Phosphoinositide 3-Kinase Regulates Glycolysis through Mobilization of Aldolase from the Actin Cytoskeleton.

The phosphoinositide 3-kinase (PI3K) pathway regulates multiple steps in glucose metabolism and also cytoskeletal functions, such as cell movement and attachment. Here, we show that PI3K directly coordinates glycolysis with cytoskeletal dynamics in an AKT-independent manner. Growth factors or insulin stimulate the PI3K-dependent activation of Rac, leading to disruption of the actin cytoskeleton, release of filamentous actin-bound aldolase A, and an increase in aldolase activity. Consistently, PI3K inhibitors, but not AKT, SGK, or mTOR inhibitors, cause a significant decrease in glycolysis at the step catalyzed by aldolase, while activating PIK3CA mutations have the opposite effect. These results point toward a master regulatory function of PI3K that integrates an epithelial cell's metabolism and its form, shape, and function, coordinating glycolysis with the energy-intensive dynamics of actin remodeling.

Active growth signaling promotes senescence and cancer cell sensitivity to CDK7 inhibition.

Tumor growth is driven by continued cellular growth and proliferation. Cyclin-dependent kinase 7's (CDK7) role in activating mitotic CDKs and global gene expression makes it therefore an attractive target for cancer therapies. However, what makes cancer cells particularly sensitive to CDK7 inhibition (CDK7i) remains unclear. Here, we address this question. We show that CDK7i, by samuraciclib, induces a permanent cell-cycle exit, known as senescence, without promoting DNA damage signaling or cell death. A chemogenetic genome-wide CRISPR knockout screen identified that active mTOR (mammalian target of rapamycin) signaling promotes samuraciclib-induced senescence. mTOR inhibition decreases samuraciclib sensitivity, and increased mTOR-dependent growth signaling correlates with sensitivity in cancer cell lines. Reverting a growth-promoting mutation in PIK3CA to wild type decreases sensitivity to CDK7i. Our work establishes that enhanced growth alone promotes CDK7i sensitivity, providing an explanation for why some cancers are more sensitive to CDK inhibition than normally growing cells.

Safety and clinical activity of JNJ-78306358, a human leukocyte antigen-G (HLA-G) x CD3 bispecific antibody, for the treatment of advanced stage solid tumors.

BACKGROUND: JNJ-78306358 is a bispecific antibody that redirects T cells to kill human leukocyte antigen-G (HLA-G)-expressing tumor cells. This dose escalation study evaluated the safety, pharmacokinetics, pharmacodynamics, and preliminary antitumor activity of JNJ-78306358 in patients with advanced solid tumors. METHODS: Adult patients with metastatic/unresectable solid tumors with high prevalence of HLA-G expression were enrolled. Dose escalation was initiated with once-weekly subcutaneous administration with step-up dosing to mitigate cytokine release syndrome (CRS). RESULTS: Overall, 39 heavily pretreated patients (colorectal cancer: n = 23, ovarian cancer: n = 10, and renal cell carcinoma: n = 6) were dosed in 7 cohorts. Most patients (94.9%) experienced ≥ 1 treatment-emergent adverse events (TEAEs); 87.2% had ≥ 1 related TEAEs. About half of the patients (48.7%) experienced CRS, which were grade 1/2. Nine patients (23.1%) received tocilizumab for CRS. No grade 3 CRS was observed. Dose-limiting toxicities (DLTs) of increased transaminases, pneumonitis and recurrent CRS requiring a dose reduction were reported in 4 patients, coinciding with CRS. No treatment-related deaths reported. No objective responses were noted, but 2 patients had stable disease > 40 weeks. JNJ-78306358 stimulated peripheral T cell activation and cytokine release. Anti-drug antibodies were observed in 45% of evaluable patients with impact on exposure. Approximately half of archival tumor samples (48%) had expression of HLA-G by immunohistochemistry. CONCLUSION: JNJ-78306358 showed pharmacodynamic effects with induction of cytokines and T cell activation. JNJ-78306358 was associated with CRS-related toxicities including increased transaminases and pneumonitis which limited its dose escalation to potentially efficacious levels. Trial registration number ClinicalTrials.gov (No. NCT04991740).

Phase I Study of JNJ-74699157 in Patients with Advanced Solid Tumors Harboring the KRAS G12C Mutation.

