Potential of mTOR inhibitors as therapeutic agents in hematological malignancies

DCZ0814 induces apoptosis and G0/G1 phase cell cycle arrest in myeloma by dual inhibition of mTORC1/2

Purpose: The present study investigates the effect of DCZ0814 in multiple myeloma (MM) cells, and determines the molecular mechanism of its antitumor activity against MM.

Methods: The effects of DCZ0814 were evaluated in vitro using human MM cell lines (ARP1 and OCI-MY5) and in vivo in a murine xenograft MM model. Cell viability was measured with the CCK-8 assay and mitochondrial membrane potential (MMP) was assessed with the JC-1 dye. Apoptosis and cell cycle distribution were examined by flow cytometry. Inhibition of mTORC1 and mTORC2 was assessed by western blot analysis, and the synergistic effect of DCZ0814 and known MM drugs was assessed by calculating the combination index value, using the CalcuSyn software.

Results: DCZ0814 effectively inhibited proliferation in MM cells, an effect that was associated with the induction of apoptosis, G0/G1 cell cycle arrest, MMP reduction and reactive oxygen species (ROS) generation. Meanwhile, DCZ0814 repressed the mTOR signaling via dual mTORC1/C2 inhibition and overcame the protective effect of the bone marrow (BM) microenvironment in myeloma cells. In addition, co-treatment with DCZ0814 and other anti-MM agents induced synergistic effects. Finally, the efficacy of the DCZ0814 treatment was confirmed in an MM xenograft mouse model.

Conclusion: DCZ0814 exhibits potent anti-MM activity and abrogates the activation of the mTOR/Akt signaling pathway mediated by the BM stroma-derived cytokines. Our results provide a theoretical basis for the development of novel therapeutic strategies in MM using DCZ0814 as a natural product combination compound.

Targeting Focal Adhesion Kinase and Resistance to mTOR Inhibition in Pancreatic Neuroendocrine Tumors

BACKGROUND

Focal adhesion kinase (FAK) mediates survival of normal pancreatic islets through activation of AKT. Upon malignant transformation of islet cells into pancreatic neuroendocrine tumors (PanNETs), AKT is frequently overexpressed and mutations in the AKT/mTOR pathway are detected. Because mTOR inhibitors rarely induce PanNET tumor regression, partly because of feedback activation of AKT, novel combination strategies are needed to target FAK/AKT/mTOR signaling.

METHODS

We characterized the activation of FAK in PanNETs using immunohistochemistry and Western blot analysis and tested the FAK inhibitor PF-04554878 in human PanNET cells in vitro and in vivo (at least three mice per group). In addition, we evaluated the effect of combined FAK and mTOR inhibition on PanNET viability and apoptosis. All statistical tests were two-sided.

RESULTS

We found that FAK is overexpressed and hyperphosphorylated in human PanNETs and that PF-04554878 strongly inhibited FAK (Tyr397) autophosphorylation in a dose-dependent manner. We found that PF-04554878 inhibited cell proliferation and clonogenicity and induced apoptosis in PanNET cells. Moreover, oral administration of PF-04554878 statistically significantly reduced tumor growth in a patient-derived xenograft model of PanNET (P = .02) and in a human PanNET xenograft model of peritoneal carcinomatosis (P = .03). Importantly, PF-04554878 synergized with the mTOR inhibitor everolimus by preventing feedback AKT activation.

CONCLUSIONS

We demonstrate for the first time that FAK is overexpressed in PanNETs and that inhibition of FAK activity induces apoptosis and inhibits PanNET proliferation. We found that the novel FAK inhibitor PF-04554878 synergizes with everolimus, a US Food and Drug Administration-approved agent for PanNETs. Our findings warrant the clinical investigation of combined FAK and mTOR inhibition in PanNETs.