CLINICAL PHARMACOLOGY
Mechanism Of Action
Topoisomerase I relieves
torsional strain in DNA by inducing reversible single-strand breaks. Topotecan
binds to the topoisomerase I-DNA complex and prevents re-ligation of these
single-strand breaks. The cytotoxicity of topotecan is thought to be due to
double-strand DNA damage produced during DNA synthesis, when replication
enzymes interact with the ternary complex formed by topotecan, topoisomerase I,
and DNA. Mammalian cells cannot efficiently repair these double-strand breaks.
Pharmacokinetics
Following administration of HYCAMTIN for injection at
doses of 0.5 to 1.5 mg/m² (0.1 to 0.3 times the recommended single agent dose)
administered as a 30-minute infusion, area under the curve (AUC) increases
proportionally with dose.
Distribution
Protein binding of topotecan is
approximately 35%.
Elimination
The terminal half-life of topotecan is 2 to 3
hours following intravenous administration.
Metabolism
Topotecan undergoes a
reversible pH-dependent hydrolysis of its pharmacologically active lactone
moiety. At pH less than or equal to 4, the lactone is exclusively present,
whereas the ring-opened hydroxy-acid form predominates at physiologic pH.
Topotecan is metabolized to an N-demethylated metabolite in vitro. The mean
metabolite: parent AUC ratio was about 3% for total topotecan and topotecan
lactone following intravenous administration.
Excretion
The overall recovery of total
topotecan and its N-desmethyl metabolite in urine and feces over 9 days
averaged 73% ± 2% following an intravenous dose. Mean values of 51% ± 3% as
total topotecan and 3% ± 1% as Ndesmethyl topotecan were excreted in the urine.
Fecal elimination of total topotecan accounted for 18% ± 4% while fecal
elimination of N-desmethyl topotecan was 1.7% ± 0.6%. An O-glucuronidation
metabolite of topotecan and N-desmethyl topotecan has been identified in the
urine.
Specific Populations
No clinically significant
differences in the pharmacokinetics of topotecan were observed based on age,
sex, or hepatic impairment following intravenous administration.
Patients With Renal Impairment
Compared to patients with CLcr (calculated by the
Cockcroft-Gault method using ideal body weight) greater than 60 mL/min, plasma
clearance of topotecan lactone decreased by 33% in patients with CLcr 40-60
mL/min and decreased 65% in patients with CLcr 20-39 mL/min. The effect on
topotecan pharmacokinetics in patients with CLcr less than 20 mL/min is unknown
[see DOSAGE AND ADMINISTRATION].
Drug Interaction Studies
Clinical Studies
No clinically significant changes in topotecan
pharmacokinetics were observed when coadministered cisplatin.
No clinically significant changes in the pharmacokinetics
of free platinum were observed in patients coadministered cisplatin with
topotecan.
In Vitro Studies
Topotecan does not inhibit CYP1A2, CYP2A6, CYP2C8/9,
CYP2C19, CYP2D6, CYP2E, CYP3A, or CYP4A or dihydropyrimidine dehydrogenase.
Clinical Studies
Ovarian Cancer
The efficacy of HYCAMTIN for injection was evaluated in
two clinical trials of 223 patients with metastatic ovarian cancer. All
patients had disease that had recurred on, or was unresponsive to, a
platinum-containing regimen. Patients in these trials received an initial dose
of 1.5 mg/m² as an intravenous infusion for 5 consecutive days, starting on Day
1 of a 21-day cycle.
One trial (Study 039) was a randomized trial of 112
patients who received HYCAMTIN for injection and of 114 patients who received
paclitaxel (175 mg/m² intravenously over 3 hours on Day 1 of a 21-day cycle).
All patients had recurrent ovarian cancer after a platinum-containing regimen
or had not responded to at least 1 prior platinum-containing regimen. Patients
who did not respond to the trial therapy, or who progressed, could be given the
alternative treatment. The efficacy outcome measures were overall response
rate, response duration, time to progression, and overall survival (OS).
The results of the trial did not show statistically
significant improvements in response rates, response duration, time to
progression, and OS as shown in Table 4.
