Membrane-to-nucleus signaling links insulin-like growth factor-1- and stem cell factor-activated pathways

PTPRG-AS1 regulates the KITLG/KIT pathway through the ceRNA axis to promote the malignant progression of gastric cancer and the intervention effect of Compound Kushen injection on it

Gastric cancer (GC) is a common malignant tumor with high mortality, recurrence, and metastasis rates. Compound Kushen injection (CKI) combination chemotherapy has been clinically used for the treatment of GC in China for many years, but its underlying mechanisms of action remain unclear. Recent reports have highlighted the important role of the competing endogenous RNA (ceRNA) mechanism of noncoding RNA (ncRNA) and messenger RNA (mRNA) formation in GC and other tumors. This study aimed to investigate the effects of CKI on GC from the ceRNA perspective. We confirmed the inhibitory effect of CKI on GC in mouse models and cell lines. By examining the GC cell lines sensitive to CKI treatment, we developed the CNScore method to analyze the ceRNA network, revealing that the CKI-GC ceRNA network promotes GC proliferation and metastasis through the PTPRG-AS1/hsa-miR-421/KITLG axis. Finally, we constructed GC cell models with PTPRG-AS1 overexpression or knockdown and GC liver metastasis models and found that PTPRG-AS1 can sponge hsa-miR-421, releasing KITLG and promoting GC proliferation and metastasis through the KITLG/KIT pathway. Taken together, CKI can suppress these malignant phenotypes by regulating the PTPRG-AS1/hsa-miR-421/KITLG axis.

Cellular and molecular mechanisms underlying aging-related gastric neuromuscular dysfunction

Aging is linked to a gradual decline in the gastric motor function, contributing to reduced food intake, and its association with frailty and sarcopenia. A key cellular change in the gastric neuromuscular apparatus is the loss of interstitial cells of Cajal (ICC), pacemaker cells of the gut. The ICC function as pacemakers that generate electrical slow waves and mediate enteric neurotransmission, playing a critical role in gastric motility. Aging-related ICC depletion leads to impaired gastric compliance and reduced slow wave activity, which contributes to early satiety and reduced food intake. Recent studies have elucidated the molecular and epigenetic mechanisms underlying aging-related ICC decline, highlighting the roles of ICC stem/precursor cells (ICC-SCs), transformation-related protein 53 (TRP53), extracellular signal-regulated kinase (ERK), and insulin-like growth factor 1 (IGF1) pathways, and epigenetic regulation mediated by the histone methyltransferase enhancer of zeste 2 (EZH2). By synthesizing the current findings, this review aims to provide a comprehensive understanding of the mechanisms driving ICC decline and to explore potential therapeutic strategies for preserving gastric motility in aging populations. Future research should aim to translate these discoveries into clinical applications to improve the gastric motor function and overall health in the aging population. Identifying effective interventions targeting ICC maintenance may ultimately help to alleviate age-related gastric motor dysfunction and its associated health burdens, including frailty, malnutrition, and impaired quality of life.

Inhibition of EZH2 Reduces Aging-Related Decline in Interstitial Cells of Cajal of the Mouse Stomach

BACKGROUND & AIMS

Restricted gastric motor functions contribute to aging-associated undernutrition, sarcopenia, and frailty. We previously identified a decline in interstitial cells of Cajal (ICC; gastrointestinal pacemaker and neuromodulator cells) and their stem cells (ICC-SC) as a key factor of gastric aging. Altered functionality of the histone methyltransferase enhancer of zeste homolog 2 (EZH2) is central to organismal aging. Here, we investigated the role of EZH2 in the aging-related loss of ICC/ICC-SC.

METHODS

klotho mice, a model of accelerated aging, were treated with the most clinically advanced EZH2 inhibitor, EPZ6438 (tazemetostat; 160 mg/kg intraperitoneally twice a day for 3 weeks). Gastric ICC were analyzed by Western blotting and immunohistochemistry. ICC and ICC-SC were quantified by flow cytometry. Gastric slow wave activity was assessed by intracellular electrophysiology. Ezh2 was deactivated in ICC by treating KitcreERT2/+;Ezh2fl/fl mice with tamoxifen. TRP53, a key mediator of aging-related ICC loss, was induced with nutlin 3a in gastric muscle organotypic cultures and an ICC-SC line.

