Quantitative Determination of the Alternative Isoprenoid Generation Pathway as a Tool to Exploit the Mevalonate pathway in Cancer Cells

Cancer stem cells and mutant p53 expressing tumors are highly dependent on the mevalonate pathway. Statins inhibit this pathway resulting in growth inhibition of these cells independent of inhibition of cholesterol biosynthesis and of protein farnesylation. Protein prenylation substrates farnesyl‐ and geranylgeranyl diphosphates are synthesized by the mevalonate pathway without producing their corresponding isoprenols. However, cells incorporate exogenously supplied isoprenols into mevalonate pathway metabolites and proteins using a poorly characterized process. In order to quantify this alternative to the mevalonate pathway, we synthesized natural and unnatural analogs of farnesol and geranylgeraniol, including stable isotope‐labeled farnesol and aniline substituted isoprenols. Using tandem mass spectrometry we quantitatively monitored the formation of diphosphate derivatives of these isoprenols and their utilization as prenylation substrates when incubated with cultured cells. Our results reveal that in some cells the capacity to use exogenous isoprenols is comparable to that of the mevalonate pathway raising the possibility that this alternative pathway could have important therapeutic implications