Cancer-specific mutations in PIK3CA are oncogenic in vivo

[Angiosarcoma]

Angiosarcomas are rare tumors accounting for 1-2% of all soft tissue sarcomas. Nonetheless a dermatologist needs to be knowledgeable about this tumor because the prognosis is particularly poor. Angiosarcoma favors superficial soft tissues and skin (60%) with a clear predilection for the head and neck region. The average age of the patients presenting with cutaneous angiosarcomas is around 70 years with a peak incidence in the 8th decade. However, some subtypes may occur in children and adolescents. Secondary angiosarcoma after tissue-conserving radiation therapy for carcinoma of the breast represents an increasing problem, both the differentiation between atypical vascular lesions and true aggressive angiosarcoma and the therapy are challenging. The prognosis for angiosarcoma patients is gloomy despite all therapeutic efforts. Only early therapy seems to influence the outcome at all. There are some established guidelines for the primary and palliative therapy. Interesting new options of biomodulatory and molecularly targeted therapy can be envisioned.

[Angiosarcoma]

Angiosarcomas are rare tumors accounting for 1-2% of all soft tissue sarcomas. Nonetheless a dermatologist needs to be knowledgeable about this tumor because the prognosis is particularly poor. Angiosarcoma favors superficial soft tissues and skin (60%) with a clear predilection for the head and neck region. The average age of the patients presenting with cutaneous angiosarcomas is around 70 years with a peak incidence in the 8th decade. However, some subtypes may occur in children and adolescents. Secondary angiosarcoma after tissue-conserving radiation therapy for carcinoma of the breast represents an increasing problem, both the differentiation between atypical vascular lesions and true aggressive angiosarcoma and the therapy are challenging. The prognosis for angiosarcoma patients is gloomy despite all therapeutic efforts. Only early therapy seems to influence the outcome at all. There are some established guidelines for the primary and palliative therapy. Interesting new options of biomodulatory and molecularly targeted therapy can be envisioned.

Class 1A PI3K regulates vessel integrity during development and tumorigenesis

PI3K is important in the regulation of growth, proliferation, and survival of tumor cells. We show that class 1A PI3K is also critical in the tumor microenvironment by regulating the integrity of the tumor vasculature. Using Tie2Cre-mediated deletion of the PI3K regulatory subunits (p85alpha, p55alpha, p50alpha, and p85beta), we generated mice with endothelial cell-specific loss of class 1A PI3K. Complete loss of all subunits caused acute embryonic lethality at E11.5 due to hemorrhaging, whereas retention of a single p85alpha allele yielded viable mice that survived to adulthood. These heterozygous mice exhibited no vascular defects until challenged with a pathological insult, such as tumor cells or high levels of VEGF. Under these pathological conditions, heterozygous mice exhibited localized vascular abnormalities, including vessel leakage and the inability to maintain large vessels, which caused a deceleration of tumorigenesis. Furthermore, we show that a PI3K inhibitor can mimic the effects of class 1A PI3K loss, which suggests that targeting class 1A PI3K may be a promising therapy for blocking tumor angiogenesis.

Identification and characterization of NVP-BEZ235, a new orally available dual phosphatidylinositol 3-kinase/mammalian target of rapamycin inhibitor with potent in vivo antitumor activity

The phosphatidylinositol 3-kinase (PI3K)/Akt/mammalian target of rapamycin inhibitor (mTOR) pathway is often constitutively activated in human tumor cells, providing unique opportunities for anticancer therapeutic intervention. NVP-BEZ235 is an imidazo[4,5-c]quinoline derivative that inhibits PI3K and mTOR kinase activity by binding to the ATP-binding cleft of these enzymes. In cellular settings using human tumor cell lines, this molecule is able to effectively and specifically block the dysfunctional activation of the PI3K pathway, inducing G(1) arrest. The cellular activity of NVP-BEZ235 translates well in in vivo models of human cancer. Thus, the compound was well tolerated, displayed disease stasis when administered orally, and enhanced the efficacy of other anticancer agents when used in in vivo combination studies. Ex vivo pharmacokinetic/pharmacodynamic analyses of tumor tissues showed a time-dependent correlation between compound concentration and PI3K/Akt pathway inhibition. Collectively, the preclinical data show that NVP-BEZ235 is a potent dual PI3K/mTOR modulator with favorable pharmaceutical properties. NVP-BEZ235 is currently in phase I clinical trials.

Essential roles of PI(3)K-p110beta in cell growth, metabolism and tumorigenesis

On activation by receptors, the ubiquitously expressed class IA isoforms (p110alpha and p110beta) of phosphatidylinositol-3-OH kinase (PI(3)K) generate lipid second messengers, which initiate multiple signal transduction cascades. Recent studies have demonstrated specific functions for p110alpha in growth factor and insulin signalling. To probe for distinct functions of p110beta, we constructed conditional knockout mice. Here we show that ablation of p110beta in the livers of the resulting mice leads to impaired insulin sensitivity and glucose homeostasis, while having little effect on phosphorylation of Akt, suggesting the involvement of a kinase-independent role of p110beta in insulin metabolic action. Using established mouse embryonic fibroblasts, we found that removal of p110beta also had little effect on Akt phosphorylation in response to stimulation by insulin and epidermal growth factor, but resulted in retarded cell proliferation. Reconstitution of p110beta-null cells with a wild-type or kinase-dead allele of p110beta demonstrated that p110beta possesses kinase-independent functions in regulating cell proliferation and trafficking. However, the kinase activity of p110beta was required for G-protein-coupled receptor signalling triggered by lysophosphatidic acid and had a function in oncogenic transformation. Most strikingly, in an animal model of prostate tumour formation induced by Pten loss, ablation of p110beta (also known as Pik3cb), but not that of p110alpha (also known as Pik3ca), impeded tumorigenesis with a concomitant diminution of Akt phosphorylation. Taken together, our findings demonstrate both kinase-dependent and kinase-independent functions for p110beta, and strongly indicate the kinase-dependent functions of p110beta as a promising target in cancer therapy.

