Tellurophene-Tagging of Teniposide Facilitates Monitoring by Mass Cytometry

Target engagement and the biodistribution of exogenously administered small molecules is rarely homogenous. Methods to determine the biodistribution at the cellular level are limited by the ability to detect the small molecule and simultaneously identify the cell types or tissue structures with which it is associated. The highly multiplexed nature of mass cytometry could facilitate these studies provided a heavy isotope label was available in the molecule of interest. Here we show it is possible to append a tellurophene to a known chemotherapeutic, teniposide, to follow this molecule in vivo. A semi-synthetic approach offers an efficient route to the teniposide analogue which is found to have similar characteristics when compared with the parent teniposide in vitro. Using mass cytometry we find the teniposide analogue has significant nonspecific binding to cells. In vivo the tellurium bearing teniposide produces the expected DNA damage in a PANC-1 xenograft model. The distribution of Te in the tissue is near the limits of detection and further work will be required to characterize the localization of this analogue with respect to cell type distributions.