Research on psoralen has historically focused on interactions with DNA and RNA (in particular, ICL formation). Psoralen, however, has also been shown to block signaling of the ErbB2 receptor which is overexpressed in certain aggressive types of breast cancer. A synthetic derivative of bergapten, 5-(4-phenoxybutoxy)psoralen, shows promise as an immunosuppressant by inhibiting a specific potassium channel. Its structure prevents intercalation into DNA, and it only very weakly produces singlet oxygen, majorly reducing unwanted toxicity and mutagenicity "in vivo". This has implications for the treatment of various autoimmune diseases (e.g. multiple sclerosis, type-1 diabetes, and rheumatoid arthritis). While cell-surface modification and ion channel blocking are two newly discovered mechanisms of action, much research remains to be done.