Pharmacokinetics and pharmacodynamics of topotecan administered daily for 5 days every 3 weeks

Topotecan and Ginkgolic Acid Inhibit the Expression and Transport Activity of Human Organic Anion Transporter 3 by Suppressing SUMOylation of the Transporter

Organic anion transporter 3 (OAT3), expressed at the basolateral membrane of kidney proximal tubule cells, facilitates the elimination of numerous metabolites, environmental toxins, and clinically important drugs. An earlier investigation from our laboratory revealed that OAT3 expression and transport activity can be upregulated by SUMOylation, a post-translational modification that covalently conjugates SUMO molecules to substrate proteins. Topotecan is a semi-synthetic derivative of the herbal extract camptothecin, approved by the FDA to treat several types of cancer. Ginkgolic acid (GA) is one of the major components in the extract of Ginkgo biloba leaves that has long been used in food supplements for preventing dementia, high blood pressure, and supporting stroke recovery. Both topotecan and GA have been shown to affect protein SUMOylation. In the current study, we tested our hypothesis that topotecan and GA may regulate OAT3 SUMOylation, expression, and transport function. Our data show that the treatment of OAT3-expressing cells with topotecan or GA significantly decreases the SUMOylation of OAT3 by 50% and 75%, respectively. The same treatment also led to substantial reductions in OAT3 expression and the OAT3-mediated transport of estrone sulfate, a prototypical substrate. Such reductions in cell surface expression of OAT3 correlated well with an increased rate of OAT3 degradation. Mechanistically, we discovered that topotecan enhanced the association between OAT3 and the SUMO-specific protease SENP2, a deSUMOylation enzyme, which contributed to the significant decrease in OAT3 SUMOylation. In conclusion, this study unveiled a novel role of topotecan and GA in inhibiting OAT3 expression and transport activity and accelerating OAT3 degradation by suppressing OAT3 SUMOylation. During comorbidity therapies, the use of topotecan or Ginkgo biloba extract could potentially decrease the transport activity of OAT3 in the kidneys, which will in turn affect the therapeutic efficacy and toxicity of many other drugs that are substrates for the transporter.

FF-10850, a Novel Liposomal Topotecan Achieves Superior Antitumor Activity via Macrophage- and Ammonia-Mediated Payload Release in the Tumor Microenvironment

Topotecan, an approved treatment for refractory or recurrent ovarian cancer, has clinical limitations such as rapid clearance and hematologic toxicity. To overcome these limitations and maximize clinical benefit, we designed FF-10850, a dihydrosphingomyelin-based liposomal topotecan. FF-10850 demonstrated superior antitumor activity to topotecan in ovarian cancer cell line-based xenograft models, as well as in a clinically relevant DF181 platinum-refractory ovarian cancer patient-derived xenograft model. The safety profile was also improved with mitigation of hematologic toxicity. The improved antitumor activity and safety profile are achieved via its preferential accumulation and payload release triggered in the tumor microenvironment. Our data indicate that tumor-associated macrophages internalize FF-10850, resulting in complete payload release. The release mechanism also appears to be mediated by high ammonia concentration resulting from glutaminolysis, which is activated by tumor metabolic reprogramming. In ammonia-rich conditions, FF-10850 released payload more rapidly and to a greater extent than liposomal doxorubicin, a currently approved treatment for ovarian cancer. FF-10850 significantly enhanced antitumor activity in combination with carboplatin or PARP inhibitor without detrimental effects on body weight in murine xenograft models, and demonstrated synergistic antitumor activity combined with anti-PD-1 antibody with the development of tumor antigen-specific immunity. These results support phase I investigation of FF-10850 for the treatment of solid tumors including ovarian cancer (NCT04047251), and further evaluation in combination settings.

Extended topoisomerase 1 inhibition through liposomal irinotecan results in improved efficacy over topotecan and irinotecan in models of small-cell lung cancer

Liposomal irinotecan (irinotecan liposome injection, nal-IRI), a liposomal formulation of irinotecan, is designed for extended circulation relative to irinotecan and for exploiting discontinuous tumor vasculature for enhanced drug delivery to tumors. Following tumor deposition, nal-IRI is taken up by phagocytic cells followed by irinotecan release and conversion to its active metabolite, SN-38. Sustained inhibition of topoisomerase 1 by extended SN-38 exposure as a result of delivery by nal-IRI is hypothesized to enable superior antitumor activity compared with traditional topoisomerase 1 inhibitors such as conventional irinotecan and topotecan. We evaluated the antitumor activity of nal-IRI compared with irinotecan and topotecan in preclinical models of small-cell lung cancer (SCLC) including in a model pretreated with carboplatin and etoposide, a first-line regimen used in SCLC. Nal-IRI demonstrated antitumor activity in xenograft models of SCLC at clinically relevant dose levels, and resulted in complete or partial responses in DMS-53, DMS-114, and NCI-H1048 cell line-derived models as well as in three patient-derived xenograft models. The antitumor activity of nal-IRI was superior to that of topotecan in all models tested, which generally exhibited limited control of tumor growth and was superior to irinotecan in four out of five models. Further, nal-IRI demonstrated antitumor activity in tumors that progressed following treatment with topotecan or irinotecan, and demonstrated significantly greater antitumor activity than both topotecan and irinotecan in NCI-H1048 tumors that had progressed on previous carboplatin plus etoposide treatment. These results support the clinical development of nal-IRI in patients with SCLC.

Do topotecan concentrations in saliva reflect plasma concentrations?

Purpose. There is an increasing interest to use saliva as biological fluid for drug monitoring as it reflects adequately, in some cases, drug concentrations in plasma. A great advantage is that it can be obtained conveniently by a noninvasive method. We describe our experience with respect to the practical use of saliva for pharmacokinetic monitoring of the novel anticancer agent topotecan.

Patients and Methods. Eighty-one saliva sam ples and corresponding plasma samples were ob tained 2 hours after the end of infusion from 15 patients with either ovarian cancer or small cell lung cancer, receiving 1.5 mg/m 2 per day topotecan for 5 consecutive days every 3 weeks. Saliva was obtained by a citric-acid containing dental cotton roll which stimulated the saliva flow.

Results. The plasma topotecan concentrations varied between 3.67 and 24.4 ng/mL, with an intrapa tient (day-to-day) variation of only 9.8%, and an inter patient variation of 27.2%. The saliva concentrations varied between 5.34 and 74.2 ng/mL, with an intrapa tient variation of 25.3%, and an interpatient variation of 53.5%. The mean plasma/saliva topotecan ratio was 0.66 (range 0.21 to 1.58) and was both patient dependent and dependent on the sampling time. The day-to-day variation of the plasma/saliva concentra tion ratio in this daily times five schedule was 27.6%, and the interpatient variation was 45.5%. The saliva concentrations of topotecan were not related to the occurrence of mucositis, which was noted in some patients.

Conclusion. Based on the large variability in the plasma/saliva ratios, we conclude that in our investi gational setting saliva is not a reliable matrix for topotecan analysis and that plasma sampling is to be preferred.

Extravasation of topotecan, a report of two cases

Objective. Extravasations of anticancer agents may give serious complications and specific therapy might be needed. Topotecan is a new cytotoxic drug and is used in many clinical studies. In our clinic two extravasations of topotecan occurred, and the clinical consequences are discussed.

Clinical Features. The extravasations oc curred in two patients who were receiving topo tecan intravenously because of ovarian carcinoma stage III. The patients experienced some discom fort caused by the expansion of soft tissue. How ever, no serious complications were observed.

Case Progress and Outcome. Both patients received all further courses of topotecan without any negative effects.

Conclusion. In conclusion, besides stopping the injection, trying to aspirate the fluid, keeping the arm high, and cooling the swelling, we advise no specific measures to be taken after extravasa tion of topotecan.

Review : Topoisomerase I inhibitors: 1. Topotecan

Purpose. The primary objective of this article is to discuss the pharmacology, pharmacokinetics, clin ical use, and adverse effects of the approved topoisomerase I inhibitors. This is the first in a series of two articles and will focus on topotecan.