BACKGROUND: Patients with KRAS-mutant cancers have limited treatment options. Here we present a phase I study of JNJ-74699157, an oral, selective, covalent inhibitor of the KRAS G12C isoform, in patients with advanced cancer harboring the KRAS G12C mutation. METHODS: Eligible patients (aged ≥18 years) who had previously received or were ineligible for standard treatment received JNJ-74699157 once daily on a 21-day cycle. Dose escalation was guided by a modified continual reassessment method. RESULTS: Ten patients (100 mg: 9 and 200 mg: 1) were enrolled. Tumor types included non-small cell lung cancer (n = 5), colorectal cancer (n = 4), and carcinoma of unknown primary site (n = 1). The median age was 65 (range: 36-74) years and median treatment duration was 2.91 (range: 0.5-7.5) months. Dose-limiting toxicities of grades 3-4 increased blood creatinine phosphokinase (CPK) were observed in 100 mg and 200 mg dose levels. The most common adverse event was increased blood CPK (6 patients). No significant clinical benefit was observed; the best response was stable disease in 4 patients (40%). CONCLUSION: Based on dose-limiting skeletal muscle toxicities and the lack of efficacy at the 100 mg dose, further enrollment was stopped. The safety profile of JNJ-74699157 was not considered favorable for further clinical development. CLINICALTRIALS.GOV IDENTIFIER: NCT04006301.

Clinical Benefit to an Aurora A Kinase Inhibitor in a Patient with Metastatic Integrase Interactor 1-Deficient Carcinoma.

Integrase interactor 1 (INI-1)-deficient carcinoma is a rare cancer characterized by the loss of the SWItch/Sucrose Non-Fermentable-related matrix-associated actin-dependent regulator of chromatin subfamily B member 1 gene (SMARCB1) and tends to follow an aggressive clinical course. There is no currently available standard therapy option, although a few promising treatment strategies, including enhancer of zeste homolog 2 (EZH2) inhibition, are under active investigation. This report describes a 30-year-old woman with INI-1-deficient carcinoma who progressed on combination chemotherapy and an EZH2 inhibitor. Next-generation-sequencing-based targeted cancer-related gene assay confirmed SMARCB1 loss and revealed other mutations in breast cancer 1 gene and checkpoint kinase 2 gene, which may have impacted her clinical course. After discussion at the molecular tumor board, she was offered alisertib, an aurora A kinase inhibitor, on a single-patient expanded-use program and achieved prolonged disease stabilization. Aurora A kinase inhibition may have an important role in the management of patients with INI-1-deficient tumors, warranting further evaluation in clinical studies. KEY POINTS: Loss of the SWItch/Sucrose Non-Fermentable-related matrix-associated actin-dependent regulator of chromatin subfamily B member 1 gene (SMARCB1), which encodes integrase interactor 1 (INI-1), is associated with various mesenchymal malignancies, but a few carcinomas with rhabdoid features have been recently described as a distinct entity.INI-1-deficient carcinoma can be very aggressive, and there is no known treatment option available.There are encouraging preliminary data with an enhancer of zeste homolog 2 inhibitor, tazematostat, in INI-1-deficient malignancies, including INI-1-deficient carcinomas.Loss of INI-1 can activate aurora A kinase (AurkA), and inhibition of AurkA by alisertib could be a viable option and warrants further investigation in this cancer.Clinical genomic profiling can confirm diagnosis of molecularly defined malignancy and provide insights on therapeutic options.

NSD2 links dimethylation of histone H3 at lysine 36 to oncogenic programming.

The histone lysine methyltransferase NSD2 (MMSET/WHSC1) is implicated in diverse diseases and commonly overexpressed in multiple myeloma due to a recurrent t(4;14) chromosomal translocation. However, the precise catalytic activity of NSD2 is obscure, preventing progress in understanding how this enzyme influences chromatin biology and myeloma pathogenesis. Here, we show that dimethylation of histone H3 at lysine 36 (H3K36me2) is the principal chromatin-regulatory activity of NSD2. Catalysis of H3K36me2 by NSD2 is sufficient for gene activation. In t(4;14)-positive myeloma cells, the normal genome-wide and gene-specific distribution of H3K36me2 is obliterated, creating a chromatin landscape that selects for a transcription profile favorable for myelomagenesis. Catalytically active NSD2 confers xenograft tumor formation upon t(4;14)-negative cells and promotes oncogenic transformation of primary cells in an H3K36me2-dependent manner. Together, our findings establish H3K36me2 as the primary product generated by NSD2 and demonstrate that genomic disorganization of this canonical chromatin mark by NSD2 initiates oncogenic programming.

