Circulating tumor DNA: current challenges for clinical utility

Cancer cells shed naked DNA molecules into the circulation. This circulating tumor DNA (ctDNA) has become the predominant analyte for liquid biopsies to understand the mutational landscape of cancer. Coupled with next-generation sequencing, ctDNA can serve as an alternative substrate to tumor tissues for mutation detection and companion diagnostic purposes. In fact, recent advances in precision medicine have rapidly enabled the use of ctDNA to guide treatment decisions for predicting response and resistance to targeted therapies and immunotherapies. An advantage of using ctDNA over conventional tissue biopsies is the relatively noninvasive approach of obtaining peripheral blood, allowing for simple repeated and serial assessments. Most current clinical practice using ctDNA has endeavored to identify druggable and resistance mutations for guiding systemic therapy decisions, albeit mostly in metastatic disease. However, newer research is evaluating potential for ctDNA as a marker of minimal residual disease in the curative setting and as a useful screening tool to detect cancer in the general population. Here we review the history of ctDNA and liquid biopsies, technologies to detect ctDNA, and some of the current challenges and limitations in using ctDNA as a marker of minimal residual disease and as a general blood-based cancer screening tool. We also discuss the need to develop rigorous clinical studies to prove the clinical utility of ctDNA for future applications in oncology.

Secretory pathway Ca2+-ATPase SPCA2 regulates mitochondrial respiration and DNA damage response through store-independent calcium entry

A complex interplay between the extracellular space, cytoplasm and individual organelles modulates Ca2+ signaling to impact all aspects of cell fate and function. In recent years, the molecular machinery linking endoplasmic reticulum stores to plasma membrane Ca2+ entry has been defined. However, the mechanism and pathophysiological relevance of store-independent modes of Ca2+ entry remain poorly understood. Here, we describe how the secretory pathway Ca2+-ATPase SPCA2 promotes cell cycle progression and survival by activating store-independent Ca2+ entry through plasma membrane Orai1 channels in mammary epithelial cells. Silencing SPCA2 expression or briefly removing extracellular Ca2+ increased mitochondrial ROS production, DNA damage and activation of the ATM/ATR-p53 axis leading to G0/G1 phase cell cycle arrest and apoptosis. Consistent with these findings, SPCA2 knockdown confers redox stress and chemosensitivity to DNA damaging agents. Unexpectedly, SPCA2-mediated Ca2+ entry into mitochondria is required for optimal cellular respiration and the generation of mitochondrial membrane potential. In hormone receptor positive (ER+/PR+) breast cancer subtypes, SPCA2 levels are high and correlate with poor survival prognosis. We suggest that elevated SPCA2 expression could drive pro-survival and chemotherapy resistance in cancer cells, and drugs that target store-independent Ca2+ entry pathways may have therapeutic potential in treating cancer.

An integrated functional and clinical genomics approach reveals genes driving aggressive metastatic prostate cancer

Genomic sequencing of thousands of tumors has revealed many genes associated with specific types of cancer. Similarly, large scale CRISPR functional genomics efforts have mapped genes required for cancer cell proliferation or survival in hundreds of cell lines. Despite this, for specific disease subtypes, such as metastatic prostate cancer, there are likely a number of undiscovered tumor specific driver genes that may represent potential drug targets. To identify such genetic dependencies, we performed genome-scale CRISPRi screens in metastatic prostate cancer models. We then created a pipeline in which we integrated pan-cancer functional genomics data with our metastatic prostate cancer functional and clinical genomics data to identify genes that can drive aggressive prostate cancer phenotypes. Our integrative analysis of these data reveals known prostate cancer specific driver genes, such as AR and HOXB13, as well as a number of top hits that are poorly characterized. In this study we highlight the strength of an integrated clinical and functional genomics pipeline and focus on two top hit genes, KIF4A and WDR62. We demonstrate that both KIF4A and WDR62 drive aggressive prostate cancer phenotypes in vitro and in vivo in multiple models, irrespective of AR-status, and are also associated with poor patient outcome.

