Disclosed herein, the invention pertains to methods and compositions that find use in radiosensitization of tumors and tumor samples based on the ability of a tumor sample to cleave a MTS molecule of the present invention. The MTS molecules of the present invention have a formula as disclosed herein and wherein A is a peptide with a sequence comprising 5 to 9 consecutive acidic amino acids, wherein the amino acids are selected from: aspartates and glutamates; B is a peptide with a sequence comprising 5 to 20 consecutive basic amino acids; X and Y are linkers; P is an optional pre-targeting moiety; M is an optional macromolecular carrier; and T is a radiosensitization agent for delivery to a target, including for example a therapeutic compound.