RESULTS

In klotho mice, EPZ6438 treatment mitigated the decline in the ICC growth factor KIT ligand/stem cell factor and gastric ICC. EPZ6438 also improved gastric slow wave activity and mitigated the reduced food intake and impaired body weight gain characteristic of this strain. Conditional genomic deletion of Ezh2 in Kit-expressing cells also prevented ICC loss. In organotypic cultures and ICC-SC, EZH2 inhibition prevented the aging-like effects of TRP53 stabilization on ICC/ICC-SC.

CONCLUSIONS

Inhibition of EZH2 with EPZ6438 mitigates aging-related ICC/ICC-SC loss and gastric motor dysfunction, improving slow wave activity and food intake in klotho mice.

Protocol for gene knockdown using siRNA in organotypic cultures of murine gastric muscle

Understanding the molecular interactions within the neuromuscular apparatus in the stomach is crucial for understanding their role in maintaining interstitial cells, such as the interstitial cells of Cajal (ICC), smooth muscle, and enteric neurons, as well as their contribution to gastric motility in both healthy and diseased states. Disruptions of these systems can lead to various gastric motor disorders and diseases, making it essential to explore their functions in detail. We herein present a protocol for gene knockdown using small interfering RNA (siRNAs) in organotypic culture. This ex vivo approach allows the precise manipulation of the gene expression in a tissue environment that closely mimics in vivo conditions, providing valuable insights into the gene function and its effects on gastric physiology. The protocol includes detailed steps for tissue preparation to ensure the preservation of the gastric muscles and the associated neuromuscular apparatus. We then describe the process of siRNA-mediated gene knockdown, offering tips for optimizing transfection efficiency and gene silencing. Additionally, we outline methods for analyzing the effectiveness of knockdown, including both quantitative and qualitative methods for the evaluation of the target gene expression. This protocol is adaptable to various research needs, allowing researchers to focus on specific genes of interest within the neuromuscular system of the stomach. By applying this approach, investigators can deepen their understanding of the molecular mechanisms underlying gastric motility and contribute to the development of new therapeutic strategies for treating gastric motor disorders and diseases.

The Crucial Role of the Interstitial Cells of Cajal in Neurointestinal Diseases

Neurointestinal diseases result from dysregulated interactions between the nervous system and the gastrointestinal (GI) tract, leading to conditions such as Hirschsprung's disease and irritable bowel syndrome. These disorders affect many people, significantly diminishing their quality of life and overall health. Central to GI motility are the interstitial cells of Cajal (ICC), which play a key role in muscle contractions and neuromuscular transmission. This review highlights the role of ICC in neurointestinal diseases, revealing their association with various GI ailments. Understanding the functions of the ICC could lead to innovative perspectives on the modulation of GI motility and introduce new therapeutic paradigms. These insights have the potential to enhance efforts to combat neurointestinal diseases and may lead to interventions that could alleviate or even reverse these conditions.

Multiple intratumoral sources of kit ligand promote gastrointestinal stromal tumor

Gastrointestinal stromal tumor (GIST) is the most common human sarcoma and is typically driven by a single mutation in the Kit or PDGFRA receptor. While highly effective, tyrosine kinase inhibitors (TKIs) are not curative. The natural ligand for the Kit receptor is Kit ligand (KitL), which exists in both soluble and membrane-bound forms. While KitL is known to stimulate human GIST cell lines in vitro, we used a genetically engineered mouse model of GIST containing a common human KIT mutation to investigate the intratumoral sources of KitL, importance of KitL during GIST oncogenesis, and contribution of soluble KitL to tumor growth in vivo. We discovered that in addition to tumor cells, endothelia and smooth muscle cells produced KitL in KitV558Δ/+ tumors, even after imatinib therapy. Genetic reduction of total KitL in tumor cells of KitV558Δ/+ mice impaired tumor growth in vivo. Similarly, genetic reduction of tumor cell soluble KitL in KitV558Δ/+ mice decreased tumor size. By RNA sequencing, quantitative PCR, and immunohistochemistry, KitL expression was heterogeneous in human GIST specimens. In particular, PDGFRA-mutant tumors had much higher KitL expression than Kit-mutant tumors, suggesting the benefit of Kit activation in the absence of mutant KIT. Serum KitL was higher in GIST patients with tumors resistant to imatinib and in those with tumors expressing more KitL RNA. Overall, KitL supports the growth of GIST at baseline and after imatinib therapy and remains a potential biomarker and therapeutic target.