Data Sources. We reviewed the literature through a MEDLINE search of English language articles from 1985 through 1997. Relevant articles cited in the titles obtained from the MEDLINE search were also used. The following terms were used for purpose of conducting the MEDLINE search: topoisomerase inhibitors, topotecan, topo isomerase I, Hycamtin, SKF 104864.

Data Extraction. We reviewed the current literature in order to discuss the pharmacology, pharmacokinetics, clinical use, toxicity, drug inter actions, indications, formulation, dosage and ad ministration, and pharmaceutical issues surround ing the use of topotecan.

Data Synthesis. The topoisomerase I inhibi tors are new antineoplastic agents with a unique mechanism of action. Promising areas of applica tion include ovarian cancer, lung cancer, radiation sensitization, and refractory leukemias. Clinical tri als detailing its activity in these areas are pre sented.

Pilot induction regimen incorporating pharmacokinetically guided topotecan for treatment of newly diagnosed high-risk neuroblastoma: a Children's Oncology Group study

PURPOSE

To assess the feasibility of adding dose-intensive topotecan and cyclophosphamide to induction therapy for newly diagnosed high-risk neuroblastoma (HRNB).

PATIENTS AND METHODS

Enrolled patients received two cycles of topotecan (approximately 1.2 mg/m(2)/d) and cyclophosphamide (400 mg/m(2)/d) for 5 days followed by four cycles of multiagent chemotherapy (Memorial Sloan-Kettering Cancer Center [MSKCC] regimen). Pharmacokinetically guided topotecan dosing (target systemic exposure with area under the curve of 50 to 70 ng/mL/hr) was performed. Peripheral-blood stem cell (PBSC) harvest and surgical resection of residual primary tumor occurred after cycles 2 and 5, respectively. Patients achieving at least a partial response received myeloablative chemotherapy with PBSC rescue and radiation to the presurgical primary tumor volume. Oral 13-cis-retinoic acid maintenance therapy was administered twice daily for 14 days in six 28-day cycles.

RESULTS

Thirty-one patients were enrolled onto the study. No deaths related to toxicity or dose-limiting toxicities occurred during induction. Mucositis rarely occurred after topotecan cycles (9.7%) in contrast to 30% after MSKCC cycles. Thirty patients underwent PBSC collection with median 31.1 × 10(6) CD34+ cells/kg (range, 1.8 to 541.8 × 10(6) CD34+ cells/kg), all negative for tumor contamination by immunocytochemical analysis. Targeted topotecan systemic exposure was achieved in 26 (84%) of 31 patients. At the end of induction, 26 patients (84%) had tumor response and one patient had progressive disease. In the overall cohort, 3-year event-free and overall survival were 37.8% ± 9.4% and 57.1% ± 9.4%, respectively.

CONCLUSION

This pilot induction regimen was well tolerated with expected and reversible toxicities. These data support investigation of efficacy in a phase III clinical trial for newly diagnosed HRNB.

A phase II clinical trial of topotecan in Japanese patients with relapsed ovarian carcinoma

OBJECTIVE

This Phase II study was carried out to investigate the efficacy, safety and pharmacokinetics of topotecan in Japanese patients with relapsed ovarian carcinoma.

METHODS

Patients with relapsed ovarian carcinoma after having received one regimen containing platinum-based chemotherapy were eligible for this study. Topotecan was administered at 1.2 mg/m(2)/day for five consecutive days, repeated every 3 weeks.

RESULTS

Seventy-two patients were enrolled in the study. The response rate was 28.2% (95% confidence interval, 18.1-40.1%). Signs of myelosuppression, such as neutropenia (Grade 3, 12.5%; Grade 4, 83.3%), thrombocytopenia (Grade 3, 36.2%; Grade 4, 4.2%) and decreased hemoglobin (Grade 3, 36.1%; Grade 4, 11.1%), were the most common hematological toxicities. Grade 3 febrile neutropenia occurred in 5 (6.9%) patients. There was little intraindividual or interindividual variability in the pharmacokinetics of topotecan.

CONCLUSIONS

Topotecan at 1.2 mg/m(2)/day is an effective and tolerable therapeutic option for Japanese patients with relapsed ovarian carcinoma.

Phase I and pharmacologic study of weekly bolus topotecan for advanced non-small-cell lung cancer

PURPOSE

We conducted a phase I trial of the topoisomerase I inhibitor topotecan for the purpose of determining the maximum tolerated dose (MTD) and the dose-limiting toxicities (DLTs) of topotecan when administered weekly to patients with advanced non-small-cell lung cancer.

PATIENTS AND METHODS

Twelve patients with stage IIIB or IV disease were treated with topotecan by 30-minute intravenous infusion on days 1, 8, and 15 every 4 weeks. The dose was escalated in 2-mg/m2 increments from the starting dose of 4 mg/m2 until the MTD was reached. After the MTD had been reached in previously treated patients, chemotherapy-naive patients were enrolled for treatment at that dose, and the dose was escalated to estimate the MTD in the treatment-naive group.

RESULTS

The MTD of topotecan was determined to be 6 mg/m2 in the previously treated group and 8 mg/m2 in the chemotherapy-naive group. All 3 previously treated patients experienced DLT at the 6-mg/m2 dose level. Although only 1 of the 3 previously treated patients experienced DLT (grade 4 neutropenia for > or = 3 days) at the 8-mg/m2 dose level, skipping the topotecan dose on day 15 because of neutropenia was reported in 2 patients. Anorexia and general fatigue were the common nonhematologic toxicities.

CONCLUSION

The recommended dose of topotecan for phase II studies in previously untreated patients is 6 mg/m2 on days 1, 8, and 15, every 28 days, and 4 mg/m2 appears to be a suitable dose for use in previously treated patients with this schedule.

A phase I study to characterize the safety, tolerability, and pharmacokinetics of topotecan at 4 mg/m2 administered weekly as a 30-minute intravenous infusion in patients with cancer

Topotecan pharmacokinetics at higher infusion rates (4 mg/m2 over 30 minutes) have not been studied. The authors report a pharmacokinetics and safety study of this dose in advanced cancer patients. Sixteen patients were given a 4-mg/m2 topotecan infusion intravenously (IV) over 30 minutes weekly for 3 weeks, repeated every 28 days. Pharmacokinetics were determined after the first dose. Plasma concentrations of total topotecan were measured to derive CL, V(ss), C(max), t(max), t(1/2), AUC(0-t), and AUC(0-infinity). Plasma total topotecan concentrations decreased biexponentially, with a mean CL value of 20.6 L/h, V(ss) value of 101 L, and t(1/2) value of 5.0 h. Nine significant adverse events (all hematologic) were topotecan related. Grade 3 or less adverse events included anemia, thrombocytopenia, leukopenia, and fatigue. Pharmacokinetics of the 4-mg/m2 infusion of topotecan over 30 minutes are comparable to findings from studies of lower and higher doses. Toxicities are similar to previous reports.

P-glycoprotein and breast cancer resistance protein: two dominant transporters working together in limiting the brain penetration of topotecan

PURPOSE

The brain is a pharmacologic sanctuary site, due to the presence of the blood-brain barrier (BBB). Whereas the effect of P-glycoprotein (P-gp) at the BBB is well established, the role of breast cancer resistance protein (BCRP) that is also expressed at the BBB is not.

EXPERIMENTAL DESIGN

We have studied the effect of BCRP by administering topotecan to wild-type (WT), single Mdr1a/b(-/-) and Bcrp1(-/-), and compound Mdr1a/b(-/-)Bcrp1(-/-) knockout mice. Drug levels in plasma and tissues were determined by high-performance liquid chromatography.

