SF3B1 mutation and ATM deletion codrive leukemogenesis via centromeric R-loop dysregulation.

RNA splicing factor SF3B1 is recurrently mutated in various cancers, particularly in hematologic malignancies. We previously reported that coexpression of Sf3b1 mutation and Atm deletion in B cells, but not either lesion alone, leads to the onset of chronic lymphocytic leukemia (CLL) with CLL cells harboring chromosome amplification. However, the exact role of Sf3b1 mutation and Atm deletion in chromosomal instability (CIN) remains unclear. Here, we demonstrated that SF3B1 mutation promotes centromeric R-loop (cen-R-loop) accumulation, leading to increased chromosome oscillation, impaired chromosome segregation, altered spindle architecture, and aneuploidy, which could be alleviated by removal of cen-R-loop and exaggerated by deletion of ATM. Aberrant splicing of key genes involved in R-loop processing underlay augmentation of cen-R-loop, as overexpression of the normal isoform, but not the altered form, mitigated mitotic stress in SF3B1-mutant cells. Our study identifies a critical role of splice variants in linking RNA splicing dysregulation and CIN and highlights cen-R-loop augmentation as a key mechanism for leukemogenesis.

Emerging Therapies in CLL in the Era of Precision Medicine.

Over the past decade, the treatment landscape of CLL has vastly changed from the conventional FC (fludarabine and cyclophosphamide) and FCR (FC with rituximab) chemotherapies to targeted therapies, including inhibitors of Bruton tyrosine kinase (BTK) and phosphatidylinositol 3-kinase (PI3K) as well as inhibitors of BCL2. These treatment options dramatically improved clinical outcomes; however, not all patients respond well to these therapies, especially high-risk patients. Clinical trials of immune checkpoint inhibitors (PD-1, CTLA4) and chimeric antigen receptor T (CAR T) or NK (CAR NK) cell treatment have shown some efficacy; still, long-term outcomes and safety issues have yet to be determined. CLL remains an incurable disease. Thus, there are unmet needs to discover new molecular pathways with targeted or combination therapies to cure the disease. Large-scale genome-wide whole-exome and whole-genome sequencing studies have discovered genetic alterations associated with disease progression, refined the prognostic markers in CLL, identified mutations underlying drug resistance, and pointed out critical targets to treat the disease. More recently, transcriptome and proteome landscape characterization further stratified the disease and revealed novel therapeutic targets in CLL. In this review, we briefly summarize the past and present available single or combination therapies, focusing on potential emerging therapies to address the unmet clinical needs in CLL.

MGA deletion leads to Richter's transformation via modulation of mitochondrial OXPHOS.

Richter's transformation (RT) is a progression of chronic lymphocytic leukemia (CLL) to aggressive lymphoma. MGA ( Max gene associated ), a functional MYC suppressor, is mutated at 3% in CLL and 36% in RT. However, genetic models and molecular mechanisms of MGA deletion driving CLL to RT remain elusive. We established a novel RT mouse model by knockout of Mga in the Sf3b1 / Mdr CLL model via CRISPR-Cas9 to determine the role of Mga in RT. Murine RT cells exhibit mitochondrial aberrations with elevated oxidative phosphorylation (OXPHOS). We identified Nme1 (Nucleoside diphosphate kinase) as a Mga target through RNA sequencing and functional characterization, which drives RT by modulating OXPHOS. As NME1 is also a known MYC target without targetable compounds, we found that concurrent inhibition of MYC and ETC complex II significantly prolongs the survival of RT mice in vivo . Our results suggest that Mga-Nme1 axis drives murine CLL-to-RT transition via modulating OXPHOS, highlighting a novel therapeutic avenue for RT. Statement of Significance: We established a murine RT model through knockout of Mga in an existing CLL model based on co-expression of Sf3b1 -K700E and del ( 13q ). We determined that the MGA/NME1 regulatory axis is essential to the CLL-to-RT transition via modulation of mitochondrial OXPHOS, highlighting this pathway as a novel target for RT treatment.

Molecular characterization of lung squamous cell carcinoma tumors reveals therapeutically relevant alterations.