Insulin-Like Growth Factor1 Preserves Gastric Pacemaker Cells and Motor Function in Aging via ERK1/2 Activation

BACKGROUND & AIMS

Impaired gastric motor function in the elderly causes reduced food intake leading to frailty and sarcopenia. We previously found that aging-related impaired gastric compliance was mainly owing to depletion of interstitial cells of Cajal (ICC), pacemaker cells, and neuromodulator cells. These changes were associated with reduced food intake. Transformation-related protein 53-induced suppression of extracellular signal-regulated protein kinase (ERK)1/2 in ICC stem cell (ICC-SC) cell-cycle arrest is a key process for ICC depletion and gastric dysfunction during aging. Here, we investigated whether insulin-like growth factor 1 (IGF1), which can activate ERK in gastric smooth muscles and invariably is reduced with age, could mitigate ICC-SC/ICC loss and gastric dysfunction in klotho mice, a model of accelerated aging.

METHODS

Klotho mice were treated with the stable IGF1 analog LONG R3 recombinant human (rh) IGF1 (150 μg/kg intraperitoneally twice daily for 3 weeks). Gastric ICC/ICC-SC and signaling pathways were studied by flow cytometry, Western blot, and immunohistochemistry. Gastric compliance was assessed in ex vivo systems. Transformation-related protein 53 was induced with nutlin 3a and ERK1/2 signaling was activated by rhIGF-1 in the ICC-SC line.

RESULTS

LONG R3 rhIGF1 treatment prevented reduced ERK1/2 phosphorylation and gastric ICC/ICC-SC decrease. LONG R3 rhIGF1 also mitigated the reduced food intake and impaired body weight gain. Improved gastric function by LONG R3 rhIGF1 was verified by in vivo systems. In ICC-SC cultures, rhIGF1 mitigated nutlin 3a-induced reduced ERK1/2 phosphorylation and cell growth arrest.

CONCLUSIONS

IGF1 can mitigate age-related ICC/ICC-SC loss by activating ERK1/2 signaling, leading to improved gastric compliance and increased food intake in klotho mice.

Wnt-induced, TRP53-mediated Cell Cycle Arrest of Precursors Underlies Interstitial Cell of Cajal Depletion During Aging

BACKGROUND & AIMS

Gastric dysfunction in the elderly may cause reduced food intake, frailty, and increased mortality. The pacemaker and neuromodulator cells interstitial cells of Cajal (ICC) decline with age in humans, and their loss contributes to gastric dysfunction in progeric klotho mice hypomorphic for the anti-aging Klotho protein. The mechanisms of ICC depletion remain unclear. Klotho attenuates Wnt (wingless-type MMTV integration site) signaling. Here, we examined whether unopposed Wnt signaling could underlie aging-associated ICC loss by up-regulating transformation related protein TRP53 in ICC stem cells (ICC-SC).

METHODS

Mice aged 1-107 weeks, klotho mice, APC^Δ468 mice with overactive Wnt signaling, mouse ICC-SC, and human gastric smooth muscles were studied by RNA sequencing, reverse transcription-polymerase chain reaction, immunoblots, immunofluorescence, histochemistry, flow cytometry, and methyltetrazolium, ethynyl/bromodeoxyuridine incorporation, and ex-vivo gastric compliance assays. Cells were manipulated pharmacologically and by gene overexpression and RNA interference.

