Bioavailability and pharmacokinetics of oral topotecan: a new topoisomerase I inhibitor

Assessment of contribution of BCRP to intestinal absorption of various drugs using portal-systemic blood concentration difference model in mice

Prediction of the intestinal absorption of new chemical entities (NCEs) is still difficult, in part because drug efflux transporters, including breast cancer resistance protein (BCRP) and P-glycoprotein (P-gp), restrict their intestinal permeability. We have demonstrated that the absorptive quotient (AQ) obtained from the in vitro Caco-2 permeability study would be a valuable parameter for estimating the impact of BCRP on the intestinal absorption of drugs. In this study, in order to assess the correlation between the in vitro AQ for BCRP and in vivo contribution of BCRP on drug absorption, we evaluated the oral absorption of various compounds by portal-systemic blood concentration (P-S) difference method in wild-type (WT), Bcrp(-/-), and Mdr1a/1b(-/-) mice. In addition, we also calculated a rate of BCRP contribution (Rbcrp ). Ciprofloxacin and nitrofurantoin showed the low Rbcrp value (0.05 and 0.15), and their apparent fractions of intestinal absorption in WT mice were 46.5% and 63.7%, respectively. These results suggest that BCRP hardly affects their intestinal absorption in mice. On the other hand, the apparent fraction of intestinal absorption of topotecan and sulfasalazine was significantly lower in WT mice than in Bcrp(-/-) mice. Moreover, their Rbcrp values were 0.42 and 0.79, respectively, indicating the high contribution of BCRP to their oral absorption. Furthermore, in vivo Rbcrp calculated in this study was almost comparable to in vitro AQ obtained from Caco-2 permeability study. This study provides useful concepts in assessing the contribution of BCRP on intestinal absorption in drug discovery and development process.

Topoisomerases as anticancer targets

Many cancer type-specific anticancer agents have been developed and significant advances have been made toward precision medicine in cancer treatment. However, traditional or nonspecific anticancer drugs are still important for the treatment of many cancer patients whose cancers either do not respond to or have developed resistance to cancer-specific anticancer agents. DNA topoisomerases, especially type IIA topoisomerases, are proved therapeutic targets of anticancer and antibacterial drugs. Clinically successful topoisomerase-targeting anticancer drugs act through topoisomerase poisoning, which leads to replication fork arrest and double-strand break formation. Unfortunately, this unique mode of action is associated with the development of secondary cancers and cardiotoxicity. Structures of topoisomerase-drug-DNA ternary complexes have revealed the exact binding sites and mechanisms of topoisomerase poisons. Recent advances in the field have suggested a possibility of designing isoform-specific human topoisomerase II poisons, which may be developed as safer anticancer drugs. It may also be possible to design catalytic inhibitors of topoisomerases by targeting certain inactive conformations of these enzymes. Furthermore, identification of various new bacterial topoisomerase inhibitors and regulatory proteins may inspire the discovery of novel human topoisomerase inhibitors. Thus, topoisomerases remain as important therapeutic targets of anticancer agents.

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.

Population Pharmacokinetics of Oral Topotecan in Infants and Very Young Children with Brain Tumors Demonstrates a Role of ABCG2 rs4148157 on the Absorption Rate Constant

