Robert Torka

The E3 ligase Cbl-b and TAM receptors regulate cancer metastasis via natural killer cells

Tumour metastasis is the primary cause of mortality in cancer patients and remains the key challenge for cancer therapy. New therapeutic approaches to block inhibitory pathways of the immune system have renewed hopes for the utility of such therapies. Here we show that genetic deletion of the E3 ubiquitin ligase Cbl-b (casitas B-lineage lymphoma-b) or targeted inactivation of its E3 ligase activity licenses natural killer (NK) cells to spontaneously reject metastatic tumours. The TAM tyrosine kinase receptors Tyro3, Axl and Mer (also known as Mertk) were identified as ubiquitylation substrates for Cbl-b. Treatment of wild-type NK cells with a newly developed small molecule TAM kinase inhibitor conferred therapeutic potential, efficiently enhancing anti-metastatic NK cell activity in vivo. Oral or intraperitoneal administration using this TAM inhibitor markedly reduced murine mammary cancer and melanoma metastases dependent on NK cells. We further report that the anticoagulant warfarin exerts anti-metastatic activity in mice via Cbl-b/TAM receptors in NK cells, providing a molecular explanation for a 50-year-old puzzle in cancer biology. This novel TAM/Cbl-b inhibitory pathway shows that it might be possible to develop a ‘pill’ that awakens the innate immune system to kill cancer metastases.

Integrin-linked kinase is required for epidermal and hair follicle morphogenesis

Integrin-linked kinase (ILK) links integrins to the actin cytoskeleton and is believed to phosphorylate several target proteins. We report that a keratinocyte-restricted deletion of the ILK gene leads to epidermal defects and hair loss. ILK-deficient epidermal keratinocytes exhibited a pronounced integrin-mediated adhesion defect leading to epidermal detachment and blister formation, disruption of the epidermal–dermal basement membrane, and the translocation of proliferating, integrin-expressing keratinocytes to suprabasal epidermal cell layers. The mutant hair follicles were capable of producing hair shaft and inner root sheath cells and contained stem cells and generated proliferating progenitor cells, which were impaired in their downward migration and hence accumulated in the outer root sheath and failed to replenish the hair matrix. In vitro studies with primary ILK-deficient keratinocytes attributed the migration defect to a reduced migration velocity and an impaired stabilization of the leading-edge lamellipodia, which compromised directional and persistent migration. We conclude that ILK plays important roles for epidermis and hair follicle morphogenesis by modulating integrin-mediated adhesion, actin reorganization, and plasma membrane dynamics in keratinocytes.

Determination of features indicating progression in atypical squamous cells with undetermined significance: human papillomavirus typing and DNA ploidy analysis from liquid-based cytologic samples.

The Bethesda System of cervical cytologic findings introduced the term ASCUS (atypical squamous cells of undetermined significance) to cover the broad zone separating normal cytomorphology from definitive squamous intraepithelial lesions (SILs). The management of patients with ASCUS is particularly problematic as approximately 10% of ASCUS patients develop SIL and 1 per 1000 develop cervical carcinoma.

Human papillomavirus typing and DNA ploidy determination of squamous intraepithelial lesions in liquid‐based cytologic samples

Infection by high‐risk human papillomavirus (HPV) plays a role in the evolution of cervical carcinoma. Cellular atypia and consecutive DNA content alterations in cytologic samples are consequences of a preexisting viral infection.

Activation of HER3 Interferes with Antitumor Effects of Axl Receptor Tyrosine Kinase Inhibitors: Suggestion of Combination Therapy