Dysregulation of the phosphatidylinositol 3-kinase pathway in thyroid neoplasia

The phosphatidylinositol 3-kinase (PI3K) signaling pathway is an important regulator of many cellular events, including apoptosis, proliferation, and motility. Enhanced activation of this pathway can occur through several mechanisms, such as inactivation of its negative regulator, phosphatase and tensin homolog deleted on chromosome ten (PTEN), and activating mutations and gene amplification of the gene encoding the catalytic subunit of PI3K (PIK3CA). These genetic abnormalities have been particularly associated with follicular thyroid neoplasia and anaplastic thyroid cancer, suggesting an important role for PI3K signaling in these disorders. In this article, the role of PI3K pathway activation in thyroid cancer is discussed, with a focus on recent advances.

Defining the blueprint of the cancer genome

It is widely accepted that cancer is a disease caused by accumulation of mutations in specific genes. These tumor-specific mutations provide clues to the cellular processes underlying tumorigenesis and have proven useful for diagnostic and therapeutic purposes. To date, however, only a small fraction of genes has been analyzed and the number and type of alterations responsible for the development of common tumor types are unknown. The determination of the human genome sequence coupled with improvements in sequencing and bioinformatic approaches have made it possible to examine the cancer cell genome in a comprehensive and unbiased manner. Systematic sequencing studies have been performed on gene families involved in signal transduction in several tumor types, and have now been extended to include the majority of protein-coding genes in breast and colorectal cancers. These analyses have identified new genes and pathways that had not been linked previously to human cancer. One example has been the discovery of genetic alterations in the PIK3CA gene encoding p110alpha phosphatidylinositol 3-kinase and in related pathway genes in >30% of colon and breast cancers. These mutational analyses provide a window into the genetic landscape of human cancer, indicate new targets for personalized diagnostic and therapeutic intervention, and suggest lessons for future large-scale genomic analyses in human tumors.

PIK3CA-activating mutations and chemotherapy sensitivity in stage II-III breast cancer

Introduction

In vitro evidence suggests that PIK3CA (phosphatidylinositol 3-kinase, catalytic, alpha polypeptide) activation may be associated with altered chemotherapy sensitivity in cancer.

Methods

Tumor DNA from 140 patients with stage II–III breast cancer undergoing neoadjuvant chemotherapy was sequenced for PIK3CA mutations on exons 1, 9, and 20. Mutation status was correlated with clinical/pathological parameters and chemotherapy response as (a) pathological complete response (pCR) versus residual cancer or (b) quantitative residual cancer burden (RCB) scores, including stratification for estrogen receptor (ER) expression status, type of chemotherapy, and by exons.

Results

Twenty-three patients (16.4%) harbored a PIK3CA mutation, with 12, 11, and 0 mutations located in exons 9, 20, and 1, respectively. PIK3CA exon 9 mutations were more frequent among node-negative (52% versus 25%; P = 0.012) than node-positive tumors, particularly among ER-positive tumors. pCR rates and RCB scores were similar among patients with the wild-type and mutant PIK3CA genes, even after stratification by ER status, chemotherapy regimen (anthracycline versus anthracycline plus paclitaxel), or exon.

Conclusion

PIK3CA mutations are not associated with altered sensitivity to preoperative anthracycline-based or taxane-based chemotherapies in ER-positive and ER-negative breast tumors. In this study, PIK3CA mutation was associated with a decreased rate of node-positive disease, particularly among ER-positive tumors.

PIK3CA, HRAS and KRAS gene mutations in human penile cancer

PURPOSE

The knowledge of somatic mutations that arise in penile cancer is limited. We examined the dysregulation of components in the phosphatidylinositol 3-kinase and Ras pathways.

MATERIALS AND METHODS

Using single stranded conformational analysis and direct sequencing we performed mutational analysis of the PIK3CA, PTEN, HRAS, KRAS, NRAS and BRAF genes in 28 penile tumors.

RESULTS

We identified somatic missense mutations in 11 of the 28 penile cancer samples (39%). In the PIK3CA gene 8 mutations (29%) were identified that were E542K or E545K. In the HRAS gene a G12S and a Q61L mutation were found (7%). The KRAS gene contained 1 mutation (3%), that is a G12S change. PIK3CA mutations were found in all grades and stages, whereas HRAS and KRAS mutations were found in larger and more advanced tumors. The mutations were mutually exclusive, suggesting that dysregulation of either pathway is sufficient for the development and progression of penile carcinoma.

CONCLUSIONS

The high frequency of mutations in the PIK3CA, HRAS and KRAS genes leads us to believe that dysregulation of the phosphatidylinositol 3-kinase or Ras pathway is significant for the development and progression of penile carcinoma.

Taming the PI3K team to hold inflammation and cancer at bay

Recent progress in understanding the molecular mechanisms of receptor signal transduction is continuously highlighting new unforeseen potential drug targets for yet unmet therapeutic needs. While the large number of different cell surface receptors challenge the concept of antagonists development, the finding of signal transduction platforms common to multiple receptor families has boosted the development of new therapeutic approaches. The identification of the role of phosphoinositide 3-kinase family members downstream receptors as directors of multiple cellular responses ranging from cell proliferation and survival to immunity and cardiovascular control, is an example of successful drug target validation studies. This review will focus on these findings and on the ongoing efforts to tame this family of enzymes to beat inflammation and cancer.

Insights into the oncogenic effects of PIK3CA mutations from the structure of p110alpha/p85alpha

Phosphatidylinositide-3-kinases (PI3K) initiate a number of signaling pathways by recruiting other kinases, such as Akt, to the plasma membrane. One of the isoforms, PI3Kalpha, is an oncogene frequently mutated in several cancer types. These mutations increase PI3K kinase activity, leading to increased cell survival, cell motility, cell metabolism, and cell cycle progression. The structure of the complex between the catalytic subunit of PI3Kalpha, p110alpha, and a portion of its regulatory subunit, p85alpha reveals that the majority of the oncogenic mutations occur at the interfaces between p110 domains and between p110 and p85 domains. At these positions, mutations disrupt interactions resulting in changes in the kinase domain that may increase enzymatic activity. The structure also suggests that interaction with the membrane is mediated by one of the p85 domains (iSH2). These findings may provide novel structural loci for the design of new anti-cancer drugs.