For infants and very young children with brain tumors, chemotherapy after surgical resection is the main treatment due to neurologic and neuroendocrine adverse effects from whole brain irradiation. Topotecan, an anticancer drug with antitumor activity against pediatric brain tumors, can be given intravenous or orally. However, high interpatient variability in oral drug bioavailability is common in children less than 3 years old. Therefore, this study aimed to determine the population pharmacokinetics of oral topotecan in infants and very young children, specifically evaluating the effects of age and ABCG2 and ABCB1 on the absorption rate constant (Ka), as well as other covariate effects on all pharmacokinetic parameters. A nonlinear mixed effects model was implemented in Monolix 4.3.2 (Lixoft, Orsay, France). A one-compartment model with first-order input and first-order elimination was found to adequately characterize topotecan lactone concentrations with population estimates as [mean (S.E.)]; Ka = 0.61 (0.11) h(-1), apparent volume of distribution (V/F) = 40.2 (7.0) l, and apparent clearance (CL/F) = 40.0 (2.9) l/h. After including the body surface area in the V/F and CL/F as a power model centered on the population median, the ABCG2 rs4148157 allele was found to play a significant role in the value of Ka Patients homozygous or heterozygous for G>A demonstrated a Ka value 2-fold higher than their GG counterparts, complemented with a 2-fold higher maximal concentration as well. These results demonstrate a possible role for the ABCG2 rs4148157 allele in the pharmacokinetics of oral topotecan in infants and very young children, and warrants further investigation.

Pharmacodynamics and pharmacokinetics of oral topotecan in patients with advanced solid tumours and impaired renal function

AIMS

The aim of the study was to determine the effect of renal impairment and prior platinum-based chemotherapy on the toxicity and pharmacokinetics of oral topotecan and to identify recommended doses for patients with renal impairment or prior platinum-based (PB) chemotherapy.

METHODS

A multicentre phase I toxicity and pharmacokinetic study of oral topotecan was conducted in patients with advanced solid tumours. Patients were grouped by normal renal function with limited or prior PB chemotherapy or impaired renal function (mild [creatinine clearance (CLcr)  = 50-79 ml min(-1) ], moderate [CLcr  = 30-49 ml min(-1) ], severe [CLcr <30 ml min(-1) ]).

RESULTS

Fifty-nine patients were evaluable. Topotecan lactone and total topotecan area under the concentration-time curve (AUC) was significantly increased in patients with moderate and severe renal impairment (109% and 174%, respectively, topotecan lactone and 148% and 298%, respectively, total topotecan). Asian patients (23 in total) had higher AUCs than non-Asian patients with the same degree of renal impairment. Thirteen dose-limiting toxicities (DLTs) were observed, which were mostly haematological. The maximum tolerated dose (MTD) was 2.3 mg m(-2) day(-1) , given on days 1 to 5 in a 21 day cycle, for patients with prior PB chemotherapy or mild renal impairment, and 1.2 mg m(-2) day(-1) for patients with moderate renal impairment (suggested dose 1.9 mg m(-2) day(-1) for non-Asians). Due to incomplete enrolment of patients with severe renal impairment, the MTD was determined as ≥ 0.6 mg m(-2) day(-1) in this cohort.

CONCLUSIONS

Oral topotecan dose adjustments are not required in patients with prior PB chemotherapy or mildly impaired renal function, but reduced doses are required for patients with moderate or severe renal impairment.

Oral topotecan: Bioavailability, pharmacokinetics and impact of ABCG2 genotyping in Chinese patients with advanced cancers

Oral topotecan (Hycamtin(®)) has been recently approved for the treatment of relapsed small cell lung cancer (SCLC) in 2007, however, the bioavailability and pharmacokinetic data of topotecan for Chinese patients is still limited. Xinze(®) is a new and the only capsule formulation of topotecan used in China that is similar to Hycamtin(®). The current study aimed to investigate the absolute bioavailability and pharmacokinetics of Xinze(®) in Chinese patients with advanced cancers. On day 1, an IV dose of 1.5 mg/m(2)/d as a 30 min continuous infusion was administered. Patients took the oral topotecan at one of two dose levels: 1.5 mg/m(2)/d (six patients) or 1.9 mg/m(2)/d (seven patients) on day 2. Plasma pharmacokinetics of total topotecan and topotecan in the lactone form were performed on both days using ultra-high-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS). Single-nucleotide polymorphisms (SNPs) identified in exon 5 (421C>A) and in exon 2 (34G>A) in ATP-binding cassette sub-family G member 2 (ABCG2) were analyzed by direct sequencing. Safety assessments were performed throughout the study. The maximum plasma concentration (Cmax) reached at 1-2 h and the elimination half-life time (T1/2) was approximately 4.2 h after oral administration. The absolute bioavailability of total topotecan in the 1.5 mg/m(2)/d and 1.9 mg/m(2)/d groups averaged 41.23 ± 11.8% and 36.00 ± 14.8%, respectively. The patients with heterozygous SNPs had essentially the same bioavailability and pharmacokinetics. The bioavailability of topotecan after oral administration illustrates good systemic exposure at dosages of 1.5 mg/m(2)/d and 1.9 mg/m(2)/d over a five-day schedule in Chinese patients. On a dose-normalized basis, the values of Cmax and AUC0-t for total topotecan in Chinese patients were higher than in Caucasians following oral and intravenous administration, while the T1/2 was consistent.

