P53 Tumor Suppressor Research Articles

Discovery of novel octahydroquinazoline scaffolds endowed with dual inhibition of tubulin polymerization/Eg5 against HCC: Apoptotic and radio-chemotherapeutic studies

Mitotic kinesin Eg5 isozyme as a motor protein plays a critical role in cell division of tumor cells. Kinesin Eg5 selective inhibitors and Colchicine binding site suppressors are essential targets for many anticancer drugs and radio chemotherapies. On this work, a new series of octahydroquinazoline as anti-mitotic candidates 2–13 has been synthesized with dual inhibition of tubulin polymerization/Eg5 against HCC cell line. All octahydroquinazolines have been in vitro assayed against HepG-2 cytotoxicity, Eg5 inhibitory and anti-tubulin polymerization activities. The most active analogues 7, 8, 9, 10, and 12 against HepG-2 were further subjected to in vitro cytotoxic assay against HCT-116 and MCF-7 cell lines. Chalcones 9, 10, and 12 displayed the most cytotoxic potency and anti-tubulin aggregation in comparable with reference standard colchicine and potential anti-mitotic Eg5 inhibitory activity in comparison with Monastrol as well. Besides, they exhibited cell cycle arrest at the G2/M phase. Moreover, good convinced apoptotic activities have been concluded as overexpression of caspase-3 levels and tumor suppressive gene p53 in parallel with higher induction of Bax and inhibition of Bcl-2 biomarkers. Octahydroquinazoline 10 displayed an increase in caspase-3 by 1.12 folds compared to standard colchicine and induce apoptosis and demonstrated cell cycle arrest in G2/M phase arrest by targeting p53 pathway. Analogue 10 has considerably promoted cytotoxic radiation activity and boosted apoptotic induction in HepG-2 cells by 1.5 fold higher than standard colchicine.

Transfected SARS-CoV-2 spike DNA for mammalian cell expression inhibits p53 activation of p21(WAF1), TRAIL Death Receptor DR5 and MDM2 proteins in cancer cells and increases cancer cell viability after chemotherapy exposure.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and COVID-19 infection has led to worsened outcomes for patients with cancer. SARS-CoV-2 spike protein mediates host cell infection and cell-cell fusion that causes stabilization of tumor suppressor p53 protein. In-silico analysis previously suggested that SARS-CoV-2 spike interacts with p53 directly but this putative interaction has not been demonstrated in cells. We examined the interaction between SARS-CoV-2 spike, p53 and MDM2 (E3 ligase, which mediates p53 degradation) in cancer cells using an immunoprecipitation assay. We observed that SARS-CoV-2 spike protein interrupts p53-MDM2 protein interaction but did not detect SARS-CoV-2 spike bound with p53 protein in the cancer cells. We further observed that SARS-CoV-2 spike suppresses p53 transcriptional activity in cancer cells including after nutlin exposure of wild-type p53-, spike-expressing tumor cells and inhibits chemotherapy-induced p53 gene activation of p21(WAF1), TRAIL Death Receptor DR5 and MDM2. The suppressive effect of SARS-CoV-2 spike on p53-dependent gene activation provides a potential molecular mechanism by which SARS-CoV-2 infection may impact tumorigenesis, tumor progression and chemotherapy sensitivity. In fact, cisplatin-treated tumor cells expressing spike were found to have increased cell viability as compared to control cells. Further observations on γ-H2AX expression in spike-expressing cells treated with cisplatin may indicate altered DNA damage sensing in the DNA damage response pathway. The preliminary observations reported here warrant further studies to unravel the impact of SARS-CoV-2 and its various encoded proteins including spike on pathways of tumorigenesis and response to cancer therapeutics. More efforts should be directed at studying the effects of the SARS-CoV-2 spike and other viral proteins on host DNA damage sensing, response and repair mechanisms. A goal would be to understand the structural basis for maximal anti-viral immunity while minimizing suppression of host defenses including the p53 DNA damage response and tumor suppression pathway. Such directions are relevant and important including not only in the context of viral infection and mRNA vaccines in general but also for patients with cancer who may be receiving cytotoxic or other cancer treatments.

