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TP53 , a critical tumour suppressor gene, is mutated in over half of all cancers resulting in mutant-p53 protein accumulation and poor patient survival. Therapeutic strategies to target mutant-p53 cancers are urgently needed. We show that accumulated mutant-p53 protein suppresses the expression of SLC7A11 , a component of the cystine/glutamate antiporter, system x C − , through binding to the master antioxidant transcription factor NRF2. This diminishes glutathione synthesis, rendering mutant-p53 tumours susceptible to oxidative damage. System x C − inhibitors specifically exploit this vulnerability to preferentially kill cancer cells with stabilized mutant-p53 protein. Moreover, we demonstrate that SLC7A11 expression is a novel and robust predictive biomarker for APR-246, a first-in-class mutant-p53 reactivator that also binds and depletes glutathione in tumours, triggering lipid peroxidative cell death. Importantly, system x C − antagonism strongly synergizes with APR-246 to induce apoptosis in mutant-p53 tumours. We propose a new paradigm for targeting cancers that accumulate mutant-p53 protein by inhibiting the SLC7A11–glutathione axis. Efficient therapeutic strategies to target mutant-p53 cancers are needed. Here, the authors demonstrate the molecular mechanism through which mutant-p53 tumours are susceptible to oxidative damage and propose a potential strategy for targeting such cancers by inhibiting the SLC7A11-glutathione axis.

In heterogeneous head and neck cancer (HNC), subtype-specific treatment regimens are currently missing. An integrated analysis of patient HNC subtypes using single-cell sequencing and proteome profiles reveals an epithelial-mesenchymal transition (EMT) signature within the epithelial cancer-cell population. The EMT signature coincides with PI3K/mTOR inactivation in the mesenchymal subtype. Conversely, the signature is suppressed in epithelial cells of the basal subtype which exhibits hyperactive PI3K/mTOR signalling. We further identify YBX1 phosphorylation, downstream of the PI3K/mTOR pathway, restraining basal-like cancer cell proliferation. In contrast, YBX1 acts as a safeguard against the proliferation-to-invasion switch in mesenchymal-like epithelial cancer cells, and its loss accentuates partial-EMT and in vivo invasion. Interestingly, phospho-YBX1 that is mutually exclusive to partial-EMT, emerges as a prognostic marker for overall patient outcomes. These findings create a unique opportunity to sensitise mesenchymal cancer cells to PI3K/mTOR inhibitors by shifting them towards a basal-like subtype as a promising therapeutic approach against HNC. The understanding of molecular mechanisms in different subtypes of head and neck cancer (HNC) will define subtype-specific treatment options. Here the authors show that PI3K-phospho-YBX1 axis promotes tumour growth in basal subtype of HNC, while unphosphorylated YBX1 acts as a suppressor of metastasis in the mesenchymal subtype with inactive PI3K signalling.

Mutations in PIK3CA , the gene encoding the p110α catalytic subunit of PI3K, are among the most common mutations in human cancers and overgrowth syndromes. The ubiquitous expression of the activating Pik3ca H1047R mutation results in reduced survival, organomegaly, hypoglycaemia and hypoinsulinemia in mice. Here we demonstrate that in vivo expression of Pik3ca H1047R attenuates the rise in blood glucose in response to oral glucose administration, stimulates glucose uptake in peripheral tissues, inhibits hepatic gluconeogenesis and pancreatic insulin secretion, and increases adipose lipolysis and white adipose tissue browning. Together, our data reveal that the systemic activation of the PI3K pathway in mice disrupts glucose homeostasis through the regulation of hepatic gluconeogenesis, and leads to increased lipolysis of adipose tissue.

