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ORIGINAL PAPER |
a Response Oncology, Memphis, Tennessee, USA; b Central Georgia Hematology Oncology Associates, Macon, Georgia, USA; c Tennessee Oncology, Nashville, Tennessee, USA; d Phoebe Cancer Center, Albany, Georgia, USA; e Oncology Consultants, Houston, Texas, USA
Correspondence: Robert Birch, Ph.D., Online Collaborative Oncology Group, 1805 Moriah Woods Boulevard, Memphis, Tennessee 38117, USA. Telephone: 901-684-1900; Fax: 901-684-6168; e-mail: b.birch{at}ocog.net
| ABSTRACT |
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Key Words. Drug therapy • Paclitaxel • Lung neoplasms • Topotecan
| INTRODUCTION |
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Several promising agents with novel mechanisms of action have recently emerged as effective agents in extensive SCLC, including paclitaxel, topotecan, irinotecan, and gemcitabine [9]. Paclitaxel (Taxol®; Bristol-Myers Squibb Co.; Princeton, NJ) is a taxane that promotes the assembly and stabilization of microtubules. Inappropriate stabilization of microtubules leads to an accumulation of cells in the mitotic phase, which leads to apoptosis. The efficacy of paclitaxel in patients with previously untreated SCLC was established in two phase II studies by the Eastern Cooperative Oncology Group (ECOG) and the North Central Cancer Treatment Group. These studies reported an objective response rate of 53%-68% and a median survival of 7.3-11 months [10, 11].
Another agent with a novel mechanism of action for the treatment of SCLC is topotecan. Topotecan (Hycamtin®; GlaxoSmithKline; Brentford, UK) is a topoisomerase I inhibitor that prevents the re-ligation of single-stranded DNA breaks, leading to irreparable double-stranded DNA damage during replication. The efficacy of topotecan in the treatment of SCLC was demonstrated in three phase II studies and one phase III study in patients who had failed first-line chemotherapy [1215]Topotecan is currently approved for second-line therapy in SCLC at a starting dose of 1.5 mg/m2 by a daily 30-minute i.v. infusion for 5 consecutive days of a 21-day course. The primary dose-limiting toxicity associated with the 5-day regimen is myelosuppression. In some patients, myelosuppression can lead to treatment interruptions or dose reductions that could potentially limit tumor response. Therefore, the optimal dosing strategy has not yet been defined. As a consequence, alternative doses and schedules of topotecan are currently under investigation.
It is widely accepted that combinations of cytotoxic drugs produce higher response rates and survival rates in patients with SCLC compared with single-agent therapy. Combinations of agents with unique, nonoverlapping mechanisms of action may offer synergy with respect to antitumor activity. In vitro studies have indicated that the combination of topotecan/ paclitaxel results in synergistic activity in both cell lines and primary cultures of human tumor cells [16, 17]. Therefore, a combination of topotecan and paclitaxel may provide antitumor activity in the clinical setting. In addition, the combination of these two agents with nonoverlapping mechanisms of action may provide improved antitumor activity compared with cisplatin/etoposide, the current standard of care in previously untreated patients with SCLC.
As a single agent, topotecan has demonstrated antitumor activity in previously untreated patients with extensive SCLC, with an objective response rate of 40% and a median survival of 10 months [18]. Recently, 5-day topotecan in combination with paclitaxel was investigated by several groups for the treatment of SCLC patients with extensive disease [1923]. Although topotecan/paclitaxel was felt to be active, there was a high incidence of serious hematologic toxicity, which was not prevented with the use of G-CSF or filgrastim support, especially when combined with higher paclitaxel doses (
175 mg/m2). Because of the high incidence of myelosuppression associated with the standard 5-day topotecan regimen, several alternative dosing regimens have been investigated. The feasibility of a 3-day topotecan regimen has been reported in patients with ovarian cancer [24, 25]. The 3-day topotecan regimen was less toxic than the 5-day topotecan regimen and showed promising antitumor activity. A 3-day topotecan regimen is likely to provide a similar safety profile advantage in patients with SCLC, particularly if topotecan is combined with another agent that is associated with significant hematologic toxicity.
In a Cancer and Leukemia Group B (CALGB) phase I study, the maximum tolerated doses (MTDs) for topotecan in combination with paclitaxel, when using the standard 5-day dosing regimen for topotecan, were paclitaxel 80 mg/m2 on day 1 and topotecan 1.0 mg/m2 on days 1-5 of a 21-day course [26]. With G-CSF support, paclitaxel could be escalated to as high as 230 mg/m2 following topotecan 1.0 mg/m2. We hypothesized that administration of topotecan over 3 days would allow dose escalation of both topotecan and paclitaxel without routine use of G-CSF support. Therefore, the objective of this study was to determine the MTD of 3-day topotecan that could be administered with paclitaxel. Because of associated hypersensitivity reactions with paclitaxel, we chose to first escalate topotecan, followed by an escalation of paclitaxel if toxicity permitted. A preliminary report of this study was previously published [27].
