Abstract 751: In vitro activity of dianhydrogalactitol alone or with platinum drugs in the treatment of non-small cell lung cancer

Abstract

Abstract The median overall survival time for patients with stage IV non-small cell lung cancer (NSCLC) is 4 months, and 1- and 5-year survival is less than 16% and 2%, respectively. NSCLC is usually treated with surgery followed by treatment with either Tyrosine Kinase Inhibitors (TKIs) or platinum-based regimens. Unfortunately, TKI resistance has emerged as a significant unmet medical need, and long-term prognosis with platinum-based therapies is poor. Dianhydrogalactitol (VAL-083) is a structurally unique bi-functional alkylating agent mediating interstrand DNA crosslinks at N7 of guanine. It has previously demonstrated activity against NSCLC in preclinical and clinical trials, and is approved for treatment of lung cancer in China, suggesting that it may be a therapeutic option for drug-resistant NSCLC. However, the underlying basis for its activity remains unclear. We thus aimed to investigate in vitro i) the role of p53 status in the activity of VAL-083, ii) VAL-083 activity in comparison to cisplatin and oxaliplatin, and iii) the combination of VAL-083 with cisplatin or oxaliplatin. The dependence on p53 status was investigated in isogenic models with (HCT-116p53-/-) or without (HCT-116p53+/+) p53 knockout. The cytotoxic activity of VAL-083 was tested in a panel of 9 human NSCLC cell lines, of which 4 were wild-type (wt) p53, 4 were mutant p53 and 1 was null for p53. The potential for combination was investigated by determining superadditivity and assessing synergy using the criteria of combination index (CI) of <1, obtained by following the Compusyn constant-dose ratio protocol. Cytotoxicty in all cases was monitored on day 5 with the MTT assay. Studies in HCT-116 models demonstrated that loss of p53 increased resistance to cisplatin and oxaliplatin by 3- and 6-fold, respectively, whereas resistance to VAL-083 was <2-fold. As single agents, VAL-083, cisplatin and oxaliplatin displayed cytotoxic activity in all 9 NSCLC cell lines to varying degrees, with H460 being the most sensitive to the three agents (IC50 < 0.5 uM). The IC50 in the other cell lines ranged from 0.9 to 6.1 μM, 0.5 to 2.2 μM and 0.6 to 2.6 μM for VAL-083, cisplatin and oxaliplatin, respectively, and there was no overt difference in drug sensitivity between the wt and mutant/null p53 group. This suggests that either wt p53 is not activated and/or other genetic alterations attenuate cytotoxic activities. If the agents have similar mode of action, then combinations may only demonstrate cytotoxic additivity. However, the combination of VAL-083 with cisplatin or oxaliplatin in the A549 NSCLC model, demonstrated significant superadditivity (p<0.05) and synergism (CI < 1) for both combinations. This strongly favors non-overlapping mechanism of action between the platinum drugs and VAL-083. In conclusion, VAL-083 is less dependent on p53 for its activity, and demonstrates superadditivity/synergy against NSCLC cells when combined with either cisplatin or oxaliplatin. Citation Format: Anne Steino, Guangan He, Jeffrey A. Bacha, Sarath Kanekal, Dennis M. Brown, Zahid H. Siddik. In vitro activity of dianhydrogalactitol alone or with platinum drugs in the treatment of non-small cell lung cancer. [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 751. doi:10.1158/1538-7445.AM2015-751