TERT promoter mutations and monoallelic activation of TERT in cancer

Here we report that promoter mutations in telomerase (TERT), the most common noncoding mutations in cancer, give rise to monoallelic expression of TERT. Through deep RNA sequencing, we find that TERT activation in human cancer cell lines can occur in either mono- or biallelic manner. Without exception, hotspot TERT promoter mutations lead to the re-expression of only one allele, accounting for approximately half of the observed cases of monoallelic TERT expression. Furthermore, we show that monoallelic TERT expression is highly prevalent in certain tumor types and widespread across a broad spectrum of cancers. Taken together, these observations provide insights into the mechanisms of TERT activation and the ramifications of noncoding mutations in cancer.

Successful whole-exome sequencing from a prostate cancer bone metastasis biopsy

BACKGROUND

Comprehensive molecular characterization of cancer that has metastasized to bone has proved challenging, which may limit the diagnostic and potential therapeutic opportunities for patients with bone-only metastatic disease.

METHODS

We describe successful tissue acquisition, DNA extraction, and whole-exome sequencing from a bone metastasis of a patient with metastatic, castration-resistant prostate cancer (PCa).

RESULTS

The resulting high-quality tumor sequencing identified plausibly actionable somatic genomic alterations that dysregulate the phosphoinostide 3-kinase pathway, as well as a theoretically actionable germline variant in the BRCA2 gene.

CONCLUSIONS

We demonstrate the feasibility of diagnostic bone metastases profiling and analysis that will be required for the widespread application of prospective 'precision medicine' to men with advanced PCa.

Oncogenic and drug-sensitive NTRK1 rearrangements in lung cancer

We identified new gene fusions in patients with lung cancer harboring the kinase domain of the NTRK1 gene that encodes the high-affinity nerve growth factor receptor (TRKA protein). Both the MPRIP-NTRK1 and CD74-NTRK1 fusions lead to constitutive TRKA kinase activity and are oncogenic. Treatment of cells expressing NTRK1 fusions with inhibitors of TRKA kinase activity inhibited autophosphorylation of TRKA and cell growth. Tumor samples from 3 of 91 patients with lung cancer (3.3%) without known oncogenic alterations assayed by next-generation sequencing or fluorescence in situ hybridization demonstrated evidence of NTRK1 gene fusions.

S3-4: ER Downregulation with Fulvestrant in Combination with pan-PI3K Inhibitor BKM120 Synergizes Against ER+/PI3K-Mutant Breast Cancer Xenografts In Vivo

ER+ breast cancers typically respond to aromatase inhibitors (AIs), but a significant fraction exhibit de novo or acquired resistance. To discover mechanisms of resistance to AIs, we maintained four ER+, hormone-dependent human breast cancer cell lines in hormone-depleted conditions for several months until estrogen-independent populations emerged (termed long-term estrogen-deprived, LTED). A siRNA kinome screen identified 42 kinases that suppressed hormone-independent MCF-7/LTED cell growth ≥33% (p<0.05). Pathway analysis revealed phosphatidylinositol 3-kinase (PI3K) as a central hub which integrates signaling from, or emits signaling to many of these 42 kinases. Further, treatment with the PI3K/mTOR dual inhibitor BEZ235 or the pan-PI3K inhibitor BKM120 suppressed LTED cell growth, and prevented the emergence of hormone-independent cells.

Activating mutations in PIK3CA, the gene encoding the p110α catalytic subunit of PI3K, are present in about 35% of ER+ breast cancers. We investigated whether PIK3CA mutations modify the tumor response to estrogen deprivation with letrozole in a pre-surgical clinical trial (NCT00651976). Twenty-one patients with stage I-II operable ER+/HER2− breast cancer were treated with letrozole for 10–21 days up to 24 h prior to surgery. Core tumor biopsies were obtained before treatment and at the time of surgical resection. Ki67 immunohistochemistry (IHC) was scored in pre- and post-letrozole specimens. The change in natural log of the Ki67 score between pre-and post-treatment samples was stratified by PIK3CA mutant vs. wildtype (WT) status. PIK3CA-mutant tumors exhibited a statistically lower reduction in Ki67 score compared to tumors with WT PIK3CA (p=0.03). These findings suggest that mutational activation of PI3K attenuates the response to estrogen deprivation.