Rediagnosis of Lung Cancer as NUT Midline Carcinoma Based on Clues From Tumor Genomic Profiling.

Tumor DNA sequencing can identify rare driver genomic alterations that suggest targets for cancer therapy, even when these drivers cannot be suspected on clinical grounds. In some cases, genomic alterations identified in the tumor can lead to a change in diagnosis with implications for prognosis and therapy. This report describes a case in which evaluation of tumor sequencing results by a molecular tumor board (MTB) led to rediagnosis of a non-small cell lung cancer as highly aggressive NUT midline carcinoma, with implications for targeted therapy using an investigational bromodomain and extraterminal (BET) inhibitor. We discuss the molecular biology and diagnosis of this rare tumor, and suggest how improved annotation of tumor sequencing reports and multidisciplinary expertise of MTBs can facilitate timely diagnosis of rare tumors and application of potential targeted therapies.

NDRG1 links p53 with proliferation-mediated centrosome homeostasis and genome stability.

The tumor protein 53 (TP53) tumor suppressor gene is the most frequently somatically altered gene in human cancers. Here we show expression of N-Myc down-regulated gene 1 (NDRG1) is induced by p53 during physiologic low proliferative states, and mediates centrosome homeostasis, thus maintaining genome stability. When placed in physiologic low-proliferating conditions, human TP53 null cells fail to increase expression of NDRG1 compared with isogenic wild-type controls and TP53 R248W knockin cells. Overexpression and RNA interference studies demonstrate that NDRG1 regulates centrosome number and amplification. Mechanistically, NDRG1 physically associates with γ-tubulin, a key component of the centrosome, with reduced association in p53 null cells. Strikingly, TP53 homozygous loss was mutually exclusive of NDRG1 overexpression in over 96% of human cancers, supporting the broad applicability of these results. Our study elucidates a mechanism of how TP53 loss leads to abnormal centrosome numbers and genomic instability mediated by NDRG1.

HER2 missense mutations have distinct effects on oncogenic signaling and migration.

Recurrent human epidermal growth factor receptor 2 (HER2) missense mutations have been reported in human cancers. These mutations occur primarily in the absence of HER2 gene amplification such that most HER2-mutant tumors are classified as "negative" by FISH or immunohistochemistry assays. It remains unclear whether nonamplified HER2 missense mutations are oncogenic and whether they are targets for HER2-directed therapies that are currently approved for the treatment of HER2 gene-amplified breast cancers. Here we functionally characterize HER2 kinase and extracellular domain mutations through gene editing of the endogenous loci in HER2 nonamplified human breast epithelial cells. In in vitro and in vivo assays, the majority of HER2 missense mutations do not impart detectable oncogenic changes. However, the HER2 V777L mutation increased biochemical pathway activation and, in the context of a PIK3CA mutation, enhanced migratory features in vitro. However, the V777L mutation did not alter in vivo tumorigenicity or sensitivity to HER2-directed therapies in proliferation assays. Our results suggest the oncogenicity and potential targeting of HER2 missense mutations should be considered in the context of cooperating genetic alterations and provide previously unidentified insights into functional analysis of HER2 mutations and strategies to target them.

PIK3CA mutations and TP53 alterations cooperate to increase cancerous phenotypes and tumor heterogeneity.

BACKGROUND/PURPOSE: The combined contributions of oncogenes and tumor suppressor genes toward carcinogenesis remain poorly understood. Elucidation of cancer gene cooperativity can provide new insights leading to more effective use of therapies. EXPERIMENTAL DESIGN/METHODS: We used somatic cell genome editing to introduce singly and in combination PIK3CA mutations (E545K or H1047R) with TP53 alterations (R248W or knockout), to assess any enhanced cancerous phenotypes. The non-tumorigenic human breast epithelial cell line, MCF10A, was used as the parental cell line, and resultant cells were assessed via various in vitro assays, growth as xenografts, and drug sensitivity assays using targeted agents and chemotherapies. RESULTS: Compared to single-gene-targeted cells and parental controls, cells with both a PIK3CA mutation and TP53 alteration had increased cancerous phenotypes including cell proliferation, soft agar colony formation, aberrant morphology in acinar formation assays, and genomic heterogeneity. Cells also displayed varying sensitivities to anti-neoplastic drugs, although all cells with PIK3CA mutations showed a relative increased sensitivity to paclitaxel. All cell lines remained non-tumorigenic. CONCLUSIONS: This cell line panel provides a resource for further elucidating cooperative genetic mediators of carcinogenesis and response to therapies.

