Abstract #1708: Voreloxin is active in breast cancer biopsies and potency is enhanced in a BRCA2 mutant background
Authors: Rachael Hawtin, David Stockett, Cecilia Lundin, Thomas Helleday, Judith Fox
Journal: Cancer Research (2009)

Voreloxin is a novel naphthyridine analog, structurally related to the quinolones, and currently in clinical trials in acute myeloid leukemia (AML) and platinum-resistant ovarian cancer. Clinical responses have been observed in these indications (Lancet et al., 2007; McGuire et al., SGO 2008). Voreloxin\#8217;s mechanism of action involves DNA intercalation and inhibition of topoisomerase II that induces site-selective DNA double-strand breaks (DSB), G2 arrest and apoptosis. Potency was reported in primary patient biopsies from triple negative breast cancer, ovarian cancer and AML, including samples that are resistant to the topoisomerase II inhibitor doxorubicin, with activity independent of p53 family members (Hawtin et al AACR 2008). Here we report that toxic DSBs are generated at the replication fork, triggering homologous recombination repair (HRR) and that BRCA2 mutation increases sensitivity to voreloxin. We also show that the agent is active in breast cancer biopsies from patients with ductal or metastatic disease. The influence of BRCA2 on sensitivity to voreloxin was evaluated by proliferation assay in cells mutant and complemented for functional BRCA-2 (V-C8 and V-C8-B2). Activity in these assays was compared with doxorubicin. In cells mutant for BRCA2 an approximately 5-fold increase in sensitivity was identified for voreloxin as compared to cells expressing functional BRCA2 (IC 50  0.14 \#956;M vs 0.72 \#956;M). Doxorubicin sensitivity was increased approximately 4-fold (IC 50  0.05 \#956;M vs 0.19 \#956;M ). These studies were extended to the human sarcoma cell line U-20S, comparing wild-type cells to those depleted for BRCA2 using siRNA. The BRCA2 influence on sensitivity to voreloxin was evaluated by clonogenic survival and compared with doxorubicin. Voreloxin cytotoxicity toward 9 ductal and 8 metastatic primary breast cancer biopsies was determined using the Extreme Drug Resistance (EDR) proliferation assay. Voreloxin was potent in samples that were resistant to the topoisomerase II inhibitors doxorubicin and / or etoposide, and was also active in cisplatin-resistant samples. Voreloxin at 1µM (the plasma concentration sustained for approximately 24 hr in Phase 2 clinical studies) inhibited proliferation >90% in 8/9 ductal biopsies, with none being resistant to the agent. Proliferation was also inhibited >90% in 4/8 metastatic samples with only one being resistant to 1µM voreloxin. In conclusion, voreloxin induces DNA DSBs that are repaired by HRR, and BRCA2 mutations sensitize cells to the agent. Voreloxin is active in breast cancer biopsies, including those resistant to other topoisomerase II inhibitors. Combined with potent activity in triple-negative breast cancer biopsies and the known mechanism of action of voreloxin, these data support expansion of the clinical evaluation of voreloxin to include breast cancer, in which other topoisomerase II inhibitors are active.   Citation Information:  In: Proc Am Assoc Cancer Res; 2009 Apr 18-22; Denver, CO. Philadelphia (PA): AACR; 2009. Abstract nr 1708.