Phase 1b study of enzalutamide plus CC-115, a dual mTORC1/2 and DNA-PK inhibitor, in men with metastatic castration-resistant prostate cancer (mCRPC).

BACKGROUND: CC-115, a dual mTORC1/2 and DNA-PK inhibitor, has promising antitumour activity when combined with androgen receptor (AR) inhibition in pre-clinical models. METHODS: Phase 1b multicentre trial evaluating enzalutamide with escalating doses of CC-115 in AR inhibitor-naive mCRPC patients (n = 41). Primary endpoints were safety and RP2D. Secondary endpoints included PSA response, time-to-PSA progression, and radiographic progression. RESULTS: Common adverse effects included rash (31.7% Grades 1-2 (Gr); 31.7% Gr 3), pruritis (43.9% Gr 1-2), diarrhoea (37% Gr 1-2), and hypertension (17% Gr 1-2; 9.8% Gr 3). CC-115 RP2D was 5 mg twice a day. In 40 evaluable patients, 80% achieved ≥50% reduction in PSA (PSA50), and 58% achieved ≥90% reduction in PSA (PSA90) by 12 weeks. Median time-to-PSA progression was 14.7 months and median rPFS was 22.1 months. Stratification by PI3K alterations demonstrated a non-statistically significant trend towards improved PSA50 response (PSA50 of 94% vs. 67%, p = 0.08). Exploratory pre-clinical analysis suggested CC-115 inhibited mTOR pathway strongly, but may be insufficient to inhibit DNA-PK at RP2D. CONCLUSIONS: The combination of enzalutamide and CC-115 was well tolerated. A non-statistically significant trend towards improved PSA response was observed in patients harbouring PI3K pathway alterations, suggesting potential predictive biomarkers of response to a PI3K/AKT/mTOR pathway inhibitor. CLINICAL TRIAL REGISTRATION: ClinicalTrials.gov identifier: NCT02833883.

Dynamic expression of Schlafen 11 (SLFN11) in circulating tumour cells as a liquid biomarker in small cell lung cancer.

INTRODUCTION: Small cell lung cancer (SCLC) is an aggressive malignancy with no established biomarkers. Schlafen 11(SLFN11), a DNA/RNA helicase that sensitises cancer cells to DNA-damaging agents, has emerged as a promising predictive biomarker for several drug classes including platinum and PARP inhibitors. Detection of SLFN11 in circulating tumour cells (CTCs) may provide a valuable alternative to tissue sampling. METHODS: SLFN11 expression was evaluated in tumour samples and characterised in circulating tumour cells (CTC) longitudinally to determine its potential role as a biomarker of response. RESULTS: Among 196 SCLC tumours, 51% expressed SLFN11 by IHC. In addition, 20/29 extra-thoracic high-grade neuroendocrine tumours expressed SLFN11 expression. In 64 blood samples from 42 SCLC patients, 83% (53/64) of samples had detectable CTCs, and SLFN11-positive CTCs were detected in 55% (29/53). Patients actively receiving platinum treatment had the lowest number of CTCs and a lower percentage of SLFN11-positive CTCs (p = 0.014). Analysis from patients with longitudinal samples suggest a decrease in CTC number and in SLFN11 expression that correlates with clinical response. CONCLUSIONS: SLFN11 levels can be monitored in CTCs from SCLC patients using non-invasive liquid biopsies. The ability to detect SLFN11 in CTCs from SCLC patients adds a valuable tool for the detection and longitudinal monitoring of this promising biomarker.

The endoplasmic reticulum HSP40 co-chaperone ERdj3/DNAJB11 assembles and functions as a tetramer.

ERdj3/DNAJB11 is an endoplasmic reticulum (ER)-targeted HSP40 co-chaperone that performs multifaceted functions involved in coordinating ER and extracellular proteostasis. Here, we show that ERdj3 assembles into a native tetramer that is distinct from the dimeric structure observed for other HSP40 co-chaperones. An electron microscopy structural model of full-length ERdj3 shows that these tetramers are arranged as a dimer of dimers formed by distinct inter-subunit interactions involving ERdj3 domain II and domain III Targeted deletion of residues 175-190 within domain II renders ERdj3 a stable dimer that is folded and efficiently secreted from mammalian cells. This dimeric ERdj3 shows impaired substrate binding both in the ER and extracellular environments and reduced interactions with the ER HSP70 chaperone BiP. Furthermore, we show that overexpression of dimeric ERdj3 exacerbates ER stress-dependent reductions in the secretion of a destabilized, aggregation-prone protein and increases its accumulation as soluble oligomers in extracellular environments. These results reveal ERdj3 tetramerization as an important structural framework for ERdj3 functions involved in coordinating ER and extracellular proteostasis in the presence and absence of ER stress.

