Topoisomerases I and II are en-zymes that alter the topologicstate of DNA through DNA strand cleavage, strand passage, and religation. They participate in most aspects of DNA metabolism and are therefore vital to the cell undergoing division. Topoisomerases I and II are critical cellular targets for several antitumor agents: camptothecin derivatives interact with topoisomerase I, and anthracycline derivatives and epipodophyllotoxine derivatives with topoisomerase II.
Since the discovery of the parent compound 20(s)-camptothecin in 1966, several derivatives have been prepared. Two such agents, irinotecan(Drug information on irinotecan) (CPT-11, Camptosar) and topotecan(Drug information on topotecan) (Hycamtin), have been approved for medical use in the United States.[4,5] Camptothecins are active agents in the treatment of gastrointestinal malignancies, ovarian cancer, lung cancer, and myelodysplastic syndrome, with activity also reported in other tumors such as brain and breast malignancies. Irinotecan is currently the leading camptothecin used worldwide. The most significant impact of irinotecan to date has been in the management of metastatic colorectal cancer, but clinically relevant activity in many other diseases has been documented as well.
Anthracyclines are antitumor antibiotics active against a wide range of hematologic and solid cancers. Anthracyclines inhibit topoisomerase II and are involved in oxidation/reduction reactions through the generation of free radicals. Antiproliferative activity is thought to result from these and other mechanisms. Since its introduction into clinical practice in the 1960s, doxorubicin(Drug information on doxorubicin) has been recognized as one of the most active antineoplastic agents available, with a wide spectrum of antitumor efficacy. Epirubicin (Ellence) hydrochloride is a synthetic derivative of daunorubicin(Drug information on daunorubicin) (DaunoXome), the prototype anthracycline. Epirubicin(Drug information on epirubicin) is the 4¢ epimer of doxorubicin; its structure differs from that of doxorubicin only in the reorientation of a single hydroxyl group at the 4¢ position. Epirubicin was identified through screening a series of doxorubicin derivatives that could potentially improve therapeutic index as compared with the parent compound.
Combination chemotherapy is important in the treatment of many tumor types, as it can achieve additive or synergistic cytotoxic activities.[9,10] The DNA topoisomerases I and II are targets of several antineoplastic agents. Depletion of the target topoisomerase can be accompanied with reciprocal changes in the other topoisomerases. Targeting both topoisomerases I and II could therefore offer significant synergy. In preclinical models, inhibition of topoisomerases I and II has resulted in synergistic activity when such agents were administered sequentially in several tumor types. While clinical data are limited, a phase I study with topotecan (topoisomerase I inhibitor) followed sequentially with doxorubicin (topoisomerase II inhibitor) showed that this combination can be given safely with hematologic toxicity as the dose-limiting toxicity.
Both irinotecan and epirubicin play important roles in cancer therapies today. Each has a broad spectrum of action with the additional potential for clinical synergy. Except for bone marrow toxicity, the two agents have few toxicities in common. The phase I study reported herein is exploring the clinical potential of the combination of irinotecan (topoisomerase I inhibitor) and epirubicin (topoisomerase II inhibitor) in patients with advanced cancer. Only very preliminary data are available so far for this ongoing trial.
Study objectives are to determine the dose-limiting toxicity and maximum tolerated dose of the combination of irinotecan and epirubicin when administered in a day 1 and day 8, every-28-days cycle. Additional goals are to determine the pharmacokinetics of each agent to assess potential drug interactions, and to document any observed antitumor responses in the hopes of focusing phase II efforts with this combination.
Extra care was taken due to the high probability of myelosuppression, as was seen with similar combinations. The starting irinotecan dose was 100 mg/m² on days 1 and 8 given every 28 days. This dose represents less than 50% of the recommended phase II dose of 125 mg/m² weekly for 4 weeks followed by a 2-week rest. In the literature, the recommended epirubicin dose is 135 mg/m² given every 3 weeks as a single agent or 60 mg/m² on days 1 and 8 every 4 weeks when used in a combination regimen. The starting epirubicin dose in this phase I study was 40 mg/m² on days 1 and 8, which is 59% of the single-dose epirubicin given every 3 weeks and 66% of the epirubicin dose when given on days 1 and 8 every 4 weeks. Dose escalation is detailed in Table 1.
