Concomitant DNA repair inhibition and chemotherapy with CPX-351 reduces leukemia preclinically

Most chemotherapy agents act by damaging the DNA of cancer cells, thus leading to cell death. CPX-351, a liposomal cytarabine–daunorubicin formulation, is one such example that has been approved by the U.S. Food and Drug Administration (FDA) and the European Medicines Agency (EMA) for its use in patients with secondary acute myeloid leukemia (AML). Despite the great potential of frontline chemotherapeutic agents, a proportion of patients with AML relapse following treatment, indicating the need for improved regimens for this subset of patients.^1,2

At the Virtual Edition of the 25th European Hematology Association (EHA) Annual Congress, Yuki Nishida et al.¹ presented a poster with promising preclinical data on the combinatory use of CPX-351 with the DNA repair inhibitor, M3814. More specifically, M3814 inhibits the actions of the DNA-dependent protein kinase catalytic subunit (DNA-PKcs), which plays a key role in DNA double-strand break repair. The authors hypothesized that DNA damage, induced by CPX-351, together with DNA repair inhibition by M3814, might provide a stronger anti-leukemic strategy than DNA damage alone.

Study design

• AML cell lines used for in vitro experiments:
  • Wild-type p53 cells (TP53^WT): MOLM-13, MV4;11, MOLM-14
  • Null p53 cells (TP53^null): THP-1, HL-60
  • Mutated p53 cells (TP53^mut): isogenic MOLM-13 cells with TP53 mutations p.R248W and p.R213, established by long-term exposure to idasanutlin
• In some experiments, AML cell lines were cocultured with mesenchymal stromal cells to mimic the bone marrow milieu
• Cellular apoptosis was detected by annexin V/propidium iodide, while DNA damage was detected by g-H2AX flow cytometry
• In vivo AML model:
  • Patient-derived xenograft AML model with TP53^WT (with FLT3-ITD, DNMT3A, IDH1, KIT, and NPM1 mutations in NRG mice)
• CPX-351 was administered in vivo at a dose of 0.15 U/kg on Days 1, 4, and 7
• M3814 was administered in vivo at a dose of 25 mg/kg twice daily on Days 1–14

Results

In vitro data

• DNA-PKcs inhibition by M3814 in combination with CPX-351 led to increased apoptosis when compared with CPX-351 alone in TP53^WT, TP53^null, and TP53^mut AML cells
• DNA-PKcs inhibition by M3814 increased the levels of DNA damage (γ-H2AX positivity) induced by CPX-351 in both TP53^WT and TP53^mut AML cells
• The authors also investigated the efficacy of the CPX-351 + M3814 combination in cocultures of mesenchymal stromal cells with either TP53^WT or TP53^mut AML cells: 
  • The CPX-351 + M3814 combination again led to enhanced CPX-351-induced apoptosis of both TP53^WT and TP53^mut AML cells

In vivo data

• In the APX mouse model, administration of the CPX-351 + M3814 combination led to significantly reduced numbers of circulating blasts when compared with vehicle (p < 0.0001) and CPX-351 treatment alone (p < 0.0001)
• Moreover, significant spleen size reduction was observed in both CPX-351-treated mice and those treated with the CPX-351 + M3814 combination, when compared with vehicle-treated controls
• No significant changes in hemoglobin or platelet levels at Week 4 were observed between vehicle-treated and CPX-351 + M3814 combination-treated mice

Conclusion

Both the in vitro and in vivo data of this study indicate that, when combined, CPX-351 and M3814 lead to superior anti-leukemic effects compared with CPX-351 chemotherapy alone. The combination treatment was well tolerated in vivo and, together with its observed promising efficacy, is paving the way for the further clinical investigation of DNA damage and DNA repair inhibitor combinations for the treatment of AML.