Activity of the kinesin spindle protein inhibitor ispinesib (SB-715992) in models of breast cancer.

PURPOSE: Ispinesib (SB-715992) is a potent inhibitor of kinesin spindle protein, a kinesin motor protein essential for the formation of a bipolar mitotic spindle and cell cycle progression through mitosis. Clinical studies of ispinesib have shown a 9% response rate in patients with locally advanced or metastatic breast cancer and a favorable safety profile without significant neurotoxicities, gastrointestinal toxicities, or hair loss. To better understand the potential of ispinesib in the treatment of breast cancer, we explored the activity of ispinesib alone and in combination with several therapies approved for the treatment of breast cancer. EXPERIMENTAL DESIGN: We measured the ispinesib sensitivity and pharmacodynamic response of breast cancer cell lines representative of various subtypes in vitro and as xenografts in vivo and tested the ability of ispinesib to enhance the antitumor activity of approved therapies. RESULTS: In vitro, ispinesib displayed broad antiproliferative activity against a panel of 53 breast cell lines. In vivo, ispinesib produced regressions in each of five breast cancer models and tumor-free survivors in three of these models. The effects of ispinesib treatment on pharmacodynamic markers of mitosis and apoptosis were examined in vitro and in vivo, revealing a greater increase in both mitotic and apoptotic markers in the MDA-MB-468 model than in the less sensitive BT-474 model. In vivo, ispinesib enhanced the antitumor activity of trastuzumab, lapatinib, doxorubicin, and capecitabine and exhibited activity comparable with paclitaxel and ixabepilone. CONCLUSIONS: These findings support further clinical exploration of kinesin spindle protein inhibitors for the treatment of breast cancer.

Synthesis and protein kinase inhibitory activity of balanol analogues with modified benzophenone subunits.

A series of analogues of the protein kinase C (PKC) inhibitory natural product balanol which bear modified benzophenone subunits are described. The analogues were designed with the goal of uncovering structure-activity features that could be used in the development of PKC inhibitors with a reduced polar character compared to balanol itself. The results of these studies suggest that most of the benzophenone features found in the natural product are important for obtaining potent PKC inhibitory compounds. However, several modifications were found to lead to selective inhibitors of the related enzyme protein kinase A (PKA), and several specific modifications to the polar structural elements of the benzophenone were found to provide potent PKC inhibitors. In particular, it was found that replacement of the benzophenone carboxylate with bioisosteric equivalents could lead to potent analogues. Further, a tolerance for lipophilic substituents on the terminal benzophenone ring was uncovered. These results are discussed in light of recently available structural information for PKA.