Ex vivo expansion of lung cancer-derived disseminated cancer cells from lymph nodes identifies cells associated with metastatic progression

The cellular basis of the apparent aggressiveness in lung cancer is poorly understood but likely associated with functional or molecular features of disseminated cancer cells (DCCs). DCCs from epithelial cancers are mostly detected by antibodies directed against histogenetic markers such as cytokeratin or EpCAM. It has been argued that marker-negative metastatic founder cells might escape detection. We therefore used ex vivo sphere formation for functional detection of candidate metastasis founders. We generated cell suspensions from 199 LN samples of 131 lung cancer patients and placed them into non-adherent cell culture. Sphere formation was associated with detection of DCCs using EpCAM immunocytology and with significantly poorer prognosis. The prognostic impact of sphere formation was strongly associated with high numbers of EpCAM-positive DCCs and aberrant genotypes of expanded spheres. We also noted sphere formation in patients with no evidence of lymphatic spread, however such spheres showed infrequent expression of signature genes associated with spheres from EpCAM-positive samples and displayed neither typical lung cancer mutations (KRAS, TP53, ERBB1) nor copy number variations, but might be linked to disease progression >5 years post curative surgery. We conclude that EpCAM identifies relevant disease-driving DCCs, that such cells can be expanded for model generation and that further research is needed to clarify the functional and prognostic role of rare EpCAM-negative sphere forming cells.

Abstract LB-312: Interleukin 6 transsignaling is a candidate mechanism to drive progression of human DCCs during periods of clinical latency

While thousands of breast cancer cells disseminate and home to bone marrow (BM) until primary surgery, usually less than a handful will succeed in establishing manifest metastases months to years later. Signals and mechanisms determining failure or success of disseminated cancer cells (DCCs) are largely unknown and there is no in vivo model available to study the spontaneous progression and genomic evolution from early bone marrow infiltration to manifestation of bone metastasis, as spontaneous or transgenic mouse models do not generate bone metastases. We therefore profiled DCCs from BM of breast cancer patients long before manifestation of metastasis by RNAseq to identify signals supporting survival or outgrowth of DCCs and identified IL6/PTEN/PI3K signaling as candidate pathway for DCC activation. Since early DCCs often display close-to-normal genomes we used mammary epithelial cells ex vivo isolated from reduction mammoplasties and immortalized pre-malignant breast cancer cell lines as model for functional testing in vitro. Using specific activators and inhibitors of IL6 signaling revealed that IL6 trans, but not classical signaling, regulates stemness of mammary epithelial cells. Moreover, knock-down of PTEN revealed that PI3K/PTEN pathway activation renders cells independent of IL6 trans-signaling. Interestingly, gp130 expression, a pre-requisite for IL6 trans-signaling was found to be down-regulated by bone marrow stromal and endosteal, but not vascular niche cells, and as a consequence the number of cells with stem-like ability was significantly reduced. Consistent with a bottleneck function of microenvironmental DCC control, we found PIK3CA mutations highly associated with late-stage metastatic DCCs and CTCs while generally absent in early DCCs. Our data suggest that the initial steps of metastasis formation depend on microenvironmental signals and are not cancer cell-autonomous.

Citation Format: Melanie Werner-Klein, Ana Grujovic, Milan Obradovic, Martin Hoffmann, Xin Lu, Stefan Kirsch, Steffi Treitschke, Cäcilia Köstler, Kathrin Weidele, Christoph Irlbeck, Catherine Botteron, Christian Werno, Bernhard Polzer, Miodrag Guzvic, Stefan Buchholz, Petra Rümmele, Norbert Heine, Stefan Rose-John, Christoph A. Klein. Interleukin 6 transsignaling is a candidate mechanism to drive progression of human DCCs during periods of clinical latency [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 LB-312.

