DCLK1 Regulates Tumor Stemness and Cisplatin Resistance in Non-small Cell Lung Cancer via ABCD-Member-4

Linking ABC transporters to the hallmarks of cancer

Human ATP-binding cassette (ABC) transporters are ubiquitously expressed and transport a broad range of endogenous and xenobiotic substrates across extra- and intracellular membranes. Mutations in ABC genes cause 21 monogenic diseases, and polymorphisms in these genes are associated with susceptibility to complex diseases. ABC transporters also play a major role in drug bioavailability, and they mediate multidrug resistance in cancer. At least 13 ABC transporters were shown to be involved in drug resistance in vitro. In the past decade, efforts have been made to elucidate their roles in tumor biology. Herein, we explore their involvement in tumorigenesis, focusing on the hallmarks of cells as they make their way from normalcy to neoplastic growth states.

DCLK1 is Overexpressed and Associated with Immune Cell Infiltration in Hepatocellular Carcinoma

Recent research has shown that Doublecortin-like kinase 1 (DCLK1) is overexpressed in different types of cancer. It has recently been described as a cancer stem cells (CSCs) marker, is associated with carcinogenesis, and positively correlates with infiltration of multiple immune cell types in some cancers. However, studies focused on assessing DCLK1 expression in HCC are limited, and the role of DCLK1 in HCC tumor immunity remains to be determined. In this study, we used a modified model of the resistant hepatocyte (MRHM) to evaluate DCLK1 expression in HCC. Furthermore, DCLK1 expression in HCC was analyzed using TIMER 2.0, UALCAN, GEPIA, GEO, and HPA web-based tools. Correlations between DCLK1 expression and clinicopathological factors in patients were analyzed using the UALCAN web-based tool. Finally, correlations between DCLK1 and immune infiltrates were investigated using the TIMER 2.0 and TISIDB web-based tools. The results showed that DCLK1 is significantly overexpressed during progression of the HCC carcinogenic process in the MRHM. DCLK1 is overexpressed in HCC according to multiple publics web-based tools, and its overexpression is associated with cancer stage. Furthermore, DCLK1 expression was correlated with infiltration levels of multiple immune cells, immunomodulatory factors, immunoinhibitors, MHC molecules, chemokines, receptors, and immune cell-specific markers. These results suggest that DCLK1 is a potential prognostic biomarker that determines cancer progression and correlates with immune cell infiltration in HCC.

DCLK1 and its oncogenic functions: A promising therapeutic target for cancers

Doublecortin-like kinase 1 (DCLK1), a significant constituent of the protein kinase superfamily and the doublecortin family, has been recognized as a prooncogenic factor that exhibits a strong association with the malignant progression and clinical prognosis of various cancers. DCLK1 serves as a stem cell marker that governs tumorigenesis, tumor cell reprogramming, and epithelial-mesenchymal transition. Multiple studies have indicated the capable of DCLK1 in regulating the DNA damage response and facilitating DNA damage repair. Additionally, DCLK1 is involved in the regulation of the immune microenvironment and the promotion of tumor immune evasion. Recently, DCLK1 has emerged as a promising therapeutic target for a multitude of cancers. Several small-molecule inhibitors of DCLK1 have been identified. Nevertheless, the biological roles of DCLK1 are mainly ambiguous, particularly with the disparities between its α- and β-form transcripts in the malignant progression of cancers, which impedes the development of more precisely targeted drugs. This article focuses on tumor stem cells, tumor epithelial-mesenchymal transition, the DNA damage response, and the tumor microenvironment to provide a comprehensive overview of the association between DCLK1 and tumor malignant progression, address unsolved questions and current challenges, and project future directions for targeting DCLK1 for the diagnosis and treatment of cancers.

Targeting doublecortin-like kinase 1 reveals a novel strategy to circumvent chemoresistance and metastasis in ovarian cancer

Ovarian cancer (OvCa) has a dismal prognosis because of its late-stage diagnosis and the emergence of chemoresistance. Doublecortin-like kinase 1 (DCLK1) is a serine/threonine kinase known to regulate cancer cell "stemness", epithelial-mesenchymal transition (EMT), and drug resistance. Here we show that DCLK1 is a druggable target that promotes chemoresistance and tumor progression of high-grade serous OvCa (HGSOC). Importantly, high DCLK1 expression significantly correlates with poor overall and progression-free survival in OvCa patients treated with platinum chemotherapy. DCLK1 expression was elevated in a subset of HGSOC cell lines in adherent (2D) and spheroid (3D) cultures, and the expression was further increased in cisplatin-resistant (CPR) spheroids relative to their sensitive controls. Using cisplatin-sensitive and resistant isogenic cell lines, pharmacologic inhibition (DCLK1-IN-1), and genetic manipulation, we demonstrate that DCLK1 inhibition was effective at re-sensitizing cells to cisplatin, reducing cell proliferation, migration, and invasion. Using kinase domain mutants, we demonstrate that DCLK1 kinase activity is critical for mediating CPR. The combination of cisplatin and DCLK1-IN-1 showed a synergistic cytotoxic effect against OvCa cells in 3D conditions. Targeted gene expression profiling revealed that DCLK1 inhibition in CPR OvCa spheroids significantly reduced TGFβ signaling, and EMT. We show in vivo efficacy of combined DCLK1 inhibition and cisplatin in significantly reducing tumor metastases. Our study shows that DCLK1 is a relevant target in OvCa and combined targeting of DCLK1 in combination with existing chemotherapy could be a novel therapeutic approach to overcome resistance and prevent OvCa recurrence.

