Wild-type PTEN Research Articles

BIOM-45. DETERMINANTS OF GBM VULNERABILITY TO INHIBITORS OF NEDD8 ACTIVATING ENZYME (NAE)

Abstract Advancing new therapeutics to FDA approval for GBM is hampered by intra- and inter-tumoral heterogeneity. Design of clinical trials to enroll patients likely to respond to a new treatment seems critical to build the arsenal of agents against this disease. Neddylation is a protein modification pathway aligned to protein degradation and cytological localization within the ubiquitin/proteasome system. Components of the neddylation pathway are frequently overexpressed or hyperactivated in GBM, and whose upregulation has been associated with glioma progression and worse survival. Among glioblastoma cell lines and patient-derived stem cells, subsets were found to be selectively susceptible to NAE inhibitors. We previously showed that PTEN signaling, DNA replication, and chromatin instability pathways are the most significant differentiators between MLN4924 sensitive vs. non-sensitive models. To test a candidate molecular “signature of vulnerability”, two subsets of PDX models (PTEN wildtype and PTEN del or mutated) were treated with a panel of 3 NAE inhibitors. 5 GBM PTENwt models were shown vulnerable to MLN4924 and TAS4464 with average EC50 values 5-10 folds lower than 6 PTENmt/del models. CDC activity was greater against PTENwt, but only 2-fold different vs PTENmt/del. Transcriptomic data mining uncovered additional determinants of response to NAE inhibitors. To disclose the relationship between constitutive expression of three gene sets: DNA Replication Fork Progressing, Replication Fork Protection, and Replication Fork Protection Complex, we found that the genes involved in these are significantly under expressed in PTENmt models when comparing to PTENwt models. The molecular determinants of drug response to NAE inhibitors will be further verified in the extended preclinical models and lead to a patient-enrollment “signature of vulnerability” to increase the likelihood of demonstrating therapeutic efficacy in the early stage of clinical trials.

Prognostic Utility of Biopsy-Based PTEN and ERG Status on Biochemical Progression and Overall Survival after SBRT for Localized Prostate Cancer

<h3>Purpose/Objective(s)</h3> PTEN deletions and ERG rearrangements are two of the most common genetic abnormalities associated with prostate cancer. Prior studies revealed that changes in wild-type PTEN and ERG portend worse clinical outcomes. While early studies were performed on whole-gland samples after radical prostatectomy, subsequent biopsy-based analyses have led to their inclusion in several genomic assays and prostate cancer outcome scores. However, evaluations of therapeutic response to radiotherapy are quite heterogenous. Our objective is to evaluate the impact of biopsy-determined <i>PTEN</i> losses and <i>TMPRSS2-ERG</i> fusion on biochemical disease-free survival (bDFS) in patients who receive SBRT for localized prostate cancer. <h3>Materials/Methods</h3> Patients included in this analysis underwent SBRT for localized prostate cancer and are followed on an institutional prospective quality of life and survival study. For each patient, the single biopsy core with the highest volume of cancer was evaluated for PTEN and ERG abnormalities. Differences in baseline patient and disease characteristics between groups were analyzed using ANOVA for age and χ<b>²</b> for categorical groupings. bDFS and OS were calculated using the Kaplan Meier (KM) method with Log-Rank test comparison between groups. Predictors of bDFS and OS were evaluated using Cox proportional hazard method. For all analyses, <i>p</i> <0.05 was considered statistically significant. <h3>Results</h3> Ninety-three patients were included in the analysis with a median follow up of 72 months (IQR 52 - 85 months). The 5-year bDFS for all patients was 85.2% with a median bDFS of 98 months. The 5-year OS for all patients was 91.8% with a median OS of 123 months. Differences between ERG and PTEN status groups by age, race, T-stage, NCCN risk group, PSA group, PSA density group, and Charlson Comorbidity Index were not statistically significant. Differences in grade group were statistically significant (<i>p</i> = 0.0329). The estimated 5-year bDFS was 100%, 76.6%, 72.9%, and 63.8% for the ERG+/PTEN, ERG-/PTEN+, ERG+/PTEN-, and ERG-/PTEN- groups respectively (<i>p</i> =0.0107). Multivariate analysis (MVA) confirmed an increased likelihood of 5-year biochemical progression with higher NCCN risk group (<i>p</i> <0.0001) and increasing ERG/PTEN mutational burden (<i>p</i><0.0001). <h3>Conclusion</h3> <i>ERG Fusion with PTEN</i> loss is associated with an increased risk of biochemical progression. However, <i>ERG</i> status alone is not predictive of bPFS. Biopsy-based PTEN and ERG assays demonstrate utility in predicting 5-year oncologic outcomes in patients who receive prostate SBRT.

PTEN Protein Phosphatase Activity Is Not Required for Tumour Suppression in the Mouse Prostate.

Loss PTEN function is one of the most common events driving aggressive prostate cancers and biochemically, PTEN is a lipid phosphatase which opposes the activation of the oncogenic PI3K-AKT signalling network. However, PTEN also has additional potential mechanisms of action, including protein phosphatase activity. Using a mutant enzyme, PTEN Y138L, which selectively lacks protein phosphatase activity, we characterised genetically modified mice lacking either the full function of PTEN in the prostate gland or only lacking protein phosphatase activity. The phenotypes of mice carrying a single allele of either wild-type Pten or PtenY138L in the prostate were similar, with common prostatic intraepithelial neoplasia (PIN) and similar gene expression profiles. However, the latter group, lacking PTEN protein phosphatase activity additionally showed lymphocyte infiltration around PIN and an increased immune cell gene expression signature. Prostate adenocarcinoma, elevated proliferation and AKT activation were only frequently observed when PTEN was fully deleted. We also identify a common gene expression signature of PTEN loss conserved in other studies (including Nkx3.1, Tnf and Cd44). We provide further insight into tumour development in the prostate driven by loss of PTEN function and show that PTEN protein phosphatase activity is not required for tumour suppression.

