Bromodeoxyuridine

Bromodeoxyuridine (5-bromo-2'-deoxyuridine, BrdU, BUdR, BrdUrd) is a synthetic nucleoside that is an analog of thymidine. BrdU is commonly used in the detection of proliferating cells in living tissues. 5-Bromodeoxycytidine is deaminated to form BrdU.

BrdU can be incorporated into the newly synthesized DNA of replicating cells (during the S phase of the cell cycle during which DNA is replicated), substituting for thymidine during DNA replication. Antibodies specific for BrdU can then be used to detect the incorporated chemical (see immunohistochemistry), thus indicating cells that were actively replicating their DNA. Binding of the antibody requires denaturation of the DNA, usually by exposing the cells to acid or heat.

BrdU can be passed to daughter cells upon replication. BrdU has been demonstrated to be detectable over two years post-infusion.

Because BrdU can replace thymidine during DNA replication, it can cause mutations, and its use is therefore potentially a health hazard. However, because it is neither radioactive nor myelotoxic at labeling concentrations, it is widely preferred for in vivo studies of cancer cell proliferation. However, at radiosensitizing concentrations, BrdU becomes myelosuppressive thus limiting its use for radiosensitizing.