ATF4 induction through an atypical integrated stress response to ONC201 triggers p53-independent apoptosis in hematological malignancies

Abstract

The clinical challenge posed by p53 abnormalities in hematological malignancies requires therapeutic strategies other than standard genotoxic chemotherapies. ONC201 is a first-in-class small molecule that activates p53-independent apoptosis, has a benign safety profile, and is in early clinical trials. We found that ONC201 caused p53-independent apoptosis and cell cycle arrest in cell lines and in mantle cell lymphoma (MCL) and acute myeloid leukemia (AML) samples from patients; these included samples from patients with genetic abnormalities associated with poor prognosis or cells that had developed resistance to the nongenotoxic agents ibrutinib and bortezomib. Moreover, ONC201 caused apoptosis in stem and progenitor AML cells and abrogated the engraftment of leukemic stem cells in mice while sparing normal bone marrow cells. ONC201 caused changes in gene expression similar to those caused by the unfolded protein response (UPR) and integrated stress responses (ISRs), which increase the translation of the transcription factor ATF4 through an increase in the phosphorylation of the translation initiation factor eIF2α. However, unlike the UPR and ISR, the increase in ATF4 abundance in ONC201-treated hematopoietic cells promoted apoptosis and did not depend on increased phosphorylation of eIF2α. ONC201 also inhibited mammalian target of rapamycin complex 1 (mTORC1) signaling, likely through ATF4-mediated induction of the mTORC1 inhibitor DDIT4. Overexpression of BCL-2 protected against ONC201-induced apoptosis, and the combination of ONC201 and the BCL-2 antagonist ABT-199 synergistically increased apoptosis. Thus, our results suggest that by inducing an atypical ISR and p53-independent apoptosis, ONC201 has clinical potential in hematological malignancies.

ONC201 kills solid tumor cells by triggering an integrated stress response dependent on ATF4 activation by specific eIF2α kinases

“…Increased ATF4 abundance can be cytoprotective, (24, 25), anti-proliferative or cytotoxic, in part due to ATF4’s potential to regulate more than 400 genes (10) and to interact with more than 17 proteins (26). It is not surprising, therefore, that the consequences of ATF4 induction by ONC201 are not identical in all cell types, as we and Ishikawa et al (23) have shown. In HCT116 colorectal cancer cells and potentially in other solid tumor cell types, ATF4 may suppress the Akt pathway and induce apoptosis, in part through TRB3, TRAIL, and DR5.…”

Preclinical evaluation of the imipridone family, analogs of clinical stage anti-cancer small molecule ONC201, reveals potent anti-cancer effects of ONC212

“…1,2 Similarly, ONC212 and ONC206 significantly induced Sub-G1 apoptotic cells and/or cell cycle arrest. Interestingly, ONC212 and ONC206 did not induce cell cycle arrest in a colorectal cell line with acquired ONC201-resistance (RKO-ONC201 resistant 2 ), suggesting cross-resistance between the compounds.…”

“…[1][2][3] When activated by the ligand TRAIL, DR5 triggers the extrinsic cell death pathway that selectively induces apoptosis in a variety of tumor and transformed cells, including cancer stem cells, without affecting normal cells. 4,5 The unique ability of ONC201 to induced TRAIL-based signaling to induce apoptosis in cancer cells and not normal cells leads to a wide therapeutic index and favorable characteristics as an anti-cancer therapeutic.…”

“…4,5 The unique ability of ONC201 to induced TRAIL-based signaling to induce apoptosis in cancer cells and not normal cells leads to a wide therapeutic index and favorable characteristics as an anti-cancer therapeutic. [1][2][3]6,7 The TRAIL pathway is a powerful effector cytokine in the innate host immune response that suppresses tumor development, progression and metastasis. Early results from a Phase I clinical trial in advanced solid tumors demonstrated that ONC201 has a therapeutic PK profile, exceptional safety, induction of pharmacodynamics (PD) markers, and preliminary evidence of efficacy in various types of cancers.…”

Physiological/pathological ramifications of transcription factors in the unfolded protein response

“…Glutamine depletion selectively induces apoptosis in oncogenic MYC-overexpressing cells through ATF4-dependent induction of proapoptotic proteins PUMA and NOXA (Qing et al 2012). The anti-cancer drug ONC201 induces tumor cell death through ATF4-mediated transactivation of the proapoptotic protein TRAIL and its receptor, death receptor 5 (DR5) (Ishizawa et al 2016). ATF4-driven expression of CHOP is enhanced by a histone deacetylase (HDAC) inhibitor, thereby enhancing apoptosis upon proteasome inhibitor treatment (Kikuchi et al 2015).…”