PIK3CA mutation status in Japanese esophageal squamous cell carcinoma

BACKGROUND

A somatic mutation of the PIK3CA (phosphatidylinositol 3-kinase catalytic subunit) gene has been found in human cancer patients. However, this mutation has not yet been extensively studied in esophageal squamous cell carcinomas.

MATERIALS AND METHODS

We analyzed a mutation of the PIK3CA gene in 88 Japanese cases of esophageal squamous cell carcinomas that had all undergone surgery at the Department of Surgery II, Nagoya City University Medical School, between 1996 and 2003. The TE and KYSE series of cell lines are human esophageal cancer cell lines. Two PIK3CA mutation hot spots (exon 9 and exon 20) were analyzed by a real time polymerase chain reaction (PCR)-based assay and the data were confirmed by direct sequencing. We performed a cell proliferation assay to determine the effects of a PI3K inhibitor LY294002.

RESULT

In exon 9, a somatic mutation was found in two patients (2.2%) and in two cell lines. The mutations included three E545K (G1633A) mutations and one E545Q (G1633C) mutation. However, in exon 20, no mutation was observed in our esophageal cancer patients. PI3K inhibitor (LY294002) inhibited the growth of an esophageal cancer cell line with a PIK3CA mutation (E545K) in vitro.

CONCLUSIONS

We found LY294002 to reduce the proliferation of the esophageal cancer cell line in vitro. Importantly, a cell line with a PIK3CA gene mutation was more susceptible to a PI3K inhibition than those without any such mutation. Further functional analyses of the PIK3CA mutations are warranted to determine whether or not they may be potentially useful targets of therapy for esophageal cancer.

Helical domain and kinase domain mutations in p110alpha of phosphatidylinositol 3-kinase induce gain of function by different mechanisms

The phosphatidylinositol 3-kinase (PI3K) signaling pathway is up-regulated in cancer. PIK3CA, the gene coding for the catalytic subunit p110alpha of PI3K, is mutated in approximately 30% of tumors of the prostate, breast, cervix, and endometrium. The most prominent of these mutants, represented by single amino acid substitutions in the helical or kinase domain, show a gain of enzymatic function, activate AKT signaling, and induce oncogenic transformation. We have carried out a genetic and biochemical analysis of these hot-spot mutations in PIK3CA. The results of this study suggest that the helical and kinase domain mutations trigger gain of function through different mechanisms. They show different requirements for interaction with the PI3K regulatory subunit p85 and with RAS-GTP. The gain of function induced by helical domain mutations is independent of binding to p85 but requires interaction with RAS-GTP. In contrast, the kinase domain mutation is active in the absence of RAS-GTP binding but is highly dependent on the interaction with p85. We speculate that the contrasting roles of p85 and RAS-GTP in helical and kinase domain mutations reflect two distinct states of mutated p110alpha. These two states differ in mutation-induced surface charges and also may differ in conformational properties that are controlled by interactions with p85 and RAS-GTP. The two states do not appear mutually exclusive because the helical and kinase domain mutations act synergistically when present in the same p110alpha molecule. This synergism also supports the conclusion that the helical and kinase domain mutations operate by two different and independent mechanisms.

PIK3CA cancer mutations display gender and tissue specificity patterns

The occurrence of oncogenic alleles can display striking tissue specificity. For example KRAS mutations are very frequent in pancreatic cancers but relatively rare in melanomas. The opposite is true for BRAF mutations. Somatic mutations in the gene encoding for the phosphatidylinositol 3-kinase (PI3KCA) catalytic subunit, PIK3CA, occur at high frequency in many solid cancers. We have examined whether PI3K oncogenic mutations (exons 9 and 20) might exhibit gender and/or tissue specificity. By examining large cohorts of breast and colorectal cancers affecting both men and women we found that the pattern of PIK3CA mutations is distinctive. In colorectal cancers, PIK3CA (but not KRAS, APC, or TP53) mutations display a gender bias occurring at higher frequencies in women. We also found that male breast cancers display PIK3CA mutations at an overall frequency similar to that observed in female breast tumors. In male breast cancers, however, PIK3CA mutations are found mainly in exon 20. We conclude that PI3KCA mutations affecting exons 9 and 20 display gender- and tissue-specific patterns, thus suggesting that the different amino acid changes could exert distinct functional effects on the oncogenic properties of this enzyme. Furthermore, we propose that sexual dimorphisms and tissue specific factors might directly or indirectly influence the occurrence of PI3KCA cancer alleles.

PIK3CA exon 20 mutation is independently associated with a poor prognosis in breast cancer patients

BACKGROUND

Prognostic factors that could select breast cancer patients with poor survival, and influence clinical trials of targeted therapy, are needed. However, the reported observations regarding the impact of PI3KCA mutation on breast cancers are controversial.

METHODS

We analyzed exons 4, 7, 9, and 20 of PI3KCA on a series of 158 patients. Clinicopathological characteristics were correlated with the mutation data.

RESULTS

Among 152 patients who were available for follow-up (median follow-up time, 6.57 years), 26% had PIK3CA mutations, more than half of which occurred in exon 20. The five-year survival rate of patients with exon 20 mutations (46%) was significantly lower than that of patients without (75%) (p = 0.0054). Multivariate analysis showed that PIK3CA exon 20 mutations and nodal involvement were independent risk factors for overall survival. The relative risk of death in patients with PIK3CA exon 20 mutations was 2.881 (95% CI, 1.406-5.900; p = 0.0038).

