FAK inhibitors as promising anticancer targets: present and future directions

FAK, a nonreceptor tyrosine kinase, has been recognized as a novel target class for the development of targeted anticancer agents. Overexpression of FAK is a common occurrence in several solid tumors, in which the kinase has been implicated in promoting metastases. Consequently, designing and developing potent FAK inhibitors is becoming an attractive goal, and FAK inhibitors are being recognized as a promising tool in our armamentarium for treating diverse cancers. This review comprehensively summarizes the different classes of synthetically derived compounds that have been reported as potent FAK inhibitors in the last three decades. Finally, the future of FAK-targeting smart drugs that are designed to slow down the emergence of drug resistance is discussed.

The nonreceptor tyrosine kinase SRMS inhibits autophagy and promotes tumor growth by phosphorylating the scaffolding protein FKBP51

Nutrient-responsive protein kinases control the balance between anabolic growth and catabolic processes such as autophagy. Aberrant regulation of these kinases is a major cause of human disease. We report here that the vertebrate nonreceptor tyrosine kinase Src-related kinase lacking C-terminal regulatory tyrosine and N-terminal myristylation sites (SRMS) inhibits autophagy and promotes growth in a nutrient-responsive manner. Under nutrient-replete conditions, SRMS phosphorylates the PHLPP scaffold FK506-binding protein 51 (FKBP51), disrupts the FKBP51-PHLPP complex, and promotes FKBP51 degradation through the ubiquitin-proteasome pathway. This prevents PHLPP-mediated dephosphorylation of AKT, causing sustained AKT activation that promotes growth and inhibits autophagy. SRMS is amplified and overexpressed in human cancers where it drives unrestrained AKT signaling in a kinase-dependent manner. SRMS kinase inhibition activates autophagy, inhibits cancer growth, and can be accomplished using the FDA-approved tyrosine kinase inhibitor ibrutinib. This illuminates SRMS as a targetable vulnerability in human cancers and as a new target for pharmacological induction of autophagy in vertebrates.

Inhibiting FAK–Paxillin Interaction Reduces Migration and Invadopodia-Mediated Matrix Degradation in Metastatic Melanoma Cells

The nonreceptor tyrosine kinase FAK is a promising target for solid tumor treatment because it promotes invasion, tumor progression, and drug resistance when overexpressed. Investigating the role of FAK in human melanoma cells, we found that both in situ and metastatic melanoma cells strongly express FAK, where it controls tumor cells’ invasiveness by regulating focal adhesion-mediated cell motility. Inhibiting FAK in human metastatic melanoma cells with either siRNA or a small inhibitor targeting the kinase domain impaired migration but led to increased invadopodia formation and extracellular matrix degradation. Using FAK mutated at Y397, we found that this unexpected increase in invadopodia activity is due to the lack of phosphorylation at this residue. To preserve FAK–Src interaction while inhibiting pro-migratory functions of FAK, we found that altering FAK–paxillin interaction, with either FAK mutation in the focal adhesion targeting (FAT) domain or a competitive inhibitor peptide mimicking paxillin LD domains drastically reduces cell migration and matrix degradation by preserving FAK activity in the cytoplasm. In conclusion, our data show that targeting FAK–paxillin interactions could be a potential therapeutic strategy to prevent metastasis formation, and molecules targeting this interface could be alternative to inhibitors of FAK kinase activity which display unexpected effects.

Lymphocyte-specific Protein Tyrosine Kinase Regulates Homologous Recombination (HR) DNA Repair and Targeting Enhances PARPi Utility in HR Proficient Ovarian Cancer

