Serum lemur tyrosine kinase 3 expression in colorectal cancer patients predicts cancer progression and prognosis

Lemur tail kinase 3 serves as a predictor of patient outcomes and a target for the treatment of ovarian cancer

Lemur tail kinase 3 (LMTK3) belongs to a family of tyrosine kinases that are known to correlate with tumor grade and patient survival in some cancers. Here, we validated LMTK3 as a specific target and a prognostic biomarker in ovarian cancer (OC). In samples from 204 stage I-II OC patients, immunohistochemical studies revealed a higher cytoplasmic-to-nuclear staining intensity of LMTK3, which correlated with worse overall survival (p < 0.001). Efficacy studies utilizing novel LMTK3 binding peptides (LMTK3BPs) showed that all chemosensitive and chemoresistant OC cells were killed without affecting normal cells (p < 0.005), with synergistic effects shown following cisplatin and docetaxel treatment. In an orthotopic xenograft mouse model of OC, we saw a 35% tumor reduction in response to intravenous injections of 2 mg/kg LMTK3BP given three times a week for 3 weeks. Furthermore, in vivo safety studies showed no signs of toxicity after LMTK3BP treatment, even at doses as high as 40 mg/kg. This study highlights LMTK3 as a predictor of patient clinical outcomes. More importantly, novel LMTK3BPs represent potential safe treatment options, either alone or in combination with therapies, for OC.

A revised nomenclature for the lemur family of protein kinases

The lemur family of protein kinases has gained much interest in recent years as they are involved in a variety of cellular processes including regulation of axonal transport and endosomal trafficking, modulation of synaptic functions, memory and learning, and they are centrally placed in several intracellular signalling pathways. Numerous studies have also implicated role of the lemur kinases in the development and progression of a wide range of cancers, cystic fibrosis, and neurodegenerative diseases. However, parallel discoveries and inaccurate prediction of their kinase activity have resulted in a confusing and misleading nomenclature of these proteins. Herein, a group of international scientists with expertise in lemur family of protein kinases set forth a novel nomenclature to rectify this problem and ultimately help the scientific community by providing consistent information about these molecules.

The Inhibitory Properties of a Novel, Selective LMTK3 Kinase Inhibitor

Recently, the oncogenic role of lemur tyrosine kinase 3 (LMTK3) has been well established in different tumor types, highlighting it as a viable therapeutic target. In the present study, using in vitro and cell-based assays coupled with biophysical analyses, we identify a highly selective small molecule LMTK3 inhibitor, namely C36. Biochemical/biophysical and cellular studies revealed that C36 displays a high in vitro selectivity profile and provides notable therapeutic effect when tested in the National Cancer Institute (NCI)-60 cancer cell line panel. We also report the binding affinity between LMTK3 and C36 as demonstrated via microscale thermophoresis (MST). In addition, C36 exhibits a mixed-type inhibition against LMTK3, consistent with the inhibitor overlapping with both the adenosine 5'-triphosphate (ATP)- and substrate-binding sites. Treatment of different breast cancer cell lines with C36 led to decreased proliferation and increased apoptosis, further reinforcing the prospective value of LMTK3 inhibitors for cancer therapy.

Lemur tyrosine kinase-3 (LMTK3) induces chemoresistance to cetuximab in colorectal cancer via the ERK/MAPK pathway

As an oncogenic kinase in multiple cancers, LMTK3 was deeply implicated in cancer pathogenesis. Nevertheless, its biological function in colorectal cancer (CRC) is still unclear. In this study, LMTK3 mRNA expression was assessed by RT-qPCR. LMTK3, phospho-ERK1/2 (p-ERK1/2), ERK1/2, and cleaved caspase-3 protein levels were detected by western blotting. Cetuximab (CTX)-resistant CRC cell models were constructed to investigate the mechanism of LMTK3-regulated CTX resistance in CRC. CTX half-maximal inhibitory concentration (IC₅₀), viability, apoptosis, cell cycle, migration, and invasion of CRC cells were analyzed via Cell Counting Kit-8 (CCK-8), flow cytometry, wound healing, and transwell assays. We found LMTK3 was distinctly upregulated in CRC tissues and cells, particularly in CTX-resistant CRC tissues and cells. LMTK3 inhibition lowered CTX half-maximal inhibitory concentration (IC₅₀) value, inhibited cell viability, induced cell apoptosis, triggered cell-cycle arrest, and impaired cell metastatic capability in CTX-resistant CRC cells. Moreover, we also demonstrated that LMTK3 induced CTX resistance in CRC via the activation of ERK/MAPK signaling in vitro. These results suggested a novel molecular mechanism by which LMTK3 participates in the development of CTX resistance in CRC.