Table 4: Efficacy Results in Ovarian Cancer in Study 039
Parameter |
HYCAMTIN for injection
(n = 112) |
Paclitaxel
(n = 114) |
Overall response rate (95% CI) |
21% (13%, 28%) |
14% (8%, 20%) |
Complete response rate |
5% |
3% |
Partial response rate |
16% |
11% |
Response durationa (months) |
Median (95% CI) |
6 (5.1, 7.6) |
5 (3.7, 7.8) |
Time to progression (months) |
Median (95% CI) |
4.4 (2.8, 5.4) |
3.4 (2.7, 4.2) |
Hazard ratio (95% CI) |
0.76 (0.57, 1.02) |
Overall survival (months) |
Median (95% CI) |
14.5 (10.7, 16.5) |
12.2 (9.7, 15.8) |
Hazard ratio (95% CI) |
0.97 (0.71, 1.34) |
Abbreviation: CI, confidence interval.
a The calculation for response duration was based on the interval
between first response and time to progression. |
The median time to response was
7.6 weeks (3.1 weeks to 5 months) with HYCAMTIN for injection compared with 6
weeks (2.4 weeks to 4.1 months) with paclitaxel. In the cross-over phase, 13%
of 61 patients who received HYCAMTIN after paclitaxel had a partial response
and 10% of 49 patients who received paclitaxel after HYCAMTIN had a response (2
complete responses).
HYCAMTIN for injection was
active in ovarian cancer patients who had developed resistance to
platinum-containing therapy, defined as tumor progression while on, or tumor
relapse within 6 months after completion of, a platinum-containing regimen. One
complete and 6 partial responses were seen in 60 patients, for a response rate
of 12%. In the same trial, there were no complete responders and 4 partial
responders on the paclitaxel arm, for a response rate of 7%.
HYCAMTIN for injection was also
studied in an open-label, non-comparative trial in 111 patients with recurrent
ovarian cancer after treatment with a platinum-containing regimen, or who had
not responded to 1 prior platinum-containing regimen. The response rate was 14%
(95% CI: 7%, 20%). The median duration of response was 5 months (4.6 weeks to
9.6 months). The time to progression was 2.6 months (5 days to 1.4 years). The
median survival was 1.3 years (1.4 weeks, to 2.2 years).
Small Cell Lung Cancer
The efficacy of HYCAMTIN for injection
was evaluated in 426 patients with recurrent or progressive small cell lung
cancer (SCLC) in a randomized, comparative trial and in 3 single-arm trials.
Randomized Comparative Trial
In a randomized, comparative
trial, 211 patients were randomized 1:1 to receive HYCAMTIN for injection (1.5
mg/m² once daily intravenously for 5 days starting on Day 1 of a 21-day cycle)
or CAV (cyclophosphamide 1,000 mg/m², doxorubicin 45 mg/m², vincristine 2 mg
administered sequentially on Day 1 of a 21-day cycle). All patients were
considered sensitive to first-line chemotherapy (responders who then
subsequently progressed greater than or equal to 60 days after completion of
first-line therapy). A total of 77% of patients treated with HYCAMTIN for
injection and 79% of patients treated with CAV received platinum/etoposide with
or without other agents as first-line chemotherapy. The efficacy outcome
measures were overall response rate, response duration, time to progression or
OS.
The results of the trial did
not show statistically significant improvements in response rate, response
duration, time to progression, or OS as shown in Table 5.
Table 5: Efficacy Results in
Patients with Small Cell Lung Cancer Sensitive to First-Line Chemotherapy in
Study 090
Parameter |
HYCAMTIN for injection
(n = 107) |
CAVb
(n = 104) |
Overall response rate (95% CI) |
24% (16%, 32%) |
18% (11%, 26%) |
Complete response rate |
0% |
1% |
Partial response rate |
24% |
17% |
Response durationa (months) |
Median (95% CI) |
3.3 (3, 4.1) |
3.5 (3, 5.3) |
Time to progression (months) |
Median (95% CI) |
3.1 (2.6, 4.1) |
2.8 (2.5, 3.2) |
Hazard ratio (95% CI) |
0.92 (0.69, 1.22) |
Overall survival (months) |
Median (95% CI) |
5.8 (4.7, 6.8) |
5.7 (5, 7) |
Hazard ratio (95% CI) |
1.04 (0.78, 1.39) |
Abbreviations: CI, confidence interval.