Identification and Characterization of Circulating Tumor Cells in Men Who have Undergone Prostatectomy for Clinically Localized, High Risk Prostate Cancer.

PURPOSE: Approximately 15% of men with newly diagnosed prostate cancer have high risk features which increase the risk of recurrence and metastasis. Better predictive biomarkers could allow for earlier detection of biochemical recurrence and change surveillance and adjuvant treatment paradigms. Circulating tumor cells are thought to represent the earliest form of metastases. However, their role as biomarkers in men with high risk, localized prostate cancer is not well defined. MATERIALS AND METHODS: Two to 5 months after prostatectomy we obtained blood samples from 37 patients with high risk, localized prostate cancer, defined as stage T3a or higher, Gleason score 8 or greater, or prostate specific antigen 20 ng/ml or greater. Circulating tumor cells were enumerated using a commercial platform. Matched tumor and single circulating tumor cell sequencing was performed. RESULTS: Circulating tumor cells were detected in 30 of 37 samples (81.1%) with a median of 2.4 circulating tumor cells per ml (range 0 to 22.9). Patients with detectable circulating tumor cells showed a trend toward shorter recurrence time (p=0.12). All patients with biochemical recurrence had detectable circulating tumor cells. Androgen receptor over expression was detected in 7 of 37 patients (18.9%). Patients with biochemical recurrence had more circulating tumor cell copy number aberrations (p=0.027). Matched tumor tissue and single circulating tumor cell sequencing revealed heterogeneity. CONCLUSIONS: We noted a high incidence of circulating tumor cell detection after radical prostatectomy and shorter time to biochemical recurrence in men with a higher circulating tumor cell burden and more circulating tumor cell copy number aberrations. Genomic alterations consistent with established copy number aberrations in prostate cancer were detectable in circulating tumor cells but often discordant with cells analyzed in bulk from primary lesions. With further testing in appropriately powered cohorts early circulating tumor cell detection could be an informative biomarker to assist with adjuvant treatment decisions.

Molecular crowding enhances facilitated diffusion of two human DNA glycosylases.

Intracellular space is at a premium due to the high concentrations of biomolecules and is expected to have a fundamental effect on how large macromolecules move in the cell. Here, we report that crowded solutions promote intramolecular DNA translocation by two human DNA repair glycosylases. The crowding effect increases both the efficiency and average distance of DNA chain translocation by hindering escape of the enzymes to bulk solution. The increased contact time with the DNA chain provides for redundant damage patrolling within individual DNA chains at the expense of slowing the overall rate of damaged base removal from a population of molecules. The significant biological implication is that a crowded cellular environment could influence the mechanism of damage recognition as much as any property of the enzyme or DNA.

Microscopic mechanism of DNA damage searching by hOGG1.

The DNA backbone is often considered a track that allows long-range sliding of DNA repair enzymes in their search for rare damage sites in DNA. A proposed exemplar of DNA sliding is human 8-oxoguanine ((o)G) DNA glycosylase 1 (hOGG1), which repairs mutagenic (o)G lesions in DNA. Here we use our high-resolution molecular clock method to show that macroscopic 1D DNA sliding of hOGG1 occurs by microscopic 2D and 3D steps that masquerade as sliding in resolution-limited single-molecule images. Strand sliding was limited to distances shorter than seven phosphate linkages because attaching a covalent chemical road block to a single DNA phosphate located between two closely spaced damage sites had little effect on transfers. The microscopic parameters describing the DNA search of hOGG1 were derived from numerical simulations constrained by the experimental data. These findings support a general mechanism where DNA glycosylases use highly dynamic multidimensional diffusion paths to scan DNA.

Timing facilitated site transfer of an enzyme on DNA.

