Discovery of Rezatapopt (PC14586), a First-in-Class, Small-Molecule Reactivator of p53 Y220C Mutant in Development

ACS Med. Chem. Lett., 2025, 16, 1, 34–39

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Precision medicine (used interchangeably with “personalised medicine”) is a broad term that refers to the grouping of patient populations into those that are likely to respond to a particular treatment and those who are not. The potential benefits include sparing mismatched patients from the side-effect, time and financial cost of treatments that are not predicted to be effective.

The more you think about it, the more you realise that this is not a novel concept. Observers frequently quote the ancient Greek physician Hippocrates, as he would write about the individuality of disease and the need to divide patient population by factors such as age, physique and more. The real paradigm shift caused by modern precision medicine over the last half-century, is the ability to group patients genetically (at the molecular level). This is enabled by advanced analytical and diagnostic testing, and detailed molecular understanding of disease progression. Both of these factors are constantly improving, as we learn more through modern science.

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Figure 1: Graphic from the 2022 PMC report on personalized medicine in FDA approvals

In 2022, the Personalized Medicine Coalition (PMC) published a report[4] on precision medicine in FDA approvals, showing a sustained portion (≥25%) of approved therapeutics over the last 10 years falling into this category (Fig. 1, above). On top of approved new molecular entities (NMEs), the FDA have also been expanding indications for given precision therapies and combinations thereof. This redefines the intended population of a given drug and offers more personalised treatment options.

The field in which precision medicine has seen the most recent application is oncology, where the presence and expression level of oncogenes can be screened-for in cancer patients to find those likely to respond to given treatments. The most famous example of this is the Her2/Neu proto-oncogene, which is amplified in 25-30% of human breast cancers.[8] Screening for Her2/Neu is now routine for breast cancer patients, this is essential for decision-making in prescribing the Her2 receptor blocker trastuzumab (Herceptin) due to the risk of severe side effects. It wouldn’t be right to subject patients to this risk if it was unlikely that they could see any benefit.

The topic of this paper is another proto-oncogene, arguably the most important one of all, mutations in which occur in more than half of human cancers. This is of course p53, commonly referred to as the tumour-suppressor gene, and “The Guardian of the Genome” due to its roles in DNA repair and cell cycle pathways (Fig. 2, below).

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Figure 2: Overview of signalling cascades that are regulated by p53 (Source: https://www.rockland.com/resources/p53-pathway-antibodies/)

 

Most oncogenic mutations of the p53 gene are missense mutations within the DNA-binding domain (DBD) of the encoded protein, stopping it from binding to DNA. The authors identified the point mutant Y220C (accounting for 1.8% of somatic p53 mutations), which is unstable at physiological temperature and cannot carry out the normal p53 function, this leads to tumour growth. The goal is to stabilise this mutant with a small molecule prosthetic, thereby rescuing the ability of the p53 protein to bind DNA normally and carry out its wild-type function. In isolation, this should lead to tumour regression.

The primary assay for screening compounds was the DNA-binding assay based on a FRET couple, providing SC150 values, which are the concentrations of substrate required to increase the DNA binding ability 1.5-fold. Key results were followed up with in-situ 1H/15N HSQC NMR studies with 15N-labelled p53 Y220C to check for a real interaction between protein and substrate, ruling out false positives.

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Figure 3: Inspiration for the present p53 Y220C stabiliser series initiated by compound 1. Adapted from: https://doi.org/10.1021/acsmedchemlett.4c00379

Starting from a combination of two distinct chemical series found in the literature (Fig. 3, above), a carbazole fragment (PhiKan083)[9] and an internal alkyne containing compound (PK1596),[10] the authors could access analogues easily due to a convenient retrosynthetic disconnection splitting the compounds effectively in half via a Sonogashira coupling reaction.

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Figure 4: Mutant (Y220C) p53 bound to stabiliser compound (rcsb: 9BR4, grey, bottom left) aligned and juxtaposed with WT p53 DBD (rcsb: 2XWR, cyan, bottom right), overlay (top)

 

SAR studies using the DNA binding assay were conducted until SC150 values of <100 nM were obtained. The authors were then able to get a crystal structure of the p53(Y220C) DBD bound to the stabiliser (Fig. 4, above), showing them exactly how their stabiliser compounds sat in the void created by the key Tyr220 mutation to Cys. This nicely guided further potency gains, and allowed them to prioritise solvent-facing vectors as opportunities for the tuning of physicochemical properties.

Cellular potency was assessed using cancer cell lines that are known to harbour the p53 Y220C mutation. Proof-of-concept was thus obtained with good EC50 values against these cancer cell lines and a full manuscript detailing selectivity against cell lines that don’t harbour the key mutation is expected to be published in due course. With this remarkable set of results in hand, they then demonstrated in-vivo efficacy in a nude mouse xenograft study.[11]

The clinical candidate: rezatapopt, is currently undergoing Phase II trials against solid tumours harbouring the p53 Y220C mutation that are KRAS WT. Precision oncology approaches such as this show great promise and should be watched closely!

References:

  1. https://www.astrazeneca.com/what-science-can-do/topics/technologies/precision-medicine-history.html
  2. https://www.nature.com/scitable/topicpage/personalized-medicine-hope-or-hype-815/
  3. https://www.personalizedmedicinecoalition.org/Userfiles/PMC-Corporate/file/PM_at_FDA_A_Progress_and_Outlook_Report.pdf
  4. https://www.personalizedmedicinecoalition.org/Userfiles/PMC-Corporate/file/report.pdf
  5. https://accp1.onlinelibrary.wiley.com/doi/abs/10.1177/0091270005281091
  6. https://www.science.org/doi/10.1126/science.1156604
  7. https://www.genome.gov/human-genome-project
  8. org/10.1126/science.2470152
  9. https://doi.org/10.1073/pnas.0805326105
  10. https://doi.org/10.1021/ja301056a
  11. https://doi.org/10.1158/1538-7445.AM2021-LB006