SOX17 enables immune evasion of early colorectal adenomas and cancers

A hallmark of cancer is the avoidance of immune destruction. This process has been primarily investigated in locally advanced or metastatic cancer1-3; however, much less is known about how pre-malignant or early invasive tumours evade immune detection. Here, to understand this process in early colorectal cancers (CRCs), we investigated how naive colon cancer organoids that were engineered in vitro to harbour Apc-null, KrasG12D and Trp53-null (AKP) mutations adapted to the in vivo native colonic environment. Comprehensive transcriptomic and chromatin analyses revealed that the endoderm-specifying transcription factor SOX17 became strongly upregulated in vivo. Notably, whereas SOX17 loss did not affect AKP organoid propagation in vitro, its loss markedly reduced the ability of AKP tumours to persist in vivo. The small fraction of SOX17-null tumours that grew displayed notable interferon-γ (IFNγ)-producing effector-like CD8+ T cell infiltrates in contrast to the immune-suppressive microenvironment in wild-type counterparts. Mechanistically, in both endogenous Apc-null pre-malignant adenomas and transplanted organoid-derived AKP CRCs, SOX17 suppresses the ability of tumour cells to sense and respond to IFNγ, preventing anti-tumour T cell responses. Finally, SOX17 engages a fetal intestinal programme that drives differentiation away from LGR5+ tumour cells to produce immune-evasive LGR5- tumour cells with lower expression of major histocompatibility complex class I (MHC-I). We propose that SOX17 is a transcription factor that is engaged during the early steps of colon cancer to orchestrate an immune-evasive programme that permits CRC initiation and progression.

Ultrasensitive Detection of Circulating LINE-1 ORF1p as a Specific Multicancer Biomarker

Improved biomarkers are needed for early cancer detection, risk stratification, treatment selection, and monitoring treatment response. Although proteins can be useful blood-based biomarkers, many have limited sensitivity or specificity for these applications. Long INterspersed Element-1 (LINE-1) open reading frame 1 protein (ORF1p) is a transposable element protein overexpressed in carcinomas and high-risk precursors during carcinogenesis with negligible expression in normal tissues, suggesting ORF1p could be a highly specific cancer biomarker. To explore ORF1p as a blood-based biomarker, we engineered ultrasensitive digital immunoassays that detect mid-attomolar (10-17 mol/L) ORF1p concentrations in plasma across multiple cancers with high specificity. Plasma ORF1p shows promise for early detection of ovarian cancer, improves diagnostic performance in a multianalyte panel, provides early therapeutic response monitoring in gastroesophageal cancers, and is prognostic for overall survival in gastroesophageal and colorectal cancers. Together, these observations nominate ORF1p as a multicancer biomarker with potential utility for disease detection and monitoring.

SIGNIFICANCE

The LINE-1 ORF1p transposon protein is pervasively expressed in many cancers and is a highly specific biomarker of multiple common, lethal carcinomas and their high-risk precursors in tissue and blood. Ultrasensitive ORF1p assays from as little as 25 μL plasma are novel, rapid, cost-effective tools in cancer detection and monitoring. See related commentary by Doucet and Cristofari, p. 2502. This article is featured in Selected Articles from This Issue, p. 2489.

Beta-Hydroxybutyrate Augments Oxaliplatin-Induced Cytotoxicity by Altering Energy Metabolism in Colorectal Cancer Organoids

Deregulation of cellular metabolism has recently emerged as a notable cancer characteristic. This reprogramming of key metabolic pathways supports tumor growth. Targeting cancer metabolism demonstrates the potential for managing colorectal cancer. Beta-hydroxybutyrate (BOHB) acts as an acetyl-CoA source for the tricarboxylic acid (TCA) cycle, possibly redirecting energy metabolic pathways towards the TCA cycle that could enhance sensitivity to oxaliplatin, through the generation of reactive oxygen species (ROS). This study explores the potential of BOHB to enhance oxaliplatin's cytotoxic effect by altering the energy metabolism in colorectal cancer. The study employed advanced in vitro organoid technology, which successfully emulates in vivo physiology. The combination treatment efficacy of BOHB and oxaliplatin was evaluated via cell viability assay. The levels of key proteins involved in energy metabolism, apoptotic pathways, DNA damage markers, and histone acetylation were analyzed via Western Blot. ROS levels were evaluated via flow cytometer. Non-toxic doses of BOHB with oxaliplatin significantly amplified cytotoxicity in colorectal cancer organoids. Treatment with BOHB and/or melatonin resulted in significantly decreased lactate dehydrogenase A and increased mitochondrial carrier protein 2 levels, indicating inhibited aerobic glycolysis and an increased oxidative phosphorylation rate. This metabolic shift induced apoptotic cell death mediated by oxaliplatin, owing to high levels of ROS. Melatonin counteracted this effect by protecting cancer cells from high oxidative stress conditions. BOHB may enhance the efficacy of chemotherapeutics with a similar mechanism of action to oxaliplatin in colorectal cancer treatment. These innovative combinations could improve treatment outcomes for colorectal cancer patients.

Chronic metabolic stress drives developmental programs and loss of tissue functions in non-transformed liver that mirror tumor states and stratify survival

Under chronic stress, cells must balance competing demands between cellular survival and tissue function. In metabolic dysfunction-associated steatotic liver disease (MASLD, formerly NAFLD/NASH), hepatocytes cooperate with structural and immune cells to perform crucial metabolic, synthetic, and detoxification functions despite nutrient imbalances. While prior work has emphasized stress-induced drivers of cell death, the dynamic adaptations of surviving cells and their functional repercussions remain unclear. Namely, we do not know which pathways and programs define cellular responses, what regulatory factors mediate (mal)adaptations, and how this aberrant activity connects to tissue-scale dysfunction and long-term disease outcomes. Here, by applying longitudinal single-cell multi -omics to a mouse model of chronic metabolic stress and extending to human cohorts, we show that stress drives survival-linked tradeoffs and metabolic rewiring, manifesting as shifts towards development-associated states in non-transformed hepatocytes with accompanying decreases in their professional functionality. Diet-induced adaptations occur significantly prior to tumorigenesis but parallel tumorigenesis-induced phenotypes and predict worsened human cancer survival. Through the development of a multi -omic computational gene regulatory inference framework and human in vitro and mouse in vivo genetic perturbations, we validate transcriptional (RELB, SOX4) and metabolic (HMGCS2) mediators that co-regulate and couple the balance between developmental state and hepatocyte functional identity programming. Our work defines cellular features of liver adaptation to chronic stress as well as their links to long-term disease outcomes and cancer hallmarks, unifying diverse axes of cellular dysfunction around core causal mechanisms.

