Abstract 667: Anticancer activity and tumor selectivity of LOR-253, a novel drug candidate, in lung carcinoma

Abstract

Abstract LOR-253 is a novel drug candidate entering a first in man dose escalation Phase I clinical trial in patients with advanced solid tumors. LOR-253 was well tolerated in single and repeat-dose GLP-toxicology studies conducted in rats and dogs at significantly higher doses than equivalent efficacious doses determined in xenograft models in mice, which indicates a potential wide therapeutic window. Previously we reported that LOR-253 reduced the levels of intracellular labile zinc leading to cell cycle arrest, through the down regulation of the metal-responsive transcription factor 1 (MTF-1) and the induction of the Krüppel like factor 4 (KLF4). KLF4 is a G1/S cell cycle checkpoint gene with tumor suppressor function in a variety of cancers. A recent study demonstrated dramatically decreased levels of KLF4 expression in most primary lung tumors (Hu et al. Clin Cancer Res 2009; 15 (18): 5688-95). Anti-tumor activity of KLF4 was demonstrated when KLF4 expression was enforced in cancer cell lines with low basal KLF4 expression levels. In addition, tumor growth in animals was highly compromised when KLF4 gene was stably transfected. The aim of this study was to investigate differential effects of LOR-253 on normal lung fibroblasts vs lung cancer cell lines with different basal levels of KLF4 expression. We found an inverse correlation between LOR-253 sensitivity and basal KLF4 expression. LOR-253 was highly active in three different NSCLC cell lines (H1299, H322 and H226) as shown by much lower IC50 values. KLF4 expression levels in these cell lines were significantly lower than that in normal cells. In contrast, tumor cell lines with KLF4 expression levels similar or higher than normal cells were less sensitive to LOR-253 treatment. Similar results were obtained in in vivo xenograft models, which showed higher in vivo efficacy of LOR-253 in treated mice harboring low basal KLF4-expressing tumors. A time-course gene and protein expression of KLF4 and cyclin D1 in normal lung fibroblast (HFL1) and in NSCLC H226 cells treated with LOR-253 demonstrated a differential effect between normal vs cancer cells. A maximum expression of KLF4 and suppression of cyclin D1 in H226 cells were observed between 16 and 24 hours of treatment while there was no significant effect on HFL1 cells. Based on these results the cell line H226 was selected for further LOR-253 target validation and efficacy biomarker expression studies. A dose-response effect of LOR-253 treatment on tumor growth and KLF4 and cyclin D1 expression was observed in the H226 xenograft model using RT-PCR, Western blot and immunohistochemical analysis. Studies are underway to determine the expression levels of other biomarkers such as MTF-1, HIF-1 a and b-catenin in response to LOR-253 treatment, as well as the effect of in vivo gene knock down and over-expression of MTF-1, KLF4 and other biomarkers on the antitumor activity of LOR-253. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 667. doi:10.1158/1538-7445.AM2011-667