Protein expression and localization of ABC transporters in pancreatic adenocarcinoma: Prognostic role of ABCC8

BACKGROUND

ATP-binding cassette (ABC) transporters translocate various substances across cellular membranes. Their deregulation may cause cancer drug resistance or perturbations in the supply of building blocks for cancer cells and modify patients' prognosis. This study investigated protein expression and cellular localization of the previously suggested putative prognostic biomarkers - ABCB2/TAP1, ABCC7/CFTR, ABCC8/SUR1, and ABCD4 in patients with pancreatic ductal adenocarcinoma (PDAC).

METHODS

Protein expression and localization were assessed by immunohistochemistry in formalin-fixed paraffin-embedded primary tumor tissue blocks of 61 PDAC patients and associated with clinical data and the survival of patients.

RESULTS

No CFTR protein expression was observed in PDAC, while TAP1 and ABCC8 were expressed predominantly in the cytoplasm of tumor cells. Most samples (81 %) had detectable both membranous and cytoplasmic ABCD4 staining and 42 % had ABCD4 expressed in the apical orientation. Negative membranous ABCD4 staining was significantly more frequent in advanced stage III or IV tumors (p = 0.022). Small or medium counts of individual ABCC8-positive cells in the stroma surrounding tumor tubules were also more often found in stage III or IV (p = 0.044). Patients with moderate or strong ABCC8 cytoplasmic staining intensity in tumor cells had a 3.5-fold higher risk of disease progression than those with weak staining (p = 0.002).

CONCLUSIONS

The study shows for the first time that the cytoplasmic ABCC8 protein expression has prognostic value in PDAC.

Role of DCLK1/Hippo pathway in type II alveolar epithelial cells differentiation in acute respiratory distress syndrome

BACKGROUND

Delay in type II alveolar epithelial cell (AECII) regeneration has been linked to higher mortality in patients with acute respiratory distress syndrome (ARDS). However, the interaction between Doublecortin-like kinase 1 (DCLK1) and the Hippo signaling pathway in ARDS-associated AECII differentiation remains unclear. Therefore, the objective of this study was to understand the role of the DCLK1/Hippo pathway in mediating AECII differentiation in ARDS.

MATERIALS AND METHODS

AECII MLE-12 cells were exposed to 0, 0.1, or 1 μg/mL of lipopolysaccharide (LPS) for 6 and 12 h. In the mouse model, C57BL/6JNarl mice were intratracheally (i.t.) injected with 0 (control) or 5 mg/kg LPS and were euthanized for lung collection on days 3 and 7.

RESULTS

We found that LPS induced AECII markers of differentiation by reducing surfactant protein C (SPC) and p53 while increasing T1α (podoplanin) and E-cadherin at 12 h. Concurrently, nuclear YAP dynamic regulation and increased TAZ levels were observed in LPS-exposed AECII within 12 h. Inhibition of YAP consistently decreased cell levels of SPC, claudin 4 (CLDN-4), galectin 3 (LGALS-3), and p53 while increasing transepithelial electrical resistance (TEER) at 6 h. Furthermore, DCLK1 expression was reduced in isolated human AECII of ARDS, consistent with the results in LPS-exposed AECII at 6 h and mouse SPC-positive (SPC+) cells after 3-day LPS exposure. We observed that downregulated DCLK1 increased p-YAP/YAP, while DCLK1 overexpression slightly reduced p-YAP/YAP, indicating an association between DCLK1 and Hippo-YAP pathway.

CONCLUSIONS

We conclude that DCLK1-mediated Hippo signaling components of YAP/TAZ regulated markers of AECII-to-AECI differentiation in an LPS-induced ARDS model.

Epigenetic Landscape and Therapeutic Implication of Gene Isoforms of Doublecortin-Like Kinase 1 for Cancer Stem Cells

While significant strides have been made in understanding cancer biology, the enhancement in patient survival is limited, underscoring the urgency for innovative strategies. Epigenetic modifications characterized by hereditary shifts in gene expression without changes to the DNA sequence play a critical role in producing alternative gene isoforms. When these processes go awry, they influence cancer onset, growth, spread, and cancer stemness. In this review, we delve into the epigenetic and isoform nuances of the protein kinase, doublecortin-like kinase 1 (DCLK1). Recognized as a hallmark of tumor stemness, DCLK1 plays a pivotal role in tumorigenesis, and DCLK1 isoforms, shaped by alternative promoter usage and splicing, can reveal potential therapeutic touchpoints. Our discussion centers on recent findings pertaining to the specific functions of DCLK1 isoforms and the prevailing understanding of its epigenetic regulation via its two distinct promoters. It is noteworthy that all DCLK1 isoforms retain their kinase domain, suggesting that their unique functionalities arise from non-kinase mechanisms. Consequently, our research has pivoted to drugs that specifically influence the epigenetic generation of these DCLK1 isoforms. We posit that a combined therapeutic approach, harnessing both the epigenetic regulators of specific DCLK1 isoforms and DCLK1-targeted drugs, may prove more effective than therapies that solely target DCLK1.