Dietary fat and lipid metabolism in the tumor microenvironment

Metabolic reprogramming has been considered a core hallmark of cancer, in which excessive accumulation of lipids promote cancer initiation, progression and metastasis. Lipid metabolism often includes the digestion and absorption of dietary fat, and the ways in which cancer cells utilize lipids are often influenced by the complex interactions within the tumor microenvironment. Among multiple cancer risk factors, obesity has a positive association with multiple cancer types, while diets like calorie restriction and fasting improve health and delay cancer. Impact of these diets on tumorigenesis or cancer prevention are generally studied on cancer cells, despite heterogeneity of the tumor microenvironment. Cancer cells regularly interact with these heterogeneous microenvironmental components, including immune and stromal cells, to promote cancer progression and metastasis, and there is an intricate metabolic crosstalk between these compartments. Here, we focus on discussing fat metabolism and response to dietary fat in the tumor microenvironment, focusing on both immune and stromal components and shedding light on therapeutic strategies surrounding lipid metabolic and signaling pathways.

Ablative radiotherapy improves survival but does not cure autochthonous mouse models of prostate and colorectal cancer

BACKGROUND

Genetically engineered mouse models (GEMMs) of cancer are powerful tools to study mechanisms of disease progression and therapy response, yet little is known about how these models respond to multimodality therapy used in patients. Radiation therapy (RT) is frequently used to treat localized cancers with curative intent, delay progression of oligometastases, and palliate symptoms of metastatic disease.

METHODS

Here we report the development, testing, and validation of a platform to immobilize and target tumors in mice with stereotactic ablative RT (SART). Xenograft and autochthonous tumor models were treated with hypofractionated ablative doses of radiotherapy.

RESULTS

We demonstrate that hypofractionated regimens used in clinical practice can be effectively delivered in mouse models. SART alters tumor stroma and the immune environment, improves survival in GEMMs of primary prostate and colorectal cancer, and synergizes with androgen deprivation in prostate cancer. Complete pathologic responses were achieved in xenograft models, but not in GEMMs.

CONCLUSIONS

While SART is capable of fully ablating xenografts, it is unable to completely eradicate disease in GEMMs, arguing that resistance to potentially curative therapy can be modeled in GEMMs.

Stiffness Restricts the Stemness of the Intestinal Stem Cells and Skews Their Differentiation Toward Goblet Cells

BACKGROUND & AIMS

Fibrosis and tissue stiffening are hallmarks of inflammatory bowel disease (IBD). We have hypothesized that the increased stiffness directly contributes to the dysregulation of the epithelial cell homeostasis in IBD. Here, we aim to determine the impact of tissue stiffening on the fate and function of the intestinal stem cells (ISCs).

METHODS

We developed a long-term culture system consisting of 2.5-dimensional intestinal organoids grown on a hydrogel matrix with tunable stiffness. Single-cell RNA sequencing provided stiffness-regulated transcriptional signatures of the ISCs and their differentiated progeny. YAP-knockout and YAP-overexpression mice were used to manipulate YAP expression. In addition, we analyzed colon samples from murine colitis models and human IBD samples to assess the impact of stiffness on ISCs in vivo.

RESULTS

We demonstrated that increasing the stiffness potently reduced the population of LGR5+ ISCs and KI-67+-proliferating cells. Conversely, cells expressing the stem cell marker, olfactomedin-4, became dominant in the crypt-like compartments and pervaded the villus-like regions. Concomitantly, stiffening prompted the ISCs to preferentially differentiate toward goblet cells. Mechanistically, stiffening increased the expression of cytosolic YAP, driving the extension of olfactomedin-4+ cells into the villus-like regions, while it induced the nuclear translocation of YAP, leading to preferential differentiation of ISCs toward goblet cells. Furthermore, analysis of colon samples from murine colitis models and patients with IBD demonstrated cellular and molecular remodeling reminiscent of those observed in vitro.

CONCLUSIONS

Collectively, our findings highlight that matrix stiffness potently regulates the stemness of ISCs and their differentiation trajectory, supporting the hypothesis that fibrosis-induced gut stiffening plays a direct role in epithelial remodeling in IBD.

An RNA Damage Response Network Mediates the Lethality of 5-FU in Clinically Relevant Tumor Types

5-fluorouracil (5-FU) is a successful and broadly used anti-cancer therapeutic. A major mechanism of action of 5-FU is thought to be through thymidylate synthase (TYMS) inhibition resulting in dTTP depletion and activation of the DNA damage response. This suggests that 5-FU should synergize with other DNA damaging agents. However, we found that combinations of 5-FU and oxaliplatin or irinotecan failed to display any evidence of synergy in clinical trials, and resulted in sub-additive killing in a panel of colorectal cancer (CRC) cell lines. In seeking to understand this antagonism, we unexpectedly found that an RNA damage response during ribosome biogenesis dominates the drug's efficacy in tumor types for which 5-FU shows clinical benefit. 5-FU has an inherent bias for RNA incorporation, and blocking this greatly reduced drug-induced lethality, indicating that accumulation of damaged RNA is more deleterious than the lack of new RNA synthesis. Using 5-FU metabolites that specifically incorporate into either RNA or DNA revealed that CRC cell lines and patient-derived colorectal cancer organoids are inherently more sensitive to RNA damage. This difference held true in cell lines from other tissues in which 5-FU has shown clinical utility, whereas cell lines from tumor tissues that lack clinical 5-FU responsiveness typically showed greater sensitivity to the drug's DNA damage effects. Analysis of changes in the phosphoproteome and ubiquitinome shows RNA damage triggers the selective ubiquitination of multiple ribosomal proteins leading to autophagy-dependent rRNA catabolism and proteasome-dependent degradation of ubiquitinated ribosome proteins. Further, RNA damage response to 5-FU is selectively enhanced by compounds that promote ribosome biogenesis, such as KDM2A inhibitors. These results demonstrate the presence of a strong RNA damage response linked to apoptotic cell death, with clear utility of combinatorially targeting this response in cancer therapy.

Metabolism and Colorectal Cancer

Reprogrammed metabolism is a hallmark of colorectal cancer (CRC). CRC cells are geared toward rapid proliferation, requiring nutrients and the removal of cellular waste in nutrient-poor environments. Intestinal stem cells (ISCs), the primary cell of origin for CRCs, must adapt their metabolism along the adenoma-carcinoma sequence to the unique features of their complex microenvironment that include interactions with intestinal epithelial cells, immune cells, stromal cells, commensal microbes, and dietary components. Emerging evidence implicates modifiable risk factors related to the environment, such as diet, as important in CRC pathogenesis. Here, we focus on describing the metabolism of ISCs, diets that influence CRC initiation, CRC genetics and metabolism, and the tumor microenvironment. The mechanistic links between environmental factors, metabolic adaptations, and the tumor microenvironment in enhancing or supporting CRC tumorigenesis are becoming better understood. Thus, greater knowledge of CRC metabolism holds promise for improved prevention and treatment.