Abstract SoA2-02: Implications of therapy induced senescence in breast cancer

Abstract The goal of breast cancer treatment is to cause cellular stress sufficient to kill and eliminate the tumor cells. Unfortunately, in many cases cancer cells survive and are not removed by surgery and thus can cause relapse and eventual mortality. Surviving cells have necessarily avoided both intrinsic (e.g., apoptosis) and extrinsic (e.g., immune surveillance) mechanisms of death. Studies over the last 20 years have shown that chemotherapy-treated breast cancer cells can evade cell death by activating programs of cellular senescence mediated by the tumor suppressor p53. While p53 can induce apoptosis in response to stress in some cell types, in breast cancer, p53 preferentially induces cell cycle arrest and senescence in response to chemotherapy. Data show that patients with breast cancers that are wild type for TP53 have a much lower probability of being eradicated by chemotherapy, and have a much shorter survival, compared to patients with TP53 mutant tumors. Human and mouse mammary tumors induce many markers of senescence after chemotherapy treatment, including those associated with cell cycle arrest and the senescence associated secretory phenotype (SASP). These arrested tumors evade death from mitotic catastrophe and can block apoptotic programs via elevated activity of BCL2 family members. More recent studies have addressed how induction of senescence deters immune surveillance. Breast cancer cells exposed to chemotherapy reorganize chromatin structure that amplifies stromal derived signals that stimulate expression of many immune genes, including checkpoint ligands such as PD-L1 and Galectin-9. Further, p53 can directly transactivate other immune modulatory genes such as CD80. Collectively, these properties of senescent cells enable their persistence following treatment and contribute to their potential to drive relapse. These same properties, however, can also be exploited as vulnerabilities to therapeutics such as senolytic drugs that target reliance on BCL2 family members or immunotherapies that target PD-L1 expression. Citation Format: J. Jackson. Implications of therapy induced senescence in breast cancer [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr SoA2-02.

Withaferin A Inhibits Liver Cancer Tumorigenesis by Suppressing Aerobic Glycolysis through the p53/IDH1/HIF-1α Signaling Axis.

The energy supply of certain cancer cells depends on aerobic glycolysis rather than oxidative phosphorylation. Our previous studies have shown that withaferin A (WA), a lactone compound derived from Withania somnifera, suppresses skin carcinogenesis at least partially by stabilizing IDH1 and promoting oxidative phosphorylation. Here, we have extended our studies to evaluate the anti-tumor effect of WA in liver cancer. Differential expression of glycolysis-related genes between liver cancer tissues and normal tissues and prognosis were verified using an online database. Glycolysis-related protein expression was detected using western blot after overexpression and knockdown of IDH1 and mitochondrial membrane potential assay based on JC-1, and mitochondrial complex I activity was also detected. The inhibitory effect of WA on the biological functions of HepG2 cells was detected along with cell viability using MTT assay, scratch assay, clone formation assay, glucose consumption and lactate production assay. Western blot and qRT-PCR were used to detect the expression of proteins and genes related to IDH1, p53 and HIF1α signaling pathways. We first identified that IDH1 expression was downregulated in human liver cancer cells compared to normal liver cells. Next, we found that treatment of HepG2 cells with WA resulted in significantly increased protein levels of IDH1, accompanied by decreased levels of several glycolytic enzymes. Furthermore, we found that WA stabilized IDH1 proteins by inhibiting the degradation by the proteasome. The tumor suppressor p53 was also upregulated by WA treatment, which played a critical role in the upregulation of IDH1 and downregulation of the glycolysis-related genes. Under hypoxic conditions, glycolysis-related genes were induced, which was suppressed by WA treatment, and IDH1 expression was still maintained at higher levels under hypoxia. Taken together, our results indicated that WA suppresses liver cancer tumorigenesis by p53-mediated IDH1 upregulation, which promotes mitochondrial respiration, thereby inhibiting the HIF-1α pathway and blocking aerobic glycolysis.

ARTS and small-molecule ARTS mimetics upregulate p53 levels by promoting the degradation of XIAP

Mutations resulting in decreased activity of p53 tumor suppressor protein promote tumorigenesis. P53 protein levels are tightly regulated through the Ubiquitin Proteasome System (UPS). Several E3 ligases were shown to regulate p53 stability, including MDM2. Here we report that the ubiquitin E3 ligase XIAP (X-linked Inhibitors of Apoptosis) is a direct ligase for p53 and describe a novel approach for modulating the levels of p53 by targeting the XIAP pathway. Using in vivo (live-cell) and in vitro (cell-free reconstituted system) ubiquitylation assays, we show that the XIAP-antagonist ARTS regulates the levels of p53 by promoting the degradation of XIAP. XIAP directly binds and ubiquitylates p53. In apoptotic cells, ARTS inhibits the ubiquitylation of p53 by antagonizing XIAP. XIAP knockout MEFs express higher p53 protein levels compared to wild-type MEFs. Computational screen for small molecules with high affinity to the ARTS-binding site within XIAP identified a small-molecule ARTS-mimetic, B3. This compound stimulates apoptosis in a wide range of cancer cells but not normal PBMC (Peripheral Blood Mononuclear Cells). Like ARTS, the B3 compound binds to XIAP and promotes its degradation via the UPS. B3 binding to XIAP stabilizes p53 by disrupting its interaction with XIAP. These results reveal a novel mechanism by which ARTS and p53 regulate each other through an amplification loop to promote apoptosis. Finally, these data suggest that targeting the ARTS binding pocket in XIAP can be used to increase p53 levels as a new strategy for developing anti-cancer therapeutics.

