Low-Dose Triptolide Promotes MDM2 Inhibitor Nutlin3a to Induce Acute Myeloid Leukemia Cell Death Via p53-Dependent and -Independent Mechanisms

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.