stimulation. At the molecular level, the induction of oncogene-induced senescence (OIS) was accompanied by activation of the MEK/ERK, PI3K/AKT, p53/p21WAF/CIP/Rb, and p38/p16INK4a/Rb pathways; however, inhibiting either pathway did not prevent cell cycle arrest. PTEN loss was established as an additional feature of HRASG12V-induced senescence in EnSCs. Using CRISPR-Cas9-mediated PTEN knockout, we identified PTEN loss-induced senescence as a reserve molecular mechanism to prevent the transformation of HRASG12V-expressing EnSCs. The present study highlights oncogene-induced senescence as an antitumor defense mechanism of EnSCs controlled by multiple backup molecular pathways.

MYC Deregulation and PTEN Loss Model Tumor and Stromal Heterogeneity of Aggressive Triple-Negative Breast Cancer

Triple-negative breast cancer (TNBC) patients have a poor prognosis and few treatment options. Mouse models of TNBC are important for development of new therapies, however, few mouse models represent the complexity of TNBC. Here, we develop a female TNBC murine model by mimicking two common TNBC mutations with high co-occurrence: amplification of the oncogene MYC and deletion of the tumor suppressor PTEN. This Myc;Ptenfl model develops heterogeneous triple-negative mammary tumors that display histological and molecular features commonly found in human TNBC. Our research involves deep molecular and spatial analyses on Myc;Ptenfl tumors including bulk and single-cell RNA-sequencing, and multiplex tissue-imaging. Through comparison with human TNBC, we demonstrate that this genetic mouse model develops mammary tumors with differential survival and therapeutic responses that closely resemble the inter- and intra-tumoral and microenvironmental heterogeneity of human TNBC, providing a pre-clinical tool for assessing the spectrum of patient TNBC biology and drug response.

P02.23.A MDM2/X ALTERATIONS IN A MULTICOHORT RETROSPECTIVE ANALYSIS: A POTENTIAL TARGET OF TREATMENT IN PATIENTS WITH PRIMARY BRAIN TUMORS

Abstract BACKGROUND Primary brain tumors (pBTs) are a heterogeneous group of neoplasms with limited therapeutic alternatives. Disruption of the TP53 tumor suppressor pathway occurs in most high-grade gliomas. While TP53 loss-of-function mutations are poorly targetable, in 14% of patients this disruption is due to a Mouse double minute 2 homolog (MDM2) amplification. We aim to describe the characteristics of patients with MDM2 amplification and analyze its clinical and molecular factors using a cohort of patients with NGS data. MATERIAL AND METHODS Patients currently enrolled in the institutionally approved, retrospective multicenter study ESCAT-pBTs, which includes patients with pBT profiled used NGS methods (Foundation Medicine®, local NGS, Caris®, Oncomine®, copy number alterations (CNA), and fusion panels) were analyzed to determine the presence of MDM2 alterations (MDM2alt) and clinical factors including WHO 2021 diagnosis, sex, age, ECOG and other molecular findings. RESULTS A total of 493 pts with NGS and CNA were collected between Feb 2018 and January 2023 at 5 hospitals in Spain. The median age was 50.3 (range, 3.3-83.8), 14.2% had ECOG ≥2, 39.1% were women, 26.9% were 40 or younger, 21.5% had IDH1mut and 24.3% were methylated. The diagnosis of GBM (WHO 2021) was present in 68.8% of the patients and 33.8% had mutations or CNV in TP53. The overall prevalence of MDM2alt was 8.5%(42 pts), 92.9% gene amplifications, and 7,1% mutations. No differences were found in gender proportion between MDM2alt and no MDM2alt (Female: 37.1% vs 39.4% p:0.64) and no major variance in the percentage of ECOG ≥2 (16.6% vs 17.6% p:0.77). Prevalence in patients with GBM was: 11.8% vs 1.3% in patients with other pBTs. Concurrent mutations in MDM2alt patients were: CDK-4 copy number gain in 76,2%; a similar proportion of mutations in PI3KCA/PTEN was observed compared with the non-MDM2alt population in the pts with GBM (38,3% vs 50%, p:0.15). No significant variation was found in EGFR amplifications (42,9% vs 32% p:0.10) and EGFR mutations GBM MDM2 and no MDM2alt respectively (19% vs 18,7% p: 0.84). The median TMB was 5.22 (range from 2.24 to 13 mutations/megabase) in pts with MDM2alt and 4.76 (range from 1.26 to 53.7 mutations/megabase). 97,6% of the MDM2alt population was TP53 wild type. CONCLUSION MDM2alt is a common genomic event in patients with molecularly defined GBM and has a low prevalence in other pBT. The presence of MDM2alt is associated in our series with other genomic events such as PTEN loss, low TMB, and a high degree of CDK4 amplification. No statistically significant differences were found between the GBM MDM2alt and no MDM2alt subgroup in terms of molecular alterations and clinical aspects studied. These findings should inform the further clinical development of treatment strategies for MDM2alt pts.

