Combined inhibition of GLI and FLT3 signaling leads to effective anti-leukemic effects in human acute myeloid leukemia

Abstract

Activation of the Hedgehog pathway has been implicated in the pathogenesis of several tumor types including myeloid leukemia. Previously we demonstrated that overexpression of Hedgehog downstream mediators GLI1/2 confers an adverse prognosis to patients with acute myeloid leukemia (AML) and is correlated with a FLT3 mutated status. To analyze a possible non-canonical activation of the Hedgehog pathway via FLT3 and PI3K, we performed blocking experiments utilizing inhibitors for FLT3 (sunitinib), PI3K (PF-04691502) and GLI1/2 (GANT61) in FLT3-mutated and FLT3 wildtype AML cell lines and primary blasts. Combination of all three compounds had stronger anti-leukemic effects in FLT3-mutated compared to FLT3 wildtype AML cells in vitro. Interestingly, the colony growth of normal CD34+ cells from healthy donors was not impeded by the triple inhibitor combination possibly opening a therapeutic window for the clinical use of inhibitor combinations. Besides, combined treatment with sunitinib, PF-04691502 and GANT61 significantly prolonged the survival of mice transplanted with FLT3-mutated MV4-11 cells compared to the single agent treatments. Furthermore, the inhibition of FLT3 and PI3K resulted in reduced GLI protein expression and promotor activity in FLT3-mutated but not in FLT3 wildtype AML cell lines in western blotting and GLI1/2 promoter assays supporting our hypothesis of non-canonical GLI activation via FLT3.In summary, FLT3-mutated in contrast to FLT3 wildtype cells or normal human hematopoietic progenitor cells are exquisitely sensitive to combined inhibition by FLT3, PI3K and GLI1/2 overcoming some of the limitations of current FLT3 directed therapy in AML. The development of GLI1/2 inhibitors is highly desirable.

Preclinical Evidence for Targeting PI3K/mTOR Signaling with Dual-Inhibitors as a Therapeutic Strategy against Cutaneous T-Cell Lymphoma

“…However, to our knowledge, dual-PI3K/mTOR inhibitors have never been tested in CTCL. PF-502 showed antitumor activity in preclinical studies on a variety of tumors (Fang et al, 2013;Herzog et al, 2013;Kinross et al, 2011;Latuske et al, 2017;Yuan et al, 2011), including B lymphomas (Blunt et al, 2015;Chen et al, 2016). However, it has not been evaluated in clinical trials for hematological cancers (Del Campo et al, 2016;Wainberg et al, 2017) (NCT00927823, NCT01420081, NCT01430585).…”

Targeting GLI Transcription Factors in Cancer

“…These inhibitors block tumor cell proliferation in vitro and suppress tumor cell growth in vivo. For example, GANT61 demonstrated a GLI-specific antitumor activity in lung carcinoma xenograft model [ 102 ], acute myeloid leukemia [ 103 ], rhabdomyosarcoma [ 104 ], neuroblastoma [ 105 ], breast cancer [ 106 ], and pancreatic cancer [ 101 ]. Notably, these studies also showed substantial benefit of GANT61 over SMO inhibitors, further confirming critical role of GLIs in cancer [ 101 , 102 , 106 ].…”

Analysis of hedgehog signaling in periocular sebaceous carcinoma

“…Vismodegib has been trialed in a variety of cancers, including pancreatic, ovarian cancer, breast and prostate cancers, and other SMO inhibitors are emerging such as sonidegib and BMS-833923 [ 44 ]. Gli antagonists have been developed too, and this may be a more promising level to block the pathway, especially Gli2 and could be used in combination to either block Hh at multiple levels or activated pathways [ 45 ]. It is possible that these agents could be efficacious in advanced or metastatic SC and if such a neoadjuvant response could be replicated, it may allow the preservation of sight by averting the need for a blinding exenteration.…”