Combination metronomic oral topotecan and pazopanib: a pharmacokinetic study in patients with gynecological cancer

BACKGROUND

Combination metronomic topotecan plus pazopanib is active against preclinical models of gynecological cancer. Both agents are substrates for ATP-binding cassette family transporters so there is an increased likelihood for pharmacokinetic (PK) drug-drug interactions.

PATIENTS AND METHODS

PK analyses of topotecan were performed during three cycles of a phase I dose-escalation study of metronomic topotecan and pazopanib in consenting adult patients with gynecological cancer. Concentration time data were analyzed using a population PK approach.

RESULTS

Twenty-one patients were evaluable for serial PK studies. Considerable inter- and intra-patient variability was observed in the PK parameters, attributable primarily to highly variable oral bioavailability. No difference in topotecan disposition was detected between administration cycles, nor between the off- versus on-pazopanib studies.

CONCLUSION

The lack of a statistically significant drug-drug interaction agrees with preclinical findings suggesting that pazopanib does not influence the PK of metronomic topotecan. No adjustment of low dose metronomic topotecan dosing is merited when used in conjunction with pazopanib.

Topotecan exposure estimation in pediatric acute myeloid leukemia supported by LC-MS-based drug monitoring and pharmacokinetic analysis

Individualization of the topotecan dosing can reduce inter-patient variability, toxicity, and at the same time increases chemotherapy efficacy. Topotecan dosing based on simultaneous drug monitoring and pharmacokinetic analysis can yield more accurate and precise estimation of the topotecan systemic exposure than that attainable with the fixed dosing approach. Therefore, a combined approach could provide a tool assisting the clinicians in individualization of the topotecan dosing. The aim of the study was to estimate the topotecan exposure in pediatric patients with acute myeloid leukemia (AML) based on the plasma concentration-time data and using the pharmacokinetic analysis. The primary goal was achieve the correct estimation of the target plasma area against the topotecan concentration-time curve (AUC) in a 5 day course of cladribine followed by monitored topotecan in pediatric patients with recurrent/refractory AML. A sensitive and selective reversed-phase liquid chromatographic-mass spectrometry (LC-MS) assay was developed to quantify total topotecan in the human plasma samples. This method, with its lower quantification limit of 1 ng/ml, was validated over a linear range of 1-150 ng/ml. Under the proposed approach, the topotecan dosing was selected so as to achieve the final AUC value of 140±20 ng/ml h. The presented analytical and pharmacokinetic data demonstrate that the proposed approach can be a practical, useful, efficient, and accurate tool for individualizing the topotecan dosing in children with AML.