Abstract 1667: Synthetic essentiality between PTEN and core dependency factor PAX7 dictates rhabdomyosarcoma identity

Abstract Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma in children with no improvements in treatment options for RMS patients over the past four decades. Therefore, it is critical to understand the fundamental processes underlying RMS tumorigenesis. RMS is divided into two major histologic subtypes - alveolar and embryonal RMS. Nearly all alveolar RMS express oncogenic fusions of PAX3-FOXO1 or PAX7-FOXO1 whereas embryonal RMS are not driven by these fusion proteins. Instead, embryonal or fusion-negative (FN-RMS) are molecularly heterogeneous. Approximately one-third of fusion-negative RMS (FN-RMS) patients have copy number loss of PTEN (phosphatase and tensin homolog), and approximately 90% of tumors are hypermethylated at the PTEN promoter leading to decreased PTEN expression. This indicates a near universal role for PTEN loss in FN-RMS, but the functional role of PTEN is still unclear. To determine PTEN’s function in FN-RMS, we bred Ptenflox alleles into our aP2-Cre;SmoM2 (ASPWT) FN-RMS mouse model to obtain aP2-Cre;SmoM2;Ptenflox/flox mice (ASPcKO). Conditional Pten deletion accelerated tumorigenesis and produced a tumor with a less differentiated histological appearance, much like human FN-RMS. Interestingly, in PtenWT tumors, we found predominant PTEN immunoreactivity within the nucleus suggesting a role for nuclear PTEN in FN-RMS. Transcriptome analyses revealed robust gene expression changes between the ASPWT and ASPcKO tumors. The top overexpressed gene in ASPcKO tumors was Dbx1 (Developing brain homeobox 1), a homeobox transcription factor with no known cancer function but involved in innate behavioral processes such as breathing. We found FN-RMS patient-derived xenografts are dependent on DBX1 expression, and that DBX1 expression is controlled by PAX7 (Paired Box 7). PAX7 is a transcription factor expressed in satellite cells and maintains a de-differentiated state in FN-RMS. PAX7 expression is also increased in our ASPcKO tumors, and we show that human FN-RMS cells are dependent on PAX7 expression for proliferation. This suggests PTEN loss in FN-RMS engages a new transcriptional program necessary for FN-RMS survival. To determine if Pax7 loss can rescue the deleterious effects of Pten loss in our murine FN-RMS model, we deleted both Pten and Pax7 in our aP2-Cre;SmoM2 mice (ASPcKOP7cKO). ASPcKOP7cKO tumor onset kinetics resembled tumors with wild-type PTEN and were negative for skeletal muscle markers MYOD1 and MYOGENIN. However, these tumors were positive for leiomyosarcoma markers smooth muscle actin and CALDESMON. Together, our data suggests PTEN and PAX7 have a synthetic essential relationship in FN-RMS and that PAX7 is a proliferative driver and lineage dependency for FN-RMS tumors. This work also illustrates the power of murine models to unravel the genetic dependencies underlying both tumor maintenance and identity. Citation Format: Casey G. Langdon, Katherine E. Gadek, Matthew R. Garcia, Myron K. Evans, Kristin B. Reed, Madeline Bush, Jason A. Hanna, Catherine J. Drummond, Matthew C. Maguire, Patrick J. Leavey, David Finkelstein, Hongjian Jin, Patrick A. Schreiner, Jerold E. Rehg, Mark E. Hatley. Synthetic essentiality between PTEN and core dependency factor PAX7 dictates rhabdomyosarcoma identity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1667.

PTEN/PI3K/Akt pathway alters sensitivity of T-cell acute lymphoblastic leukemia to l-asparaginase

Childhood T-cell acute lymphoblastic leukemia (T-ALL) still remains a therapeutic challenge due to relapses which are resistant to further treatment. l-asparaginase (ASNase) is a key therapy component in pediatric T-ALL and lower sensitivity of leukemia cells to this drug negatively influences overall treatment efficacy and outcome. PTEN protein deletion and/or activation of the PI3K/Akt signaling pathway leading to altered cell growth and metabolism are emerging as a common feature in T-ALL. We herein investigated the relationship amongst PTEN deletion, ASNase sensitivity and glucose metabolism in T-ALL cells. First, we found significant differences in the sensitivity to ASNase amongst T-ALL cell lines. While cell lines more sensitive to ASNase were PTEN wild type (WT) and had no detectable level of phosphorylated Akt (P-Akt), cell lines less sensitive to ASNase were PTEN-null with high P-Akt levels. Pharmacological inhibition of Akt in the PTEN-null cells rendered them more sensitive to ASNase and lowered their glycolytic function which then resembled PTEN WT cells. In primary T-ALL cells, although P-Akt level was not dependent exclusively on PTEN expression, their sensitivity to ASNase could also be increased by pharmacological inhibition of Akt. In summary, we highlight a promising therapeutic option for T-ALL patients with aberrant PTEN/PI3K/Akt signaling.

