Pre-clinical activity of the PARP inhibitor AZD2281 in human breast cancer cell lines and in combination with DNA damaging agents.

Abstract

Abstract Abstract #1038 Background: Deficiencies in DNA repair mechanisms have been associated with breast cancer. AZD2281, a potent, oral, PARP inhibitor has been shown to have clinical activity in patients with BRCA mutant breast cancers. Laboratory studies have suggested that non-BRCA mutant breast cancers may also be sensitive to PARP inhibition in tumors as a consequence of deficiencies in other homologous recombination (HR) repair components. Using a large panel of human breast cancer cell lines we tested the hypotheses that (1) there may be a subset of non-BRCA mutant breast cancers that are sensitive to single-agent AZD2281 and (2) AZD2281 would potentiate the cytotoxic effects of the DNA damaging agent cisplatin. Methods: 43 human cell lines representing known molecular subgroups of breast cancer (i.e. ER+, HER2 amplified, “triple-negative”), and 3 immortalized breast lines were treated in duplicate in adherent plates with AZD2281 using two-fold dilutions over 6 concentrations for 6 days. Dose response curves were generated using a cell count assay to calculate the IC50 of AZD2281. In addition, a subset of cell lines that grow under anchorage independent conditions were grown in triplicate in the presence and absence of 1 µM AZD2281 in soft agar for at least 3 weeks and growth inhibition was calculated as per cent of untreated control. Cell lines (both sensitive and resistant to single agent AZD2281) were also evaluated in combination with cisplatin in a cell count assay to assess the interaction between the two agents.
 Results: The majority of breast cancer cell lines evaluated in the short term 2-D growth assay did not show significant growth inhibition (IC50 < 1 µM) following AZD2281 treatment, including a known BRCA mutant cell line, suggesting this assay may not be ideal for determining sensitivity to AZD2281. However, in the longer term anchorage independent clonogenic assay, approximately half of the cell lines evaluated demonstrated an IC50 < 1 µM. Of note, the majority of the cell lines representing a “triple-negative” phenotype appeared sensitive to AZD2281 in this assay. In addition, pre-treatment with AZD2281 prior to cisplatin, potentiated the growth inhibition seen with cisplatin in both AZD2281 sensitive and resistant cell lines. Additional studies evaluating predictive markers other than BRCA status are ongoing. Conclusion: The PARP inhibitor AZD2281 has significant pre-clinical activity in human breast cancer cell lines. In a clonogenic assay, cell lines representing the “triple negative” subtype were especially sensitive to AZD2281 supporting clinical development in this population, regardless of BRCA status. In addition, these pre-clinical data support the hypothesis that PARP inhibition may potentiate the effects of chemotherapy induced DNA damage and provide further rationale for clinical development. Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 1038.