INTRODUCTION: Unlike lung adenocarcinoma patients, there is no FDA-approved targeted-therapy likely to benefit lung squamous cell carcinoma patients. MATERIALS AND METHODS: We performed survival analyses of lung squamous cell carcinoma patients harboring therapeutically relevant alterations identified by whole exome sequencing and mass spectrometry-based validation across 430 lung squamous tumors. RESULTS: We report a mean of 11.6 mutations/Mb with a characteristic smoking signature along with mutations in TP53 (65%), CDKN2A (20%), NFE2L2 (20%), FAT1 (15%), KMT2C (15%), LRP1B (15%), FGFR1 (14%), PTEN (10%) and PREX2 (5%) among lung squamous cell carcinoma patients of Indian descent. In addition, therapeutically relevant EGFR mutations occur in 5.8% patients, significantly higher than as reported among Caucasians. In overall, our data suggests 13.5% lung squamous patients harboring druggable mutations have lower median overall survival, and 19% patients with a mutation in at least one gene, known to be associated with cancer, result in significantly shorter median overall survival compared to those without mutations. CONCLUSIONS: We present the first comprehensive landscape of genetic alterations underlying Indian lung squamous cell carcinoma patients and identify EGFR, PIK3CA, KRAS and FGFR1 as potentially important therapeutic and prognostic target.

Inhibition of SETMAR-H3K36me2-NHEJ repair axis in residual disease cells prevents glioblastoma recurrence.

BACKGROUND: Residual disease of glioblastoma (GBM) causes recurrence. However, targeting residual cells has failed, due to their inaccessibility and our lack of understanding of their survival mechanisms to radiation therapy. Here we deciphered a residual cell-specific survival mechanism essential for GBM relapse. METHODS: Therapy resistant residual (RR) cells were captured from primary patient samples and cell line models mimicking clinical scenario of radiation resistance. Molecular signaling of resistance in RR cells was identified using RNA sequencing, genetic and pharmacological perturbations, overexpression systems, and molecular and biochemical assays. Findings were validated in patient samples and an orthotopic mouse model. RESULTS: RR cells form more aggressive tumors than the parental cells in an orthotopic mouse model. Upon radiation-induced damage, RR cells preferentially activated a nonhomologous end joining (NHEJ) repair pathway, upregulating Ku80 and Artemis while downregulating meiotic recombination 11 (Mre11) at protein but not RNA levels. Mechanistically, RR cells upregulate the Su(var)3-9/enhancer-of-zeste/trithorax (SET) domain and mariner transposase fusion gene (SETMAR), mediating high levels of H3K36me2 and global euchromatization. High H3K36me2 leads to efficiently recruiting NHEJ proteins. Conditional knockdown of SETMAR in RR cells induced irreversible senescence partly mediated by reduced H3K36me2. RR cells expressing mutant H3K36A could not retain Ku80 at double-strand breaks, thus compromising NHEJ repair, leading to apoptosis and abrogation of tumorigenicity in vitro and in vivo. Pharmacological inhibition of the NHEJ pathway phenocopied H3K36 mutation effect, confirming dependency of RR cells on the NHEJ pathway for their survival. CONCLUSIONS: We demonstrate that the SETMAR-NHEJ regulatory axis is essential for the survival of clinically relevant radiation RR cells, abrogation of which prevents recurrence in GBM.

ERBB2 and KRAS alterations mediate response to EGFR inhibitors in early stage gallbladder cancer.

The uncommonness of gallbladder cancer in the developed world has contributed to the generally poor understanding of the disease. Our integrated analysis of whole exome sequencing, copy number alterations, immunohistochemical, and phospho-proteome array profiling indicates ERBB2 alterations in 40% early-stage rare gallbladder tumors, among an ethnically distinct population not studied before, that occurs through overexpression in 24% (n = 25) and recurrent mutations in 14% tumors (n = 44); along with co-occurring KRAS mutation in 7% tumors (n = 44). We demonstrate that ERBB2 heterodimerizes with EGFR to constitutively activate the ErbB signaling pathway in gallbladder cells. Consistent with this, treatment with ERBB2-specific, EGFR-specific shRNA or with a covalent EGFR family inhibitor Afatinib inhibits tumor-associated characteristics of the gallbladder cancer cells. Furthermore, we observe an in vivo reduction in tumor size of gallbladder xenografts in response to Afatinib is paralleled by a reduction in the amounts of phospho-ERK, in tumors harboring KRAS (G13D) mutation but not in KRAS (G12V) mutation, supporting an essential role of the ErbB pathway. In overall, besides implicating ERBB2 as an important therapeutic target under neo-adjuvant or adjuvant settings, we present the first evidence that the presence of KRAS mutations may preclude gallbladder cancer patients to respond to anti-EGFR treatment, similar to a clinical algorithm commonly practiced to opt for anti-EGFR treatment in colorectal cancer.