In some LTED cell lines, downregulation of ER with fulvestrant or siRNA inhibited estrogen-independent growth, suggesting that the unliganded ER can maintain proliferation of cells adapted to estrogen deprivation. Prior work suggested that PI3K-ER crosstalk promotes resistance to estrogen deprivation. However, inhibition of PI3K/AKT/TORC1 signaling did not alter ERS167 phosphorylation in LTED cells, and ER downregulation with fulvestrant did not inhibit PI3K/AKT, suggesting that PI3K and ER modulate non-overlapping pathways in cells adapted to estrogen deprivation. Treatment with BKM120 synergized with fulvestrant to inhibit the growth of 6/8 ER+ breast cancer cell lines in estrogen-depleted conditions. Treatment with single-agent fulvestrant or BKM120 in athymic mice devoid of estrogen supplementation partially inhibited the growth of ER+/PI3K-mutant MCF-7 xenografts, while the combination induced near-complete tumor regression. IHC analysis showed increased cleaved caspase-3+ cells in BKM120-treated tumors and decreased Ki67+ cells in fulvestrant-treated tumors, implying that the combination induced tumor regression by both inhibition of tumor cell proliferation and induction of apoptosis. These data suggest that upon progression on an aromatase inhibitor, patients with ER+/PI3K-mutant breast cancer would benefit from a combination of an ER downregulator and a PI3K pathway inhibitor.

Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr S3-4.

Integrated genomic profiling of endometrial carcinoma associates aggressive tumors with indicators of PI3 kinase activation

Although 75% of endometrial cancers are treated at an early stage, 15% to 20% of these recur. We performed an integrated analysis of genome-wide expression and copy-number data for primary endometrial carcinomas with extensive clinical and histopathological data to detect features predictive of recurrent disease. Unsupervised analysis of the expression data distinguished 2 major clusters with strikingly different phenotypes, including significant differences in disease-free survival. To identify possible mechanisms for these differences, we performed a global genomic survey of amplifications, deletions, and loss of heterozygosity, which identified 11 significantly amplified and 13 significantly deleted regions. Amplifications of 3q26.32 harboring the oncogene PIK3CA were associated with poor prognosis and segregated with the aggressive transcriptional cluster. Moreover, samples with PIK3CA amplification carried signatures associated with in vitro activation of PI3 kinase (PI3K), a signature that was shared by aggressive tumors without PIK3CA amplification. Tumors with loss of PTEN expression or PIK3CA overexpression that did not have PIK3CA amplification also shared the PI3K activation signature, high protein expression of the PI3K pathway member STMN1, and an aggressive phenotype in test and validation datasets. However, mutations of PTEN or PIK3CA were not associated with the same expression profile or aggressive phenotype. STMN1 expression had independent prognostic value. The results affirm the utility of systematic characterization of the cancer genome in clinically annotated specimens and suggest the particular importance of the PI3K pathway in patients who have aggressive endometrial cancer.

"Lineage addiction" in human cancer: lessons from integrated genomics

Genome-era advances in the field of oncology endorse the notion that many tumors may prove vulnerable to targeted therapeutic avenues once their salient molecular alterations are elucidated. Accomplishing this requires both detailed genomic characterization and the ability to identify in situ the critical dependencies operant within individual tumors. To this end, DNA microarray platforms such as high-density single-nucleotide polymorphism (SNP) arrays enable large-scale cancer genome characterization, including copy number and loss-of-heterozygosity analyses at high resolution. Clustering analyses of SNP array data from a large collection of tumor samples and cell lines suggest that certain copy number alterations correlate strongly with the tissue of origin. Such lineage-restricted alterations may harbor novel cancer genes directing genesis or progression of tumors from distinct tissue types. We have explored this notion through combined analysis of genome-scale data sets from the NCI60 cancer cell line collection. Here, several melanoma cell lines clustered on the basis of increased dosage at a region of chromosome 3p containing the master melanocyte regulator MITF. Combined analysis of gene expression data and additional functional studies established MITF as an amplified oncogene in melanoma. MITF may therefore represent a nodal point within a critical lineage survival pathway operant in a subset of melanomas. These findings suggest that, like oncogene addiction, "lineage addiction" may represent a fundamental tumor survival mechanism with important therapeutic implications.

The role(s) of lipophosphoglycan (LPG) in the establishment of Leishmania major infections in mammalian hosts

The abundant cell surface glycolipid lipophosphoglycan (LPG) was implicated in many steps of the Leishmania infectious cycle by biochemical tests. The presence of other abundant surface or secreted glycoconjugates sharing LPG domains, however, has led to uncertainty about the relative contribution of LPG in vivo. Here we used an Leishmania major lpg1- mutant, which lacks LPG alone and shows attenuated virulence, to dissect the role of LPG in the establishment of macrophage infections in vivo. lpg1- was highly susceptible to human complement, had lost the ability to inhibit phagolysosomal fusion transiently, and was oxidant sensitive. Studies of mouse mutants defective in relevant defense mechanisms confirmed the role of LPG in oxidant resistance but called into question the importance of transient inhibition of phagolysosomal fusion for Leishmania macrophage survival. Moreover, the limited lytic activity of mouse complement appears to be an ineffective pathogen defense mechanism in vitro and in vivo, unlike human hosts. In contrast, lpg1- parasites bound C3b and resisted low pH and proteases normally, entered macrophages efficiently and silently, and continued to inhibit host-signaling pathways. These studies illustrate the value of mechanistic approaches focusing on both parasite and host defense pathways in dissecting the specific biological roles of complex virulence factors such as LPG.

