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Abstract

PMID

Authors

Michael Hulse; Anjana Agarwal; Min Wang; Jack Carter; Monisha Sivakumar; Brian Vidal; Justin Brown; Andrew Moore; Alexander Grego; Neha Bhagwat; Joseph Rager; Liang Lu; Corey Basch; Klare Bersch; Chaofeng Dai; Philip Pitis; Andrew Combs; Bruce Ruggeri; Kris Vaddi; Peggy Scherle; Koichi Ito

Title

Abstract 3263: Preclinical characterization of PRT3789, a potent and selective SMARCA2 targeted degrader

Journal	Vol	Issue	Date	Pages	Journal Short Title
Cancer Research	82	12_Supplement	June 15, 2022

URL

https://aacrjournals.org/cancerres/article/82/12_Supplement/3263/703325/Abstract-3263-Preclinical-characterization-of

Abstract Text

SWI/SNF complexes play an important role in controlling gene expression by remodeling chromatin. SMARCA2 (BRM) and SMARCA4 (BRG1) are the core catalytic subunits of the SWI/SNF complexes, containing an ATPase domain and a DNA binding bromodomain. SMARCA4 protein expression is lost in some cancers due to nonsense mutations, and SMARCA4-deleted cancer cells are highly dependent on its paralog gene SMARCA2 for their survival. Therefore, targeting SMARCA2 in SMARCA4-deleted cancers using selective SMARCA2 degraders induces synthetic lethality while sparing SMARCA4 wild type (WT) normal cells. We have identified PRT3789, a potent and selective SMARCA2 targeted degrader, that selectively inhibits proliferation of SMARCA4-deleted cancer cells. Here, we describe the potential mechanism of action for PRT3789 at the molecular level and the in vitro and in vivo anti-tumor activity in SMARCA4-deleted cancer cells. To further elucidate the SMARCA2 degradation selectivity of PRT3789, we performed mass spectrometry to identify the selective SMARCA2 lysine residues ubiquitinated following treatment with PRT3789. This data, in combination with site-directed mutagenesis against these SMARCA2-specific ubiquitinated residues, has revealed important insights into the mechanism of action of PRT3789. In addition, to further understand the specific vulnerability of SMARCA2 in SMARCA4-deleted cells, we investigated whether PRT3789 affected the integrity of the residual SWI/SNF complex. Coimmunoprecipitation of SMARCC1 revealed that PRT3789 disrupts specific SWI/SNF complex subunits, including ACTL6A (BAF53). Functional genome-wide experiments are ongoing to evaluate the impact of this finding and the residual activity of the SWI/SNF complex. Furthermore, treatment with PRT3789 demonstrated robust inhibition of cell proliferation of SMARCA4-deleted non-small cell lung cancer (NSCLC) cells in vitro and NSCLC PDX tumors ex vivo, but not SMARCA4 WT cancer cells, in a concentration-dependent manner. Lastly, PRT3789 shows favorable pharmacokinetic properties in vivo, which correlate to its pharmacodynamics effects as evidenced by reduced SMARCA2 protein and KRT80 mRNA levels in tumor tissues. In subcutaneous cell-line derived xenograft (CDX) models of NSCLC, administration of PRT3789 demonstrated significant dose-related inhibition of SMARCA4-deleted NSCLC growth at tolerated doses, but no effect on the growth of SMARCA4 WT cancers. In summary, consistent with our previous validation studies and genomic perturbation analyses, our potent and selective SMARCA2 targeted degrader PRT3789 induces strong synthetic lethality in SMARCA4-deleted cancers in vitro and in vivo.

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Molecular Profile	Treatment Approach

Gene Name	Source	Synonyms	Protein Domains	Gene Description	Gene Role

Therapy Name	Drugs	Efficacy Evidence	Clinical Trials
PRT3789	PRT3789	3	1

Drug Name	Trade Name	Synonyms	Drug Classes	Drug Description
PRT3789		PRT-3789\|PRT 3789		PRT3789 is a SMARCA2 degrader, which potentially decreases proliferation of tumor cells with SMARCA4 loss and inhibits tumor growth (Cancer Res 2022;82(12_Suppl):Abstract nr 3263).

Gene	Variant	Impact	Protein Effect	Variant Description	Associated with drug Resistance

Molecular Profile	Indication/Tumor Type	Response Type	Therapy Name	Approval Status	Evidence Type	Efficacy Evidence	References
SMARCA4 del	lung non-small cell carcinoma	predicted - sensitive	PRT3789	Preclinical - Pdx & cell culture	Actionable	In a preclinical study, PRT3789 inhibited proliferation of non-small cell lung cancer cells with deletion of SMARCA4 in culture and inhibited tumor growth in cell line xenograft and patient-derived xenograft (PDX) models (Cancer Res 2022;82(12_Suppl):Abstract nr 3263).	detail...