Change or die: targeting adaptive signaling to kinase inhibition in cancer cells

Fibroblast growth factor receptor signalling dysregulation and targeting in breast cancer

Fibroblast Growth Factor Receptor (FGFR) signalling plays a critical role in breast embryonal development, tissue homeostasis, tumorigenesis and metastasis. FGFR, its numerous FGF ligands and signalling partners are often dysregulated in breast cancer progression and are one of the causes of resistance to treatment in breast cancer. Furthermore, FGFR signalling on epithelial cells is affected by signals from the breast microenvironment, therefore increasing the possibility of breast developmental abnormalities or cancer progression. Increasing our understanding of the multi-layered roles of the complex family of FGFRs, their ligands FGFs and their regulatory partners may offer novel treatment strategies for breast cancer patients, as a single agent or rational co-target, which will be explored in depth in this review.

Bruton's tyrosine kinase inhibition induces rewiring of proximal and distal B-cell receptor signaling in mice

Bruton′s tyrosine kinase (Btk) is a crucial signaling molecule in BCR signaling and a key regulator of B‐ cell differentiation and function. Btk inhibition has shown impressive clinical efficacy in various B‐cell malignancies. However, it remains unknown whether inhibition additionally induces changes in BCR signaling due to feedback mechanisms, a phenomenon referred to as BCR rewiring. In this report, we studied the impact of Btk activity on major components of the BCR signaling pathway in mice. As expected, NF‐κB and Akt/S6 signaling was decreased in Btk‐deficient B cells. Unexpectedly, phosphorylation of several proximal signaling molecules, including CD79a, Syk, and PI3K, as well as the key Btk‐effector PLCγ2 and the more downstream kinase Erk, were significantly increased. This pattern of BCR rewiring was essentially opposite in B cells from transgenic mice overexpressing Btk. Importantly, prolonged Btk inhibitor treatment of WT mice or mice engrafted with leukemic B cells also resulted in increased phosho‐CD79a and phospho‐PLCγ2 in B cells. Our findings show that Btk enzymatic function determines phosphorylation of proximal and distal BCR signaling molecules in B cells. We conclude that Btk inhibitor treatment results in rewiring of BCR signaling, which may affect both malignant and healthy B cells.

Study of Molecular Mechanism of the Interaction Between MEK1/2 and Trametinib with Docking and Molecular Dynamic Simulation

Trametinib was endorsed by the FDA in 2013 as a single agent for adult melanoma patients. Trametinib inhibits cell growth and proliferation in multiple tumor xenografts by preventing RAF phosphorylation of MEK and thus restricting accumulation of activated MEK. In this study, the focus of investigation was the mechanism of the interaction between trametinib and MEK1/2 via computational simulation. To specify the best interaction site of inhibitor with MEK1/2 based on the interaction energy ranking, first we performed a docking and then we studied the interactions of the ATP-bound MEK with trametinib, with RAF and the complex of the ATP-bound MEK-trametinib with RAF via molecular dynamic simulations. The results showed that trametinib inactivates the enzyme by bonding to a group of amino acids including Lys97/101, SER218/216, Asp208/212, and Met143/147 in MEK1/2. By bonding to the essential amino acids, trametinib inhibits the activity of the enzyme. All in all, the acquired results can be of great use in designing new inhibitors.

miR-579-3p controls melanoma progression and resistance to target therapy

Therapy of melanoma patients harboring activating mutations in the BRAF (V-raf murine sarcoma viral oncogene homolog B1) oncogene with a combination of BRAF and MEK inhibitors is plagued by the development of drug resistance. Mutational events, as well as adaptive mechanisms, contribute to the development of drug resistance. In this context we uncover here the role of a miRNA, miR-579-3p. We first show that low expression of miR-579-3p is a negative prognostic factor correlating with poor survival. Expression levels of miR-579-3p decrease from nevi to stage III/IV melanoma samples and even further in cell lines resistant to BRAF/MEK inhibitors. Mechanistically, we demonstrate that miR-579-3p acts as an oncosuppressor by targeting the 3'UTR of two oncoproteins: BRAF and an E3 ubiquitin protein ligase, MDM2. Moreover miR-579-3p ectopic expression impairs the establishment of drug resistance in human melanoma cells. Finally, miR-579-3p is strongly down-regulated in matched tumor samples from patients before and after the development of resistance to targeted therapies.

