Abstract 5363: Navitoclax (Nav) and BMN 673 yield cytotoxicity with lower doses than used for single agents in high-grade serous ovarian cancer (HGSOC)
Authors: Yokoyama Takuhei , Gordon Nicolas , Yu Minshu , Kohn Elise C. , Lee Jung-Min 
Published: August 2015

Background: The apoptosis inhibitor Bcl-xL is upregulated in recurrent ovarian cancer (OvCa). Modest clinical activity with Nav, a Bcl-2/Bcl-xL inhibitor, was observed in hematologic malignancies, although significant thrombocytopenia has been a challenge to its development. BMN 673 is a PARP inhibitor (PARPi) and is more potent at a molar level than other PARPi in preclinical studies. We observed a decrease in Bim and Bcl-2 protein expression in OvCa tissue after 1 cycle of olaparib (PARPi) and carboplatin compared to pretreatment levels; this change correlated with duration of response in BRCA1/2 mutation-related breast and OvCa patients (r2 = -0.86, p&lt;0.05). We hypothesize the combination of BMN 673 with Nav will yield preclinical synergy at or below clinically attainable concentrations.

Methods: We examined cell injury, DNA damage, and apoptosis by XTT, comet assay, and caspase-3 activity in two HGSOC cell lines, CAOV3 and OVCAR8. We examined a dose range based on clinically achievable concentrations of Nav (1-8 μM) and BMN 673 (25-100 nM) and calculated IC50 concentrations for cytotoxicity. 2 μM Nav and 50 nM BMN 673 were selected to examine alone and in combination measures of DNA damage and apoptosis. Controls were cells with no treatment for comet assay, and with DMSO vehicle control for caspase-3 activity. The combination index (CI) was calculated to evaluate synergism. All experiments were performed in at least 3 replicates in all cell lines. Results are presented as mean ± SEM.

Result: Nav yielded cytotoxicity in CAOV3 and OVCAR8 cells with IC50 2.67 μM and 4.39 μM, respectively. BMN 673 100 nM monotherapy yielded up to 40% cell injury in CAOV3 and 20% in OVCAR8 cells. The combination of BMN 673 50 nM and Nav 2 μM resulted in more than 80% and 30% cell injury in CAOV3 and OVCAR8, respectively. The CI indicates there is synergism in cell injury between the two drugs at or below clinically attainable concentrations. BMN 673 alone and with Nav augmented% DNA in tail in an additive fashion, over control or Nav alone in both cell lines. The effect with the combination v. Nav alone was significant in OVCAR8 (12.74% +/- 0.38 v. 9.49% +/- 0.55, p&lt;0.05); the change was not significant in CAOV3. Nav alone caused greater caspase-3 activity than seen in control or BMN 673-treated CAOV3 cells (p&lt;0.05), but the difference was not significant in OVCAR8. No additive caspase-3 activity was seen with the combination. Additional HGSOC cell lines are under evaluation. Annexin V/PI flow cytometric analysis and cell cycle analysis will be used to examine both caspase-dependent and caspase-independent mechanisms of cell death.

Conclusion: Our preliminary results suggest that the combination of PARP inhibition and Bcl2/Bcl-xL neutralization may be cooperative in yielding better results than either drug alone in HGSOC. Further experiments are currently underway to evaluate this novel drug combination.

Citation Format: Takuhei Yokoyama, Nicolas Gordon, Minshu Yu, Elise C. Kohn, Jung-Min Lee. Navitoclax (Nav) and BMN 673 yield cytotoxicity with lower doses than used for single agents in high-grade serous ovarian cancer (HGSOC). [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 5363. doi:10.1158/1538-7445.AM2015-5363