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Camptothecin and Taxane Regimens for Small-Cell Lung Cancer

Camptothecin and Taxane Regimens for Small-Cell Lung Cancer

ABSTRACT: For more than 2 decades, combination chemotherapy has been the standard treatment for patients with small-cell lung cancer. Despite high initial response rates in both extensive- and limited-stage disease, long-term survival rates are only 10% to 20%. Camptothecins and taxanes are newer classes of agents that have shown significant activity against small-cell lung cancer. Their incorporation into chemotherapy regimens for small-cell lung cancer is being actively studied. In one randomized multicenter study, patients with advanced small-cell lung cancer treated with irinotecan (CPT-11, Camptosar) and cisplatin had a better survival time than patients receiving standard therapy. The combination of taxanes and irinotecan holds promise as an active regimen that may be tolerated better than cisplatin and irinotecan. [ONCOLOGY 16(Suppl 9):33-38, 2002]

The Centers for Disease Control and Prevention recently reported
that the annual mortality for lung cancer in the United States is 154,000.[1]
Small-cell lung cancer accounts for approximately 15% of these tumors. Over the
past 2 decades, combination chemotherapy has become the standard of care for
patients who present with extensive disease. Regimens such as EP (etoposide,
cisplatin [Platinol]), CAV (cyclophosphamide [Cytoxan, Neosar], doxorubicin [Adriamycin],
vincristine), and EC (etoposide, carboplatin [Paraplatin]) can produce response
rates as high as 80%. Nevertheless, for patients with extensive-stage disease,
the median survival is just 7 to 11 months and few patients are alive 2 years
from diagnosis. Even in limited-stage disease, combined modality treatment with
concurrent chemotherapy and radiation produces long-term survival in only 15% of
patients.

As a result, evaluation of newer agents in treatment of
small-cell lung cancer is of critical importance. Newer agents that are active
in small-cell lung cancer include irinotecan (CPT-11, Camptosar), docetaxel (Taxotere),
gemcitabine (Gemzar), ifosfamide (Ifex), paclitaxel, topotecan (Hycamtin), and
vinorelbine (Navelbine).[2] In this article, we will focus on progress in the
development of camptothecin/taxane combinations in the management of small-cell
lung cancer.

Role of Camptothecin Derivatives in
Small-Cell Lung Cancer

The mechanism of action of camptothecin analogs involves their
interaction with topoisomerase I. As a result, the DNA/topoisomerase complex is
bound and normal DNA replication is disrupted, leading to double-stranded DNA
breaks and cell death. Semisynthetic compounds in this class include topotecan
and irinotecan.

Irinotecan has shown activity against a broad range of animal
and human malignancies, including lung cancer. In chemotherapy-naive small-cell
lung cancer patients, Negoro et al reported a 50% response rate to single-agent
irinotecan in a small series.[3] In previously treated small-cell lung cancer
patients, response rates of 16% to 47% have been reported.[4] More recently, a
Japan Clinical Oncology Group phase III trial of 152 extensive-stage small-cell
lung cancer patients showed superiority of irinotecan/cisplatin over etoposide/cisplatin
in terms of median survival (411 vs 282 days, P = .0021), overall response rate
(83% vs 68%), and 2-year survival rate (19% vs 7%).[5] Two North American phase
III trials are under way to further define the role of irinotecan/cisplatin
combinations in small-cell lung cancer.

Topotecan is the other approved semisynthetic camptothecin.
Schiller et al treated 48 newly diagnosed extensive-stage patients with
topotecan at 2 mg/m²/d for 5 days every 3 weeks. The response rate was 40% and
median survival was 10 months.[6] Pooled data of 168 patients with sensitive
relapse (defined as relapse occurring more than 3 months after previous
chemotherapy) showed that 18% responded to topotecan with a median survival of
30 weeks and a 1-year survival rate of 21%.[7] A randomized trial comparing
topotecan with CAV in patients with sensitive relapse demonstrated comparable
response rates and survival times for the two regimens. In that study, topotecan
was more effective in controlling disease-related symptoms.[8] In a recent
Eastern Cooperative Oncology Group (ECOG) study of 223 patients with
extensive-stage small-cell lung cancer, topotecan given after four cycles of EP
improved progression-free survival by 1.3 months when compared to observation.
However, overall survival and quality of life were not statistically different
in the two arms.[9]

Role of Taxanes in Small-Cell Lung Cancer

The taxanes promote microtubular assembly but prevent their
disassembly, thus interfering with normal tubulin polymerization and cell
division. Both the Pacific yew-derived paclitaxel and the semisynthetic
compound docetaxel show promise in the treatment of small-cell lung cancer.

