REDD1 is a determinant of the sensitivity of renal cell carcinoma cells to autophagy inhibition that can be therapeutically exploited by targeting PIM kinase activity
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Purpose
Repurposing FDA approved drugs with off-target autophagy inhibition such as chloroquine/hydroxychloroquine (CQ, HCQ) has produced modest anticancer activity in clinical trials, due in part, to a failure to define predictive biomarkers that enable the selection of patients that best respond to this treatment strategy. We identified a new role for REDD1 as a determinant of sensitivity to autophagy inhibition in renal cell carcinoma (RCC).
Experimental Design
RNA sequencing, qRT-PCR, immunoblotting, gene silencing, knockout and overexpression studies revealed that REDD1 expression is a key regulator of cell death stimulated by autophagy inhibitors. Comprehensive in vitro and in vivo studies were conducted to evaluate the selectivity, tolerability, and efficacy of the PIM kinase inhibitor TP-3654 and CQ in preclinical models of renal cell carcinoma (RCC). Markers of autophagy inhibition and cell death were evaluated in tumor specimens.
Results
Transcriptomic analyses identified REDD1 ( DDIT4 ) as a highly induced gene in RCC cells treated with the PIM kinase inhibitor TP-3654. Focused studies confirmed that PIM1 inhibition was sufficient to induce REDD1 and stimulate autophagy through the AMPK cascade. DDIT4 knockout and overexpression studies established its mechanistic role as a regulator of sensitivity to autophagy inhibition. Inhibition of autophagy with CQ synergistically enhanced the i n vitro and in vivo anticancer activity of TP-3654.
Conclusions
Our findings identify REDD1 as a novel determinant of the sensitivity of RCC cells to autophagy inhibition and support further investigation of PIM kinase inhibition as a precision strategy to drive sensitivity to autophagy-targeted therapies through REDD1 upregulation.
Translational Relevance
PIM kinases are overexpressed in renal cell carcinoma (RCC) and other malignancies. Here we show that targeting PIM1 significantly upregulates REDD1/ DDIT4 expression, resulting in inhibition of mTOR and autophagy activation. REDD1 induction was determined to be a major factor that regulates the sensitivity of RCC cells to autophagy inhibition. Comprehensive in vitro and in vivo studies in preclinical models of RCC demonstrated that the PIM kinase inhibitor TP-3654 induced REDD1-mediated autophagy and synergistically sensitized cells to autophagy inhibition. Our findings define a new role for REDD1 as a determinant of the sensitivity of RCC cells to autophagy inhibition and demonstrate that antagonizing PIM kinase activity is a precision approach to augment REDD1 levels and potentiate the therapeutic benefit of targeting the autophagy pathway.
