Introduction In many tumors the mutational make up is taken into account by using targeted therapies.
However, in pancreatic ductal adenocarcinoma (PDAC) these approaches often failed
leaving standard chemotherapies as only first-line options. One of the most promising
subtypes to be targeted is the genomic unstable one, counting for >10 % of all PDACs.
ATM serine/threonine kinase (ATM) is the most frequently mutated gene in this subgroup.
ATM is important for the DNA-damage response (DDR) via homologous recombination (HR).
The PARP inhibitor olaparib showed first response in HR-deficient (HRD) PDAC as maintenance
therapy in a phase III trial.
Aim We aimed to preclinically establish a novel genotype-tailored targeted therapy for
HRD PDAC.
Methods We established primary murine PDAC cell lines from AKC (
A
tmfl/fl;LSL-KrasG12D/+;Ptf1aCre/+
) and KC (LSL-KrasG12D/+;Ptf1aCre/+
) mice. Human translation was done via deletion of one or both ATM alleles in MIA
PaCa-2 and PANC-1 cells by CRISPR/Cas9. All generated cell lines were screened for
combinational genotype specific synergies. Finally, results were validated in vivo.
Results Making use of combinational triple inhibition of PARP, ATR, and DNA-PKcs (PAD) causes
synthetic lethality in HR-deficient murine and human PDAC. PAD therapy causes aneuploidy
and a tremendous increase of mitosis aberrations. PAD induces PARP trapping and replication
fork stalling, that finally end in P53-mediated apoptosis. All data was confirmed
in vivo with a significantly improved disease control rate (DCR) in transplanted HRD AKC
compared to HR-proficient KC cell lines by PAD. Most strikingly, human HRD cell lines
showed exactly the same synergistic effects of PAD in vitro and in vivo. Furthermore, chemical inhibition of ATM sensitized ATM-proficient human PDAC cells
to PAD, resulting also in significantly improved DCR in vivo. Finally this could be transferred to patient derived pancreatic organoids showing
a significant response to ATM inhibition and PAD therapy.
Conclusion With the triple inhibition of PARP, ATR, and DNA-PKcs we present a novel in-depth
preclinically elaborated therapeutic approach for the targeted treatment of HR-deficient
PDAC. This could be extended to a global genotype-independent level by chemical ATM-inhibition.