Attenuation of intestinal absorption by major efflux transporters: quantitative tools and strategies using a Caco-2 model

Efflux transporters expressed in the apical membrane of intestinal enterocytes have been implicated in drug oral absorption. The current study presents a strategy and tools to quantitatively predict the impact of efflux on oral absorption for new chemical entities (NCEs) in early drug discovery. Sixty-three marketed drugs with human absorption data were evaluated in the Caco-2 bidirectional permeability assay and subjected to specific transporter inhibition. A four-zone graphical model was developed from apparent permeability and efflux ratios to quickly identify compounds whose efflux activity may distinctly influence human absorption. NCEs in "zone 4" will probably have efflux as a barrier for oral absorption and further mechanistic studies are required. To interpret mechanistic results, we introduced a new quantitative substrate classification parameter, transporter substrate index (TSI). TSI allowed more flexibility and considered both in vitro and in vivo outcomes. Its application ranged from addressing the challenge of overlapping substrate specificity to projecting the role of transporter(s) on exposure or potential drug-drug interaction risk. The potential impact of efflux transporters associated with physicochemical properties on drug absorption is discussed in the context of TSI and also the previously reported absorption quotient. In this way, the chemistry strategy may be differentially focused on passive permeability or efflux activity or both.

5,7-Dimethoxyflavone and multiple flavonoids in combination alter the ABCG2-mediated tissue distribution of mitoxantrone in mice

PURPOSE

The objective of our study was to investigate the effect of 5,7-DMF on the accumulation of mitoxantrone (MX) in BCRP-expressing normal cells and to investigate its impact on the PK and tissue distribution of MX in mice.

METHODS

The in vitro effect of 5,7-DMF on MX accumulation was examined in MDCK cells transfected with BCRP. The pharmacokinetic and tissue distribution of mitoxantrone, with and without co-administration of 5,7-DMF or multiple flavonoid combinations, were determined in mice.

RESULTS

In the presence of 2.5 μM or 25 μM of 5,7-DMF, the intracellular concentration of MX was significantly increased in MDCK/Bcrp1 and MDCK/BCRP cells, but not in MDCK/Mock cells. The AUC values of MX in several tissues were significantly increased when MX was co-administered with 5,7-DMF. The most substantial elevations of MX AUC in the presence of 5,7-DMF occurred in the liver (94.5%) and kidneys (61.9%), which is in apparent agreement with the relatively high levels of mouse Bcrp1 expression in these two tissues.

CONCLUSIONS

Bcrp1-mediated DMF-MX interactions occur both in vitro and in vivo. 5,7-DMF represents a novel and very promising chemosensitizing agent for the BCRP-mediated MDR due to its low toxicity and potent BCRP inhibition.

Cancer therapies utilizing the camptothecins: a review of the in vivo literature

This review summarizes the in vivo assessment-preliminary, preclinical, and clinical-of chemotherapeutics derived from camptothecin or a derivative. Camptothecin is a naturally occurring, pentacyclic quinoline alkaloid that possesses high cytotoxic activity in a variety of cell lines. Major limitations of the drug, including poor solubility and hydrolysis under physiological conditions, prevent full clinical utilization. Camptothecin remains at equilibrium in an active lactone form and inactive hydrolyzed carboxylate form. The active lactone binds to DNA topoisomerase I cleavage complex, believed to be the single site of activity. Binding inhibits DNA religation, resulting in apoptosis. A series of small molecule camptothecin derivatives have been developed that increase solubility, lactone stability and bioavailability to varying levels of success. A number of macromolecular agents have also been described wherein camptothecin(s) are covalently appended or noncovalently associated with the goal of improving solubility and lactone stability, while taking advantage of the tumor physiology to deliver larger doses of drug to the tumor with lower systemic toxicity. With the increasing interest in drug delivery and polymer therapeutics, additional constructs are anticipated. The goal of this review is to summarize the relevant literature for others interested in the field of camptothecin-based therapeutics, specifically in the context of biodistribution, dosing regimens, and pharmacokinetics with the desire of providing a useful source of comparative data. To this end, only constructs where in vivo data is available are reported. The review includes published reports in English through mid-2009.

Altered intravenous pharmacokinetics of topotecan in rats with acute renal failure (ARF) induced by uranyl nitrate: Do adenosine A1antagonists (selective/non-selective) normalize the altered topotecan kinetics in ARF?