The multifaceted role of lemur tyrosine kinase 3 in health and disease

In the last decade, LMTK3 (lemur tyrosine kinase 3) has emerged as an important player in breast cancer, contributing to the advancement of disease and the acquisition of resistance to therapy through a strikingly complex set of mechanisms. Although the knowledge of its physiological function is largely limited to receptor trafficking in neurons, there is mounting evidence that LMTK3 promotes oncogenesis in a wide variety of cancers. Recent studies have broadened our understanding of LMTK3 and demonstrated its importance in numerous signalling pathways, culminating in the identification of a potent and selective LMTK3 inhibitor. Here, we review the roles of LMTK3 in health and disease and discuss how this research may be used to develop novel therapeutics to advance cancer treatment.

AKT1 Polymorphism (rs10138227) and Risk of Colorectal Cancer in Moroccan Population: A Case Control Study

BACKGROUND

LMTK3 and AKT1 each have a role in carcinogenesis and tumor progression. The analysis of single nucleotide polymorphisms of AKT1 and LMTK3 could lead to more complete and accurate risk estimates for colorectal cancer.

AIM

We evaluated the association between single nucleotide polymorphisms (SNPs) of AKT1 and LMTK3 and the risk of colorectal cancer in a case-control study in Moroccan population.

METHODS

Genomic DNA from 70 colorectal cancer patients and 50 healthy control subjects was extracted from whole blood. Genotyping was performed by direct sequencing after polymerase chain reactions for the 7 SNPs (AKT1rs1130214G/T, AKT1rs10138227C/T, AKT1rs3730358C/T, AKT1rs1000559097G/A, AKT1rs2494737A/T, LMTK3rs8108419G/A, and LMTK3rs9989661A/G.). Study subjects provided detailed information during the collection. All P values come from bilateral tests.

RESULTS

In the logistic regression analysis, a significantly high risk of colorectal cancer was associated with TC/TT genotypes of rs10138227 with adjusted odds ratio [OR] equal to 2.82 and 95% confidence interval [CI] of 1.15 to 6.91.

CONCLUSION

Our results suggest that the SNP AKT1rs10138227 could affect susceptibility to CRC, probably by modulating the transcriptional activity of AKT1. However, larger independent studies are needed to validate our results.

LMTK3 promotes tumorigenesis in bladder cancer via the ERK/MAPK pathway

Lemur tyrosine kinase 3 (LMTK3) is a key member of the serine–threonine tyrosine kinase family. It plays an important role in breast cancer tumorigenesis and progression. However, its biological role in bladder cancer remains elusive. In this study, we demonstrated that LMTK3 was overexpressed in bladder cancer and was positively correlated with bladder cancer malignancy. High LMTK3 expression predicted poor overall survival. Knockdown of LMTK3 in bladder cancer cells triggered cell‐cycle arrest at G2/M phase, suppressed cell growth, and induced cell apoptosis in bladder cancer cells. Furthermore, Transwell assays revealed that reduction of LMTK3 decreased cell migration by regulating the epithelial‐to‐mesenchymal transition pathway. Conversely, LKTM3 overexpression was shown to promote proliferation and migration of bladder cancer cells. We assessed phosphorylation of MEK and ERK1/2 in bladder cancer cells depleted of LMTK3 and demonstrated a reduced phosphorylation status compared with the control group. Using an MAPK signaling‐specific inhibitor, U0126, we could rescue the promotion of proliferation and viability in LMTK3‐overexpressing cells. In conclusion, we extend the status of LMTK3 as an oncogene in bladder cancer and provide evidence for its function via the activation of the ERK/MAPK pathway. Thus, targeting LMTK3 may hold potential as a diagnostic and prognostic biomarker and as a possible future treatment for bladder cancer.