Pten knockout affects drug resistance differently in melanoma and kidney cancer

BackgroundPTEN is a tumor suppressor that is often mutated and nonfunctional in many types of cancer. The high heterogeneity of PTEN function between tumor types makes new Pten knockout models necessary to assess its impact on cancer progression and/or treatment outcomes.MethodsWe aimed to show the effect of CRISPR/Cas9-mediated Pten knockout on murine melanoma (B16 F10) and kidney cancer (Renca) cells. We evaluated the effect of PTEN deregulation on tumor progression in vivo and in vitro, as well as on the effectiveness of drug treatment in vitro. In addition, we studied the molecular changes induced by Pten knockout.ResultsIn both models, Pten mutation did not cause significant changes in cell proliferation in vitro or in vivo. Cells with Pten knockout differed in sensitivity to cisplatin treatment: in B16 F10 cells, the lack of PTEN induced sensitivity and, in Renca cells, resistance to drug treatment. Accumulation of pAKT was observed in both cell lines, but only Renca cells showed upregulation of the p53 level after Pten knockout. PTEN deregulation also varied in the way that it altered PAI-1 secretion in the tested models, showing a decrease in PAI-1 in B16 F10 Pten/KO and an increase in Renca Pten/KO cells. In kidney cancer cells, Pten knockout caused changes in epithelial to mesenchymal transition marker expression, with downregulation of E-cadherin and upregulation of Snail, Mmp9, and Acta2 (α-SMA).ConclusionsThe results confirmed heterogenous cell responses to PTEN loss, which may lead to a better understanding of the role of PTEN in particular types of tumors and points to PTEN as a therapeutic target for personalized medicine.

PTEN loss in intraductal carcinoma of the prostate has low incidence in Japanese patients.

Clinical and genomic features of prostate cancer (PCa) vary considerably between Asian and Western populations. PTEN loss is the most frequent abnormality in intraductal carcinoma of the prostate (IDC-P) in Western populations. However, its prevalence and significance in Asian populations have not yet been well studied. In the present study, we evaluated PTEN expression in IDC-P in a Japanese population and its association with ERG expression. This study included 45 and 59 patients with PCa with and without IDC-P, respectively, who underwent radical prostatectomy. PTEN loss was observed in 10 patients with PCa with IDC-P (22%) and nine patients with PCa without IDC-P (17%). ERG expression was relatively frequent in patients with PCa with PTEN loss, although a significant difference was not observed. The co-occurrence of PTEN loss and ERG expression was observed in four patients with PCa with IDC-P and one without IDC-P. PTEN loss and ERG expression did not affect progression-free survival, regardless of the presence of IDC-P. The frequency of PTEN loss in IDC-P is lower in Asian patients than in Western patients. Our results indicate that mechanisms underlying IDC-P in Asian populations are different from those of Western populations.

