Small-cell lung cancer (SCLC), an aggressive neuroendocrine tumor with early dissemination and dismal prognosis, accounts for 15-20% of lung cancer cases and ∼200,000 deaths each year. Most cases are ...inoperable, and biopsies to investigate SCLC biology are rarely obtainable. Circulating tumor cells (CTCs), which are prevalent in SCLC, present a readily accessible 'liquid biopsy'. Here we show that CTCs from patients with either chemosensitive or chemorefractory SCLC are tumorigenic in immune-compromised mice, and the resultant CTC-derived explants (CDXs) mirror the donor patient's response to platinum and etoposide chemotherapy. Genomic analysis of isolated CTCs revealed considerable similarity to the corresponding CDX. Most marked differences were observed between CDXs from patients with different clinical outcomes. These data demonstrate that CTC molecular analysis via serial blood sampling could facilitate delivery of personalized medicine for SCLC. CDXs are readily passaged, and these unique mouse models provide tractable systems for therapy testing and understanding drug resistance mechanisms.
In this issue of Cancer Cell, Gay et al. describe a molecular classification of small cell lung cancers and extend prior studies that highlight the potential for personalized treatments. Notably, ...they identify a new “inflamed” subtype that may emerge following acquired chemoresistance but which may become more susceptible to immunotherapy.
In this issue of Cancer Cell, Gay et al. describe a molecular classification of small cell lung cancers and extend prior studies that highlight the potential for personalized treatments. Notably, they identify a new “inflamed” subtype that may emerge following acquired chemoresistance but which may become more susceptible to immunotherapy.
Facilitated binding of p53 to DNA by high mobility group B1 (HMGB1) may involve interaction between the N-terminal region of p53 and the high mobility group (HMG) boxes, as well as HMG-induced ...bending of the DNA. Intramolecular shielding of the boxes by the HMGB1 acidic tail results in an unstable complex with p53 until the tail is truncated to half its length, at which point the A box, proposed to be the preferred binding site for p53(1–93), is exposed, leaving the B box to bind and bend DNA. The A box interacts with residues 38–61 (TAD2) of the p53 transactivation domain. Residues 19–26 (TAD1) bind weakly, but only in the context of p53(1–93) and not as a free TAD1 peptide. We have solved the structure of the A-box/p53(1–93) complex by nuclear magnetic resonance spectroscopy. The incipient amphipathic helix in TAD2 recognizes the concave DNA-binding face of the A box and may be acting as a single-stranded DNA mimic.
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► Binding of p53 to its cognate DNA is facilitated by HMGB1 ► The N-terminal region of p53 (residues 38–61; TAD2) interacts with the HMG boxes ► The acidic tail of HMGB1 masks the p53 binding site in the free proteins ► The structure of the A-box/p53(1–93) complex shows that TAD2 acts as an ss-DNA mimic
HMGB1 facilitates binding of p53 to its cognate, DNA, through interaction between the N-terminal region of p53 (p53N) and the HMG boxes. Rowell et al. report a structure of the complex between HMGB1 A-box and p53N, showing that p53N recognizes the DNA-binding face of the A box, potentially acting as an ssDNA mimic.
Small cell lung cancer (SCLC) is characterized by prevalent circulating tumour cells (CTCs), early metastasis and poor prognosis. We show that SCLC patients (37/38) have rare CTC subpopulations ...co-expressing vascular endothelial-cadherin (VE-cadherin) and cytokeratins consistent with vasculogenic mimicry (VM), a process whereby tumour cells form 'endothelial-like' vessels. Single-cell genomic analysis reveals characteristic SCLC genomic changes in both VE-cadherin-positive and -negative CTCs. Higher levels of VM are associated with worse overall survival in 41 limited-stage patients' biopsies (P<0.025). VM vessels are also observed in 9/10 CTC patient-derived explants (CDX), where molecular analysis of fractionated VE-cadherin-positive cells uncovered copy-number alterations and mutated TP53, confirming human tumour origin. VE-cadherin is required for VM in NCI-H446 SCLC xenografts, where VM decreases tumour latency and, despite increased cisplatin intra-tumour delivery, decreases cisplatin efficacy. The functional significance of VM in SCLC suggests VM regulation may provide new targets for therapeutic intervention.