Abstract 1125: Secretory pathway calcium ATPase-2 (SPCA2) regulates metastasis by suppressing mesenchymal markers in triple negative breast cancer cell lines

Introduction: Over 90% of cancer deaths in breast cancer are associated with metastasis. Epithelial-mesenchymal transition (EMT) is the hallmark of metastasis. Dysregulation of the Ca2+ toolkit has profound consequences for tumor growth and metastasis, raising hopes for novel avenues of therapeutic intervention. The Secretory Pathway Ca2+-ATPase Isoform 2 (SPCA2) transports Ca2+ from cytoplasm to the Golgi, and elicits Ca2+ influx by interacting with plasma membrane Ca2+ channels. Previously, we showed that SPCA2 is implicated in breast cancer progression (Feng et al., Cell 2010). Furthermore, low SPCA2 expression is associated with triple negative breast cancers (TNBC), which are highly metastatic. Therefore, we investigated if ectopic expression of SPCA2 modulates EMT in TNBC cell lines.

Methods: TCGA invasive breast carcinoma project datasets were accessed through cBioPortal. Gene expression was determined by qPCR and protein expression by Immunoblotting and confocal microscopy. Live cell calcium imaging was performed using Fura-2 AM dye. NSG mice were used for in vivo studies.

Results: Low SPCA2 expression was associated with poor survival in TNBC patients (n=255, P < 0.05). TNBC cell lines show low SPCA2 expression compared to receptor positive cell lines, when normalized to non-tumorigenic epithelial cell line MCF-10A. Similarly, significantly low SPCA2 expression (P < 0.001) was observed in TNBC patients compared to receptor positive subtypes. Interestingly, we did not observe these results in SPCA1, the housekeeping SPCA isoform, revealing isoform-specific function of Golgi calcium pumps in breast cancer subtypes. Ectopic expression of SPCA2 in TNBC cell line MDA-MB-231 significantly increased baseline intracellular Ca2+ levels (P < 0.001) and uptake of extracellular Ca2+ (P < 0.001) through store independent calcium entry. Increased SPCA2 expression suppressed mesenchymal gene markers (CDH2, SNAI1, SNAI2, VIM and ZEB1, P < 0.05), and decreased cell migration in vitro (P < 0.05) in TNBC cell lines. Overexpression of SPCA2 in MDA-MB-231-luc-D3H2LN cell line reduced metastasis in vivo (quantified 5-weeks after injection in mammary fat pad, P < 0.01) (n=6) compared to control group. Treatment of metastatic TNBC patients with histone deacetylase (HDAC) inhibitors is currently being evaluated in clinical trials. We found treatment of TNBC cell lines with FDA-approved HDAC inhibitors vorinostat and romidepsin elevated SPCA2 expression in a dose-dependent manner (P < 0.05), simultaneously decreasing mesenchymal gene expression (P < 0.05).

Conclusion: These novel findings point to a causal link between low SPCA2 levels, poor prognosis, and the epithelial-mesenchymal transition required for breast cancer metastasis. Restoration of SPCA2 expression in TNBC by HDAC inhibitors may have therapeutic potential.

Citation Format: Monish Ram Makena, Donna K. Dang, Myungjun Ko, Manuj Bandral, Rajini Rao. Secretory pathway calcium ATPase-2 (SPCA2) regulates metastasis by suppressing mesenchymal markers in triple negative breast cancer cell lines [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1125.

A Ca2+-ATPase Regulates E-cadherin Biogenesis and Epithelial-Mesenchymal Transition in Breast Cancer Cells