A synthetic-lethality RNAi screen reveals an ERK-mTOR co-targeting pro-apoptotic switch in PIK3CA+ oral cancers

mTOR inhibition has emerged as a promising strategy for head and neck squamous cell carcinomas (HNSCC) treatment. However, most targeted therapies ultimately develop resistance due to the activation of adaptive survival signaling mechanisms limiting the activity of targeted agents. Thus, co-targeting key adaptive mechanisms may enable more effective cancer cell killing. Here, we performed a synthetic lethality screen using shRNA libraries to identify druggable candidates for combinatorial signal inhibition. We found that the ERK pathway was the most highly represented. Combination of rapamycin with trametinib, a MEK1/2 inhibitor, demonstrated strong synergism in HNSCC-derived cells in vitro and in vivo, including HNSCC cells expressing the HRAS and PIK3CA oncogenes. Interestingly, cleaved caspase-3 was potently induced by the combination therapy in PIK3CA+ cells in vitro and tumor xenografts. Moreover, ectopic expression of PIK3CA mutations into PIK3CA- HNSCC cells sensitized them to the pro-apoptotic activity of the combination therapy. These findings indicate that co-targeting the mTOR/ERK pathways may provide a suitable precision strategy for HNSCC treatment. Moreover, PIK3CA+ HNSCC are particularly prone to undergo apoptosis after mTOR and ERK inhibition, thereby providing a potential biomarker of predictive value for the selection of patients that may benefit from this combination therapy.

Combinatorial drug screening and molecular profiling reveal diverse mechanisms of intrinsic and adaptive resistance to BRAF inhibition in V600E BRAF mutant melanomas

Over half of BRAFV600E melanomas display intrinsic resistance to BRAF inhibitors, in part due to adaptive signaling responses. In this communication we ask whether BRAFV600E melanomas share common adaptive responses to BRAF inhibition that can provide clinically relevant targets for drug combinations. We screened a panel of 12 treatment-naïve BRAFV600E melanoma cell lines with MAP Kinase pathway inhibitors in pairwise combination with 58 signaling inhibitors, assaying for synergistic cytotoxicity. We found enormous diversity in the drug combinations that showed synergy, with no two cell lines having an identical profile. Although the 6 lines most resistant to BRAF inhibition showed synergistic benefit from combination with lapatinib, the signaling mechanisms by which this combination generated synergistic cytotoxicity differed between the cell lines. We conclude that adaptive responses to inhibition of the primary oncogenic driver (BRAFV600E) are determined not only by the primary oncogenic driver but also by diverse secondary genetic and epigenetic changes ("back-seat drivers") and hence optimal drug combinations will be variable. Because upregulation of receptor tyrosine kinases is a major source of drug resistance arising from diverse adaptive responses, we propose that inhibitors of these receptors may have substantial clinical utility in combination with inhibitors of the MAP Kinase pathway.

Therapeutic control and resistance of the EGFR-driven signaling network in glioblastoma

The alteration of the epidermal growth factor receptor (EGFR)-driven signaling network is a characteristic feature of glioblastomas (GBM), and its inhibition represents a treatment strategy. However, EGFR-targeted interventions have been largely ineffective. Complex perturbations in this system are likely to be central to tumor cells with high adaptive capacity and resistance to therapies. We review key concepts and mechanisms relevant to EGFR-targeted treatment resistance at a systems level. Our understanding of treatment resistance as a systems-level phenomenon is necessary to develop effective therapeutic options for GBM patients. This is allowing us to go beyond the notion of therapeutic targets as single molecular components, into strategies that can weaken cancer signaling robustness and boost inherent network-level vulnerabilities.