Mutant p53 establishes targetable tumor dependency by promoting unscheduled replication

Gain-of-function (GOF) p53 mutations are observed frequently in most intractable human cancers and establish dependency for tumor maintenance and progression. While some of the genes induced by GOF p53 have been implicated in more rapid cell proliferation compared with p53-null cancer cells, the mechanism for dependency of tumor growth on mutant p53 is unknown. This report reveals a therapeutically targetable mechanism for GOF p53 dependency. We have shown that GOF p53 increases DNA replication origin firing, stabilizes replication forks, and promotes micronuclei formation, thus facilitating the proliferation of cells with genomic abnormalities. In contrast, absence or depletion of GOF p53 leads to decreased origin firing and a higher frequency of fork collapse in isogenic cells, explaining their poorer proliferation rate. Following genome-wide analyses utilizing ChIP-Seq and RNA-Seq, GOF p53–induced origin firing, micronuclei formation, and fork protection were traced to the ability of GOF p53 to transactivate cyclin A and CHK1. Highlighting the therapeutic potential of CHK1’s role in GOF p53 dependency, experiments in cell culture and mouse xenografts demonstrated that inhibition of CHK1 selectively blocked proliferation of cells and tumors expressing GOF p53. Our data suggest the possibility that checkpoint inhibitors could efficiently and selectively target cancers expressing GOF p53 alleles

Zn(II)-curc targets p53 in thyroid cancer cells

P53 mutation is a common event in many cancers, including thyroid carcinoma. Defective p53 activity promotes cancer resistance to therapies and a more malignant phenotype, acquiring oncogenic functions. Rescuing the function of mutant p53 (mutp53) protein is an attractive anticancer therapeutic strategy. Zn(II)-curc is a novel small molecule that has been shown to target mutp53 protein in several cancer cells, but its effect in thyroid cancer cells remains unclear. Here, we investigated whether Zn(II)-curc could affect p53 in thyroid cancer cells with both p53 mutation (R273H) and wild-type p53. Zn(II)-curc induced mutp53H273 downregulation and reactivation of wild-type functions, such as binding to canonical target promoters and target gene transactivation. This latter effect was similar to that induced by PRIMA-1. In addition, Zn(II)-curc triggered p53 target gene expression in wild-type p53-carrying cells. In combination treatments, Zn(II)-curc enhanced the antitumor activity of chemotherapeutic drugs, in both mutant and wild-type-carrying cancer cells. Taken together, our data indicate that Zn(II)-curc promotes the reactivation of p53 in thyroid cancer cells, providing in vitro evidence for a potential therapeutic approach in thyroid cancers

p53-R273H Sustains ROS, Pro-Inflammatory Cytokine Release and mTOR Activation While Reducing Autophagy, Mitophagy and UCP2 Expression, Effects Prevented by wtp53

p53 is the most frequently mutated or inactivated gene in cancer, as its activity is not reconcilable with tumor onset and progression. Moreover, mutations in the p53 gene give rise to mutant proteins such as p53‐R273H that, besides losing the wild type p53 (wtp53) capacity to safeguard genome integrity, may promote carcinogenesis, mainly due to its crosstalk with pro-oncogenic pathways. Interestingly, the activation of oncogenic pathways is interconnected with reactive oxygen species (ROS) and the release of pro‐inflammatory cytokines that contribute to create an inflammatory/pro‐tumorigenic milieu. In this study, based on experiments involving p53‐ R273H silencing and transfection, we showed that this mutant p53 (mutp53) promoted cancer cell survival by increasing intracellular ROS level and pro‐inflammatory/immune suppressive cytokine release, activating mTOR, reducing autophagy and mitophagy and downregulating uncoupling protein 2 (UCP2). Interestingly, p53‐R273H transfection into cancer cells carrying wtp53 induced none of these effects and resulted in p21 upregulation. This suggests that wtp53 may counteract several pro‐tumorigenic activities of p53‐R273H and this could explain the lower aggressiveness of cancers carrying heterozygous mutp53 in comparison to those harboring homozygous mutp53

MicroRNA Profiling Implies New Markers of Gemcitabine Chemoresistance in Mutant p53 Pancreatic Ductal Adenocarcinoma

Background: No reliable predictors of susceptibility to gemcitabine chemotherapy exist in pancreatic ductal adenocarcinoma (PDAC). MicroRNAs (miR) are epigenetic gene regulators with tumorsuppressive or oncogenic roles in various carcinomas. This study assesses chemoresistant PDAC for its specific miR expression pattern. Methods: Gemcitabine-resistant variants of two mutant p53 human PDAC cell lines were established. Survival rates were analyzed by cytotoxicity and apoptosis assays. Expression of 1733 human miRs was investigated by microarray and validated by qRT-PCR. After in-silico analysis of specific target genes and proteins of dysregulated miRs, expression of MRP-1, Bcl-2, mutant p53, and CDK1 was quantified by Western blot. Results: Both established PDAC clones showed a significant resistance to gemcitabine (p<0.02) with low apoptosis rate (p<0.001) vs. parental cells. MiR-screening revealed significantly upregulated (miR-21, miR-99a, miR-100, miR-125b, miR-138, miR-210) and downregulated miRs (miR-31*, miR-330, miR-378) in chemoresistant PDAC (p<0.05). Bioinformatic analysis suggested involvement of these miRs in pathways controlling cell death and cycle. MRP-1 (p<0.02) and Bcl-2 (p<0.003) were significantly overexpressed in both resistant cell clones and mutant p53 (p = 0.023) in one clone. Conclusion: Consistent miR expression profiles, in part regulated by mutant TP53 gene, were identified in gemcitabine-resistant PDAC with significant MRP-1 and Bcl-2 overexpression. These results provide a basis for further elucidation of chemoresistance mechanisms and therapeutic approaches to overcome chemoresistance in PDAC