PTEN: Sumoylation Function is the Key to the Maintenance of Genomic Stability of Cell

Phosphatase and tensin homolog deleted on chromosome 10 (PTEN), a tumor suppressor protein with dual phosphatase activity, is found to be frequently mutated in various cancers. PTEN is post-translationally modulated at various amino acid residues which are crucial for sub-cellular localization as well as its catalytic functions rendering genomic stability. Recent reports suggest that PTEN also acts as a DNA repair protein. But how post-translational modulation of PTEN affects cytological damage and aneuploidy is not studied in detail. Here, we focus on the role of sumoylation of PTEN in context with DNA damage induced cytological damage like micronucleus (MNi), nuclear bud (NB), and nuclear bridge formation. Our data suggest that wild type PTEN but not sumo-dead PTEN significantly reduces cytological damage in PTEN mutant PC3 cells. In case of sumo-dead PTEN, the cytological parameters are increased during 24[Formula: see text]h recovery time point after DNA damage. Next, we measured the effectiveness of the sumo-dead (PTEN-K254R) mutant on aneuploidy, where we found that sumoylation is essential for maintaining chromosome number. As chromosome number variation in daughter cell is due to multiple spindle pole formation, we qualitatively and quantitatively evaluate the [Formula: see text] tubulin pole formation in PTEN-K254R clone transfected cells. We found aberrant pole formation is significantly increased in PTEN-K254R transfected cells compared to wild-type PTEN. Further depletion of sumoylation activity of PTEN increases the expression of phosphorylated form of Aurora kinase A (AURKA) (T288) and PLK1 (T210) proteins with or without nocodazole, a microtubule depolymerizing agent compared to cells expressing wild-type PTEN. Thus, sumoylation of PTEN is essential for maintaining genomic stability.

Fumarate inhibits PTEN to promote tumorigenesis and therapeutic resistance of type2 papillary renal cell carcinoma

Fumarate is an oncometabolite. However, the mechanism underlying fumarate-exerted tumorigenesis remains unclear. Here, utilizing human type2 papillary renal cell carcinoma (PRCC2) as a model, we show that fumarate accumulates in cells deficient in fumarate hydratase (FH) and inhibits PTEN to activate PI3K/AKT signaling. Mechanistically, fumarate directly reacts with PTEN at cysteine 211 (C211) to form S-(2-succino)-cysteine. Succinated C211 occludes tethering of PTEN with the cellular membrane, thereby diminishing its inhibitory effect on the PI3K/AKT pathway. Functionally, re-expressing wild-type FH or PTEN C211S phenocopies an AKT inhibitor in suppressing tumor growth and sensitizing PRCC2 to sunitinib. Analysis of clinical specimens indicates that PTEN C211 succination levels are positively correlated with AKT activation in PRCC2. Collectively, these findings elucidate a non-metabolic, oncogenic role of fumarate in PRCC2 via direct post-translational modification of PTEN and further reveal potential stratification strategies for patients with FH loss by combinatorial AKTi and sunitinib therapy.

Significance of a PTEN Mutational Status-Associated Gene Signature in the Progression and Prognosis of Endometrial Carcinoma.

Background PTEN mutations have been reported to be involved in the development and prognosis of endometrial carcinoma (EC). However, a prognostic gene signature associated with PTEN mutational status has not yet been developed. In this study, we generated a PTEN mutation-associated prognostic gene signature for EC. Methods We obtained the single-nucleotide variation and transcriptomic profiling data from The Cancer Genome Atlas database as training data and implemented the least absolute shrinkage and selection operator (LASSO) Cox regression algorithm to establish a PTEN mutation-associated prognostic gene signature. The overall survival rates of the high-risk and low-risk groups were determined with the Kaplan-Meier (K-M) method, and the accuracy of risk score prediction was tested by using the receiver operating characteristic (ROC) curve. Results The K-M curves revealed that the EC patients with PTEN mutations augured favorable survival outcomes. Differential expression analysis between the EC patients with PTEN mutation and wild-type PTEN identified 224 differentially expressed genes (DEGs). Eighty-four DEGs that manifested prognostic value were fitted into the LASSO-Cox analysis, and a PTEN gene signature with seven mutation-associated prognostic genes that showed robust prognostic ability was constructed; this signature was then successfully validated in the other two datasets from the cBioPortal database as well as with 60 clinical specimens. Furthermore, the PTEN mutation-associated prognostic gene signature proved to be an independent prognostic predictor of EC. Remarkably, the EC patients in the high-risk group were characterized by higher tumor stages and grades as well as lower tumor mutation burden with respect to EC, with a poor survival outcome. Collectively, the PTEN mutation-associated prognostic gene signature that we developed could now be used as a favorable prognostic biomarker for EC. Conclusion In summary, we developed and validated a prognostic predictor for EC associated with PTEN mutational status that may be used as a favorable prognostic biomarker and therapeutic target for EC.

Abstract PD3-01: Inducible nitric oxide synthase activates PI3K/Akt signaling via PTEN S-nitrosylation in triple-negative breast cancer