a The calculation for duration of response was based on the interval
between first response and time to progression.
b CAV = cyclophosphamide, doxorubicin and vincristine. |
The median time to response was similar in both arms:
HYCAMTIN, 6 weeks (2.4 weeks to 3.6 months) versus CAV, 6 weeks (5.1 weeks to
4.2 months).
Changes on a disease-related
symptom scale are presented in Table 6. It should be noted that not all
patients had all symptoms, nor did all patients respond to all questions. Each
symptom was rated on a 4-category scale with an improvement defined as a change
in 1 category from baseline sustained over 2 courses. Limitations in
interpretation of the rating scale and responses preclude formal statistical
analysis.
Table 6: Symptom Improvementa in Patients with Small
Cell Lung Cancer in Study 090
Symptom |
HYCAMTIN for injection
(n = 107) |
CAV
(n = 104) |
nb |
(%) |
nb |
(%) |
Shortness of breath |
68 |
28 |
61 |
7 |
Interference with daily activity |
67 |
27 |
63 |
11 |
Fatigue |
70 |
23 |
65 |
9 |
Hoarseness |
40 |
33 |
38 |
13 |
Cough |
69 |
25 |
61 |
15 |
Insomnia |
57 |
33 |
53 |
19 |
Anorexia |
56 |
32 |
57 |
16 |
Chest pain |
44 |
25 |
41 |
17 |
Hemoptysis |
15 |
27 |
12 |
33 |
a Defined as improvement sustained over at
least 2 courses compared with baseline.
b Number of patients with baseline and at least 1 post-baseline
assessment. |
Single-Arm Trials
HYCAMTIN for injection was also
studied in three open-label, non-comparative trials (Studies 014, 092 and 053)
in a total of 319 patients with recurrent or progressive SCLC after treatment
with first-line chemotherapy. In all three trials, patients were stratified as
either sensitive (responders who then subsequently progressed greater than or
equal to 90 days after completion of first-line therapy) or refractory (no
response to first-line chemotherapy or who responded to first-line therapy and
then progressed within 90 days of completing first-line therapy). Response
rates ranged from 11% to 31% for sensitive patients and 2% to 7% for refractory
patients. Median time to progression and median survival were similar in all
three trials and the comparative trial.
Cervical Cancer
The efficacy of HYCAMTIN for injection was evaluated in a
multi-center, randomized (1:1), open-label study (Study GOG 0179) conducted in
147 patients with histologically confirmed Stage IV-B, recurrent, or persistent
cervical cancer considered not amenable to curative treatment with surgery
and/or radiation. Patients were randomized to HYCAMTIN for injection (0.75 mg/m²
once daily intravenously for 3 consecutive days starting on Day 1 of a 21-day
cycle) with cisplatin (50 mg/m² intravenously on Day 1) or cisplatin as a
single agent. Fifty-six percent of patients treated with HYCAMTIN with
cisplatin and 56% of patients treated with cisplatin had received prior
cisplatin with or without other agents as first-line chemotherapy. The efficacy
outcome measure was OS.
Median OS of eligible patients receiving HYCAMTIN with
cisplatin was 9.4 months (95% CI: 7.9, 11.9) compared with 6.5 months (95% CI:
5.8, 8.8) among patients randomized to cisplatin alone with a log rank P-value
of 0.033 (significance level was 0.044 after adjusting for the interim
analysis). The unadjusted hazard ratio for OS was 0.76 (95% CI: 0.59, 0.98).
Figure 1: Kaplan-Meier Curves for Overall Survival in
Cervical Cancer in Study GOG 0179
REFERENCES
1. “OSHA Hazardous Drugs.” OSHA.
http://www.osha.gov/SLTC/hazardousdrugs/index.html.