RESULTS

The area under the plasma and tissue concentration-time curve (AUC) of topotecan in brains of Mdr1a/b(-/-) and Bcrp1(-/-) mice was only 1.5-fold higher compared with WT mice, but in Mdr1a/b(-/-)Bcrp1(-/-) mice, where both transporters are absent, the AUC increased by 12-fold. The AUC in plasma was approximately 0.75-, 2.4-, and 3.7-fold higher in Mdr1a/b(-/-), Bcrp1(-/-), and Mdr1a/b(-/-)Bcrp1(-/-) mice, respectively, resulting in 2.0-fold (P < 0.01), 0.65-fold (P, not significant), and 3.2-fold (P < 0.01), respectively, higher brain-to-plasma AUC ratios. Results using Mrp4(-/-) mice showed that this transporter had no effect on the brain penetration of topotecan. The P-gp/BCRP inhibitor elacridar fully inhibited P-gp-mediated transport of topotecan, whereas inhibition of Bcrp1-mediated transport by elacridar was minimal.

CONCLUSIONS

Our results using Mdr1a/b(-/-)Bcrp1(-/-) mice clearly show the effect of Bcrp1 at the BBB and also show how two drug transporters act in concert to limit the brain penetration of topotecan. We expect that this finding will also apply to other drugs that are substrates of both P-gp and BCRP. Consequently, to improve the brain penetration of such compounds for targeting intracranial malignancies in patients, it will be essential to use potent inhibitors of both drug transporters.

Mathematical modeling of topotecan pharmacokinetics and toxicodynamics in mice

The objective of this study was to investigate the pharmacokinetics and toxicodynamics of topotecan (TPT) in mice and to develop an integrated pharmacokinetic/toxicodynamic (PK/TD) model to characterize the relationship between the time course of TPT disposition and the time course of TPT-induced toxicity. TPT was administered to groups of 3-5 mice via i.v. bolus injection, i.p. bolus injection, and by i.p. infusion over 24, 72 and 168 h. Body weight was monitored to assess TPT-induced toxicity, and serial blood samples were collected and analyzed via HPLC to assess TPT pharmacokinetics. We found that TPT-induced toxicity increased dose-dependently for each mode of dosing investigated. The time course of topotecan-induced body weight-loss was delayed relative to the time course of topotecan disposition; nadir body weight was observed as late as 6 days following i.p. bolus dosing, and 3-5 days following termination of i.p. infusion. TPT exhibited non-linear disposition, which was well-characterized through the use of a two-compartment model with saturable elimination from the central compartment. Toxicodynamic data were characterized with an integrated PK/TD model that incorporated an indirect-effect model and four transit compartments to describe transduction events associated with TPT-induced toxicity. This model will be used to support the development of an inverse-targeting strategy that aims to enhance topotecan safety and efficacy.

International Society of Geriatric Oncology (SIOG) recommendations for the adjustment of dosing in elderly cancer patients with renal insufficiency

A SIOG taskforce was formed to discuss best clinical practice for elderly cancer patients with renal insufficiency. This manuscript outlines recommended dosing adjustments for cancer drugs in this population according to renal function. Dosing adjustments have been made for drugs in current use which have recommendations in renal insufficiency and the elderly, focusing on drugs which are renally eliminated or are known to be nephrotoxic. Recommendations are based on pharmacokinetic and/or pharmacodynamic data where available. The taskforce recommend that before initiating therapy, some form of geriatric assessment should be conducted that includes evaluation of comorbidities and polypharmacy, hydration status and renal function (using available formulae). Within each drug class, it is sensible to use agents which are less likely to be influenced by renal clearance. Pharmacokinetic and pharmacodynamic data of anticancer agents in the elderly are needed in order to maximise efficacy whilst avoiding unacceptable toxicity.

Determination of topotecan in human and mouse plasma and in mouse tissue homogenates by reversed-phase high-performance liquid chromatography

A sensitive and selective reversed-phase high-performance liquid chromatographic (HPLC) assay has been developed and validated for quantification of total topotecan in human and mouse plasma and in mouse tissue samples. Isocratic separation was achieved on a Zorbax SB-C(18) column and topotecan was monitored fluorimetrically. Two ranges of calibrations curves were used to determine lower levels of topotecan more accurately. Acceptable accuracy and precision was achieved for all matrices. Topotecan was stable upon repeated freeze-thawing for three cycles or storage for 24 h at ambient temperatures in spiked plasma samples and tissue homogenates, except in heart homogenates. In an additional validation experiment in which (14)C-labeled topotecan was administered to mice, the levels of unchanged topotecan were about 80-90% of the total radioactivity in tissue homogenates collected 10 min after drug administration and virtually similar as in plasma samples. However, results in tissue homogenates obtained 4 h post-drug administration indicated substantial metabolism of topotecan. This assay is suitable for studying the pharmacokinetics and tissue distribution of topotecan in mice. Our results demonstrate the importance of including all tissues of interest for pharmacokinetic studies in the validation procedure.

Potential use of the adenosine triphosphate cell viability assay in endometrial cancer

OBJECTIVE

Adenosine triphosphate cell viability assay (ATP-CVA) was used previously to evaluate chemotherapy in uterine cancer cell lines. In this study, we have performed the ATP-CVA on endometrial cancer patients to study the feasibility of using ATP-CVA in endometrial cancer to determine the intrinsic chemosensitivity of the cytotoxic drugs.

METHODS

Thirty-three patients with endometrial adenocarcinoma who presented for a staging operation were recruited. Endometrial cancer samples were obtained at the time of operation. In vitro ATP-CVA and chemosensitivity testing was performed using cisplatin, carboplatin, paclitaxel, etoposide, doxorubicin, 4-epidoxorubicin, and topotecan.

RESULTS

Thirty-two of the 33 endometrial cancer samples were evaluable for SF50 (survival fraction at 50% of the peak plasma concentration [PPC]) using ATP-CVA. The median SF50 of carboplatin (0.33) was significantly less than the median SF50 of cisplatin (0.71), topotecan (0.93), paclitaxel (0.68), doxorubicin (1.0), etoposide (0.70), or 4-epidoxorubicin (0.88) (Wilcoxon signed rank test, P <.001).

CONCLUSION

This study showed the feasibility of using the ATP-CVA in endometrial cancer to determine the intrinsic chemosensitivity of cytotoxic drugs.

Liquid chromatography-mass spectrometry for the quantitative bioanalysis of anticancer drugs

The monitoring of anticancer drugs in biological fluids and tissues is important during both pre-clinical and clinical development and often in routine clinical use. Traditionally, liquid chromatography (LC) in combination with ultraviolet (UV), fluorescence, or electrochemical detection is employed for this purpose. The successful hyphenation of LC and mass spectrometry (MS), however, has dramatically changed this. MS detection provides better sensitivity and selectivity than UV detection and, in addition, is applicable to a significantly larger group of compounds than fluorescence or electrochemical detection. Therefore, LC-MS has now become the method of first choice for the quantitative bioanalysis of many anticancer agents. There are still, however, a lot of new developments to be expected in this area, such as the introduction of more sensitive and robust mass spectrometers, high-throughput analyses, and further optimization of the coupled LC systems. Many articles have appeared in this field in recent years and are reviewed here. We conclude that LC-MS is an extremely powerful tool for the quantitative analysis of anticancer drugs in biological samples.

A phase I trial defining the maximum tolerated systemic exposure of topotecan in combination with Carboplatin and Etoposide in extensive stage small cell lung cancer

PURPOSE

Topotecan is active in relapsed small cell lung cancer; thus, its addition to the standard carboplatin-etoposide regimen may improve outcomes in extensive-stage small cell lung cancer (ES-SCLC) patients. Significant interpatient variability in the topotecan systemic exposure results when it is dosed based on body surface area (mg/m2). The purpose of this Phase I trial was to determine the maximally tolerated systemic exposure (MTSE) of topotecan in combination with carboplatin and etoposide.

METHODS

Thirty-four chemotherapy-naïve ES-SCLC patients received topotecan in combination with carboplatin AUC 5 mg/mL*min and oral etoposide 100 mg/m2/day. Topotecan was administered as a 30-minute infusion either on Days 1-5 or Days 1-3 and the dosage was individualized to attain a topotecan lactone AUC range (ng/mL*hr) in successive patient cohorts from 7 to 23; 24 to 36; 37 to 53; 54 to 66.

