DNA Damage Sensing and TP53 Function as Modulators of Sensitivity to Calicheamicin-Based Antibody-Drug Conjugates for...

Approved for treatment of acute leukemia, gemtuzumab ozogamicin (GO) and inotuzumab ozogamicin (InO) are antibody-drug conjugates (ADCs) that deliver a toxic calicheamicin (CLM) derivative. The resistance mechanisms to GO/InO remain incompletely understood.

We performed a genome-wide clustered regularly interspaced short palindromic repeat (CRISPR)/Cas9 screen for CLM sensitivity genes, and then performed confirmatory cytotoxicity assays.

Several DNA damage pathway regulation genes were identified, most notably TP53. Across 13 acute leukemia cell lines, the six TP53-mutant cell lines (TP53^MUT) were indeed 10- to 1000-fold less sensitive to CLM than the seven TP53^WT cell lines. In five TP53^WT/KO syngeneic cell line pairs we generated, TP53^KO cells were significantly less sensitive to CLM than their TP53^WT counterparts. In TP53^WT but not TP53^MUT cells, the MDM2 inhibitor and p53 activator, idasanutlin, enhanced CLM cytotoxicity, demonstrating that decoupling of cells from MDM2-p53 regulation sensitizes leukemia cells to CLM. The ATM inhibitors AZD1390 and lartesertib also significantly enhanced CLM efficacy but did so independent of the TP53 status. In contrast, neither an ATR inhibitor, Chk1/Chk2 inhibitor, Chk2 inhibitor, or a PARP inhibitor significantly impacted CLM-induced cytotoxicity across the thirteen cell lines. Together, our studies identify ATM, MDM2, and TP53-which are in the same cellular response to DNA damage pathway-as key modulators of CLM-induced cytotoxicity in acute leukemia cells.

These results support further evaluation of combination therapies with corresponding small-molecule inhibitors (currently pursued for therapy of other cancers) toward clinical testing as novel strategies to increase the efficacy of CLM-based ADCs such as GO and InO.