PBOX-15, a novel microtubule targeting agent, induces apoptosis, upregulates death receptors, and potentiates TRAIL-mediated apoptosis in multiple myeloma cells

Abstract

Background:In recent years, much progress has been made in the treatment of multiple myeloma. However, a major limitation of existing chemotherapeutic drugs is the eventual emergence of resistance; hence, the development of novel agents with new mechanisms of action is pertinent. Here, we describe the activity and mechanism of action of pyrrolo-1,5-benzoxazepine-15 (PBOX-15), a novel microtubule-targeting agent, in multiple myeloma cells.Methods:The anti-myeloma activity of PBOX-15 was assessed using NCI-H929, KMS11, RPMI8226, and U266 cell lines, and primary myeloma cells. Cell cycle distribution, apoptosis, cytochrome c release, and mitochondrial inner membrane depolarisation were analysed by flow cytometry; gene expression analysis was carried out using TaqMan Low Density Arrays; and expression of caspase-8 and Bcl-2 family of proteins was assessed by western blot analysis.Results:Pyrrolo-1,5-benzoxazepine-15 induced apoptosis in ex vivo myeloma cells and in myeloma cell lines. Death receptor genes were upregulated in both NCI-H929 and U266 cell lines, which displayed the highest and lowest apoptotic responses, respectively, following treatment with PBOX-15. The largest increase was detected for the death receptor 5 (DR5) gene, and cotreatment of both cell lines with tumour necrosis factor-related apoptosis-inducing ligand (TRAIL), the DR5 ligand, potentiated the apoptotic response. In NCI-H929 cells, PBOX-15-induced apoptosis was shown to be caspase-8 dependent, with independent activation of extrinsic and intrinsic apoptotic pathways. A caspase-8-dependent decrease in expression of BimEL preceded downregulation of other Bcl-2 proteins (Bid, Bcl-2, Mcl-1) in PBOX-15-treated NCI-H929 cells.Conclusion:PBOX-15 induces apoptosis and potentiates TRAIL-induced cell death in multiple myeloma cells. Thus, PBOX-15 represents a promising agent, with a distinct mechanism of action, for the treatment of this malignancy.

The microtubule targeting agent PBOX-15 inhibits integrin-mediated cell adhesion and induces apoptosis in acute lymphoblastic leukaemia cells

“…Here, we show anti-cancer activity of a novel MTA compound, PBOX-15, in cell line models representing poor prognostic subgroups of ALL: relapsed childhood T-ALL (CCRF-CEM) and BCR-ABL positive adult B-ALL (SD-1). Similar to our previous studies on the effect of PBOX-15 on other cancer cell types (5,6,10), we showed that PBOX-15-induced G2/M cell cycle arrest and growth inhibition was associated with the induction of apoptosis in B-ALL and T-ALL cells. A pan-caspase pharmacological inhibitor inhibited PBOX-15-induced apoptosis in both T-ALL and B-ALL cells, while caspase-3 and 8 pharmacological inhibitors inhibited apoptosis in T-ALL cells.…”

“…A pan-caspase pharmacological inhibitor inhibited PBOX-15-induced apoptosis in both T-ALL and B-ALL cells, while caspase-3 and 8 pharmacological inhibitors inhibited apoptosis in T-ALL cells. We have recently shown caspase-8-dependent PBOX-15-induced apoptosis in CLL and myeloma cells using a pharmacological inhibitor and siRNA knockdown of caspase-8 expression (7,10). However, caspase inhibitors only partially inhibited PBOX-15-induced apoptosis suggesting that caspase-independent mechanisms are also involved in PBOX-15-induced apoptosis in ALL cells (33).…”

“…We have previously described a novel MTA, pyrrolo-1,5-benzoxazepine-15 (PBOX-15), which exhibits anticancer activity against a variety of human tumour cell types, including those derived from both solid and haematological malignancies (5)(6)(7)(8)(9)(10). Importantly, PBOX-15 and other related PBOX compounds display minimal toxicity against normal human blood and bone marrow cells, and are well tolerated by both tumour-bearing and healthy mice (7,11).…”

Role of Bim in apoptosis induced in H460 lung tumor cells by the spindle poison Combretastatin-A4

“…On the other side, the role of Bim in apoptosis engaged by agents known to affect the microtubular integrity, as the spindle poisons, has been only poorly investigated so far, except for microtubular-stabilising agents as taxanes [26,27], persins [30] and for PBOX-15, a novel microtubule targeting agent [31]. Both Bim-dependent apoptosis in lymphocytes [32], non-small-cell lung cancer lines [26], kidney epithelial cells [33], and Bim-independent apoptosis in HeLa and breast cancer cells [27] have been reported, so suggesting cell specificity in paclitaxel-induced cell death.…”

Antitumor effect of pyrrolo-1,5-benzoxazepine-15 and its synergistic effect with Oxaliplatin and 5-FU in colorectal cancer cells

“…19,30,31 Therefore, it seemed interesting to assess whether, at doses lower than those used in the assessment of cell proliferation, PBOX-15 is able to improve the sensitivity to treatment with oxaliplatin or with 5-FU. Oxaliplatin in combination with 5-Fluorouracil and leucovorin (FOLFOX) has been approved for metastatic CRC therapy.…”