RESULTS

The majority (67 percent) of the measured topotecan AUCs were within target range. Overall, 8 of 34 patients experienced Cycle 1 dose-limiting toxicity (DLT), either neutropenia or thrombocytopenia. Carboplatin administration prior to topotecan resulted in 2 of 6 patients having Cycle 1 DLT. When the administration sequence was changed (topotecan, carboplatin, etoposide), Cycle 1 hematologic toxicity decreased; however, the maximum topotecan lactone AUC of 24-36 ng/mL*hr (median dose 0.82 mg/m2) had significant cumulative hematologic toxicity. The number of topotecan doses were reduced from 5 to 3, which resulted in a maximum topotecan lactone AUC of 37 to 53 ng/mL*hr with only 1 of 6 patients having Cycle 1 DLT. Overall response rate was 71 percent with median survival of 10.8 months.

CONCLUSION

It is feasible to target topotecan lactone AUC in adult ES-SCLC patients. However, this triplet regimen resulted in considerable hematologic toxicity and has a median survival comparable to carboplatin-etoposide. Alternative, less toxic regimens should be investigated for improving survival in ES-SCLC.

Development and validation of limited sampling models for topotecan lactone pharmacokinetic studies in children

PURPOSE

To develop and validate a pharmacokinetic limited sampling model (LSM) for intravenous and oral topotecan pharmacokinetic studies in children.

METHODS

Topotecan lactone concentration-time data from five trials were used to develop and validate LSM for intravenous and oral topotecan. Based on full sampling from one intravenous study (30 patients; 195 studies), a LSM for intravenous topotecan was determined using a modification of the D-optimality algorithm. For oral topotecan we used full sampling data from one oral topotecan study (27 patients; 47 studies) to develop an LSM. Accuracy and bias of each LSM were determined relative to the full sampling method. Predictive performance of the LSM was validated using additional data and Monte-Carlo simulations based on these data.

RESULTS

LSM for intravenous topotecan includes: 5 min, 1.5, and 2.5 h after the end of the 30 min infusion. The median accuracy (absolute predicted error) and bias (predicted error) are < or =8% and < or =6.1%, respectively. For oral topotecan, the optimal LSM includes: 15 min, 1.5, and 6 h. The median accuracy and bias are 6% and 4%, respectively.

CONCLUSIONS

Our results indicate that the optimal sampling times for the intravenous LSM for topotecan in children consist of: predose, and 5 min, 1.5, and 2.5 h after the end of infusion. For oral topotecan the sample times are predose, 15 min, 1.5, and 6 h after dose administration. These LSM are invaluable to children receiving topotecan because it minimizes inconvenience and blood collection.

Improved Response in High-Risk Neuroblastoma With Protracted Topotecan Administration Using a Pharmacokinetically Guided Dosing Approach

Purpose

To estimate the response rate and toxicity associated with intravenous topotecan when it is administered on a protracted schedule according to a pharmacokinetically guided dosing approach to treat childhood high-risk neuroblastoma.

Patients and Methods

In this prospective phase II trial, topotecan was administered intravenously daily for 5 days for each of 2 consecutive weeks for two cycles. On the basis of topotecan systemic clearance, doses were individualized to attain a single-day topotecan lactone area under the plasma concentration-time curve (AUC) of 80 to 120 ng/mL · h. Patients subsequently received standard treatment.

Results

Both cycles were administered to 28 (93%) of the 30 enrolled patients (median age, 3.1 years). Target topotecan AUCs were achieved in 92 (72%) of the 127 measurements conducted after pharmacokinetically guided adjustment; the median dosage required to achieve target AUCs was 2.7 mg/m2(range, 0.95 to 3.8 mg/m2). The response rate was 60% (95% CI, 41% to 77%); there were one complete and 17 partial responses. No patient experienced disease progression during initial topotecan therapy. Primary tumor volumes decreased (median decrease, −58.2%; range, −95.1% to −4.9%) in the 26 patients with available size data. Homovanillic acid levels in 16 (89%) of 18 patients and vanillylmandelic acid levels in 14 (78%) of 18 patients were lower (P = .002 and P = .018, respectively) after topotecan therapy. Reversible grade 4 myelosuppression occurred in all patients, but no deaths occurred as a result of infection or toxicity.

Conclusion

Topotecan is active against neuroblastoma when it is administered on a protracted schedule and targeted systemic exposure is achieved.

High-performance liquid chromatographic assay for the determination of total and free topotecan in the presence and absence of anti-topotecan antibodies in mouse plasma

A rapid and sensitive high-performance liquid chromatographic (HPLC) assay has been developed to allow determination of total (i.e. bound and unbound) and free (i.e. unbound) topotecan (TPT) in mouse plasma in the presence and absence of anti-TPT antibodies. The chromatographic analysis was carried out using reversed-phase isocratic elution with a Nova-Pak C18 column (3.9 mm x 150 mm, 4 microm) protected by a Nova-Pak C18 guard column (3.9 mm x 20 mm, 4 microm), where 10 mM KH(2)PO(4)-methanol-triethylamine (72:26:2 (v/v/v), pH 3.5) was used as the mobile phase. Topotecan was quantified with fluorescence detection using an excitation wavelength of 361 nm and an emission wavelength of 527 nm. The retention time for the internal standard, acridine, and TPT were 7.4 and 9.0 min, respectively. The lower limit of quantitation (LOQ) for TPT was determined as 0.02 ng in mouse plasma and mouse plasma ultrafiltrate, corresponding to a concentration of 1 ng/ml in 20 microl mouse plasma. The assay was shown to be linear over a concentration range of 1-500 ng/ml. The recoveries of free and total TPT from spiked mouse plasma were within 10% of theoretical values (assessed at 1, 20 and 500 ng/ml). The validated HPLC assay was applied to evaluate TPT pharmacokinetics following administration of TPT to Swiss Webster mice and to hyperimmunized and control BALB/c mice. The assay has been shown to be capable for measuring total and free TPT in mouse plasma with high sensitivity and will allow the testing of the effect of anti-TPT antibodies on the disposition of TPT.

Pharmacokinetic model-predicted anticancer drug concentrations in human tumors

In an era when molecular and targeted anticancer therapeutics is a major focus and when understanding drug dynamics in tumor is critical, it seems advantageous to be able to relate drug concentrations in tumors to corresponding biological end points. To that end, a novel method, based on physiologically based hybrid pharmacokinetic models, is presented to predict human tumor drug concentrations. Such models consist of a forcing function, describing the plasma drug concentration-time profile, which is linked to a model describing drug disposition in tumors. The hybrid models are originally derived from preclinical data and then scaled to humans. Integral to the scale-up procedure is the ability to derive human forcing functions directly from clinical pharmacokinetic data. Three examples of this approach are presented based on preclinical investigations with carboplatin, topotecan, and temozolomide. Translation of these preclinical hybrid models to humans used a Monte Carlo simulation technique that accounted for intrasubject and intersubject variability. Different pharmacokinetic end points, such as the AUC tumor, were extracted from the simulated human tumor drug concentrations to show how the predicted drug concentrations might be used to select drug-dosing regimens. It is believed that this modeling strategy can be used as an aid in the drug development process by providing key insights into drug disposition in tumors and by offering a foundation to optimize drug regimen design.