Post-fast refeeding enhances intestinal stem cell-mediated regeneration and tumourigenesis through mTORC1-dependent polyamine synthesis

For more than a century, fasting regimens have improved health, lifespan, and tissue regeneration in diverse organisms, including humans. However, how fasting and post-fast refeeding impact adult stem cells and tumour formation has yet to be explored in depth. Here, we demonstrate that post-fast refeeding increases intestinal stem cell (ISC) proliferation and tumour formation: Post-fast refeeding augments the regenerative capacity of Lgr5+ intestinal stem cells (ISCs), and loss of the tumour suppressor Apc in ISCs under post-fast refeeding leads to a higher tumour incidence in the small intestine and colon than in the fasted or ad libitum (AL) fed states. This demonstrates that post-fast refeeding is a distinct state. Mechanistically, we discovered that robust induction of mTORC1 in post-fast-refed ISCs increases protein synthesis via polyamine metabolism to drive these changes, as inhibition of mTORC1, polyamine metabolite production, or protein synthesis abrogates the regenerative or tumourigenic effects of post-fast refeeding. Thus, fast-refeeding cycles must be carefully considered when planning diet-based strategies for regeneration without increasing cancer risk, as post-fast refeeding leads to a burst not only in stem cell-driven regeneration but also in tumourigenicity.

Single-cell profiling of environmental enteropathy reveals signatures of epithelial remodeling and immune activation

Environmental enteropathy (EE) is a subclinical condition of the small intestine that is highly prevalent in low- and middle-income countries. It is thought to be a key contributing factor to childhood malnutrition, growth stunting, and diminished oral vaccine responses. Although EE has been shown to be the by-product of a recurrent enteric infection, its full pathophysiology remains unclear. Here, we mapped the cellular and molecular correlates of EE by performing high-throughput, single-cell RNA-sequencing on 33 small intestinal biopsies from 11 adults with EE in Lusaka, Zambia (eight HIV-negative and three HIV-positive), six adults without EE in Boston, United States, and two adults in Durban, South Africa, which we complemented with published data from three additional individuals from the same clinical site. We analyzed previously defined bulk-transcriptomic signatures of reduced villus height and decreased microbial translocation in EE and showed that these signatures may be driven by an increased abundance of surface mucosal cells-a gastric-like subset previously implicated in epithelial repair in the gastrointestinal tract. In addition, we determined cell subsets whose fractional abundances associate with EE severity, small intestinal region, and HIV infection. Furthermore, by comparing duodenal EE samples with those from three control cohorts, we identified dysregulated WNT and MAPK signaling in the EE epithelium and increased proinflammatory cytokine gene expression in a T cell subset highly expressing a transcriptional signature of tissue-resident memory cells in the EE cohort. Together, our work elucidates epithelial and immune correlates of EE and nominates cellular and molecular targets for intervention.

Lymphatics and fibroblasts support intestinal stem cells in homeostasis and injury

Lgr5⁺ intestinal stem cells (ISCs) depend on niche factors for their proper function. However, the source of these ISC niche factors and how they support ISCs in vivo remain controversial. Here, we report that ISCs depend on lymphatic endothelial cells (LECs) and RSPO3⁺GREM1⁺ fibroblasts (RGFs). In the intestine and colon, LECs are surrounded by RGFs and are located near ISCs at the crypt base. Both LECs and RGFs provide the critical ISC niche factor RSPO3 to support ISCs, where RSPO3 loss in both cell types drastically compromises ISC numbers, villi length, and repair after injury. In response to injury, LEC and RGF numbers expand and produce greater amounts of RSPO3 and other growth/angiocrine factors to foster intestinal repair. We propose that LECs represent a novel niche component for ISCs, which together with RGFs serve as the major in vivo RSPO3 source for ISCs in homeostasis and injury-mediated regeneration.

Screening for modulators of the cellular composition of gut epithelia via organoid models of intestinal stem cell differentiation

The cellular composition of barrier epithelia is essential to organismal homoeostasis. In particular, within the small intestine, adult stem cells establish tissue cellularity, and may provide a means to control the abundance and quality of specialized epithelial cells. Yet, methods for the identification of biological targets regulating epithelial composition and function, and of small molecules modulating them, are lacking. Here we show that druggable biological targets and small-molecule regulators of intestinal stem cell differentiation can be identified via multiplexed phenotypic screening using thousands of miniaturized organoid models of intestinal stem cell differentiation into Paneth cells, and validated via longitudinal single-cell RNA-sequencing. We found that inhibitors of the nuclear exporter Exportin 1 modulate the fate of intestinal stem cells, independently of known differentiation cues, significantly increasing the abundance of Paneth cells in the organoids and in wild-type mice. Physiological organoid models of the differentiation of intestinal stem cells could find broader utility for the screening of biological targets and small molecules that can modulate the composition and function of other barrier epithelia.

Combined Supplementation with Vitamin B-6 and Curcumin is Superior to Either Agent Alone in Suppressing Obesity-Promoted Colorectal Tumorigenesis in Mice

BACKGROUND

Obesity increases the colorectal cancer risk, in part by elevating colonic proinflammatory cytokines. Curcumin (CUR) and supplemental vitamin B-6 each suppress colonic inflammation.

OBJECTIVES

We examined whether the combination of CUR and vitamin B-6 amplifies each supplement's effects and thereby suppress obesity-promoted tumorigenesis.

METHODS

Male Friend Virus B (FVB) mice (4-week-old; n = 110) received 6 weekly injections of azoxymethane beginning 1 week after arrival. Thereafter, they were randomized to receive a low-fat diet (10% energy from fat), a high-fat diet (HFD; 60% energy from fat), a HFD containing 0.2% CUR, a HFD containing supplemental vitamin B-6 (24 mg pyridoxine HCl/kg), or a HFD containing both CUR and supplemental vitamin B-6 (C + B) for 15 weeks. Colonic inflammation, assessed by fecal calprotectin, and tumor metrics were the primary endpoints. The anti-inflammatory efficacy of the combination was also determined in human colonic organoids.

