Dysregulation of MDM2, a p53 negative regulator, frequently occurs in acute myeloid leukemia (AML) and is associated with unfavorable prognoses, rendering the p53-MDM2 axis an attractive target for the development of small-molecule inhibitors. MDM2 antagonists have been intensely developed but only lead to limited clinical activity, suggesting combination with additional drugs is an unmet medical need. In this study, we reported that Triptolide synergized with MDM2 inhibitor Nutlin-3a to suppress cell proliferation and induce mitochondrial-mediated apoptosis in p53 wt AML in vitro and ex vivo. More importantly, Triptolide cooperated with Nutlin-3a to delay tumor growth and abrogate leukemia burden in an AML xenograft model. In addition, we observed that Triptolide and Nutlin-3a were also cooperative in part of p53 deficient cases. Mechanistically, Nutlin-3a upregulated the transcriptional expressions of the p53 downstream targets PUMA and p21, while Triptolide declined the mRNA levels of two anti-apoptotic factors, XIAP and Mcl-1, in p53 wt cells. These effects were more notable when Triptolide and Nutlin-3a were combined. Our results revealed that Triptolide monotherapy exerted its antileukemia effect via both p53-dependent and independent ways, with the latter through perturbation of the MYC-ATF4 axis-mediated ER stress. Collectively, these data suggested that the Triptolide-Nutlin-3a combination might be a novel potential therapeutic intervention for patients with AML and it warrants further clinical evaluations.
The tumor suppressor p53 is central to hematopoietic stem cell function. Loss of p53 function is associated with poor prognosis of acute myeloid leukemia (AML). P53 negative regulator MDM2 is frequently overexpressed in AML, thus it becomes an attractive therapeutic target for the treatment of AML with wild-type p53 (Wt-p53). Targeting MDM2 to restore p53 activity has been assessed in AML, but clinical outcomes are less promising. Notably, p53-mutated AML still lacks effective treatment approaches. Therefore, our study strived to explore potent therapeutics to target AML with p53 wild-type and mutations.
Triptolide (TPL), an ancient herbal medicine, has been used to treat immune disorders for centuries. Accumulating evidence including ours have proven that low dose of TPL potentiates the efficacy of chemotherapies in a broad range of tumor types. In this study, we evaluated the anti-leukemic efficacy of combining low dose TPL with Nutlin3a, a MDM2 inhibitor, against AML with p53 wild-type and mutations. We found that low-dose TPL synergized with Nutlin3a to induce mitochondrial apoptosis in AML cells with Wt-p53 bothin vitroandin vivo. Underlying mechanism for the synergy showed that Nutlin3a upregulated pro-apoptosis factors (e.g. PUMA, p21), while low-dose TPL suppressed MDM2 transcription and reduced anti-apoptosis proteins (e.g. XIAP, Mcl-1) in Wt-p53 AML cells. Interestingly, we also observed that TPL but not Nutlin3a induced cell death in p53 shRNA knockdown, p53 deficiency cell lines (e.g. THP-1, HL-60) and primary samples. Thus, the p53-independent role of TPL was consequently focused. Our RNA-Seq analysis identified 621 differential expression genes (DEGs) after TPL treatment. These genes, including MYC, ATF4 and 4EBP1, were enriched in intrinsic apoptosis pathway responding to ER stress and thus we concluded that Triptolide played its p53 independent role via MYC-ATF4 axis.
Collectively, these findings suggest that coadministration of Nutlin3a with low dose TPL would benefit for AML patients.
Disclosures
Carter: AstraZeneca:Research Funding;Syndax:Research Funding;Ascentage:Research Funding;Amgen:Research Funding.
OffLabel Disclosure:
Triptolide (TPL), an ancient herbal medicine, is applying to treat immune disorders.
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