The Axl receptor tyrosine kinase (RTK) has been established as a strong candidate for targeted therapy of cancer. However, the benefits of targeted therapies are limited due to acquired resistance and activation of alternative RTKs. Therefore, we asked if cancer cells are able to overcome targeted Axl therapies. Here, we demonstrate that inhibition of Axl by short interfering RNA or the tyrosine kinase inhibitor (TKI) BMS777607 induces the expression of human epidermal growth factor receptor 3 (HER3) and the neuregulin 1(NRG1)-dependent phosphorylation of HER3 in MDA-MB231 and Ovcar8 cells. Moreover, analysis of 20 Axl-expressing cancer cell lines of different tissue origin indicates a low basal phosphorylation of RAC-α serine/threonine-protein kinase (AKT) as a general requirement for HER3 activation on Axl inhibition. Consequently, phosphorylation of AKT arises as an independent biomarker for Axl treatment. Additionally, we introduce phosphorylation of HER3 as an independent pharmacodynamic biomarker for monitoring of anti-Axl therapy response. Inhibition of cell viability by BMS777607 could be rescued by NRG1-dependent activation of HER3, suggesting an escape mechanism by tumor microenvironment. The Axl-TKI MPCD84111 simultaneously blocked Axl and HER2/3 signaling and thereby prohibited HER3 feedback activation. Furthermore, dual inhibition of Axl and HER2/3 using BMS777607 and lapatinib led to a significant inhibition of cell viability in Axl-expressing MDA-MB231 and Ovcar8 cells. Therefore, we conclude that, in patient cohorts with expression of Axl and low basal activity of AKT, a combined inhibition of Axl and HER2/3 kinase would be beneficial to overcome acquired resistance to Axl-targeted therapies.

Combined inhibition of AXL, Lyn and p130Cas kinases block migration of triple negative breast cancer cells

Blocking the migration of metastatic cancer cells is a major goal in the therapy of cancer. The receptor tyrosine kinase AXL is one of the main triggers for cancer cell migration in neoplasia of breast, colon, skin, thyroid and prostate. In our study we analyzed the effect of AXL inhibition on cell motility and viability in triple negative breast cancer cell lines overexpressing AXL. Thereby we reveal that the compound BMS777607, exhibiting the lowest IC50 values for inhibition of AXL kinase activity in the studied cell lines, attenuates cell motility to a lower extent than the kinase inhibitors MPCD84111 and SKI606. By analyzing the target kinases of MPCD84111 and SKI606 with kinase profiling assays we identified Lyn, a Src family kinase, as a target of both compounds. Knockdown of Lyn and the migration-related CRK-associated substrate (p130Cas), had a significant inhibitory effect on cell migration. Taken together, our findings highlight the importance of combinatorial or multikinase inhibition of non-receptor tyrosine kinases and AXL receptor tyrosine kinase in the therapy of triple negative breast cancer.

Discovery and Biological Evaluation of Novel Dual EGFR/c-Met Inhibitors.

Activating mutations in the epidermal growth factor receptor (EGFR) have been identified in a subset of non-small cell lung cancer (NSCLC), which is one of the leading cancer types worldwide. Application of EGFR tyrosine kinase inhibitors leads to acquired resistance by secondary EGFR mutations or by amplification of the hepatocyte growth factor receptor (c-Met) gene. Although several EGFR and c-Met inhibitors have been reported, potent dual EGFR/c-Met inhibitors, which can overcome this latter resistance mechanism, have hitherto not been published and have not reached clinical trials. In the present study we have identified dual EGFR/c-Met inhibitors and designed novel N-[4-(quinolin-4-yloxy)-phenyl]-biarylsulfonamide derivatives, which inhibit the c-Met receptor and both the wild-type and the activating mutant EGFR kinases in nanomolar range. We have demonstrated by Western blot analysis that compound 10 inhibits EGFR and c-Met phosphorylation at cellular level and effectively inhibits viability of the NSCLC cell lines.

Pharmacophore and binding analysis of known and novel B-RAF kinase inhibitors.

The extensively investigated serine/threonine kinase, B-RAF, is a member of the RAS/RAF/MEK/ERK pathway. It plays important role in the regulation of cell growth, differentiation and survival. The mutation of B-RAF occurs frequently in melanomas and colon tumors; therefore, it is considered as an outstanding therapeutic target. In recent years a great number of B-RAF inhibitors have been reported and this number is expected to increase. The aim of our work was to compare the structures and binding mode of the published B-RAF inhibitors, and then to apply the correlations found for the explanation of our experimental results. In the first part of this paper we describe the main pharmacophore features of the co-crysallized B-RAF inhibitors published in the literature, focusing on the binding modes and common structural elements. In the second part we present and characterize our recently developed B-RAF inhibitor family by application of in silico methods and in vitro kinetic profiling. The inhibitory activity of these compounds was determined in biochemical kinase- and cell-based assays. The docking and assay results support our conclusion that the presented compound family belongs to the type I 1/2 subgroup, they inhibit B-RAF and B-RAF(V600E) mutant in a sub-micromolar range and most of them show selectivity towards B-RAF(V600E) mutant expressing cell lines with equal or even better IC50 values than sorafenib.