RESULTS

HFD-induced obesity produced a 2.6-fold increase in plasma IL-6 (P < 0.02), a 1.9-fold increase in fecal calprotectin (P < 0.05), and a 2.2-fold increase in tumor multiplicity (P < 0.05). Compared to the HFD group, the C + B combination, but not the individual agents, decreased fecal calprotectin (66%; P < 0.01) and reduced tumor multiplicity and the total tumor burden by 60%-80% (P < 0.03) in an additive fashion. The combination of C + B also significantly downregulated colonic phosphatidylinositol-4,5-bisphosphate 3-kinase, Wnt, and NF-κB signaling by 31%-47% (P < 0.05), effects largely absent with the single agents. Observations that may explain how the 2 agents work additively include a 2.8-fold increased colonic concentration of 3-hydroxyanthranillic acid (P < 0.05) and a 1.3-fold higher colonic concentration of the active coenzymatic form of vitamin B-6 (P < 0.05). In human colonic organoids, micromolar concentrations of CUR, vitamin B-6, and their combination suppressed secreted proinflammatory cytokines by 41%-93% (P < 0.03), demonstrating relevance to humans.

CONCLUSIONS

In this mouse model, C + B is superior to either agent alone in preventing obesity-promoted colorectal carcinogenesis. Augmented suppression of procancerous signaling pathways may be the means by which this augmentation occurs.

Transcriptome-wide In Vitro Effects of Aspirin on Patient-derived Normal Colon Organoids

Mechanisms underlying aspirin chemoprevention of colorectal cancer remain unclear. Prior studies have been limited because of the inability of preclinical models to recapitulate human normal colon epithelium or cellular heterogeneity present in mucosal biopsies. To overcome some of these obstacles, we performed in vitro aspirin treatment of colon organoids derived from normal mucosal biopsies to reveal transcriptional networks relevant to aspirin chemoprevention. Colon organoids derived from 38 healthy individuals undergoing endoscopy were treated with 50 μmol/L aspirin or vehicle control for 72 hours and subjected to bulk RNA sequencing. Paired regression analysis using DESeq2 identified differentially expressed genes (DEG) associated with aspirin treatment. Cellular composition was determined using CIBERSORTx. Aspirin treatment was associated with 1,154 significant (q < 0.10) DEGs prior to deconvolution. We provide replication of these findings in an independent population-based RNA-sequencing dataset of mucosal biopsies (BarcUVa-Seq), where a significant enrichment for overlap of DEGs was observed (P < 2.2E-16). Single-cell deconvolution revealed changes in cell composition, including a decrease in transit-amplifying cells following aspirin treatment (P = 0.01). Following deconvolution, DEGs included novel putative targets for aspirin such as TRABD2A (q = 0.055), a negative regulator of Wnt signaling. Weighted gene co-expression network analysis identified 12 significant modules, including two that contained hubs for EGFR and PTGES2, the latter being previously implicated in aspirin chemoprevention. In summary, aspirin treatment of patient-derived colon organoids using physiologically relevant doses resulted in transcriptome-wide changes that reveal altered cell composition and improved understanding of transcriptional pathways, providing novel insight into its chemopreventive properties. PREVENTION RELEVANCE: Numerous studies have highlighted a role for aspirin in colorectal cancer chemoprevention, though the mechanisms driving this association remain unclear. We addressed this by showing that aspirin treatment of normal colon organoids diminished the transit-amplifying cell population, inhibited prostaglandin synthesis, and dysregulated expression of novel genes implicated in colon tumorigenesis.

Cell size is a determinant of stem cell potential during aging

Stem cells are remarkably small. Whether small size is important for stem cell function is unknown. We find that hematopoietic stem cells (HSCs) enlarge under conditions known to decrease stem cell function. This decreased fitness of large HSCs is due to reduced proliferation and was accompanied by altered metabolism. Preventing HSC enlargement or reducing large HSCs in size averts the loss of stem cell potential under conditions causing stem cell exhaustion. Last, we show that murine and human HSCs enlarge during aging. Preventing this age-dependent enlargement improves HSC function. We conclude that small cell size is important for stem cell function in vivo and propose that stem cell enlargement contributes to their functional decline during aging.

Dietary suppression of MHC class II expression in intestinal epithelial cells enhances intestinal tumorigenesis

Little is known about how interactions of diet, intestinal stem cells (ISCs), and immune cells affect early-stage intestinal tumorigenesis. We show that a high-fat diet (HFD) reduces the expression of the major histocompatibility complex class II (MHC class II) genes in intestinal epithelial cells, including ISCs. This decline in epithelial MHC class II expression in a HFD correlates with reduced intestinal microbiome diversity. Microbial community transfer experiments suggest that epithelial MHC class II expression is regulated by intestinal flora. Mechanistically, pattern recognition receptor (PRR) and interferon-gamma (IFNγ) signaling regulates epithelial MHC class II expression. MHC class II-negative (MHC-II-) ISCs exhibit greater tumor-initiating capacity than their MHC class II-positive (MHC-II+) counterparts upon loss of the tumor suppressor Apc coupled with a HFD, suggesting a role for epithelial MHC class II-mediated immune surveillance in suppressing tumorigenesis. ISC-specific genetic ablation of MHC class II increases tumor burden cell autonomously. Thus, HFD perturbs a microbiome-stem cell-immune cell interaction that contributes to tumor initiation in the intestine.

Live cell tagging tracking and isolation for spatial transcriptomics using photoactivatable cell dyes

A cell's phenotype and function are influenced by dynamic interactions with its microenvironment. To examine cellular spatiotemporal activity, we developed SPACECAT-Spatially PhotoActivatable Color Encoded Cell Address Tags-to annotate, track, and isolate cells while preserving viability. In SPACECAT, samples are stained with photocaged fluorescent molecules, and cells are labeled by uncaging those molecules with user-patterned near-UV light. SPACECAT offers single-cell precision and temporal stability across diverse cell and tissue types. Illustratively, we target crypt-like regions in patient-derived intestinal organoids to enrich for stem-like and actively mitotic cells, matching literature expectations. Moreover, we apply SPACECAT to ex vivo tissue sections from four healthy organs and an autochthonous lung tumor model. Lastly, we provide a computational framework to identify spatially-biased transcriptome patterns and enriched phenotypes. This minimally perturbative and broadly applicable method links cellular spatiotemporal and/or behavioral phenotypes with diverse downstream assays, enabling insights into the connections between tissue microenvironments and (dys)function.