In vitro tissue microarrays for quick and efficient spheroid characterisation

Three-dimensional in vitro microphysiological cultures, such as spheroids and organoids, promise increased patient relevance and therapeutic predictivity compared to reductionist cell monolayers. However, high-throughput characterisation techniques for 3D models are currently limited to simplistic live/dead assays. By sectioning and staining in vitro microtissues researchers can examine their structure, detect DNA, RNA and protein targets and visualise them at the level of single cells. The morphological examination and immunochemistry staining for in vitro cultures has historically been done in a laborious manner involving testing one set of cultures at a time. We have developed a technology to rapidly screen spheroid phenotype and protein expression by arranging 66 spheroids in a gel array for paraffin-embedding, sectioning and immunohistochemsitry. The process is quick, mostly automatable and uses 11 times less reagents compared to conventional techniques. Here we showcase the capabilities of the technique in an array made up of 11 different cell lines stained in conventional H&E staining, as well as immunohistochemistry staining for estrogen (ER), progesterone (PR) human epidermal growth factor receptors (Her-2) and TP53. This new methodology can be used in optimising stem cell-based models of disease and development, for tissue engineering, safety screening and for efficacy screens in cancer research

Investigation of Gain-of-Function Induced by Mutant p53

p53 is mutated in 50% of all human cancers, and up to 70% of lung cancer. Mutant p53 is usually expressed at elevated levels in cancer cells and has been correlated with a poor prognosis. Cancer cells that express mutant p53 show an increase in oncogenic phenotypes including an increase in growth rate, resistance to chemotherapeutic drugs, and an increase in motility and tumorigenicity to name a few. We have identified several genes involved in cell growth and survival that are upregulated by expression of common p53 mutants: NFκB2, Axl, and epidermal growth factor receptor (EGFR). The aim of this study was to determine the role NFκB2, Axl, and EGFR play in mutant p53’s gain of function (GOF) phenotype and to determine a mechanism for upregulation of mutant p53 target gene upregulation. Inhibition of mutant p53 in various cancer cell lines using RNAi in the form of transient siRNA transfection or stable shRNA cell line generation caused a decrease in the gain of function ability of those cells in the form of reduced chemoresistance, reduced cell growth and motility, and a reduction in tumor formation. Additionally, inhibition of NFκB2, Axl, and EGFR also showed similar effects. Promoter deletion analysis of the NFκB2 promoter did not show a specific mutant p53 response element needed for mutant p53 mediated transactivation. Similarly, deletion of the p53/p63 binding site on the Axl promoter did not inhibit mutant p53 transactivation. Sequence analysis of the NFκB2, Axl, and EGFR promoters revealed several transcription factor binding sites located throughout the promoters. ChIP analysis of mutant p53 and the promoter-specific transcription factor binding revealed that in the presence of mutant p53, individual transcription factor binding is increased to the NFκB2, Axl, and EGFR promoters as well as an increase in acetylated histone binding. This data suggests that mutant p53 promotes an increase in transcription by inducing acetylation of histones via recruitment of transcription factors to the promoters of mutant p53 target genes

Targeting the Achilles’ Heel of Lung Cancer Induced by Oncogenic P53

Mutations of the tumor suppressor gene, TP53, are the most prevalent oncogenic mutations in lung cancer, occurring in up to 70% of human non-small cell lung cancer (NSCLC). The majority of mutations in p53 are missense mutations that cause not only a loss of tumor suppressor function, but also gain of oncogenic functions, like tumorigenicity, immune suppression, and chemoresistance. Previous studies have shown that the depletion of gain-of-function (GOF) p53 or disruption of its ability to transactivate the expression of genes related to oncogenesis eliminates its tumorigenic properties indicating a dependency of human lung cancer cells expressing GOF p53 to execute its tumor formation ability. Thus, we hypothesized that targeting GOF p53 and its ability to transactivate gene expression could serve as a promising therapeutic target in lung cancer. Previously our laboratory developed a novel detection system to identify compounds that inhibit GOF p53-induced transactivation. In this study, we performed colony formation assays and xenograft tumor assays to evaluate one of the most promising compounds, 2-Amino-N-[[4-(5-bromopyrimidin-2-yl)oxy-3-chlorophenyl]carbomoyl] benzamide (referred to hereafter as Benzamide G3), for its ability to inhibit GOF p53-mediated transactivation. Through single-cell RNA sequencing analysis of orthotopic tumors generated in an immunocompromised mouse model, we found that treatment with Benzamide G3 resulted in differential expression of genes related to tumor-immune crosstalk in lung cancer cells containing GOF p53. Additionally, we found that treatment of lung cancer tumors harboring GOF p53 with Benzamide G3 resulted in a different tumor immune microenvironment when compared to vehicle-treated orthotopic tumors. This suggests a potential mechanism in which GOF p53-specific transactivation regulates epithelial-mesenchymal transition (EMT), by downregulating CDH1, and tumor-immune crosstalk by downregulating the expression of cytokines related to the recruitment and differentiation of macrophages, such as TNFSF15, CSF2, and GDF15. Using Benzamide G3 to specifically inhibit GOF p53-induced transcription may be useful in the development of lung cancer therapeutics