RESULTS

The klotho and aged mice showed similar ICC loss and impaired gastric compliance. ICC-SC decline preceded ICC depletion. Canonical Wnt signaling and TRP53 increased in gastric muscles of klotho and aged mice and middle-aged humans. Overstimulated canonical Wnt signaling increased DNA damage response and TRP53 and reduced ICC-SC self-renewal and gastric ICC. TRP53 induction persistently inhibited G₁/S and G₂/M cell cycle phase transitions without activating apoptosis, autophagy, cellular quiescence, or canonical markers/mediators of senescence. G₁/S block reflected increased cyclin-dependent kinase inhibitor 1B and reduced cyclin D1 from reduced extracellular signal-regulated kinase activity.

CONCLUSIONS

Increased Wnt signaling causes age-related ICC loss by up-regulating TRP53, which induces persistent ICC-SC cell cycle arrest without up-regulating canonical senescence markers.

Linsitinib (OSI-906) for the Treatment of Adult and Pediatric Wild-Type Gastrointestinal Stromal Tumors, a SARC Phase II Study

PURPOSE

Most gastrointestinal stromal tumors (GIST) have activating mutations of KIT, PDGFRA, or uncommonly BRAF. Fifteen percent of adult and 85% of pediatric GISTs are wild type (WT), commonly having high expression of IGF-1R and loss of succinate dehydrogenase (SDH) complex function. We tested the efficacy of linsitinib, an oral TKI IGF-1R inhibitor, in patients with WT GIST.

PATIENTS AND METHODS

A multicenter phase II trial of linsitinib was conducted. The primary endpoint was objective response rate. Secondary endpoints were clinical benefit rate: complete response, partial response, and stable disease (SD) ≥ 9 months, and quantitative 2[18F]fluoro-2-deoxy-D-glucose (FDG) metabolic response (MR) at week 8. Serum levels for glucose, insulin, IGF-1R ligand IGF1, and binding proteins were obtained to explore correlations to patient outcomes and FDG-PET results.

RESULTS

Twenty patients were accrued in a 6-month period. Grade 3-4 toxicities possibly related to linsitinib were uncommon (8.5%). No objective responses were seen. Clinical benefit rate (CBR) at 9 months was 40%. Intense FDG uptake was observed at baseline, with partial MR of 12% and stable metabolic disease of 65% at week 8; these patients had RECIST 1.1 SD as their best response. Progression-free survival (PFS) and overall survival Kaplan-Meier estimates at 9 months were 52% and 80%, respectively. SDHA/B loss determined by IHC was seen in 35% and 88% of cases, respectively.

CONCLUSIONS

Linsitinib is well tolerated in patients with WT GIST. Although the 9-month CBR was 40%, and PFS at 9 months was 52%, no objective responses were observed. Rapid accrual to this study demonstrates that clinical trials of experimental agents in selected subtypes of GIST are feasible.

Hedgehog pathway dysregulation contributes to the pathogenesis of human gastrointestinal stromal tumors via GLI-mediated activation of KIT expression

Gastrointestinal stromal tumors (GIST) arise within the interstitial cell of Cajal (ICC) lineage due to activating KIT/PDGFRA mutations. Both ICC and GIST possess primary cilia (PC), which coordinate PDGFRA and Hedgehog signaling, regulators of gastrointestinal mesenchymal development. Therefore, we hypothesized that Hedgehog signaling may be altered in human GIST and controls KIT expression. Quantitative RT-PCR, microarrays, and next generation sequencing were used to describe Hedgehog/PC-related genes in purified human ICC and GIST. Genetic and pharmacologic approaches were employed to investigate the effects of GLI manipulation on KIT expression and GIST cell viability. We report that Hedgehog pathway and PC components are expressed in ICC and GIST and subject to dysregulation during GIST oncogenesis, irrespective of KIT/PDGFRA mutation status. Using genomic profiling, 10.2% of 186 GIST studied had potentially deleterious genomic alterations in 5 Hedgehog-related genes analyzed, including in the PTCH1 tumor suppressor (1.6%). Expression of the predominantly repressive GLI isoform, GLI3, was inversely correlated with KIT mRNA levels in GIST cells and non-KIT/non-PDGFRA mutant GIST. Overexpression of the 83-kDa repressive form of GLI3 or small interfering RNA-mediated knockdown of the activating isoforms GLI1/2 reduced KIT mRNA. Treatment with GLI1/2 inhibitors, including arsenic trioxide, significantly increased GLI3 binding to the KIT promoter, decreased KIT expression, and reduced viability in imatinib-sensitive and imatinib-resistant GIST cells. These data offer new evidence that genes necessary for Hedgehog signaling and PC function in ICC are dysregulated in GIST. Hedgehog signaling activates KIT expression irrespective of mutation status, offering a novel approach to treat imatinib-resistant GIST.

