Recent investigations have shown that approximately half of the observed oxidatively generated DNA damage in cells treated with Aza or 6-thioguanine (6tGua) originates from the direct photoactivation of the metabolized 6tGuo nucleotide in the intracellular pool. This raises an important question as to whether Aza and 6MP themselves can induce oxidatively generated damage to cellular DNA in the intracellular pool and to the proteome. To narrow this knowledge gap, a thorough investigation of the photochemical properties of both drugs in aqueous solutions under physiological-relevant conditions must be performed. Such a study can reveal the phototoxic likelihood of these drugs to cells and if it is necessary to investigate their direct participation in UVA-induced cellular damage. Indeed, UVA-excited 6tGua has been shown to induce oxidatively generated damage to nucleotides in the intracellular pool, forming the 2'-deoxy-8-oxoguanosine nucleotide, which is then incorporated into cellular DNA, leading to indirect DNA damage.