The ECOG performed a phase II study of single-agent paclitaxel
in previously untreated extensive-stage small-cell lung cancer patients.
Paclitaxel at 250 mg/m² infused over 24 hours produced a response rate of 34%,
but 56% of patients had grade 4 leukopenia.[10] The North Central Cancer
Treatment Group used a similar paclitaxel schedule with the addition of
granulocyte colony stimulating factor (G-CSF [Neupogen]) support and reported a
53% response rate and a reduction to 14% in the rate of grade 4 leukopenia.[11]
In a small trial involving pretreated patients with early relapses, paclitaxel
was associated with a 29% response rate.[12] When paclitaxel was combined with
cisplatin, Nair et al reported impressive response rates of 71% to 89% in
extensive-stage small-cell lung cancer patients.[13]

Docetaxel has also been studied for the treatment of small-cell
lung cancer. In a phase II trial of chemotherapy-naive small-cell lung cancer
patients conducted by the Southwest Oncology Group (SWOG), docetaxel at 100
mg/m² produced a response rate of 25% and a median survival of 9 months.[14] The
European Organization for Research and Treatment of Cancer (EORTC) reported a
response rate of 25% with single-agent docetaxel at a dose of 60 mg/m² in
previously treated patients.[15]

Combinations of Docetaxel and Irinotecan

In animal and human cell lines, the combination of taxanes and
camptothecins can be additive or synergistic, but results have been conflicting.
Chou et al showed synergism between paclitaxel and topotecan in human
teratocarcinoma cell line,[16] but Kaufman et al actually showed antagonism when
this combination was used in a human lung cancer cell line.[17] In vitro studies
of the combination of docetaxel and irinotecan showed notable activity in many
models. There was the suggestion that their activity in combination may be
dependent on dosing, sequencing, and cell type.

Couteau et al showed in a phase I study that when docetaxel was
given prior to irinotecan, no relevant drug interaction was detected and the
pharmacokinetics were consistent with the behavior of each drug given
individually.[18] Takeda et al gave the irinotecan prior to docetaxel and
reported a mild increase in docetaxel clearance.[19] The bulk of evidence
suggests no clinically significant interaction between these two drugs with
respect to pharmacokinetics.[18-21]

In terms of dosing schedule, initial studies administered the
medications on an every 3-week cycle. However, high rates of neutropenia and
late diarrhea were reported in such studies (see Table
1
). Couteau et al
reported 85% with grade 4 leukopenia lasting a median of 5 days (and 22.5% with
febrile neutropenia).[18] Adjei et al reported 94% with grade 3/4 leukopenia and
17% with febrile neutropenia.[22] Masuda et al reported grade 3 or 4 neutropenia
in only 19% with only 6% having febrile neutropenia, but this study employed
lower dose intensity. Most phase II trials of docetaxel/irinotecan also report
neutropenia as the most frequent toxicity.

When given with equivalent dose intensity, docetaxel on a weekly
schedule has a lower incidence of neutropenia compared to a 3-week schedule.
Additionally, more frequent administration allows the option of withholding
doses when neutrophil counts are borderline. Additionally, irinotecan displays a
more favorable toxicity profile when given on a weekly basis. Major toxicities
of irinotecan when given on an every-3-week schedule tend to be granulocytopenia,
febrile neutropenia, and/or late diarrhea. When given on a weekly schedule,
irinotecan has lower incidences of severe neutropenia and diarrhea. Thus giving
docetaxel/irinotecan combinations on a weekly schedule should be considered as a
means of increasing the safety of administration.

At the Yale Cancer Center, we have conducted a phase I study
evaluating weekly docetaxel/irinotecan. We originally delivered the medications
weekly for 4 weeks on an every-6-week cycle, but due to frequent treatment
delays at day 21 due to neutropenia, we amended the dosing guidelines. We found
that the combination was better tolerated when docetaxel at 35 mg/m² and
irinotecan at 60 mg/m² were given on days 1 and 8 of an every-3-week cycle. In
44 patients studied, preliminary data show grade 3 or 4 neutropenia in 25% and
only 1 patient had dose-limiting febrile neutropenia (2.3%). Diarrhea became the
dose-limiting toxicity, but first-cycle grade 3 or 4 diarrhea was only present
in 11.3%. Font et al, Vernejoux et al, and Seneviratne et al also reported
reduced complications of neutropenia in weekly docetaxel/irinotecan regimens and
various gastrointestinal toxicities then became dose-limiting
toxicities.[21,23,24] Thus, weekly combinations appear to allow safer
administration of docetaxel/irinotecan.

Phase II studies of docetaxel/irinotecan have been reported at
least in abstract form for non-small-cell lung cancer, ovarian cancer, gastric
cancer, pancreatic cancer, and mesothelioma.[25-29] Unfortunately, progress in
the evaluation of small-cell lung cancer has been slower. Possible reasons
include lower incidence of small-cell lung cancer patients compared to non-small-cell
lung cancer, and preferential enrollment in standard regimen or other clinical
trials (such as phase III studies of cisplatin/irinotecan). Nevertheless,
studies of this promising combination should be pursued for patients with
extensive disease.

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