Functional analysis reveals driver cooperativity andnovel mechanisms in endometrial carcinogenesis.

High-risk endometrial cancer has poor prognosis and is increasing in incidence. However, understanding of the molecular mechanisms which drive this disease is limited. We used genetically engineered mouse models (GEMM) to determine the functional consequences of missense and loss of function mutations in Fbxw7, Pten and Tp53, which collectively occur in nearly 90% of high-risk endometrial cancers. We show that Trp53 deletion and missense mutation cause different phenotypes, with the latter a substantially stronger driver of endometrial carcinogenesis. We also show that Fbxw7 missense mutation does not cause endometrial neoplasia on its own, but potently accelerates carcinogenesis caused by Pten loss or Trp53 missense mutation. By transcriptomic analysis, we identify LEF1 signalling as upregulated in Fbxw7/FBXW7-mutant mouse and human endometrial cancers, and in human isogenic cell lines carrying FBXW7 mutation, and validate LEF1 and the additional Wnt pathway effector TCF7L2 as novel FBXW7 substrates. Our study provides new insights into the biology of high-risk endometrial cancer and suggests that targeting LEF1 may be worthy of investigation in this treatment-resistant cancer subgroup.

PTEN deficiency exposes a requirement for an ARF GTPase module for integrin‐dependent invasion in ovarian cancer

Dysregulation of the PI3K/AKT pathway is a common occurrence in high‐grade serous ovarian carcinoma (HGSOC), with the loss of the tumour suppressor PTEN in HGSOC being associated with poor prognosis. The cellular mechanisms of how PTEN loss contributes to HGSOC are largely unknown. We here utilise time‐lapse imaging of HGSOC spheroids coupled to a machine learning approach to classify the phenotype of PTEN loss. PTEN deficiency induces PI(3,4,5)P3‐rich and ‐dependent membrane protrusions into the extracellular matrix (ECM), resulting in a collective invasion phenotype. We identify the small GTPase ARF6 as a crucial vulnerability of HGSOC cells upon PTEN loss. Through a functional proteomic CRISPR screen of ARF6 interactors, we identify the ARF GTPase‐activating protein (GAP) AGAP1 and the ECM receptor β1‐integrin (ITGB1) as key ARF6 interactors in HGSOC regulating PTEN loss‐associated invasion. ARF6 functions to promote invasion by controlling the recycling of internalised, active β1‐integrin to maintain invasive activity into the ECM. The expression of the CYTH2‐ARF6‐AGAP1 complex in HGSOC patients is inversely associated with outcome, allowing the identification of patient groups with improved versus poor outcome. ARF6 may represent a therapeutic vulnerability in PTEN‐depleted HGSOC.

Acquired PTEN Loss May Mediate Dabrafenib and Trametinib Resistance in BRAF V600E-Mutated Epithelioid Glioblastoma: A Case Report and Literature Review

Epithelioid glioblastoma is a rare and aggressive variant of glioblastoma that is common in children and young adults. This variant frequently has a BRAF V600E mutation, and in recent years, this is often treated with BRAF and mitogen-activated protein kinase kinase inhibitors. An 18-year-old female initially presented with headaches and vomiting. They were diagnosed with an epithelioid glioblastoma and treated with temozolomide chemoradiotherapy. Upon progression, they had to redo surgery and then received dabrafenib and trametinib. They had one last surgery shortly before fatal tumour progression. Retrospective molecular analysis of three tumour specimens showed a PTEN mutation that arose upon first progression, but was not there initially. There were no new tumour mutations after initiation of dabrafenib and trametinib. The acquired PTEN mutation may have conferred resistance to dabrafenib and trametinib. This case highlights the potential importance of early treatment with BRAF and mitogen-activated protein kinase kinase inhibitors in high-grade BRAF V600E-mutated gliomas, ideally before the tumour develops resistance to targeted therapy.