Abstract Our previous findings have shown that increased inducible nitric oxide synthase (iNOS) expression is a poor prognostic indicator and associated with worse overall survival in TNBC patients. Growing evidence has also suggested that hyperactivation of the phosphoinositide-3-kinase (PI3K) survival signaling pathway is one of the most common oncogenic aberrations in TNBC. Nitric oxide (NO) is a unique molecule in its ability to target multiple oncogenic pathways in a spatial and temporal manner, such as PI3K, extracellular signal-regulated kinase (ERK), β-catenin pathway, transforming growth factor beta (TGFβ) signaling, and hypoxia-inducible factor (HIF). This study investigates the role of NO in PI3K-Akt pathway activation in human TNBC cells, in conditions with extracellular NO donor exposure and increased intracellular iNOS (NOS2) expression. TNBC cell lines BT549, HCC1937, Hs578T, SUM159, MDA-MB-231, and BT-20 were exposed to the NO donor DETA NONOate at increasing concentrations (0-500 µM) for 12 hours. Significant elevation in phosphorylation of Akt (Ser473 and Thr308) in response to increase NO donor concentration was found only in cell lines with wild-type PTEN and PIK3R1, such as SUM159, MDA-MB-231, and BT20. To evaluate whether NO-induced activation of Akt was PI3K-dependent, SUM159 (wild-type PTEN) and HCC1937 (PTEN mutant) cells were also pre-treated with PI3K inhibitor alpelisib before NO exposure. PI3K inhibition was only able to eliminate basal phospho-Akt and prevent NO-induced Akt activation in the SUM159 cell line. Furthermore, compared to vehicle control treated cells, we found that NO donor-induced activation enhanced phosphorylation in 15/18 Akt signaling proteins in SUM159 cells (PTEN intact) and 3/18 Akt signaling proteins in HCC1937 cells (PTEN loss). In Hs578T cells in which NOS2 was either overexpressed or knocked down via lentiviral transduction, we found that enhanced expression of NOS2 was associated with increased p-Akt expression and knock-down of NOS2 led to reduced p-Akt. This result suggests that iNOS, as opposed to other NOS isoforms, is more associated with modulating PI3K signaling in TNBC.We also analyzed TNBC data from The Cancer Genome Atlas and found that patients with positive iNOS mRNA expression had significantly higher phospho-Akt (Ser473 and Thr308) [p≤0.0001] expression compared to patients with no iNOS expression. When we stratified this patient cohort based on both iNOS and PTEN expression, we only found significantly higher phospho-Akt (Ser473 and Thr308) [p≤0.01] expression in patients with positive iNOS and PTEN expression, supporting the hypothesis that NO may impair PTEN’s function as a PI3K antagonist. Ongoing studies are directed to investigate mechanisms of iNOS-PTEN physical interactions, iNOS-dependent post-translational modifications to PTEN, and whether iNOS and PTEN are dual prognostic markers in TNBC patients. Citation Format: Tejaswini P. Reddy, Liliana Guzman-Rojas, Roberto R. Rosato, Wei Qian, Hong Zhao, Jenny C. Chang. Inducible nitric oxide synthase activates PI3K/Akt signaling via PTEN S-nitrosylation in triple-negative breast cancer [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr PD3-01.

Hydrazonoyl chlorides possess promising antitumor properties

Aimsthe main purpose of this study was to identify new selective antitumor agents. Main methodsseveral hydrazonoyl chlorides (HCs) were synthesized and human tumor cell line viability was determined using the MTT assay. Tumor development was assessed using Ehrlich ascites carcinoma (EAC)-bearing mice. Key findingsour results showed that 2-oxo-N-phenyl-2-(phenylamino)acetohydrazonoyl chloride (compound 4; CPD 4) and 2-oxo-2-(phenylamino)-N-(p-tolyl)acetohydrazonoyl chloride (CPD 5) were the most cytotoxic HCs to human cervical tumor HeLa (IC50: 20 and 25 μM for CPD 4 and 5 respectively), breast MCF7 (IC50: 29 and 34 μM for CPD 4 and 5 respectively) and colon HCT116 cancer cells (IC50: 26 and 25 μM for CPD 4 and 5 respectively) with the least cytotoxicity to human non-tumor CCD-18Co colon fibroblasts as well as murine splenocytes. The active compounds significantly inhibited colony formation as well as tumor development in EAC-bearing mice. We also observed that PTEN-deficient cells displayed greater sensitivity than cells expressing wild type PTEN. At the molecular level, comet and cell cycle analyses indicated that the active compounds generate DNA damage. In light of the PTEN-dependent sensitivity and genomic instability we examined the influence of HCs on the DNA repair enzyme polynucleotide kinase/phosphatase (PNKP) and the PI3K/AKT/mTOR pathway, which are each known to be synthetic lethal with PTEN. We found that both PNKP and the PI3K/AKT/mTOR pathway to be adversely affected by the HCs, which may partially account for their toxicity. Significancehydrazonoyl chlorides can be considered as hit compounds for the development of new antitumor agents.

Evaluation of Molecular Determinants Related to Outcomes in Recurrent High Grade Glioma Treated With Hypofractionated Stereotactic Radiotherapy (HFSRT) and Immune Checkpoint Blockade