Microfluidic enrichment, isolation and characterization of disseminated melanoma cells from lymph node samples

For the first time in melanoma, novel therapies have recently shown efficacy in the adjuvant therapy setting, which makes companion diagnostics to guide treatment decisions a desideratum. Early spread of disseminated cancer cells (DCC) to sentinel lymph nodes (SLN) is indicative of poor prognosis in melanoma and early DCCs could therefore provide important information about the malignant seed. Here, we present a strategy for enrichment of DCCs from SLN suspensions using a microfluidic device (Parsortix™, Angle plc). This approach enables the detection and isolation of viable DCCs, followed by molecular analysis and identification of genetic changes. By optimizing the workflow, the established protocol allows a high recovery of DCC from melanoma patient-derived lymph node (LN) suspensions with harvest rates above 60%. We then assessed the integrity of the transcriptome and genome of individual, isolated DCCs. In LNs of melanoma patients, we detected the expression of melanoma-associated transcripts including MLANA (encoding for MelanA protein), analyzed the BRAF and NRAS mutational status and confirmed the malignant origin of isolated melanoma DCCs by comparative genomic hybridization. We demonstrate the feasibility of epitope-independent isolation of LN DCCs using Parsortix™ for subsequent molecular characterization of isolated single DCCs with ample application fields including the use for companion diagnostics or subsequent cellular studies in personalized medicine.

The NAD+ precursor nicotinic acid improves genomic integrity in human peripheral blood mononuclear cells after X-irradiation

NAD⁺ is an essential cofactor for enzymes catalyzing redox-reactions as well as an electron carrier in energy metabolism. Aside from this, NAD⁺ consuming enzymes like poly(ADP-ribose) polymerases and sirtuins are important regulators involved in chromatin-restructuring processes during repair and epigenetics/transcriptional adaption. In order to replenish cellular NAD⁺ levels after cleavage, synthesis starts from precursors such as nicotinamide, nicotinamide riboside or nicotinic acid to match the need for this essential molecule. In the present study, we investigated the impact of supplementation with nicotinic acid on resting and proliferating human mononuclear blood cells with a focus on DNA damage and repair processes. We observed that nicotinic acid supplementation increased NAD⁺ levels as well as DNA repair efficiency and enhanced genomic stability evaluated by micronucleus test after x-ray treatment. Interestingly, resting cells displayed lower basal levels of DNA breaks compared to proliferating cells, but break-induction rates were identical. Despite similar levels of p53 protein upregulation after irradiation, higher NAD⁺ concentrations led to reduced acetylation of this protein, suggesting enhanced SIRT1 activity. Our data reveal that even in normal primary human cells cellular NAD⁺ levels may be limiting under conditions of genotoxic stress and that boosting the NAD⁺ system with nicotinic acid can improve genomic stability.

Abstract 472: A digital sorting-based detection and isolation assay for single disseminated cancer cells from lymph nodes of melanoma patients

We recently showed that sentinel lymph node (SLN) disaggregation followed by immunocytology enables precise quantification of disseminated cancer cells (DCC). We demonstrated that this approach has a 20-fold higher sensitivity to detect melanoma DCCs than routine histopathology and that the DCC density (DCCD, defined as the number of DCCs per million lymph node cells) together with ulceration state and tumor thickness enables individual risk prediction superior to current AJCC guidelines (Ulmer et al., PLoS Medicine, 2014). Here, we present the adaptation of this method to a semi-automated workflow, including automated single cell detection and isolation by DEPArrayTM technology for subsequent molecular analysis of DCCs from SLN of melanoma patients.

The developed workflow includes a mechanical disaggregation of lymph node tissue and collection of the mononuclear cells after Percoll density centrifugation. Several tumor cell enrichment methods were tested (CellSearch® and size-based enrichment technologies), however, failed to process cell suspensions generated from lymph nodes due to clumping of cells during the enrichment procedure. Tumor cell enrichment using MACS depletion of CD45+ cells delivered approx. 50% of spiked-in cell line cells with a mean depletion rate of lymphocytes and erythrocytes > 98%. To prevent limitations in DCC detection caused by phenotypic heterogeneity of tumor cells, we established a double staining against two melanoma-associated markers gp100 and MCSP. Individual melanoma cells are then detected and isolated by DEPArrayTM technology enabling single cell whole genome amplification (Ampli1TM) for subsequent molecular analysis as assessment of copy number alterations (e.g. by arrayCGH) or sequence analysis for melanoma specific point mutations (e.g. BRAF or NRAS). We successfully applied the workflow to first SLN samples from melanoma patients.

The established workflow enables a standardized detection of single DCCs from lymph nodes of melanoma patients applicable in clinical diagnostic labs. Automated single cell isolation and subsequent molecular analysis of DCCs is feasible within short time after SLN biopsy. In the future, this approach could help to select individualized therapies for melanoma patients.