Many enzymes that react with specific sites in DNA have the property of facilitated diffusion, in which the DNA chain is used as a conduit to accelerate site location. Despite the importance of such mechanisms in gene regulation and DNA repair, there have been few viable approaches to elucidate the microscopic process of facilitated diffusion. Here we describe a new method in which a small-molecule trap (uracil) is used to clock a DNA repair enzyme as it hops and slides between damaged sites in DNA. The 'molecular clock' provides unprecedented information: the mean length for DNA sliding, the one-dimensional diffusion constant, the maximum hopping radius and the time frame for DNA hopping events. In addition, the data establish that the DNA phosphate backbone is a sufficient requirement for DNA sliding.

Post-therapy emergence of an NBN reversion mutation in a patient with pancreatic acinar cell carcinoma.

Pancreatic acinar cell carcinoma (PACC) is a rare form of pancreatic cancer that commonly harbors targetable alterations, including activating fusions in the MAPK pathway and loss-of-function (LOF) alterations in DNA damage response/homologous recombination DNA repair-related genes. Here, we describe a patient with PACC harboring both somatic biallelic LOF of NBN and an activating NTRK1 fusion. Upon disease progression following 13 months of treatment with folinic acid, fluorouracil, irinotecan, and oxaliplatin (FOLFIRINOX), genomic analysis of a metastatic liver biopsy revealed the emergence of a novel reversion mutation restoring the reading frame of NBN. To our knowledge, genomic reversion of NBN has not been previously reported as a resistance mechanism in any tumor type. The patient was treated with, but did not respond to, targeted treatment with a selective NTRK inhibitor. This case highlights the complex but highly actionable genomic landscape of PACC and underlines the value of genomic profiling of rare tumor types such as PACC.

Ataxia telangiectasia and Rad3-related (ATR) inhibitor camonsertib dose optimization in patients with biomarker-selected advanced solid tumors (TRESR study).

BACKGROUND: Camonsertib is a selective oral inhibitor of ataxia telangiectasia and Rad3-related (ATR) kinase with demonstrated efficacy in tumors with DNA damage response gene deficiencies. On-target anemia is the main drug-related toxicity typically manifesting after the period of dose-limiting toxicity evaluation. Thus, dose and schedule optimization requires extended follow-up to assess prolonged treatment effects. METHODS: Long-term safety, tolerability, and antitumor efficacy of 3 camonsertib monotherapy dosing regimens were assessed in the TRESR study dose-optimization phase: 160 mg once daily (QD) 3 days on, 4 days off (160 3/4; the preliminary recommended Phase II dose [RP2D]) and two step-down groups of 120 mg QD 3/4 (120 3/4) and 160 mg QD 3/4, 2 weeks on, 1 week off (160 3/4, 2/1w). Safety endpoints included incidence of treatment-related adverse events (TRAEs), dose modifications, and transfusions. Efficacy endpoints included overall response rate, clinical benefit rate, progression-free survival, and circulating tumor DNA (ctDNA)-based molecular response rate. RESULTS: The analysis included 119 patients: 160 3/4 (n = 67), 120 3/4 (n = 25), and 160 3/4, 2/1w (n = 27) treated up to 117.1 weeks as of the data cutoff. The risk of developing grade 3 anemia was significantly lower in the 160 3/4, 2/1w group compared with the preliminary RP2D group (hazard ratio = 0.23, 2-sided P = .02), translating to reduced transfusion and dose reduction requirements. The intermittent weekly schedule did not compromise antitumor activity. CONCLUSION: The 160 3/4, 2/1w dose was established as an optimized regimen for future camonsertib monotherapy studies offering a substantial reduction in the incidence of anemia without any compromise to efficacy. CLINICAL TRIAL ID: NCT04497116.

DNA translocation by human uracil DNA glycosylase: the case of single-stranded DNA and clustered uracils.