TMC-SNPdb: an Indian germline variant database derived from whole exome sequences.

Cancer is predominantly a somatic disease. A mutant allele present in a cancer cell genome is considered somatic when it's absent in the paired normal genome along with public SNP databases. The current build of dbSNP, the most comprehensive public SNP database, however inadequately represents several non-European Caucasian populations, posing a limitation in cancer genomic analyses of data from these populations. We present the T: ata M: emorial C: entre-SNP D: ata B: ase (TMC-SNPdb), as the first open source, flexible, upgradable, and freely available SNP database (accessible through dbSNP build 149 and ANNOVAR)-representing 114 309 unique germline variants-generated from whole exome data of 62 normal samples derived from cancer patients of Indian origin. The TMC-SNPdb is presented with a companion subtraction tool that can be executed with command line option or using an easy-to-use graphical user interface with the ability to deplete additional Indian population specific SNPs over and above dbSNP and 1000 Genomes databases. Using an institutional generated whole exome data set of 132 samples of Indian origin, we demonstrate that TMC-SNPdb could deplete 42, 33 and 28% false positive somatic events post dbSNP depletion in Indian origin tongue, gallbladder, and cervical cancer samples, respectively. Beyond cancer somatic analyses, we anticipate utility of the TMC-SNPdb in several Mendelian germline diseases. In addition to dbSNP build 149 and ANNOVAR, the TMC-SNPdb along with the subtraction tool is available for download in the public domain at the following:Database URL: http://www.actrec.gov.in/pi-webpages/AmitDutt/TMCSNP/TMCSNPdp.html.

Non-typhoidal Salmonella DNA traces in gallbladder cancer.

BACKGROUND: We earlier proposed a genetic model for gallbladder carcinogenesis and its dissemination cascade. However, the association of gallbladder cancer and 'inflammatory stimulus' to drive the initial cascade in the model remained unclear. A recent study suggested infection with Salmonella can lead to changes in the host signalling pathways in gallbladder cancer. FINDINGS: We examined the whole exomes of 26 primary gall bladder tumour and paired normal samples for presence of 143 HPV (Human papilloma virus) types along with 6 common Salmonella serotypes (S. typhi Ty2, S. typhi CT18, S. typhimurium LT2, S. choleraesuis SCB67, S. paratyphi TCC, and S. paratyphi SPB7) using a computational subtraction pipeline based on the HPVDetector, we recently described. Based on our evaluation of 26 whole exome gallbladder primary tumours and matched normal samples: association of typhoidal Salmonella species were found in 11 of 26 gallbladder cancer samples, and non-typhoidal Salmonella species in 12 of 26 gallbladder cancer, with 6 samples were found co-infected with both. CONCLUSIONS: We present the first evidence to support the association of non-typhoidal Salmonella species along with typhoidal strains in gallbladder cancer. Salmonella infection in the chronic carrier state fits the role of the 'inflammatory stimulus' in the genetic model for gallbladder carcinogenesis that may play a role in gallbladder cancer analogous to Helicobacter pylori in gastric cancer.

Integrated genomics approach to identify biologically relevant alterations in fewer samples.

BACKGROUND: Several statistical tools have been developed to identify genes mutated at rates significantly higher than background, indicative of positive selection, involving large sample cohort studies. However, studies involving smaller sample sizes are inherently restrictive due to their limited statistical power to identify low frequency genetic variations. RESULTS: We performed an integrated characterization of copy number, mutation and expression analyses of four head and neck cancer cell lines - NT8e, OT9, AW13516 and AW8507 - by applying a filtering strategy to prioritize for genes affected by two or more alterations within or across the cell lines. Besides identifying TP53, PTEN, HRAS and MET as major altered HNSCC hallmark genes, this analysis uncovered 34 novel candidate genes altered. Of these, we find a heterozygous truncating mutation in Nuclear receptor binding protein, NRBP1 pseudokinase gene, identical to as reported in other cancers, is oncogenic when ectopically expressed in NIH-3 T3 cells. Knockdown of NRBP1 in an oral carcinoma cell line bearing NRBP1 mutation inhibit transformation and survival of the cells. CONCLUSIONS: In overall, we present the first comprehensive genomic characterization of four head and neck cancer cell lines established from Indian patients. We also demonstrate the ability of integrated analysis to uncover biologically important genetic variation in studies involving fewer or rare clinical specimens.