Screening Psoralens for Enhanced UV‐dependent Cytotoxicity. 73 psoralen derivatives were screened for their ability to reduce cell proliferation in the B16 murine melanoma cell line. 1.0 μm of each compound was incubated with cultured cells followed by irradiation with 1J UVA (365 nm). 4,5′,8‐Trimethylpsoralen (TMP), 4’‐Aminomethyl‐4,5’,8‐trimethylpsoralen (AMT), 8‐Methoxypsoralen (8‐MOP) and unmodified psoralen were included as benchmarks for assessing increases or decreases in potency (bars with darker shading). Psoralens are ranked according to their mean UV‐dependent toxicity. 1H and 4B correspond to the 25th and 75th percentiles for our dataset, respectively. (Inset) Without UVA activation, psoralen derivatives are generally inert. Among all derivatives, 10B was the most toxic without UVA activation, inducing ~18% cell death. All psoralen derivatives were screened in duplicate (n = 2).