A series of exploratory investigations with multiple agents was carried out in normal rats and in rats with uranyl nitrate-induced acute renal failure to understand the disposition characteristics of intravenous topotecan (TPT) used as a model substrate. The disposition of TPT was unaltered in normal rats when treated with methotrexate, whereas treatment with probenecid increased the systemic exposure of TPT. In case of uranyl nitrate-induced acute renal failure (UN-ARF) rats, the systemic exposure of TPT was increased when compared with normal rats, whereas in UN-ARF rats treated with probenecid a further reduction in renal clearance of TPT was noted as compared with that of UN-ARF induced rats. Thus, TPT may be involved in the tubular secretory pathway when a passive glomerular filtration pathway for elimination was not possible. The disposition of TPT did not normalize in UN-ARF rats when treated with caffeine, a non-selective adenosine A1 receptor antagonist, whereas the selective adenosine A1 receptor antagonist (1,3-dipropyl-8-phenylxanthine, DPPX) normalized TPT pharmacokinetic disposition by improving renal function. Renal excretion studies demonstrated that CLR improved by almost fivefold following DPPX treatment in ARF rats. In addition, the qualitative stability/metabolism pattern of TPT in liver microsomes prepared from various groups of rats (normal rats, UN-ARF rats, rats treated with DPPX, and UN-ARF rats treated with DPPX) was found to be similar. In summary, using a pharmacokinetic tool as a surrogate, it has been shown that the pharmacokinetic disposition of TPT improved considerably upon treatment with DPPX, a selective adenosine A1 antagonist.

Modulation of Oral Drug Bioavailability: From Preclinical Mechanism to Therapeutic Application

Currently, more than one fourth of all anticancer drugs are developed as oral formulations, and it is expected that this number will increase substantially in the near future. To enable oral drug therapy, adequate oral bioavailability must be achieved. Factors that have proved to be important in limiting the oral bioavailability are the presence of ATP-binding cassette drug transporters (ABC transporters) and the cytochrome P450 enzymes. We discuss the tissues distribution and physiological function of the ABC transporters in the human body, their expression in tumors, currently known polymorphisms and drugs that are able to inhibit their function as transporter. Furthermore, the role of the ABC transporters and drug-metabolizing enzymes as mechanisms to modulate the pharmacokinetics of anticancer agents, will be reviewed. Finally, some clinical examples of oral drug modulation are discussed. Among these examples are the coadministration of paclitaxel with CsA, a CYP3A4 substrate with P-glycoprotein (P-gp) modulating activity, and topotecan combined with the BCRP/P-gp transport inhibitor elacridar. Both are good examples of improvement of oral drug bioavailability by temporary inhibition of drug transporters in the gut epithelium.

Polymeric micelles in oral chemotherapy

Oral administration of anticancer agents is preferred by patients for its convenience and potential for use in outpatient and palliative setting. In addition, oral administration facilitates a prolonged exposure to the cytotoxic agents. Enhancement of bioavailability of emerging cytotoxic agents is a pre-requisite for successful development of oral modes of cancer treatment. Over the last decade, our studies have focused specifically on the utilization of large (MW>10(5)) and non-degradable polymers in oral chemotherapy. A family of block-graft copolymers of the poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO) Pluronic(R) polyethers and poly(acrylic acid) (PAA) bound by carbon-carbon bonds emerged, wherein both polymeric components are generally recognized as safe. Animal studies with Pluronic-PAA copolymers demonstrated that these molecules are excreted when administered orally and do not absorb into the systemic circulation. The Pluronic-PAA copolymers are surface-active and self-assemble, at physiological pH, into intra- and intermolecular micelles with hydrophobic cores of dehydrated PPO and multilayered coronas of hydrophilic PEO and partially ionized PAA segments. These micelles efficiently solubilize hydrophobic drugs such as paclitaxel and steroids and protect molecules such as camptothecins from the hydrolytic reactions. High surface activity of the Pluronic-PAA copolymers in water results in interactions with cell membranes and suppression of the membrane pumps such as P-glycoprotein. The ionizable carboxyls in the micellar corona facilitate mucoadhesion that enhances the residence time of the micelles and solubilized drugs in the gastrointestinal tract. Large payloads of the Pluronic-PAA micelles with weakly basic and water-soluble drugs such as doxorubicin and its analogs, mitomycin C, mitoxantrone, fluorouracil, and cyclophosphamide are achieved through electrostatic interactions with the micellar corona. Mechanical and physical properties of the Pluronic-PAA powders, blends, and micelles allow for formulation procedures where an active is simply dispersed into an aqueous Pluronic-PAA micellar formulation followed by optional lyophilization and processing into a ready dosage form. We review a number of in vivo and in vitro experiments demonstrating that that the oral administration of the cytotoxics formulated with the Pluronic-PAA copolymer micelles results in enhanced drug bioavailability.