Tumor microenvironment-induced tumor cell plasticity: relationship with hypoxic stress and impact on tumor resistance

The role of tumor interaction with stromal components during carcinogenesis is crucial for the design of efficient cancer treatment approaches. It is widely admitted that tumor hypoxic stress is associated with tumor aggressiveness and thus impacts susceptibility and resistance to different types of treatments. Notable biological processes that hypoxia functions in include its regulation of tumor heterogeneity and plasticity. While hypoxia has been reported as a major player in tumor survival and dissemination regulation, the significance of hypoxia inducible factors in cancer stem cell development remains poorly understood. Several reports indicate that the emergence of cancer stem cells in addition to their phenotype and function within a hypoxic tumor microenvironment impacts cancer progression. In this respect, evidence showed that cancer stem cells are key elements of intratumoral heterogeneity and more importantly are responsible for tumor relapse and escape to treatments. This paper briefly reviews our current knowledge of the interaction between tumor hypoxic stress and its role in stemness acquisition and maintenance. Our review extensively covers the influence of hypoxia on the formation and maintenance of cancer stem cells and discusses the potential of targeting hypoxia-induced alterations in the expression and function of the so far known stem cell markers in cancer therapy approaches. We believe that a better and integrated understanding of the effect of hypoxia on stemness during carcinogenesis might lead to new strategies for exploiting hypoxia-associated pathways and their targeting in the clinical setting in order to overcome resistance mechanisms. More importantly, at the present time, efforts are oriented towards the design of innovative therapeutical approaches that specifically target cancer stem cells.

DCLK1 Drives EGFR-TKI-Acquired Resistance in Lung Adenocarcinoma by Remodeling the Epithelial-Mesenchymal Transition Status

OBJECTIVE

Epidermal growth factor receptor-tyrosine kinase inhibitor (EGFR-TKI) is a first-line treatment for lung adenocarcinoma with EGFR-sensitive mutations, but acquired resistance to EGFR-TKIs remains a problem in clinical practice. The development of epithelial-mesenchymal transition (EMT) is a critical mechanism that induces acquired resistance to TKIs. Reversing acquired resistance to EGFR-TKIs through targeting the key molecules driving EMT provides an alternative choice for patients. We, therefore, aimed to explore the role of doublecortin-like kinase 1 (DCLK1) as an EMT driver gene in the acquired resistance of lung adenocarcinoma to EGFR-TKIs.

METHODS

The IC₅₀ of Gefitinib or Osimertinib in PC9/HCC827 cells was measured using a cell counting kit-8 (CCK8) assay. The expression levels of EMT-related genes in PC9 and HCC827 cells were detected using RT-PCR and Western blot. Cell migration and invasion abilities were assessed via a transwell assay. For the in vivo experiments, PC9 cells were subcutaneously injected into BALB/c nude mice to form tumors. Upon harvesting, tumor tissues were retained for RT-PCR, Western blot, and polychromatic fluorescence staining to detect biomarker changes in the EMT process.

RESULTS

Gefitinib-resistant PC9 (PC9/GR) and Osimertinib-resistant HCC827 (HCC827/OR) cells showed remarkable activation of EMT and enhanced migration and invasion abilities compared to TKI-sensitive cells. In addition, DCLK1 expression was markedly increased in EGFR-TKI-resistant lung adenocarcinoma cells. The targeted knockout of DCLK1 effectively reversed the EMT phenotype in TKI-resistant cells and improved EGFR-TKI sensitivity, which was further validated by the in vivo experiments.

CONCLUSIONS

DCLK1 facilitates acquired resistance to EGFR-TKI in lung adenocarcinoma by inducting EMT and accelerating the migration and invasion abilities of TKI-resistant cells.

Structure-Guided Prediction of the Functional Impact of DCLK1 Mutations on Tumorigenesis

Doublecortin-like kinase 1 (DCLK1) is a functional serine/threonine (S/T)-kinase and a member of the doublecortin family of proteins which are characterized by their ability to bind to microtubules (MTs). DCLK1 is a proposed cancer driver gene, and its upregulation is associated with poor overall survival in several solid cancer types. However, how DCLK1 associates with MTs and how its kinase function contributes to pro-tumorigenic processes is poorly understood. This review builds on structural models to propose not only the specific functions of the domains but also attempts to predict the impact of individual somatic missense mutations on DCLK1 functions. Somatic missense mutations in DCLK1 are most frequently located within the N-terminal MT binding region and likely impact on the ability of DCLK1 to bind to αβ-tubulin and to polymerize and stabilize MTs. Moreover, the MT binding affinity of DCLK1 is negatively regulated by its auto-phosphorylation, and therefore mutations that affect kinase activity are predicted to indirectly alter MT dynamics. The emerging picture portrays DCLK1 as an MT-associated protein whose interactions with tubulin heterodimers and MTs are tightly controlled processes which, when disrupted, may confer pro-tumorigenic properties.