| MATERIALS AND METHODS |
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18 years of age with histologically confirmed extensive SCLC with measurable or evaluable disease were eligible. Patients were required to have an ECOG performance score of
2, normal liver function (bilirubin
1.5 mg/dl), and normal renal function (creatinine
1.5 mg/dl). Patients were required to have WBC counts
4,000 cells/µl and platelet counts
100,000/µl. Patients with brain metastases were eligible and could receive whole-brain irradiation concurrently with the chemotherapy, but only if they had minimal neurologic symptoms and met all other eligibility criteria. Patients with a history of prior malignancy within 5 years, with the exception of skin cancer and cervical carcinoma in situ, were ineligible, as were patients who had received prior treatment for SCLC. Patients with severe coexisting medical illnesses that would prevent them from receiving combination regimens, and patients with a history of allergic reactions to drugs mixed with a polyoxyethylated castor oil (Cremophor®; BASF AG; Stuttgart, Germany) stabilizer were also ineligible. Women who were pregnant or lactating were ineligible, and women on the study who were capable of childbearing were required to take appropriate precautions to prevent pregnancy during treatment. All patients were required to give written informed consent.
Study Design
This was an open-label, phase I, dose-escalation study planned for topotecan on days 1-3 and paclitaxel on day 1 of a 21-day course. All patients received premedication for paclitaxel, including oral dexamethasone 20 mg, 12 and 6 hours prior to treatment; i.v. diphenhydramine 50 mg; i.v. ranitidine 50 mg; and i.v. dexamethasone 20 mg, 30 minutes prior to treatment. The first cohort of patients received i.v. paclitaxel 135 mg/m2 administered over 1 hour on day 1, followed by i.v. topotecan 1.25 mg/m2 over 30 minutes on days 1-3. Patients in the second cohort received i.v. paclitaxel 135 mg/m2 administered over 1 hour on day 1, followed by i.v. topotecan 1.5 mg/m2 over 30 minutes on days 1-3. The third cohort of patients received i.v. paclitaxel 175 mg/m2 administered over 1 hour on day 1, followed by i.v. topotecan 1.5 mg/m2 over 30 minutes on days 1-3. These regimens were repeated at 21- to 28-day intervals for a total of four courses. Complete restaging was performed after the completion of four courses, with partial responders receiving up to two additional courses at the discretion of the physician. Complete responders were to receive no further treatment.
Safety and Tolerability Assessments
Dose-limiting toxicity was defined as at least one of three patients per cohort experiencing grade 4 toxicity, or at least two of three patients per cohort experiencing grade 3 toxicity. In such a case, three additional patients were enrolled at that dose level. If at least two of six patients experienced grade 4 toxicity, or if at least four of six patients experienced grade 3 toxicity in a given cohort, that dose was then considered to be a toxic dose and the dose at the previous cohort was considered the MTD.
Because myelosuppression was expected to be the major toxicity for this regimen, blood counts were obtained on a weekly basis with predetermined dose-reduction criteria. If WBC counts were <2,500 cells/µl or platelet counts were <75,000/µl at day 21, treatment was delayed 1 week or until WBC counts were
2,500 cells/µl and platelet counts were
75,000/µl. Patients were treated at full doses on hematologic recovery. Patients who developed grade 4 neutropenia and fever (>38.5°C) or who experienced reversible nonhematologic grade 3/4 toxicity received 75% of the total dose of both drugs during subsequent courses. Patients who developed severe acute hypersensitivity to paclitaxel did not receive further doses of paclitaxel but continued receiving topotecan. Patients were discontinued from the study if they could no longer tolerate their assigned dose level or if they demonstrated disease progression. Patients failing to respond to dose reduction or failing to achieve hematologic recovery were also discontinued from the study at the discretion of the investigator. Prophylactic hematologic support with G-CSF was not routinely used in this study.
Response Criteria
Tumor response was assessed using World Health Organization criteria [28]. Measurable disease was defined as any mass that was reproducibly measurable in two perpendicular diameters by either physical examination, x-ray, computed tomography, or magnetic resonance imaging. Tumor markers, visceromegaly, bone lesions detectable only by bone scan, ill-defined chest radiographic lesions involving infiltrates, serous effusions, and diffuse skin lesions were not considered measurable disease. Evaluable disease was defined as lesions apparent on x-ray, computed tomography, or magnetic resonance imaging scans, but that were accurately measurable in only one dimension, or ill-defined masses that could not be accurately measured in more than one dimension. Other examples of evaluable disease included positive cytology, tumor markers, and lesions seen on bone scan. Fluid collections including pericardial, pleural, and peritoneal were not considered measurable or evaluable. Because of the availability of tumor markers and scans, and factors that influence their size, visceromegaly such as hepatomegaly or splenomegaly was not considered either measurable or evaluable disease. However, lesions within these tissues, such as hepatic or splenic metastases, were considered measurable or evaluable if they passed all other criteria.
For measurable and evaluable disease, a complete response was defined as the disappearance of all known disease for
4 weeks with no new lesions appearing. A partial response was defined as a
50% reduction in the diameter product (product of two perpendicular diameters) of all measurable lesions with a response of
4 weeks in duration with no new lesions appearing, or as an estimated decrease of
50% for >4 weeks for evaluable disease. Stable disease was defined as a <50% reduction or <25% increase in the diameter product of all measurable lesions without the appearance of new lesions, or an estimated reduction <50% or an estimated increase <25% for evaluable disease. Progressive disease was defined as an increase
25% in the diameter product of all measurable disease or the appearance of new lesions, or an estimated increase of
25% for evaluable disease.