Recent advances with topotecan in the treatment of lung cancer

Topotecan is a semisynthetic derivative of camptothecin that specifically targets topoisomerase I. It has well-established antineoplastic properties and has been successfully combined with other antineoplastic agents with activity dependent on DNA disruption, such as cisplatin and etoposide. Topotecan is indicated for the treatment of small cell lung cancer (SCLC) sensitive disease after failure of first-line chemotherapy and metastatic ovarian carcinoma after failure of initial or subsequent chemotherapy. Since the approval of topotecan for the second-line treatment of SCLC, studies have been conducted in the first-line setting. Recent studies demonstrate the utility of i.v. topotecan in combination with cisplatin for untreated SCLC. Further, an oral formulation of topotecan is currently under investigation and may provide added convenience for patients. Oral topotecan has been studied in the first- and second-line settings for both SCLC and non-small cell lung cancer (NSCLC). Three recent phase III trials have demonstrated the activity of oral topotecan. In the first study of chemotherapy-naïve patients with extensive-disease SCLC, oral topotecan plus cisplatin provided efficacy and safety similar to those of etoposide plus cisplatin. In a second study of patients with relapsed SCLC, treatment with oral topotecan showed a statistically significant and clinically meaningful longer overall survival time and improvement in dyspnea and quality of life compared with best supportive care alone in all prognostic groups. Finally, in previously treated patients with NSCLC, single-agent oral topotecan was shown to be noninferior in 1-year survival rate relative to the current standard of i.v. docetaxel. In future studies, oral topotecan will represent a good candidate for combination therapy with other i.v. or oral chemotherapy agents, monoclonal antibodies, and small molecule tyrosine kinase inhibitors.

Phase II trial of paclitaxel-topotecan-etoposide followed by consolidation chemoradiotherapy for limited-stage small cell lung cancer: CALGB 30002

PURPOSE

We sought to evaluate the activity and tolerance of the rationally designed sequence of paclitaxel-topotecan-etoposide, a nonplatinum regimen, as induction therapy for limited-stage small-cell lung cancer before combined chemo- and radiotherapy.

PATIENTS AND METHODS

Patients with measurable disease, performance status 0 to 2, no prior therapy, and adequate organ function were eligible. Paclitaxel (110 mg/m2, administered intravenously on day 1), topotecan (1.5 mg/m2, administered orally on days 2 to 4), and etoposide (160 mg/m2, administered orally on days 5 to 7 every 21 days), with filgrastim for two cycles, were followed by chest irradiation to 70 Gy (to postinduction tumor volume) concurrent with carboplatin (area under the curve of 5, administered intravenously on day 1) and etoposide (100 mg/m2 on days 1 to 3 every 21 days) without filgrastim for three cycles (five chemotherapy cycles total). We aimed to determine the response rates to induction and overall therapy, overall and failure-free survival, and toxicity. The primary statistical endpoint was to differentiate between complete response rates of 50 and 70% for the overall treatment program.

