BV6

BV6 is a selective inhibitor of IAP family with IC50 value of 7.2 μM when tested with H460 cells [1].
IAP (inhibitor of apoptosis) is a family protein consists of 8 members and serves as endogenous inhibitors of programmed cell death. Until now, more than 5 human IAPs have been discovered includes XIAP, c-IAP1, c-IAP-2, NAIP, Livin and Survivin. It is reported that IAPs overexpression protects cells against a number of proapoptotic stimuli which enables IAPs play a pivotal role in promoting cancer cell survival [2, 3].
BV6 is an inhibitor of IAP family and often used as an adjuvant to sensitize the cancer cells to radiotherapy or chemotherapy. When tested with H460 NSCLC cells, pre-treatment BV6 sensitized the cells to radiation and increased the apoptosis in a time- and dose- dependent manner via reducing the expression of cIAP1 and XIAP [1]. In hematological THP-1 cells, pre-treatment with BV6 increased the CIK cells killing ability and the same results were achieved in solid malignancy RH30 cells [4]
In BALB/c mice model with transplanted abdominal cavities from donor mouse uterine tissue, intraperitoneally with BV6 repressed the advancement of endometriosis, cell proliferative activity via inhibiting the expression of IAPs [5].
References:
[1].    Li, W., et al., BV6, an IAP antagonist, activates apoptosis and enhances radiosensitization of non-small cell lung carcinoma in vitro. J Thorac Oncol, 2011. 6(11): p. 1801-9.
[2].    Altieri, D.C., Survivin - The inconvenient IAP. Semin Cell Dev Biol, 2015.
[3].    Fulda, S., Smac mimetics as IAP antagonists. Semin Cell Dev Biol, 2014.
[4].    Rettinger, E., et al., SMAC Mimetic BV6 Enables Sensitization of Resistant Tumor Cells but also Affects Cytokine-Induced Killer (CIK) Cells: A Potential Challenge for Combination Therapy. Front Pediatr, 2014. 2: p. 75.
[5].    Uegaki, T., et al., Inhibitor of apoptosis proteins (IAPs) may be effective therapeutic targets for treating endometriosis. Hum Reprod, 2015. 30(1): p. 149-58.

The SMAC mimetic BV6 sensitizes colorectal cancer cells to ionizing radiation by interfering with DNA repair processes and enhancing apoptosis.[Pubmed:26383618]

Radiat Oncol. 2015 Sep 17;10:198.

BACKGROUND: In the present study, we aimed to investigate the effect of counteracting inhibitor of apoptosis (IAP) proteins using the small molecule Second Mitochondria-derived Activator of Caspase (SMAC) mimetic BV6 in combination with ionizing radiation on apoptosis, cell cycle regulation, DNA double-strand break (DSB) repair, three-dimensional (3D) clonogenic survival and expression of IAPs in colorectal carcinoma cells. MATERIAL AND METHODS: Colorectal cancer cell lines (HCT-15, HT-29, SW480) were subjected to BV6 treatment (0-4 muM) with or without irradiation (2-8 Gy, single dose) followed by MTT, Caspase 3/7 activity, gammaH2AX/53BP1 foci assays, AnnexinV staining, cell cycle analysis, 3D colony forming assays and Western blotting (cellular IAP1 (cIAP1) and cIAP2, Survivin, X-linked IAP (XIAP)). RESULTS: BV6 treatment decreased cell viability and significantly increased irradiation-induced apoptosis as analyzed by Caspase 3/7 activity, AnnexinV-positive and subG1 phase cells. While basal 3D clonogenic survival was decreased in a cell line-dependent manner, BV6 significantly enhanced cellular radiosensitivity of all cell lines in a concentration-dependent manner and increased the number of radiation-induced gammaH2AX/53BP1-positive foci. Western blot analysis revealed a markedly reduced cIAP1 expression at 4 h after BV6 treatment in all cell lines, a substantial reduction of XIAP expression in SW480 and HT-29 cells at 24 h and a slightly decreased cIAP2 expression in HCT-15 cells at 48 h after treatment. Moreover, single or double knockdown of cIAP1 and XIAP resulted in significantly increased residual gammaH2AX/53BP1-positive foci 24 h after 2 Gy and radiosensitization relative to control small interfering RNA (siRNA)-treated cells. CONCLUSION: The SMAC mimetic BV6 induced apoptosis and hampered DNA damage repair to radiosensitize 3D grown colorectal cancer cells. Our results demonstrate IAP targeting as a promising strategy to counteract radiation resistance of colorectal cancer cells.

The SMAC mimetic BV6 induces cell death and sensitizes different cell lines to TNF-alpha and TRAIL-induced apoptosis.[Pubmed:27465142]

Exp Biol Med (Maywood). 2016 Dec;241(18):2015-2022.

