Programmed genome rearrangements in Oxytricha produce transcriptionally active extrachromosomal circular DNA.

Extrachromosomal circular DNA (eccDNA) is both a driver of eukaryotic genome instability and a product of programmed genome rearrangements, but its extent had not been surveyed in Oxytricha, a ciliate with elaborate DNA elimination and translocation during development. Here, we captured rearrangement-specific circular DNA molecules across the genome to gain insight into its processes of programmed genome rearrangement. We recovered thousands of circularly excised Tc1/mariner-type transposable elements and high confidence non-repetitive germline-limited loci. We verified their bona fide circular topology using circular DNA deep-sequencing, 2D gel electrophoresis and inverse polymerase chain reaction. In contrast to the precise circular excision of transposable elements, we report widespread heterogeneity in the circular excision of non-repetitive germline-limited loci. We also demonstrate that circular DNAs are transcribed in Oxytricha, producing rearrangement-specific long non-coding RNAs. The programmed formation of thousands of eccDNA molecules makes Oxytricha a model system for studying nucleic acid topology. It also suggests involvement of eccDNA in programmed genome rearrangement.

Trastuzumab emtansine for HER2-positive advanced breast cancer.

BACKGROUND: Trastuzumab emtansine (T-DM1) is an antibody-drug conjugate incorporating the human epidermal growth factor receptor 2 (HER2)-targeted antitumor properties of trastuzumab with the cytotoxic activity of the microtubule-inhibitory agent DM1. The antibody and the cytotoxic agent are conjugated by means of a stable linker. METHODS: We randomly assigned patients with HER2-positive advanced breast cancer, who had previously been treated with trastuzumab and a taxane, to T-DM1 or lapatinib plus capecitabine. The primary end points were progression-free survival (as assessed by independent review), overall survival, and safety. Secondary end points included progression-free survival (investigator-assessed), the objective response rate, and the time to symptom progression. Two interim analyses of overall survival were conducted. RESULTS: Among 991 randomly assigned patients, median progression-free survival as assessed by independent review was 9.6 months with T-DM1 versus 6.4 months with lapatinib plus capecitabine (hazard ratio for progression or death from any cause, 0.65; 95% confidence interval [CI], 0.55 to 0.77; P<0.001), and median overall survival at the second interim analysis crossed the stopping boundary for efficacy (30.9 months vs. 25.1 months; hazard ratio for death from any cause, 0.68; 95% CI, 0.55 to 0.85; P<0.001). The objective response rate was higher with T-DM1 (43.6%, vs. 30.8% with lapatinib plus capecitabine; P<0.001); results for all additional secondary end points favored T-DM1. Rates of grade 3 or 4 adverse events were higher with lapatinib plus capecitabine than with T-DM1 (57% vs. 41%). The incidences of thrombocytopenia and increased serum aminotransferase levels were higher with T-DM1, whereas the incidences of diarrhea, nausea, vomiting, and palmar-plantar erythrodysesthesia were higher with lapatinib plus capecitabine. CONCLUSIONS: T-DM1 significantly prolonged progression-free and overall survival with less toxicity than lapatinib plus capecitabine in patients with HER2-positive advanced breast cancer previously treated with trastuzumab and a taxane. (Funded by F. Hoffmann-La Roche/Genentech; EMILIA ClinicalTrials.gov number, NCT00829166.).

Exploration of the Nuclear Proteomes in the Ciliate Oxytricha trifallax.

Nuclear dimorphism is a fundamental feature of ciliated protozoa, which have separate somatic and germline genomes in two distinct organelles within a single cell. The transcriptionally active somatic genome, contained within the physically larger macronucleus, is both structurally and functionally different from the silent germline genome housed in the smaller micronucleus. This difference in genome architecture is particularly exaggerated in Oxytricha trifallax, in which the somatic genome comprises tens of thousands of gene-sized nanochromosomes maintained at a high and variable ploidy, while the germline has a diploid set of megabase-scale chromosomes. To examine the compositional differences between the nuclear structures housing the genomes, we performed a proteomic survey of both types of nuclei and of macronuclear histones using quantitative mass spectrometry. We note distinct differences between the somatic and germline nuclei, with many functional proteins being highly enriched in one of the two nuclei. To validate our conclusions and the efficacy of nuclear separation, we used protein localization through a combination of transformations and immunofluorescence. We also note that the macronuclear histones strikingly display only activating marks, consistent with the conclusion that the macronucleus is the hub of transcription. These observations suggest that the compartmentalization of different genome features into separate structures has been accompanied by a similar specialization of nuclear components that maintain and facilitate the functions of the genomes specific to each nucleus.

