Identification of a Small Molecule That Overcomes HdmX-Mediated Suppression of p53

Abstract

Inactivation of the p53 tumor suppressor by mutation or overexpression of negative regulators occurs frequently in cancer. Since p53 plays a key role in regulating proliferation or apoptosis in response to DNA damaging chemotherapies, strategies aimed at reactivating p53 are increasingly being sought. Strategies to reactivate wild-type p53 include the use of small molecules capable of releasing wild-type p53 from key, cellular negative regulators, such as Hdm2 and HdmX. Derivatives of the Hdm2 antagonist Nutlin-3 are in clinical trials. However, Nutlin-3 specifically disrupts Hdm2-p53, leaving tumors harboring high levels of HdmX resistant to Nutlin-3 treatment. Here we identify CTX1, a novel small molecule that overcomes HdmX-mediated p53 repression. CTX1 binds directly to HdmX to prevent p53-HdmX complex formation, resulting in the rapidly induction of p53 in a DNA damage-independent manner. Treatment of a panel of cancer cells with CTX1 induced apoptosis or suppressed proliferation and importantly, CTX1 demonstrates promising activity as a single agent in a mouse model of circulating primary human leukemia. CTX1 is a small molecule HdmX inhibitor that demonstrates promise as a cancer therapeutic candidate.

Targeting MDMX for Cancer Therapy: Rationale, Strategies, and Challenges

“…Due to advances in understanding the structure and binding mechanisms of p53-MDM2 and p53-MDMX complexes, many inhibitors have been developed to dually inhibit the interactions of p53-MDM2/MDMX, which have been comprehensively discussed in the recent review articles ( 26 – 29 ). Several specific p53-MDMX binding inhibitors, including, but not limited to, SAH-p53-8 ( 92 ), SJ-172550 ( 94 ), compound B1 ( 96 ), CTX1 ( 97 ), and K-178 ( 98 ) have recently been discovered and shown promising anticancer efficacy and safety profiles in preclinical models in vitro and in vivo ( Table 2 ). Bernal et al have designed and synthesized a stapled p53 helix, named SAH-p53-8 that specifically binds to MDMX with strong affinity ( K D = 2.3 nM) ( 92 ).…”

“…Karan et al have also performed a cell-based screening of a compound library (over 20,000 small molecules) and identified a lead compound CTX1, which induces strong p53-dependent activation in MCF-7 cells expressing a high level of MDMX ( 97 ). Further studies have shown that CTX1 directly binds to MDMX ( K D = 450 nM), prevents the formation of p53-MDMX complex, and activates p53 without causing DNA damage ( 97 ).…”

“…Karan et al have also performed a cell-based screening of a compound library (over 20,000 small molecules) and identified a lead compound CTX1, which induces strong p53-dependent activation in MCF-7 cells expressing a high level of MDMX ( 97 ). Further studies have shown that CTX1 directly binds to MDMX ( K D = 450 nM), prevents the formation of p53-MDMX complex, and activates p53 without causing DNA damage ( 97 ). CTX1 alone or in combination with an MDM2 inhibitor nutlin-3 has been found to induce cancer cell growth arrest and apoptosis in vitro and extend the survival of mice bearing acute myeloid leukemia (AML) xenograft tumors in vivo ( 97 ).…”

“…Further studies have shown that CTX1 directly binds to MDMX ( K D = 450 nM), prevents the formation of p53-MDMX complex, and activates p53 without causing DNA damage ( 97 ). CTX1 alone or in combination with an MDM2 inhibitor nutlin-3 has been found to induce cancer cell growth arrest and apoptosis in vitro and extend the survival of mice bearing acute myeloid leukemia (AML) xenograft tumors in vivo ( 97 ). In addition, Uesato et al have designed and synthesized a class of o-aminothiophenol derivatives as selective p53-MDMX binding inhibitors.…”

Reviving the guardian of the genome: Small molecule activators of p53

“…Additional studies demonstrated XI-006's and XI-011's efficacy in Ewing sarcoma (Pishas et al, 2015) and head and neck cancer cells (Roh, Park, & Kim, 2014), respectively. Subsequent efforts in constructing molecules against MDMX have yielded CTX1, identified by a cell-based screen, which demonstrated efficacy in and synergy with Nutlin against a panel of cancer cells containing wild-type p53 and in a mouse xenograft model using primary human AML cells (Karan et al, 2016). Vassilev et al have also discovered RO-2443 and RO-5963, an indolyl hydantoin series capable of imposing dimerization of MDM2 and MDMX, preventing either of their interactions with p53 (Graves et al, 2012).…”