A phase I trial of intravenous bromodeoxyuridine and radiation therapy for pancreatic cancer

Ethynyldeoxyuridine (EdU) suppresses in vitro population expansion and in vivo tumor progression of human glioblastoma cells

Thymidine analogs (TAs) are synthetic nucleosides that incorporate into newly synthesized DNA. Halogenated pyrimidines (HPs), such as bromodeoxyuridine (BrdU), are a class of TAs that can be detected with antibodies and are commonly used for birthdating individual cells and for assessing the proliferative index of cell populations. It is well established that HPs can act as radiosensitizers when incorporated into DNA chains, but they are generally believed not to impair normal cell function in the absence of secondary stressors. However, we and others have shown that HP incorporation leads to a sustained suppression of cell cycle progression in mammalian cells, resulting in cellular senescence in somatic cells. In addition, we have shown that HP incorporation results in delayed tumor progression in a syngeneic rat model of glioma. Here we examine ethynyldeoxyuridine (EdU), a newly developed and alkylated TA, for its anti-cancer activity, both in vitro and in vivo. We show that EdU, like HPs, leads to a severe reduction in the proliferation rate of normal and transformed cells in vitro. Unlike HPs, however, EdU incorporation also causes DNA damage resulting in the death of a substantial subset of treated cells. When administered over an extended time as a monotherapy to mice bearing subcutaneous xenografts of human glioblastoma multiforme tumors, EdU significantly reduces tumor volume and increases survival without apparent significant toxicity. These results, combined with the fact that EdU readily crosses the blood-brain barrier, support the continued investigation of EdU as a potential therapy for malignant brain tumors.

Bromodeoxyuridine inhibits cancer cell proliferation in vitro and in vivo

The thymidine analog bromodeoxyuridine (BrdU) is incorporated into newly synthesized DNA and has been shown to increase the susceptibility of incorporating cells to ionizing radiation. However, in the absence of secondary stressors, BrdU is thought to substitute relatively benignly for thymidine and is commonly used to "birth-date" proliferative cells. We report a novel antiproliferative effect of BrdU on cancer cells, which is independent of its role in radiosensitization. A single, brief in vitro exposure to BrdU induces a profound and sustained reduction in the proliferation rate of all cancer cells examined. Cells do not die but variably up-regulate some senescence-associated proteins as they accumulate in the G1 phase of the cell cycle. Bromodeoxyuridine also impairs the proliferative capacity of primary tumor-initiating human glioma cells and may therefore represent a means of targeting cancer stem cells. Finally, conservative in vivo BrdU regimens--in the absence of any other treatment--significantly suppress the progression of gliomas in the highly aggressive, syngeneic RG2 model. These results suggest that BrdU may have an important role as an adjunctive therapeutic for a wide variety of cancers based on new insights into its effect as a negative regulator of cell cycle progression.

Targeting DNA mismatch repair for radiosensitization

Postreplicational mismatch repair (MMR) proteins are capable of recognizing and processing not only single base-pair mismatches and insertion-deletion loops (IDLs) that occur during DNA replication, but also adducts in DNA resulting from treatment with cancer chemotherapy agents. These include widely varying types of DNA adducts resulting from methylating agents such as MNNG, MNU, temozolomide, and procarbazine; CpG crosslinks resulting from cisplatin and carboplatin; and S(6)-thioguanine and S(6)-methylthioguanine residues in DNA. Although MMR proteins can recognize both replicational errors and chemotherapy-induced adducts in DNA, the end results of this recognition are very different. Base-base mismatches and IDLs can be repaired by MMR, restoring genomic integrity, whereas MMR-mediated recognition and processing of chemotherapy-induced adducts in DNA results in apoptosis. After the loss of MMR, the inability of cells to recognize and correct single base-pair mismatches and insertion-deletion loops can lead to secondary mutations in proto-oncogenes and tumor-suppressor genes, thereby contributing to the development of cancer. In addition, the inability of MMR-deficient cells to recognize chemotherapy-induced adducts in DNA can result in a damage-tolerant phenotype that translates to clinically significant resistance by allowing for selection of MMR-deficient cancer cells. We have shown recently that these MMR-deficient, drug-resistant cells can be targeted for radiosensitization by the halogenated thymidine analogs iododeoxyuridine (IdUrd) and bromodeoxyuridine (BrdUrd). These thymidine (dThd) analogs become incorporated into DNA and form reactive uracil radicals after ionizing radiation (IR), increasing strand breaks. IdUrd and BrdUrd appear to be removed from DNA in MMR-proficient cells with limited toxicity or disruption of the cell cycle, while accumulating at much higher levels in MMR-deficient cells. As a result, it is possible to effectively increase the radiosensitization of MMR-deficient cells at levels of halogenated dThd analog that demonstrate limited toxicity to MMR-proficient cells. This indicates that a combined approach of IdUrd or BrdUrd with IR may be effective in killing MMR-deficient tumors in patients, which are resistant to many cancer chemotherapy agents commonly used in the clinic.

Adjuvant therapy for pancreatic cancer: current treatment approaches and future challenges

The past several decades have witnessed advances in the management of pancreatic cancer; however, much remains to be accomplished. Emerging techniques in the fields of surgery, RT, chemotherapy, and immunotherapy offer hope for greater locoregional control, survival, and quality of life for these patients.

AGA technical review on the epidemiology, diagnosis, and treatment of pancreatic ductal adenocarcinoma. American Gastroenterological Association

This literature review and the recommendations therein were prepared for the American Gastroenterological Association Clinical Practice and Practice Economics Committee. The paper was approved by the Committee in March 1999 and by the AGA Governing Board in May 1999.

Bromodeoxyuridine alternating with radiation for advanced uterine cervix cancer: a phase I and drug incorporation study

PURPOSE

Preclinical studies show a significant increase in the ratio of the radiosensitizer bromodeoxyuridine (BUdR) in tumors versus the intestinal mucosa during the drug elimination period, compared with the ratio during drug infusion. We constructed a phase I study in patients with locally advanced cervix cancer, using alternating cycles of BUdR and radiation therapy (RT).

PATIENTS AND METHODS

Eighteen patients with stage IIB to IVA cervix cancer participated. A treatment cycle consisted of a 4-day BUdR infusion followed by a week of pelvic RT, 15 Gy twice daily in 1.5-Gy fractions. After three cycles, additional BUdR was infused, followed by brachytherapy. The fraction of thymidine replaced by BUdR and the fraction of cells incorporating BUdR were determined in rectal mucosa and tumor biopsies at the end of the first BUdR infusion (day 5), at the middle of the first RT week (day 10), and at the time of brachytherapy.

RESULTS

Dose-limiting toxicity was observed in one of 16 patients receiving 1,000 mg/m2/d x 4 days and in both patients receiving 1,333 mg/m2/d x 4 days each cycle. After a median follow-up of 39 months, 12 patients (66%) were free of pelvic disease and nine (50%) were alive and disease free. The ratio of tumor to rectum BUdR incorporation averaged 1.5 to 1.8 and did not differ significantly between day 5 and day 10. A trend toward reduced ratio was observed at brachytherapy. Drug-containing cells in rectal biopsies migrated from the crypts to the mucosal surface.

CONCLUSION

In this schedule, 1,000 mg/m2/d is the maximum-tolerated dose of BUdR. BUdR incorporation levels in tumors were consistent with clinically significant radiosensitization. The migration of BUdR-containing rectal mucosa cells from the crypts to the surface at the time of RT suggests that this regimen may offer a relative sparing of the mucosa from radiosensitization.