Abstract B41: Identification of a time- and dose-responsive transcriptional signature of Notch pathway inhibition in plucked human hair follicles following exposure to the gamma-secretase inhibitor MK-0752 (2009)

Abstract Introduction: Gamma-secretase inhibitors (GSIs) inhibit Notch pathway signaling and have potential as cancer therapeutics. Clinical development of GSIs has been complicated by mechanism-related goblet cell hyperplasia and dose-limiting diarrhea. A non-invasive biomarker of Notch pathway inhibition would facilitate the identification of a well-tolerated dose/schedule with maximal biological effect. In this study, a transcriptional biomarker of Notch pathway inhibition was developed from whole genome profiling of human plucked hair follicles (PHFs) for use in demonstrating target engagement and defining a PK/PD relationship. Procedures: This randomized, placebo-controlled, 3-period crossover study evaluated the effects of 350mg or 1000mg of the oral GSI MK-0752 on PHF gene expression in 30 healthy male subjects. Pooled PHFs, single anagen hairs, and whole blood samples were collected at various timepoints for pharmacokinetic and pharmacodynamic (mRNA profiling) analysis. Results: There was a significant decrease in a pre-specified 15-gene Notch signature score (NSS) at 8.5, 28.5, 48 and 96 hours in response to either 350mg or 1000mg MK-0752, compared to placebo, at the nominal 1-sided 0.05 level. The maximum response in pooled PHFs was seen following administration 1000mg MK-0752, which resulted in a significant (p &amp;lt;0.001) decrease from baseline in the NSS at 8.5 hours post-treatment, with an observed effect size of 2.34. A smaller, but significant, decrease from baseline in the NSS was seen in single anagen hairs at 8.5h post-treatment for 1000mg MK-0752 compared to placebo (effect size 1.40, p&amp;lt;0.001). Changes in the hair follicle NSS were driven primarily by 5 Notch pathway genes. A linear concentration-effect relationship was shown to be consistent across both dose levels using PHFs. In addition to Notch pathway changes, transcriptional signatures of PI3K signaling and cell proliferation were shown to be suppressed at 8.5h and 28.5h post-dose, respectively. Treatment with MK-0752 also resulted in various late (48h post-dose) transcriptional changes in hair follicles including the upregulation of other signaling pathways including Wnt and receptor tyrosine kinases. Conclusions: The results of this study demonstrate the development of a compound-specific biomarker in a novel surrogate tissue. This is the first known report of whole genome mRNA profiling of human hair follicles in response to a GSI, and demonstrates that PHFs contain cells with intact Notch signaling pathways responsive to MK-0752. A 1000mg dose of MK-0752, which is smaller than the clinically-tolerated dose of 1800mg/week, decreases expression of canonical Notch pathway genes for up to 96 hours. In addition, treatment with a GSI results in various biological changes in PHFs, including early downregulation of PI3K pathway and proliferation genes, and a late (48h) upregulation of other signaling pathways that are potentially relevant to cancer cell proliferation. This novel plucked hair follicle biomarker provides important insights into the effect of GSIs on cell signaling, and also facilitates the development of gamma secretase targeted drugs for oncology indications. Citation Information: Mol Cancer Ther 2009;8(12 Suppl):B41.