Voreloxin is an anticancer quinolone derivative that intercalates DNA and poisons topoisomerase II.

BACKGROUND: Topoisomerase II is critical for DNA replication, transcription and chromosome segregation and is a well validated target of anti-neoplastic drugs including the anthracyclines and epipodophyllotoxins. However, these drugs are limited by common tumor resistance mechanisms and side-effect profiles. Novel topoisomerase II-targeting agents may benefit patients who prove resistant to currently available topoisomerase II-targeting drugs or encounter unacceptable toxicities. Voreloxin is an anticancer quinolone derivative, a chemical scaffold not used previously for cancer treatment. Voreloxin is completing Phase 2 clinical trials in acute myeloid leukemia and platinum-resistant ovarian cancer. This study defined voreloxin's anticancer mechanism of action as a critical component of rational clinical development informed by translational research. METHODS/PRINCIPAL FINDINGS: Biochemical and cell-based studies established that voreloxin intercalates DNA and poisons topoisomerase II, causing DNA double-strand breaks, G2 arrest, and apoptosis. Voreloxin is differentiated both structurally and mechanistically from other topoisomerase II poisons currently in use as chemotherapeutics. In cell-based studies, voreloxin poisoned topoisomerase II and caused dose-dependent, site-selective DNA fragmentation analogous to that of quinolone antibacterials in prokaryotes; in contrast etoposide, the nonintercalating epipodophyllotoxin topoisomerase II poison, caused extensive DNA fragmentation. Etoposide's activity was highly dependent on topoisomerase II while voreloxin and the intercalating anthracycline topoisomerase II poison, doxorubicin, had comparable dependence on this enzyme for inducing G2 arrest. Mechanistic interrogation with voreloxin analogs revealed that intercalation is required for voreloxin's activity; a nonintercalating analog did not inhibit proliferation or induce G2 arrest, while an analog with enhanced intercalation was 9.5-fold more potent. CONCLUSIONS/SIGNIFICANCE: As a first-in-class anticancer quinolone derivative, voreloxin is a toposiomerase II-targeting agent with a unique mechanistic signature. A detailed understanding of voreloxin's molecular mechanism, in combination with its evolving clinical profile, may advance our understanding of structure-activity relationships to develop safer and more effective topoisomerase II-targeted therapies for the treatment of cancer.

SNS-314, a pan-Aurora kinase inhibitor, shows potent anti-tumor activity and dosing flexibility in vivo.

PURPOSE: The Aurora family of serine/threonine kinases (Aurora-A, Aurora-B, and Aurora-C) plays a key role in cells orderly progression through mitosis. Elevated expression levels of Aurora kinases have been detected in a high percentage of melanoma, colon, breast, ovarian, gastric, and pancreatic tumors. We characterized the biological and pharmacological properties of SNS-314, an ATP-competitive, selective, and potent inhibitor of Aurora kinases. METHODS: We studied the biochemical potency and selectivity of SNS-314 to inhibit Aurora kinases A, B, and C. The inhibition of cellular proliferation induced by SNS-314 was evaluated in a broad range of tumor cell lines and correlated to inhibition of histone H3 phosphorylation, inhibition of cell-cycle progression, increase in nuclear content and cell size, loss of viability, and induction of apoptosis. The dose and administration schedule of SNS-314 was optimized for in vivo efficacy in mouse xenograft models of human cancer. RESULTS: In the HCT116 human colon cancer xenograft model, administration of 50 and 100 mg/kg SNS-314 led to dose-dependent inhibition of histone H3 phosphorylation for at least 10 h, indicating effective Aurora-B inhibition in vivo. HCT116 tumors from animals treated with SNS-314 showed potent and sustained responses including reduction of phosphorylated histone H3 levels, increased caspase-3 and appearance of increased nuclear size. The compound showed significant tumor growth inhibition in a dose-dependent manner under a variety of dosing schedules including weekly, bi-weekly, and 5 days on/9 days off. CONCLUSIONS: SNS-314 is a potent small-molecule inhibitor of Aurora kinases developed as a novel anti-cancer therapeutic agent for the treatment of diverse human malignancies.

SNS-032 is a potent and selective CDK 2, 7 and 9 inhibitor that drives target modulation in patient samples.

PURPOSE: SNS-032 (formerly BMS-387032) is a potent, selective inhibitor of cyclin-dependent kinases (CDK) 2, 7 and 9, currently in phase 1 clinical trial for chronic lymphocytic leukemia (CLL) and multiple myeloma (MM). We used the MM cell line RPMI-8226 to evaluate the relationship between duration of SNS-032 exposure, target modulation of CDKs 2, 7 and 9, and induction of apoptosis. We also assessed target modulation in patient peripheral blood mononuclear cells (PBMCs) from phase 1 solid tumor patients treated with SNS-032. METHODS: Proliferation and colony forming assays were used to evaluate cytotoxicity, Western blot analyses to evaluate target modulation, FACS analysis to assess cell cycle distribution, RT-PCR to evaluate transcriptional inhibition. RESULTS: SNS-032 blocks the cell cycle via inhibition of CDKs 2 and 7, and transcription via inhibition of CDKs 7 and 9. Treatment of RPMI-8226 MM cells at 300 nM (IC(90)) for 6 h was sufficient for commitment to apoptosis. This correlated with inhibition of CDKs 2, 7 and 9, as reflected in substrate signaling molecules. SNS-032 activity was unaffected by human serum. Target modulation was observed in PBMC from treated patients. CONCLUSIONS: These results demonstrate SNS-032 target modulation of CDKs 2, 7 and 9, and establish 6 h exposure as sufficient to commit RPMI-8226 MM cells to apoptosis. Combined with the demonstration of target modulation in PBMC from phase 1 solid tumor patients treated with SNS-032, these data support the ongoing clinical study of SNS-032 in MM and CLL.