Abstract

The lack of tumor-specific targets that allow for selective eradication of malignant cells without affecting healthy tissues is a major drawback of cancer chemotherapy. In contrast to normal cells, tumor cells frequently contain multiple centrosomes, associated with the formation of multipolar mitotic spindles and chromosome segregation defects. In many tumor types, mitotic stability is regained after clonal selection by coalescence of multiple centrosomes into two functional spindle poles (centrosomal clustering). To identify potent and selective inhibitors of centrosomal clustering, we recently described a phenotype-based small molecule screening strategy directed to induce tumor cells with supernumerary centrosomes to undergo multipolar mitoses, thereby resulting in apoptotic cell death (

Rebacz et al.,
Cancer Res
2007
;
67
:
6342
–6350
). We here describe the novel small molecule GF-15, which is a derivative of griseofulvin and a potent inhibitor of centrosomal clustering, thereby inducing multipolar spindles followed by apoptosis. We tested more than 25 cancer cell lines from hematologic malignancies (including acute and chronic leukemias, lymphomas and multiple myeloma) as well as solid tumors (including glioblastoma, colon, cervix, and pancreatic cancers) and found mean inhibitory concentrations (IC50) for proliferation and survival in the range of 1–5μM GF-15, associated with activation of caspases 8, 9, and 3. As expected, tumor cell lines displaying only limited centrosomal aberrations or microsatellite instability were less sensitive to treatment with GF-15. Importantly, non-malignant cells without supernumerary centrosomes including PBMCs, immortalized hepatocytes, and bone marrow stromal cells, did not reach their IC50 even at 30μM GF-15. Specifically, cell cycle analysis of synchronized tumor cells showed marked G2/M arrest, followed by a dramatic increase of the sub-G1 fraction, after treatment with GF-15. In addition, short term treatment with GF-15 was also associated with inhibition of cytokine-triggered cell migration. Finally, both intraperitoneal and oral GF-15 treatment of murine xenograft models of human colon cancer and multiple myeloma resulted in tumor growth inhibition and significantly prolonged survival in vivo. Taken together, our results demonstrate the in vitro and in vivo anti-tumor efficacy of a first in class small molecule inhibitor of centrosomal clustering with specificity for tumor cells, and strongly support its clinical evaluation to improve patient outcome in both hematologic malignancies and solid tumors.

Disclosures: No relevant conflicts of interest to declare.

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