Statistical Methods
All patients who received at least one cycle of chemotherapy were evaluable for response and tolerability. Descriptive summary statistics were used to evaluate demographics and adverse events. Toxicity was graded according to Common Toxicity Criteria. Serious adverse events included grade 3/4 hematologic and nonhematologic toxicities. Response was summarized and tabulated by cohort.
| RESULTS |
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Antitumor Activity
Preliminary antitumor response data in this phase I trial were encouraging. Of the 17 patients, nine (53%) achieved a partial response, with five, one, and three patients achieving a partial response in cohorts 1, 2, and 3, respectively. Of the 17 patients, three (18%) achieved stable disease, and five (29%) experienced progressive disease. Restaging occurred after four cycles of treatment, and patients with a complete or partial response could receive two additional cycles of therapy. One patient in cohort 1, one patient in cohort 2, and two patients in cohort 3 completed six cycles.
| DISCUSSION |
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Topotecan has demonstrated antitumor activity in the treatment of extensive SCLC in the second-line setting, with overall response rates of 11%-25% [12, 13, 15, 32]. Further, topotecan has been investigated in the first-line setting. In a preliminary feasibility study, Schiller et al. [18] reported a 40% overall response rate and a median survival of 10 months with single-agent topotecan (5-day) treatment in previously untreated patients with extensive SCLC. Topotecan is also being investigated in the first-line setting in combination with other cytotoxic agents, with improved antitumor activity and overall response rates ranging from 42%-95% [3336].
Because paclitaxel and topotecan have unique and nonoverlapping mechanisms of action and have non-cross-reactive antitumor activity, several groups have investigated the combination of these two agents for the first-line treatment of patients with extensive SCLC. When patients received paclitaxel 135 mg/m2 on day 5 with topotecan 1.0-1.25 mg/m2 on days 1-5, 60%-92% of patients achieved an overall response [2123]. The CALGB reported a 61%-68% overall response rate with a regimen of paclitaxel 175-230 mg/m2 on day 1 plus topotecan 1 mg/m2 on days 1-5 of a 21-day course [19, 20]. However, despite G-CSF support, 54%-69% of those patients experienced grade 3/4 neutropenia.
All of the previously reported topotecan and paclitaxel regimens used the currently recommended 5-day topotecan regimen. A shorter dosing regimen for topotecan may ameliorate myelosuppression associated with topotecan treatment. Indeed, the feasibility of a 3-day topotecan regimen in ovarian cancer patients was recently reported by Brown et al. [24] and Markman et al. [25]. This regimen is more convenient for patients and appears to provide a more favorable hematologic toxicity profile. We therefore investigated the feasibility of a 3-day regimen of topotecan combined with paclitaxel therapy in patients with extensive SCLC.
In the current study, the MTD for 3-day topotecan in combination with paclitaxel was investigated. In contrast with previous reports, routine G-CSF support was not used in the current study. Nevertheless, only 24% of patients experienced grade 3/4 neutropenia. Further, three of the four patients who experienced grade 3/4 neutropenia were in cohort 3 and received paclitaxel 175 mg/m2 and topotecan 1.5 mg/m2. Based on the safety profile observed in these patients, the MTD for 3-day topotecan with paclitaxel was determined to be topotecan 1.5 mg/m2 and paclitaxel 135 mg/m2. Given that three of the four patients with grade 3/4 neutropenia received topotecan at a higher dose level than the MTD, the combination of 3-day topotecan plus paclitaxel is likely to be better tolerated than 5-day topotecan plus paclitaxel.
Preliminary efficacy of the 3-day topotecan and paclitaxel combination showed promise. Our overall response of 53% was similar to response rates observed using the 5-day topotecan regimen in combination with other agents, including etoposide and carboplatin [3336], yet with a better hematologic toxicity profile. Further, one-third of the patients in this study were treated at doses below the MTD, which may have resulted in an underestimation of the true overall response rate. The overall response in this study is higher than the overall response reported with first-line single-agent topotecan in patients with extensive SCLC (40%) [18]. It is important to again point out that prophylactic hematologic support was not routinely used in the current study. It is possible that the antitumor activity of 3-day topotecan with paclitaxel may be increased if hematologic support is used routinely to allow for an increase in the dose levels of topotecan and paclitaxel. However, the value of dose intensification requires further investigation.
| CONCLUSION |
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| ACKNOWLEDGMENT |
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| REFERENCES |
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This article has been cited by other articles:
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D. J. Stewart Topotecan in the First-Line Treatment of Small Cell Lung Cancer Oncologist, December 1, 2004; 9(suppl_6): 33 - 42. [Abstract] [Full Text] [PDF] |
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B. A. Chabner A Plea for Phase I Clinical Trials Oncologist, February 1, 2003; 8(1): 1 - 1. [Full Text] [PDF] |
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