CONCLUSIONS

PIK3CA mutations are common in invasive ductal carcinomas of the breast. Our result suggests that PIK3CA exon 20 mutation is an independent risk factor for poor prognosis in breast cancer patients, indicating that differences in patient numbers with PIK3CA exon 20 mutations in study and control arms should be avoided in clinical trials of PI3K inhibitors.

Biochemical and biological characterization of tumor-associated mutations of p110alpha

Signaling by class I phosphatidylinositol 3-kinase (PI3K) controls cell growth, replication, motility, and metabolism. The PI3K pathway commonly shows gain of function in cancer. Two small GTPases, Rheb (Ras homolog enriched in brain) and Ras (rat sarcoma viral oncogene), play important roles in PI3K signaling. Rheb activates the TOR (target of rapamycin) kinase in a GTP-dependent manner; it links TOR to upstream signaling components, including the tuberous sclerosis complex (TSC) and Akt (homolog of the Akt8 murine lymphoma viral oncoprotein). Constitutively active, GTP-bound Rheb is oncogenic in cell culture, and activity that requires farnesylation. Ras activates PI3K by recruitment to the plasma membrane and possibly by inducing a conformational change in the catalytic subunit p110 of PI3K. In return, Ras signaling through the MAP kinase (MAPK) pathway is activated by PIP(3), the product of PI3K. Loss of Ras function can interfere with PI3K signaling. Various lines of evidence suggest complementary roles for PI3K and MAPK signaling in oncogenesis.

The structure of a human p110alpha/p85alpha complex elucidates the effects of oncogenic PI3Kalpha mutations

PIK3CA, one of the two most frequently mutated oncogenes in human tumors, codes for p110alpha, the catalytic subunit of a phosphatidylinositol 3-kinase, isoform alpha (PI3Kalpha, p110alpha/p85). Here, we report a 3.0 angstrom resolution structure of a complex between p110alpha and a polypeptide containing the p110alpha-binding domains of p85alpha, a protein required for its enzymatic activity. The structure shows that many of the mutations occur at residues lying at the interfaces between p110alpha and p85alpha or between the kinase domain of p110alpha and other domains within the catalytic subunit. Disruptions of these interactions are likely to affect the regulation of kinase activity by p85 or the catalytic activity of the enzyme, respectively. In addition to providing new insights about the structure of PI3Kalpha, these results suggest specific mechanisms for the effect of oncogenic mutations in p110alpha and p85alpha.

Imidazo[4,5-c]quinolines as inhibitors of the PI3K/PKB-pathway

Imidazo[4,5-c]quinoline derivatives have been discovered and developed as potent and effective modulators of the phosphatidylinositol 3-kinase (PI3K)/protein kinase B (PKB) pathway to lead to clinical development candidates. The SAR data of representative examples of this compound class and their biological profiling in cellular and in vivo settings are presented and discussed.

Comprehensive analysis of oncogenic effects of PIK3CA mutations in human mammary epithelial cells

More than 20 different PIK3CA gene mutations were identified in breast cancer with different frequencies. Whether these breast cancer associated mutations have similar biological effects is largely unknown. In this study, we established a novel cell model using the lentivirus system to express 10 different PIK3CA genes (wild type and mutant) based on the human mammary epithelial cell MCF10A. We found that nine different PIK3CA mutants harbor different abilities to promote cell proliferation and EGF independent growth. In addition, most PIK3CA mutants (except for the wild type PIK3CA, the Q60K and the K111N mutants) had the ability to change the morphogenesis of the MCF10A cell in 3D Matrigel assay. Moreover, different PIK3CA mutants have different abilities to promote colony formation and cell invasion. We further observed that most of the PIK3CA mutants could activate p-AKT and p-p70-S6K in the absence of EGF stimulation. Finally, LY294002, a PI3K inhibitor, can effectively inhibit cell growth in cell lines with different PIK3CAs. Taken together, our results support the notion that different PIK3CA mutations differentially contribute to breast cancer transformation, and exploration of the therapeutic application of these mutations will benefit breast cancer patients with the PIK3CA mutations.

Mutations of the PIK3CA gene in hereditary colorectal cancers

Somatic mutations of the PIK3CA gene have recently been detected in various human cancers, including sporadic colorectal cancer. However, mutations of the PIK3CA gene in hereditary colorectal cancers have not been clarified. To elucidate the mutation status in familial adenomatous polyposis (FAP) and hereditary nonpolyposis colorectal cancer (HNPCC), which are the most common hereditary colorectal cancers, we investigated PIK3CA mutations in 163 colorectal tumors, including adenomas, intramucosal carcinomas and invasive carcinomas. For comparison, we also analyzed mutations of the same gene in 160 sporadic colorectal tumors at various histopathological stages. Analysis at exons 1, 7, 9 and 20 of the PIK3CA gene revealed somatic mutations in 21% (8 of 39) of FAP invasive carcinomas, 21% (7 of 34) of HNPCC invasive carcinomas, 15% (8 of 52) of sporadic invasive carcinomas, and 14% (7 of 50) of sporadic colorectal metastases in the liver. Mutations in FAP and HNPCC carcinomas predominantly occurred in the kinase domain (exon 20), while the majority of mutations in sporadic cases occurred in the helical domain (exon 9). Adenomas and intramucosal carcinomas from all patients exhibited no mutations (0 of 148). Our data suggest that PIK3CA mutations contribute to the invasion step from intramucosal carcinoma to invasive carcinoma in colorectal carcinogenesis in FAP and HNPCC patients at a similar extent to that seen in sporadic patients.

PIK3CA mutations and PTEN loss correlate with similar prognostic factors and are not mutually exclusive in breast cancer

PURPOSE

The phosphatidylinositol 3'-kinase/Akt pathway is frequently altered in breast cancer. PTEN, a phosphatase that opposes the effect of phosphatidylinositol 3'-kinase, can be mutated or lost, whereas the PIK3CA gene is mutated. These have been proposed as alternative mechanisms, and their clinicalpathology significance is under discussion. In this study, we aimed to explore whether PIK3CA mutations and PTEN loss are mutually exclusive mechanisms, correlate with other known clinicopathologic markers, or have clinical implication in breast cancer.