Human uracil DNA glycosylase (hUNG) plays a central role in DNA repair and programmed mutagenesis of Ig genes, requiring it to act on sparsely or densely spaced uracil bases located in a variety of contexts, including U/A and U/G base pairs, and potentially uracils within single-stranded DNA (ssDNA). An interesting question is whether the facilitated search mode of hUNG, which includes both DNA sliding and hopping, changes in these different contexts. Here we find that hUNG uses an enhanced local search mode when it acts on uracils in ssDNA, and also, in a context where uracils are densely clustered in duplex DNA. In the context of ssDNA, hUNG performs an enhanced local search by sliding with a mean sliding length larger than that of double-stranded DNA (dsDNA). In the context of duplex DNA, insertion of high-affinity abasic product sites between two uracil lesions serves to significantly extend the apparent sliding length on dsDNA from 4 to 20 bp and, in some cases, leads to directionally biased 3' → 5' sliding. The presence of intervening abasic product sites mimics the situation where hUNG acts iteratively on densely spaced uracils. The findings suggest that intervening product sites serve to increase the amount of time the enzyme remains associated with DNA as compared to nonspecific DNA, which in turn increases the likelihood of sliding as opposed to falling off the DNA. These findings illustrate how the search mechanism of hUNG is not predetermined but, instead, depends on the context in which the uracils are located.

DNA translocation by human uracil DNA glycosylase: role of DNA phosphate charge.

Human DNA repair glycosylases must encounter and inspect each DNA base in the genome to discover damaged bases that may be present at a density of <1 in 10 million normal base pairs. This remarkable example of specific molecular recognition requires a reduced dimensionality search process (facilitated diffusion) that involves both hopping and sliding along the DNA chain. Despite the widely accepted importance of facilitated diffusion in protein-DNA interactions, the molecular features of DNA that influence hopping and sliding are poorly understood. Here we explore the role of the charged DNA phosphate backbone in sliding and hopping by human uracil DNA glycosylase (hUNG), which is an exemplar that efficiently locates rare uracil bases in both double-stranded DNA and single-stranded DNA. Substitution of neutral methylphosphonate groups for anionic DNA phosphate groups weakened nonspecific DNA binding affinity by 0.4-0.5 kcal/mol per substitution. In contrast, sliding of hUNG between uracil sites embedded in duplex and single-stranded DNA substrates persisted unabated when multiple methylphosphonate linkages were inserted between the sites. Thus, a continuous phosphodiester backbone negative charge is not essential for sliding over nonspecific DNA binding sites. We consider several alternative mechanisms for these results. A model consistent with previous structural and nuclear magnetic resonance dynamic results invokes the presence of open and closed conformational states of hUNG. The open state is short-lived and has weak or nonexistent interactions with the DNA backbone that are conducive for sliding, and the populated closed state has stronger interactions with the phosphate backbone. These data suggest that the fleeting sliding form of hUNG is a distinct weakly interacting state that facilitates rapid movement along the DNA chain and resembles the transition state for DNA dissociation.

Analysis of BRCA2 Copy Number Loss and Genomic Instability in Circulating Tumor Cells from Patients with Metastatic Castration-resistant Prostate Cancer.

BACKGROUND: BRCA2 alterations predict for a response to poly-ADP-ribose polymerase inhibition in metastatic castration-resistant prostate cancer (mCRPC). However, detection is hindered by insufficient tumor tissue and low sensitivity of cell-free DNA for detecting copy number loss. OBJECTIVE: To evaluate the BRCA2 loss detection using single-cell, shallow whole-genome sequencing (sWGS) of circulating tumor cells (CTCs) in patients with mCRPC. DESIGN, SETTING, AND PARTICIPANTS: We analyzed CTC samples collected concurrently with tumor biopsies intended for clinical sequencing in patients with progressing mCRPC. OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS: Differences in proportions were evaluated using the chi-square test. Correlations between assays were analyzed in linear regression models. Associations between alterations and genomic instability were assessed on the single-cell level using mixed-effect negative binomial models. RESULTS AND LIMITATIONS: We identified 138 patients with concurrent CTC and biopsy samples. CTC sWGS generated copy number profiles in a similar proportion of patients to biopsy samples (83% vs 78%, p = 0.23), but was more effective than bone biopsies (79% vs 50%; p = 0.009). CTC sWGS detected BRCA2 loss in more patients than tissue at the ≥1 (42% vs 16%; p < 0.001) and ≥2 (27% vs 16%; p = 0.028) CTC thresholds. The overall prevalence of BRCA2 loss was not increased in CTCs using sample-level composite z scores (p = 0.4), but was significantly increased compared with a lower-than-expected prevalence in bone samples (21% vs 3%, p = 0.014). Positive/negative predictive values for CTC BRCA2 loss were 89%/96% using the ≥1 CTC threshold and 67%/92% using the composite z score. CTC BRCA2 loss was associated with higher genomic instability in univariate (1.4-fold large-scale transition difference, 95% confidence interval [CI]: 1.2-1.6; p < 0.001) and multivariable analysis (1.4-fold difference, 95% CI: 1.2-1.6; p < 0.001). CONCLUSIONS: Copy number profiles can reliably be generated using CTC sWGS, which detected a majority of tissue-confirmed BRCA2 loss and "CTC-only" losses. BRCA2 losses were supported by increases in genomic instability. PATIENT SUMMARY: Current testing strategies have limitations in their ability to detect BRCA2 loss, a relatively common alteration in prostate cancer that is used to identify patients who may benefit from targeted therapy. In this paper, we evaluated whether we could detect BRCA2 loss in individual tumor cells isolated from patient blood samples and found this method to be suitable for further analysis.