MACROD2 overexpression mediates estrogen independent growth and tamoxifen resistance in breast cancers.

Tamoxifen is effective for treating estrogen receptor-alpha (ER) positive breast cancers. However, few molecular mediators of tamoxifen resistance have been elucidated. Here we describe a previously unidentified gene, MACROD2 that confers tamoxifen resistance and estrogen independent growth. We found MACROD2 is amplified and overexpressed in metastatic tamoxifen-resistant tumors. Transgene overexpression of MACROD2 in breast cancer cell lines results in tamoxifen resistance, whereas RNAi-mediated gene knock down reverses this phenotype. MACROD2 overexpression also leads to estrogen independent growth in xenograft assays. Mechanistically, MACROD2 increases p300 binding to estrogen response elements in a subset of ER regulated genes. Primary breast cancers and matched metastases demonstrate MACROD2 expression can change with disease evolution, and increased expression and amplification of MACROD2 in primary tumors is associated with worse overall survival. These studies establish MACROD2 as a key mediator of estrogen independent growth and tamoxifen resistance, as well as a potential novel target for diagnostics and therapy.

A Polycythemia Vera JAK2 Mutation Masquerading as a Duodenal Cancer Mutation.

Next-generation sequencing (NGS) is increasingly being used in cancer care to identify both somatic tumor driver mutations that can be targeted for therapy, and heritable mutations in the germline associated with increased cancer risk. This report presents a case of a JAK2 V617F mutation falsely identified as a duodenal cancer mutation via NGS. The patient was found to have a history of polycythemia vera, a disorder with a high incidence of JAK2 somatic mutations. Buccal cell DNA showed heterozygosity for the mutation, suggesting that it was potentially germline. However, subsequent resequencing of tumor, adjacent normal tissue, and fingernail DNA confirmed the mutation was somatic, and its presence in tumor and buccal cells resulted from contaminating blood cells. This report highlights important nuances of NGS that can lead to misinterpretation of results with potential clinical implications.

Engineering targeted chromosomal amplifications in human breast epithelial cells.

Chromosomal amplifications are among the most common genetic alterations found in human cancers. However, experimental systems to study the processes that lead to specific, recurrent amplification events in human cancers are lacking. Moreover, some common amplifications, such as that at 8p11-12 in breast cancer, harbor multiple driver oncogenes, which are poorly modeled by conventional overexpression approaches. We sought to develop an experimental system to model recurrent chromosomal amplification events in human cell lines. Our strategy is to use homologous-recombination-mediated gene targeting to deliver a dominantly selectable, amplifiable marker to a specified chromosomal location. We used adeno-associated virus vectors to target human MCF-7 breast cancer cells at the ZNF703 locus, in the recurrent 8p11-12 amplicon, using the E. coli inosine monophosphate dehydrogenase (IMPDH) enzyme as a marker. We applied selective pressure using IMPDH inhibitors. Surviving clones were found to have increased copy number of ZNF703 (average 2.5-fold increase) by droplet digital PCR and FISH. Genome-wide array comparative genomic hybridization confirmed that amplifications had occurred on the short arm of chromosome 8, without changes on 8q or other chromosomes. Patterns of amplification were variable and similar to those seen in primary human breast cancers, including "sawtooth" patterns, distal copy number loss, and large continuous regions of copy number gain. This system will allow study of the cis- and trans-acting factors that are permissive for chromosomal amplification and provide a model to analyze oncogene cooperativity in amplifications harboring multiple candidate driver genes.

Mutation of a single allele of the cancer susceptibility gene BRCA1 leads to genomic instability in human breast epithelial cells.

Biallelic inactivation of cancer susceptibility gene BRCA1 leads to breast and ovarian carcinogenesis. Paradoxically, BRCA1 deficiency in mice results in early embryonic lethality, and similarly, lack of BRCA1 in human cells is thought to result in cellular lethality in view of BRCA1's essential function. To survive homozygous BRCA1 inactivation during tumorigenesis, precancerous cells must accumulate additional genetic alterations, such as p53 mutations, but this requirement for an extra genetic "hit" contradicts the two-hit theory for the accelerated carcinogenesis associated with familial cancer syndromes. Here, we show that heterozygous BRCA1 inactivation results in genomic instability in nontumorigenic human breast epithelial cells in vitro and in vivo. Using somatic cell gene targeting, we demonstrated that a heterozygous BRCA1 185delAG mutation confers impaired homology-mediated DNA repair and hypersensitivity to genotoxic stress. Heterozygous mutant BRCA1 cell clones also showed a higher degree of gene copy number loss and loss of heterozygosity in SNP array analyses. In BRCA1 heterozygous clones and nontumorigenic breast epithelial tissues from BRCA mutation carriers, FISH revealed elevated genomic instability when compared with their respective controls. Thus, BRCA1 haploinsufficiency may accelerate hereditary breast carcinogenesis by facilitating additional genetic alterations.