The inhibitors of apoptosis proteins are implicated in promoting cancer cells survival and resistance toward immune surveillance and chemotherapy. Second mitochondria-derived activator of caspases (SMAC) mimetics are novel compounds developed to mimic the inhibitory effect of the endogenous SMAC/DIABLO on these IAPs. Here, we examined the potential effects of the novel SMAC mimetic BV6 on different human cancer cell lines. Our results indicated that BV6 was able to induce cell death in different human cancer cell lines. Mechanistically, BV6 dose dependently induced degradation of IAPs, including cIAP1 and cIAP2. This was coincided with activating the non-canonical NF -kappa B (NF-kappaB) pathway, as indicated by stabilizing NF-kappaB-inducing kinase (NIK) for p100 processing to p52. More interestingly, BV6 was able to sensitize some of the resistant cancer cell lines to apoptosis induced by the death ligands tumor necrosis factor-alpha (TNF-alpha) and TNF-related apoptosis-inducing ligand (TRAIL) that are produced by different cells of the immune system. Such cell death enhancement was mediated by inducing an additional cleavage of caspase-9 to augment that of caspase-8 induced by death ligands. This eventually led to more processing of the executioner caspase-3 and poly (ADP-ribose) polymerase (PARP). In conclusion, therapeutic targeting of IAPs by BV6 might be an effective approach to enhance cancer regression induced by immune system. Our data also open up the future possibility of using BV6 in combination with other antitumor therapies to overcome cancer drug resistance.

The Smac Mimetic BV6 Improves NK Cell-Mediated Killing of Rhabdomyosarcoma Cells by Simultaneously Targeting Tumor and Effector Cells.[Pubmed:28326081]

Front Immunol. 2017 Mar 7;8:202.

Rhabdomyosarcoma (RMS), the most common cancer of connective tissues in pediatrics, is often resistant to conventional therapies. One underlying mechanism of this resistance is the overexpression of Inhibitor of Apoptosis (IAP) proteins, leading to a dysfunctional cell death program within tumor cells. Smac mimetics (SM) are small molecules that can reactivate the cell death program by antagonizing IAP proteins and thereby compensating their overexpression. Here, we report that SM sensitize two RMS cell lines (RD and RH30) toward natural killer (NK) cell-mediated killing on the one hand, and increase the cytotoxic potential of NK cells on the other. The SM-induced sensitization of RH30 cells toward NK cell-mediated killing is significantly reduced through blocking tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) on NK cells prior to coculture. In addition, the presence of zVAD.fmk, a pancaspase inhibitor, rescues tumor cells from the increase in killing, indicating an apoptosis-dependent cell death. On the NK cell side, the presence of SM in addition to IL-2 during the ex vivo expansion leads to an increase in their cytotoxic activity against RH30 cells. This effect is mainly TNFalpha-dependent and partially mediated by NK cell activation, which is associated with transcriptional upregulation of NF-kappaB target genes such as IkappaBalpha and RelB. Taken together, our findings implicate that SM represent a novel double-hit strategy, sensitizing tumor and activating NK cells with one single drug.

SMAC Mimetic BV6 Enables Sensitization of Resistant Tumor Cells but also Affects Cytokine-Induced Killer (CIK) Cells: A Potential Challenge for Combination Therapy.[Pubmed:25101252]

Front Pediatr. 2014 Jul 18;2:75.

Allogeneic hematopoietic stem cell transplantation (HSCT) is an established treatment option for high-risk hematological malignancies, and may also be offered to patients with solid malignancies refractory to conventional therapies. In case of patients' relapse, refractory tumor cells may then be targeted by cellular therapy-based combination strategies. Here, we investigated the potential of small molecule IAP (SMAC mimetic) BV6 in increasing cytokine-induced killer (CIK) cell-mediated cytotoxicity against different tumor targets. Four-hour pre-incubation with 2.5 muMol BV6 moderately enhanced CIK cell-mediated lysis of hematological (H9, THP-1, and Tanoue) and solid malignancies (RH1, RH30, and TE671). However, BV6 also increased apoptosis of non-malignant cells like peripheral blood mononuclear cells and most notably had an inhibitory effect on immune cells potentially limiting their cytotoxic potential. Hence, cytotoxicity increased in a dose-dependent manner when BV6 was removed before CIK cells were added to tumor targets. However, cytotoxic potential was not further increasable by extending BV6 pre-incubation period of target cells from 4 to 12 h. Molecular studies revealed that BV6 sensitization of target cells involved activation of caspases. Here, we provide evidence that SMAC mimetic may sensitize targets cells for CIK cell-induced cell death. However, BV6 also increased apoptosis of non-malignant cells like CIK cells and peripheral mononuclear cells. These findings may therefore be important for cell- and small molecule IAP-based combination therapies of resistant cancers after allogeneic HSCT.