Camonsertib in DNA damage response-deficient advanced solid tumors: phase 1 trial results.

Predictive biomarkers of response are essential to effectively guide targeted cancer treatment. Ataxia telangiectasia and Rad3-related kinase inhibitors (ATRi) have been shown to be synthetic lethal with loss of function (LOF) of ataxia telangiectasia-mutated (ATM) kinase, and preclinical studies have identified ATRi-sensitizing alterations in other DNA damage response (DDR) genes. Here we report the results from module 1 of an ongoing phase 1 trial of the ATRi camonsertib (RP-3500) in 120 patients with advanced solid tumors harboring LOF alterations in DDR genes, predicted by chemogenomic CRISPR screens to sensitize tumors to ATRi. Primary objectives were to determine safety and propose a recommended phase 2 dose (RP2D). Secondary objectives were to assess preliminary anti-tumor activity, to characterize camonsertib pharmacokinetics and relationship with pharmacodynamic biomarkers and to evaluate methods for detecting ATRi-sensitizing biomarkers. Camonsertib was well tolerated; anemia was the most common drug-related toxicity (32% grade 3). Preliminary RP2D was 160 mg weekly on days 1-3. Overall clinical response, clinical benefit and molecular response rates across tumor and molecular subtypes in patients who received biologically effective doses of camonsertib (>100 mg d-1) were 13% (13/99), 43% (43/99) and 43% (27/63), respectively. Clinical benefit was highest in ovarian cancer, in tumors with biallelic LOF alterations and in patients with molecular responses. ClinicalTrials.gov registration: NCT04497116 .

Direct experimental evidence for quadruplex-quadruplex interaction within the human ILPR.

Here we report the analysis of dual G-quadruplexes formed in the four repeats of the consensus sequence from the insulin-linked polymorphic region (ACAGGGGTGTGGGG; ILPR(n)(=4)). Mobilities of ILPR(n)(=4) in nondenaturing gel and circular dichroism (CD) studies confirmed the formation of two intramolecular G-quadruplexes in the sequence. Both CD and single molecule studies using optical tweezers showed that the two quadruplexes in the ILPR(n)(=4) most likely adopt a hybrid G-quadruplex structure that was entirely different from the mixture of parallel and antiparallel conformers previously observed in the single G-quadruplex forming sequence (ILPR(n)(=2)). These results indicate that the structural knowledge of a single G-quadruplex cannot be automatically extrapolated to predict the conformation of multiple quadruplexes in tandem. Furthermore, mechanical pulling of the ILPR(n)(=4) at the single molecule level suggests that the two quadruplexes are unfolded cooperatively, perhaps due to a quadruplex-quadruplex interaction (QQI) between them. Additional evidence for the QQI was provided by DMS footprinting on the ILPR(n)(=4) that identified specific guanines only protected in the presence of a neighboring G-quadruplex. There have been very few experimental reports on multiple G-quadruplex-forming sequences and this report provides direct experimental evidence for the existence of a QQI between two contiguous G-quadruplexes in the ILPR.

Circulating tumor cell heterogeneity in neuroendocrine prostate cancer by single cell copy number analysis.

Neuroendocrine prostate cancer is an aggressive variant of prostate cancer that may arise de novo or develop from pre-existing prostate adenocarcinoma as a mechanism of treatment resistance. The combined loss of tumor suppressors RB1, TP53, and PTEN are frequent in NEPC but also present in a subset of prostate adenocarcinomas. Most clinical and preclinical studies support a trans-differentiation process, whereby NEPC arises clonally from a prostate adenocarcinoma precursor during the course of treatment resistance. Here we highlight a case of NEPC with significant intra-patient heterogeneity observed across metastases. We further demonstrate how single-cell genomic analysis of circulating tumor cells combined with a phenotypic evaluation of cellular diversity can be considered as a window into tumor heterogeneity in patients with advanced prostate cancer.

