A major limitation of clinically used cancer drugs is the lack of specificity resulting in toxicity. To address this, we performed a phenotypically-driven screen to identify optimal multidrug combinations acting with high efficacy and selectivity in clear cell renal cell carcinoma (ccRCC). The search was performed using the Therapeutically Guided Multidrug Optimization (TGMO) method in ccRCC cells (786-O) and nonmalignant renal cells and identified a synergistic low-dose four-drug combination (C2) with high efficacy and negligible toxicity. We discovered that C2 inhibits multipolar spindle pole clustering, a survival mechanism employed by cancer cells with spindle abnormalities. This phenotype was also observed in 786-O cells resistant to sunitinib, the first line ccRCC treatment, as well as in melanoma cells with distinct percentages of supernumerary centrosomes. We conclude that C2-treatment shows a high efficacy in cells prone to form multipolar spindles. Our data suggest a highly effective and selective C2 treatment strategy for malignant and drug-resistant cancers.

Centrioles are central structural elements of centrosomes and cilia. In human cells daughter centrioles are assembled adjacent to existing centrioles in S-phase and reach their full functionality with the formation of distal and subdistal appendages one-and-a-half cell cycle later, as they exit their second mitosis. Current models postulate that the centriolar protein centrobin acts as placeholder for distal appendage proteins that must be removed to complete distal appendage formation. Here, we investigated in non-transformed human epithelial RPE1 cells the mechanisms controlling centrobin removal and its effect on distal appendage formation. Our data are consistent with a speculative model in which centrobin is removed from older centrioles due to a higher affinity for the newly born daughter centrioles, under the control of the centrosomal kinase Plk1. This removal also depends on the presence of subdistal appendage proteins on the oldest centriole. Removing centrobin, however, is not required for the recruitment of distal appendage proteins, even though this process is equally dependent on Plk1. We conclude that Plk1 kinase regulates centrobin removal and distal appendage formation during centriole maturation via separate pathways.

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