Development of small molecules restoring the tumor suppression functions of p53 – Galina Selivanova Group

Mutant p53 is expressed in cancers, where it adopts an unfolded conformation resulting in loss of DNA binding and in some cases gaining oncogenic function. Thus, our hypothesis is to stabilize p53 conformation by small molecule to restore the DNA binding tumor suppressor function of p53. Since around 50% of all human tumors carry mutations in p53, it could be widely applicable in clinic. We have identified a small molecule PRIMA-1MET by screening NCI chemical library using cell-based assay (Bykov et al, Nature Medicine, 2002). PRIMA-1^MET(commercial name APR-246, please see www.aprea.com) restores the active conformation and DNA binding of mutant p53 in cells and in vitro, re-activates the function of mutant p53 in tumor cells of different origin and suppreses the growth of human xenograft tumors in mice.  

APR-246 has been tested in patients in Phase I clinical trial and in March 2020 APR-246 received Fast Track and Breakthrough Therapy designations from FDA based on outstanding results of Phase II trial in MDS patients. These prompted the start of Phase III randomized trial in MDS.

We are addressing the fundamental questions that need to be solved for the efficient application of p53-targeting medicines and their combinations in clinic, i.e. thorough understanding of the mechanism of action of the identified compounds, including target specificity in vitro and in vivo and off-target effects.

While p53 reactivating molecules have been shown to kill cancer cells, the question remains open how p53 reinstatement will affect tumor microenvironment, cancer-associated fibroblasts in particular, as well as anti-cancer immune response. 

Our ambition is to provide basis for innovative p53-based treatment strategies targeting both cancer cells and tumor microenvironment to generate synergistic anti-tumor effects that result in long term survival of patients. Defining this concept, its mechanisms and implications for novel anti-cancer therapies form the main objectives of our studies.

In addition to applied aspects, we are actively working on important basic aspects of tumor biology, including genetic screens for p53 regulators and identification of novel factors which control p53 activity in tumor and in normal cells, which can serve as targets for therapeutic intervention in a future. In essence, to understand p53 is to understand how its interaction with proteins, and thus DNA, is controlled. In order to address these challenging questions we will employ a comprehensive and multidisciplinary approach. We will apply cutting-edge molecular and cell biology methodologies, multi-omics analyses and systems biology analysis, combined with ex vivo 3D cell & tissue culture and in vivo models. We combine hypothesis-driven strategy with unbiased multi-omics approach and apply the analysis of publicly available patient data sets (e.g., TCGA), as well as newly obtained data from patient material via my collaborations with clinicians in Sweden and abroad.

We perform highly parallel and comprehensive search for p53 modulators and identify their functional significance by inter-disciplinary integration of genome-wide expression profiling, ChIP-seq and proteomic approaches, followed by systems biology analysis. This will pave the way to the identification of key p53 target genes and factors contributing to alternative biological responses. These will be thoroughly validated in cells, mouse models and patient samples using functional genomics and protein-protein interaction assays. Selected factors will be used for chemical libraries screens to identify small molecules that target them.  We hope our studies will open the way for the development of novel therapeutic approaches.

In a recent study published in Cancer Discovery in 2021, we demonstrated that pharmacological activation of p53 induces the expression of ERVs and generation of double-stranded (ds) RNA which caused intracellular dsRNA stress leading to type 1 and type 3 IFN responses and induction of  antigen processing and presentation  (APP) genes.  Notably, we found that p53 activation promotes the recruitment of immune cells to tumors in vivo in mouse models and sensitizes refractory tumors to programmed cell death protein 1 (PD-1) blockade.  

Importantly, the analysis of pre- and post-treatment tumor biopsy samples from melanoma patients treated with the experimental MDM2 inhibitor ALRN-6924,  revealed the induction of viral mimicry response genes, as well as immune function signatures suggesting infiltration of cytotoxic CD8+ T cells.

Our results suggest the potential role of  p53-reactivating compounds with checkpoint inhibitors. In conclusion, our data presented across cancer cell lines, tumor-bearing mouse models, and melanoma patients suggest that pharmacological p53 reactivation triggers the ERV-dsRNA-IFN pathway within tumor cells, thereby altering the tumor microenvironment evoking tumor immune surveillance.

Ingemar Ernberg Group

Our primary research interest is infection and cancer in humans.  We particularly study Epstein-Barr Virus (EBV)-infection, which can also be used as a model to study early steps in in vitro transformation, viral genetic switches, non-genetic variation and cancer cell metabolism.