Circulating Tumor Cell Chromosomal Instability and Neuroendocrine Phenotype by Immunomorphology and Poor Outcomes in Men with mCRPC Treated with Abiraterone or Enzalutamide.

PURPOSE: While the detection of AR-V7 in circulating tumor cells (CTC) is associated with resistance to abiraterone or enzalutamide in men with metastatic castration-resistant prostate cancer (mCRPC), it only accounts for a minority of this resistance. Neuroendocrine (NE) differentiation or chromosomal instability (CIN) may be additional mechanisms that mediate resistance. EXPERIMENTAL DESIGN: PROPHECY was a multicenter prospective study of men with high-risk mCRPC starting abiraterone or enzalutamide. A secondary objective was to assess Epic CTC CIN and NE phenotypes before abiraterone or enzalutamide and at progression. The proportional hazards (PH) model was used to investigate the prognostic importance of CIN and NE in predicting progression-free survival and overall survival (OS) adjusting for CTC number (CellSearch), AR-V7, prior therapy, and clinical risk score. The PH model was utilized to validate this association of NE with OS in an external dataset of patients treated similarly at Memorial Sloan Kettering Cancer Center (MSKCC; New York, NY). RESULTS: We enrolled 118 men with mCRPC starting on abiraterone or enzalutamide; 107 were evaluable on the Epic platform. Of these, 36.4% and 8.4% were CIN positive and NE positive, respectively. CIN and NE were independently associated with worse OS [HR, 2.2; 95% confidence interval (CI), 1.2-4.0 and HR 3.8; 95% CI, 1.2-12.3, respectively] when treated with abiraterone/enzalutamide. The prognostic significance of NE positivity for worse OS was confirmed in the MSKCC dataset (n = 173; HR, 5.7; 95% CI, 2.6-12.7). CONCLUSIONS: A high CIN and NE CTC phenotype is independently associated with worse survival in men with mCRPC treated with abiraterone/enzalutamide, warranting further prospective controlled predictive studies to inform treatment decisions.

Circulating Tumor Cell Subtypes and T-cell Populations as Prognostic Biomarkers to Combination Immunotherapy in Patients with Metastatic Genitourinary Cancer.

PURPOSE: Circulating tumor cells (CTC) are under investigation as a minimally invasive liquid biopsy that may improve risk stratification and treatment selection. CTCs uniquely allow for digital pathology of individual malignant cell morphology and marker expression. We compared CTC features and T-cell counts with survival endpoints in a cohort of patients with metastatic genitourinary cancer treated with combination immunotherapy. EXPERIMENTAL DESIGN: Markers evaluated included pan-CK/CD45/PD-L1/DAPI for CTCs and CD4/CD8/Ki-67/DAPI for T cells. ANOVA was used to compare CTC burden and T-cell populations across timepoints. Differences in survival and disease progression were evaluated using the maximum log-rank test. RESULTS: From December 2016 to January 2019, 183 samples from 81 patients were tested. CTCs were found in 75% of patients at baseline. CTC burden was associated with shorter overall survival (OS) at baseline (P = 0.022), but not on-therapy. Five morphologic subtypes were detected, and the presence of two specific subtypes with unique cellular features at baseline and on-therapy was associated with worse OS (0.9-2.3 vs. 28.2 months; P < 0.0001-0.013). Increasing CTC heterogeneity on-therapy had a trend toward worse OS (P = 0.045). PD-L1+ CTCs on-therapy were associated with worse OS (P < 0.01, cycle 2). Low baseline and on-therapy CD4/CD8 counts were also associated with poor OS and response category. CONCLUSIONS: Shorter survival may be associated with high CTC counts at baseline, presence of specific CTC morphologic subtypes, PD-L1+ CTCs, and low %CD4/8 T cells in patients with metastatic genitourinary cancer. A future study is warranted to validate the prognostic utility of CTC heterogeneity and detection of specific CTC morphologies.