Chemotherapeutic drugs elicit stemness and metabolic alteration to mediate acquired drug-resistant phenotype in acute myeloid leukemia cell lines

Chemotherapy resistance leading to disease relapse is a significant barrier in treating acute myeloid leukemia (AML). Metabolic adaptations have been shown to contribute to therapy resistance. However, little is known about whether specific therapies cause specific metabolic changes. We established cytarabine-resistant (AraC-R) and Arsenic trioxide-resistant (ATO-R) AML cell lines, displaying distinct cell surface expression and cytogenetic abnormalities. Transcriptomic analysis revealed a significant difference in the expression profiles of ATO-R and AraC-R cells. Geneset enrichment analysis showed AraC-R cells rely on OXPHOS, while ATO-R cells on glycolysis. ATO-R cells were also enriched for stemness gene signatures, whereas AraC-R cells were not. The mito stress and glycolytic stress tests confirmed these findings. The distinct metabolic adaptation of AraC-R cells increased sensitivity to the OXPHOS inhibitor venetoclax. Cytarabine resistance was circumvented in AraC-R cells by combining Ven and AraC. In vivo, ATO-R cells showed increased repopulating potential, leading to aggressive leukemia compared to the parental and AraC-R. Overall, our study shows that different therapies can cause different metabolic changes and that these metabolic dependencies can be used to target chemotherapy-resistant AML.

Thrombin induces IL-8/CXCL8 expression by DCLK1-dependent RhoA and YAP activation in human lung epithelial cells

Background

Doublecortin-like kinase 1 (DCLK1) has been recognized as a marker of cancer stem cell in several malignancies. Thrombin is crucial in asthma severity as it can promote IL-8/CXCL8 production in lung epithelial cells, which is a potent chemoattractant for neutrophils. However, the pathologic role of DCLK1 in asthma and its involvement in thrombin-stimulated IL-8/CXCL8 expression remain unknown.

Methods

IL-8/CXCL8, thrombin, and DCLK1 expression were observed in the lung tissues of severe asthma patients and ovalbumin (OVA)-induced asthmatic mice model. A549 and BEAS-2B cells were either pretreated with inhibitors or small interfering RNAs (siRNAs) before being treated with thrombin. IL-8/CXCL8 expression and the molecules involved in signaling pathway were performed using ELISA, luciferase activity assay, Western blot, or ChIP assay.

Results

IL-8/CXCL8, thrombin, and DCLK1 were overexpressed in the lung tissues of severe asthma patients and ovalbumin (OVA)-induced asthmatic mice model. Our in vitro study found that DCLK siRNA or LRKK2-IN-1 (DCLK1 inhibitor) attenuated IL-8/CXCL8 release after thrombin induction in A549 and BEAS-2B cells. Thrombin activated DCLK1, RhoA, and YAP in a time-dependent manner, in which DCLK1 siRNA inhibited RhoA and YAP activation. YAP was dephosphorylated on the Ser127 site after thrombin stimulation, resulting in YAP translocation to the nucleus from the cytosol. DCLK1, RhoA and YAP activation following thrombin stimulation were inhibited by U0126 (ERK inhibitor). Moreover, DCLK1 and YAP siRNA inhibited κB-luciferase activity. Thrombin stimulated the recruitment of YAP and p65 to the NF-κB site of the IL-8/CXCL8 promoter and was inhibited by DCLK1 siRNA.

Conclusions

Thrombin activates the DCLK1/RhoA signaling pathway, which promotes YAP activation and translocation to the nucleus from the cytosol, resulting in YAP/p65 formation, and binding to the NF-κB site, which enhances IL-8/CXCL8 expression. DCLK1 might be essential in thrombin-stimulated IL-8/CXCL8 expression in asthmatic lungs and indicates a potential therapeutic strategy for severe asthma treatment.

Pleiotropic effects of DCLK1 in cancer and cancer stem cells

Doublecortin-like kinase 1 (DCLK1), a protein molecule, has been identified as a tumor stem cell marker in the cancer cells of gastrointestinal, pancreas, and human colon. DCLK1 expression in cancers, such as breast carcinoma, lung carcinoma, hepatic cell carcinoma, tuft cells, and human cholangiocarcinoma, has shown a way to target the DCLK1 gene and downregulate its expression. Several studies have discussed the inhibition of tumor cell proliferation along with neoplastic cell arrest when the DCLK1 gene, which is expressed in both cancer and normal cells, was targeted successfully. In addition, previous studies have shown that DCLK1 plays a vital role in various cancer metastases. The correlation of DCLK1 with numerous stem cell receptors, signaling pathways, and genes suggests its direct or an indirect role in promoting tumorigenesis. Moreover, the impact of DCLK1 was found to be related to the functioning of an oncogene. The downregulation of DCLK1 expression by using targeted strategies, such as embracing the use of siRNA, miRNA, CRISPR/Cas9 technology, nanomolecules, specific monoclonal antibodies, and silencing the pathways regulated by DCLK1, has shown promising results in both in vitro and in vivo studies on gastrointestinal (GI) cancers. In this review, we will discuss about the present understanding of DCLK1 and its role in the progression of GI cancer and metastasis.

