Combining APR-246 and HDAC-Inhibitors: A Novel Targeted Treatment Option for Neuroblastoma

SIMPLE SUMMARY: Preclinical analyses identified APR-246 as a potent treatment option for neuroblastoma. However, a specific mode of action, sufficient biomarkers and promising combination partners are still missing. Here, we analyze the susceptibilities of different entities and relate them to gene expression profiles and previously described biomarkers. We propose a gene signature, consisting of 13 genes, as a novel predictive biomarker. Furthermore, we provide evidence that APR-246 directly targets metabolic weaknesses in neuroblastoma cell lines, thus hampering ROS detoxification. This makes APR-246 suitable to be combined with ROS-inducing HDAC inhibitors, a treatment combination that has not been described for neuroblastoma thus far. ABSTRACT: APR-246 (Eprenetapopt/PRIMA-1(Met)) is a very potent anti-cancer drug in clinical trials and was initially developed as a p53 refolding agent. As an alternative mode of action, the elevation of reactive oxygen species (ROS) has been proposed. Through an in silico analysis, we investigated the responses of approximately 800 cancer cell lines (50 entities; Cancer Therapeutics Response Portal, CTRP) to APR-246 treatment. In particular, neuroblastoma, lymphoma and acute lymphocytic leukemia cells were highly responsive. With gene expression data from the Cancer Cell Line Encyclopedia (CCLE; n = 883) and patient samples (n = 1643) from the INFORM registry study, we confirmed that these entities express low levels of SLC7A11, a previously described predictive biomarker for APR-246 responsiveness. Combining the CTRP drug response data with the respective CCLE gene expression profiles, we defined a novel gene signature, predicting the effectiveness of APR-246 treatment with a sensitivity of 90% and a specificity of 94%. We confirmed the predicted APR-246 sensitivity in 8/10 cell lines and in ex vivo cultures of patient samples. Moreover, the combination of ROS detoxification-impeding APR-246 with approved HDAC-inhibitors, known to elevate ROS, substantially increased APR-246 sensitivity in cell cultures and in vivo in two zebrafish neuroblastoma xenograft models. These data provide evidence that APR-246, in combination with HDAC-inhibitors, displays a novel potent targeted treatment option for neuroblastoma patients.