Preclinical models that replicate patient tumours as closely as possible are crucial for translational cancer research. While in vitro cancer models have many advantages in assessing tumour response therapy, in vivo systems are essential to enable evaluation of the role of the tumour cell extrinsic factors, such as the tumour microenvironment and host immune system. The requirement for a functional immune system is particularly important given the current focus on immunotherapies. Therefore, we set out to generate an immunocompetent, transplantable model of colorectal cancer suitable for in vivo assessment of immune-based therapeutic approaches. Intestinal tumours from a genetically engineered mouse model, driven by expression of a Pik3ca mutation and loss of Apc , were transplanted into wild type C57BL/6 host mice and subsequently passaged to form a novel syngeneic transplant model of colorectal cancer. Our work confirms the potential to develop a panel of mouse syngeneic grafts, akin to human PDX panels, from different genetically engineered, or carcinogen-induced, mouse models. Such panels would allow the in vivo testing of new pharmaceutical and immunotherapeutic treatment approaches across a range of tumours with a variety of genetic driver mutations.

Anal squamous cell carcinoma is a human papillomavirus-related disease, in which no substantial advances in treatment have been made in over 40 years, especially for those patients who develop disease relapse and for whom no surgical options exist. HPV can evade the immune system and its role in disease progression can be exploited in novel immunotherapy platforms. Although several studies have investigated the expression and inactivation (through loss of heterozygosity) of tumour suppressor genes in the pathways to cancer, no clinically valuable biomarkers have emerged. Regulators of apoptosis, including survivin, and agents targeting the PI3K/AKT pathway, offer opportunities for targeted therapy, although robust data are scarce. Additionally, antibody therapy targeting EGFR may prove effective, although its safety profile in combination with standard chemoradiotherapy has proven to be suboptimal. Finally, progress in the treatment of anal cancer has remained stagnant due to a lack of preclinical models, including cell lines and mouse models. In this Review, we discuss the molecular biology of anal squamous cell carcinoma, clinical trials in progress, and implications for novel therapeutic targets. Future work should focus on preclinical models to provide a resource for investigation of new molecular pathways and for testing novel targets.

Mutations in PIK3CA are very frequent in cancer and lead to sustained PI3K pathway activation. The impact of acute expression of mutant PIK3CA during early stages of malignancy is unknown. Using a mouse model to activate the Pik3ca H1047R hotspot mutation in the heterozygous state from its endogenous locus, we here report that mutant Pik3ca induces centrosome amplification in cultured cells (through a pathway involving AKT, ROCK and CDK2/Cyclin E-nucleophosmin) and in mouse tissues, and increased in vitro cellular tolerance to spontaneous genome doubling. We also present evidence that the majority of PIK3CA H1047R mutations in the TCGA breast cancer cohort precede genome doubling. These previously unappreciated roles of PIK3CA mutation show that PI3K signalling can contribute to the generation of irreversible genomic changes in cancer. While this can limit the impact of PI3K-targeted therapies, these findings also open the opportunity for therapeutic approaches aimed at limiting tumour heterogeneity and evolution. Activated PI3K causes cancer, but the role of active PI3K mutations in early stages of malignancy are unclear. Here, the authors show in a mouse model that active PI3K induces centrosome amplification via AKT, ROCK, CDK2/Cyclin E and nucleophosmin, and increased tolerance of genome doubling.

PIK3CA mutations are reported to be present in approximately 25% of breast cancer (BC), particularly the estrogen receptor—positive (ER+) and HER2-overexpressing (HER2+) subtypes, making them one of the most common genetic aberrations in BC. In experimental models, these mutations have been shown to activate AKT and induce oncogenic transformation, and hence these lesions have been hypothesized to render tumors highly sensitive to therapeutic PI3K/mTOR inhibition. By analyzing gene expression and protein data from nearly 1,800 human BCs, we report that a PIK3CA mutation—associated gene signature (PIK3CA-GS) derived from exon 20 (kinase domain) mutations was able to predict PIK3CA mutation status in two independent datasets, strongly suggesting a characteristic set of gene expression—induced changes. However, in ER+/HER2—BC despite pathway activation, PIK3CA mutations were associated with a phenotype of relatively low mTORC1 signaling and a good prognosis with tamoxifen monotherapy. The relationship between clinical outcome and the PIK3CA-GS was also assessed. Although the PIK3CA-GS was not associated with prognosis in ER — and HER2+BC, it could identify better clinical outcomes in ER+/HER2— disease. In ER+ BC cell lines, PIK3CA mutations were also associated with sensitivity to tamoxifen. These findings could have important implications for the treatment of PIK3CA-mutant BCs and the development of PI3K/mTOR inhibitors.

