Uptake of 5(125I) iodo-2-deoxyuridine (IDU) in plasma and cerebrospinal fluid in a case of herpes encephalitis with a comparative study on the uptake in plasma, cerebrospinal fluid and brain tissue in dogs

5-[125]iodo-2'-deoxyuridine in the radiotherapy of solid CNS tumors in rats

We have been investigating the therapeutic efficacy of the thymidine analog 5-iodo-2'-deoxyuridine (IUdR) when radiolabeled with the Auger electron emitter 125I in rats bearing intrathecal (i.t.) or intracerebral (i.c.) 9L gliosarcoma solid tumors. [125I]IUdR was infused i.t. (via subarachnoid catheters) or intracerebrally over a 5- or 2-day period; equimolar concentrations of [127I]IUdR were infused into control animals. Hind-leg paralysis and/or survival were followed over time. The results indicate that compared with [127I]IUdR, rats bearing intrathecal tumors and infused i.t. with [125I]IUdR showed significant prolongation of the onset of median paralysis (15.2 versus 9 days). Similarly, the median survival of rats bearing intracerebral tumors and infused i.c. with [125I]IUdR was significantly increased (24 versus 17 days). The data substantiate the antineoplastic potential of [125I]IUdR and indicate a promising role for this radiopharmaceutical in the treatment of CNS cancers.

5-[123I]iodo-2'-deoxyuridine in the radiotherapy of an early ascites tumor model

The extreme biological toxicity of Auger emitters is caused by the decay-associated, highly localized deposition of energy. The antineoplastic capability of an Auger-electron emitter, iodine-123, incorporated into the thymidine analog, 5-iodo-2'-deoxyuridine (IUdR) was evaluated in an intraperitoneal (i.p.) murine ovarian tumor (MOT) in female C3HeB/FeJ mice. Total doses of 0.37 to 8.88 MBq (10-240 microCi) 123IUdR were administered i.p. in five equally divided fractions at 24, 28, 32, 36, and 40 hr after the i.p. inoculation of 0.5 to 1.6 x 10(6) tumor cells per mouse. Control tumor-bearing animals were injected with identical volumes of saline at 4-hr intervals. Biodistribution studies demonstrated a distinct and localized uptake of 123IUdR in the MOT cells (1% of the injected dose was associated with MOT cells 24 hr after the last injection), whereas in animals without tumor there was no radioactivity associated with the peritoneal cells. Analogous results were obtained from scintigraphic images where the focal area of abdominal activity persisted only in MOT-bearing mice while it cleared from the abdomen of the controls. The 50% survival (median survival) of the control group was 19 days for an inoculum of 1.6 x 10(6) MOT cells per animal, whereas the median survival of MOT-bearing animals treated with 123IUdR increased by 11 days for the highest administered dose (8.88 MBq, 240 microCi) and resulted in a 20% absolute survival at 7 weeks. Statistically significant absolute survival prolongation was found with all of the total administered doses. The prolongation of both median and absolute survival time of the tumor-bearing animals treated with 123IUdR conclusively indicates the substantial antineoplastic activity of the Auger-electron emitter iodine-123.

Non-specific esterase activity in reactive cells in injured nervous tissue labeled with 3H-thymidine or 125iododeoxyuridine injected before injury

Tritiated thymidine (3H-TdR) injected before a stab wound of the spinal cord or transection of the hypoglossal nerve has resulted in many labeled reactive cells in the CNS after injury, most of which have the ultrastructural features of microglia. To test for the possible origin of these labeled cells from monocytes, we examined them for the presence of sodium fluoride- (NaF) sensitive non-specific esterase (NSE), an enzyme characteristic of monocytes. Some of the labeled cells in stab wounds had NaF-sensitive NSE, but no such cells were found in the nucleus of the injured hypoglossal nerve. To test for the possibility that the NSE-negative labeled cells had been labeled by reutilization of 3H-TdR, we used 125I-5-iodo-2'-deoxyuridine (125I-UdR), a thymidine analogue with a much lower rate of reutilization, to label blood mononuclear cells prior to either a spinal cord stab wound or hypoglossal axotomy. The number of labeled cells was decreased in the spinal cord wound, but more than half were NSE-negative. No labeled blood mononuclear cells were found in the hypoglossal nucleus, although there was no decrease in the hyperplasia of unlabeled non-neuronal cells. When 125I-UdR was injected on the fourth day after hypoglossal axotomy, or when both 3H-TdR and 125I-UdR were injected simultaneously before hypoglossal axotomy, many labeled cells were found in the hypoglossal nucleus, indicating that 125I-UdR can be used by the reactive cells and that it did not inhibit their proliferation. Therefore, the microglial cells that proliferate in response to peripheral nerve injury are not recently derived from any type of circulating large blood mononuclear cell. The most likely explanation for the presence of the 3H-TdR-labeled cells in the nucleus of the injured hypoglossal nerve is that they were proliferating intrinsic cells labeled by reutilization of 3H-TdR.