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On/off Switch for a Platinum Anticancer Complex
They have shown by EPR spin trapping that irradiation of trans,trans,trans-[Pt(N3)2(OH)2(py)2] with visible blue light (463 nm) results in the production of azidyl radicals. Remarkably, biologically relevant concentrations of the amino acid L-tryptophan quench azidyl radical trapping due to the rapid reaction between the free radical and the amino acid. A consequence of this interaction in cells is the reduced photocytotoxicity induced by the platinum(IV) diazido complex. These new findings imply that the high anticancer potency of trans,trans,trans-[Pt(N3)2(OH)2(py)2] involves a dual mechanism of action: an acute phase involving azidyl radicals and a chronic phase due to PtII photoproducts. L-Tryptophan might therefore be useful to control the activity of this platinum complex in photochemotherapy. Some cancer patients (lung, ovarian and breast cancer) are known to have depleted levels of L-Trp, and the amino acid is commonly taken as a supplement in gram quantities.