Recent consensus defines four SCLC subtypes on the basis of transcription factor expression: ASCL1, NEUROD1, POU2F3, and YAP1. The rare YAP1 subtype is associated with “neuroendocrine (NE)-low” cells ...among SCLC cell lines and patient samples. We evaluated YAP1 in 39 patients with phenotypically diverse circulating tumor cell–derived explant (CDX) models and revisited YAP1 in terms of prevalence, cell phenotype, and intertumor and intratumor heterogeneity.
YAP1 transcript and protein expression were assessed by RNA sequencing and immunohistochemistry or multiplexed immunofluorescence of NE and non-NE CDX subpopulations. Physically separated NE and non-NE CDX ex vivo culture lysates were Western blotted for YAP1, NE marker SYP, and AXL.
RNA sequencing normalized for the four subtype transcription factors identified YAP1 expression in 14 of 39 CDX. A total of 10 CDX expressed YAP1 protein, and eight had strong YAP1 expression confined to rare non-NE cell clusters. This was confirmed in ex vivo CDX cultures in which adherent non-NE cells lacking SYP expression expressed YAP1. However, in two CDX, weaker cellular YAP1 expression was observed, widely dispersed in SYP-positive NE cells.
YAP1 was predominantly expressed in non-NE cell clusters in SCLC CDX, but two of 39 CDX expressed YAP1 in NE cells. CDX22P, with relatively high YAP1 expression, is an ASCL1 NE subtype with a low NE score and an outlier within this subtype in our CDX biobank. These descriptive data reveal subtly different YAP1 expression profiles, paving the way for functional studies to compare YAP1 signaling in non-NE and low NE cell contexts for potentially personalized therapeutic approaches.
Introduced in 1987, platinum-based chemotherapy remains standard of care for small cell lung cancer (SCLC), a most aggressive, recalcitrant tumor. Prominent barriers to progress are paucity of tumor ...tissue to identify drug targets and patient-relevant models to interrogate novel therapies. Following our development of circulating tumor cell patient-derived explants (CDX) as models that faithfully mirror patient disease, here we exploit CDX to examine new therapeutic options for SCLC.
We investigated the efficacy of the PARP inhibitor olaparib alone or in combination with the WEE1 kinase inhibitor AZD1775 in 10 phenotypically distinct SCLC CDX
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These CDX represent chemosensitive and chemorefractory disease including the first reported paired CDX generated longitudinally before treatment and upon disease progression.
There was a heterogeneous depth and duration of response to olaparib/AZD1775 that diminished when tested at disease progression. However, efficacy of this combination consistently exceeded that of cisplatin/etoposide, with cures in one CDX model. Genomic and protein analyses revealed defects in homologous recombination repair genes and oncogenes that induce replication stress (such as MYC family members), predisposed CDX to combined olaparib/AZD1775 sensitivity, although universal predictors of response were not noted.
These preclinical data provide a strong rationale to trial this combination in the clinic informed by prevalent, readily accessed circulating tumor cell-based biomarkers. New therapies will be evaluated in SCLC patients after first-line chemotherapy, and our data suggest that the combination of olaparib/AZD1775 should be used as early as possible and before disease relapse.
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The localization of mRNA to defined cytoplasmic sites in eukaryotic cells not only allows localized protein production but also determines the fate of mRNAs. For instance, translationally repressed ...mRNAs localize to P-bodies and stress granules where their decay and storage, respectively, are directed. Here, we find that several mRNAs are localized to granules in unstressed, actively growing cells. These granules play a key role in the stress-dependent formation of P-bodies. Specific glycolytic mRNAs are colocalized in multiple granules per cell, which aggregate during P-body formation. Such aggregation is still observed under conditions or in mutants where P-bodies do not form. In unstressed cells, the mRNA granules appear associated with active translation; this might enable a coregulation of protein expression from the same pathways or complexes. Parallels can be drawn between this coregulation and the advantage of operons in prokaryotic systems.