Function of insulin-like growth factor 1 receptor in cancer resistance to chemotherapy

Drug resistance is a primary cause of chemotherapeutic failure; however, how this resistance develops is complex. A comprehensive understanding of chemotherapeutic resistance mechanisms may aid in identifying more effective drugs and improve the survival rates of patients with cancer. Insulin-like growth factor 1 receptor (IGF1R), a member of the insulin receptor family, has been extensively assessed for biological activity, and its putative contribution to tumor cell development and progression. Furthermore, researchers have attended to drugs that target IGF1R since IGF1R functions as a membrane receptor. However, how IGF1R participates in chemotherapeutic resistance remains unclear. Therefore, the present study described the IGF1R gene and its associated signaling pathways, and offered details of IGF1R-induced tumor chemoresistance associated with promoting cell proliferation, inhibition of apoptosis, regulation of ATP-binding cassette transporter proteins and interactions with the extracellular matrix. The present study offered additional explanations for tumor chemotherapy resistance and provided a theoretical basis of IGF1R and its downstream pathways for future possible chemotherapy treatment options.

Hyperglycemia Increases Interstitial Cells of Cajal via MAPK1 and MAPK3 Signaling to ETV1 and KIT, Leading to Rapid Gastric Emptying

BACKGROUND & AIMS

Depletion of interstitial cells of Cajal (ICCs) is common in diabetic gastroparesis. However, in approximately 20% of patients with diabetes, gastric emptying (GE) is accelerated. GE also occurs faster in obese individuals, and is associated with increased blood levels of glucose in patients with type 2 diabetes. To understand the fate of ICCs in hyperinsulinemic, hyperglycemic states characterized by rapid GE, we studied mice with mutation of the leptin receptor (Lepr^db/db), which in our colony had accelerated GE. We also investigated hyperglycemia-induced signaling in the ICC lineage and ICC dependence on glucose oxidative metabolism in mice with disruption of the succinate dehydrogenase complex, subunit C gene (Sdhc).

METHODS

Mice were given breath tests to analyze GE of solids. ICCs were studied by flow cytometry, intracellular electrophysiology, isometric contractility measurement, reverse-transcription polymerase chain reaction, immunoblot, immunohistochemistry, enzyme-linked immunosorbent assays, and metabolite assays; cells and tissues were manipulated pharmacologically and by RNA interference. Viable cell counts, proliferation, and apoptosis were determined by methyltetrazolium, Ki-67, proliferating cell nuclear antigen, bromodeoxyuridine, and caspase-Glo 3/7 assays. Sdhc was disrupted in 2 different strains of mice via cre recombinase.

RESULTS

In obese, hyperglycemic, hyperinsulinemic female Lepr^db/db mice, GE was accelerated and gastric ICC and phasic cholinergic responses were increased. Female Kit^K641E/+ mice, which have genetically induced hyperplasia of ICCs, also had accelerated GE. In isolated cells of the ICC lineage and gastric organotypic cultures, hyperglycemia stimulated proliferation by mitogen-activated protein kinase 1 (MAPK1)- and MAPK3-dependent stabilization of ets variant 1-a master transcription factor for ICCs-and consequent up-regulation of v-kit Hardy-Zuckerman 4 feline sarcoma viral oncogene homolog (KIT) receptor tyrosine kinase. Opposite changes occurred in mice with disruption of Sdhc.