Recurrent high-grade glioma (rHGG) continues to cause increased morbidity and mortality. To date, salvage therapy for rHGG remains ineffective, even with novel immune checkpoint blockade approaches. Here we evaluate molecular factors that may influence outcomes in rHGG patients treated with HFSRT and immunotherapy.This retrospective analysis identified 76 continuous rHGG patients treated with HFSRT and PD-1 inhibitors on or off trial protocol with > 3 months of follow-up from 2010 to 2020. Clinical characteristics, treatment, outcomes, and available molecular alterations in IDH1 (n = 74), PTEN (n = 54), EGFRvIII (n = 64) or amplification (n = 56), CDKN2A (n = 42), TERT (n = 42) and MGMT promoter methylation (n = 69) were collected. Time to recurrence (TTR) and overall survival (OS) were estimated from the end of HFSRT with univariable (UVA) Kaplan-Meier methods compared via log-rank test as well as Cox regression analyses.The median age at HFSRT was 55 years (range: 22-83) with a KPS of 80 (range: 50-100). The majority (63%) of patients were male, 35% had > 2 recurrences of HGG before HFSRT and 55% underwent salvage surgery. A total of 11 patients (15%) received bevacizumab (Bev) prior to HFSRT. The median HFSRT dose was 35 Gy (range: 30-40 Gy) given in 5-10 fractions. Sixty-six (87%) patients were treated with concurrent HFSRT and Bev followed by immunotherapy. At a median follow-up from HFSRT of 13.8 months (range: 8.7-18.9), 55 (72%) patients relapsed with a median TTR of 6.94 months (5.0-8.87) and OS of 10.1 months (7.4-12.9); this included Bev-naïve and -resistant patients. Bev vs no Bev with HFSRT improved TTR (13.7 vs 6.3 months, P < 0.001), though Bev with HFSRT was not associated with improved OS. Of interest, no Bev prior to HFSRT improved OS from HFSRT (12.0 vs 8.4 months, P = 0.01). No molecular factors were associated with TTR after HFSRT, though IDH1-mut (P = 0.001) and wild-type PTEN (P = 0.02) and EGFR (P = 0.02) were related with prolonged OS. Similarly, mutations in TERT were associated with inferior OS (26.7 vs 60.7 months, P < 0.001). MGMT methylation status was not associated with TTR of OS.Salvage treatments for rHGG remain a challenge. This study provides further insight into prognostic molecular determinants in the setting of HFSRT, PD-1 blockade and Bev.E. Guvenli: None. D. Grass: None. D.E. Oliver: None. A.B. Etame: None. N. Tran: None. R.J. Macaulay: None. P. Forsyth: Research Grant; NIH/NCI, CDMRP, Department of Defense, Pfizer, State of Florida - Bankhead Coley, Moffitt Center of Excellence Celgene project, NIH/NCI. Honoraria; BTG, NIH, Ziopharm, Tocagen, NCRI. Consultant; AbbVie, Inc, Ziopharm, Novellus, NCI Neuro-Oncology Branch Peer Review, Physical Sciences Oncology Network, Tocagen. Advisory Boar. S. Sahebjam: Research Grant; Merck, Bristol Myers Squibb, Brooklyn Immunotherapeutics. Advisory Board; Merck, Boehringer Ingelheim. Travel Expenses; Eli Lilly. H.M. Yu: Honoraria; UpToDate. Speaker's Bureau; BrainLab. Advisory Board; Novocure, AbbVie.

Brain and Breast Cancer Cells with PTEN Loss of Function Reveal Enhanced Durotaxis and RHOB Dependent Amoeboid Migration Utilizing 3D Scaffolds and Aligned Microfiber Tracts.

Simple SummaryGlioblastoma multiforme (GBM) and metastatic triple-negative breast cancer (TNBC) with PTEN mutations are associated with brain tumor spreading and poor patient outcomes. GBM, and possibly TNBC, migrate on axons and blood vessels to disseminate in the brain; however, the mechanism is unresolved. There is a need for new therapeutic targets to blunt brain tumor spreading. Using 3D aligned printed microfibers mimicking brain structures proved that RHOB, in addition to ROCK and PTEN signaling, were essential for GBM and TNBC 3D cell migration. GBM and TNBC cell lines with PTEN loss of function and high RHOB expression exhibited amoeboid morphology with increased durotaxis, binding and migration speed on 3D microfibers, in contrast to the PTEN wildtype. Depending on the PTEN genotype, RHO-ROCK-PTEN inhibitors or PTEN rescue significantly regulated these properties. Regarding GBM and brain metastasizing TNBC, we conclude that RHOB inhibitors could play a novel role for improved therapy response and patient outcome.Background: Glioblastoma multiforme (GBM) and metastatic triple-negative breast cancer (TNBC) with PTEN mutations often lead to brain dissemination with poor patient outcome, thus new therapeutic targets are needed. To understand signaling, controlling the dynamics and mechanics of brain tumor cell migration, we implemented GBM and TNBC cell lines and designed 3D aligned microfibers and scaffolds mimicking brain structures. Methods: 3D microfibers and scaffolds were printed using melt electrowriting. GBM and TNBC cell lines with opposing PTEN genotypes were analyzed with RHO-ROCK-PTEN inhibitors and PTEN rescue using live-cell imaging. RNA-sequencing and qPCR of tumor cells in 3D with microfibers were performed, while scanning electron microscopy and confocal microscopy addressed cell morphology. Results: In contrast to the PTEN wildtype, GBM and TNBC cells with PTEN loss of function yielded enhanced durotaxis, topotaxis, adhesion, amoeboid migration on 3D microfibers and significant high RHOB expression. Functional studies concerning RHOB-ROCK-PTEN signaling confirmed the essential role for the above cellular processes. Conclusions: This study demonstrates a significant role of the PTEN genotype and RHOB expression for durotaxis, adhesion and migration dependent on 3D. GBM and TNBC cells with PTEN loss of function have an affinity for stiff brain structures promoting metastasis. 3D microfibers represent an important tool to model brain metastasizing tumor cells, where RHO-inhibitors could play an essential role for improved therapy.

Histological and Somatic Mutational Profiles of Mismatch Repair Deficient Endometrial Tumours of Different Aetiologies.