EXPERIMENTAL DESIGN

Exons 9 and 20 of the PIK3CA gene were analyzed in 270 breast tumors, and mutations were detected by single-stranded conformational analysis followed by sequencing. The expression of PTEN was evaluated by immunohistochemistry in 201 tumors.

RESULTS

PIK3CA mutations were found in 24% of the tumors and associated with estrogen receptor(+) status, small size, negative HER2 status, high Akt1, and high cyclin D1 protein expression. PTEN was negative in 37% of the cases and PTEN loss was associated with PIK3CA mutations (P = 0.0024). Tumors presenting PTEN loss or both alterations were often estrogen receptor(+), small in size, and HER2(-). PIK3CA mutations predicted for longer local recurrence-free survival. Moreover, PTEN loss by itself or combined with mutated PIK3CA tended to confer radiosensitivity. In addition, the patients with high S-phase fraction had longer recurrence-free survival if they carried mutations in the PIK3CA gene and/or had lost PTEN, whereas the same alterations were associated with shorter recurrence-free survival among patients with low S-phase fraction.

CONCLUSIONS

PIK3CA mutations and PTEN loss were not mutually exclusive events and associated with similar prognostic factors.

PIK3CA mutation and amplification in human lung cancer

To explore the significance of phosphatidylinositol-3-kinase, catalytic, alpha (PIK3CA) in the carcinogenesis in human lung, mutations and copy number changes were investigated in 148 Japanese patients with primary cancer of the lung. For biological validation, the effects of exogenously expressed wild-type and mutated PIK3CA were studied in an immortalized human airway epithelial cell line. Mutations in PIK3CA were found in five (3.6%) of the 139 available patients, and copy number gains were found in 21 (18.3%) of 115 patients, respectively. Overall, mutations or copy number gains were detected in 24 of the 106 patients (22.6%) for whom results in both analyses were available. The prevalence of copy number gains was higher in men, smokers, and in patients with squamous cell carcinoma than in the opposite categories. The copy number changes showed a trend toward higher prevalence in the earlier stages (P = 0.038). Interestingly, the presence of mutations and of copy number alterations were mutually exclusive in the present patients, implying that both entail equivalent oncogenic potential. Over-expressed wild-type PIK3CA and its two common mutants, K545E and H1047R, significantly enhanced the anchorage-independent growth activity and migration activity of immortalized airway epithelium 16HBE14o- cells, but the effects of the K545E and H1047R mutants were more remarkable than those of the wild-type. The present demonstrates an important role of PIK3CA in human lung carcinogenesis.

Dissecting the Akt/mammalian target of rapamycin signaling network: emerging results from the head and neck cancer tissue array initiative

PURPOSE

As an approach to evaluate the expression pattern and status of activation of signaling pathways in clinical specimens from head and neck squamous cell carcinoma (HNSCC) patients, we established the Head and Neck Cancer Tissue Array Initiative, an international consortium aimed at developing a high-density HNSCC tissue microarray, with a high representation of oral squamous cell carcinoma.

EXPERIMENTAL DESIGN

These tissue arrays were constructed by acquiring cylindrical biopsies from multiple individual tumor tissues and transferring them into tissue microarray blocks. From a total of 1,300 cases, 547 cores, including controls, were selected and used to build the array.

RESULTS

Emerging information by the use of phosphospecific antibodies detecting the activated state of signaling molecules indicates that the Akt-mammalian target of rapamycin (mTOR) pathway is frequently activated in HNSCC, but independently from the activation of epidermal growth factor receptor or the detection of mutant p53. Indeed, we identified a large group of tissue samples displaying active Akt and mTOR in the absence of epidermal growth factor receptor activation. Furthermore, we have also identified a small subgroup of patients in which the mTOR pathway is activated but not Akt, suggesting the existence of an Akt-independent signaling route stimulating mTOR.

CONCLUSIONS

These findings provide important information about the nature of the dysregulated signaling networks in HNSCC and may also provide the rationale for the future development of novel mechanism-based therapies for HNSCC patients.

Oncogenic PIK3CA mutations occur in epidermal nevi and seborrheic keratoses with a characteristic mutation pattern

Activating mutations of the p110 alpha subunit of PI3K (PIK3CA) oncogene have been identified in a broad spectrum of malignant tumors. However, their role in benign or preneoplastic conditions is unknown. Activating FGF receptor 3 (FGFR3) mutations are common in benign skin lesions, either as embryonic mutations in epidermal nevi (EN) or as somatic mutations in seborrheic keratoses (SK). FGFR3 mutations are also common in low-grade malignant bladder tumors, where they often occur in association with PIK3CA mutations. Therefore, we examined exons 9 and 20 of PIK3CA and FGFR3 hotspot mutations in EN (n = 33) and SK (n = 62), two proliferative skin lesions lacking malignant potential. Nine of 33 (27%) EN harbored PIK3CA mutations; all cases showed the E545G substitution, which is uncommon in cancers. In EN, R248C was the only FGFR3 mutation identified. By contrast, 10 of 62 (16%) SK revealed the typical cancer-associated PIK3CA mutations E542K, E545K, and H1047R. The same lesions displayed a wide range of FGFR3 mutations. Corresponding unaffected tissue was available for four EN and two mutant SK: all control samples displayed a WT sequence, confirming the somatic nature of the mutations found in lesional tissue. Forty of 95 (42%) lesions showed at least one mutation in either gene. PIK3CA and FGFR3 mutations displayed an independent distribution; 5/95 lesions harbored mutations in both genes. Our findings suggest that, in addition to their role in cancer, oncogenic PIK3CA mutations contribute to the pathogenesis of skin tumors lacking malignant potential. The remarkable genotype-phenotype correlation as observed in this study points to a distinct etiopathogenesis of the mutations in keratinocytes occuring either during fetal development or in adult life.