Quality‐of‐Life Considerations in Patients with Advanced Lung Cancer: Effect of Topotecan on Symptom Palliation and Quality of Life

Key goals in the treatment of lung cancer are to improve both survival and quality of life (QOL). While formal techniques are frequently used to evaluate survival and response, such rigor is used less often in assessing the impact of treatment on quality of life. Many patients with lung cancer are elderly and have complex medical histories and a myriad of comorbidities. In these patients, with limited survival expectations, symptom palliation, quality of life, and convenience of therapy are especially important end points. Indeed, clinical trials are now incorporating symptom scores and QOL outcomes in their designs (now combined as "patient reported outcomes" or PROs). Moreover, symptom palliation correlates well with QOL and survival duration, providing further rationale for therapy selection based on these parameters. The potential palliative and QOL benefits of chemotherapy have been investigated for several agents in lung cancer trials. Of these, topotecan (Hycamtin; GlaxoSmithKline; Philadelphia, PA) is the best characterized in relapsed small cell lung cancer (SCLC). In a phase III trial of topotecan versus cyclophosphamide, doxorubicin (Adriamycin; Bedford Laboratories; Bedford, OH), and vincristine (Oncovin; Eli Lilly and Company; Indianapolis, IN) (CAV) in patients with recurrent SCLC, topotecan was associated with statistically significant (p < 0.05) improvements in general symptoms (e.g., fatigue and interference with daily activity) and disease-specific symptoms (e.g., dyspnea and hoarseness). Moreover, the introduction of oral therapies, such as oral topotecan, may increase the convenience of therapy by reducing the time needed for therapy and the need for frequent venipuncture. This review summarizes the role of chemotherapy in symptom palliation, with an emphasis on the impact of topotecan therapy on symptom parameters in patients with relapsed SCLC and the emerging role of oral therapy in this setting.

Topoisomerase I Inhibitors in the Treatment of Gastrointestinal Cancer: From Intravenous to Oral Administration

This article reviews the current status of the topoisomerase I (top I) inhibitors in the treatment of gastrointestinal (GI) malignancies. We focus on oral drug administration, the mode of administration that is generally preferred by patients with cancer. However, the great majority of the studies have been performed with intravenous (I.V.) administration. The most extensively investigated GI malignancy in phase I/II studies is colorectal cancer (CRC), for which I.V. irinotecan is currently approved in the United States and Europe. We discuss the activity and efficacy of irinotecan as a single agent in CRC and in combination regimens. Also, results obtained with monotherapy and in combination treatment in other GI malignancies such as esophageal, gastric, and pancreatic cancer are discussed. Few phase I studies have been performed with oral irinotecan and its clinical activity has not yet been fully determined. Several top I inhibitors are discussed, including topotecan, 9-aminocamptothecin, rubitecan, exatecan, and lurtotecan. None of these agents, given orally or intravenously, have shown activity in CRC similar to that of I.V. irinotecan. However, several agents show promising results in other GI malignancies, eg, rubitecan and exatecan in pancreatic cancer. A complicating factor in the oral administration of the top I inhibitors is the often encountered low and variable oral bioavailability. This can partly be explained by the high affinity for the drug efflux pumps BCRP (ABCG2) and P-glycoprotein, which are highly expressed in the epithelial apical membrane of the GI tract. A novel approach to improve the oral bioavailability of the top I inhibitors by temporary blockade of the drug transporter BCRP is described.

Phase I and pharmacokinetic study of the combination of topotecan and ifosfamide administered intravenously every 3 weeks

To determine the maximum-tolerated dose (MTD), dose-limiting toxicities, and pharmacokinetics of topotecan administered as a 30-min intravenous (i.v.) infusion over 5 days in combination with a 1-h i.v. infusion of ifosfamide (IF) for 3 consecutive days every 3 weeks. Patients with advanced malignancies refractory to standard therapy were entered into the study. The starting dose of topotecan was 0.4 mg m⁻² day⁻¹ × 5 days. Ifosfamide was administered at a fixed dose of 1.2 g m⁻² day⁻¹ × 3 days. In all, 36 patients received 144 treatment courses. Owing to toxicities, the schedule of topotecan administration was reduced from 5 to 3 days. The MTD was reached at topotecan 1.2 mg m⁻² day⁻¹ × 3 days with IF 1.2 g m⁻² day⁻¹ × 3 days. Haematological toxicities were dose limiting. Neutropenia was the major toxicity. Thrombocytopenia and anaemia were rare. Nonhaematological toxicities were relatively mild. Partial responses were documented in three patients with ovarian cancer dosed below the MTD. Topotecan and IF did not appear to interact pharmacokinetically. The relationships between the exposure to topotecan lactone and total topotecan, and the decrease in absolute neutrophil count and the decrease in thrombocytes, were described with sigmoidal–E_max models. The combination of 1.0 mg m⁻² day⁻¹ topotecan administered as a 30-min i.v. infusion daily times three with 1.2 g m⁻² day⁻¹ IF administered as a 1-h i.v. infusion daily times three every 3 weeks was feasible. However, the combination schedule of topotecan and IF did result in considerable haematological toxicity and in conjunction with previously reported pronounced nonhaematological toxicities and treatment related deaths, it may be concluded that this is not a favourable combination.

Factors affecting pharmacokinetic variability of oral topotecan: a population analysis

The aim of this study was to characterise the pharmacokinetics of the anticancer agent topotecan, and explore the influence of patient covariates and interoccasion variability on drug disposition. Data were obtained from 190 patients who received the drug as a 30-min infusion (N=72) or orally (N=118). The population model was built with the use of NONMEM to identify candidate covariates, and obtain models for clearance (CL) and volume of distribution. The final models were based on first-order absorption with lag-time (oral data), and a two-compartment model with linear elimination from the central compartment. The Cockcroft–Gault creatinine clearance (CrCl) and WHO performance status (PS) were the only significant covariates: CL=(12.8+2.1 × CrCl) × (1−0.12 × PS). For the volume of distribution, a correlation was found between body weight and the central volume (V1)=0.58 × body weight. Based on the structural models, a limited-sampling strategy was developed with minor bias and good precision that can be applied a posteriori using timed samples obtained at 1.5, and 6 h after the administration of topotecan. In conclusion, a population pharmacokinetic model for topotecan has been developed that incorporates measures of renal function and PS to predict CL. In combination with drug monitoring, the limited sampling strategy allows individualised treatment for patients receiving oral topotecan.

Influence of the cisplatin hydration schedule on topotecan pharmacokinetics

The study described here was designed to investigate the influence of the hydration schedule of cisplatin on the pharmacokinetics of topotecan. To test this hypothesis, 13 adult cancer patients were treated with intravenous (i.v.) cisplatin followed by i.v. topotecan for 5 days every 3 weeks using a short hydration schedule (SHS) for cisplatin in the first course and a hyper-hydration schedule (HHS) in the second course or vice versa. Topotecan pharmacokinetic analysis was performed in plasma, whole blood and red blood cells in both courses on days 1, 2 and 5. 11 patients received both courses and were pharmacokinetically evaluable. No significant differences between the two studied schedules were noted in the clearances of topotecan on day 1 in the different matrices. However, in both hydration schedules, on average, slightly lower topotecan clearances were observed on both days 2 and 5 compared with day 1 in all of the matrices, while no differences were noted between days 2 and 5. This alteration was independent of the schedule used and was less pronounced than that which has been initially reported for SHS and, overall, will not have clinical consequences.

Pharmacokinetic-pharmacodynamic guided trial design in oncology

The application of pharmacokinetic (PK) and pharmacodynamic (PD) modeling in drug development has emerged during the past decades and it is has been suggested that the investigation of PK-PD relationships during drug development may facilitate and optimize the design of subsequent clinical development. Especially in oncology, well designed PK-PD modeling could be extremely useful as anticancer agents usually have a very narrow therapeutic index. This paper describes the application of the current insights in the use of PK-PD modeling to the design of clinical trials in oncology. The application of PK-PD modeling in each separate stage of (pre)clinical drug development of anticancer agents is discussed. The implementation of this approach is illustrated with the clinical development of docetaxel.

