Pim inhibition leads to MM cell proliferation inhibition and represses mTOR-C1 signaling. (A) Pim inhibition leads to reduced MM cell growth. KMS-11.luc, KMS-26, KMS-34, and H929 cells were treated with increasing doses of selective Pim kinase inhibitor LGB321 for 3 days. Cell growth was measured by CTG assay. (B) Pim inhibition does not affect apoptosis. KMS-11 and KMS-26 cells were treated with increasing doses of LGB321 (0, 0.03, 0.1, 0.33, 1.0 μM) for 2 days (12-hour treatment with staurosporine as positive control), PARP cleavage was examined by immunoblotting. (C) Pim inhibition leads to a severe decrease of mTOR-C1 pathway activity. KMS-11 and KMS-26 cells were treated with increasing doses of LGB321 (0, 0.03, 0.1, 0.33, 1.0 μM) for 2 hours; mTOR-C1 pathway activity was examined by the level of p-P70S6K (T389) and p-S6RP (S235/S236) through immunoblotting. (D) Pim2 knockdown by shRNAs leads to inhibition of mTOR-C1 pathway. Pim2-specific shRNAs were delivered into KMS-11, KMS-26, KMS-34, and H929 cells through lentiviral infection. At 48 hours post infection, lysates were examined for Pim2 knockdown and p-S6RP (S235/S236) by immunoblotting.