The Hedgehog pathway as targetable vulnerability with 5-azacytidine in myelodysplastic syndrome and acute myeloid leukemia

Abstract

BackgroundTherapy and outcome for elderly acute myeloid leukemia (AML) patients has not improved for many years. Similarly, there remains a clinical need to improve response rates in advanced myelodysplastic syndrome (MDS) patients treated with hypomethylating agents, and few combination regimens have shown clinical benefit. We conducted a 5-azacytidine (5-Aza) RNA-interference (RNAi) sensitizer screen to identify gene targets within the commonly deleted regions (CDRs) of chromosomes 5 and 7, whose silencing enhances the activity of 5-Aza.Methods and resultsAn RNAi silencing screen of 270 genes from the CDRs of chromosomes 5 and 7 was performed in combination with 5-Aza treatment in four AML cell lines (TF-1, THP-1, MDS-L, and HEL). Several genes within the hedgehog pathway (HhP), specifically SHH, SMO, and GLI3, were identified as 5-Aza sensitizing hits. The smoothened (SMO) inhibitors LDE225 (erismodegib) and GDC0449 (vismodegib) showed moderate single-agent activity in AML cell lines. Further studies with erismodegib in combination with 5-Aza demonstrated synergistic activity with combination index (CI) values of 0.48 to 0.71 in seven AML lines. Clonogenic growth of primary patient samples was inhibited to a greater extent in the combination than with single-agent erismodegib or 5-Aza in 55 % (6 of 11) primary patient samples examined. There was no association of the 5-Aza/erismodegib sensitization potential to clinical-cytogenetic features or common myeloid mutations. Activation of the HhP, as determined by greater expression of HhP-related genes, showed less responsiveness to single-agent SMO inhibition, while synergy between both agents was similar regardless of HhP gene expression. In vitro experiments suggested that concurrent dosing showed stronger synergy than sequential dosing.ConclusionsInhibition of the HhP with SMO inhibitors in combination with the hypomethylating agent 5-Aza demonstrates synergy in vitro and inhibits long-term repopulation capacity ex vivo in AML and MDS. A clinical trial combining 5-Aza with LDE225 (erismodegib) in MDS and AML is ongoing based on these results as well as additional publications suggesting a role for HhP signaling in myeloid disease.Electronic supplementary materialThe online version of this article (doi:10.1186/s13045-015-0211-8) contains supplementary material, which is available to authorized users.

Glasdegib in combination with cytarabine and daunorubicin in patients with AML or high‐risk MDS: Phase 2 study results

“…Previous studies have reported glasdegib inhibition of SMO reduced the expression of key intracellular leukemia stem cell regulators (eg, GLI2) and enhanced cell cycle transit . These results and preclinical evidence that Hh inhibition may sensitize cells to cytarabine or azacitidine provided rationale for evaluating glasdegib in combination with chemotherapeutic agents to reduce resistance and leukemic persistence or progression.…”

Targeting High Mobility Group Box-1 (HMGB1) Promotes Cell Death in Myelodysplastic Syndrome

“…2F). High doses of azacitidine like 10 mmol/L used in these studies exert direct cytotoxic effects (20). Because high versus low doses azacitidine could result in differential mechanisms of anticancer effects, with low doses causing sustained alterations in gene expressions of crucial cancer signaling pathways (21), we also tested clinically relevant lower doses of azacitidine and sivelestat.…”

Gli-1/PI3K/AKT/NF-kB pathway mediates resistance to radiation and is a target for reversion of responses in refractory acute myeloid leukemia cells

“…Other studies have shown that Hh signaling is essential for the survival and drug resistance of leukemia cells [22, 23]. Interestingly, a recent report has demonstrated that inhibition of the Hh pathway with LDE225 sensitizes AML cells to 5-azacytidine, and a clinical trial based on these results is ongoing [24]. However, there are no reports of the effects and mechanisms of Hh pathway signaling on radiation resistance or the application of inhibitors to AML.…”