CONCLUSIONS

Hyperglycemia increases ICCs via oxidative metabolism-dependent, MAPK1- and MAPK3-mediated stabilization of ets variant 1 and increased expression of KIT, causing rapid GE. Increases in ICCs might contribute to the acceleration in GE observed in some patients with diabetes.

Altered gut microbiota in female mice with persistent low body weights following removal of post-weaning chronic dietary restriction

BACKGROUND

Nutritional interventions often fail to prevent growth failure in childhood and adolescent malnutrition and the mechanisms remain unclear. Recent studies revealed altered microbiota in malnourished children and anorexia nervosa. To facilitate mechanistic studies under physiologically relevant conditions, we established a mouse model of growth failure following chronic dietary restriction and examined microbiota in relation to age, diet, body weight, and anabolic treatment.

METHODS

Four-week-old female BALB/c mice (n = 12/group) were fed ad libitum (AL) or offered limited food to abolish weight gain (LF). A subset of restricted mice was treated with an insulin-like growth factor 1 (IGF1) analog. Food access was restored in a subset of untreated LF (LF-RF) and IGF1-treated LF mice (TLF-RF) on day 97. Gut microbiota were determined on days 69, 96-99 and 120 by next generation sequencing of the V3-5 region of the 16S rRNA gene. Microbiota-host factor associations were analyzed by distance-based PERMANOVA and quantified by the coefficient of determination R² for age, diet, and normalized body weight change (Δbwt). Microbial taxa on day 120 were compared following fitting with an overdispersed Poisson regression model. The machine learning algorithm Random Forests was used to predict age based on the microbiota.

RESULTS

On day 120, Δbwt in AL, LF, LF-RF, and TLF-RF mice was 52 ± 3, -6 ± 1*, 40 ± 3*, and 46 ± 2 % (*, P < 0.05 versus AL). Age and diet, but not Δbwt, were associated with gut microbiota composition. Age explained a larger proportion of the microbiota variability than diet or Δbwt. Random Forests predicted chronological age based on the microbiota and indicated microbiota immaturity in the LF mice before, but not after, refeeding. However, on day 120, the microbiota community structure of LF-RF mice was significantly different from that of both AL and LF mice. IGF1 mitigated the difference from the AL group. Refed groups had a higher abundance of Bacteroidetes and Proteobacteria and a lower abundance of Firmicutes than AL mice.

CONCLUSIONS

Persistent growth failure can be induced by 97-day dietary restriction in young female mice and is associated with microbiota changes seen in lean mice and individuals and anorexia nervosa. IGF1 facilitates recovery of body weights and microbiota.

Platelet-Derived Growth Factor Receptor-α Regulates Proliferation of Gastrointestinal Stromal Tumor Cells With Mutations in KIT by Stabilizing ETV1

BACKGROUND & AIMS

In gastrointestinal muscles, v-kit Hardy-Zuckerman 4 feline sarcoma viral oncogene homolog (KIT) is predominantly expressed by interstitial cells of Cajal (ICC) and platelet-derived growth factor receptor-α (PDGFRA) polypeptide is expressed by so-called fibroblast-like cells. KIT and PDGFRA have been reported to be coexpressed in ICC precursors and gastrointestinal stromal tumors (GISTs), which originate from the ICC lineage. PDGFRA signaling has been proposed to stimulate growth of GISTs that express mutant KIT, but the effects and mechanisms of selective blockade of PDGFRA are unclear. We investigated whether inhibiting PDGFRA could reduce proliferation of GIST cells with mutant KIT via effects on the KIT-dependent transcription factor ETV1.

