Cisplatin with high-dose infusions of hydroxyurea to inhibit DNA repair. A phase II study in non-small-cell lung cancer

Hydroxyurea: a key player in cancer chemotherapy

Hydroxyurea (HU) is a simple organic compound currently used as a cancer chemotherapeutic agent. It acts specifically on the S-phase of the cell cycle by inhibiting the enzyme ribonucleoside diphosphate reductase, thereby hindering the reductive conversion of ribonucleotides to deoxyribonucleotides and thus limiting de novo DNA synthesis. HU is employed in hemotological settings as a first-line treatment of myeloproliferative disorders, such as polycythemia vera, essential thrombocythemia and primary myelofibrosis, apart from having a vital role in combination therapy for management of malignant melanoma, head and neck cancers and brain tumors. It offers an advantage that the patient may take this drug on an ambulatory basis with minimum clinical toxicity, while some of its limitations include gastrointestinal disturbance and bone marrow depression. This review will summarize and present the overall effects of HU and its combination therapy as an anticancer agent.

A phase I trial of high-dose continuous-infusion hydroxyurea

Hydroxyurea inhibits ribonucleotide reductase, resulting in depletion of intracellular deoxynucleotide pools and inhibition of DNA repair. It has been used in a variety of malignancies and is usually given orally. Deoxynucleotide depletion is directly related to the concentration of and duration of exposure to hydroxyurea; thus, prolonged continuous infusion may result in increased therapeutic efficacy. A total of 30 patients were treated on this trial, designed to determine the maximum tolerated doses (MTD) of intravenous hydroxyurea given as a 24- or 48-h continuous infusion. The MTD for the 24-h infusion was 13,520 mg/m2 following a bolus of 1,690 mg/m2, and the mean (+/- SD) plasma steady-state concentration was 1.93 +/- 0.52 mM. For the 48-h infusion, the MTD was 17,576 mg/m2 following a bolus of 2,197 mg/m2 and the mean steady-state level was 1.43 +/- 0.31 mM. The dose-limiting toxicity on both schedules was marrow suppression manifesting as neutropenia and thrombocytopenia. Pharmacokinetic analysis revealed decreasing clearance with increasing dose, implying that drug elimination is saturable. Pharmacodynamic analysis showed a slight correlation between steady-state plasma levels and the degree of marrow suppression.

5-Fluorouracil, leucovorin, hydroxyurea, and escalating doses of continuous-infusion cisplatin with concomitant radiotherapy: a clinical and pharmacologic study

Cisplatin (CDDP), 5-fluorouracil (5-FU), and hydroxyurea (HU) have individually demonstrated activity against several solid tumors, act synergistically with each other in vitro, and may act as radiation sensitizers. Therefore, we designed a phase I study to determine the maximally tolerated dose of cisplatin as given in addition to our previously described combination of 5-FU, HU, and concomitant radiotherapy (XRT). Patients exhibiting advanced solid tumors requiring palliative XRT were eligible. The regimen consisted of 1 g HU given p.o.b.i.d. on days 1-5, 600 mg/m2 5-FU given i.v. daily by continuous infusion (c.i.) on days 1-5, escalating doses of cisplatin starting at 10 mg/m2 daily given by c.i. on days 1-5, and involved-field XRT carried out on days 1-5. The cycle was repeated every 14 days until the target XRT dose had been reached. In all, 19 patients were entered at the first dose level, and cumulative grade 3-4 myelosuppression was seen in 16 subjects. As no dose escalation was feasible, the chemotherapy was subsequently altered by using the above regimen for cycles 1, 3, 5, and 7 and substituting the less myelosuppressive regimen of 1 g HU given p.o.b.i.d. on days 1-5, 400 mg/m2 5-FU given i.v. daily by c.i., and 100 mg leucovorin given p.o.4 h on days 1-5 for cycles 2, 4, and 6. On this alternating program, 28 patients were treated with escalating doses of CDDP. The dose-limiting toxicity was again myelosuppression, which was prohibitive at a CDDP dose of 20 mg/m2 daily. In the final phase of the protocol, 30 subjects were treated with the above alternating-cycle regimen at a CDDP dose of 20 mg/m2 daily and a decreased HU dose of 500 mg p.o.b.i.d. in an attempt to circumvent the myelosuppression associated with this dose of CDDP. Although severe acute toxicity (cycles 1 and 2) was observed less frequently, cumulative toxicity (all cycles) remained pronounced. The other major toxicity encountered was mucositis, which was particularly pronounced in patients receiving radiation to the head and neck and following leucovorin-containing cycles. Plasma concentrations of free platinum did not correlate with the CDDP dose, possibly due to the narrow range of doses given. Pharmacodynamic modeling demonstrated that the CDDP dose and the HU dose were associated with leukopenia. Antitumor activity was demonstrated in a number of solid tumors particularly non-small-cell lung cancer and head and neck cancer.(ABSTRACT TRUNCATED AT 400 WORDS)

Inhibition of DNA repair and the enhancement of cytotoxicity of alkylating agents

DNA damage was evaluated by flow cytometric (FCM) analysis of cells treated with L-phenylalanine mustard (L-PAM) and stained with anti-DNA monoclonal antibody (MAb) F7-26. DNA damage was rapidly repaired, as indicated by the loss of DNA immunoreactivity after removal of L-PAM. Two types of drug combinations were found to inhibit DNA repair. Combinations containing inhibitors of DNA polymerase (ara-C, aphidicolin) or these inhibitors and hydroxyurea inhibited DNA repair in A2780/PAM and A549 cells. The inhibition of DNA repair by combinations of DNA-damaging agents thioTEPA or cisplatin and DNA polymerase inhibitors is a novel observation based on the specificity of DNA damage assay with MAb F7-26. Combinations containing thioTEPA or cisplatin inhibited DNA repair in A549 but not in A2780/PAM cells. Drug combinations which inhibited DNA repair also significantly enhanced cell killing by L-PAM. Cell survival in cultures treated with L-PAM and efficient inhibitors was 2 to 3 orders of magnitude lower than was expected for additive survival. ThioTEPA and cisplatin play a dual role in combination chemotherapy by inducing DNA damage and inhibiting repair of DNA damage. FCM analysis of DNA repair may be a useful component of drug evaluation and could be applied to determine cell-type specific sensitivity to inhibitors of DNA repair.