Microtubule-targeting-compound PBOX-15 radiosensitizes cancer cells in vitro

Abstract

BackgroundMicrotubule-targeting agents, such as taxanes (paclitaxel and docetaxel) and vinca alkaloids (vincristine and vinblastine), act by suppressing microtubule dynamics and disrupting mitotic spindle configuration.1 These compounds are cell cycle specific, arresting the cell cycle in the G 2 /M phase.2 Because G 2 /M cells are most radiosensitive, these agents have been investigated as radiosensitizers. The combination of chemotherapy and radiation therapy indeed presents a number of advantages: because radiation is a local therapy and chemotherapy targets systemic spread, spatial co-operation of both modalities may participate in reduced local failure rates, eradication of micro metastases, improved distant control, organ function preservation and decreased tumor mass prior to surgery making complete resection possible.3 A clinical limitation to these combination therapies is the acquired or intrinsic resistance of tumors to established microtubule-targeting agents. Pyrrolo-1,5-benzoxazepines (PBOX) are a family of novel compounds with anticancer properties. We have previously demonstrated that several PBOX compounds induce apoptosis in a number Background: We proposed to investigate the radiosensitizing properties of pBOX-15, a novel microtubule-disrupting agent, in a panel of cancer cell lines.Results: pBOX-15 treatment was associated with significant cell kill and increased radiosensitivity in all three cell lines tested. The number of surviving cells in response to the combined treatment was significantly less than pBOX-15 alone in 22Rv1 cells. In these cells, radiosensitisation correlated with induction of G 2 /M cell cycle arrest by pBOX-15. The compound sustained its activity and increased hIF-1α expression under hypoxic conditions. pBOX-15 prevented onset of hypoxia-induced radioresistance in hypoxic prostate cells and reduced the surviving fraction of irradiated hypoxic cells to levels similar to those achieved under aerobic conditions. Methods: Clonogenic assays were used to determine sensitivity of a panel of cancer cell lines (22Rv1, a549, U87) to pBOX-15 alone or in combination with a single 2 Gy dose fraction. Induction of cell cycle arrest and apoptosis was investigated in 22Rv1 prostate cancer cells. The cytotoxic properties of the compound under hypoxic conditions were correlated with hypoxia Inducible Factor 1alpha (hIF-1α) gene and protein expression levels and its radiosensitisation potential was investigated in hypoxic 22Rv1 using clonogenic assays.Conclusions: This preliminary data identifies the potential of pBOX-15 as a novel radiosensitising agent for the management of solid tumors and eradication of hypoxic cells.

Inhibition of late-stage autophagy synergistically enhances pyrrolo-1,5-benzoxazepine-6-induced apoptotic cell death in human colon cancer cells

“…We have previously published preclinical data demonstrating successful combinations of the PBOXs with the tyrosine kinase inhibitor, imatinib mesylate (37,38), the cyclin dependent kinase inhibitor, flavopiridol (39,40) and also with the tumour necrosis factor-related apoptosis-inducing ligand (36). Furthermore, we have demonstrated potential clinical benefits in combining the PBOXs with radiotherapy for the treatment of prostate cancer (41).…”

Hypoxia, notch signalling, and prostate cancer

“…89 Similarly, we have reported sensitivity of hypoxic prostate cancer cells to docetaxel and a novel microtubule disrupting agent pyrrolo-1,5-benzoxazepine 15 (PBOX-15). 90,91 Understanding the relationship between these three pathways could, therefore, uncover key targets for optimizing treatment response.…”

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

“…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).…”