Red blood cells: a neglected compartment in topotecan pharmacokinetic analysis

Previously, a gender dependency of topotecan was found in the pharmacokinetics in the plasma compartment. Here, we prospectively studied the red blood cell (RBC) partitioning of topotecan and evaluated its consequences for overall drug disposition. Blood samples were obtained from 12 patients receiving cisplatin followed by i.v. topotecan. Topotecan pharmacokinetic analysis was performed in whole blood, plasma and RBCs. Significantly slower clearance was noted in females (n=7) compared to males (n=5) for lactone and total topotecan in plasma (p<0.0001), and for total drug in RBCs (p=0.027), but not in whole blood. In addition, no gender-dependent differences were observed in the terminal half-lives of topotecan in any of the compartments. The area under the curve ratios for RBC total to plasma lactone were 2.53+/-0.0640 and 2.13+/-0.442 in males and females, respectively. Hence, topotecan displays preferential affinity for RBCs compared to plasma, although these cells do not act as a depot in which drug accumulates over time. RBCs thus play a principal role in the distribution kinetics of topotecan and have a major impact on its plasma pharmacokinetics. The data warrant a change from current practice in pharmacokinetic studies with this agent and provide further evidence that, in general, the choice of the appropriate assay matrix should be rationally based.

Simple and sensitive determination of the new antitumor drug CKD-602 in human plasma by liquid chromatography

A simple and sensitive high-performance liquid chromatographic with fluorescence detection method has been developed and validated for the determination of the new antitumor agent CKD-602 in human plasma. Plasma proteins were precipitated with methanol and the samples were acidified with 7% (v/v) perchloric acid. The supernatants were analyzed by HPLC using a Capcell Pak C(18) UG120 column and a mixture of methanol-0.1 M hexane-1-sulfonic acid in methanol-0.01 M TEMED in water at pH 6.0 (40:1:59, v/v) as the mobile phase. The lower limit of quantification was 0.2 ng/ml using 200 microliter plasma samples. Mean within-run precision and between-run precision at six tested concentrations (0.2-400 ng/ml) were </=10% and mean accuracy was </=15%. Stability studies showed that CKD-602 is stable in both plasma and methanol extracts for at least 3 months at -30 degrees C. The described method was used for the pharmacokinetic analysis of CKD-602 during clinical phase I studies, in patients with solid tumors.

Topotecan preceded by oxaliplatin using a 3 week schedule: a phase I study in advanced cancer patients

Combinations of topoisomerase I (topo I) poisons and platinum derivatives have synergistic antitumoral effects. However, their clinical development is limited by supra-additive haematological toxicity. The aim of this study was to determine whether sustained doses of topotecan and oxaliplatin could be achieved using a synergistic sequence. 34 advanced cancer patients and 186 cycles were evaluable for toxicity over five dosing levels. Oxaliplatin at 85-110 mg/m(2) was given on day 1, followed by topotecan 0.5-1.25 mg/m(2)/day x 5 from day 1 to 5, every 3 weeks. Plasma pharmacokinetics (PK) of total and ultrafiltrable platinum, total and lactone forms of topotecan were determined in the first cycle. The dose-limiting toxicity (DT) was identified as grade 4 thrombocytopenia. The occurrence of grade 4 thrombocytopenia did not correlate with topotecan PK, but it did with the patient's characteristics. Severe thrombocytopenia was seen in 1/8 of patients without clinical or biological evidence of malnutrition, with a creatinine clearance higher than 1 ml/s, and no more than two previous chemotherapy regimens, while it was seen in 8/10 patients with one of these characteristics (P<0.004). In conclusion, the recommended doses of oxaliplatin 110 mg/m(2) and topotecan 1 mg/m(2)/day, every 3 weeks can be administered to patients with a favourable general status and pretreatment characteristics and a phase II study is worthwhile in ovarian cancer patients.

Topotecan in combination with carboplatin: phase I trial evaluation of two treatment schedules

BACKGROUND

Topotecan and cisplatin combinations have shown schedule-dependent toxicity, which may in part be due to cisplatin nephrotoxicity. As carboplatin is less nephrotoxic and increasingly replacing cisplatin in clinical practice, the aim of this study was to define the optimal sequence and dose for topotecan in combination with carboplatin.

PATIENTS AND METHODS

Two parallel phase I trials, with pharmacokinetic studies, were conducted administering carboplatin on day 1 with topotecan on days 1-5 (schedule A) or days 8-12 (schedule B). repeated every 3 weeks.

RESULTS

Twenty-one patients were treated over two dose levels, carboplatin AUC 4 [glomerular filtration rate (GFR) calculated from 51Cr-EDTA clearance] with topotecan 0.5 or 0.75 mg/m2. At the first dose level, six patients were evaluable for each schedule. With schedule A, from 34 cycles, there were two dose reductions and 10 treatment delays due to myelosuppression. With schedule B from 25 cycles, there was one reduction and 10 delays. At dose level 2, both patients in schedule A had dose-limiting neutropenia. In contrast, there was no dose-limiting toxicity with schedule B in six patients, although the majority of cycles were delayed.

CONCLUSION

The combination of topotecan and carboplatin using these 3-weekly schedules lead to significant myelotoxicity with attendant dose reductions and delays; the optimal scheduling of these agents remains to be defined.

Population pharmacokinetic and dynamic analysis of the topoisomerase I inhibitor lurtotecan in phase II studies

Population pharmacokinetic-dynamic analysis was prospectively integrated in a broad phase II program of lurtotecan (GI147211), a novel camptothecin derived topoisomerase I inhibitor, to determine the population pharmacokinetic profile in a larger population, to estimate individual pharmacokinetic parameters and to investigate relationships with clinical outcome. A sparse sampling method was applied during course one, which involved two sampling time-points. A Bayesian algorithm was used to estimate individual pharmacokinetic parameters, in particular total plasma clearance (CL) and volume of distribution. In total, samples were collected of 109 (63%) of 173 patients. Pharmacokinetic-dynamic evaluation could be carried out successfully in 85 (78%) of the sampled patients. CL of lurtotecan showed substantial variability (mean 87 +/- 28 L/h) and was of the same magnitude as in the phase I studies where full pharmacokinetic curves were used. Residual variability in the population estimate of CL was 9.9%. No significant relationships were observed between exposure parameters and toxicity nor likelihood of tumor response, however the latter relationship may well have been obscured by the heterogeneity of the studied population. Prospective implementation of large scale population pharmacokinetic-dynamic analysis is feasible and important to establish whether interpatient variability in drug exposure is a major determinant of toxicity or activity.

The use of oral cytotoxic and cytostatic drugs in cancer treatment

Although with a few exceptions, most new anticancer agents are initially developed for intravenous use, oral treatment with anticancer agents is, if feasible, to be preferred, as this route of administration is convenient to patients, reduces administration costs and facilitates the use of more chronic treatment regimens. Recent studies have identified various physiological barriers limiting the oral absorption of anticancer drugs. Presently, several strategies are explored to alter the low and variable oral bioavailability of several important anticancer agents by taking advantage of an intentional interaction between anticancer agents and drugs that modulate active intestinal drug transporters or (intestinal) enzymes.

Salivary and plasma pharmacokinetics of topotecan in patients with metastatic epithelial ovarian cancer

The comparative saliva/plasma pharmacokinetics of topotecan were investigated in 13 patients with metastatic epithelial ovarian cancer receiving topotecan (30-min intravenous (i.v.) infusion) on a five consecutive day schedule every 3 weeks. During the first and the second courses of treatment, each patient underwent pharmacokinetic evaluation. Quantitation of the total topotecan (lactone plus carboxylate form) was assessed by a highly specific high-performance liquid chromatographic (HPLC) method. Large patient-to-patient variations in the plasma and saliva concentrations were observed. Plasma and saliva pharmacokinetics could be described using a biexponential pattern. From the saliva data, the half-life of the terminal part of the curve was 2.64 h, it was of the same order of magnitude as the topotecan elimination half-life determined from the plasma data, 3.18 h. Topotecan concentrations were higher in the saliva than in the plasma, the saliva/plasma concentration ratio averaged 2.31 and the ratio area under the parotid saliva (AUC(s)) over plasma (AUC(p)) concentration-time curve (AUC(s)/AUC(p)) averaged 2.11. For each individual, a significant relationship was found between topotecan concentrations in the saliva and in the plasma, the coefficients of correlation ranged from 0.75 to 0.92 according to the patient. Myelosuppression, especially granulocytopenia was the most frequent toxicity encountered during the trial. The percent decrease in the leucocyte count, absolute neutrophil count and platelet count were related to the AUCp/day using sigmoidal E(max) models. The high values of the Hill constant found reflect the very steep AUC-haematoxicity relationship observed. In most cases, abdominal pain occurred in patients presenting high saliva concentrations. One patient with high salivary concentrations (mean S/P ratio=4.60) had grade 1 mucositis. In conclusion, the concentration of topotecan in saliva appeared to be useful as an indirect, non-invasive estimation of the levels of topotecan in the plasma; thus, saliva concentrations could be a good predictor of the behaviour of topotecan in the body.