High-fat diet-activated fatty acid oxidation mediates intestinal stemness and tumorigenicity

Obesity is an established risk factor for cancer in many tissues. In the mammalian intestine, a pro-obesity high-fat diet (HFD) promotes regeneration and tumorigenesis by enhancing intestinal stem cell (ISC) numbers, proliferation, and function. Although PPAR (peroxisome proliferator-activated receptor) nuclear receptor activity has been proposed to facilitate these effects, their exact role is unclear. Here we find that, in loss-of-function in vivo models, PPARα and PPARδ contribute to the HFD response in ISCs. Mechanistically, both PPARs do so by robustly inducing a downstream fatty acid oxidation (FAO) metabolic program. Pharmacologic and genetic disruption of CPT1A (the rate-controlling enzyme of mitochondrial FAO) blunts the HFD phenotype in ISCs. Furthermore, inhibition of CPT1A dampens the pro-tumorigenic consequences of a HFD on early tumor incidence and progression. These findings demonstrate that inhibition of a HFD-activated FAO program creates a therapeutic opportunity to counter the effects of a HFD on ISCs and intestinal tumorigenesis.

100 Years of Exploiting Diet and Nutrition for Tissue Regeneration

In this forum piece, we review progress in exploiting diet and nutrition for enhancing tissue regeneration with a particular emphasis on how dietary composition and diet-induced physiology influence adult stem cell biology.

Nutritional Control of Intestinal Stem Cells in Homeostasis and Tumorigenesis

Food and nutrition have a profound impact on organismal health and diseases, and tissue-specific adult stem cells play a crucial role in coordinating tissue maintenance by responding to dietary cues. Emerging evidence indicates that adult intestinal stem cells (ISCs) actively adjust their fate decisions in response to diets and nutritional states to drive intestinal adaptation. Here, we review the signaling mechanisms mediating the dietary responses imposed by caloric intake and nutritional composition (i.e., macronutrients and micronutrients), fasting-feeding patterns, diet-induced growth factors, and microbiota on ISCs and their relevance to the beginnings of intestinal tumors.

Regenerative Reprogramming of the Intestinal Stem Cell State via Hippo Signaling Suppresses Metastatic Colorectal Cancer

Although the Hippo transcriptional coactivator YAP is considered oncogenic in many tissues, its roles in intestinal homeostasis and colorectal cancer (CRC) remain controversial. Here, we demonstrate that the Hippo kinases LATS1/2 and MST1/2, which inhibit YAP activity, are required for maintaining Wnt signaling and canonical stem cell function. Hippo inhibition induces a distinct epithelial cell state marked by low Wnt signaling, a wound-healing response, and transcription factor Klf6 expression. Notably, loss of LATS1/2 or overexpression of YAP is sufficient to reprogram Lgr5+ cancer stem cells to this state and thereby suppress tumor growth in organoids, patient-derived xenografts, and mouse models of primary and metastatic CRC. Finally, we demonstrate that genetic deletion of YAP and its paralog TAZ promotes the growth of these tumors. Collectively, our results establish the role of YAP as a tumor suppressor in the adult colon and implicate Hippo kinases as therapeutic vulnerabilities in colorectal malignancies.

High-fat diet in a mouse insulin-resistant model induces widespread rewiring of the phosphotyrosine signaling network

Obesity-associated type 2 diabetes and accompanying diseases have developed into a leading human health risk across industrialized and developing countries. The complex molecular underpinnings of how lipid overload and lipid metabolites lead to the deregulation of metabolic processes are incompletely understood. We assessed hepatic post-translational alterations in response to treatment of cells with saturated and unsaturated free fatty acids and the consumption of a high-fat diet by mice. These data revealed widespread tyrosine phosphorylation changes affecting a large number of enzymes involved in metabolic processes as well as canonical receptor-mediated signal transduction networks. Targeting two of the most prominently affected molecular features in our data, SRC-family kinase activity and elevated reactive oxygen species, significantly abrogated the effects of saturated fat exposure in vitro and high-fat diet in vivo. In summary, we present a comprehensive view of diet-induced alterations of tyrosine signaling networks, including proteins involved in fundamental metabolic pathways.

Region-Specific Proteome Changes of the Intestinal Epithelium during Aging and Dietary Restriction

The small intestine is responsible for nutrient absorption and one of the most important interfaces between the environment and the body. During aging, changes of the epithelium lead to food malabsorption and reduced barrier function, thus increasing disease risk. The drivers of these alterations remain poorly understood. Here, we compare the proteomes of intestinal crypts from mice across different anatomical regions and ages. We find that aging alters epithelial immunity, metabolism, and cell proliferation and is accompanied by region-dependent skewing in the cellular composition of the epithelium. Of note, short-term dietary restriction followed by refeeding partially restores the epithelium by promoting stem cell differentiation toward the secretory lineage. We identify Hmgcs2 (3-hydroxy-3-methylglutaryl-coenzyme A [CoA] synthetase 2), the rate-limiting enzyme for ketogenesis, as a modulator of stem cell differentiation that responds to dietary changes, and we provide an atlas of region- and age-dependent proteome changes of the small intestine.

Gut organoids: mini-tissues in culture to study intestinal physiology and disease

In vitro, cell cultures are essential tools in the study of intestinal function and disease. For the past few decades, monolayer cellular cultures, such as cancer cell lines or immortalized cell lines, have been widely applied in gastrointestinal research. Recently, the development of three-dimensional cultures known as organoids has permitted the growth of normal crypt-villus units that recapitulate many aspects of intestinal physiology. Organoid culturing has also been applied to study gastrointestinal diseases, intestinal-microbe interactions, and colorectal cancer. These models are amenable to CRISPR gene editing and drug treatments, including high-throughput small-molecule testing. Three-dimensional intestinal cultures have been transplanted into mice to develop versatile in vivo models of intestinal disease, particularly cancer. Limitations of currently available organoid models include cost and challenges in modeling nonepithelial intestinal cells, such as immune cells and the microbiota. Here, we describe the development of organoid models of intestinal biology and the applications of organoids for study of the pathophysiology of intestinal diseases and cancer.

Ketone Body Signaling Mediates Intestinal Stem Cell Homeostasis and Adaptation to Diet

Little is known about how metabolites couple tissue-specific stem cell function with physiology. Here we show that, in the mammalian small intestine, the expression of Hmgcs2 (3-hydroxy-3-methylglutaryl-CoA synthetase 2), the gene encoding the rate-limiting enzyme in the production of ketone bodies, including beta-hydroxybutyrate (βOHB), distinguishes self-renewing Lgr5⁺ stem cells (ISCs) from differentiated cell types. Hmgcs2 loss depletes βOHB levels in Lgr5⁺ ISCs and skews their differentiation toward secretory cell fates, which can be rescued by exogenous βOHB and class I histone deacetylase (HDAC) inhibitor treatment. Mechanistically, βOHB acts by inhibiting HDACs to reinforce Notch signaling, instructing ISC self-renewal and lineage decisions. Notably, although a high-fat ketogenic diet elevates ISC function and post-injury regeneration through βOHB-mediated Notch signaling, a glucose-supplemented diet has the opposite effects. These findings reveal how control of βOHB-activated signaling in ISCs by diet helps to fine-tune stem cell adaptation in homeostasis and injury.

