Novel microtubule-targeting agents, pyrrolo-1,5-benzoxazepines, induce cell cycle arrest and apoptosis in prostate cancer cells

Seema-Maria Nathwani, Suzanne M Cloonan, Maeve Stronach, Giuseppe Campiani, Mark Lawler, D Clive Williams, Daniela M Zisterer, Mark Lawler

Research output: Contribution to journalArticlepeer-review

9 Citations (Scopus)


Advanced hormone-refractory prostate cancer is associated with poor prognosis and limited treatment options. Members of the pyrrolo-1,5-benzoxazepine (PBOX) family of compounds exhibit anti-cancer properties in cancer cell lines (including multi-drug resistant cells), ex vivo patient samples and in vivo mouse tumour models with minimal toxicity to normal cells. Recently, they have also been found to possess anti-angiogenic properties in vitro. However, both the apoptotic pathways and the overall extent of the apoptotic response induced by PBOX compounds tend to be cell-type specific. Since the effect of the PBOX compounds on prostate cancer has not yet been elucidated, the purpose of this study was to investigate if PBOX compounds induce anti-proliferative effects on hormone-refractory prostate cancer cells. We examined the effect of two representative PBOX compounds, PBOX-6 and PBOX-15, on the androgen-independent human prostate adenocarcinoma cell line, PC3. PBOX-6 and -15 displayed anti-proliferative effects on PC3 cells, mediated initially through a sustained G2/M arrest. G2/M arrest, illustrated as DNA tetraploidy, was accompanied by microtubule depolymerisation and phosphorylation of anti-apoptotic proteins Bcl-2 and Bcl-xL and the mitotic spindle checkpoint protein BubR1. Phosphorylation of BubR1 is indicative of an active mitotic checkpoint and results in maintenance of cell cycle arrest. G2/M arrest was followed by apoptosis illustrated by DNA hypoploidy and PARP cleavage and was accompanied by degradation of BubR1, Bcl-2 and Bcl-xL. Furthermore, sequential treatment with the CDK1-inhibitor, flavopiridol, synergistically enhanced PBOX-induced apoptosis. In summary, this in vitro study indicates that PBOX compounds may be useful alone or in combination with other agents in the treatment of hormone-refractory prostate cancer.

Original languageEnglish
Pages (from-to)1499-507
Number of pages9
JournalOncology Reports
Issue number6
Publication statusPublished - Dec 2010


  • Adenocarcinoma
  • Antineoplastic Agents
  • Apoptosis
  • Cell Cycle
  • Cell Line, Tumor
  • Cell Proliferation
  • Dose-Response Relationship, Drug
  • Drug Evaluation, Preclinical
  • Humans
  • Inhibitory Concentration 50
  • Male
  • Models, Biological
  • Oxazepines
  • Prostatic Neoplasms
  • Pyrroles
  • Tubulin Modulators


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