Targeting the mesenchymal subtype in glioblastoma and other cancers via inhibition of diacylglycerol kinase alpha

Background

The mesenchymal phenotype in glioblastoma (GBM) and other cancers drives aggressiveness and treatment resistance, leading to therapeutic failure and recurrence of disease. Currently, there is no successful treatment option available against the mesenchymal phenotype.

Methods

We classified patient-derived GBM stem cell lines into 3 subtypes: proneural, mesenchymal, and other/classical. Each subtype's response to the inhibition of diacylglycerol kinase alpha (DGKα) was compared both in vitro and in vivo. RhoA activation, liposome binding, immunoblot, and kinase assays were utilized to elucidate the novel link between DGKα and geranylgeranyltransferase I (GGTase I).

Results

Here we show that inhibition of DGKα with a small-molecule inhibitor, ritanserin, or RNA interference preferentially targets the mesenchymal subtype of GBM. We show that the mesenchymal phenotype creates the sensitivity to DGKα inhibition; shifting GBM cells from the proneural to the mesenchymal subtype increases ritanserin activity, with similar effects in epithelial-mesenchymal transition models of lung and pancreatic carcinoma. This enhanced sensitivity of mesenchymal cancer cells to ritanserin is through inhibition of GGTase I and downstream mediators previously associated with the mesenchymal cancer phenotype, including RhoA and nuclear factor-kappaB. DGKα inhibition is synergistic with both radiation and imatinib, a drug preferentially affecting proneural GBM.

Conclusions

Our findings demonstrate that a DGKα-GGTase I pathway can be targeted to combat the treatment-resistant mesenchymal cancer phenotype. Combining therapies with greater activity against each GBM subtype may represent a viable therapeutic option against GBM.

Spider prey-wrapping silk is an α-helical coiled-coil/β-sheet hybrid nanofiber

Solid-State NMR results on 13C-Ala/Ser and 13C-Val enriched Argiope argentata prey-wrapping silk show that native, freshly spun aciniform silk nanofibers are dominated by α-helical (∼50% total) and random-coil (∼35% total) secondary structures, with minor β-sheet nanocrystalline domains (∼15% total). This is the most in-depth study to date characterizing the protein structural conformation of the toughest natural biopolymer: aciniform prey-wrapping silks.

Combined c-Met/Trk Inhibition Overcomes Resistance to CDK4/6 Inhibitors in Glioblastoma

Glioblastoma (GBM) is the most common primary brain malignancy and carries an extremely poor prognosis. Recent molecular studies revealed the CDK4/6-Rb-E2F axis and receptor tyrosine kinase (RTK) signaling to be deregulated in most GBM, creating an opportunity to develop more effective therapies by targeting both pathways. Using a phospho-RTK protein array, we found that both c-Met and TrkA-B pathways were significantly activated upon CDK4/6 inhibition in GBM cells. We therefore investigated the efficacy of combined CDK4/6 and c-Met/TrkA-B inhibition against GBM. We show that both c-Met and TrkA-B pathways transactivate each other, and targeting both pathways simultaneously results in more efficient pathway suppression. Mechanistically, inhibition of CDK4/6 drove NF-κB-mediated upregulation of hepatocyte growth factor, brain-derived neurotrophic factor, and nerve growth factor that in turn activated both c-Met and TrkA-B pathways. Combining the CDK4/6 inhibitor abemaciclib with the c-Met/Trk inhibitor altiratinib or the corresponding siRNAs induced apoptosis, leading to significant synergy against GBM. Collectively, these findings demonstrate that the activation of c-Met/TrkA-B pathways is a novel mechanism involved in therapeutic resistance of GBM to CDK4/6 inhibition and that dual inhibition of c-Met/Trk with CDK4/6 should be considered in future clinical trials.Significance: CDK4/6 inhibition in glioblastoma activates the c-Met and TrkA-B pathways mediated by NF-κB and can be reversed by a dual c-Met/Trk inhibitor. Cancer Res; 78(15); 4360-9. ©2018 AACR.

Combined CDK4/6 and mTOR Inhibition Is Synergistic against Glioblastoma via Multiple Mechanisms

Purpose: Glioblastoma (GBM) is a deadly brain tumor marked by dysregulated signaling and aberrant cell-cycle control. Molecular analyses have identified that the CDK4/6-Rb-E2F axis is dysregulated in about 80% of GBMs. Single-agent CDK4/6 inhibitors have failed to provide durable responses in GBM, suggesting a need to combine them with other agents. We investigate the efficacy of the combination of CDK4/6 inhibition and mTOR inhibition against GBM.Experimental Design: Preclinical in vitro and in vivo assays using primary GBM cell lines were performed.Results: We show that the CDK4/6 inhibitor palbociclib suppresses the activity of downstream mediators of the mTOR pathway, leading to rebound mTOR activation that can be blocked by the mTOR inhibitor everolimus. We further show that mTOR inhibition with everolimus leads to activation of the Ras mediator Erk that is reversible with palbociclib. The combined treatment strongly disrupts GBM metabolism, resulting in significant apoptosis. Further increasing the utility of the combination for brain cancers, everolimus significantly increases the brain concentration of palbociclib.Conclusions: Our findings demonstrate that the combination of CDK4/6 and mTOR inhibition has therapeutic potential against GBM and suggest it should be evaluated in a clinical trial. Clin Cancer Res; 23(22); 6958-68. ©2017 AACR.

A Cathepsin-L is required for invasive behavior during Air Sac Primordium development in Drosophila melanogaster

The Drosophila Air Sac Primordium (ASP) has emerged as an important structure where cellular, genetic and molecular events responsible for invasive behavior and branching morphogenesis can be studied. In this report we present data which demonstrate that a Cathepsin-L encoded by the gene CP1 in Drosophila is necessary for invasive behavior during ASP development. We find that CP1 is expressed in ASP and knockdown of CP1 results in suppression of migratory and invasive behavior observed during ASP development. We further show that CP1 possibly regulates invasive behavior by promoting degradation of Basement Membrane. Our data provide clues to the possible role of Cathepsin L in human lung development and tumor invasion, especially, given the similarities between human lung and Drosophila ASP development.