Notum produced by Paneth cells attenuates regeneration of aged intestinal epithelium

A decline in stem cell function impairs tissue regeneration during ageing, but the role of the stem-cell-supporting niche in ageing is not well understood. The small intestine is maintained by actively cycling intestinal stem cells that are regulated by the Paneth cell niche^1,2. Here we show that the regenerative potential of human and mouse intestinal epithelium diminishes with age owing to defects in both stem cells and their niche. The functional decline was caused by a decrease in stemness-maintaining Wnt signalling due to production of Notum, an extracellular Wnt inhibitor, in aged Paneth cells. Mechanistically, high activity of mammalian target of rapamycin complex 1 (mTORC1) in aged Paneth cells inhibits activity of peroxisome proliferator activated receptor α (PPAR-α)³, and lowered PPAR-α activity increased Notum expression. Genetic targeting of Notum or Wnt supplementation restored function of aged intestinal organoids. Moreover, pharmacological inhibition of Notum in mice enhanced the regenerative capacity of aged stem cells and promoted recovery from chemotherapy-induced damage. Our results reveal a role of the stem cell niche in ageing and demonstrate that targeting of Notum can promote regeneration of aged tissues.

Genetic editing of colonic organoids provides a molecularly distinct and orthotopic preclinical model of serrated carcinogenesis

OBJECTIVE

Serrated colorectal cancer (CRC) accounts for approximately 25% of cases and includes tumours that are among the most treatment resistant and with worst outcomes. This CRC subtype is associated with activating mutations in the mitogen-activated kinase pathway gene, BRAF, and epigenetic modifications termed the CpG Island Methylator Phenotype, leading to epigenetic silencing of key tumour suppressor genes. It is still not clear which (epi-)genetic changes are most important in neoplastic progression and we begin to address this knowledge gap herein.

DESIGN

We use organoid culture combined with CRISPR/Cas9 genome engineering to sequentially introduce genetic alterations associated with serrated CRC and which regulate the stem cell niche, senescence and DNA mismatch repair.

RESULTS

Targeted biallelic gene alterations were verified by DNA sequencing. Organoid growth in the absence of niche factors was assessed, as well as analysis of downstream molecular pathway activity. Orthotopic engraftment of complex organoid lines, but not BrafV600E alone, quickly generated adenocarcinoma in vivo with serrated features consistent with human disease. Loss of the essential DNA mismatch repair enzyme, Mlh1, led to microsatellite instability. Sphingolipid metabolism genes are differentially regulated in both our mouse models of serrated CRC and human CRC, with key members of this pathway having prognostic significance in the human setting.

CONCLUSION

We generate rapid, complex models of serrated CRC to determine the contribution of specific genetic alterations to carcinogenesis. Analysis of our models alongside patient data has led to the identification of a potential susceptibility for this tumour type.

DNA Intercalation Facilitates Efficient DNA-Targeted Covalent Binding of Phenanthriplatin

Phenanthriplatin, a monofunctional anticancer agent derived from cisplatin, shows significantly more rapid DNA covalent-binding activity compared to its parent complex. To understand the underlying molecular mechanism, we used single-molecule studies with optical tweezers to probe the kinetics of DNA-phenanthriplatin binding as well as DNA binding to several control complexes. The time-dependent extensions of single λ-DNA molecules were monitored at constant applied forces and compound concentrations, followed by rinsing with a compound-free solution. DNA-phenanthriplatin association consisted of fast and reversible DNA lengthening with time constant τ ≈ 10 s, followed by slow and irreversible DNA elongation that reached equilibrium in ∼30 min. In contrast, only reversible fast DNA elongation occured for its stereoisomer  trans-phenanthriplatin, suggesting that the distinct two-rate kinetics of phenanthriplatin is sensitive to the geometric conformation of the complex. Furthermore, no DNA unwinding was observed for pyriplatin, in which the phenanthridine ligand of phenanthriplatin is replaced by the smaller pyridine molecule, indicating that the size of the aromatic group is responsible for the rapid DNA elongation. These findings suggest that the mechanism of binding of phenanthriplatin to DNA involves rapid, partial intercalation of the phenanthridine ring followed by slower substitution of the adjacent chloride ligand by, most likely, the N7 atom of a purine base. The cis isomer affords the proper stereochemistry at the metal center to facilitate essentially irreversible DNA covalent binding, a geometric advantage not afforded by trans-phenanthriplatin. This study demonstrates that reversible DNA intercalation provides a robust transition state that is efficiently converted to an irreversible DNA-Pt bound state.

Nutritional Regulation of Intestinal Stem Cells

Dietary composition and calorie intake are major determinants of health and disease. Calorie restriction promotes metabolic changes that favor tissue regeneration and is arguably the most successful and best-conserved antiaging intervention. Obesity, in contrast, impairs tissue homeostasis and is a major risk factor for the development of diseases including cancer. Stem cells, the central mediators of tissue regeneration, integrate dietary and energy cues via nutrient-sensing pathways to maintain growth or respond to stress. We discuss emerging data on the effects of diet and nutrient-sensing pathways on intestinal stem cells, as well as their potential application in the development of regenerative and therapeutic interventions.

Abstract B38: In vivo genome editing and organoid transplantation models of colorectal cancer and metastasis

In vivo interrogation of the function of genes implicated in tumorigenesis is limited by the need to generate and cross germline mutant mice. Here we describe approaches to model colorectal cancer (CRC) and metastasis that rely on in situ gene editing and orthotopic organoid transplantation in mice without cancer-predisposing mutations. Autochthonous tumor formation is induced by CRISPR/Cas9-based editing of the Apc and Trp53 tumor suppressor genes in colon epithelial cells and by orthotopic transplantation of Apc-edited colon organoids. ApcΔ/Δ;KrasG12D/+;Trp53Δ/Δ (AKP) mouse colon organoids and human CRC organoids engraft in the distal colon and metastasize to the liver. Finally, we apply the orthotopic transplantation model to characterize the clonal dynamics of Lgr5+ stem cells and demonstrate sequential activation of an oncogene in established colon adenomas. These experimental systems enable rapid in vivo characterization of cancer-associated genes and reproduce the entire spectrum of tumor progression and metastasis.

