A Predictive Factor for Eribulin Treatment of Breast Cancer

Institution: University of California, Santa Barbara
Investigator(s): Jennifer Smith, B.S. -
Award Cycle: 2009 (Cycle 15) Grant #: 15GB-0026 Award: $74,988
Award Type: Dissertation Award
Research Priorities
Detection, Prognosis and Treatment>Innovative Treatment Modalities: search for a cure

Initial Award Abstract (2009)

Eribulin mesylate is an analog of the natural compound halichondrin B, initially isolated from a sponge, and is in phase II and III clinical trials for the treatment of metastatic breast cancer. Eribulin targets and binds to tubulin, an important cellular protein involved in cell division. Anti-cancer drugs that block microtubule assembly (e.g., Vinblastine) or disassembly (e.g. Paclitaxel) have a long history of use, but variable response rates and toxicity limits their effectiveness. Thus, other targeted therapeutics are need to selectively block microtubule-dependent cell division specific to cancer cells, or predict which patients will respond to existing drugs. Stathmin is a microtubule-associated protein, which binds both soluble tubulin and polymerized microtubules. It is also a prognostic factor for breast cancer, and is found to be overexpressed in approximately 25% of breast cancers, most often in aggressive and highly proliferative tumors. Stathmin is also being examined as a predictive factor for tumor response to anti-tubulin agents.

The goal of this dissertation project is to nvestigate the interactions between stathmin protein and eribulin, both biochemically (structural analysis) and functionally in cultured breast cancer cells. Because stathmin binds and forms a complex with tubulin, I will investigate the effects of stathmin on eribulin binding. To relate these findings to cancer treatment, I will vary stathmin expression within breast cancer cell lines, and test the cells for their sensitivity to eribulin. For biochemical studies we will use a radioactively-labeled drug conjugate of eribulin and purified tubulin and stathmin. Cell function studies will be carried out by altering stathmin levels using siRNA (inhibitory RNA) and a stathmin expression vector (increases stathmin amounts). I will use two breast cancer cell lines: BT549 and MCF7. BT549 expresses stathmin at 11-fold higher levels than normal breast tissue. I will reduce stathmin in these cells and test their sensitivity to eribulin. MCF7 cells have a slightly lower than normal stathmin expression. In these cells, I will overexpress stathmin to test for altered sensitivity or resistance to eribulin.

Stathmin has the potential to be an important biomarker in breast cancer, and might be used to predict response to tubulin-targeting anti-cancer drugs. Understanding how stathmin interacts with these compounds, and how these interactions can influence tumor response, will better our ability to treat cancers based on individual protein expression. Improvements in biomarker discovery and testing will allow oncologists to tailor chemotherapy regimens to individual patients, improving treatment response and reducing side-effects.

Final Report (2011)

Microtubules are long polymers composed of tubulin protein and associated factors, which are vital to many cellular functions, such as cell proliferation, cell motility, and intracellular transport. Microtubule-targeting chemotherapeutic drugs inhibit tumor growth by interrupting the normal function of microtubules, triggering a programmed cell death known as apoptosis. One such microtubule-targeting drug (MTD) is eribulin, a synthetic analog of the natural compound halichondrin B. Eribulin binds to tubulin and microtubules, inhibiting the polymerization of the microtubule ends, causing mitotic arrest and apoptosis.

This project was aimed at examining the activity of eribulin in breast cancer cells in relation to the expression of the microtubule-associate protein stathmin, which is positively correlated with malignant cancer and poor disease prognosis. I hypothesized that stathmin expression in a tumor cell would change its sensitivity to eribulin, based on the knowledge that stathmin binds tubulin and microtubules and affects microtubule function. My previous goal to examine the mechanism of eribulin in the absence and presence of stathmin in cells using RNA interference to reduce stathmin expression in cancer cells has proved problematic. Therefore, I have used the stathmin overexpressing metastatic breast cancer cell line, BT549, to examine and characterize the anti-mitotic mechanism of eribulin treatment. I found that this cell line was similarly sensitive to eribulin, compared to a variety of other cancer cell lines. This includes the MCF7 breast cancer cell line, which has a very different cancer profile from BT549 and does not overexpress stathmin. This suggests that the anti-cancer activitiy of eribulin does not appear to be influenced by stathmin expression. I also found that eribulin induced a mitotic arrest and inhibited clonogenicity of the BT549 breast cancer cell line at the same concentrations as those which inhibited proliferation, strongly suggesting that eribulinís anti-cancer activity is a direct result of its induction of mitotic arrest. The mitotic arrest induced by eribulin was mostly due to uncongressed chromosomes (i.e. not aligned at the metaphase plate prior to separation to form daughter cells), and there was little perturbation of the mitotic spindle structure. This was in contrast to another MTD, ixabepilone, which caused dramatic changes in mitotic spindle structure, and was more similar to the arrest induced by vincristine, a MTD with a similar mechanism of action to eribulin.