Abstract Background: PIM2 is overexpressed in hematopoietic and solid cancers, and is involved in multiple signaling pathways. In hematologic malignancies, PIM2 has been shown to be a pro-survival factor and demonstrated to be a possible therapeutic target. However, the role of PIM2 as a therapeutic target in solid cancers has not been fully elucidated. Methods: PIM2 expression was compared between normal and cancer tissues in The Cancer Genome Atlas (TCGA) datasets. Pan-PIM inhibitor treatment, as well as PIM2 overexpression/knockdown technique was utilized to investigate the PIM2 role in solid cancers. Multiple cancer models were utilized for in vitro and in vivo experiments to investigate if PIM2 as a therapeutic target and examine mechanism of anti-tumor activity by JP11646. Results: PIM2 was overexpressed in several types of cancer tissues, including breast, esophageal, head-neck, kidney, liver and endometrial cancers in TCGA. PIM2 overexpression promoted tumor growth in in vivo breast cancer mouse model. PIM2 inhibition by siRNA as well as pan-PIM inhibitor JP11646 activated apoptosis as seen by increased cleaved PARP. JP11646 treatment inhibited cancer cell proliferation in a dose-dependent manner in vitro in various types of solid cancers, including head-neck, ovarian, breast, prostate, liver, pancreatic, colorectal and non-small cell lung cancers. Interestingly, treatment with pan-PIM inhibitor JP11646 resulted in selective downregulation of PIM2 protein expression, but not PIM1 or PIM3 in breast cancer cell lines, BT549 and MDA-MB-231. The treatment also resulted in downregulation of phosphorylated downstream targets, 4EBP1 and TSC2 in breast cancer cells. However, additional proteasome inhibitor treatment blocked PIM2 downregulation and apoptosis activation was not seen. The result suggests that proteasome complex is required for PIM2 degradation which is necessary to induce apoptosis. JP11646 treatment inhibited tumor growth in breast, liver, pancreas, and non-small cell lung cancer in vivo xenograft models and was compared to multiple standard of care treatments showing advantage in lung tumors. Conclusion: We found that PIM2 promoted cancer progression in solid tumors. We show novel mechanism of JP11646 targeting PIM2 for degradation and induction of apoptosis. We show that PIM2 may serve as a novel therapeutic target for multiple types of solid cancers with enhanced therapeutic effect through protein degradation rather than kinase inhibition alone. Citation Format: Eriko Katsuta, Kazuaki Takabe, Alex Adjei, Mateusz Opyrchal. Novel mechanism of PIM2 inhibition leads to significant effect on solid tumors [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 6426.
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