Poly-ADP Ribose Polymerase (PARP) inhibitors are clinically approved for the treatment of homologous recombination (HR) repair deficient tumors. PARP targeted therapy has limited efficacy in HR-proficient cancer. In this study, we identified the non-receptor lymphocyte-specific protein tyrosine kinase (LCK) as a novel regulator of HR repair pathways in endometrioid epithelial ovarian cancer (eEOC). Inhibition of LCK attenuates the expression of RAD51, BRCA1, and BRCA2 proteins necessary for HR-mediated DNA repair. HR repair in eEOC cells is LCK dependent. Upon DNA damage LCK expression is increased, and autophosphorylated, activated LCK is localized in the nucleus. LCK inhibition impairs RAD51 foci formation but augments γH2AX formation during DDR indicating reduced ability to repair DNA damage. DNA damage leads to direct interaction of LCK with RAD51 and BRCA1. Finally, attenuation of LCK sensitized HR-proficient eEOC cells to PARP inhibitor. Collectively, the findings identify a mechanism for expanding utility of PARP inhibitors.Graphical AbstractIn BriefDey and colleagues identify the nonreceptor tyrosine kinase LCK as a mediator of homologous recombination directed DNA repair in ovarian cancer. The studies show that LCK inhibition (LCKi) is sufficient to augment Poly (ADP-Ribose) Polymerase inhibitor efficacy in Homologous Recombination (HR) proficient endometrioid ovarian cancer.HighlightsNonreceptor tyrosine kinase LCK regulates expression of HR repair proteins RAD51, BRCA1 and BRCA2.LCKi induces HR deficiency in endometrioid epithelial ovarian cancer.DNA damage leads to autophosphorylation of LCK and co-immunoprecipitation with RAD51 and BRCA1.LCKi potentiates PARP targeted therapy in HR proficient ovarian cancer and expands the utility of the highly successful PARP inhibitors in the clinic.Statement of significanceThis study identifies a novel regulator and signaling pathway for maintaining HR repair during DNA damage. It further demonstrates a new opportunity to increase the utility of PARP inhibitors in HR-proficient eEOC cells.

CTIM-20. PHASE I STUDY OF IBRUTINIB WITH RADIATION AND TEMOZOLOMIDE IN PATIENTS WITH NEWLY DIAGNOSED GLIOBLASTOMA

BACKGROUND Glioblastoma is a devastating disease that is notoriously resistant to current therapies, leading to dismal patient outcomes and a median survival of just 14.6 months. A major problem in glioblastoma treatment is the inability to effectively target the cell population that gives rise to recurrence. These cells, known as glioma stem cells (GSCs) or tumor propagating cells are endowed with a large capacity for self-renewal to propagate the tumor. GSCs are resistant to radiation. Ibrutinib is a first-in-class, potent, orally administered, covalently binding Inhibitor of Bruton’s Tyrosine Kinase (BTK). Ibrutinib is a small-molecule tyrosine kinase. It also inhibits BMX. Bone marrow X-linked (BMX) nonreceptor tyrosine kinase activates STAT3 signaling to maintain self-renewal and tumorigenic potential of GSCs. Hence a combination of ibrutinib with radiation and or temozolomide in patients with newly diagnosed Glioblastoma is warranted. METHODS This is a two arm study. Arm 1 is for patients with unmethylated MGMT Glioblastoma. Every patient gets ibrutinib and 60 Gy radiation over 6 weeks. Patients will undergo a 4-week break and Ibrutinib treatment will then continue until disease progression, intolerable toxicity or death. Arm 2 is for patients with MGMT methylated glioblastoma. Every patient will receive Ibrutinib and 60 Gy radiation and daily Temozolomide at 75 mg/m2 for 6 weeks. Patients will undergo a 4-week break then receive daily ibrutinib and adjuvant Temozolomide. The temozolomide will continue until disease progression, intolerable toxicity or death or maximum of 6 cycles. Ibrutinib treatment will continue until disease progression, intolerable toxicity or death. RESULTS The maximum tolerated dose (MTD) of Ibrutinib with radiation (2 Gy x 30) in patients in each arm will be reported. The safety of Ibrutinib with radiation and with radiation and temozolomide will be reported. The Progression free survival and overall survival in each arm will be reported. CONCLUSION This is an ongoing clinical trial. Results will be reported once study is complete.

Abl2:cortactin interactions regulate dendritic spine stability via control of a stable filamentous actin pool

Dendritic spines are enriched with stable and dynamic actin filaments, which determine their structure and shape. Disruption of the Abl2/Arg nonreceptor tyrosine kinase in mice compromises spine stability and size. We provide evidence that binding to cortactin tethers Abl2 in spines, where Abl2 and cortactin maintain the small pool of stable actin required for dendritic spine stability. Using fluorescence recovery after photobleaching of GFP-actin, we find that disruption of Abl2:cortactin interactions eliminates stable actin filaments in dendritic spines, significantly reducing spine density. A subset of spines remaining after Abl2 depletion retain their stable actin pool and undergo activity-dependent spine enlargement associated with increased cortactin levels. Finally, tonic increases in synaptic activity rescue spine loss upon Abl2 depletion by promoting cortactin enrichment in vulnerable spines. Together, our findings strongly suggest Abl2:cortactin interactions promote spine stability by maintaining pools of stable actin filaments in spines.