The phosphoinositide-3-kinase-Akt-mTOR pathway as a therapeutic target in breast cancer.

The phosphoinositide-3-kinase (PI3-kinase)-Akt-mTOR pathway is a central signal transduction pathway that regulates many critical aspects of normal and cancer physiology, including cell proliferation, apoptosis, cell morphology and migration, protein synthesis, and integration of metabolism. In breast cancer, somatic mutations that activate the pathway occur in more than 50% of tumors, underscoring the potentially broad impact of targeting the pathway for therapy. A vast body of preclinical data demonstrates the efficacy of pathway inhibition on tumor growth, and evidence also shows that activation of the pathway occurs in models of acquired resistance to hormonal therapy. This preclinical work led to the investigation of allosteric mTOR inhibitors, everolimus and temsirolimus, in metastatic hormone receptor-positive breast cancer. The recent BOLERO-2 trial comparing everolimus plus exemestane versus placebo plus exemestane in women with resistance to nonsteroidal aromatase inhibitors demonstrated a 6-month improvement in progression-free survival and led to FDA approval of everolimus for this indication in the United States. This landmark trial is the first demonstration of significant clinical benefit using drugs targeting this pathway in breast cancer. Many questions remain about the role of everolimus and other pathway-targeting drugs in clinical development in breast cancer treatment. This article reviews the role of the PI3-kinase-Akt-mTOR pathway in breast cancer biology and the clinical trial evidence available to date.

Phase 1 Study of JNJ-64619178, a Protein Arginine Methyltransferase 5 Inhibitor, in Advanced Solid Tumors.

PURPOSE: In this first-in-human, Phase 1, open-label, multicenter study, we evaluated JNJ-64619178, a selective and potent PRMT5 inhibitor, in patients with advanced malignant solid tumors or non-Hodgkin lymphomas (NHL). The primary objective was to evaluate the safety and to identify a recommended Phase 2 dose (RP2D) of JNJ-64619178. PATIENTS AND METHODS: Adult patients with treatment-refractory advanced solid tumors or NHL and measurable disease received escalating doses of JNJ-64619178 following two schedules (Schedule A: 14 days on/7 days off; Schedule B: every day on a 21-day cycle). Safety, pharmacokinetics (PK), pharmacodynamics (PD), and clinical activity were evaluated. RESULTS: Ninety patients received JNJ-64619178. Thrombocytopenia was identified as the only dose-limiting toxicity. JNJ-64619178 showed dose-proportional PK and robust target engagement, as measured by plasma symmetric dimethylarginine, across all dose levels. The objective response rate was 5.6% (5 of 90). Patients with adenoid cystic carcinoma (ACC) had an ORR of 11.5% (3 of 26) and a median progression-free survival of 19.1 months. CONCLUSIONS: JNJ-64619178 demonstrated manageable dose-dependent toxicity and preliminary evidence of antitumor activity in ACC and other tumor types. Plasma exposure was dose dependent, and target inhibition was maintained with intermittent and continuous dosing. On the basis of safety, clinical activity, PK, and PD findings, two provisional RP2Ds were selected: 1.5 mg intermittently and 1.0 mg once daily. Aside from ACC, clinical benefit was limited, and biomarkers to enrich for responsiveness to PRMT5 inhibition will be needed for further development.

Phase 1 study of JNJ-64619178, a protein arginine methyltransferase 5 inhibitor, in patients with lower-risk myelodysplastic syndromes.

