Preclinical Development Autophagy Inhibition Synergistically Enhances Anticancer Efficacy of RAMBA, VN/12-1 in SKBR-3 Cells, and Tumor Xenografts

VN/12-1 is a novel retinoic acidmetabolism blocking agent discovered in our laboratory. The purpose of the studywas to elucidate themolecularmechanismof anticancer activity ofVN/12-1 inbreast cancer cell lines and in tumor xenografts.We investigated the effects of VN/12-1 on induction of autophagy and apoptosis in SKBR3 cells. Furthermore, we also examined the impact of pharmacologic and genomic inhibition of autophagy on anticancer activity of VN/12-1. Finally, the antitumor activity of VN/12-1 was evaluated as a single agent and in combinationwith autophagy inhibitor chloroquine in an SKBR-3mouse xenograft model. Short exposure of low dose (<10 mmol/L) of VN/12-1 induced endoplasmic reticulum stress, autophagy, and inhibited G1–S phase transition and caused a protective response. However, a higher dose of VN/12-1 initiated apoptosis in vitro. Inhibition of autophagy using either pharmacologic inhibitors or RNA interference of Beclin-1 enhanced anticancer activity induced by VN/12-1 in SKBR-3 cells by triggering apoptosis. Importantly, VN/12-1 (5 mg/kg twice weekly) and the combination of VN/12-1 (5 mg/kg twice weekly) þ chloroquine (50 mg/kg twice weekly) significantly suppressed established SKBR-3 tumor growth by 81.4% (P < 0.001 vs. control) and 96.2% (P < 0.001 vs. control), respectively. Our novel findings suggest that VN/12-1may be useful as a single agent or in combination with autophagy inhibitors for treating human breast cancers. Our data provides a strong rationale for clinical evaluation of VN/12-1 as single agent or in combination with autophagy inhibitors. Mol Cancer Ther; 11(4); 898–908. 2012 AACR.