Targeting DCLK1 overcomes 5-fluorouracil resistance in colorectal cancer through inhibiting CCAR1/β-catenin pathway-mediated cancer stemness

Background

To date, 5‐fluorouracil‐based chemotherapy is very important for locally advanced or metastatic colorectal cancer (CRC). However, chemotherapy resistance results in tumor recurrence and metastasis, which is a major obstacle for treatment of CRC.

Methods

In the current research, we establish 5‐fluorouracil resistant cell lines and explore the potential targets associated with 5‐fluorouracil resistance in CRC. Moreover, we perform clinical specimen research, in vitro and in vivo experiments and molecular mechanism research, to reveal the biological effects and the mechanism of DCLK1 promoting 5‐fluorouracil resistance, and to clarify the potential clinical value of DCLK1 as a target of 5‐fluorouracil resistance in CRC.

Results

We discover that doublecortin‐like kinase 1 (DCLK1), a cancer stem cell maker, is correlated with 5‐fluorouracil resistance, and functionally promotes cancer stemness and 5‐fluorouracil resistance in CRC. Mechanistically, we elucidate that DCLK1 interacts with cell cycle and apoptosis regulator 1 (CCAR1) through the C‐terminal domain, and phosphorylates CCAR1 at the Ser343 site, which is essential for CCAR1 stabilisation. Moreover, we find that DCLK1 positively regulates β‐catenin signalling via CCAR1, which is responsible for maintaining cancer stemness. Subsequently, we prove that blocking β‐catenin inhibits DCLK1‐mediated 5‐fluorouracil resistance in CRC cells. Importantly, we demonstrate that DCLK1 inhibitor could block CCAR1/β‐catenin pathway‐mediated cancer stemness and consequently suppresses 5‐fluorouracil resistant CRC cells in vitro and in vivo.

Conclusions

Collectively, our findings reveal that DCLK1 promotes 5‐fluorouracil resistance in CRC by CCAR1/β‐catenin pathway‐mediated cancer stemness, and suggest that targeting DCLK1 might be a promising method to eliminate cancer stem cells for overcoming 5‐fluorouracil resistance in CRC.

Interaction between avian leukosis virus subgroup J surface protein and doublecortin-like kinase 1 accelerates cell proliferation and epithelial-mesenchymal transition

Avian leukosis virus subgroup J (ALV-J) induces myelocytomas, which can metastasize to multiple organs in diseased chicken. Although metastasis is the primary cause of death in such cases, the mechanism for it remains unclear. Here, we found that interaction between ALV-J surface protein (SU) and doublecortin-like kinase 1 (DCLK1) promotes epithelial-mesenchymal transition (EMT) and cell proliferation. We found that ALV-J can activate EMT in infected cells. Subsequently, proteomics analysis revealed that DCLK1, a well-established putative tumor stem cell marker, which is highly expressed in ALV-J-infected DF-1 cells and chickens, might be a potential factor mediating EMT. Furthermore, using immunofluorescence and immunoprecipitation, we verified that SU interacts with DCLK1. Functional studies suggested that overexpression of DCLK1 increased viral replication, and promoted cell proliferation by accelerating the progression of cells from the G0/G1 phase to the S phase of cell cycle, whereas RNA-interference of DCLK1 reduced viral replication and arrested cell proliferation by retarding cell cycle progression from the late G1 phase into the S phase in ALV-J-infected cells. Moreover, we demonstrate that the increased accumulation of DCLK1 promotes EMT by increasing the expression of N-cadherin, vimentin, MMP2, transcription factor Snail1, and decreasing the expression of epithelial marker E-cadherin. These results suggest that ALV-J SU interacts with DCLK1, and accelerates cell proliferation, leading to increased viral replication, and ultimately activating EMT, which paves the way for tumor metastasis. IMPORTANCE Tumor metastasis is a major challenge in cancer research, because of its systemic nature and the resistance of disseminated tumor cells to existing therapeutic agents. It is estimated that >90% of mortality from cancer is attributable to metastases. We found that ALV-J can activate EMT, which plays a critical role in cancer metastasis. Subsequently, we identified a tumor stem cell marker, DCLK1, in ALV-J infected cells, which interacts with surface protein (SU) of ALV-J to promote virus replication, activate EMT, and accelerate cell proliferation enabling ALV-J to obtain metastatic ability. Understanding the process of participation of ALV-J in EMT and the route of metastasis will help elucidate the mechanism of virus-induced tumor metastasis, and help identify promising molecular targets and key obstacles for ALV-J control and clinical technology development.

