Next, HeLa cells were monitored for up to 6 days after treatment with 1 μM of caged and uncaged PROTACs (Figure ). The cell proliferation profile without irradiation highlights the different mode of action between PROTAC 2 and 3. While the caged compound 3 displayed a cytostatic profile over time (average proliferation fold change = 1), the uncaged PROTAC 2 reduced cell count by half (average proliferation fold change < 0.5) after 48 h. Most importantly, uncaging of compound 3 was characterized by a striking change in the growth curve profile that exactly overlaid with 2, confirming mechanistically the release of the active degrader upon irradiation.