PMC

Deletion of SIR3 or SIR4 suppresses the camptothecin hypersensitivity of tof1∆ and csm3∆ cells.Deletion of SIR2 also suppresses camptothecin hypersensitivity of tof1∆ cells and reduces camptothecin sensitivity of a wild‐type strain.Deletion of SIR2 cannot suppress camptothecin hypersensitivity of a rad51∆ strain.Inhibition of Sir2 deacetylase activity with sirtinol suppresses camptothecin hypersensitivity of tof1∆ cells.Mutations that mimic a permanently acetylated H4‐K16 (K16Q) or that remove the binding site for Sir3 (K16G) also suppress camptothecin sensitivity of wild‐type and tof1∆ strains.

Disruption of the rDNA locus is not sufficient to suppress camptothecin hypersensitivity of tof1∆ cells.A mutation in RAP1 that disrupts telomeric silencing does not suppress camptothecin hypersensitivity of tof1∆ cells.Deletion of SIR1 suppresses camptothecin sensitivity in wild‐type and tof1∆ cells. SIR1 deletion is epistatic with SIR2 deletion with respect to suppression of camptothecin hypersensitivity of tof1∆ strains.Homozygous tof1∆/tof1∆ diploid cells are as sensitive to camptothecin as tof1∆ haploids, and their hypersensitivity can be alleviated by sirtinol.

A. Percentage of camptothecin in the lactone form in its formulation alone and with PAMAM G4.0 (100 and 300 mg/kg), and G3.5 (300 and 1000 mg/kg). Significant difference between camptothecin alone and camptothecin formulation with G4.0, G3.5, * p<0.05, ***p<0.001 by one-way ANOVA. Camptothecin formulated with PAMAM to form a soluble formulation had a higher % of drug in the lactone (unionized form) compared to camptothecin solution alone suggesting potential encapsulation of camptothecin within the interior cavities of both cationic G4.0 and anionic G3.5. B. Percentage of total camptothecin solubilized in simulated gastric and intestinal fluids at 2 and 3 hours respectively; n=3; Significant difference between camptothecin alone and camptothecin formulation with G4.0, G3.5, *** p<0.001 by one-way ANOVA.

Spontaneous suppressors of camptothecin sensitivity of tof1∆ cells.Suppressor strains recovered from the tof1∆ synthetic viability screen are G418 resistant, suggesting presence of the TOF1 deletion cassette.Deletion of IRC15 does not suppress tof1∆ camptothecin hypersensitivity.Deletion of IME2 does not suppress tof1∆ camptothecin hypersensitivity.Deletion of SIR2 and deletion of TOP1 lead to similar levels of camptothecin resistance, and combining the two mutations does not further increase camptothecin resistance.Deletion of HML does not alter the camptothecin hypersensitivity of tof1∆ cells. tof1∆ cells and congenic wild‐type cells were pre‐grown either in the absence or in the presence of sirtinol. They were subsequently synchronised in G1 and released into S phase in the presence of camptothecin, either with or without sirtinol. Cell cycle progression was monitored by FACS analysis.