Discovery of cyclic guanidine-linked sulfonamides as inhibitors of LMTK3 kinase

Lemur tyrosine kinase 3 (LMTK3) is oncogenic in various cancers. In breast cancer, LMTK3 phosphorylates and modulates the activity of estrogen receptor-α (ERα) and is essential for the growth of ER-positive cells. LMTK3 is highly expressed in ER-negative breast cancer cells, where it promotes invasion via integrin β1. LMTK3 abundance and/or high nuclear expression have been linked to shorter disease free and overall survival time in a variety of cancers, supporting LMTK3 as a potential target for anticancer drug development. We sought to identify small molecule inhibitors of LMTK3 with the ultimate goal to pharmacologically validate this kinase as a novel target in cancer. We used a homogeneous time resolve fluorescence (HTRF) assay to screen a collection of mixture-based combinatorial chemical libraries containing over 18 million compounds. We identified several cyclic guanidine-linked sulfonamides with sub-micromolar activity and evaluated their binding mode using a 3D homology model of the LMTK3 K_D.

Targeting Protein Kinases to Enhance the Response to anti-PD-1/PD-L1 Immunotherapy

The interaction between programmed cell death protein (PD-1) and its ligand (PD-L1) is one of the main pathways used by some tumors to escape the immune response. In recent years, immunotherapies based on the use of antibodies against PD-1/PD-L1 have been postulated as a great promise for cancer treatment, increasing total survival compared to standard therapy in different tumors. Despite the hopefulness of these results, a significant percentage of patients do not respond to such therapy or will end up evolving toward a progressive disease. Besides their role in PD-L1 expression, altered protein kinases in tumor cells can limit the effectiveness of PD-1/PD-L1 blocking therapies at different levels. In this review, we describe the role of kinases that appear most frequently altered in tumor cells and that can be an impediment for the success of immunotherapies as well as the potential utility of protein kinase inhibitors to enhance the response to such treatments.

Molecular screening and docking analysis of LMTK3and AKT1 combined inhibitors

The abnormal activation of AKT/mTOR signaling pathway and overexpression of LMTK3, are the main factors involved in the generation of drug resistance. Therefore, the use of computer-aided drug design in the inhibitors discovery offers an advantage to provide new candidates for the treatment of this resistance. We realised the virtual screening and molecular docking of AKT1 and LMTK3 proteins by the Dockblaster server. In addition, with abundance of candidates under development for AKT1 kinase, we have also conducted a Quantitative Structure-Activity Relationship (QSAR) study based on these compounds, in order to design more active compounds and predict their activity for development of a new inhibitor of AKT1. QSAR tests were performed for AKT1 using the Partial Least Squares method with a correlation coefficient of R2=0.8062 and a cross-validation of q2=0.6995. This test has selected five compounds as competitive inhibitors-AKT1-ATP with a better biological activities. In parallel the molecular screening has selected five other compounds as competitive ATP-inhibitors of LMTK3. One of them is a common inhibitor with AKT1, and it is marketed as a moderate to severe pain therapy. The ADME predictions confirmed the inhibitors pharmacological activity of these compounds for potential consideration as drug candidates.

LMTK3 confers chemo-resistance in breast cancer

Lemur tyrosine kinase 3 (LMTK3) is an oncogenic kinase that is involved in different types of cancer (breast, lung, gastric, colorectal) and biological processes including proliferation, invasion, migration, chromatin remodeling as well as innate and acquired endocrine resistance. However, the role of LMTK3 in response to cytotoxic chemotherapy has not been investigated thus far. Using both 2D and 3D tissue culture models, we found that overexpression of LMTK3 decreased the sensitivity of breast cancer cell lines to cytotoxic (doxorubicin) treatment. In a mouse model we showed that ectopic overexpression of LMTK3 decreases the efficacy of doxorubicin in reducing tumor growth. Interestingly, breast cancer cells overexpressing LMTK3 delayed the generation of double strand breaks (DSBs) after exposure to doxorubicin, as measured by the formation of γH2AX foci. This effect was at least partly mediated by decreased activity of ataxia-telangiectasia mutated kinase (ATM) as indicated by its reduced phosphorylation levels. In addition, our RNA-seq analyses showed that doxorubicin differentially regulated the expression of over 700 genes depending on LMTK3 protein expression levels. Furthermore, these genes were found to promote DNA repair, cell viability and tumorigenesis processes / pathways in LMTK3-overexpressing MCF7 cells. In human cancers, immunohistochemistry staining of LMTK3 in pre- and post-chemotherapy breast tumor pairs from four separate clinical cohorts revealed a significant increase of LMTK3 following both doxorubicin and docetaxel based chemotherapy. In aggregate, our findings show for the first time a contribution of LMTK3 in cytotoxic drug resistance in breast cancer.