Progression of benign tumors to invasive, metastatic cancer is accompanied by the epithelial-to-mesenchymal transition (EMT), characterized by loss of the cell-adhesion protein E-cadherin. Although silencing mutations and transcriptional repression of the E-cadherin gene have been widely studied, not much is known about posttranslational regulation of E-cadherin in tumors. We show that E-cadherin is tightly coexpressed with the secretory pathway Ca²⁺-ATPase isoform 2, SPCA2 (ATP2C2), in breast tumors. Loss of SPCA2 impairs surface expression of E-cadherin and elicits mesenchymal gene expression through disruption of cell adhesion in tumorspheres and downstream Hippo-YAP signaling. Conversely, ectopic expression of SPCA2 in triple-negative breast cancer elevates baseline Ca²⁺ and YAP phosphorylation, enhances posttranslational expression of E-cadherin, and suppresses mesenchymal gene expression. Thus, loss of SPCA2 phenocopies loss of E-cadherin in the Hippo signaling pathway and EMT-MET transitions, consistent with a functional role for SPCA2 in E-cadherin biogenesis. Furthermore, we show that SPCA2 suppresses invasive phenotypes, including cell migration in vitro and tumor metastasis in vivo. Based on these findings, we propose that SPCA2 functions as a key regulator of EMT and may be a potential therapeutic target for treatment of metastatic cancer. IMPLICATIONS: Posttranslational control of E-cadherin and the Hippo pathway by calcium signaling regulates EMT in breast cancer cells.

NHA2 promotes cyst development in an in vitro model of polycystic kidney disease

KEY POINTS

Significant and selective up-regulation of the Na⁺ /H⁺ exchanger NHA2 (SLC9B2) was observed in cysts of patients with autosomal dominant polycystic kidney disease. Using the MDCK cell model of cystogenesis, it was found that NHA2 increases cyst size. Silencing or pharmacological inhibition of NHA2 inhibits cyst formation in vitro. Polycystin-1 represses NHA2 expression via Ca²⁺ /NFAT signalling whereas the dominant negative membrane-anchored C-terminal fragment (PC1-MAT) increased NHA2 levels. Drugs (caffeine, theophylline) and hormones (vasopressin, aldosterone) known to exacerbate cysts elicit NHA2 expression. Taken together, the findings reveal NHA2 as a potential new player in salt and water homeostasis in the kidney and in the pathogenesis of polycystic kidney disease.

ABSTRACT

Autosomal dominant polycystic kidney disease (ADPKD) is caused by mutations in PKD1 and PKD2 encoding polycystin-1 (PC1) and polycystin-2 (PC2), respectively. The molecular pathways linking polycystins to cyst development in ADPKD are still unclear. Intracystic fluid secretion via ion transporters and channels plays a crucial role in cyst expansion in ADPKD. Unexpectedly, we observed significant and selective up-regulation of NHA2, a member of the SLC9B family of Na⁺ /H⁺ exchangers, that correlated with cyst size and disease severity in ADPKD patients. Using three-dimensional cultures of MDCK cells to model cystogenesis in vitro, we showed that ectopic expression of NHA2 is causal to increased cyst size. Induction of PC1 in MDCK cells inhibited NHA2 expression with concordant inhibition of Ca²⁺ influx through store-dependent and -independent pathways, whereas reciprocal activation of Ca²⁺ influx by the dominant negative membrane-anchored C-terminal tail fragment of PC1 elevated NHA2. We showed that NHA2 is a target of Ca²⁺ /NFAT signalling and is transcriptionally induced by methylxanthine drugs such as caffeine and theophylline, which are contraindicated in ADPKD patients. Finally, we observed robust induction of NHA2 by vasopressin, which is physiologically consistent with increased levels of circulating vasopressin and up-regulation of vasopressin V2 receptors in ADPKD. Our findings have mechanistic implications on the emerging use of vasopressin V2 receptor antagonists such as tolvaptan as safe and effective therapy for polycystic kidney disease and reveal a potential new regulator of transepithelial salt and water transport in the kidney.

Episode treatment groups: an illness classification and episode building system--Part II

The episode treatment group (ETG) methodology is a case-mix adjustment and episode-building system that uses routinely collected claims data. The resulting 558 clinically homogeneous groups adjust for severity by the presence of complicating conditions, comorbidities, and other characteristics of a patient's condition that affect resource utilization. The groups identify both complete and incomplete episodes in addition to those episodes which, from a cost perspective, are either low or high outliers. As a grouping ¿engine,¿ the user controls the amount and format of the claims data as input, providing essentially unlimited provider profiling, demand analysis, disease management, and capitation and predictive modeling possibilities.