PTEN, more than the AKT pathway

Phosphatase and tensin homolog deleted on chromosome 10 (PTEN)/phosphatidylinositol 3-kinase (PI3K)/AKT constitute an important pathway regulating the signaling of multiple biological processes such as apoptosis, metabolism, cell proliferation and cell growth. PTEN is a dual protein/lipid phosphatase and its main substrate phosphatidyl-inositol 3,4,5 triphosphate (PIP3) is the product of PI3K. Increase in PIP3 recruits AKT to the membrane where is activated by other kinases also dependent on PIP3. Many components of this pathway have been described as causal forces in cancer. PTEN activity is lost by mutations, deletions or promoter methylation silencing at high frequency in many primary and metastatic human cancers. Germ line mutations of PTEN are found in several familial cancer predisposition syndromes. Recently, many activating mutations in the PI3KCA gene (coding for the p110alpha catalytic subunit of PI3K) have been described in human tumors. Activation of PI3K and AKT are reported to occur in breast, ovarian, pancreatic, esophageal and other cancers. Genetically modified mice confirm these PTEN activities. Tissue-specific deletions of PTEN usually provoke cancer. Moreover, an absence of PTEN cooperates with an absence of p53 to promote cancer. However, we have observed very different results with the expression of activated versions of AKT in several tissues. Activated AKT transgenic lines do not develop tumors in breast or prostate tissues and do not cooperate with an absence of p53. This data suggest that an AKT-independent mechanism contributes to PTEN tumorigenesis. Crosses with transgenic mice expressing possible PTEN targets indicate that neither cyclin D1 nor p53 are these AKT-independent targets. However, AKT is more than a passive bridge toward PTEN tumorigenesis, since its expression not only allows but also enforces and accelerates the tumorigenic process in combination with other oncogenes.

Cancer-specific mutations in phosphatidylinositol 3-kinase

Cancer-specific mutations in the catalytic subunit of phosphatidylinositol 3-kinase (PI3K) p110 alpha occur in diverse tumors in frequencies that can exceed 30%. The majority of these mutations map to one of three hot spots in the gene, and the rest are distributed over much of the PI3K coding sequence. Most of the cancer-specific mutations induce a gain of function that results in oncogenicity, elevated lipid kinase activity and constitutive signaling through the kinases Akt and TOR. The location of the mutations on a model structure of p110 alpha indicates several distinct mechanisms for the gain of function. The mutated p110 alpha proteins are promising cancer targets. Although identification of mutant-specific small-molecule inhibitors seems technically challenging, the therapeutic benefits from such inhibitors could be extremely important.

Overexpression of p101 activates PI3Kgamma signaling in T cells and contributes to cell survival

p101, the regulatory subunit of phosphatidylinositol-3-kinase-gamma (PI3Kgamma), was recently reported as a common site of retroviral insertion in T-cell lymphomas induced in mice by MoFe2-MuLV, a unique recombinant gammaretrovirus. The common interruption of p101 by retroviral integration suggests that the locus encodes an oncogene whose altered expression is related to the induction of T-cell malignancy. To examine a possible role in the malignant process, p101 was overexpressed in human T-cell lines Molt-4 and Jurkat. Transient overexpression of p101 induced apoptosis in recipient cells; however, stable expression could be established in cells that expressed moderate levels of p101. Constitutive p101 overexpression in those cells conferred significant protection against ultraviolet-induced apoptosis. Protection against apoptotic induction was attributed to p101-mediated activation of the Akt pathway. Constitutive overexpression of p101 enhanced the activity of p110gamma and further sensitized it to activation upon stimulation of G protein-coupled receptor. These findings are the first to implicate altered expression of p101 in malignancy, specifically in T-cell lymphoma. The findings further provide insight into the regulation of p110gamma, indicating that the stoichiometry of p110gamma and p101 are important in regulating PI3Kgamma signaling.

Phosphatidylinositol-3-OH kinase or RAS pathway mutations in human breast cancer cell lines

Constitutive activation of the phosphatidylinositol-3-OH kinase (PI3K) and RAS signaling pathways are important events in tumor formation. This is illustrated by the frequent genetic alteration of several key players from these pathways in a wide variety of human cancers. Here, we report a detailed sequence analysis of the PTEN, PIK3CA, KRAS, HRAS, NRAS, and BRAF genes in a collection of 40 human breast cancer cell lines. We identified a surprisingly large proportion of cell lines with mutations in the PI3K or RAS pathways (54% and 25%, respectively), with mutants for each of the six genes. The PIK3CA, KRAS, and BRAF mutation spectra of the breast cancer cell lines were similar to those of colorectal cancers. Unlike in colorectal cancers, however, mutational activation of the PI3K pathway was mutually exclusive with mutational activation of the RAS pathway in all but 1 of 30 mutant breast cancer cell lines (P = 0.001). These results suggest that there is a fine distinction between the signaling activators and downstream effectors of the oncogenic PI3K and RAS pathways in breast epithelium and those in other tissues.

Rare cancer-specific mutations in PIK3CA show gain of function

Fifteen rare cancer-derived mutants of PIK3CA, the gene coding for the catalytic subunit p110alpha of phosphatidylinositol 3-kinase (PI3K), were examined for their biological and biochemical properties. Fourteen of these mutants show a gain of function: they induce rapamycin-sensitive oncogenic transformation of chicken embryo fibroblasts, constitutively activate Akt and TOR-mediated signaling, and show enhanced lipid kinase activity. Mapping of these mutants on a partial structural model of p110alpha suggests three groups of mutants, defined by their location in distinct functional domains of the protein. We hypothesize that each of these three groups induces a gain of PI3K function by a different molecular mechanism. Mutants in the C2 domain increase the positive surface charge of this domain and therefore may enhance the recruitment of p110alpha to cellular membranes. Mutants in the helical domain map to a contiguous surface of the protein and may affect the interaction with other protein(s). Mutants in the kinase domain are located near the hinge of the activation loop. They may alter the position and mobility of the activation loop. Arbitrarily introduced mutations that have no detectable phenotype map either to the interior of the protein or are positioned on a surface region that lies opposite to the exposed surfaces containing gain-of-function mutants. Engineered mutants that exchange acidic or neutral residues for basic residues on the critical surfaces show a gain of function.