Insertional mutagenesis by a modified in vitro Ty1 transposition system

Transposable elements are useful tools for insertional mutagenesis and have many potential applications in the characterization of complex genomes. Here we describe a system which facilitates the construction of large transposon insertion libraries useful for genome sequencing and functional genomic analysis. We developed two transposons, TyK and TyK'GFP+, which can be introduced into target DNAs by Ty1-mediated transposition in vitro, and several modifications which decrease the frequency of false transposition events and direct the recovery of transpositions into passenger rather than vector DNA. Insertions of TyK'GFP+ additionally may yield fusions to the Aequorea green fluorescent protein (GFP), useful in studies of gene expression and protein targeting. Transposition in vitro was obtained into target DNAs of up to 50 kb in size, restriction mapping showed insertion to be relatively random, and the sequence of 55 insertion sites showed neither strong site nor base compositional preference. Our data suggest that TyK-based artificial transposons will be suitable for a variety of genetic applications in many organisms.

Evidence that the vectorial competence of phlebotomine sand flies for different species of Leishmania is controlled by structural polymorphisms in the surface lipophosphoglycan

Phlebotomine vectors can in some instances transmit only certain species of Leishmania. Comparison of a large number of vector/parasite pairs revealed that species-specific differences in vectorial competence were in every case directly correlated with the ability of promastigotes to attach to the sand-fly midgut, the variable outcomes of which were controlled by structural polymorphisms in the surface lipophosphoglycan (LPG) of the parasite. The ability of Phlebotomus papatasi to transmit only Leishmania major could be attributed to the unique, highly substituted nature of L. major LPG that provides for multiple terminally exposed beta-linked galactose residues for binding. While the relatively unsubstituted LPGs of other Leishmania species were unable to mediate promastigote attachment to P. papatasi, they could mediate binding to midguts of Phlebotomus argentipes, which was found to be a potentially competent vector for every Leishmania species examined. The data suggest that at least some phlebotomine vectors differ with respect to the parasite recognition sites which they express and that midgut adhesion is a sufficiently critical component of vectorial competence as to provide the evolutionary drive for LPG structural polymorphisms.

Isolation of virulence genes directing surface glycosyl-phosphatidylinositol synthesis by functional complementation of Leishmania

Trypanosomatid parasites of the genus Leishmania cause a spectrum of widespread tropical diseases. In the vertebrate host they reside within the macrophage phagolysosome; however, the mechanisms employed in this remarkable survival strategy are not well understood. Recent advances in the molecular genetics of these parasites prompted us to develop methods of functional genetic complementation in Leishmania and apply them to the isolation of genes involved in the biosynthesis of the virulence determinant lipophosphoglycan, an abundant glycosyl-phosphatidylinositol-anchored polysaccharide. LPG1, the gene product identified by complementation of the R2D2 mutant, appears to be a glycosyltransferase responsible for the addition of galactofuranosyl residues to the nascent lipophosphoglycan chain. As galactofuranose is not found in mammalian cells, inhibition of the addition of this sugar could be exploited for chemotherapy. Overall, the success of the functional complementation approach opens the way to the identification of a variety of genes involved in pathogenesis and parasitism.

Human substance P receptor (NK-1): organization of the gene, chromosome localization, and functional expression of cDNA clones

The gene for the human substance P receptor (NK-1) was cloned using cDNA probes made by the polymerase chain reaction from primers based on the rat sequence. The gene spans 45-60 kb and is contained in five exons, with introns interrupting at sites homologous to those in the NK-2 receptor gene. Analysis of restriction digests of genomic DNA from mouse/human cell hybrids indicates the NK-1 receptor is a single-copy gene located on human chromosome 2. Polymerase chain reaction using primers based on the 5' and 3' ends of the coding sequence was used to generate full-length cDNAs from human lung and from IM9 lymphoblast cells. When transfected into COS-7 cells, the NK-1 receptor binds 125I-BHSP with a Kd of 0.35 +/- 0.07 nM and mediates substance P induced phosphatidylinositol metabolism. The receptor is selective for substance P; the relative affinity for neurokinin A and neurokinin B is 100- and 500-fold lower, respectively. Human IM9 lymphoblast cells express relatively high levels of the NK-1 receptor, and Northern blot analysis indicates modulation of mRNA levels by glucocorticoids and growth factors, suggesting that this cell line may be useful as a model for studying the control of NK-1 receptor gene expression.