QiDongNing induces lung cancer cell apoptosis via triggering P53/DRP1-mediated mitochondrial fission.

Non-small-cell lung cancer (NSCLC) is a major cause of worldwide cancer death, posing a challenge for effective treatment. Our previous findings showed that Chinese herbal medicine (CHM) QiDongNing (QDN) could upregulate the expression of p53 and trigger cell apoptosis in NSCLC. Here, our objective was to investigate the mechanisms of QDN-induced apoptosis enhancement. We chose A549 and NCI-H460 cells for validation invitro, and LLC cells were applied to form a subcutaneous transplantation tumour model for validation in more depth. Our findings indicated that QDN inhibited multiple biological behaviours, including cell proliferation, cloning, migration, invasion and induction of apoptosis. We further discovered that QDN increased the pro-apoptotic BAX while inhibiting the anti-apoptotic Bcl2. QDN therapy led to a decline in adenosine triphosphate (ATP) and a rise in reactive oxygen species (ROS). Furthermore, QDN elevated the levels of the tumour suppressor p53 and the mitochondrial division factor DRP1 and FIS1, and decreased the mitochondrial fusion molecules MFN1, MFN2, and OPA1. The results were further verified by rescue experiments, the p53 inhibitor Pifithrin-α and the mitochondrial division inhibitor Mdivi1 partially inhibited QDN-induced apoptosis and mitochondrial dysfunction, whereas overexpression of p53 rather increased the efficacy of the therapy. Additionally, QDN inhibited tumour growth with acceptable safety invivo. In conclusion, QDN induced apoptosis via triggering p53/DRP1-mediated mitochondrial fission in NSCLC cells.

Structural insights into the functional mechanism of the ubiquitin ligase E6AP

E6AP dysfunction is associated with Angelman syndrome and Autism spectrum disorder. Additionally, the host E6AP is hijacked by the high-risk HPV E6 to aberrantly ubiquitinate the tumor suppressor p53, which is linked with development of multiple types of cancer, including most cervical cancers. Here we show that E6AP and the E6AP/E6 complex exist, respectively, as a monomer and a dimer of the E6AP/E6 protomer. The short α1-helix of E6AP transforms into a longer helical structure when in complex with E6. The extended α1-helices of the dimer intersect symmetrically and contribute to the dimerization. The two protomers sway around the crossed region of the two α1-helices to promote the attachment and detachment of substrates to the catalytic C-lobe of E6AP, thus facilitating ubiquitin transfer. These findings, complemented by mutagenesis analysis, suggest that the α1-helix, through conformational transformations, controls the transition between the inactive monomer and the active dimer of E6AP.

Investigation of the MDM2-binding potential of de novo designed peptides using enhanced sampling simulations

The tumor suppressor p53 plays a crucial role in cellular responses to various stresses, regulating key processes such as apoptosis, senescence, and DNA repair. Dysfunctional p53, prevalent in approximately 50 % of human cancers, contributes to tumor development and resistance to treatment. This study employed deep learning-based protein design and structure prediction methods to identify novel high-affinity peptide binders (Pep1 and Pep2) targeting MDM2, with the aim of disrupting its interaction with p53. Extensive all-atom molecular dynamics simulations highlighted the stability of the designed peptide in complex with the target, supported by several structural analyses, including RMSD, RMSF, Rg, SASA, PCA, and free energy landscapes. Using the steered molecular dynamics and umbrella sampling simulations, we elucidate the dissociation dynamics of p53, Pep1, and Pep2 from MDM2. Notable differences in interaction profiles were observed, emphasizing the distinct dissociation patterns of each peptide. In conclusion, the results of our umbrella sampling simulations suggest Pep1 as a higher-affinity MDM2 binder compared to p53 and Pep2, positioning it as a potential inhibitor of the MDM2-p53 interaction. Using state-of-the-art protein design tools and advanced MD simulations, this study provides a comprehensive framework for rational in silico design of peptide binders with therapeutic implications in disrupting MDM2-p53 interactions for anticancer interventions.

Metabolic Roles of HIF1, c-Myc, and p53 in Glioma Cells.