Citation Format: Jatin Roper, Tuomas Tammela, Naniye Malli Cetinbas, Adam Akkad, Ali Roghanian, Steffen Rickelt, Mohammad Almeqdadi, Katherine Wu, Matthias Oberli, Francisco Sánchez-Rivera, Yoona Park, Xu Liang, George Eng, Martin S. Taylor, Roxana Azimi, Dmitriy Kedrin, Rachit Neupane, Semir Beyaz, Ewa T. Sicinska, Yvelisse Suarez, James Yoo, Lillian Chen, Lawrence Zukerberg, Pekka Katajisto, Vikram Deshpande, Adam Bass, Philip N. Tsichlis, Jacqueline Lees, Robert Langer, Richard O. Hynes, Jianzhu Chen, Arjun J. Bhutkar, Tyler Jacks, Ömer H. Yilmaz. In vivo genome editing and organoid transplantation models of colorectal cancer and metastasis [abstract]. In: Proceedings of the AACR Special Conference: Advances in Modeling Cancer in Mice: Technology, Biology, and Beyond; 2017 Sep 24-27; Orlando, Florida. Philadelphia (PA): AACR; Cancer Res 2018;78(10 Suppl):Abstract nr B38.

The effect of geometric isomerism on the anticancer activity of the monofunctional platinum complex trans-[Pt(NH3)2(phenanthridine)Cl]NO3

A trans-DDP based monofunctional phenanthridine Pt(ii) complex was synthesized and characterized. Its anticancer activity was studied in vitro on a panel of human cancer cell lines and mouse intestinal cancer organoids. This complex displays significant antitumor properties, with a different spectrum of activity than that of classic bifunctional cross-linking agents like cisplatin.

Colonoscopy-based colorectal cancer modeling in mice with CRISPR-Cas9 genome editing and organoid transplantation

Most genetically engineered mouse models (GEMMs) of colorectal cancer are limited by tumor formation in the small intestine, a high tumor burden that limits metastasis, and the need to generate and cross mutant mice. Cell line or organoid transplantation models generally produce tumors in ectopic locations-such as the subcutaneous space, kidney capsule, or cecal wall-that do not reflect the native stromal environment of the colon mucosa. Here, we describe detailed protocols to rapidly and efficiently induce site-directed tumors in the distal colon of mice that are based on colonoscopy-guided mucosal injection. These techniques can be adapted to deliver viral vectors carrying Cre recombinase, CRISPR-Cas9 components, CRISPR-engineered mouse tumor organoids, or human cancer organoids to mice to model the adenoma-carcinoma-metastasis sequence of tumor progression. The colonoscopy injection procedure takes ∼15 min, including preparation. In our experience, anyone with reasonable hand-eye coordination can become proficient with mouse colonoscopy and mucosal injection with a few hours of practice. These approaches are ideal for a wide range of applications, including assessment of gene function in tumorigenesis, examination of tumor-stroma interactions, studies of cancer metastasis, and translational research with patient-derived cancers.

A Wnt-producing niche drives proliferative potential and progression in lung adenocarcinoma

The heterogeneity of cellular states in cancer has been linked to drug resistance, cancer progression and presence of cancer cells with properties of normal tissue stem cells^1,2. Secreted Wnt signals maintain stem cells in various epithelial tissues, including in lung development and regeneration^3–5. Here we report that murine and human lung adenocarcinomas display hierarchical features with two distinct subpopulations, one with high Wnt signaling activity and another forming a niche that provides the Wnt ligand. The Wnt responder cells showed increased tumour propagation ability, suggesting that they have features of normal tissue stem cells. Genetic perturbation of Wnt production or signaling suppressed tumour progression. Small molecule inhibitors targeting essential post-translational modification of Wnt reduced tumour growth and dramatically decreased proliferative potential of the lung cancer cells, leading to improved survival of tumour-bearing mice. These results indicate that strategies for disrupting pathways that maintain stem-like and niche cell phenotypes can translate into effective anti-cancer therapies.

In vivo genome editing and organoid transplantation models of colorectal cancer and metastasis

In vivo interrogation of the function of genes implicated in tumorigenesis is limited by the need to generate and cross germline mutant mice. Here we describe approaches to model colorectal cancer (CRC) and metastasis, which rely on in situ gene editing and orthotopic organoid transplantation in mice without cancer-predisposing mutations. Autochthonous tumor formation is induced by CRISPR-Cas9-based editing of the Apc and Trp53 tumor suppressor genes in colon epithelial cells and by orthotopic transplantation of Apc-edited colon organoids. ApcΔ/Δ;Kras^G12D/+;Trp53Δ/Δ (AKP) mouse colon organoids and human CRC organoids engraft in the distal colon and metastasize to the liver. Finally, we apply the orthotopic transplantation model to characterize the clonal dynamics of Lgr5⁺ stem cells and demonstrate sequential activation of an oncogene in established colon adenomas. These experimental systems enable rapid in vivo characterization of cancer-associated genes and reproduce the entire spectrum of tumor progression and metastasis.

Dietary Regulation of Adult Stem Cells

PURPOSE OF REVIEW

Dietary intake is a critical regulator of organismal physiology and health. Tissue homeostasis and regeneration are dependent on adult tissue stem cells that self-renew and differentiate into the specialized cell types. As stem cells respond to cues from their environment, dietary signals and nutrients influence tissue biology by altering the function and activity of adult stem cells. In this review, we highlight recent studies that illustrate how diverse diets such as caloric restriction, fasting, high fat diets, and ketogenic diets impact stem cell function and their microenvironments.

RECENT FINDINGS

Caloric restriction generally exerts positive effects on adult stem cells, notably increasing stem cell functionality in the intestine and skeletal muscle as well as increasing hematopoietic stem cell quiescence. Similarly, fasting confers protection of intestinal, hematopoietic, and neuronal stem cells against injury. High fat diets induce intestinal stem cell niche independence and stem-like properties in intestinal progenitors, while high fat diets impair hematopoiesis and neurogenesis.

SUMMARY

Caloric restriction and fasting are generally beneficial to adult stem cell function, while high fat diets impair stem cell function or create opportunities for tumorigenesis. However, the effects of each diet on stem cell biology are complex and vary greatly between tissues. Given the recent interest in developing dietary interventions or mimetics as therapeutics, further studies, including on ketogenic diets, will be essential to understand how adult stem cells respond to diet-induced signals and physiology.