Citation Format: Sebastian Scheitler, Kathrin Weidele, Barbara Alberter, Christian Werno, Christoph A. Klein, Bernhard Polzer. A digital sorting-based detection and isolation assay for single disseminated cancer cells from lymph nodes of melanoma patients. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 472.

DNA damage in Nijmegen Breakage Syndrome cells leads to PARP hyperactivation and increased oxidative stress

Nijmegen Breakage Syndrome (NBS), an autosomal recessive genetic instability syndrome, is caused by hypomorphic mutation of the NBN gene, which codes for the protein nibrin. Nibrin is an integral member of the MRE11/RAD50/NBN (MRN) complex essential for processing DNA double-strand breaks. Cardinal features of NBS are immunodeficiency and an extremely high incidence of hematological malignancies. Recent studies in conditional null mutant mice have indicated disturbances in redox homeostasis due to impaired DSB processing. Clearly this could contribute to DNA damage, chromosomal instability, and cancer occurrence. Here we show, in the complete absence of nibrin in null mutant mouse cells, high levels of reactive oxygen species several hours after exposure to a mutagen. We show further that NBS patient cells, which unlike mouse null mutant cells have a truncated nibrin protein, also have high levels of reactive oxygen after DNA damage and that this increased oxidative stress is caused by depletion of NAD⁺ due to hyperactivation of the strand-break sensor, Poly(ADP-ribose) polymerase. Both hyperactivation of Poly(ADP-ribose) polymerase and increased ROS levels were reversed by use of a specific Poly(ADP-ribose) polymerase inhibitor. The extremely high incidence of malignancy among NBS patients is the result of the combination of a primary DSB repair deficiency with secondary oxidative DNA damage.

Damage to DNA is extremely dangerous because it can lead to mutations in genes that initiate or accelerate the development of a tumor. Evolution has led to highly complex networks of DNA repair enzymes, which for the majority of individuals are extremely effective in keeping our DNA intact. The devastating consequences of DNA damage are manifested in those individuals in which one or other of the repair pathways is non-functional. Several genetic disorders can be attributed to such DNA repair deficiencies and have the common feature of increased tumor incidence as the major life-threatening symptom. Cancer incidence varies amongst these disorders and is probably highest for the disease Nijmegen Breakage Syndrome, where more than 50% of patients develop a hematological malignancy in childhood. We have sought to understand this extremely high incidence by exploiting cells from a mouse model and cells derived from patients. We find that deficiency in the repair of DNA double-strand breaks leads to disturbances in cellular metabolism, leading ultimately to a loss of antioxidative capacity. The ensuing accumulation of highly reactive oxygen species generates further DNA lesions, thus potentiating the initial damage and increasing the likelihood of malignancy.

Ex vivo supplementation with nicotinic acid enhances cellular poly(ADP-ribosyl)ation and improves cell viability in human peripheral blood mononuclear cells

Poly(ADP-ribosyl)ation is a posttranslational modification of proteins, which is mainly catalyzed by poly(ADP-ribose) polymerase-1 (PARP-1) by using NAD(+) as substrate and is directly triggered by DNA strand breaks. Under mild genotoxic stress poly(ADP-ribose) (PAR) formation plays an important role in DNA repair whereas severe genotoxic stress and the ensuing overactivation of PARP-1 induce cellular NAD(+) depletion, energy failure and ultimately cell death. We are interested in studying the consequences of moderately enhanced enzymatic activity under conditions of DNA damage. Here we chose supplementation of cells with the NAD(+) precursor nicotinic acid (NA) as a strategy. In order to reliably assess PAR accumulation in living cells we first developed a novel, sensitive flow-cytometric method for the rapid analysis of poly(ADP-ribose) accumulation (RAPARA). Our data showed that ex vivo supplementation of human peripheral blood mononuclear cells (PBMC) with low concentrations of NA significantly raised cellular NAD(+) levels by 2.1-fold. Upon X-irradiation or exposure to hydrogen peroxide or N-methyl-N'-nitro-N-nitrosoguanidine, PAR accumulation was significantly increased and sustained in NA-supplemented cells. Furthermore, NA-supplemented PBMC displayed significantly higher cell viability due to a lower rate of necrotic cell death. In summary, ex vivo supplementation of human PBMC with NA increases cellular NAD(+) levels, boosts the cellular poly(ADP-ribosyl)ation response to genotoxic treatment, and protects from DNA-damage-induced cell death.