The metabolic reprogramming that promotes tumorigenesis in glioblastoma is induced by dynamic alterations in the hypoxic tumor microenvironment, as well as in transcriptional and signaling networks, which result in changes in global genetic expression. The signaling pathways PI3K/AKT/mTOR and RAS/RAF/MEK/ERK stimulate cell metabolism, either directly or indirectly, by modulating the transcriptional factors p53, HIF1, and c-Myc. The overexpression of HIF1 and c-Myc, master regulators of cellular metabolism, is a key contributor to the synthesis of bioenergetic molecules that mediate glioma cell transformation, proliferation, survival, migration, and invasion by modifying the transcription levels of key gene groups involved in metabolism. Meanwhile, the tumor-suppressing protein p53, which negatively regulates HIF1 and c-Myc, is often lost in glioblastoma. Alterations in this triad of transcriptional factors induce a metabolic shift in glioma cells that allows them to adapt and survive changes such as mutations, hypoxia, acidosis, the presence of reactive oxygen species, and nutrient deprivation, by modulating the activity and expression of signaling molecules, enzymes, metabolites, transporters, and regulators involved in glycolysis and glutamine metabolism, the pentose phosphate cycle, the tricarboxylic acid cycle, and oxidative phosphorylation, as well as the synthesis and degradation of fatty acids and nucleic acids. This review summarizes our current knowledge on the role of HIF1, c-Myc, and p53 in the genic regulatory network for metabolism in glioma cells, as well as potential therapeutic inhibitors of these factors.

Cymensifin A: a promising pharmaceutical candidate to defeat lung cancer via cellular reactive oxygen species-mediated apoptosis.

Background: The upgrade of natural products for cancer treatment is essential since current anticancer drugs still pose severe side effects. Cymensifin A (Cym A) isolated from an orchid Cymbidium ensifolium has shown its potential to induce the death of several cancer cells; however, its underlying molecular mechanisms are hitherto unknown. Methods: Here, we conducted a set of in vitro preliminary tests to assess the cytotoxic effects of Cym A on non-small-cell lung cancer (NSCLC) cells (A549, H23, H292, and H460). A flow cytometry system and Western blot analyses were employed to unveil molecular mechanisms underlying cancer cell apoptosis caused by Cym A. Results: Cym A at 25-50μM caused the death of all NSCLC cells tested, and its cytotoxicity was comparable to cisplatin, a currently used anticancer drug. The compound induced apoptosis of all NSCLC cells in a dose-dependent manner (5-50μM), proven by flow cytometry, but H460 cells showed more resistance compared to other cells tested. Cym A-treated H460 cells demonstrated increased reactive oxygen species (ROS) and downregulated antioxidants (catalase, superoxide dismutase, and thioredoxin). The compound also upregulated the tumor suppressor P53 and the pro-apoptotic protein BAX but downregulated pro-survival proteins (BCL-2 and MCL-1) and deactivated survival signals (AKT and ERK) in H460 cells. Cym A was proven to trigger cellular ROS formation, but P53 and BAX were 2-fold more activated by Cym A compared to those treated with hydrogen peroxide. Our findings also supported that Cym A exerted its roles in the downregulation of nuclear factor erythroid 2-related factor 2 (a regulator of cellular antioxidant activity) and the increased levels of cleaved poly (ADP-ribose) polymerase (PARP) and cleaved caspase 3/7 during apoptosis. Conclusion: We propose that Cym A induces lung cancer cell death via ROS-mediated apoptosis, while the modulation of cellular ROS/antioxidant activity, the upregulation of P53 and BAX, the downregulation or deactivation of BCL-2, MCL-1, AKT, and ERK, and the increased cleavage of PARP and caspase 3/7, were the elucidated underlying molecular mechanisms of this phytochemical. The compound can be a promising candidate for future anticancer drug development.

Genome-wide CRISPR screens identify novel regulators of wild-type and mutant p53 stability

Tumor suppressor p53 (TP53) is frequently mutated in cancer, often resulting not only in loss of its tumor-suppressive function but also acquisition of dominant-negative and even oncogenic gain-of-function traits. While wild-type p53 levels are tightly regulated, mutants are typically stabilized in tumors, which is crucial for their oncogenic properties. Here, we systematically profiled the factors that regulate protein stability of wild-type and mutant p53 using marker-based genome-wide CRISPR screens. Most regulators of wild-type p53 also regulate p53 mutants, except for p53 R337H regulators, which are largely private to this mutant. Mechanistically, FBXO42 emerged as a positive regulator for a subset of p53 mutants, working with CCDC6 to control USP28-mediated mutant p53 stabilization. Additionally, C16orf72/HAPSTR1 negatively regulates both wild-type p53 and all tested mutants. C16orf72/HAPSTR1 is commonly amplified in breast cancer, and its overexpression reduces p53 levels in mouse mammary epithelium leading to accelerated breast cancer. This study offers a network perspective on p53 stability regulation, potentially guiding strategies to reinforce wild-type p53 or target mutant p53 in cancer.