GAS6‐expressing and self‐sustaining cancer cells in 3D spheroids activate the PDK‐RSK‐mTOR pathway for survival and drug resistance

AXL receptor tyrosine kinase (RTK) inhibition presents a promising therapeutic strategy for aggressive tumor subtypes, as AXL signaling is upregulated in many cancers resistant to first‐line treatments. Furthermore, the AXL ligand growth arrest‐specific gene 6 (GAS6) has recently been linked to cancer drug resistance. Here, we established that challenging conditions, such as serum deprivation, divide AXL‐overexpressing tumor cell lines into non‐self‐sustaining and self‐sustaining subtypes in 3D spheroid culture. Self‐sustaining cells are characterized by excessive GAS6 secretion and TAM‐PDK‐RSK‐mTOR pathway activation. In 3D spheroid culture, the activation of the TAM‐PDK‐RSK‐mTOR pathway proves crucial following treatment with AXL/MET inhibitor BMS777607, when the self‐sustaining tumor cells react with TAM‐RSK hyperactivation and enhanced SRC‐AKT‐mTOR signaling. Thus, bidirectional activated mTOR leads to enhanced proliferation and counteracts the drug effect. mTOR activation is accompanied by an enhanced AXL expression and hyperphosphorylation following 24 h of treatment with BMS777607. Therefore, we elucidate a double role of AXL that can be assigned to RSK‐mTOR as well as SRC‐AKT‐mTOR pathway activation, specifically through AXL Y779 phosphorylation. This phosphosite fuels the resistance mechanism in 3D spheroids, alongside further SRC‐dependent EGFR Y1173 and/or MET Y1349 phosphorylation which is defined by the cell‐specific addiction. In conclusion, self‐sustenance in cancer cells is based on a signaling synergy, individually balanced between GAS6 TAM‐dependent PDK‐RSK‐mTOR survival pathway and the AXLY779/EGFR/MET‐driven SRC‐mTOR pathway.

Phospho-AXL is widely expressed in glioblastoma and associated with significant shorter overall survival

Receptor tyrosine kinase AXL (RTK-AXL) is regarded as a suitable target in glioblastoma (GBM) therapy. Since AXL kinase inhibitors are about to get approval for clinical use, patients with a potential benefit from therapy targeting AXL need to be identified. We therefore assessed the expression pattern of Phospho-AXL (P-AXL), the biologically active form of AXL, in 90 patients with newly diagnosed GBM, which was found to be detectable in 67 patients (corresponding to 74%). We identified three main P-AXL expression patterns: i) exclusively in the tumor vasculature (13%), ii) in areas of hypercellularity (35%), or iii) both, in the tumor vasculature and in hypercellular areas of the tumor tissue (52%). Pattern iii) is associated with significant decrease in overall survival (Hazard ratio 2.349, 95% confidence interval 1.069 to 5.162, *p=0.03). Our data suggest that P-AXL may serve as a therapeutic target in the majority of GBM patients.Receptor tyrosine kinase AXL (RTK-AXL) is regarded as a suitable target in glioblastoma (GBM) therapy. Since AXL kinase inhibitors are about to get approval for clinical use, patients with a potential benefit from therapy targeting AXL need to be identified. We therefore assessed the expression pattern of Phospho-AXL (P-AXL), the biologically active form of AXL, in 90 patients with newly diagnosed GBM, which was found to be detectable in 67 patients (corresponding to 74%). We identified three main P-AXL expression patterns: i) exclusively in the tumor vasculature (13%), ii) in areas of hypercellularity (35%), or iii) both, in the tumor vasculature and in hypercellular areas of the tumor tissue (52%). Pattern iii) is associated with significant decrease in overall survival (Hazard ratio 2.349, 95% confidence interval 1.069 to 5.162, *p=0.03). Our data suggest that P-AXL may serve as a therapeutic target in the majority of GBM patients.