Topoisomerase I inhibition with topotecan: pharmacologic and clinical issues

Topoisomerase I (topo-I) inhibitors are a new class of anticancer agents with a mechanism of action aimed at interrupting DNA replication in cancer cells, the result of which is cell death. Most, if not all, topo-I inhibitors are derivatives of the plant extract camptothecin. Topotecan is a derivative of camptothecin which has been structurally modified to increase water solubility. The pharmacokinetic profile of topotecan is usually characterised by a two-compartment model and is linear in the dose range of 0.5 - 3.5 mg/m(2). Current clinical trials suggest antitumour activity against a variety of human tumour types, including ovarian cancer, non-small cell lung cancer (NSCLC) and non-lymphocytic haematologic malignancies. The main dose-limiting toxicity (DLT) is non-cumulative myelosuppression. Non-haematologic toxicities are usually mild. Based on several Phase I studies, the recommended Phase II dose was 1.5 mg/m(2)/day iv. for 5 days. Current Phase I and Phase II trials are evaluating the combination of topotecan with other chemotherapeutic agents to increase the therapeutic benefits of topotecan. The DLT in these trials is mainly myelosuppression.

Pharmacokinetically guided administration of chemotherapeutic agents

The current practice for the dose calculation of most anticancer agents is based on body surface area in m2, although lower interpatient variation in pharmacokinetic parameters has been reported with pharmacokinetically guided administration. As chemotherapeutic agents have a narrow therapeutic window, pharmacokinetically guided administration may lead to less toxicity and higher efficacy than administration on the basis of body surface area. Pharmacokinetically guided administration, using parameters such as area under the plasma concentration-time curve (AUC), steady-state plasma drug concentration and drug exposure time above a certain plasma concentration, has been studied for many antineoplastic agents. Assessment of pharmacokinetic profiles allows the characterisation of relationships between pharmacokinetic parameters and efficacy and toxicity. AUC appears to be more closely correlated with pharmacodynamics than does the dose per unit of body surface area. In particular, the AUC-guided administration of carboplatin has been extensively studied, based on the close relationship between the renal clearance of the drug and glomerular filtration rate. Several formulae and limited sampling models have been derived to predict the AUC of carboplatin. The relationship between AUC and pharmacodynamics has also been studied for other anticancer agents, for example fluorouracil, topotecan, etoposide, cisplatin and busulfan, but all less extensively than for carboplatin. The pharmacokinetically guided administration of these agents needs to be investigated further before the use of alternative administration formulae can become standard clinical practice. Prospective studies of pharmacokinetically guided versus surface area-based administration should be performed to validate pharmacokinetic-pharmacodynamic relationships and to facilitate optimal dosage of anticancer agents in the clinic.

Clinical use of topoisomerase I inhibitors in anticancer treatment

The camptothecin analogs topotecan and irinotecan have shown to be among the most effective anticancer agents and, as S-phase specific agents, their antitumor effect is maximized when they are administered in protracted schedules. The documented activity as single agents in many adult and pediatric malignancies has been followed by their use in combination with other anticancer agents. These studies have shown promising results, and have placed topotecan and irinotecan in the first line treatment for some malignancies. However, studies to better determine the optimal schedules and sequence of combinations are needed.

Population pharmacokinetic model for topotecan derived from phase I clinical trials

PURPOSE

To characterize the pharmacokinetics of topotecan in a population model that would identify patient variables or covariates that appreciably impacted on its disposition.

PATIENTS AND METHODS

All data were collected from 82 patients entered in four different phase I trials that were previously reported as separate studies from 1992 to 1996. All patients received topotecan as a 30-minute constant-rate infusion on a daily-times-five schedule and were selected for this study because their daily dose did not exceed 2.0 mg/m(2). Among the 82 patients were 30 patients classified as having renal insufficiency and 13 patients with hepatic dysfunction. The population pharmacokinetic model was built in sequential manner, starting with a covariate-free model and progressing to a covariate model with the aid of generalized additive modeling.

RESULTS

A linear two-compartment model characterized total topotecan plasma concentrations (n = 899). Four primary pharmacokinetic parameters (total clearance, volume of the central compartment, distributional clearance, and volume of the peripheral compartment) were related to various combinations of covariates. The relationship for total clearance (TVCL [L/h] = 32.0 + [0.356(WT - 71) + 0.308(HT - 168.5) - 8.42(SCR - 1.1)] x [1 + 0.671 sex]) was dependent on the patients' weight (WT), height (HT), serum creatinine (SCR), and sex and had a moderate ability to predict (r(2) = 0.64) each patient's individual clearance value. The addition of covariates to the population model improved the prediction errors, particularly for clearance. Removal of 10 outlying patients from the analysis improved the ability of the model to predict individual clearance values (r(2) = 0.77).

CONCLUSION

A population pharmacokinetic model for total topotecan has been developed that incorporates measures of body size and renal function to predict total clearance. The model can be used prospectively to obtain a revised and validated model that can then be used to design individualized dosing regimens.

Oral topoisomerase 1 inhibitors in adult patients: present and future

The renewed interest in topoisomerase 1 inhibitors, based on new insights on the mechanism of action and the development of semi-synthetic derivates of camptothecin with a more favourable toxicity profile, has led to extensive preclinical and clinical research. Significant levels of anti-tumor activity in human tumor xenografts were seen especially with prolonged duration of exposure. Since oral drug delivery is a more convenient method for prolonged drug administration, and preferred by patients, further development of oral formulations seems attractive. Common concerns in the development of oral formulations are their sometimes low oral bioavailability and the frequently large intra- and interpatient variation in systemic exposure. Efforts to improve absorption and minimize intestinal metabolism/efflux of the oral chemotherapeutic agent using new formulas might lead to better bioavailability. Pharmacokinetic and pharmacodynamic evaluations have enabled guidance in recommendations of schedules. Given the interpatient variation in exposure it is interesting to note that flat dosing of topotecan resulted in the same systemic exposure compared with the more complex dosing per body surface area. In order to diminish the interpatient variation in exposure to 9-AC a limited sampling model for oral 9-AC was developed, enabling prediction of the systemic exposure for 9-AC and optimizing treatment for any given patient. Drug sequencing plays a key role in the combination topotecan/cisplatin and might be important for combination with other classes of drugs. Therefore, forthcoming phase 1 trials on combination therapy with oral topoisomerase 1 inhibitors should include studies on sequence dependence and pharmacokinetic analyses to evaluate any mutual interaction.

Phase I pharmacologic study of oral topotecan and intravenous cisplatin: sequence-dependent hematologic side effects

PURPOSE

In in vitro studies, synergism and sequence-dependent effects were reported for the combination of topotecan and cisplatin. Recently, an oral formulation of topotecan became available. This phase I study was performed to assess the feasibility of the combination of oral topotecan and cisplatin, the pharmacokinetic interaction, and sequence-dependent effects.

PATIENTS AND METHODS

Topotecan was administered orally (PO) daily for 5 days in escalating doses and cisplatin was given intravenously (IV) at a fixed dose of 75 mg/m(2) either before topotecan administration on day 1 (sequence CT) or after topotecan administration on day 5 (sequence TC) once every 3 weeks. Patients were treated in a randomized cross-over design.

