Background: The Hedgehog (Hh) signaling pathway is key to development, differentiation, and stem cell maintenance. In cancer, dysregulation of Hh signaling is associated with solid tumors and hematological malignancies. Hh signaling in AML and MDS is thought to promote the renewal and maintenance of leukemic stem cells, which may lead to chemotherapy resistance and recurrence. Glasdegib is a potent and selective oral inhibitor of Smoothened, a transmembrane protein that stimulates Hh signaling. Here we report the results of an exploratory analysis to profile mutations in 118 bone marrow samples and 77 peripheral blood samples of patients with previously untreated AML or high-risk MDS treated with chemotherapy with or without glasdegib in phase I/II clinical trials.

Materials and Methods: We used targeted resequencing to survey 109 genes, and a polymerase chain reaction assay to detect FLT3 internal tandem duplications. Resequencing and response data were obtained from two arms, 1) an intensive group (n=61) treated with a combination of cytarabine/daunorubicin plus glasdegib, and 2) a non-intensive group (n=73) treated with low-dose cytarabine (LDAC) plus glasdegib (n=44) or LDAC alone (n=19). We assessed significantly mutated genes by Fisher's Exact Test at p ≤ 0.05.

Results: In the combined dataset we found that mutations in NF1 (P=0.006), KRAS (P=0.028), or a combination of KRAS, NRAS, and NF1 (P=0.013) were associated with a negative response. Mutations in NPM1 (P=0.006), MPL (P=0.041), RB1 (P=0.041), or SF3B1 (P=0.041) were associated with a positive response. When split by arm, in the intensive group mutations in TP53 (P=0.001), NF1 (P=0.035), or CREBBP (P=0.041) were associated with negative response, whereas mutation in NPM1 was associated with positive response (P=0.046). In the non-intensive group, mutations in RSPH10B2 (P=0.036) or a combination of KRAS, NRAS, and NF1 (P=0.031) were associated with negative response, whereas mutation in CREBBP (P=0.007) was associated with positive response. We discuss the implications of these mutations in the context of Smoothened inhibition and the leukemic stem cell hypothesis.

Conclusions: Mutational profiling of patients with AML or high-risk MDS treated with glasdegib highlights alterations in genes associated with response and the potential role of Hh signaling in these malignancies.

Citation Format: Keith A. Ching, Donghui Huang, Kai Wang, Mark Ozeck, Paul Lira, Jingjin Gao, Jadwiga Bienkowska, Paul Rejto, James Hardwick, Thomas O'Brien, Geoffrey Chan. Analysis of mutations associated with response to glasdegib in acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr LB-215.