Abstract CT066: Phase 1 study of MDM2 antagonist ASTX295 in patients with solid tumors with wild-type TP53

Abstract Background: ASTX295 is a novel small molecule antagonist of human Murine Double Minute 2 (MDM2), which tightly regulates the level and activity of the p53 tumor suppressor. To minimize potential thrombocytopenia previously seen with antagonism of this target, ASTX295 was designed to have a short half-life (t1/2) with decreased bone marrow (BM) exposure. ASTX295 has proapoptotic and tumor growth inhibitory activity in preclinical cancer (CA) models. We report here the safety and preliminary efficacy of the phase 1 and dose expansion portions of Study ASTX295-01. Methods: ASTX295-01 is a first-in-human, open-label, multicenter, phase 1/2 study to assess safety, pharmacokinetics (PK), pharmacodynamics (PD), and preliminary clinical activity of ASTX295 (NCT03975387). Eligible patients (advanced solid tumors with Wild-Type [WT] TP53, ECOG PS 0-2, adequate organ and bone marrow function, etc.) had oral administration of ASTX295 starting at a daily dose of 15 mg. Dose escalation was by standard 3 + 3 with cohorts testing multiple regimens. Safety was assessed by CTCAE and disease was assessed by RECIST 1.1. Safety and efficacy and dosing recommendations were overseen by the Data Safety Review Committee. Results:83 subjects were enrolled in over 14 cohorts, evaluating daily (QD) and intermittent dosing regimens and the effect of food. The mean age of subjects on study was 60.1 year, 56.9 were male, with 2.94 (0-15) prior chemotherapy regimens. For PK exposure, the total weekly AUC for 400 mg QD and 660 twice a week (BIW) are similar. The median tmax is 3 hours and mean t1/2 is 4-6 hours. PD demonstrates p53 pathway modulation. Nausea, vomiting, diarrhea, and fatigue were dose limiting. RP2D regimens were 660 mg BIW and 400 mg QD and these regimens were expanded with a total of 25 additional subjects. The most common treatment related AEs for both regimens were nausea, diarrhea, and vomiting at 76.2%,76.2%, and 33.3% respectively, for daily and 71.4%, 47.6%, and 33.3%, for intermittent. Grade 3 GI AEs were reported in 14.3% of subjects in the daily cohort vs 9.5% in the intermittent; none had Grade ≥ 4. One subject had grade 2 thrombocytopenia. Based on decreased incidence and duration of GI AEs, 660 mg BIW was selected as the RP2D.Multiple objective responses were seen, including 1 subject with non-small cell lung CA and 3 subjects with liposarcoma (LPS), a tumor with frequent MDM2 amplification. For LPS the ORR is 7.9% (de-differentiated 7.7%, well differentiated 8.0%), with a PFS of 7.95 and 9.66 months respectively, along with a 16-week disease control rate of 69.2% and 72.0%. Five subjects with GBM were enrolled, 4 with MDM2 amplification, 3 of whom showed evidence of tumor regression, with one subject remaining on study for > 34 cycles. Conclusion:ASTX295 was well tolerated at doses producing p53 pathway modulation with manageable toxicities, notably avoiding significant thrombocytopenia. Preliminary single agent efficacy was observed in heavily pretreated subjects across multiple solid tumor types with WT TP53. Citation Format: Ecaterina E. Dumbrava, Fabio M. Iwamoto, Mark Agulnik, Mohammed Milhem, Anthony W. Tolcher, Rashmi Chugh, Michael J. Demeure, Alain Mita, Kurt Demel, Mark Diamond, Beloo Mirakhur, Laksmi Wilson, Aram Oganesian, Danna Chan, Harold N. Keer, Jason Taylor, Martin J. Sims, Andrea Biondo, Simone Jueliger, Alexander Spira. Phase 1 study of MDM2 antagonist ASTX295 in patients with solid tumors with wild-type TP53 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr CT066.

Abstract LB303: Suppression of stress granule formation is a novel vulnerability imposed by mutant p53

Abstract Mutation of the tumor suppressor p53 is the most common cancer specific event. Most of these mutations are missense mutations in the DNA-binding domain of p53, causing loss of wild-type p53 (wtp53) transcriptional activity. Missense mutant p53 (mutp53) also enhances cancer malignancy in a manner independent of wtp53. Hence, mutp53 is an ideal therapeutic target due to its uniqueness and high expression levels in cancers; however, directly targeting mutp53 protein itself has been challenging. To better understand the mechanism of oncogenic function of mutp53, we performed in silico TCGA database analysis and found that patients with missense mutp53-carrying hepatocellular carcinoma (HCC), but not other types of cancer, had unexpectedly better overall survival than patients with p53-null HCC. Since sorafenib (SOR) has historically been used as a single agent chemotherapy for HCC, unlike other cancer types, we hypothesized that SOR treatment may have yet unappreciated advantages for treating mutp53-expressing tumors. Indeed, knockdown of mutp53 rendered HCC cells and xenografts more resistant to SOR. Consistent with a report showing that SOR induces ER stress-mediated pro-survival stress granule (SG) formation, mutp53-expressing HCC cells, treated with SOR or other ER stress inducers, formed significantly fewer SGs with increased apoptosis, as compared with mutp53-knockdown cells. This result was partly due to mutp53’s ability to interact with an eIF2α kinase PERK and a key SG core protein, G3BP1. Moreover, the oligomerization domain of mutp53 was required for the interaction of mutp53 with G3BP1 and subsequent suppression of ER-stress-mediated SG formation and survival. These results suggest that inhibition of SG formation is a novel vulnerability imposed by mutp53, leading to sensitization of cancer cells to ER stress. Our results also emphasize the use of ER stress inducers to treat mutp53-expressing tumors and mutp53 as a biomarker of SOR sensitivity. Citation Format: Elizabeth Thoenen, Atul Ranjan, Alejandro Parrales, Shigeto Nishikawa, Dan Dixon, Sugako Oka, Tomoo Iwakuma. Suppression of stress granule formation is a novel vulnerability imposed by mutant p53 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr LB303.

