Evans, Debra L.

Abstract Elucidating mechanisms of chemoresistance is critical to improve cancer therapy, especially for the treatment of pancreatic ductal adenocarcinoma (PDAC). Genome-wide association studies have suggested the less studied gene HEAT repeat-containing protein 1 (HEATR1) as a possible determinant of cellular sensitivity to different chemotherapeutic drugs. In this study, we assessed this hypothesized link in PDAC, where HEATR1 expression is downregulated significantly. HEATR1 silencing in PDAC cells increased resistance to gemcitabine and other chemotherapeutics, where this effect was associated with increased AKT kinase phosphorylation at the Thr308 regulatory site. Mechanistically, HEATR1 enhanced cell responsiveness to gemcitabine by acting as a scaffold to facilitate interactions between AKT and the protein phosphatase PP2A, thereby promoting Thr308 dephosphorylation. Consistent with these findings, treatment with the AKT inhibitor triciribine sensitized HEATR1-depleted PDAC cells to gemcitabine, suggesting that this therapeutic combination may overcome gemcitabine resistance in patients with low HEATR1 expression. Clinically, we found that HEATR1 downregulation in PDAC patients was associated with increased AKT phosphorylation, poor response to tumor resection plus gemcitabine standard-of-care treatment, and shorter overall survival. Collectively, our findings establish HEATR1 as a novel regulator of AKT and a candidate predictive and prognostic indicator of drug responsiveness and outcome in PDAC patients. Cancer Res; 76(3); 572–81. ©2015 AACR.

Abstract Purpose: Wee1 regulates key DNA damage checkpoints, and in this study, the efficacy of the Wee1 inhibitor MK-1775 was evaluated in glioblastoma multiforme (GBM) xenograft models alone and in combination with radiation and/or temozolomide. Experimental Design: In vitro MK-1775 efficacy alone and in combination with temozolomide, and the impact on DNA damage, was analyzed by Western blotting and γH2AX foci formation. In vivo efficacy was evaluated in orthotopic and heterotopic xenografts. Drug distribution was assessed by conventional mass spectrometry (MS) and matrix-assisted laser desorption/ionization (MALDI)-MS imaging. Results: GBM22 (IC50 = 68 nmol/L) was significantly more sensitive to MK-1775 compared with five other GBM xenograft lines, including GBM6 (IC50 >300 nmol/L), and this was associated with a significant difference in pan-nuclear γH2AX staining between treated GBM22 (81% cells positive) and GBM6 (20% cells positive) cells. However, there was no sensitizing effect of MK-1775 when combined with temozolomide in vitro. In an orthotopic GBM22 model, MK-1775 was ineffective when combined with temozolomide, whereas in a flank model of GBM22, MK-1775 exhibited both single-agent and combinatorial activity with temozolomide. Consistent with limited drug delivery into orthotopic tumors, the normal brain to whole blood ratio following a single MK-1775 dose was 5%, and MALDI-MS imaging demonstrated heterogeneous and markedly lower MK-1775 distribution in orthotopic as compared with heterotopic GBM22 tumors. Conclusions: Limited distribution to brain tumors may limit the efficacy of MK-1775 in GBM. Clin Cancer Res; 21(8); 1916–24. ©2015 AACR.