Phase I and pharmacologic study of sequential topotecan, carboplatin, and etoposide

Phase I and pharmacologic study of sequential topotecan-carboplatin-etoposide in patients with extensive stage small cell lung cancer

The inhibition of topoisomerase I by topotecan results in a compensatory increase in topoisomerase II associated with increased in vitro sensitivity of tumors to etoposide. Maximal synergy has been observed for the sequence of topotecan followed by etoposide. Carboplatin has clinical activity when combined with either of these two agents. These interactions were the pharmacologic rationale for topotecan p.o. days 1-5, carboplatin i.v. day 6, and etoposide p.o. days 6-10. Three successive dose levels were explored: (1) topotecan 2mg/day, carboplatin AUC 5, etoposide 150 mg/day; (2) topotecan 3mg/day, carboplatin AUC 5, etoposide 150 mg/day; and (3) topotecan 3mg/day, carboplatin AUC 5, etoposide 200mg/day. Filgrastim 5 microg/kg/day was injected s.c. days 11-18. Up to 6 cycles were administered every 21 days. Eligible patients had measurable or evaluable, extensive disease, small lung cell lung cancer, no prior chemotherapy, ECOG performance status 0-2, and adequate hematologic, renal, and hepatic function. Follow-up was weekly for CBC. Tumor response was assessed after 2 and 6 cycles. Dose limiting toxicity (DLT) was defined as any of the following in cycle 1: grade 3 or 4 non-hematologic toxicity other than nausea and vomiting, grade 4 neutropenia lasting more than 3 days, neutropenic fever or sepsis, grade 4 thrombocytopenia, or failure to recover neutrophils >or=1500/microl or platelets >or=100,000/microl by day 28. Ten patients were enrolled: median age 62 (range, 50-79); female/male 4/6; and performance status 0/1/2 in 2/7/1. Three patients each were treated on dose levels 1 and 2 without DLT. The first 2 patients entered on dose level 3 had no DLT. The third patient on dose level 3 developed grade 4 neutropenia lasting more than 3 days, neutropenic fever, and grade 4 thrombocytopenia on day 15 of cycle 1. The fourth patient on dose level 3 developed grade 4 thrombocytopenia on day 18 of cycle 1. One patient received only 1 cycle and was not evaluable for response. Seven patients completed 6 cycles: 1 had a complete response and 6 achieved a partial response. The third patient on dose level 3 received 2 cycles and had stable disease, but had to be removed from protocol treatment because of grade 4 neutropenia despite dose reduction in cycle 2. The fourth patient on dose level 3 achieved a partial response, but had to be removed from protocol therapy after cycle 5 because of recurrent grade 4 thrombocytopenia. In conclusion, neutropenia and thrombocytopenia were dose-limiting. The maximum tolerated dose (MTD) is topotecan 3mg/day p.o. days 1-5, carboplatin AUC 5i.v. day 6, and etoposide 150 mg/day p.o. days 6-10 with filgrastim.

Purification and characterization of a novel ATP-independent type I DNA topoisomerase from a marine methylotroph

DNA topoisomerase is involved in DNA repair and replication. In this study, a novel ATP-independent 30-kDa type I DNA topoisomerase was purified and characterized from a marine methylotroph, Methylophaga sp. strain 3. The purified enzyme composed of a single polypeptide was active over a broad range of temperature and pH. The enzyme was able to relax only negatively supercoiled DNA. Mg(2+) was required for its relaxation activity, while ATP gave no effect. The enzyme was clearly inhibited by camptothecin, ethidium bromide, and single-stranded DNA, but not by nalidixic acid and etoposide. Interestingly, the purified enzyme showed Mn(2+)-activated endonuclease activity on supercoiled DNA. The N-terminal sequence of the purified enzyme showed no homology with those of other type I enzymes. These results suggest that the purified enzyme is an ATP-independent type I DNA topoisomerase that has, for the first time, been characterized from a marine methylotroph.

