Funded Grants

Dynamin as a new drug target for the treatment of glioblastoma

Brain tumors account for a relatively small proportion of all cancers. However, they are one of the most lethal forms and are the most common cause of cancer death in the 30-40 year old age group. This has a significant impact on society. The most common type of brain tumor is glioblastoma Multiforme (GBM), which is also the most lethal and difficult form to treat. With optimal therapy the median survival is approximately 40-60 weeks from diagnosis. Current chemotherapeutic agents to treat GBM include temozolomide, BCNU (Nitrosureas), cisplatin, bevacizumab, irinotecan, and a small proportion of GBM responds to the tyrosine kinase inhibitors gefitinib or erlotinib. Current targeted therapies in malignant gliomas have been associated with various response rates and modest to no survival benefits. Therefore, (1) new targets and (2) the development of improved strategies are required to improve the effectiveness of targeted agents for this devastating cancer. Our research proposal aims to address both of these issues.

Dynamin II is a novel anti-cancer target: Our findings strongly indicate that dynamin II (dynII), an endocytic protein, is a new target to develop inhibitors for pharmacological intervention for the treatment of glioblastoma. We have discovered that dynII plays a crucial role in the final stage of mitosis, cytokinesis. Cytokinesis involves ingression of the plasma membrane between segregating chromosomes followed by membrane abscission, resulting in the production of two independent daughter cells. Our studies reveal that dynII, controls the abscission step during mammalian cell cytokinesis. Several inhibitors of mitotic proteins have emerged in preclinical or early clinical development for the treatment of cancers. The target proteins to date have been cyclin-dependent kinase, checkpoint kinase, aurora kinase and polo-like kinase, and mitotic kinesin. Inhibitors of these proteins have been evaluated in various hematologic and solid malignancies. A recent manuscript reported that depletion of the mitotic protein, Aurora-B, enhances the anti-tumor effect of temozolomide in human glioma cells. This indicates that inhibitors of mitotic proteins have the potential to be useful chemotherapeutic agents for glioblastoma. The 10 year collaboration between the Robinson and McCluskey teams has resulted in development of ∼20 structurally distinct classes of dynamin inhibitors, each targeting one of the four dynamin domains. Several lines of evidence strongly support our hypothesis that dynamin inhibition is a novel approach for the treatment of cancer, specifically glioblastoma:

  • We have discovered that several small molecule dynamin inhibitors cause cytokinesis failure at the point of abscission followed by cell death in many human cancer cells. None of the other anti-mitotic inhibitors target this stage of cytokinesis exclusively.
  • Comparing ten cancer cell lines from different tissue origins, we demonstrated that glioblastoma cells are the most sensitive to growth arrest and cell death induced by dynamin inhibitors.
  • We have recently identified that the ability of the anti-psychotic drug, chlorpromazine (cpz), to inhibit endocytosis is due to inhibition of dynII. Cpz readily crosses the blood brain barrier and has been reported to contain anti-cancer properties. A reduced incidence of cancer has been observed in Schizophrenia patients taking cpz. Furthermore, cpz inhibits glioblastoma tumor growth in rat brains when used in combination with BCNU. Thus, dyn inhibitors may synergise with conventional chemotherapeutics currently used for the treatment of glioblastoma.
  • We discovered that dynamin inhibitors do not cause cell death in non-cancerous fibroblasts, suggesting they may have a relative specificity for brain cancer.

Novel drug delivery mechanism: One of the major difficulties in treating brain tumors with chemotherapeutic agents is that most of these molecules are unable to penetrate the blood brain barrier (BBB) effectively. This renders these molecules essentially useless for the treatment of glioblastoma. The inability of chemotherapeutic agents to cross the BBB can be due to their polarity, hydrophobicity and active drug efflux transporters at the blood-brain, blood-cerebrospinal and blood-tumor barriers. Several of the dynamin inhibitors we have generated have recently been tested in epilepsy mouse models at the Anti-convulsant Screening Program (NIH, Bethesda). The findings reveal a reduction in seizures following treatment with dynamin inhibitors from several different classes. Thus, we already have molecules that are capable of crossing the BBB and have a CNS action. In addition, we have identified a pharmacological mechanism of selectively targeting drugs to brain cells. This technology involves the development of two types of pro-drugs, and a combination of both. The first is a “brain-lock” chemical modification of our drugs so that they can pass through the BBB. Drug delivery through the BBB is by molecular packaging and sequential metabolism. Once it is in the brain it becomes activated by brain-cell-specific oxygenase cleavage, which transforms into a membrane impermeable molecule. Thus, molecules that have crossed the BBB are retained, and the residual excreted, ensuring that the drugs cytotoxic effects are restricted to the brain. The second is “pro-drugs” whereby cell wall permeating side chains are added to the dynamin inhibitors. This renders them temporarily inactive as inhibitors and far more membrane permeable. Once they enter cells, esterases cleave the pro-drug back to the active compound, effectively trapping it inside cells. Both pro-drug and brain-lock chemistries are well known and established by our group. However, this project will be the first time they have ever been combined into a single molecule, first targeting the brain, then the glioblastoma cells therein.

Therefore, we hypothesise that dynamin inhibitors are anti-proliferative compounds amenable to pro-drug development for the treatment of glioblastoma. The specific aims are:

  • Design and synthesis of small molecule dynamin inhibitors
    • Target the four main domains of dynamin II
  • Determine their effect on dynamin II activity
    • In vitro and in-cell based assays
  • Determine their effect on cell growth alone and in combination with conventional chemotherapeutic agents
    • Cell proliferation, cytokinesis, and cell death
  • Determine their in vivo anti-cancer efficacy
    • Glioblastoma mouse cancer model

    This proposal draws on the strengths and multi-disciplinary collaboration of six large and wellestablished research groups. All of our members have collaborated heavily with each other, but this proposal is the first to bring them all together as a single team. Our overall aim is to combine the expertise and knowledge of each individual group to identify the most efficacious dynamin inhibitor that will ultimately be investigated in human clinical trials for the treatment of glioblastoma. Our core areas of expertise are medicinal chemistry development of dynamin inhibitors, dynamin biochemistry, cell and molecular biology, characterisation of the role of dynamin in cell division and analysis of glioblastoma mouse models. The results will reveal those dynamin inhibitors that cause cell death specifically following cytokinesis failure and thus inhibit cell growth. These characteristics are extremely important as they predict that these small-molecule inhibitors will not affect non-proliferating non-tumor cells. Thus, their efficacy is expected to be dramatically improved compared to conventional chemotherapeutic agents. Our results will also identify those dynamin inhibitors that reduce glioblastoma tumor growth in a mouse cancer model. Overall, we aim to identify new anti-cancer agents that are more effective than currently used chemotherapeutic agents. A successful outcome will provide patients with an increased survival period and improved quality of life.