Molecular Pathways: Dietary Regulation of Stemness and Tumor Initiation by the PPAR-δ Pathway

Peroxisome proliferator-activated receptor delta (PPAR-δ) is a nuclear receptor transcription factor that regulates gene expression during development and disease states, such as cancer. However, the precise role of PPAR-δ during tumorigenesis is not well understood. Recent data suggest that PPAR-δ may have context-specific oncogenic and tumor-suppressive roles depending on the tissue, cell-type, or diet-induced physiology in question. For example, in the intestine, pro-obesity diets, such as a high-fat diet (HFD), are associated with increased colorectal cancer incidence. Interestingly, many of the effects of an HFD in the stem and progenitor cell compartment are driven by a robust PPAR-δ program and contribute to the early steps of intestinal tumorigenesis. Importantly, the PPAR-δ pathway or its downstream mediators may serve as therapeutic intervention points or biomarkers in colon cancer that arise in patients who are obese. Although potent PPAR-δ agonists and antagonists exist, their clinical utility may be enhanced by uncovering how PPAR-δ mediates tumorigenesis in diverse tissues and cell types as well as in response to diet. Clin Cancer Res; 22(23); 5636-41. ©2016 AACR.

The compromise of dynamic disulfide/thiol homeostasis as a biomarker of oxidative stress in trichloroethylene exposure

In this study, we aimed to investigate disulfide/thiol homeostasis in trichloroethylene (TCE) exposure. The study was carried out in 30 nonsmoker TCE-exposed workers with a variety of occupations. Additionally, 30 healthy nonsmoker volunteers were recruited as the control group. TCE exposure was determined by measuring urinary trichloroacetic acid (TCA) concentration. Median urinary TCA levels of exposed workers (20.5 mg/L) were significantly higher than control subjects (5 mg/L). Thiol and disulfide concentrations were determined using a novel automated method. Disulfide/thiol ratio was significantly higher in the exposed group ( p < 0.001). Thiol/disulfide homeostasis was found to be disturbed in TCE-exposed workers. We predict that in TCE-exposed workers this disturbance can be a therapeutic target, and the efficiency of the treatment can easily be monitored by the novel method we used.

Colorectal cancer models for novel drug discovery

INTRODUCTION

Despite increased screening rates and advances in targeted therapy, colorectal cancer (CRC) remains the third leading cause of cancer-related mortality. CRC models that recapitulate key features of human disease are essential to the development of novel and effective therapeutics. Classic methods of modeling CRC such as human cell lines and xenograft mice, while useful for many applications, carry significant limitations. Recently developed in vitro and in vivo models overcome some of these deficiencies and thus can be utilized to better model CRC for mechanistic and translational research.

AREAS COVERED

The authors review established models of in vitro cell culture and describe advances in organoid culture for studying normal and malignant intestine. They also discuss key features of classic xenograft models and describe other approaches for in vivo CRC research, including patient-derived xenograft, carcinogen-induced, orthotopic transplantation and transgenic mouse models. We also describe mouse models of metastatic CRC.

EXPERT OPINION

No single model is optimal for drug discovery in CRC. Genetically engineered models overcome many limitations of xenograft models. Three-dimensional organoids can be efficiently derived from both normal and malignant tissue for large-scale in vitro and in vivo (transplantation) studies and are thus a significant advance in CRC drug discovery.

Intestinal colonization by Candida albicans alters inflammatory responses in Bruton's tyrosine kinase-deficient mice

The commensal yeast Candida albicans is part of the human intestinal microflora and is considered a "pathobiont", a resident microbe with pathogenic potential yet harmless under normal conditions. The aim of this study was to investigate the effect of C. albicans on inflammation of the intestinal tract and the role of Bruton's tyrosine kinase (Btk). Btk is an enzyme that modulates downstream signaling of multiple receptors involved in innate and adaptive immunity, including the major anti-fungal receptor Dectin-1. Colitis was induced in wild type and Btk-/- mice by treatment with dextran sodium sulfate (DSS) and the gastrointestinal tract of selected treatment groups were then colonized with C. albicans. Colonization by C. albicans neither dampened nor exacerbated inflammation in wild type mice, but colon length and spleen weight were improved in Btk-deficient mice colonized with C. albicans. Neutrophil infiltration was comparable between wild type and Btk-/- mice, but the knockout mice displayed severely reduced numbers of macrophages in the colon during both DSS and DSS/Candida treatment. Smaller numbers and reduced responsiveness of Btk-/- macrophages might partially explain the improved colon length of Btk-/- mice as a result of Candida colonization. Surprisingly, DSS/Candida-treated Btk-/- animals had higher levels of certain pro-inflammatory cytokines and levels of the anti-inflammatory cytokine TGF-β were reduced compared to wild type. A clustering and correlation analysis showed that for wild type animals, spleen TGF-β and colon IL-10 and for Btk-/- spleen and colon levels of IL-17A best correlated with the inflammatory parameters. We conclude that in Btk-/- immunocompromised animals, colonization of the gastrointestinal tract by the commensal yeast C. albicans alters inflammatory symptoms associated with colitis.

Combination PI3K/MEK inhibition promotes tumor apoptosis and regression in PIK3CA wild-type, KRAS mutant colorectal cancer

PI3K inhibition in combination with other agents has not been studied in the context of PIK3CA wild-type, KRAS mutant cancer. In a screen of phospho-kinases, PI3K inhibition of KRAS mutant colorectal cancer cells activated the MAPK pathway. Combination PI3K/MEK inhibition with NVP-BKM120 and PD-0325901 induced tumor regression in a mouse model of PIK3CA wild-type, KRAS mutant colorectal cancer, which was mediated by inhibition of mTORC1, inhibition of MCL-1, and activation of BIM. These findings implicate mitochondrial-dependent apoptotic mechanisms as determinants for the efficacy of PI3K/MEK inhibition in the treatment of PIK3CA wild-type, KRAS mutant cancer.

Persistence of leukemia-initiating cells in a conditional knockin model of an imatinib-responsive myeloproliferative disorder

Despite remarkable responses to the tyrosine kinase inhibitor imatinib, CML patients are rarely cured by this therapy perhaps due to imatinib refractoriness of leukemia-initiating cells (LICs). Evidence for this is limited because of poor engraftment of human CML-LICs in NOD-SCID mice and nonphysiologic expression of oncogenes in retroviral transduction mouse models. To address these challenges, we generated mice bearing conditional knockin alleles of two human oncogenes: HIP1/PDGFbetaR (H/P) and AML1-ETO (A/E). Unlike retroviral transduction, physiologic expression of H/P or A/E individually failed to induce disease, but coexpression of both H/P and A/E led to rapid onset of a fully penetrant, myeloproliferative disorder, indicating cooperativity between these two alleles. Although imatinib dramatically decreased disease burden, LICs persisted, demonstrating imatinib refractoriness of LICs.