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

Abstract

Abstract. Although recent decades have seen an improved cure rate for newly diagnosed paediatric acute lymphoplastic leukaemia (ALL), the treatment options for adult ALL, T-cell ALL (T-ALL) and relapsed disease remain poor. We have developed a novel series of pyrrolo-1,5-benzoxazepine (PBOX) compounds and established their anticancer efficacy in a variety of human tumour cell types. Here, we demonstrate that PBOX-15 inhibits cell growth, and induces G2/M cell cycle arrest and apoptosis in both T-ALL and B-cell ALL (B-ALL) cells. In addition, prior to PBOX-15-induced apoptosis, PBOX-15 decreases ALL cell adhesion, spreading and migration. Concurrently, PBOX-15 differentially down-regulates β1-, β2-and α4-integrin expression in ALL cells and significantly decreases integrin-mediated cell attachment. PBOX-15 interferes with the lateral mobility and clustering of integrins in both B-ALL and T-ALL cells. These data suggest that PBOX-15 is not only effective in inducing apoptosis in ALL cells, but also has the potential to disrupt integrin-mediated adhesion of malignant lymphocytes, which represents a novel avenue for regulating leukaemic cell homing and migration. IntroductionAcute lymphoblastic leukaemia (ALL) refers to a group of malignancies arising from lymphoid progenitors that may be of B-or T-cell lineage (B-ALL or T-ALL), resulting in proliferation and expansion of lymphoid blasts in bone marrow, blood and other organs. ALL has an overall incidence of 1-1.5 per 100,000 individuals and exhibits a bimodal age distribution with an early peak between ages 2-5 years (4-5 per 100,000 individuals, accounting for 80% of all childhood leukaemia), followed by a second peak after the age of 50 years (1). The treatment of ALL involves complex therapeutic programmes using intensive combination chemotherapy in dose-and timespecific sequences resulting in survival rates greater than 80% in children (2). However, there is a need for novel treatment options as only 30-40% of adults achieve long-term diseasefree survival and both childhood T-ALL and relapsed ALL are associated with poor clinical outcome (3,4).Microtubule targeting agents (MTAs) have been shown to be effective against ALL cells and vincristine is a key component of induction, consolidation and maintenance treatment protocols (3). 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 (5-10). 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).MTA's interference with tubulin dynamics during mitotic spindle formation is well established; however, due to the critical role of microtubules in cell motility and homeostasis, the activity of MTAs may extend beyond inhibition of cytokinesis and subsequent induction of apoptosis. For example, we have...

The microtubule depolymerizing agent CYT997 effectively kills acute myeloid leukemia cells via activation of caspases and inhibition of PI3K/Akt/mTOR pathway proteins

“…When utilized as anticancer agents, MTAs generally cause cell cycle arrest and apoptosis, as a consequence of caspase activation through the intrinsic apoptotic pathway. Similar effects have been observed in leukemia cells; certain MTAs, including PBOX-15 (4), CA4P (5) and PBOX-6 (6), displayed cytotoxic efficiency in various leukemia cell types through the inhibition of cellular proliferation. In addition, it has been demonstrated that CA4P, a novel tubulin-destabilizing agent, reduced the interaction of leukemia cells with neovessels by downregulating the expression of the adhesion molecule VCAM-1, thereby increasing leukemia cell death (5).…”

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.…”

Pre-clinical evaluation of a novel class of anti-cancer agents, the Pyrrolo-1, 5-benzoxazepines.

“…The non-apoptotic subset of the PBOXs (PBOX-1,-2,-21) exert their anti-proliferative effects by inducing a G1 cell cycle arrest 2, 8, 9. On the other hand, the pro-apoptotic subset of PBOXs (PBOX-6, -15, -16) induce a G2 / M arrest subsequent to apoptosis 6, 13-15, 19-22, 24, 29. In each case, the aforementioned cell cycle arrest induced by a representative member of each group was confirmed using several biochemical techniques.…”

“…Apart from targeting tubulin in mitotic cells, the tubulin targeting properties of the PBOXs can also impede other functions involved in tumour progression such as cell adhesion, spreading, migration and angiogenesis 19, 22, 36. Tumour neovascularisation occurs by non-sprouting and sprouting angiogenesis, although the latter is more prominent 59.…”

“…PBOX-15-mediated depolymerisation and post-translational modification of tubulin can dramatically impair T-cell migration 36. Furthermore, PBOX-15 downregulated the expression of β1-, β2-, α4-integrins in human ALL cells 22. Integrins are crucial for cell migration and invasion 60.…”