RESULTS

Between June 2001 and January 2003, 65 patients were enrolled, but one never started therapy, and one was ineligible. Patient characteristics included male/female, 27/36; white/black/other/unknown, 58/3/1/1; median age 62 (range, 38-78); performance status 0/1/2, 27/33/3. Induction chemotherapy resulted in six (10%) complete responses and 35 (56%) partial responses. Overall response to chemoradiotherapy included 27 (43%; 95% confidence interval [CI] 30-56%) complete responses and 24 (38%) partial responses. Median progression-free survival is 12 months (95% CI, 9-15 months). Median overall survival is 20 months (95% CI, 16-24 months). Frequent (>20%) grade 3/4 toxicities during all therapy included neutropenia, febrile neutropenia, anemia, thrombocytopenia, fatigue, and dysphagia. One patient died of febrile neutropenia, one died of febrile neutropenia and typhlitis, and one patient who declined transfusion for anemia died of cardiac ischemia.

CONCLUSIONS

This treatment regimen has significant activity in limited-stage small-cell lung cancer but did not meet our prospectively defined criteria for further investigation in this setting. The addition of etoposide and the use of a sequenced administration schedule did not seem to improve overall activity beyond our prior experience with a topotecan-paclitaxel doublet.

Topotecan for the treatment of small-cell lung cancer

Lung cancer is the most prevalent and yet the most preventable malignancy worldwide. Owing to the propensity of small-cell lung cancer to early relapse and its relative resistance to subsequent treatment there is a need to improve currently available therapies. Topotecan has provided an efficacious and tolerable therapeutic option for patients with recurrent small-cell lung cancer, and the oral formulation has also been shown to be beneficial, even in elderly patients of poor performance status. Herein we review the role of topotecan in the treatment of small-cell lung cancer.

A phase I, randomized, open-label, parallel-cohort, dose-finding study of elacridar (GF120918) and oral topotecan in cancer patients

PURPOSE

Breast cancer resistance protein (ABCG2) substantially limits the oral bioavailability of topotecan. Coadministration with elacridar, an inhibitor of breast cancer resistance protein-mediated drug transport, increases the bioavailability of topotecan. The aim of this study was to establish the lowest effective dose of elacridar to obtain maximum oral bioavailability of topotecan and to determine the optimal schedule of coadministration of oral topotecan and elacridar. In the second part of this study, dose-limiting toxicities and maximum tolerated dose of oral topotecan coadministered with elacridar, at a daily times five regimen administered every 21 days, were established.

EXPERIMENTAL DESIGN

In part I, 20 patients were randomized to receive 100, 300, 500, 700, or 1,000 mg of elacridar on days 1 and 8 1 h before or simultaneously with 2.0 mg oral topotecan, which was also randomized. On day 15, all patients were treated with 1.5 mg/m(2) i.v. topotecan. In part II of the study, patients were treated daily with oral topotecan and with the lowest effective dose of elacridar following from part I. The maximum tolerated dose and dose-limiting toxicity were determined in cohorts of three patients. Blood samples were taken on days 1, 8, and 15 of part I and on day 1 of cycles 1 and 2 of part II.

RESULTS

Complete apparent oral bioavailability of topotecan (102 +/- 7%) for all treatment arms with elacridar in both schedules was seen in part I. In the topotecan dose escalation part, two dose-limiting toxicities were seen at the 2.5 mg topotecan dose level.

CONCLUSION

The recommended schedule is 2.0 mg oral topotecan plus 100 mg elacridar administered concomitantly daily times five every 21 days.

Phase III Study of Oral Compared With Intravenous Topotecan As Second-Line Therapy in Small-Cell Lung Cancer

Purpose

Single-agent intravenous (IV) topotecan is an effective treatment for small-cell lung cancer (SCLC) after failure of first-line chemotherapy. This open-label, randomized, phase III study compared oral and IV topotecan in patients with SCLC sensitive to initial chemotherapy.

