Selective activation of a drug precursor in an orthogonal manner can reduce the adverse systemic effects of the therapy. In a 2015 paper published in Scientific Reports (Vol 5, 9329), HypOxystation users Weiss et al. describe a therapeutic strategy to treat advanced cancers by implanting polymer-entrapped palladium nanoparticles within a tumor in order to continuously induce the activation of propargylated Pro-FUdR to FUdr, a DNA synthesis-disrupting antimetabolite, which is administered enterally. In their paper “Palladium-mediated dealkylation of N-propargyl-floxuridine as a bioorthogonal oxygen-independent prodrug strategy”, they describe the balancing act necessary to design and synthesize a compound that is inactive but resistant to metabolic degradation outside of the tumor, reducing its cytotoxicity for the patient 6,250-fold, which can then be chemically activated by palladium, aided by the specific micro­environment present inside the tumor.

The authors assayed the efficacy of the pro-drug at physiological pH ranges typical of early stage (normoxic) and also late stage (hypoxic) cancers (pH 6.5-7.5). In order to visualize the effects of their modified drug, Weiss et al. monitored the treated cells for 5 days with Essen Instruments’ Incucyte ZOOM live-cell imaging system. Another parameter characterizing cancer is the oxygen level in the tumor microenvironment, and so the authors compared the conversion efficacy of the pro-drug with colorectal cancer cells at normoxia and hypoxia (0.5% O2) using an H35 HypOxystation. They stressed the importance of confirming that the pro-drug activation would be compatible with the oxygen-deprived status of late-stage cancers. Using this strategy, Weiss’ group was able to develop a biorthogonal pro-drug which displays significantly reduced cytotoxicity while exhibiting a strong and rapid toxigenic effect in cancer cells at physiological pH and oxygen levels.

Cancer researchers such as Weiss are able to re-create the tumor microenvironment inside the closed cell culture HypOxystation by Don Whitley Scientific by adjusting oxygen, CO2, temperature, and humidity.