A phase 1 study of weekly dosing of trastuzumab emtansine (T-DM1) in patients with advanced human epidermal growth factor 2-positive breast cancer.

BACKGROUND: We conducted a phase 1, multicenter, open-label, dose-escalation study (TDM3569g) to assess the safety, tolerability, and pharmacokinetics of single-agent trastuzumab emtansine (T-DM1) administered weekly and once every 3 weeks in patients with HER2-positive metastatic breast cancer previously treated with trastuzumab. The weekly dose results are described here. METHODS: Patients were administered escalating doses of T-DM1 weekly, starting at 1.2 mg/kg. Additional patients were enrolled at the maximum tolerated dose (MTD) to better characterize tolerability and pharmacokinetics. RESULTS: Twenty-eight patients received weekly T-DM1, and the MTD was determined to be 2.4 mg/kg. In general, T-DM1 was well tolerated, requiring few dose modifications or discontinuations because of adverse events (AEs). Grade ≥ 3 AEs were reported in 19 patients (67.9%); treatment-related AEs occurred in 25 (89.3%) patients. Exposure to weekly T-DM1 was dose-proportional at ≥ 1.2 mg/kg, and accumulation of T-DM1 and total trastuzumab was observed. Objective partial tumor responses were reported in 13 (46.4%) patients; the median duration of response was 18.6 months, and the 6-month clinical benefit rate was 57.1%. CONCLUSION: The results suggest that a weekly dose of T-DM1 2.4 mg/kg has antitumor activity and is well tolerated in patients with HER2-positive metastatic breast cancer.

Comparative genomics reveals insight into the evolutionary origin of massively scrambled genomes.

Ciliates are microbial eukaryotes that undergo extensive programmed genome rearrangement, a natural genome editing process that converts long germline chromosomes into smaller gene-rich somatic chromosomes. Three well-studied ciliates include Oxytricha trifallax, Tetrahymena thermophila, and Paramecium tetraurelia, but only the Oxytricha lineage has a massively scrambled genome, whose assembly during development requires hundreds of thousands of precisely programmed DNA joining events, representing the most complex genome dynamics of any known organism. Here we study the emergence of such complex genomes by examining the origin and evolution of discontinuous and scrambled genes in the Oxytricha lineage. This study compares six genomes from three species, the germline and somatic genomes for Euplotes woodruffi, Tetmemena sp., and the model ciliate O. trifallax. We sequenced, assembled, and annotated the germline and somatic genomes of E. woodruffi, which provides an outgroup, and the germline genome of Tetmemena sp. We find that the germline genome of Tetmemena is as massively scrambled and interrupted as Oxytricha's: 13.6% of its gene loci require programmed translocations and/or inversions, with some genes requiring hundreds of precise gene editing events during development. This study revealed that the earlier diverged spirotrich, E. woodruffi, also has a scrambled genome, but only roughly half as many loci (7.3%) are scrambled. Furthermore, its scrambled genes are less complex, together supporting the position of Euplotes as a possible evolutionary intermediate in this lineage, in the process of accumulating complex evolutionary genome rearrangements, all of which require extensive repair to assemble functional coding regions. Comparative analysis also reveals that scrambled loci are often associated with local duplications, supporting a gradual model for the origin of complex, scrambled genomes via many small events of DNA duplication and decay.

Replication of Overall Survival, Progression-Free Survival, and Overall Response in Chemotherapy Arms of Non-Small Cell Lung Cancer Trials Using Real-World Data.