Caspase-2, one of the most evolutionarily conserved members of the caspase family, is an important regulator of the cellular response to oxidative stress. Given that ferroptosis is suppressed by antioxidant defense pathways, such as that involving selenoenzyme glutathione peroxidase 4 (GPX4), we hypothesized that caspase-2 may play a role in regulating ferroptosis. This study provides the first demonstration of an important and unprecedented function of caspase-2 in protecting cancer cells from undergoing ferroptotic cell death. Specifically, we show that depletion of caspase-2 leads to the downregulation of stress response genes including SESN2, HMOX1, SLC7A11 , and sensitizes mutant-p53 cancer cells to cell death induced by various ferroptosis-inducing compounds. Importantly, the canonical catalytic activity of caspase-2 is not required for its role and suggests that caspase-2 regulates ferroptosis via non-proteolytic interaction with other proteins. Using an unbiased BioID proteomics screen, we identified novel caspase-2 interacting proteins (including heat shock proteins and co-chaperones) that regulate cellular responses to stress. Finally, we demonstrate that caspase-2 limits chaperone-mediated autophagic degradation of GPX4 to promote the survival of mutant-p53 cancer cells. In conclusion, we document a novel role for caspase-2 as a negative regulator of ferroptosis in cells with mutant p53. Our results provide evidence for a novel function of caspase-2 in cell death regulation and open potential new avenues to exploit ferroptosis in cancer therapy.

The prevalence and dire implications of mutations in the tumour suppressor, p53, highlight its appeal as a chemotherapeutic target. We recently showed that impairing cellular antioxidant systems via inhibition of SLC7A11, a component of the system x c − cystine-glutamate antiporter, enhances sensitivity to mutant-p53 targeted therapy, APR-246. We investigated whether this synergy extends to other genes, such as those encoding enzymes of the pentose phosphate pathway (PPP). TKT, one of the major enzymes of the PPP, is allegedly regulated by NRF2, which is in turn impaired by accumulated mutant-p53 protein. Therefore, we investigated the relationship between mutant-p53, TKT and sensitivity to APR-246. We found that mutant-p53 does not alter expression of TKT, nor is TKT modulated directly by NRF2, suggesting a more complex mechanism at play. Furthermore, we found that in p53null cells, knockdown of TKT increased sensitivity to APR-246, whilst TKT overexpression conferred resistance to the drug. However, neither permutation elicited any effect on cells overexpressing mutant-p53 protein, despite mediating oxidative stress levels in a similar fashion to that in p53-null cells. In sum, this study has unveiled TKT expression as a determinant for sensitivity to APR-246 in p53-null cells.

The phosphatidylinositol 3-kinase (PI3K) pathway is involved in a myriad of cellular signalling pathways that regulate cell growth, metabolism, proliferation and survival. As a result, alterations in the PI3K pathway are frequently associated with human cancers. Indeed, PIK3CA—the gene encoding the p110α catalytic subunit of PI3K—is one of the most commonly mutated human oncogenes. PIK3CA mutations have also been implicated in non-malignant conditions including congenital overgrowth syndromes and vascular malformations. In order to study the role of PIK3CA mutations in driving tumorigenesis and tissue overgrowth and to test potential therapeutic interventions for these conditions, model systems are essential. In this review we discuss the various mouse models currently available for preclinical studies into the biological consequences and clinical significance of PIK3CA mutations.