LMTK3 knockdown retards cell growth and invasion and promotes apoptosis in thyroid cancer

Lemur tyrosine kinase-3 (LMTK3) is a member of the serine/threonine tyrosine kinase family, which is thought to be involved in tumor progression and prognosis. The purpose of the present study was to determine the diagnostic significance and therapeutic targets in thyroid cancer. ELISA assay was used to detect the protein expression of serum LMTK3. Immunohistochemistry and reverse transcription-quantitative polymerase chain reaction were employed to measure the expression of LMTK3. Flow cytometry was used to determine the cell cycle. Transwell assay was used to measure the invasion and migration of SW579 cells and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay to detect cell apoptosis. The LMTK3 level was positively associated with disease stage and pathological type, whereas there was no correlation between LMTK3 level and gender, age, tumor size or lymph node metastasis. The serum LMTK3 level was significantly increased in 102 thyroid carcinoma patients compared with 52 benign thyroid tumor patients and 50 healthy volunteers (P=0.001). The protein and mRNA expression of LMTK3 was markedly higher in thyroid cancer patients compared with patients with benign thyroid tumors. Notably, LMTK3 knockdown retarded proliferation, invasion and migration in SW579 cells. In addition, downregulation of LMTK3 promoted apoptosis in SW579 cells. These findings indicated that LMTK3 knockdown retards the growth of thyroid cancer cells partly through inhibiting proliferation, invasion, migration and inducing apoptosis in SW579 cells. It may serve as a useful diagnostic biomarker and a novel therapeutic target for patients with thyroid cancer.

The kinase LMTK3 promotes invasion in breast cancer through GRB2-mediated induction of integrin β₁

Lemur tyrosine kinase 3 (LMTK3) is associated with cell proliferation and endocrine resistance in breast cancer. We found that, in cultured breast cancer cell lines, LMTK3 promotes the development of a metastatic phenotype by inducing the expression of genes encoding integrin subunits. Invasive behavior in various breast cancer cell lines positively correlated with the abundance of LMTK3. Overexpression of LMTK3 in a breast cancer cell line with low endogenous LMTK3 abundance promoted actin cytoskeleton remodeling, focal adhesion formation, and adhesion to collagen and fibronectin in culture. Using SILAC (stable isotope labeling by amino acids in cell culture) proteomic analysis, we found that LMTK3 increased the abundance of integrin subunits α5 and β1, encoded by ITGA5 and ITGB1. This effect depended on the CDC42 Rho family guanosine triphosphatase, which was in turn activated by the interaction between LMTK3 and growth factor receptor-bound protein 2 (GRB2), an adaptor protein that mediates receptor tyrosine kinase-induced activation of RAS and downstream signaling. Knockdown of GRB2 suppressed LMTK3-induced CDC42 activation, blocked ITGA5 and ITGB1 expression promoted by the transcription factor serum response factor (SRF), and reduced invasive activity. Furthermore, abundance of LMTK3 positively correlated with that of the integrin β1 subunit in breast cancer patient's tumors. Our findings suggest a role for LMTK3 in promoting integrin activity during breast cancer progression and metastasis.

Prognostic role of lemur tyrosine kinase 3 in postoperative gastric cancer

The treatment of gastric cancer has been unsatisfactory thus far; therefore, novel targets and treatment strategies are urgently required. Lemur tyrosine kinase (LMTK)3 is an estrogen receptor-α (ERα) modulator with a central role in endocrine resistance in breast cancer. Moreover, the expression and polymorphisms of LMTK3 are correlated with the prognosis of breast cancer patients. Since estrogen receptor (ER) is also expressed and plays a role in gastric cancer, we herein investigated the expression of the LMTK3 protein in 83 gastric cancer patients by tissue microarray and analyzed the correlation between LMTK3 expression and the prognosis of gastric cancer. Our results demonstrated that LMTK3 was more frequently expressed in gastric cancer tissues compared to non-cancerous mucosa (79.5 vs. 45.8%, respectively; P=0.000). The LMTK3 expression was significantly correlated with the depth of invasion (P=0.002) and disease stage (P=0.035). The Kaplan-Meier analysis revealed that the postoperative survival of the LMTK3-negative group was superior to that of the LMTK3-positive group (P=0.043). Moreover, the multivariate analysis identified LMTK3 expression as an independent prognostic factor for patients with gastric cancer (P=0.019). These findings suggested that the expression of LMTK3 may be a negative prognostic factor in patients with gastric cancer. Moreover, targeting LMTK3 is a potential strategy for the treatment of gastric cancer, although the biological functions of LMTK3 in gastric cancer require further investigation.