Proline Dehydrogenase as a player in acquired resistance to Tyrosine Kinase Inhibitors

Lung cancer is one of the biggest killers among tumors. Lung adenocarcinoma (LUAD) is the prevalent subtype and is characterized by recurrent molecular alterations, including EGFR mutations. This makes possible targeted therapy with Tyrosine-Kinases Inhibitors (TKIs). Invariably, the onset of resistance leads to cancer progression. Prognostic and predictive biomarkers would be beneficial to identify in advance patients outcome and response to therapy. Proline dehydrogenase (PRODH) is a mitochondrial flavoenzyme, catalyzing proline oxidation. Its activity influences biological processes like senescence, apoptosis, and cell survival via ROS or ATP production. Elevated PRODH expression was observed in LUAD clinical samples, but not in LUAD cell lines. However, we found that PRODH expression was increased in EGFR mutant lung cell lines with in vitro acquired resistance to TKIs. We hypothesized that PRODH may be involved in this process, influencing metastasizing ability and survival of lung cancer cells, and the tumor microenvironment. Moreover, we aimed to test if mutant EGFR or activation of its downstream signaling pathways could modulate PRODH expression. PC9 and HCC827 cell lines, both harboring EGFR exon 19 deletion, and their derivatives PC9-OR and HCC827-GR5, with in vitro acquired resistance to Osimertinib or Gefitinib, respectively, were used to investigate the role of PRODH in the onset of TKIs resistance. PRODH was silenced or inhibited to study its role in cell survival and migration ability in PC9-OR and HCC827 GR5. Transfection experiments with EGFR or STAT3 expression constructs were used to investigate direct regulation of PRODH expression. Secretome analyses were performed. PRODH transcript and protein expression was increased in EGFR-mutant LUAD cell lines with in vitro acquired resistance to TKIs. The increase in transcript was not observed upon ectopic expression of EGFR activating mutations or constitutively active STAT3C. Secretome analyses showed that PRODH ectopic expression increased the levels of several cytokines involved in macrophage recruitment and polarization, and in angiogenesis. Ongoing PRODH inhibition or silencing experiments will clarify its contribution to the different phenotypes of TKI-resistant cells. Although preliminary, our results suggest that PRODH may play a role in acquired resistance to TKI and that it may be used as a prognostic and/or predictive biomarker during therapy in TKI-resistant LUAD.