Introduction: Gamma-secretase inhibitors (GSIs) inhibit Notch signaling and have potential as cancer therapeutics. A clinical trial of the oral GSI MK-0752 was conducted in healthy subjects using transcriptional profiling of human plucked hair follicles (PHFs). Data from this study were analyzed using pre-specified gene signatures reflecting Notch, proliferation, and PI3K pathway activity. De novo signature analysis was performed to identify late patterns of transcriptional response. Procedures: A randomized, placebo-controlled (PBO) trial evaluated the effects of a single 350mg or 1000mg dose of MK-0752 on PHF gene expression in healthy males. Plasma and pooled PHFs were collected for PK and PD (mRNA profiling) analyses. Results: In addition to a significant decrease in a Notch signature score (NSS, primary endpoint) which was maximal at 8.5h and significant up to 96h following a single 1000mg dose of MK-0752 compared to PBO, in a post hoc analysis we saw a significant decrease in a 101-gene Growth Factor Signature (GFS) score associated with downregulation of PI3K pathway signaling (effect size = −1.02, p < 0.001 1-sided) at 8.5h post-dose. In another post hoc analysis, we observed a significant suppression of a Proliferation Signature (PS) consisting of 50 cell cycle-associated genes (effect size = −0.57, p=0.016 1-sided) at 28.5h post-dose following a single 1000mg dose of MK-0752 compared to PBO. Dose- and time-dependent decreases were observed in both the GFS and the PS. To understand the compensatory transcriptional response at later time points, normalized data for each subject was compared to the corresponding time-point in the PBO-treated arm. In a training set, the paired t-test was used to identify 768 probes, representing genes that are strongly regulated (p < 0.005) 48-hours after treatment with MK-0752. Composite biomarker characteristics (a one-arm score, two-arm score, and AUC for the signature score in treated versus PBO groups) were calculated in validation set. Analysis of the most regulated genes at 48-hours post-dose showed significant changes in Wnt signaling and epithelial/mesenchymal transition (EMT) genes. Conclusions: Human PHFs contain cells with intact Notch signaling responsive to MK-0752. Transient inhibition of Notch leads to dose-dependent decreases in Notch and PI3K pathway genes, followed by decreases in cell cycle genes. As MK-0752 is eliminated and intrinsic Notch signaling re-established, we saw dose- and time-dependent upregulation of EMT and Wnt signaling, along with genes involved in cell communication and adhesion. These findings provide important evidence for cross-talk between Notch and other pathways relevant to oncology. These findings substantiate the rationale for combining PI3K pathway agents (e.g., an AKT or mTOR inhibitor) with a GSI for treatment of cancer.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 26.