An RNA G-quadruplex is essential for cap-independent translation initiation in human VEGF IRES.

RNA G-quadruplexes located within the 5'-UTR of mRNA are almost always known to be associated with repression of cap-dependent translation. However, in this report we present functional as well as structural evidence that sequence redundancy in a G-rich segment within the 5'-UTR of human VEGF mRNA supports a 'switchable' RNA G-quadruplex structure that is essential for IRES-mediated translation initiation. Additionally, utilization of a specific combination of G-tracts within this segment allows for the conformational switch that implies a tunable regulatory role of the quadruplex structure in translation initiation. A sequence engineered from a functionally handicapped mutant moderately rescued the activity, further indicating the importance of G-quadruplex structure for VEGF IRES-A function. This to our knowledge is the first report of a conformationally flexible RNA G-quadruplex which is essential for IRES-mediated translation initiation.

Coexistence of an ILPR i-motif and a partially folded structure with comparable mechanical stability revealed at the single-molecule level.

Investigation of i-motif is of high importance to fully understand the biological functions of G quadruplexes in the context of double-stranded DNA. Whereas single-molecule approaches have profiled G quadruplexes from a perspective unavailable by bulk techniques, there is a lack of similar literature on the i-motif in the cytosine (C)-rich region complementary to G quadruplex-forming sequences. Here, we have used laser tweezers to investigate the structures formed in 5'-(TGTCCCCACACCCC)(2), a predominate variant in the insulin-linked polymorphic region (ILPR). We have observed two species with the change in contour length (DeltaL) of 10.4 (+/-0.1) and 5.1 (+/-0.5) nm, respectively. Since DeltaL of 10.4 nm is located within the expected range for an i-motif structure, we assign this species to the i-motif. The formation of the i-motif in the same sequence has been corroborated by bulk experiments such as Br(2) footprinting, circular dichroism, and thermal denaturation. The assignment of the i-motif is further confirmed by decreased formation of this structure (23% to 1.3%) with pH 5.5 --> 7.0, which is a well-established behavior for i-motifs. In contrast to that of the i-motif, the formation of the second species with DeltaL of 5.1 nm remains unchanged (6.1 +/- 1.6%) in the same pH range, implying that pH-sensitive C:CH(+) pairs may not contribute to the structure as significantly as those to the i-motif. Compared to the DeltaG(unfold) of an i-motif (16.0 +/- 0.8 kcal/mol), the decreased free energy in the partially folded structure (DeltaG(unfold) 10.4 +/- 0.7 kcal/mol) may reflect a weakened structure with reduced C:CH(+) pairs. Both DeltaL and DeltaG(unfold) argue for the intermediate nature of the partially folded structure in comparison to the i-motif. In line with this argument, we have directly observed the unfolding of an i-motif through the partially folded structure. The i-motif and the partially folded structure share similar rupture forces of 22-26 pN, which are higher than those that can stall transcription catalyzed by RNA polymerases. This suggests, from a mechanical perspective alone, that either of the structures can stop RNA transcription.

Development of an immunofluorescent AR-V7 circulating tumor cell assay - A blood-based test for men with metastatic prostate cancer.

INTRODUCTION: Here we describe the development of a protein immunofluorescent assay for the detection of nuclear-localized androgen receptor variant 7 (AR-V7) protein within circulating tumor cells (CTCs) identified in patient blood samples. Used in the clinic, the test result serves as a validated biomarker of futility for patients with progressing metastatic castration-resistant prostate cancer (mCRPC) who are treated with androgen receptor targeted therapies (AATT) in whom nuclear-localized AR-V7 CTCs are identified and have received level 2A evidence in the 2019 National Cancer Center Network (NCCN) guidelines (v1.0). METHODS: Assay development was completed on the Epic Sciences rare cell detection platform using control cell lines of known AR-V7 status and clinical testing of mCRPC patient samples obtained at the decision point in management. RESULTS AND CONCLUSIONS: Using these samples, all assay parameters, scoring criteria, and clinical cutoffs for positivity were prospectively selected and locked. After assay lock, blinded clinical validation testing was initiated on multiple, independent, clinical cohorts as reported by Scher et al (JAMA Oncol. 2016;2:1441-1449; JAMA Oncol. 2018;4:1179-1186) and Armstrong et al (J Clin Oncol. 2019;37:1120-1129).