METHODS

We studied 53 gastric, small intestinal, rectal, or abdominal GISTs collected immediately after surgery or archived as fixed blocks at the Mayo Clinic and University of California, San Diego. In human GIST cells carrying imatinib-sensitive and imatinib-resistant mutations in KIT, PDGFRA was reduced by RNA interference (knockdown) or inhibited with crenolanib besylate (a selective inhibitor of PDGFRA and PDGFRB). Mouse ICC precursors were retrovirally transduced to overexpress wild-type Kit. Cell proliferation was analyzed by methyltetrazolium, 5-ethynyl-2'-deoxyuridine incorporation, and Ki-67 immunofluorescence assays; we also analyzed growth of xenograft tumors in mice. Gastric ICC and ICC precursors, and their PDGFRA(+) subsets, were analyzed by flow cytometry and immunohistochemistry in wild-type, Kit(+/copGFP), Pdgfra(+/eGFP), and NOD/ShiLtJ mice. Immunoblots were used to quantify protein expression and phosphorylation.

RESULTS

KIT and PDGFRA were coexpressed in 3%-5% of mouse ICC, 35%-44% of ICC precursors, and most human GIST samples and cell lines. PDGFRA knockdown or inhibition with crenolanib efficiently reduced proliferation of imatinib-sensitive and imatinib-resistant KIT(+)ETV1(+)PDGFRA(+) GIST cells (50% maximal inhibitory concentration = 5-32 nM), but not of cells lacking KIT, ETV1, or PDGFRA (50% maximal inhibitory concentration >230 nM). Crenolanib inhibited phosphorylation of PDGFRA and PDGFRB, but not KIT. However, Kit overexpression sensitized mouse ICC precursors to crenolanib. ETV1 knockdown reduced KIT expression and GIST proliferation. Crenolanib down-regulated ETV1 by inhibiting extracellular-signal-regulated kinase (ERK)-dependent stabilization of ETV1 protein and also reduced expression of KIT and PDGFRA.

CONCLUSIONS

In KIT-mutant GIST, inhibition of PDGFRA disrupts a KIT-ERK-ETV1-KIT signaling loop by inhibiting ERK activation. The PDGFRA inhibitor crenolanib might be used to treat patients with imatinib-resistant, KIT-mutant GIST.

Targeting Disease Persistence in Gastrointestinal Stromal Tumors

SummaryGastrointestinal stromal tumors (GISTs) represent 20%-40% of human sarcomas. Although approximately half of GISTs are cured by surgery, prognosis of advanced disease used to be poor due to the high resistance of these tumors to conventional chemo- and radiotherapy. The introduction of molecularly targeted therapy (e.g., with imatinib mesylate) following the discovery of the role of oncogenic mutations in the receptor tyrosine kinases KIT and platelet-derived growth factor α (PDGFRA) significantly increased patient survival. However, GIST cells persist in 95%-97% of imatinib-treated patients who eventually progress and die of the disease because of the emergence of clones with drug-resistant mutations. Because these secondary mutations are highly heterogeneous, even second- and third-line drugs that are effective against certain genotypes have only moderately increased progression-free survival. Consequently, alternative strategies such as targeting molecular mechanisms underlying disease persistence should be considered. We reviewed recently discovered cell-autonomous and microenvironmental mechanisms that could promote the survival of GIST cells in the presence of tyrosine kinase inhibitor therapy. We particularly focused on the potential role of adult precursors for interstitial cells of Cajal (ICCs), the normal counterpart of GISTs. ICC precursors share phenotypic characteristics with cells that emerge in a subset of patients treated with imatinib and in young patients with GIST characterized by loss of succinate dehydrogenase complex proteins and lack of KIT or PDGFRA mutations. Eradication of residual GIST cells and cure of GIST will likely require individualized combinations of several approaches tailored to tumor genotype and phenotype.

SIGNIFICANCE

Gastrointestinal stromal tumors (GISTs) are one of the most common connective tissue cancers. Most GISTs that cannot be cured by surgery respond to molecularly targeted therapy (e.g., with imatinib); however, tumor cells persist in almost all patients and eventually acquire drug-resistant mutations. Several mechanisms contribute to the survival of GIST cells in the presence of imatinib, including the activation of "escape" mechanisms and the selection of stem-like cells that are not dependent on the expression of the drug targets for survival. Eradication of residual GIST cells and cure of GIST will likely require individualized combinations of several approaches tailored to the genetic makeup and other characteristics of the tumors.