The protein phosphatase-2A subunit PR130 is involved in the formation of cytotoxic protein aggregates in pancreatic ductal adenocarcinoma cells

As a major source of cellular serine and threonine phosphatase activity, protein phosphatase-2A (PP2A) modulates signaling pathways in health and disease. PP2A complexes consist of catalytic, scaffolding, and B-type subunits. Seventeen PP2A B-type subunits direct PP2A complexes to selected substrates. It is ill-defined how PP2A B-type subunits determine the growth and drug responsiveness of tumor cells. Pancreatic ductal adenocarcinoma (PDAC) is a disease with poor prognosis. We analyzed the responses of murine and human mesenchymal and epithelial PDAC cells to the specific PP2A inhibitor phendione. We assessed protein levels by immunoblot and proteomics and cell fate by flow cytometry, confocal microscopy, and genetic manipulation. We show that murine mesenchymal PDAC cells express significantly higher levels of the PP2A B-type subunit PR130 than epithelial PDAC cells. This overexpression of PR130 is associated with a dependency of such metastasis-prone cells on the catalytic activity of PP2A. Phendione induces apoptosis and an accumulation of cytotoxic protein aggregates in murine mesenchymal and human PDAC cells. These processes occur independently of the frequently mutated tumor suppressor p53. Proteomic analyses reveal that phendione upregulates the chaperone HSP70 in mesenchymal PDAC cells. Inhibition of HSP70 promotes phendione-induced apoptosis and phendione promotes a proteasomal degradation of PR130. Genetic elimination of PR130 sensitizes murine and human PDAC cells to phendione-induced apoptosis and protein aggregate formation. These data suggest that the PP2A-PR130 complex dephosphorylates and thereby prevents the aggregation of proteins in tumor cells.Graphical

P16, p53 and EGFR expression in head and neck squamous cell carcinoma and their correlation with clinicopathological parameters.

Oral squamous cell carcinoma is a major cause of death throughout the developed world. Human papillomavirus (HPV) type 16 has also been suggested to play a role in etiology of head and neck squamous cell carcinoma (HNSCC). p16 expression is now being used as a surrogate marker of HPV infection in squamous cell carcinoma. Dysfunction in the p53 tumor suppressor gene is implicated in many cancers, including head and neck cancer. Overexpression or mutation of EGFR is found in 80%-100% of the patients with HNSCC, and is associated with poor prognosis and decreased survival. In this cross-sectional observation study, total of 100 cases of HNSCC were taken. p16, p53, and EGFR expression was determined by immunohistochemical staining and correlated with clinicopathological parameters. p16 expression was also correlated with expression of p53 and EGFR. The obtained results were analyzed and evaluated using Chi-square test, value of P < 0.05 was taken significant. p16, p53, and EGFR were positive in 60%, 44%, and 58% cases, respectively. A statistically significant association was observed between p16 with age, site of the tumor, abnormal sexual habits and lymph node involvement. Significant expression also seen between p53 with age and abnormal sexual habits and immunohistochemical expression of p16 with p53 and EGFR. Immunohistochemical expression of p16 can be used as a surrogate marker of HPV. Study of p16, p53, and EGFR expression may provide clinicians with more exact information in order to evaluate tumor aggressiveness and treatment modalities.

P53 rapidly restructures 3D chromatin organization to trigger a transcriptional response

Activation of the p53 tumor suppressor triggers a transcriptional program to control cellular response to stress. However, the molecular mechanisms by which p53 controls gene transcription are not completely understood. Here, we uncover the critical role of spatio-temporal genome architecture in this process. We demonstrate that p53 drives direct and indirect changes in genome compartments, topologically associating domains, and DNA loops prior to one hour of its activation, which escort the p53 transcriptional program. Focusing on p53-bound enhancers, we report 340 genes directly regulated by p53 over a median distance of 116 kb, with 74% of these genes not previously identified. Finally, we showcase that p53 controls transcription of distal genes through newly formed and pre-existing enhancer-promoter loops in a cohesin dependent manner. Collectively, our findings demonstrate a previously unappreciated architectural role of p53 as regulator at distinct topological layers and provide a reliable set of new p53 direct target genes that may help designs of cancer therapies.