Simple SummaryEndometrial cancers can arise due to an error in DNA mending known as mismatch repair. This can happen because of an error in the cancer itself (somatic) or due to an inherited error (Lynch syndrome). Treatment trials have considered endometrial cancers caused by either of these errors as identical. As it is easier to recruit people with Lynch syndrome, they may be overrepresented in this group despite being less numerous in clinical practice. This would not be an issue if somatic and Lynch syndrome-related endometrial cancers were similar at a molecular level. The data presented herein, however, indicates that these two routes to mismatch repair, although sharing many similarities, lead to endometrial cancers with distinct molecular and pathological features. This may explain the range of outcomes observed in clinical trials of endometrial cancers with mismatch repair errors.Background: Mismatch repair deficient (MMRd) tumours may arise from somatic events acquired during carcinogenesis or in the context of Lynch syndrome (LS), an inherited cancer predisposition condition caused by germline MMR pathogenic variants. Our aim was to explore whether sporadic and hereditary MMRd endometrial cancers (EC) display distinctive tumour biology. Methods: Clinically annotated LS-EC were collected. Histological slide review was performed centrally by two specialist gynaecological pathologists. Mutational analysis was by a bespoke 75- gene next-generation sequencing panel. Comparisons were made with sporadic MMRd EC. Multiple correspondence analysis was used to explore similarities and differences between the cohorts. Results: After exclusions, 135 LS-EC underwent independent histological review, and 64 underwent mutational analysis. Comparisons were made with 59 sporadic MMRd EC. Most tumours were of endometrioid histological subtype (92% LS-EC and 100% sporadic MMRd EC, respectively, p = NS). Sporadic MMRd tumours had significantly fewer tumour infiltrating lymphocytes (p ≤ 0.0001) and showed more squamous/mucinous differentiation than LS-EC (p = 0.04/p = 0.05). PTEN mutations were found in 88% sporadic MMRd and 61% LS-EC, respectively (p < 0.001). Sporadic MMRd tumours had significantly more mutations in PDGFRA, ALK, IDH1, CARD11, CIC, MED12, CCND1, PTPN11, RB1 and KRAS, while LS-EC showed more mutations affecting SMAD4 and ARAF. LS-EC showed a propensity for TGF-β signalling disruption. Cluster analysis found that wild type PTEN associates predominantly with LS-EC, whilst co-occurring mutations in PTEN, PIK3CA and KRAS predict sporadic MMRd EC. Conclusions: Whilst MMRd EC of hereditary and sporadic aetiology may be difficult to distinguish by histology alone, differences in infiltrating immune cell counts and mutational profile may predict heterogenous responses to novel targeted therapies and warrant further study.

Deconvoluting Mechanisms of Acquired Resistance to RAF Inhibitors in BRAFV600E-Mutant Human Glioma.

Selective RAF-targeted therapy is effective in some patients with BRAFV600E-mutated glioma, though emergent and adaptive resistance occurs through ill-defined mechanisms. Paired pre-/post- RAF inhibitor (RAFi)-treated glioma samples (N = 15) were obtained and queried for treatment-emergent genomic alterations using DNA and RNA sequencing (RNA-seq). Functional validation of putative resistance mechanisms was performed using established and patient-derived BRAFV600E-mutant glioma cell lines. Analysis of 15 tissue sample pairs identified 13 alterations conferring putative resistance were identified among nine paired samples (including mutations involving ERRFI1, BAP1, ANKHD1, and MAP2K1). We performed functional validation of mechanisms of resistance, including loss of NF1, PTEN, or CBL, in BRAFV600E-mutant glioma lines, and demonstrate they are capable of conferring resistance in vitro. Knockdown of CBL resulted in increased EGFR expression and phosphorylation, a possible mechanism for maintaining ERK signaling within the cell. Combination therapy with a MEKi or EGFR inhibitor was able to overcome resistance to BRAFi, in NF1 knockdown and CBL knockdown, respectively. Restoration of wild-type PTEN in B76 cells (PTEN-/-) restored sensitivity to BRAFi. We identified and validated CRAF upregulation as a mechanism of resistance in one resistant sample. RNA-seq analysis identified two emergent expression patterns in resistant samples, consistent with expression patterns of known glioma subtypes. Resistance mechanisms to BRAFi in glioma are varied and may predict effective precision combinations of targeted therapy, highlighting the importance of a personalized approach.

Defining the therapeutic selective dependencies for distinct subtypes of PI3K pathway-altered prostate cancers

Previous studies have suggested that PTEN loss is associated with p110β signaling dependency, leading to the clinical development of p110β-selective inhibitors. Here we use a panel pre-clinical models to reveal that PI3K isoform dependency is not governed by loss of PTEN and is impacted by feedback inhibition and concurrent PIK3CA/PIK3CB alterations. Furthermore, while pan-PI3K inhibition in PTEN-deficient tumors is efficacious, upregulation of Insulin Like Growth Factor 1 Receptor (IGF1R) promotes resistance. Importantly, we show that this resistance can be overcome through targeting AKT and we find that AKT inhibitors are superior to pan-PI3K inhibition in the context of PTEN loss. However, in the presence of wild-type PTEN and PIK3CA-activating mutations, p110α-dependent signaling is dominant and selectively inhibiting p110α is therapeutically superior to AKT inhibition. These discoveries reveal a more nuanced understanding of PI3K isoform dependency and unveil novel strategies to selectively target PI3K signaling nodes in a context-specific manner.

