Hydroxychloroquine Sensitivity in Human and Canine Cancer Cell Line Panels Reveals Potential Genetic Signatures of Autophagy‐Dependence and Druggable Targets
Authors: Jackon Kristen M , Conger Katherine A , Gustafson Daniel L 
Published: June 2021

BackgroundAutophagy is a lysosomal degradation pathway cells use to survive in stressed environments and has been implicated as a mechanism in cancer chemotherapy resistance. Hydroxychloroquine (HCQ) is an established autophagy inhibitor that is safe and well tolerated in humans. Subsets of cancers have also been found to be dependent on autophagy as a main means of survival even in optimal environmental conditions, and these autophagy‐dependent cancers respond favorably to autophagy inhibition alone or with combination treatments. Since subsets of the same cancer‐type are autophagy‐dependent and others are not, it is critical to understand which tumors will benefit most from autophagy inhibition in the clinic. Analyzing a large set of cell line drug responses can be beneficial in determining which tumor types will benefit from treatment with that drug or drugs with similar mechanisms of action. Further, since human and canine cancers have many commonalities including genetic similarities, comparisons between both species are important for providing new insights to cancer treatments across the oncology field. Multiple cell line data sets exist with publicly available data. The NCI60 is a panel of 60 human lines including breast, colon, lung, melanoma, ovarian, renal, prostate, leukemia, and central nervous system cancers. The Flint Animal Cancer Center (FACC) at Colorado State University has a panel of 36 canine lines with tumor types including osteosarcoma, transitional bladder cell carcinoma, melanoma, leukemia/lymphoma, mast cell, hemangiosarcoma, histiocytic sarcoma, mammary carcinoma, a soft tissue sarcoma, and a thyroid carcinoma.MethodsResponse of the canine FACC cell lines to HCQ was assessed by monitoring growth of fluorescently labeled cells. HCQ data for the human lines was obtained from the NCI60 website. A differential gene expression analysis was completed to determine genes most significantly correlated with HCQ sensitivity.ResultsHCQ Dm values (median dose of drug at which half of the cells are affected) at 96 hr in the canine cell lines ranged widely from less than 2 μM to almost 40 μM. Compared to the human cell lines whose data was collected at 48 hr using a 10 μM dose, canine cell lines appear to be more sensitive overall. However, when directly comparing just the human and canine osteosarcoma cell lines at 96 hr post treatment, they have similar differential HCQ sensitivities between the least and most affected cell lines, indicating that HCQ may have the same affect in other cancer types if the data is analyzed four days following drug dosing instead of just two days like the NCI60 data.ConclusionsThis analysis provides potential to produce a gene signature for tumors that respond favorably to HCQ treatment and may infer which tumors are more autophagy‐dependent and therefore will benefit from autophagy inhibition clinically. It also gives potential druggable gene targets for those tumors that will not benefit from autophagy inhibition (the HCQ‐resistant lines) based on which genes are upregulated in that group of tumors.Support or Funding InformationNCI R01CA190170This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.