Pharmacological p38 MAPK inhibitor SB203580 enhances AML stem cell line KG1a chemosensitivity to daunorubicin by promoting late apoptosis, cell growth arrest in S-phase, and miR-328-3p upregulation

Acute myeloid leukaemia (AML) is characterized by uncontrolled proliferation of myeloid progenitor cells and impaired maturation, leading to immature cell accumulation in the bone marrow and bloodstream, resulting in hematopoietic dysfunction. Chemoresistance, hyperactivity of survival pathways, and miRNA alteration are major factors contributing to treatment failure and poor outcomes in AML patients. This study aimed to investigate the impact of the pharmacological p38 mitogen-activated protein kinase (MAPK) inhibitor SB203580 on the chemoresistance potential of AML stem cell line KG1a to the therapeutic drug daunorubicin (DNR). KG1a and chemosensitive leukemic HL60 cells were treated with increasing concentrations of DNR. Cell Titer-Glo®, flow cytometry, phosphokinase and protein arrays, Western blot technology, and reverse transcription-quantitative polymerase chain reaction (RT-qPCR) were employed for assessment of cell viability, half-maximal inhibitory concentration (IC50) determination, apoptotic status detection, cell cycle analysis, apoptosis-related protein and gene expression monitoring. Confocal microscopy was used to visualize caspase and mitochondrial permeability transition pore (mPTP) activities. Exposed at various incubation times, higher DNR IC50 values were determined for KG1a cells than for HL60 cells, confirming KG1a cell chemoresistance potential. Exposed to DNR, late apoptosis induction in KG1a cells was enhanced after SB203580 pretreatment, defined as the combination treatment. This enhancement was confirmed by increased cleavage of poly(ADP-ribose) polymerase, caspase-9, caspase-3, and augmented caspase-3/-7 and mPTP activities in KG1a cells upon combination treatment, compared to DNR. Using phosphokinase and apoptosis protein arrays, the combination treatment decreased survival Akt phosphorylation and anti-apoptotic Bcl-2 expression levels in KG1a cells while increasing the expression levels of the tumor suppressor p53 and cyclin-dependent kinase inhibitor p21, compared to DNR. Cell cycle analysis revealed KG1a cell growth arrest in G2/M-phase caused by DNR, while combined treatment led to cell growth arrest in S-phase, mainly associated with cyclin B1 expression levels. Remarkably, the enhanced KG1a cell sensitivity to DNR after SB203580 pretreatment was associated with an increased upregulation of miR-328-3p and slight downregulation of miR-26b-5p, compared to DNR effect. Altogether, these findings could contribute to the development of a new therapeutic strategy by targeting the p38 MAPK pathway to improve treatment outcomes in patients with refractory or relapsed AML.

Deciphering the Multi-state Conformational Equilibrium of HDM2 in the Regulation of p53 Binding: Perspectives from Molecular Dynamics Simulation and NMR Analysis.

HDM2 negatively regulates the activity of the tumor suppressor p53. Previous NMR studies have shown that apo-HDM2 interconverts between an "open" state in which the N-terminal "lid" is disordered and a "closed" state in which the lid covers the p53-binding site in the core region. Molecular dynamics (MD) simulation studies have been performed to elucidate the conformational dynamics of HDM2, but the direct relevance of the experimental and computational analyses is unclear. In addition, how the phosphorylation of S17 in the lid contributes to the inhibition of p53 binding remains controversial. Here, we used both NMR and MD simulations to investigate the conformational dynamics of apo-HDM2. The NMR analysis revealed that apo-HDM2 exists in a fast-exchanging equilibrium within two closed states, closed 1 and closed 2, in addition to a previously demonstrated slow-exchanging "open-closed" equilibrium. MD simulations visualized two characteristic closed states, where the spatial orientation of the key residues corresponds well to the chemical shift changes of the NMR spectra. Furthermore, the phosphorylation of S17 induced an equilibrium shift toward closed 1, thereby suppressing the binding of p53 to HDM2. This study reveals a multi-state equilibrium of apo-HDM2 and provides new insights into the regulation mechanism of HDM2-p53 interactions.

