PI3Kβ controls immune evasion in PTEN-deficient breast tumours.

Loss of the PTEN tumour suppressor is one of the most common oncogenic drivers across all cancer types. PTEN is the major negative regulator of PI3K signalling. The PI3Kβ isoform has been shown to play an important role in PTEN-deficient tumours, but the mechanisms underlying the importance of PI3Kβ activity remain elusive.

Blocking PI3K p110β Attenuates Development of PTEN-Deficient Castration-Resistant Prostate Cancer.

Unlabelled: A common outcome of androgen deprivation in prostate cancer therapy is disease relapse and progression to castration-resistant prostate cancer (CRPC) via multiple mechanisms. To gain insight into the recent clinical findings that highlighted genomic alterations leading to hyperactivation of PI3K, we examined the roles of the commonly expressed p110 catalytic isoforms of PI3K in a murine model of Pten-null invasive CRPC. While blocking p110α had negligible effects in the development of Pten-null invasive CRPC, either genetic or pharmacologic perturbation of p110β dramatically slowed CRPC initiation and progression.

PIK3CA C-terminal frameshift mutations are novel oncogenic events that sensitize tumors to PI3K-α inhibition.

hotspot mutation is well established as an oncogenic driver event in cancer and its durable and efficacious inhibition is a focus in the development and testing of clinical cancer therapeutics. However, hundreds of cancer-associated mutations remain uncharacterized, their sensitivity to PI3K inhibitors unknown. Here, we describe a series of C-terminal mutations, primarily nucleotide insertions, that produce a frame-shifted protein product with an extended C terminus.

BRCA1-IRIS promotes human tumor progression through PTEN blockade and HIF-1α activation.

is an established breast and ovarian tumor suppressor gene that encodes multiple protein products whose individual contributions to human cancer suppression are poorly understood. BRCA1-IRIS (also known as "IRIS"), an alternatively spliced product and a chromatin-bound replication and transcription regulator, is overexpressed in various primary human cancers, including breast cancer, lung cancer, acute myeloid leukemia, and certain other carcinomas. Its naturally occurring overexpression can promote the metastasis of patient-derived xenograft (PDX) cells and other human cancer cells in mouse models.

A PI3K p110β-Rac signalling loop mediates Pten-loss-induced perturbation of haematopoiesis and leukaemogenesis.

The tumour suppressor PTEN, which antagonizes PI3K signalling, is frequently inactivated in haematologic malignancies. In mice, deletion of PTEN in haematopoietic stem cells (HSCs) causes perturbed haematopoiesis, myeloproliferative neoplasia (MPN) and leukaemia. Although the roles of the PI3K isoforms have been studied in PTEN-deficient tumours, their individual roles in PTEN-deficient HSCs are unknown.

MELK is an oncogenic kinase essential for mitotic progression in basal-like breast cancer cells.

Despite marked advances in breast cancer therapy, basal-like breast cancer (BBC), an aggressive subtype of breast cancer usually lacking estrogen and progesterone receptors, remains difficult to treat. In this study, we report the identification of MELK as a novel oncogenic kinase from an in vivo tumorigenesis screen using a kinome-wide open reading frames (ORFs) library. Analysis of clinical data reveals a high level of MELK overexpression in BBC, a feature that is largely dependent on FoxM1, a master mitotic transcription factor that is also found to be highly overexpressed in BBC.

PI3K isoform dependence of PTEN-deficient tumors can be altered by the genetic context.

There has been increasing interest in the use of isoform-selective inhibitors of phosphatidylinositide-3-kinase (PI3K) in cancer therapy. Using conditional deletion of the p110 catalytic isoforms of PI3K to predict sensitivity of cancer types to such inhibitors, we and others have demonstrated that tumors deficient of the phosphatase and tensin homolog (PTEN) are often dependent on the p110β isoform of PI3K. Because human cancers usually arise due to multiple genetic events, determining whether other genetic alterations might alter the p110 isoform requirements of PTEN-null tumors becomes a critical question.

Hematopoiesis and RAS-driven myeloid leukemia differentially require PI3K isoform p110α.

The genes encoding RAS family members are frequently mutated in juvenile myelomonocytic leukemia (JMML) and acute myeloid leukemia (AML). RAS proteins are difficult to target pharmacologically; therefore, targeting the downstream PI3K and RAF/MEK/ERK pathways represents a promising approach to treat RAS-addicted tumors. The p110α isoform of PI3K (encoded by Pik3ca) is an essential effector of oncogenic KRAS in murine lung tumors, but it is unknown whether p110α contributes to leukemia.

Spatially distinct roles of class Ia PI3K isoforms in the development and maintenance of PTEN hamartoma tumor syndrome.

PTEN hamartoma tumor syndrome (PHTS) comprises a collection of genetic disorders associated with germline mutations in the tumor suppressor gene PTEN. Therapeutic options and preventative measures for PHTS are limited. Using both genetically engineered mouse models and pharmacological PI3K isoform-selective inhibitors, we found that the roles of PI3K isoforms are spatially distinct in the skin: While p110α is responsible for the sustained survival of suprabasal cells of the epidermis in the absence of PTEN, p110β is important for the hyperproliferation of basal cells in PHTS.

Functional characterization of an isoform-selective inhibitor of PI3K-p110β as a potential anticancer agent.

Unlabelled: Genetic approaches have shown that the p110β isoform of class Ia phosphatidylinositol-3-kinase (PI3K) is essential for the growth of PTEN-null tumors. Thus, it is desirable to develop p110β-specific inhibitors for cancer therapy. Using a panel of PI3K isoform-specific cellular assays, we screened a collection of compounds possessing activities against kinases in the PI3K superfamily and identified a potent and selective p110β inhibitor: KIN-193.