PIK3CA gene mutations in pediatric and adult glioblastoma multiforme

The phosphatidylinositol 3-kinases (PI3K) are a family of enzymes that relay important cellular growth control signals. Recently, a large-scale mutational analysis of eight PI3K and eight PI3K-like genes revealed somatic mutations in PIK3CA, which encodes the p110alpha catalytic subunit of class IA PI3K, in several types of cancer, including glioblastoma multiforme. In that report, 4 of 15 (27%) glioblastomas contained potentially oncogenic PIK3CA mutations. Subsequent studies, however, showed a significantly lower mutation rate ranging from 0% to 7%. Given this disparity and to address the relation of patient age to mutation frequency, we examined 10 exons of PIK3CA in 73 glioblastoma samples by PCR amplification followed by direct DNA sequencing. Overall, PIK3CA mutations were found in 11 (15%) samples, including several novel mutations. PIK3CA mutations were distributed in all sample types, with 18%, 9%, and 13% of primary tumors, xenografts, and cell lines containing mutations, respectively. Of the primary tumors, PIK3CA mutations were identified in 21% and 17% of pediatric and adult samples, respectively. No evidence of PIK3CA gene amplification was detected by quantitative real-time PCR in any of the samples. This study confirms that PIK3CA mutations occur in a significant number of human glioblastomas, further indicating that therapeutic targeting of this pathway in glioblastomas is of value. Moreover, this is the first study showing PIK3CA mutations in pediatric glioblastomas, thus providing a molecular target in this important pediatric malignancy.

Point mutations of protein kinases and individualised cancer therapy

The treatment of cancer is rapidly changing, with an increasing focus on converting our improved understanding of the molecular basis of disease into clinical benefit for patients. Protein kinases that are mutated in cancer represent attractive targets, as they may result in cellular dependency on the mutant kinase or its associated pathway for survival, a condition known as 'oncogene addiction'. Early clinical experiences have demonstrated dramatic clinical benefit of targeting oncogenic mutations in diseases that have been largely resistant to traditional cytotoxic chemotherapy. Further, mutational activation of kinases can indicate which patients are likely to respond to targeted therapeutics. However, these experiences have also illuminated a number of critical challenges that will have to be addressed in the development of effective drugs across different cancers, to fully realise the potential of individualised molecular therapy. This review utilises examples of genetic activation of kinases to illustrate many of the lessons learned, as well as those yet to be implemented.

Inhibition of the phosphatidylinositol 3-kinase/mammalian target of rapamycin pathway in hematologic malignancies

The phosphatidylinositol 3-kinase (PI3-K)/mammalian target of rapamycin (mTOR) signal transduction pathway integrates signals from multiple receptor tyrosine kinases to control cell proliferation and survival. Key components of the pathway are the lipid kinase PI3-K, the small guanosine triphosphate-binding protein Rheb, and the protein kinases Akt and mTOR. Important natural inhibitors of the pathway include the lipid phosphatase PTEN and the tuberous sclerosis complex. Several components of this pathway are targeted by investigational antineoplastic agents. Rapamycin (sirolimus), the prototypic mTOR inhibitor, exhibits activity in acute myeloid leukemia. Three rapamycin analogs, temsirolimus, everolimus, and AP23573, are in clinical trials for various hematologic malignancies. Temsirolimus has produced a 38% overall response rate in relapsed mantle cell lymphoma, and AP23573 has demonstrated activity in acute leukemia. Everolimus is undergoing clinical testing in lymphoma (Hodgkin and non-Hodgkin) and multiple myeloma. In addition, perifosine, an inhibitor of Akt activation that exhibits substantial antimyeloma activity in preclinical models, is being examined in relapsed multiple myeloma. Based on results obtained to date, it appears that inhibitors of the PI3-K/mTOR pathway hold promise as single agents and in combination for hematologic malignancies.

PIK3CA mutation status in Japanese lung cancer patients

Somatic mutations of the PIK3CA (phosphatidylinostitol 3-kinase catalytic subunit) gene have been found in human cancer patients. Previous reports suggested that about 4% of lung cancers harbored PIK3CA gene mutations. However, the clinico-pathological background for PIK3CA gene mutations has not yet been investigated in lung cancer. We have genotyped the PIK3CA gene in Japanese lung cancer patients. The study included 235 lung cancer cases surgically removed in Nagoya City University Hospital. The two PIK3CA mutation hot spots (exon 9 and exon 20) were analyzed by real time polymerase chain reaction (PCR)-based assay. The data were confirmed by direct sequencing. In exon 9, somatic mutation was found in eight patients (3.4%). The mutation included three E542K (G1624A), three E545K (G1633A), one E542Q (G1624C), and one Q546K (C1636A). However, in exon 20, there was no mutation in our lung cancer patients. PIK3CA mutations were not correlated with gender (women versus men, p=0.4162), age (< or =60 versus >60, p=0.8027), or smoking status of the lung cancers (never versus smoker, p=0.5666). PIK3CA mutation incidence was significantly lower in adenocarcinoma (2/135, 1.5%) than in squamous cell carcinoma (5/77, 6.5%, p=0.0495). Among eight patients with a PIK3CA mutation, three patients also harbored an EGFR somatic mutation. PIK3CA gene mutations were rare in lung cancer; rarer in adenocarcinoma. Further functional analyses of the PIK3CA mutations are warranted to study if they could be the target of therapy for the lung cancer.

PIK3CA and PTEN mutations in uterine endometrioid carcinoma and complex atypical hyperplasia

PURPOSE

The tumor suppressor PTEN gene and the PIK3CA oncogene are frequently mutated in uterine endometrioid carcinoma (UEC). PTEN mutations are also common in complex atypical hyperplasia (CAH), the precursor lesion of UEC. The status of PIK3CA has not yet been explored in CAH. In this study, we evaluated both CAH and UEC for PTEN and PIK3CA mutations.