DCLK1 autoinhibition and activation in tumorigenesis

Doublecortin-like kinase 1 (DCLK1) is upregulated in many tumors and is a marker for tumor stem cells. Accumulating evidence suggests DCLK1 constitutes a promising drug target for cancer therapy. However, the regulation of DCLK1 kinase activity is poorly understood, particularly the function of its autoinhibitory domain (AID), and, moreover, no physiological activators of DCLK1 have presently been reported. Here we determined the first DCLK1 kinase structure in the autoinhibited state and identified the neuronal calcium sensor HPCAL1 as an activator of DCLK1. The C-terminal AID functions to block the ATP-binding site and is competitive with ATP. HPCAL1 binds directly to the AID in a Ca²⁺-dependent manner, which releases the autoinhibition. We also analyzed cancer-associated mutations occurring in the AID and elucidate how these mutations disrupt DCLK1 autoinhibition to elicit kinase activity upregulation. Our results present a molecular mechanism for autoinhibition and activation of DCLK1 kinase activity and provide insights into DCLK1-associated tumorigenesis.

Impact of Cancer Stem Cells and Cancer Stem Cell-Driven Drug Resiliency in Lung Tumor: Options in Sight

Causing a high mortality rate worldwide, lung cancer remains an incurable malignancy resistant to conventional therapy. Despite the discovery of specific molecular targets and new treatment strategies, there remains a pressing need to develop more efficient therapy to further improve the management of this disease. Cancer stem cells (CSCs) are considered the root of sustained tumor growth. This consensus corroborates the CSC model asserting that a distinct subpopulation of malignant cells within a tumor drives and maintains tumor progression with high heterogeneity. Besides being highly tumorigenic, CSCs are highly refractory to standard drugs; therefore, cancer treatment should be focused on eliminating these cells. Herein, we present the current knowledge of the existence of CSCs, CSC-associated mechanisms of chemoresistance, the ability of CSCs to evade immune surveillance, and potential CSC inhibitors in lung cancer, to provide a wider insight to drive a more efficient elimination of this pro-oncogenic and treatment-resistant cell fraction.

Inhibition of DCLK1 with DCLK1-IN-1 Suppresses Renal Cell Carcinoma Invasion and Stemness and Promotes Cytotoxic T-Cell-Mediated Anti-Tumor Immunity

Simple Summary

In this study, we found that the novel small molecule kinase inhibitor DCLK1-IN-1 not only inhibited DCLK1 phosphorylation, stemness, and EMT-related properties of RCC cells but also revealed its potential as an immunotherapy agent and potential combination therapy with anti-PD1 against RCC in immune co-culture experiments.

Abstract

The approval of immune checkpoint inhibitors has expanded treatment options for renal cell carcinoma (RCC), but new therapies that target RCC stemness and promote anti-tumor immunity are needed. Previous findings demonstrate that doublecortin-like kinase 1 (DCLK1) regulates stemness and is associated with RCC disease progression. Herein, we demonstrate that small-molecule kinase inhibitor DCLK1-IN-1 strongly inhibits DCLK1 phosphorylation and downregulates pluripotency factors and cancer stem cell (CSC) or epithelial-mesenchymal transition (EMT)-associated markers including c-MET, c-MYC, and N-Cadherin in RCC cell lines. Functionally, DCLK1-IN-1 treatment resulted in significantly reduced colony formation, migration, and invasion. Additionally, assays using floating or Matrigel spheroid protocols demonstrated potent inhibition of stemness. An analysis of clinical populations showed that DCLK1 predicts RCC survival and that its expression is correlated with reduced CD8+ cytotoxic T-cell infiltration and increases in M2 immunosuppressive macrophage populations. The treatment of RCC cells with DCLK1-IN-1 significantly reduced the expression of immune checkpoint ligand PD-L1, and co-culture assays using peripheral blood monocytes (PBMCs) or T-cell expanded PBMCs demonstrated a significant increase in immune-mediated cytotoxicity alone or in combination with anti-PD1 therapy. Together, these findings demonstrate broad susceptibility to DCLK1 kinase inhibition in RCC using DCLK1-IN-1 and provide the first direct evidence for DCLK1-IN-1 as an immuno-oncology agent.

Inflammatory Mediators and Gut Microbial Toxins Drive Colon Tumorigenesis by IL-23 Dependent Mechanism

Simple Summary

Western-style diet, rich in high fat, is the major cause of obesity and enhanced risk of colon cancer in the USA and worldwide. The inflammatory molecules are a well-established link between obesity and the modulation of colon tumorigenesis. In particular, IL-23 plays an important role in the impact of a western-style diet on obesity, the gut microbiome, and colon tumorigenesis. However, the underlying mechanism of IL-23 production for colon tumor progression and whether IL-23 can be a potential target is not clear. Our findings signify the role of pro-tumorigenic innate immune cells, including dendritic cells and macrophages in IL-23 production by bacterial toxins and eicosanoids. IL-23 knockdown in the tumorigenic dendritic cells and macrophages inhibited the colon tumor cell and organoids growth. Taken together, targeting IL-23 may be a promising option for the prevention and treatment of high-fat/obesity-associated colon cancer in clinical trials.