Abstract 397: Exploring the role of MDM2-TP53 pathway and ATM in regulation of ferroptosis in dedifferentiated liposarcoma

Abstract Background: Ferroptosis, a process involved in accumulation of lipid-based reactive oxygen species (ROS), is a form of cell death with unique morphologic features and regulatory mechanism. Tumor suppressor p53 (TP53) is a key factor in regulation of ferroptosis through multiple pathways. Mouse double minute 2 homolog (MDM2), a key oncogene of dedifferentiated LPS (DDLPS), is one of the negative regulators of the TP53. In our previous study, we had showed that nutlin-3, a MDM2 inhibitor, could exert synergistic cytotoxicity with ferroptosis-inducing agent (erastin and RSL3) on DDLPS in a sequential manner, possibly through upregulation of SLC3A2 with altered cystine/glutamate exchange (AACR Annual Meeting 2023 abstract#4777). Mutated in Ataxia-Telangiectasia gene (ATM) is a critical gene in DNA damage response. ATM could regulate ferroptosis either directly through altered iron pool, or indirectly through activating TP53 by phosphorylation of MDM2. In this study, we explored the role of ATM and MDM2-TP53 pathway, as well as interaction between them, in regulation of ferroptosis of DDLPS. We also studied the potential role of combination of DNA damaging agent (DDA), such as cisplatin, with ferroptosis-inducing agents in the treatment of DDLPS. Methods: We explored the possible synergistically cytotoxic effect of cisplatin and ferroptosis-inducing agents in DDLPS cell lines. We also investigated the role of ATM in this synergistic effect by using siRNA or ATM inhibitor. In addition, we used cystine uptake assay (measurement of altered cystine/glutamate exchange) and iron level assay (measurement of labile iron pool) to study the functional change responsible to ferroptosis-inducing effect of cisplatin. Finally, we used immunoblotting study to reveal the potential molecular mechanism responsible for synergistic effect of cisplatin and ferroptosis-inducing agent. Results: Cisplatin and erastin showed synergistic cytotoxicity in DDLPS cell line, most likely through ferroptosis-inducing effect. Cisplatin could activate ATM, with resultant dissociation of TP53 and MDM2. Cisplatin could exert ferroptosis-inducing effect through down-regulation SLC7A11A with resultant decrease cystine uptake, as well as increase labile iron pool. ATM inhibition could offset the ferroptosis-inducing effect of cisplatin by reversing both effects. Conclusion: Modulation of ferroptosis is a potential treatment strategy in DDLPS. MDM2-TP53 pathway and ATM as well as interaction of both may play an important role in regulation of ferroptosis in DDLPS. Combination of DDA, such as cisplatin, and ferroptosis-inducing agents is a potential strategy in DDLPS treatment. Citation Format: Chueh-Chuan Yen, San-Chi Chen, Chih-Hsueh Chen, Jir-You Wang, Chao-Ming Chen, Po-Kuei Wu, Muh-Hwa Yang, Wei-Ming Chen. Exploring the role of MDM2-TP53 pathway and ATM in regulation of ferroptosis in dedifferentiated liposarcoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 397.

Abstract 3097: CETSA HT: Employing rapid high-throughput target engagement technology in primary screening of P53

Abstract The confirmation of target engagement for candidate drugs is a fundamental requisite in drug discovery. A significant portion of projects fail to reach the clinic due to lack of efficacy or failure to show lead candidates interacting with the intended target in a more complex environment. The utility of using the CETSA® (CEllular Thermal Shift Assay) technology to measure target engagement in intact cells is increasingly exploited in high throughput screening, where examples demonstrate low false positive rates in screens of up to 500K compounds. The p53 tumor suppressor protein, a crucial guardian against cancer, functions as a transcription factor that mediates cancer suppression by regulating genes involved in a wide range of cellular processes such as DNA repair, cell cycle and apoptosis. Unfortunately, frequent mutations in the TP53 gene hinder p53's tumor suppressor role in human cancers, thus designating it as a promising target for anticancer therapy. However, attempts to restore p53 function for therapeutic purposes have not yet advanced to clinical approval, highlighting the complexities in leveraging p53 for cancer treatment. Its undruggable nature, attributed to the absence of accessible deep pockets, lack of enzymatic activity, and its intracellular location, further complicates targeted interventions with both low and high molecular weight drugs. Here, we demonstrate the analysis of a high-throughput plate based CETSA® HT screen on the challenging target p53, performed using AlphaLISA® SureFire® Ultra™ technology and our newly developed high-throughput screening platform. Hits identified from this screen are privileged from the onset by binding to the target in a physiologically relevant cellular matrix and in a binding-mode agnostic way. This is in contrast to traditional screening methods targeting activity or in vitro interaction where cellular activity is addressed in later stages. This assay cascade highlights a rapid target-to-hit lead generation strategy placing the emphasis on finding chemical matter that interacts with endogenous target in living cells first, followed by analysis of hit material activity. The ‘shortcut’ to chemical matter active in living cells represents significant potential cost savings in comparison to assay development time on recombinantly produced proteins and/or modified cell lines for traditional HTS screening approaches that still rely on target engagement assessment downstream. Citation Format: Merve Kacal, Tomas Friman, Laurence Arnold, Victoria Brehmer, Daniel Martinez Molina, Stina Lundgren. CETSA HT: Employing rapid high-throughput target engagement technology in primary screening of P53 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 3097.