Intracellular pH modulates sensitivity to an anti‐cancer lysophospholipid in yeast

We have previously established that the anti‐cancer lipid edelfosine (1‐ O ‐octadecyl‐2‐ O ‐methyl‐ rac ‐glycero‐3‐phosphocholine) induces cell death in yeast by selective modification of lipid raft composition at the plasma membrane (PM). Early interaction of the drug with the PM induces sterol internalization and displacement of the essential proton pump, Pma1p, from lipid microdomains. We have now performed a high‐throughput edelfosine sensitivity screen by robotically pinning the haploid yeast deletion mutant strain collection onto solid medium in the absence or presence of edelfosine. Fifty four genes, whose inactivation reproducibly resulted in increased sensitivity to edelfosine compared to wild type, were identified. This data set was enriched in genes known to participate in cation transport and pH homeostasis, including mutants lacking subunits of the vacuolar ATPase ( vma ) and the high affinity potassium transporter Trk1p. We tested the hypothesis that edelfosine induces cytosol acidification and in consequence, cells impaired in maintenance of pH homeostasis have a lower threshold and increased susceptibility to edelfosine. We show that the intracellular pH (pH i ) of cells treated with edelfosine declined after the first hour and dropped ~ 0.5 units by two hours of treatment, and this was exacerbated in hypersensitive mutants. This work was supported by NSERC.