EXPERIMENTAL DESIGN

Neoplastic tissue was microdissected, and DNA was extracted from 29 cases of CAH. DNA was available from 44 UEC cases previously characterized for PTEN mutations. Direct DNA sequencing of exons 9 and 20 of the PIK3CA gene was done on all 73 cases. In addition, CAH cases were analyzed for PTEN mutations. Statistical analyses were done using the Fisher's exact test.

RESULTS

Two (7%) of 29 CAH and 17 (39%) of 44 UEC cases contained a PIK3CA mutation (P = 0.003). Fourteen (48%) of 29 CAH cases had a PTEN mutation, but none contained both a PTEN and PIK3CA mutation. Twenty-five (57%) of 44 UEC cases had a PTEN mutation, and 12 (48%) of these 25 cases also contained a PIK3CA mutation. Coexistent PIK3CA and PTEN mutations were significantly correlated with UEC compared with CAH (P = 0.002), but the association in UEC did not reach statistical significance (P = 0.21).

CONCLUSIONS

PIK3CA is the most commonly mutated oncogene in UEC; however, mutations are uncommon in CAH. Thus, mutations in PIK3CA, unlike PTEN mutations, are associated with invasion. These findings suggest that mutations in PIK3CA may serve as a marker of invasion with potential clinical use. Furthermore, PIK3CA and PTEN mutations may play distinct roles in endometrial tumorigenesis.

PIK3CA mutations are an early genetic alteration associated with FGFR3 mutations in superficial papillary bladder tumors

Bladder tumors constitute a very heterogeneous disease. Superficial tumors are characterized by a high prevalence of FGFR3 mutations and chromosome 9 alterations. High-grade and muscle-invasive tumors are characterized by Tp53 mutations and aneuploidy. We have analyzed the sequence of exons 9 and 20 of PIK3CA in a panel of bladder tumors covering the whole spectrum of the disease. DNA from formalin-fixed, paraffin-embedded tumor sections was amplified by PCR and products were sequenced. In an unselected panel of tumors representative of the disease, the PIK3CA mutation prevalence was 13% (11 of 87). Mutations occurred mainly at the previously identified hotspots (codons 542, 545, 1007, and 1047). The distribution according to stage was as follows: papillary urothelial neoplasms of uncertain malignant potential (PUNLMP; 11 of 43, 25.6%), T(a) (9 of 57, 16%), T(1) (2 of 10, 20%), and muscle-invasive tumors (0 of 20, 0%; P = 0.019). Mutations were associated with low-grade tumors: grade 1 (6 of 27, 22.2%), grade 2 (3 of 23, 13%), and grade 3 (2 of 37, 5.4%; P = 0.047). Overall, PIK3CA mutations were strongly associated with FGFR3 mutations: 18 of 69 (26%) FGFR3(mut) tumors were PIK3CA(mut), versus 4 of 58 (6.9%) FGFR3(wt) tumors (P = 0.005). Our findings indicate that PIK3CA mutations are a common event that can occur early in bladder carcinogenesis and support the notion that papillary and muscle-invasive tumors arise through different molecular pathways. PIK3CA may constitute a novel diagnostic and prognostic tool, as well as a therapeutic target, in bladder cancer.

Analyzing phosphoinositides and their interacting proteins

Phosphorylated derivatives of phosphatidylinositol (PtdIns), known as phosphoinositides (PIs), are essential regulators of nuclear functions, cytoskeletal dynamics, cell signaling and membrane trafficking. These lipids are found on the cytosolic face of intracellular membranes but can also be detected in membrane-free regions of the nucleoplasm. Their downstream effectors include several proteins that contain various PI-specific domains. Because impaired PI metabolism is associated with disorders such as cancer, cardiovascular disease and immune dysfunction, there is currently great interest in studying PIs and their metabolic enzymes. Here we describe strategies and techniques for quantitative and qualitative measurement of PIs, for characterization of specific PI-binding proteins and for determination of PI kinase and phosphatase activities in vitro and in vivo.

Kinase inhibitors: vice becomes virtue

In this issue of Cancer Cell, Fan and coworkers describe a novel inhibitor of PI3 kinase (PI3K) that potently interferes with the growth of glioma cells. They show that the efficacy of this inhibitor results from dual, synergistic activity against the p110alpha subunit of PI3K and against TOR. Although p110alpha and TOR belong to the same signaling pathway, they both must be inactivated because of the need to silence the regulatory feedback loop that remains unaffected by monospecific inhibitors. The new PI3K inhibitor achieves the effects of combination therapy as a single agent by fortuitously hitting two critical targets.

The detection and prognosis of small pancreatic carcinoma

During a period of 16 years, 203 proven pancreatic ductal adenocarcinomas were studied. Tumor size was measured on either the resected or the autopsy specimen. Four tumors were smaller than 1 cm, and 17 tumors were between 1.1 and 2 cm. ERCP has been found to be the most accurate in the diagnosis of small pancreatic carcinoma. Followup of 44 patients in whom the tumor was resected showed that survival depended on tumor size. In four patients with tumors smaller than 1 cm without parenchymal invasion, the postoperative 5-yr cumulative survival rate was 100%. Pancreatic carcinoma smaller than 1 cm limited to duct epithelium is considered as early cancer. Various diagnostic imaging modalities are now available to evaluate patients in whom pancreatic carcinoma is clinically suspected. These include ultrasonography (US), computed tomography (CT), endoscopic retrograde cholangiopancreatography (ERCP), and angiography. More recently magnetic resonance imaging (MRI), endoscopic ultrasound (EUS), and peroral pancreatic ductal biopsy also have been used. This report compares diagnostic modalities for pancreatic carcinoma in order to provide a data base for their rational use in the diagnosis of small resectable pancreatic carcinomas.