20P - The essential role of DNA repair in the pharmacological activities of AST-3424

Background

AST-3424 is an AKR1C3-activated prodrug and releases a toxic bis-alkylating moiety after activation by tumor-specific AKR1C3. AST-3424 is currently being investigated in multiple phase I/II clinical trials for the treatment of various cancers. Wild-type p53 cells have checkpoint redundancy via G1/S checkpoint and G2/M checkpoint while p53-mutant tumor cells are solely dependent on G2/M checkpoint to arrest the cell cycle after DNA damage and allow DNA repair before progressing. Here, we have explored the essential role of DNA repair in AST-3424-mediated pharmacological activities in vitro and in vivo.

Methods

We employed in vitro cytotoxicity, DNA damage, apoptosis, cell cycle and cellular signaling assays in both p53-proficient H460 and p53-deficient HT29 cells as well as in vivo xenograft models to investigate the essential role of DNA repair in AST-3424-mediated pharmacological activities.

Results

AST-3424 induced cytotoxicity, DNA damage, apoptosis and cell cycle arrest at G2 phase in a dose- and AKR1C3-dependent manner in both p53-proficient H460 and p53-deficient HT29 cells. However, enhancement of AST-3424 cytotoxicity by G2 arrest inhibitors, including adavosertib, AZD7762 and ceralasertib was only observed in HT29 but not in H460 cells. Similarly, AST-3424-induced γH2AX and apoptosis were also enhanced in HT29 upon the addition of G2 arrest inhibitors. The enhanced activity of AST-3424 in HT29 cells by G2 arrest inhibitors was due to the attenuation of cell cycle G2 arrest, as evidenced by decreased phosphorylation of Cdc2-Y15 and increased phosphorylation of histone H3, as well as reduced expression of RAD51, resulting in impaired DNA repair capacity. To further examine the essential role of DNA repair in AST-3424 anti-tumor activity, we utilized two PDX models with BRCA deleterious mutations lacking capacity of double-strand DNA repair. The results showed that AST-3424 exhibited excellent anti-tumor activity in two pancreatic PDX models with BRCA deleterious mutations and high expression of AKR1C3.

Conclusions

DNA repair plays an essential role in AST-3424-mediated in vitro biological activities and in vivo anti-tumor activity. The preclinical data presented in this study support a new approach for cancer treatment.

Clinical trial identification

Editorial acknowledgement

Legal entity responsible for the study

Ascentawits Pharmaceuticals, Ltd.

Funding

The Development and Reform Commission of Shenzhen Municipality, Guangdong Province, P.R.C (XMHT20220104029, XMHT20220104047).

Disclosure

All authors have declared no conflicts of interest.