Abstract

Obesity-associated chronic inflammation predisposes colon cancer risk development. Interleukin-23 (IL-23) is a potential inflammatory mediator linking obesity to chronic colonic inflammation, altered gut microbiome, and colon carcinogenesis. We aimed to elucidate the role of pro-inflammatory eicosanoids and gut bacterial toxins in priming dendritic cells and macrophages for IL-23 secretion to promote colon tumor progression. To investigate the association of IL-23 with obesity and colon tumorigenesis, we utilized TCGA data set and colonic tumors from humans and preclinical models. To understand IL-23 production by inflammatory mediators and gut microbial toxins, we performed several in vitro mechanistic studies to mimic the tumor microenvironment. Colonic tumors were utilized to perform the ex vivo experiments. Our findings showed that IL-23 is elevated in obese individuals, colonic tumors and correlated with reduced disease-free survival. In vitro studies showed that IL-23 treatment increased the colon tumor cell self-renewal, migration, and invasion while disrupting epithelial barrier permeability. Co-culture experiments of educated dendritic cells/macrophages with colon cancer cells significantly increased the tumor aggression by increasing the secretory levels of IL-23, and these observations are further supported by ex vivo rat colonic tumor organotypic experiments. Our results demonstrate gut microbe toxins and eicosanoids facilitate IL-23 production, which plays an important role in obesity-associated colonic tumor progression. This newly identified nexus represents a potential target for the prevention and treatment of obesity-associated colon cancer.

Structural basis for small molecule targeting of Doublecortin Like Kinase 1 with DCLK1-IN-1

Doublecortin-like kinase 1 (DCLK1) is an understudied bi-functional kinase with a proven role in tumour growth and development. However, the presence of tissue-specific spliced DCLK1 isoforms with distinct biological functions have challenged the development of effective strategies to understand the role of DCLK1 in oncogenesis. Recently, DCLK1-IN-1 was reported as a highly selective DCLK1 inhibitor, a powerful tool to dissect DCLK1 biological functions. Here, we report the crystal structures of DCLK1 kinase domain in complex with DCLK1-IN-1 and its precursors. Combined, our data rationalises the structure-activity relationship that informed the development of DCLK1-IN-1 and provides the basis for the high selectivity of DCLK1-IN-1, with DCLK1-IN-1 inducing a drastic conformational change of the ATP binding site. We demonstrate that DCLK1-IN-1 binds DCLK1 long isoforms but does not prevent DCLK1's Microtubule-Associated Protein (MAP) function. Together, our work provides an invaluable structural platform to further the design of isoform-specific DCLK1 modulators for therapeutic intervention.

JARID2 promotes stemness and cisplatin resistance in non-small cell lung cancer via upregulation of Notch1

Increased stemness is causally linked to development of drug resistance in cancers. JARID2 is a member of the Jumonji family of proteins and regulates differentiation of embryonic stem cells. However, the role of JARID2 in lung cancer stemness and drug resistance is still unclear. In this study, we investigated the expression of JARID2 in parental and cisplatin (CDDP) resistant non-small cell lung cancer (NSCLC) cells. The function of JARID2 in modulating CDDP sensitivity of NSCLC cells was determined. It was found that JARID2 is upregulated in CDDP resistant NSCLC cells, which depends on SOX2 expression. JARID2 overexpression promotes CDDP resistance in NSCLC cells, whereas JARID2 depletion restores CDDP sensitivity in CDDP resistant NSCLC cells. Moreover, JARID2 overexpression enhances cancer stem cell-like properties in NSCLC cells, which is coupled with increased expression of cancer stem cell markers. Mechanistically, JARID2-induced stemness and CDDP resistance is mediated by upregulation of Notch1. In clinical settings, high expression of JARID2 is significantly associated with advanced TNM stage, shorter overall survival, and poor chemotherapeutic response. These findings point toward an important role of JARID2 in CDDP resistance and stemness of NSCLC and provide a promising target for overcoming CDDP resistance.

Research Progress of DCLK1 Inhibitors as Cancer Therapeutics

Doublecortin-like kinase 1 (DCLK1) has emerged over the last decade as a unique stem cell marker within gastrointestinal tissues. Evidence from mouse models shows that high Dclk1 expression denotes a population of cells that promote tissue regeneration and serve as potential cancer stem cells. Moreover, since specific DCLK1 isoforms are overexpressed in many cancers and not normal cells, targeting the expression or kinase activity of DCLK1 can inhibit cancer cell growth. Here we review the evidence for DCLK1 as a prospective cancer target, including its isoform-specific expression and mutational status in human cancers. We further discuss the challenges and current progress in the development of small-molecule inhibitors of DCLK1.