Topotecan in the treatment of recurrent small cell lung cancer: an update

Small cell lung cancer (SCLC) is an aggressive malignancy with a high propensity for early regional and distant metastasis. Response rates to first-line chemotherapy are typically high, but short lived. The outlook for patients with recurrent SCLC is poor. A variety of single- and multi-agent chemotherapy regimens have met with limited success in patients with recurrent SCLC, and survival is generally measured in weeks. Until recently, further chemotherapy was not widely considered appropriate for patients with relapsed SCLC. The choice of chemotherapy at relapse is dependent on many factors, including type of and response to first-line therapy, the treatment-free interval, and the patient's performance status. Intravenous topotecan (Hycamtin; GlaxoSmithKline; Philadelphia, PA) has provided oncologists and patients in many countries with an effective and tolerable therapeutic option for recurrent SCLC. The clinical profile of topotecan was established in several phase II studies and confirmed in a randomized, phase III trial versus cyclophosphamide, doxorubicin (Adriamycin; Bedford Laboratories; Bedford, OH), and vincristine (Oncovin; Eli Lilly and Company; Indianapolis, IN)--CAV. In those studies, topotecan exhibited antitumor activity in both chemosensitive and refractory disease. Further, topotecan therapy is associated with significant symptom palliation in this patient population. Because the toxicity profile of topotecan is predictable, generally manageable, and noncumulative, the agent also has potential utility in patients with a poor prognosis and/or a poor performance status. Alternative dosing regimens (lower dose, weekly) and the introduction of an oral formulation may expand the use of topotecan as a single agent and in combination therapy in the second- and first-line treatment of this disease.

Topotecan as first-line therapy for small cell lung cancer

Although current treatments for small-cell lung cancer (SCLC) yield objective response rates exceeding 50%, most patients relapse. Hence, research into the identification of novel agents and combinations that may improve therapy is ongoing. Topotecan, an established treatment for patients with recurrent SCLC, is being investigated as first-line therapy for SCLC because of its novel mechanism of action, non-cumulative toxicity and in vitro synergy with other active agents. Several phase II studies of doublet and triplet combination therapy with other agents, including paclitaxel, cisplatin, carboplatin and etoposide, have reported promising results for first-line treatment of SCLC. For example, in combination with paclitaxel, complete and overall responses were 3-67% and 45-100%, respectively, in extensive-stage disease. Furthermore, two studies of the triplet combination of topotecan with paclitaxel plus carboplatin yielded impressive complete response rates of 37-51% in limited-stage SCLC. The most frequent adverse events associated with topotecan-based regimens have been reported as neutropenia and thrombocytopenia so growth factor support is often incorporated into treatments. Several ongoing phase III studies will help to clarify the role of topotecan in the first-line treatment of SCLC.

Emerging Role of Topotecan in First-Line Therapy of Small-Cell Lung Cancer

Topotecan, a novel topoisomerase I inhibitor, is an established treatment for patients with recurrent small-cell lung cancer (SCLC), with antitumor response rates of approximately 20% and median survival of approximately 32 weeks in patients with extensive-stage disease. Topotecan's comparable activity relative to other agents used in SCLC and its novel mechanism of action, noncumulative toxicity, and in vitro synergy with other active agents have provided the rationale for investigating topotecan in first-line therapy. Furthermore, topotecan penetrates the blood-brain barrier and is potentially useful for the relatively large subset of patients with SCLC and brain metastases. In early studies of topotecan in brain metastases, encouraging antitumor activity has been observed. In several feasibility and phase II studies of topotecan as single-agent therapy in patients with extensive- and limited-stage tumors and as part of novel first-line combination regimens, overall response rates have ranged from 42% to 100%. Complete responses of 3%-67% and partial responses of 33%-80% have been observed in first-line therapy. Furthermore, the median overall survival in patients receiving topotecan in first-line therapy has ranged from approximately 8 months (extensive-stage disease) to 20 months (limited-stage disease). The most frequent adverse events associated with topotecan-based regimens include grade 3/4 neutropenia and thrombocytopenia that often require the incorporation of growth factor support into the treatment regimen. Nonhematologic adverse events associated with topotecan-based combination regimens have been mild or primarily attributed to other agents in the combination. Alternative doses and schedules (3 consecutive days and weekly) are being explored because they appear to be associated with considerably less myelosuppression. Although several trials have established the feasibility and activity of topotecan in first-line therapy of patients with SCLC, randomized phase III studies with comparison to standard therapy will be required to confirm a potential role for this active agent and to determine the optimal dosing regimen.

Topoisomerase I interactive agents

Increased insight into the mechanism of interaction of topoisomerase I interactive agents will maximize the therapeutic index and enhance the development of additional agents. Preclinical studies designed to elucidate mechanisms by which the topoisomerase I interactive agents induce cell death will be essential. The role of ABC transporters in resistance to topoisomerase I interactive agents has been recently appreciated and future studies should be directed at circumventing this resistance. The results of preclinical studies must be translated into the design of clinical trials so that these agents can be used rationally. In this regard results of preclinical studies have clearly pointed to the enhanced antitumor activity from protracted dosing of topoisomerase I interactive agents and results of clinical trials are now supporting these preclinical findings. Finally, investigators are trying to understand better the mechanism(s) of the dose-limiting toxicities observed with the currently available topoisomerase I interactive agents in an effort to enable the optimal dosing of these agents. Even though the first priority must be to determine the therapeutic potential of the currently available agents, it is reassuring to know that other topoisomerase I interactive agents are currently under development.