Hotspot mutant p53-R273H enhances mitochondrial biogenesis and cell migration in primary colorectal cancer in response to oxaliplatin

Oxaliplatin is commonly known as a successful chemotherapy for advanced colorectal cancer, improving patient survival and eradicating micro-metastases, but its use in early stages remains controversial. Mitochondria fuel energy-intensive programs such as cell migration, yet how oxaliplatin regulates the mitochondrial network in CRC - and how TP53 context shapes this - remains unclear. We investigated a matched pair of CRC cell lines from the same patient - SW480 (primary) and SW620 (lymph-node metastasis) - both harboring TP53-R273H mutation, to define differential responses in mitochondrial biogenesis, dynamics and respiration and the mechanisms underlying them. The results indicate that primary-derived colorectal cancer cell line increased cell migration, mitochondrial biogenesis, and mitochondrial respiration capacity in response to oxaliplatin through a new and firstly described gain-of-function (GOF) of p53-R273H. Additionally, in the primary-derived CRC line, oxaliplatin elicited fate heterogeneity - coexisting apoptotic and senescent fractions alongside an R273H-driven, bioenergetically primed migratory subpopulation - together with increased mitochondrial biogenesis and respiratory capacity; by contrast, the metastatic-derived line was more sensitive and displayed structural mitochondrial injury with reduced maximal respiration. More broadly, this work underscores the importance of p53 gain-of-function mutations in CRC: the same GOF (TP53-R273H) amplifies cell migration by coupling an enhanced mitochondrial biogenesis/OXPHOS program to motility. Oxaliplatin further accentuates this energetically primed, pre-metastatic state, arguing for mitochondrial-targeted combination strategies in early-stage CRC

Modulation of gene expression in U251 glioblastoma cells by binding of mutant p53 R273H to intronic and intergenic sequences

Missense point mutations in the TP53 gene are frequent genetic alterations in human tumor tissue and cell lines derived thereof. Mutant p53 (mutp53) proteins have lost sequence-specific DNA binding, but have retained the ability to interact in a structure-selective manner with non-B DNA and to act as regulators of transcription. To identify functional binding sites of mutp53, we established a small library of genomic sequences bound by p53R273H in U251 human glioblastoma cells using chromatin immunoprecipitation (ChIP). Mutp53 binding to isolated DNA fragments confirmed the specificity of the ChIP. The mutp53 bound DNA sequences are rich in repetitive DNA elements, which are dispersed over non-coding DNA regions. Stable down-regulation of mutp53 expression strongly suggested that mutp53 binding to genomic DNA is functional. We identified the PPARGC1A and FRMD5 genes as p53R273H targets regulated by binding to intronic and intra-genic sequences. We propose a model that attributes the oncogenic functions of mutp53 to its ability to interact with intronic and intergenic non-B DNA sequences and modulate gene transcription via re-organization of chromatin

Cell death mechanisms in tumoral and non-tumoral human cell lines triggered by photodynamic treatments: apoptosis, necrosis and parthanatos

Cell death triggered by photodynamic therapy can occur through different mechanisms: apoptosis, necrosis or autophagy. However, recent studies have demonstrated the existence of other mechanisms with characteristics of both necrosis and apoptosis. These new cell death pathways, collectively termed regulated necrosis, include a variety of processes triggered by different stimuli. In this study, we evaluated the cell death mechanism induced by photodynamic treatments with two photosensitizers, meso-tetrakis (4-carboxyphenyl) porphyrin sodium salt (Na-H2TCPP) and its zinc derivative Na-ZnTCPP, in two human breast epithelial cell lines, a non-tumoral (MCF-10A) and a tumoral one (SKBR-3). Viability assays showed that photodynamic treatments with both photosensitizers induced a reduction in cell viability in a concentration-dependent manner and no dark toxicity was observed. The cell death mechanisms triggered were evaluated by several assays and cell line-dependent results were found. Most SKBR-3 cells died by either necrosis or apoptosis. By contrast, in MCF-10A cells, necrotic cells and another cell population with characteristics of both necrosis and apoptosis were predominant. In this latter population, cell death was PARP-dependent and translocation of AIF to the nucleus was observed in some cells. These characteristics are related with parthanatos, being the first evidence of this type of regulated necrosis in the field of photodynamic therapy