Pathogenesis and therapeutic strategy in platinum resistance lung cancer

Platinum compounds (cisplatin and carboplatin) represent the most active anticancer agents in clinical use both of lung cancer in mono-and combination therapies. However, platinum resistance limits its clinical application. It is necessary to understand the molecular mechanism of platinum resistance, identify predictive markers, and develop newer, more effective and less toxic agents to treat platinum resistance in lung cancer. Here, it summarizes the main molecular mechanisms associated with platinum resistance in lung cancer and the development of new approaches to tackle this clinically relevant problem. Moreover, it could lead to the development of more effective treatment for refractory lung cancer in future.

Cancer stem cell marker DCLK1 reprograms small extracellular vesicles toward migratory phenotype in gastric cancer cells

Doublecortin-like kinase 1 (DCLK1) is a putative cancer stem cell marker, a promising diagnostic and prognostic maker for malignant tumors and a proposed driver gene for gastric cancer (GC). DCLK1 overexpression in a majority of solid cancers correlates with lymph node metastases, advanced disease and overall poor-prognosis. In cancer cells, DCLK1 expression has been shown to promote epithelial-to-mesenchymal transition (EMT), driving disruption of cell-cell adhesion, cell migration and invasion. Here, we report that DCLK1 influences small extracellular vesicle (sEV/exosome) biogenesis in a kinase-dependent manner. sEVs isolated from DCLK1 overexpressing human GC cell line MKN1 (MKN1^OE -sEVs), promote the migration of parental (non-transfected) MKN1 cells (MKN1^PAR ). Quantitative proteome analysis of MKN1^OE -sEVs revealed enrichment in migratory and adhesion regulators (STRAP, CORO1B, BCAM, COL3A, CCN1) in comparison to MKN1^PAR -sEVs. Moreover, using DCLK1-IN-1, a specific small molecule inhibitor of DCLK1, we reversed the increase in sEV size and concentration in contrast to other EV subtypes, as well as kinase-dependent cargo selection of proteins involved in EV biogenesis (KTN1, CHMP1A, MYO1G) and migration and adhesion processes (STRAP, CCN1). Our findings highlight a specific role of DCLK1-kinase dependent cargo selection for sEVs and shed new light on its role as a regulator of signaling in gastric tumorigenesis.

XMD-17-51 Inhibits DCLK1 Kinase and Prevents Lung Cancer Progression

Doublecortin-like kinase 1 (DCLK1) is a cancer stem cell marker that is highly expressed in various types of human cancer, and a protein kinase target for cancer therapy that is attracting increasing interest. However, no drug candidates targeting DCLK1 kinase have been developed in clinical trials to date. XMD-17-51 was found herein to possess DCLK1 kinase inhibitory activities by cell-free enzymatic assay. In non-small cell lung carcinoma (NSCLC) cells, XMD-17-51 inhibited DCLK1 and cell proliferation, while DCLK1 overexpression impaired the anti-proliferative activity of XMD-17-51 in A549 cell lines. Consequently, XMD-17-51 decreased Snail-1 and zinc-finger-enhancer binding protein 1 protein levels, but increased those of E-cadherin, indicating that XMD-17-51 reduces epithelial-mesenchymal transition (EMT). Furthermore, sphere formation efficiency was significantly decreased upon XMD-17-51 treatment, and XMD-17-51 reduced the expression of stemness markers such as β-catenin, and pluripotency factors such as SOX2, NANOG and OCT4. However, the percentage of ALDH⁺ cells was increased significantly following treatment with XMD-17-51 in A549 cells, possibly due to EMT inhibition. In combination, the present data indicated that XMD-17-51 inhibited DCLK1 kinase activity in a cell-free assay with an IC₅₀ of 14.64 nM, and decreased DCLK1 protein levels, cell proliferation, EMT and stemness in NSCLC cell lines. XMD-17-51 has the potential to be a candidate drug for lung cancer therapy.

Molecular Bases of Mechanisms Accounting for Drug Resistance in Gastric Adenocarcinoma

Gastric adenocarcinoma (GAC) is the most common histological type of gastric cancer, the fifth according to the frequency and the third among the deadliest cancers. GAC high mortality is due to a combination of factors, such as silent evolution, late clinical presentation, underlying genetic heterogeneity, and effective mechanisms of chemoresistance (MOCs) that make the available antitumor drugs scarcely useful. MOCs include reduced drug uptake (MOC-1a), enhanced drug efflux (MOC-1b), low proportion of active agents in tumor cells due to impaired pro-drug activation or active drug inactivation (MOC-2), changes in molecular targets sensitive to anticancer drugs (MOC-3), enhanced ability of cancer cells to repair drug-induced DNA damage (MOC-4), decreased function of pro-apoptotic factors versus up-regulation of anti-apoptotic genes (MOC-5), changes in tumor cell microenvironment altering the response to anticancer agents (MOC-6), and phenotypic transformations, including epithelial-mesenchymal transition (EMT) and the appearance of stemness characteristics (MOC-7). This review summarizes updated information regarding the molecular bases accounting for these mechanisms and their impact on the lack of clinical response to the pharmacological treatment currently used in GAC. This knowledge is required to identify novel biomarkers to predict treatment failure and druggable targets, and to develop sensitizing strategies to overcome drug refractoriness in GAC.