Ipatasertib, an oral AKT inhibitor, exhibits anti-proliferative and anti-tumorigenic effects in pre-clinical studies for endometrioid endometrial cancer: Endometrial Cancer Molecularly Targeted Therapy Consortium

<h3>Objectives:</h3> Ipatasertib (IPAT) is an orally administered selective protein kinase B (AKT) inhibitor that has demonstrated clinical activity in triple-negative breast and metastatic prostate cancer. Given that the AKT/mTOR pathway is altered in the vast majority of endometrioid endometrial cancers (ECs), it is logical that IPAT may also have efficacy in EC. Thus, we aimed to evaluate the anti-proliferative effects of IPAT in human endometrioid cell lines as well as in the <i>LKB1fl/flp53fl/fl</i> genetically engineered mouse model of endometrioid EC. <h3>Methods:</h3> The human endometrioid EC cell lines ECC-1 (PTEN mutant) and HEC-1A (PTEN wild type, PIK3CA mutant, KRAS mutant) were exposed to varying concentrations of IPAT (Genentech). Cell proliferation was assessed by MTT and colony assays. Cell cycle progression was measured by Cellometer. Apoptosis was assessed by cleaved caspase-3 assay. Cellular stress was assessed using tetra-methylrhodamine ester (TMRE) and DCFDA assays. Western immunoblotting determined effects of IPAT on BCL-2, MCL-1, Bip, CDK4, CDK6, cyclin D1, pAKT, pS6, PERK, calnexin, and PDI in both cell <i>lines.LKB1fl/flp53fl/fl</i> mice were used to evaluate the effect of IPAT on endometrial tumor growth. The mice were treated with placebo or IPAT (15mg/kg daily intraperitoneally for 4 weeks) starting 8 weeks after tumor induction via AdCre injection. <h3>Results:</h3> IPAT inhibited cellular proliferation in a dose dependent fashion in both cell lines after 72 hours of treatment. Median IC50 was 0.18µM in ECC-1 and 3.5µM in HEC-1A. IPAT induced the activity of cleaved caspase 3 by 15.6-fold in ECC-1 and 1.41-fold in HEC-1A (p<0.01), while simultaneously reducing expression of the apoptotic proteins MCL-1 and BCL-2. IPAT inhibited cell cycle progression by arrest in G1 phase in both cell lines after 36 hours of treatment and decreased expression of the cell cycle related proteins, CDK4, CDK6, and cyclin D1. DCFDA assay analysis demonstrated that IPAT induced ROS products by 18% and 19% (p<0.01) in the ECC-1 and HEC-1A cell lines, respectively, and increased Bip and PERK protein expression. In addition, IPAT reduced mitochondrial potential by 12% in the HEC-1A cells and 14% in the ECC-1 cells (p<0.01). Treatment of cells with IPAT at 10µM increased phosphorylated-AKT (pAKT) expression and decreased phosphorylated-S6 (p-S6) expression in a time-dependent manner in both cell lines; however, measurable changes in pAKT and pS6 were observed at concentrations as low as 0.1µM. Notably, an increase in phosphorylated-AKT was expected and is indicative of engagement and binding of IPAT with the phospho-AKT complex. Treatment of <i>LKB1fl/flp53fl/fl</i> mice with IPAT was well-tolerated and reduced tumor weight by 52.1% as compared with control mice (p<0.05). <h3>Conclusions:</h3> IPAT significantly inhibited cell proliferation and induced apoptosis and cellular stress via inhibition of the AKT/mTOR pathway in human endometrioid EC cell lines. Furthermore, IPAT reduced tumor growth in a transgenic mouse model of endometrioid EC. These results suggest that IPAT is worthy of further exploration in clinical trials for EC.

Ipatasertib, an oral AKT inhibitor, effectively inhibits cell proliferation and migration, and induces apoptosis in serous endometrial cancer cell lines in vitro: Endometrial Cancer Molecularly Targeted Therapy Consortium

<h3>Objectives:</h3> Ipatasertib (IPAT) is an orally administered selective protein kinase B (AKT) inhibitor that has demonstrated clinical activity in triple-negative breast and metastatic prostate cancer. Given that the AKT/mTOR pathway is altered in the vast majority of endometrioid endometrial cancers (ECs), it is logical that IPAT may also have efficacy in EC. Thus, we aimed to evaluate the anti-proliferative effects of IPAT in human endometrioid cell lines as well as in the <i>LKB1fl/flp53fl/fl</i> genetically engineered mouse model of endometrioid EC. <h3>Methods:</h3> The human endometrioid EC cell lines ECC-1 (PTEN mutant) and HEC-1A (PTEN wild type, PIK3CA mutant, KRAS mutant) were exposed to varying concentrations of IPAT (Genentech). Cell proliferation was assessed by MTT and colony assays. Cell cycle progression was measured by Cellometer. Apoptosis was assessed by cleaved caspase-3 assay. Cellular stress was assessed using tetramethylrhodamine ester (TMRE) and DCFDA assays. Western immunoblotting determined effects of IPAT on BCL-2, MCL-1, Bip, CDK4, CDK6, cyclin D1, pAKT, pS6, PERK, calnexin, and PDI in both cell lines. <i>LKB1fl/flp53fl/fl</i> mice were used to evaluate the effect of IPAT on endometrial tumor growth. The mice were treated with placebo or IPAT (15mg/kg daily intraperitoneally for 4 weeks) starting 8 weeks after tumor induction via AdCre injection. <h3>Results:</h3> IPAT inhibited cellular proliferation in a dose dependent fashion in both cell lines after 72 hours of treatment. Median IC50 was 0.18µM in ECC-1 and 3.5µM in HEC-1A. IPAT induced the activity of cleaved caspase 3 by 15.6-fold in ECC-1 and 1.41-fold in HEC-1A (p<0.01), while simultaneously reducing expression of the apoptotic proteins MCL-1 and BCL-2. IPAT inhibited cell cycle progression by arrest in G1 phase in both cell lines after 36 hours of treatment and decreased expression of the cell cycle related proteins, CDK4, CDK6, and cyclin D1. DCFDA assay analysis demonstrated that IPAT induced ROS products by 18% and 19% (p<0.01) in the ECC-1 and HEC-1A cell lines, respectively, and increased Bip and PERK protein expression. In addition, IPAT reduced mitochondrial potential by 12% in the HEC-1A cells and 14% in the ECC-1 cells (p<0.01). Treatment of cells with IPAT at 10µM increased phosphorylated-AKT (pAKT) expression and decreased phosphorylated-S6 (p-S6) expression in a time-dependent manner in both cell lines; however, measurable changes in pAKT and pS6 were observed at concentrations as low as 0.1µM. Notably, an increase in phosphorylated-AKT was expected and is indicative of engagement and binding of IPAT with the phospho-AKT complex. Treatment of <i>LKB1fl/flp53fl/fl</i> mice with IPAT was well-tolerated and reduced tumor weight by 52.1% as compared with control mice (p<0.05). <h3>Conclusions:</h3> IPAT significantly inhibited cell proliferation and induced apoptosis and cellular stress via inhibition of the AKT/mTOR pathway in human endometrioid EC cell lines. Furthermore, IPAT reduced tumor growth in a transgenic mouse model of endometrioid EC. These results suggest that IPAT is worthy of further exploration in clinical trials for EC.