Splicing factor (SF) gene mutations are frequent in myelodysplastic syndromes (MDS), and agents that modulate RNA splicing are hypothesized to provide clinical benefit. JNJ-64619178, a protein arginine methyltransferase 5 (PRMT5) inhibitor, was evaluated in patients with lower-risk (LR) MDS in a multi-part, Phase 1, multicenter study. The objectives were to determine a tolerable dose and to characterize safety, pharmacokinetics, pharmacodynamics, and preliminary clinical activity. JNJ-64619178 was administered on a 14 days on/7 days off schedule or every day on a 21-day cycle to patients with International Prognostic Scoring System (IPSS) Low or Intermediate-1 risk MDS who were red blood cell transfusion-dependent. Twenty-four patients were enrolled; 15 (62.5 %) patients had low IPSS risk score, while 18 (75.0 %) had an SF3B1 mutation. Median duration of treatment was 3.45 months (range: 0.03-6.93). No dose limiting toxicities were observed. The 0.5 mg once daily dose was considered better tolerated and chosen for dose expansion. Twenty-three (95.8 %) patients experienced treatment-emergent adverse events (TEAE). The most common TEAEs were neutropenia (15 [62.5 %]) and thrombocytopenia (14 [58.3 %]). JNJ-64619178 pharmacokinetics was dose-dependent. Target engagement as measured by plasma symmetric di-methylarginine was observed across all dose levels; however, variant allele frequency of clonal mutations in bone marrow or blood did not show sustained reductions from baseline. No patient achieved objective response or hematologic improvement per International Working Group 2006 criteria, or transfusion independence. A tolerable dose of JNJ-64619178 was identified in patients with LR MDS. However, no evidence of clinical benefit was observed.

The growth response to androgen receptor signaling in ERα-negative human breast cells is dependent on p21 and mediated by MAPK activation.

INTRODUCTION: Although a high frequency of androgen receptor (AR) expression in human breast cancers has been described, exploiting this knowledge for therapy has been challenging. This is in part because androgens can either inhibit or stimulate cell proliferation in pre-clinical models of breast cancer. In addition, many breast cancers co-express other steroid hormone receptors that can affect AR signaling, further obfuscating the effects of androgens on breast cancer cells. METHODS: To create better-defined models of AR signaling in human breast epithelial cells, we took estrogen receptor (ER)-α-negative and progesterone receptor (PR)-negative human breast epithelial cell lines, both cancerous and non-cancerous, and engineered them to express AR, thus allowing the unambiguous study of AR signaling. We cloned a full-length cDNA of human AR, and expressed this transgene in MCF-10A non-tumorigenic human breast epithelial cells and MDA-MB-231 human breast-cancer cells. We characterized the responses to AR ligand binding using various assays, and used isogenic MCF-10A p21 knock-out cell lines expressing AR to demonstrate the requirement for p21 in mediating the proliferative responses to AR signaling in human breast epithelial cells. RESULTS: We found that hyperactivation of the mitogen-activated protein kinase (MAPK) pathway from both AR and epidermal growth factor receptor (EGFR) signaling resulted in a growth-inhibitory response, whereas MAPK signaling from either AR or EGFR activation resulted in cellular proliferation. Additionally, p21 gene knock-out studies confirmed that AR signaling/activation of the MAPK pathway is dependent on p21. CONCLUSIONS: These studies present a new model for the analysis of AR signaling in human breast epithelial cells lacking ERα/PR expression, providing an experimental system without the potential confounding effects of ERα/PR crosstalk. Using this system, we provide a mechanistic explanation for previous observations ascribing a dual role for AR signaling in human breast cancer cells. As previous reports have shown that approximately 40% of breast cancers can lack p21 expression, our data also identify potential new caveats for exploiting AR as a target for breast cancer therapy.

Knockin of mutant PIK3CA activates multiple oncogenic pathways.

The phosphatidylinositol 3-kinase subunit PIK3CA is frequently mutated in human cancers. Here we used gene targeting to "knock in" PIK3CA mutations into human breast epithelial cells to identify new therapeutic targets associated with oncogenic PIK3CA. Mutant PIK3CA knockin cells were capable of epidermal growth factor and mTOR-independent cell proliferation that was associated with AKT, ERK, and GSK3beta phosphorylation. Paradoxically, the GSK3beta inhibitors lithium chloride and SB216763 selectively decreased the proliferation of human breast and colorectal cancer cell lines with oncogenic PIK3CA mutations and led to a decrease in the GSK3beta target gene CYCLIN D1. Oral treatment with lithium preferentially inhibited the growth of nude mouse xenografts of HCT-116 colon cancer cells with mutant PIK3CA compared with isogenic HCT-116 knockout cells containing only wild-type PIK3CA. Our findings suggest GSK3beta is an important effector of mutant PIK3CA, and that lithium, an FDA-approved therapy for bipolar disorders, has selective antineoplastic properties against cancers that harbor these mutations.