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•Specific mRNAs are localized to cytoplasmic granules in actively growing cells•After stress, the granules serve as a platform for P-body formation•Certain glycolytic mRNAs colocalize and are translated in cytoplasmic granules•Translation of functionally related mRNAs may be coregulated in the granules
Lui et al. show that specific mRNAs localize to granules in actively growing cells. These mRNA granules are associated with active translation and are proposed to allow coregulation of protein expression from the same pathway or complex. Following stress, the granules aggregate to drive the formation of P-bodies.
Although small cell lung cancer (SCLC) is treated as a homogeneous disease, biopsies and preclinical models reveal heterogeneity in transcriptomes and morphology. SCLC subtypes were recently defined ...by neuroendocrine transcription factor (NETF) expression. Circulating-tumor-cell-derived explant models (CDX) recapitulate donor patients' tumor morphology, diagnostic NE marker expression and chemotherapy responses. We describe a biobank of 38 CDX models, including six CDX pairs generated pretreatment and at disease progression revealing complex intra- and intertumoral heterogeneity. Transcriptomic analysis confirmed three of four previously described subtypes based on ASCL1, NEUROD1 and POU2F3 expression and identified a previously unreported subtype based on another NETF, ATOH1. We document evolution during disease progression exemplified by altered MYC and NOTCH gene expression, increased 'variant' cell morphology, and metastasis without strong evidence of epithelial to mesenchymal transition. This CDX biobank provides a research resource to facilitate SCLC personalized medicine.
Vasculogenic mimicry (VM) describes the formation of pseudo blood vessels constructed of tumor cells that have acquired endothelial-like properties. VM channels endow the tumor with a tumor-derived ...vascular system that directly connects to host blood vessels, and their presence is generally associated with poor patient prognosis. Here we show that the transcription factor, Foxc2, promotes VM in diverse solid tumor types by driving ectopic expression of endothelial genes in tumor cells, a process that is stimulated by hypoxia. VM-proficient tumors are resistant to anti-angiogenic therapy, and suppression of Foxc2 augments response. This work establishes co-option of an embryonic endothelial transcription factor by tumor cells as a key mechanism driving VM proclivity and motivates the search for VM-inhibitory agents that could form the basis of combination therapies with anti-angiogenics.
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•FOXC2 is upregulated in vasculogenic mimicry (VM)-proficient tumor cells•FOXC2 regulates endothelial genes in tumor cells•Severe hypoxia promotes quasi-endothelial differentiation of tumor cells•FOXC2-driven VM promotes resistance to anti-angiogenic therapy
Cannell et al. identify the transcription factor FOXC2 as a driver of vasculogenic mimicry (VM). VM describes the formation of pseudo blood vessels lined by tumor cells that have acquired endothelial-like properties. FOXC2 promotes ectopic expression of endothelial genes in tumor cells and promotes resistance to anti-angiogenic therapies.
Poorly differentiated neuroendocrine carcinomas (PD-NEC) are rare cancers garnering interest as they become more commonly encountered in the clinic. This is due to improved diagnostic methods and the ...increasingly observed phenomenon of "NE lineage plasticity," whereby nonneuroendocrine (non-NE) epithelial cancers transition to aggressive NE phenotypes after targeted treatment. Effective treatment options for patients with PD-NEC are challenging for several reasons. This includes a lack of targetable, recurrent molecular drivers, a paucity of patient-relevant preclinical models to study biology and test novel therapeutics, and the absence of validated biomarkers to guide clinical management. Although advances have been made pertaining to molecular subtyping of small cell lung cancer (SCLC), a PD-NEC of lung origin, extrapulmonary (EP)-PD-NECs remain understudied. This review will address emerging SCLC-like, same-organ non-NE cancer-like and tumor-type-agnostic biological vulnerabilities of EP-PD-NECs, with the potential for therapeutic exploitation. The hypotheses surrounding the origin of these cancers and how "NE lineage plasticity" can be leveraged for therapeutic purposes are discussed. SCLC is herein proposed as a paradigm for supporting progress toward precision medicine in EP-PD-NECs. The aim of this review is to provide a thorough portrait of the current knowledge of EP-PD-NEC biology, with a view to informing new avenues for research and future therapeutic opportunities in these cancers of unmet need.
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