Entry criteria included histologically documented incurable malignancy, age of at least 18 years, anticipated survival of at least 8 weeks, and Eastern Cooperative Oncology Group (ECOG) performance status of 0 to 2. Patients had to have adequate end organ function, including normal hepatic and renal function. Also required were a white blood cell count above 3,000/µL, an absolute neutrophil count above 1,500/µL, and a platelet count above 100,000/µL. Normal cardiac function, as measured by radionuclide ventriculogram scan (ejection fraction greater than 50%), was also required.
Patients must have recovered from the reversible side effects of previous therapy. Exclusion criteria included previous doxorubicin treatment of more than 240 mg/m², severe anorexia or vomiting, significant recent weight loss, pregnancy or lactation, serious intercurrent medical illnesses, history of congestive heart failure, and concurrent immunotherapy or radiotherapy. All patients provided written informed consent.
According to the original study plan, patients were to be enrolled at dose level 1 with starting doses of irinotecan at 100 mg/m² and epirubicin at 40 mg/m² (Table 1). One treatment cycle was 4 weeks, with study drugs administered on days 1 and 8 with the subsequent 2 weeks off. Irinotecan was to be given over 90 minutes and epirubicin was to be given over 5 minutes intravenously. Using a typical phase I dose-escalation scheme, three patients were to be treated in each cohort. If no dose-limiting toxicities were observed in the first treatment cycle, an additional three patients would be started at the next dose level. However, because significant myelosuppression was observed in patients at the first dose level, the protocol was modified as shown in Table 2.
Dose-limiting toxicity is defined as a treatment-related toxicity severe enough to preclude additional therapy for that patient, and is typically grade 3 or 4 toxicity. The maximum tolerated dose is defined as the highest dose level that does not result in dose-limiting toxicities in two or more of six patients treated at that level.
Blood samples are being obtained from all patients at predetermined intervals on day 1 only. Samples will be analyzed to determine clearance and half-life of both irinotecan and epirubicin. Specifically, this analysis will help determine whether concurrent administration of the two compounds results in any significant pharmacokinetic interactions.
All treatment is delivered on an outpatient basis. Patients are evaluated on each day of treatment by physical examination and laboratory studies including hematologic and chemistry panels. Tumor assessment is conducted at baseline and again every 8 weeks (or two cycles). Repeat ejection fraction is assessed after patients have received 450 to 500 mg/m² of epirubicin. Patients who are tolerating the therapy reasonably well and gaining clinical benefit (ie, stable or improving disease status) may continue on the study.
Four patients were accrued to the initial cohort. Their characteristics are listed in Table 3. Two patients had to be replaced due to rapid disease progression and two developed a dose-limiting toxicity. No significant acute toxicities were observed, namely, no significant diarrhea or nausea/vomiting. However, two of the four patients had myelosuppression as dose-limiting toxicity. Both patients were re-treated at reduced doses and currently remain on study. Toxicities are summarized in Table 4. One patient with metastatic gallbladder cancer had a minor response accompanied by a 50% decrease in carcinoembryonic antigen level. Another patient with metastatic pancreatic cancer had stable disease and symptomatic improvement.
The combination of topoisomerase I and II inhibitors previously has been shown to result in significant myelosuppression, and we have observed a similar effect in early results of this trial. Once a maximum tolerated dose is identified and the pharmacokinetic data analyzed, selected phase II studies will be initiated in patients with gastric cancer and cholangiocarcinoma/bile duct cancers. The day 1 and 8 schedule is convenient for patients and has resulted in acceptable acute side effects. Although it is possible that alternative schedules (such as every 14 days or every 21 days) may allow for higher dose escalation, we suspect this will not be the case.