RESULTS

Forty-nine patients were entered onto the study; one patient was not eligible. Sequence CT induced significantly more severe myelosuppression than did sequence TC, and the maximum-tolerated dosage of topotecan in sequence CT was 1.25 mg/m(2)/d x 5. In sequence TC, the maximum-tolerated dosage of topotecan was 2.0 mg/m(2)/d x 5. Dose-limiting toxicity consisted of myelosuppression and diarrhea. Pharmacokinetics of topotecan and cisplatin were linear over the dose range studied; no sequence-dependent effects were observed. In addition, topotecan did not influence the protein binding of cisplatin or the platinum-DNA adduct formation in peripheral leukocytes in either sequence.

CONCLUSION

The recommended dosages for phase II studies involving patients like the patients in our study are topotecan 1.25 mg/m(2)/d PO x 5 preceded by cisplatin 75 mg/m(2) IV day 1 once every 3 weeks, and topotecan 2.0 mg/m(2)/d PO followed by cisplatin 75 mg/m(2) IV day 5. No pharmacokinetic interaction could be discerned in our study. The antitumor efficacy of both schedules should be evaluated in a randomized phase II study.

The effect of amifostine on the in vitro cytotoxicity of chemotherapeutic agents in three epithelial ovarian carcinoma cell lines

OBJECTIVES

Amifostine protects against a spectrum of toxicities induced by chemotherapy without affecting tumor cell kill. This is supported by clinical data and in vivo animal studies. However, there is a paucity of data on its effect on the tumor cytotoxicity of several chemotherapeutic agents used in recurrent epithelial ovarian cancer. This study compares in vitro cytotoxicity before and after addition of amifostine.

METHODS

Three epithelial ovarian carcinoma cell lines (SKOV3, 420, 429) were exposed to cis-platinum, paclitaxel, doxorubicin, etoposide, 5-fluorouracil, bleomycin, 4-epidoxorubicin, 4-HC (activated cyclophosphamide), vincristine, actinomycin D, mitomycin C, and topotecan. Cells were pretreated with either 0 or 1.2 mM amifostine. Tumor cell kill after 6 days of incubation was measured using the ATP cell viability assay. Paired samples Student's t statistic was used to test the difference in mean ATP levels between drug-treated samples with and without pretreatment with amifostine.

RESULTS

SKOV3 was sensitive to paclitaxel, actinomycin D, 4-epidoxorubicin, and vincristine. Cell line 420 was sensitive to paclitaxel, etoposide, and 5-fluorouracil. Cell line 429 was sensitive to paclitaxel and 5-fluorouracil. There was no significant difference in the mean ATP levels between drug-treated samples with and without pretreatment with amifostine for each of the sensitive drugs in all three cell lines. Similarly, there was no significant difference in the mean ATP levels in cis-platinum and 4-HC treated samples with and without pretreatment with amifostine.

CONCLUSIONS

These results show that at the cellular level amifostine did not protect epithelial ovarian carcinoma cells against tumor cell kill.

Phase II trial of topotecan in advanced breast cancer: a Cancer and Leukemia Group B study

The topoisomerase I inhibitor topotecan had demonstrated good antitumor activity in several murine tumor systems and in human clonogenic assays by 1993. In that year, the Cancer and Leukemia Group B (CALGB) began a phase II trial to determine its activity in patients with breast cancer who had previously received one course of chemotherapy for advanced breast cancer. Between April 1993 and June 1994, 53 patients of performance status 0-2 entered the study, of whom 47 were eligible and 40 were evaluable. Topotecan was given at a dose of 1.5 mg/m2 over 30 minutes daily for 5 days every 21 days. In the absence of progression or withdrawal of consent, therapy was continued indefinitely. The median age was 58 years (range 30-79). There were no complete responses and four partial responses, resulting in an objective response rate of 10% (95% CI: 3-24%). Responses were noted in lymph nodes, liver, and skin. The median duration of response was 5 months. The median survival was 12 months. Life-threatening toxicities were almost exclusively hematologic. However, myelosuppression was not cumulative. It was concluded that topotecan has only modest activity among women with advanced breast cancer who have previously received one course of chemotherapy. Given its modest activity and predominant hematologic toxicity, it does not appear to be a promising drug for either single-agent or combination chemotherapy in the salvage setting of advanced breast cancer.

Topotecan: a new topoisomerase I inhibiting antineoplastic agent

OBJECTIVE

To review the pharmacologic, pharmacokinetic, therapeutic, and safety aspects of topotecan, a new antineoplastic agent, and to assess its role in the treatment of cancer.

DATA SOURCES

MEDLINE database English language only, January 1990-March 1998; SmithKline Beecham Pharmaceuticals; published articles, books, and abstracts.

STUDY SELECTION

Studies in humans with cancer, clinical case reports, open clinical trials, and controlled clinical studies. Efficacy studies were limited primarily to trials with at least 20 evaluable patients:

DATA EXTRACTION

Relevant data were extracted only from published reports. Data were obtained from studies in both articles and abstracts. Only articles written in English were reviewed.

DATA SYNTHESIS

Topotecan is an effective second- or third-line therapy for patients with advanced ovarian cancer and is comparable to ifosfamide, liposomal doxorubicin, and paclitaxel. Activity in combination with other agents and as a first-line agent is yet to be determined. Limited data indicate activity in small-cell lung cancer, cancers of the breast and uterus, and in nonlymphocytic leukemia. The dose-limiting toxicity is myelosuppression.

CONCLUSIONS

Topotecan is an effective second-line agent for patients with unresponsive or relapsed cancer of the ovary. It appears to be similar to other active agents in patients with this disease status. Its ultimate role in ovarian cancer and other neoplasms awaits additional evaluation in combination with other agents and as first-line therapy.

Clinical pharmacology of camptothecins

Camptothecins (CPTs) are a unique class of chemotherapeutic agent which inhibit DNA synthesis by inhibiting topoisomerase I activity. Structure-activity studies on the original CPT alkaloid led to the development of the new analogues irinotecan (CPT-11), topotecan, and 9-aminocamptothecin, which have improved water solubility and lower toxicity. CPT analogues exhibit interesting pharmacokinetic/pharmacodynamic and metabolic properties that are of major research and clinical interest. This review describes the clinical pharmacology of these 3 CPT analogues. Specific areas such as absorption after extravascular administration, pharmacokinetic/pharmacodynamic variability, metabolism, and administration in special populations are discussed.

Five days of oral topotecan (Hycamtin), a phase I and pharmacological study in adult patients with solid tumours

Topotecan is a specific inhibitor to topoisomerase I. An oral formulation of topotecan is available with a bioavailability of 32-44% in humans. A phase I and pharmacological study of the oral formulation of topotecan administered daily for 5 days every 21 days was performed in adult patients with solid tumours to determine the maximum tolerated dose (MTD). Adult patients with a WHO performance status < or = 2 adequate haematological, hepatic and renal functions, with malignant solid tumours refractory to standard forms were entered into the study. Pharmacokinetics were performed on days 1 and 4 of the first course using a validated high performance liquid chromatographic assay. 29 patients entered the study, all patients were evaluable for toxicity and response. The doses studied in the 29 patients were 1.2, 1.8, 2.3, 2.7 mg/m2/day and a fixed dose of 4 mg/day without surface area adjustment. A total of 109 courses were given. Dose limiting toxicity (DLT) was reached at a dose of 2.7 mg/m2/day and consisted of CTC (NCI-Common Toxicity Criteria) grade IV granulocytopenia. The regimen was well tolerated. Non-haematological toxicities were mild, including fatigue, anorexia, nausea, vomiting and diarrhoea. A significant correlation was observed between the percentage decrease in white blood cells versus the area under the curve (AUC(t)) of topotecan lactone (R = 0.76 P < 0.01) which was modelled by a sigmoidal Emax function. The correlation coefficient between the absolute topotecan dose administered and the AUC(t) was R = 0.52 (P = 0.04). Pharmacokinetics of the fixed dose of 4 mg/day were comparable to the 2.3 mg/m2/day dose. DLT in this phase I study of five daily doses of oral topotecan every 21 days was granulocytopenia. The recommended dose for phase II studies is 2.3 mg/m2/day or alternatively, a fixed dose of 4 mg/day.