PTEN Hamartoma Tumor Syndrome: Skin Manifestations and Insights Into Their Molecular Pathogenesis.

Germline PTEN pathogenic variants cause a spectrum of disorders collectively labeled PTEN Hamartoma Tumor Syndrome (PHTS) and featured by hamartomas, developmental anomalies and increased cancer risk. Studies on experimental models provided evidence that PTEN is a “haploinsufficient” tumor-suppressor gene, however, mechanisms involved in the pathogenesis of clinical manifestations in PHTS patients remain elusive. Beyond analyzing clinical and molecular features of a series of 20 Italian PHTS patients, we performed molecular investigations to explore the mechanisms involved in the pathogenesis of PTEN-associated manifestations, with special focus on mucocutaneous manifestations. Typical mucocutaneous features were present in all patients assessed, confirming that these are the most important clue to the diagnosis. The most frequent were papules located in the trunk or extremities (73.7%), oral mucosa papules (68.4%), acral/palmoplantar keratosis and facial papules (both 57.9%), according with literature data. Molecular analyses on one trichilemmoma suggested that the wild-type PTEN allele was retained and expressed, reinforcing the evidence that PTEN does not require a second somatic hit to initiate pathogenic processes. Unexpectedly, one patient also displayed a cutaneous phenotype consistent with atypical mole/melanoma syndrome; no variants were detected in known melanoma genes, but Whole Exome Sequencing showed the rare truncating variant c.495G>A in the CDH13 gene that might have cooperated with PTEN-haploinsufficiency to generate such phenotype. Our findings confirm the reproducibility of known PHTS manifestations in real-world practice, highlighting the role of mucocutaneous manifestations in facilitating prompt diagnosis of the syndrome, and provide some insights into the pathogenic process induced by PTEN alterations, which may contribute to its understanding.

PERK mediates resistance to BRAF inhibition in melanoma with impaired PTEN

Targeting mutant BRAF in patients with melanomas harboring this oncogene has been highly successful as a first-line treatment, but other mutations may affect its efficacy and alter the route of acquired resistance resulting in recurrence and poor prognosis. As an evolving strategy, melanoma treatment needs to be expanded to include targets based on newly discovered emerging molecules and pathways. We here show that PERK plays a critical role in BRAF inhibitor-acquired resistance in melanoma with impaired PTEN. Inhibition of PERK by either shRNA or a pharmacological inhibitor blocked the growth of BRAF inhibitor-resistant melanoma with impaired PTEN in vitro and in vivo, suggesting an effective approach against melanomas with mutant BRAF and PTEN deficiency. Our current findings, along with our previous discovery that the AXL/AKT axis mediates resistance to BRAF inhibition in melanoma with wild-type PTEN, provide new insights toward a strategy for combating BRAF inhibition-acquired resistance in BRAF mutant melanoma with different PTEN statuses.

Abstract 2483: Expression of microRNA and mRNA in U87 glioblastoma cells transfected with PTEN

Abstract Background: U87 glioblastoma cells (ATCC HTB-14) were transfected with a plasmid containing the wild type PTEN gene. Untransfected U87 cells and U87 cells transfected with a plasmid containing only a fluorescent marker served as controls. Methods: Cells were assessed for neurosphere formation and growth in soft agar. Genes were assessed for expression of microRNA and messenger RNA by the NanoString nCounter platform. Results: The PTEN transfectants exhibited reduced neurosphere formation and diminished growth in soft agar. The PTEN transfectants exhibited a 10-fold or greater change in 101 of 799 microRNA species assessed compared to untransfected cells. The change in microRNA expression was strongly influenced by growth in hypoxic conditions. Expression of mRNA was altered in 260 of 760 genes assessed with 8% of the genes showing a 10-fold or greater difference in expression level. A detailed summary of the NanoString results is provided. Conclusions: (1) The PTEN transfectants demonstrate growth characteristics in vitro suggestive of decreased tumorigenicity. (2) The expression level of multiple genes is affected in the PTEN transfectants. (3) Hypoxic conditions bring out the greatest change in the expression level of microRNA in the PTEN transfected cells. Citation Format: David Stefanik, Sidney Goldblatt, Rick Jordan. Expression of microRNA and mRNA in U87 glioblastoma cells transfected with PTEN [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2483.