We report on the design and synthesis of a green-emitting iridium complex–peptide hybrid (IPH) 4, which has an electron-donating hydroxyacetic acid (glycolic acid) moiety between the Ir core and the peptide part. It was found that 4 is selectively cytotoxic against cancer cells, and the dead cells showed a green emission. Mechanistic studies of cell death indicate that 4 induces a paraptosis-like cell death through the increase in mitochondrial Ca2+ concentrations via direct Ca2+ transfer from ER to mitochondria, the loss of mitochondrial membrane potential (ΔΨm), and the vacuolization of cytoplasm and intracellular organelle. Although typical paraptosis and/or autophagy markers were upregulated by 4 through the mitogen-activated protein kinase (MAPK) signaling pathway, as confirmed by Western blot analysis, autophagy is not the main pathway in 4-induced cell death. The degradation of actin, which consists of a cytoskeleton, is also induced by high concentrations of Ca2+, as evidenced by costaining experiments using a specific probe. These results will be presented and discussed.

Cholangiocarcinoma (CCC) is a strongly aggressive malignancy for which surgical resection is the only potential curative therapy. Sorafenib, a multikinase inhibitor of the RAF/MEK/ERK pathway, is a molecular-targeted drug that is approved for hepatocellular carcinoma (HCC) but not for CCC. The differences in signaling pathway characteristics under sorafenib treatment between HCC (HLF, Huh7, PLC/PRF/5) and CCC (RBE, YSCCC, Huh28) cell lines were therefore investigated using cell proliferation, western blotting, and apoptosis analyses. Sorafenib inhibited cell growth significantly less in CCC cells than in HCC cells, with lower suppression of ERK phosphorylation. Significantly decreased AKT Ser473 phosphorylation in HCC cells, and conversely enhanced phosphorylation of AKT Ser473 and mTORC2 in CCC cells, were observed with sorafenib treatment. Disassembly of the mTORC2 complex in RBE cells with siRNA targeting Rictor resulted in the downregulation of AKT Ser473 phosphorylation and enhanced apoptosis presumably via increased FOXO1, which consequently suppressed RBE cell proliferation. Phosphorylation of mTORC1 and autophagy were not influenced by sorafenib in CCC cells. Simultaneous administration of everolimus to suppress activated mTORC1 in RBE cells revealed that combined everolimus and sorafenib treatment under mTORC2 disassembly could enhance growth inhibition through the suppression of both sorafenib- and everolimus-dependent AKT Ser473 phosphorylation in addition to the inhibition of mTORC1 phosphorylation. Prevention of escape by AKT/mTOR signaling from the RAF/MEK/ERK pathway in sorafenib treatment by suppressing mTORC2 activity may lead to promising new approaches in CCC therapy.

Abstract:We previously reported the design and synthesis of amphiphilic Ir complex-cationic peptide hybrids (2a-2f ), which contain basic peptide sequences such as KKGG (K = lysine, G = glycine) at the 5′-positions (para position with respect to the C-Ir bond) of three 2-(4′-tolyl)pyridine (tpy) ligands. Among them, 2c-2e induced the necrosis-like cell death of Jurkat cells through a calcium-dependent pathway, possibly involving a Ca 2+ -calmodulin (CaM) complex. Herein, we report the synthesis of amphiphilic Ir(ppy) 3 complexes (ppy = 2-phenylpyridine) containing the KKGG sequence at the 4′-position of the ppy moiety (4a-4d) to examine the effect of the position of the cationic peptide sequence on the cytotoxicities of the com-

Cyclometalated iridium (Ir) complexes having Ir(tpy)3 (tpy=2‐(4’‐tolyl)pyridine) scaffold exhibit promising potential for the diagnosis of cancer, as phosphorescent probes for cellular imaging and in the treatment of cancer, due to their high stability, tunable photophysical properties, and biological activities. We previously reported on the synthesis of some cationic amphiphilic Ir(III) complex‐peptide hybrids (IPHs) such as 2 and 3 that contain KK(K)GG peptide units (K: lysine, G: glycine) that are attached via alkyl chain (C2∼C16) linkers and induce paraptosis‐like cell death in Jurkat (T‐lymphocyte leukemia) cancer cells through multiple cell death pathways. Herein, we report on the design and synthesis of two IPHs, 4 and 5, which possess two and one KKKGG sequences, respectively, and an examination of the effect of the number of peptide units on their anticancer activity. Our evaluations of the anticancer properties of 3–5 suggested that 3 and 4 are more cytotoxic than 5 against Jurkat cells, indicating a positive relationship between the number of H2N‐KKKGG units in 3–5 and their anticancer activity. In addition, a parallel relationship was observed between the cytotoxicity of 3–5 and Ca2+ overload in mitochondria, suggesting the direct transfer of Ca2+ from the endoplasmic reticulum to mitochondria.

In our previous paper, we reported that amphiphilic Ir complex–peptide hybrids (IPHs) containing basic peptides such as KK(K)GG (K: lysine, G: glycine) (e.g., ASb-2) exhibited potent anticancer activity against Jurkat cells, with the dead cells showing a strong green emission. Our initial mechanistic studies of this cell death suggest that IPHs would bind to the calcium (Ca2+)–calmodulin (CaM) complex and induce an overload of intracellular Ca2+, resulting in the induction of non-apoptotic programmed cell death. In this work, we conduct a detailed mechanistic study of cell death induced by ASb-2, a typical example of IPHs, and describe how ASb-2 induces paraptotic programmed cell death in a manner similar to that of celastrol, a naturally occurring triterpenoid that is known to function as a paraptosis inducer in cancer cells. It is suggested that ASb-2 (50 µM) induces ER stress and decreases the mitochondrial membrane potential (ΔΨm), thus triggering intracellular signaling pathways and resulting in cytoplasmic vacuolization in Jurkat cells (which is a typical phenomenon of paraptosis), while the change in ΔΨm values is negligibly induced by celastrol and curcumin. Other experimental data imply that both ASb-2 and celastrol induce paraptotic cell death in Jurkat cells, but this induction occurs via different signaling pathways.