PURPOSE: The utility of real-world data (RWD) for use as external controls in drug development is informed by studies that replicate trial control arms for different endpoints. The purpose of this study was to replicate control arms from four non-small cell lung cancer (NSCLC) randomized controlled trials (RCT) to analyze overall survival (OS), progression-free survival (PFS), and overall response rate (ORR) using RWD. PATIENTS AND METHODS: This study used RWD from a nationwide de-identified database and a clinico-genomic database to replicate OS, PFS, and ORR endpoints in the chemotherapy control arms of four first-line NSCLC RCTs evaluating atezolizumab [IMpower150-wild-type (WT), IMpower130-WT, IMpower131, and IMpower132]. Additional objectives were to develop a definition of real-world PFS (rwPFS) and to evaluate the real-world response rate (rwRR) endpoint. RESULTS: Baseline demographic and clinical characteristics were balanced after application of propensity score weighting methods. For rwPFS and OS, RWD external controls were generally similar to their RCT control counterparts. Across all four trials, the hazard ratio (HR) point estimates comparing trial controls with external controls were closer to 1.0 for the PFS endpoint than for the OS endpoint. An exploratory assessment of rwRR in RWD revealed a slight but nonsignificant overestimation of RCT ORR, which was unconfounded by baseline characteristics. CONCLUSIONS: RWD can be used to reasonably replicate the OS and PFS of chemotherapy control arms of first-line NSCLC RCTs. Additional studies can provide greater insight into the utility of RWD in drug development.

Transcribed germline-limited coding sequences in Oxytricha trifallax.

The germline-soma divide is a fundamental distinction in developmental biology, and different genes are expressed in germline and somatic cells throughout metazoan life cycles. Ciliates, a group of microbial eukaryotes, exhibit germline-somatic nuclear dimorphism within a single cell with two different genomes. The ciliate Oxytricha trifallax undergoes massive RNA-guided DNA elimination and genome rearrangement to produce a new somatic macronucleus (MAC) from a copy of the germline micronucleus (MIC). This process eliminates noncoding DNA sequences that interrupt genes and also deletes hundreds of germline-limited open reading frames (ORFs) that are transcribed during genome rearrangement. Here, we update the set of transcribed germline-limited ORFs (TGLOs) in O. trifallax. We show that TGLOs tend to be expressed during nuclear development and then are absent from the somatic MAC. We also demonstrate that exposure to synthetic RNA can reprogram TGLO retention in the somatic MAC and that TGLO retention leads to transcription outside the normal developmental program. These data suggest that TGLOs represent a group of developmentally regulated protein-coding sequences whose gene expression is terminated by DNA elimination.

Trastuzumab Emtansine (T-DM1) in Patients with Previously Treated HER2-Overexpressing Metastatic Non-Small Cell Lung Cancer: Efficacy, Safety, and Biomarkers.

PURPOSE: HER2-targeted therapy is not standard of care for HER2-positive non-small cell lung cancer (NSCLC). This phase II study investigated efficacy and safety of the HER2-targeted antibody-drug conjugate trastuzumab emtansine (T-DM1) in patients with previously treated advanced HER2-overexpressing NSCLC. PATIENTS AND METHODS: Eligible patients had HER2-overexpressing NSCLC (centrally tested IHC) and received previous platinum-based chemotherapy and targeted therapy in the case of EGFR mutation or ALK gene rearrangement. Patients were divided into cohorts based on HER2 IHC (2+, 3+). All patients received T-DM1 3.6 mg/kg intravenously every 3 weeks until disease progression or unacceptable toxicity. The primary endpoint was investigator-determined overall response rate (ORR) using RECIST v1.1. RESULTS: Forty-nine patients received T-DM1 (29 IHC 2+, 20 IHC 3+). No treatment responses were observed in the IHC 2+ cohort. Four partial responses were observed in the IHC 3+ cohort (ORR, 20%; 95% confidence interval, 5.7%-43.7%). Clinical benefit rates were 7% and 30% in the IHC 2+ and 3+ cohorts, respectively. Response duration for the responders was 2.9, 7.3, 8.3, and 10.8 months. Median progression-free survival and overall survival were similar between cohorts. Three of 4 responders had HER2 gene amplification. No new safety signals were observed. CONCLUSIONS: T-DM1 showed a signal of activity in patients with HER2-overexpressing (IHC 3+) advanced NSCLC. Additional investigation into HER2 pathway alterations is needed to refine the target population for T-DM1 in NSCLC; however, HER2 IHC as a single parameter was an insufficient predictive biomarker.