Patients and Methods

Patients with limited- or extensive-disease SCLC, documented complete or partial response to first-line therapy, Eastern Cooperative Oncology Group performance status ≤ 2, and measurable recurrent disease (WHO criteria) with a treatment-free interval of ≥ 90 days were assigned to treatment with either oral topotecan 2.3 mg/m2/d on days 1 through 5 or IV topotecan 1.5 mg/m2/d on days 1 through 5 every 21 days. Primary end point was response rate as confirmed by an external reviewer blinded to treatment.

Results

A total of 309 patients were randomly assigned. In intent-to-treat analysis, response rates were 18.3% with oral topotecan (n = 153) and 21.9% with IV topotecan (n = 151), with a difference (oral –IV) of −3.6% (95% CI, −12.6% to 5.5%). Median survival time was 33.0 weeks for oral and 35.0 weeks for IV topotecan; 1- and 2-year survival rates were 32.6% and 12.4% for oral topotecan, respectively, and 29.2% and 7.1% for IV topotecan, respectively. Third-line chemotherapy was similar for both groups (33% for oral; 35% for IV). Incidence of grade 4 toxicity in patients who received oral and IV topotecan was as follows: neutropenia in 47% and 64%, thrombocytopenia in 29% and 18%, grade 3 or 4 anemia in 23% and 31%, and sepsis in 3% and 3%, respectively. The most frequent nonhematologic adverse events (all grades) included nausea (43% oral; 42% IV), alopecia (26% oral; 30% IV), fatigue (31% oral; 36% IV), and diarrhea (36% oral; 20% IV).

Conclusion

Oral topotecan demonstrates activity and tolerability similar to IV topotecan in chemotherapy-sensitive SCLC patients and offers patients a convenient alternative to IV therapy.

Topotecan in the management of cervical cancer

Topotecan, a semisynthetic camptothecin, exerts its cytotoxic effect through inhibition of DNA topoisomerase I. Single-agent topotecan has demonstrated activity against persistent, metastatic and recurrent cancer of the uterine cervix. When combined with cisplatin in Phase II trials, further improved response rates have been reported. The cisplatin/topotecan doublet subsequently proved to be the first regimen in a series of multiple Phase III studies to demonstrate improved disease-free and overall survival in this setting compared with cisplatin alone, thus leading to its third indication by both the US FDA and the European Medicines Agency in 2006. This survival advantage was achieved at the expense of an increase in grade 3-4 hematologic toxicity; however, there was no difference in patient-reported quality of life between the cisplatin/topotecan doublet and single-agent cisplatin. This article reviews the pharmacology of topotecan and its evolution as an active agent in advanced and metastatic cervical cancer that is not amenable to cure with surgery or radiotherapy.

Role of the ABCG2 drug transporter in the resistance and oral bioavailability of a potent cyclin-dependent kinase/Aurora kinase inhibitor

Cell cycle kinase inhibitors have advanced into clinical trials in oncology. One such molecule, JNJ-7706621, is a broad-spectrum inhibitor of the cyclin-dependent kinases and Aurora kinases that mediate G(2)-M arrest and inhibits tumor growth in xenograft models. To determine the putative mechanisms of resistance to JNJ-7706621 that might be encountered in the clinic, the human epithelial cervical carcinoma cell line (HeLa) was exposed to incrementally increasing concentrations of JNJ-7706621. The resulting resistant cell population, designated HeLa-6621, was 16-fold resistant to JNJ-7706621, cross-resistant to mitoxantrone (15-fold) and topotecan (6-fold), and exhibited reduced intracellular drug accumulation of JNJ-7706621. ABCG2 was highly overexpressed at both the mRNA ( approximately 163-fold) and protein levels. The functional role of ABCG2 in mediating resistance to JNJ-7706621 was consistent with the following findings: (a) an ABCG2 inhibitor, fumitremorgin C, restored the sensitivity of HeLa-6621 cells to JNJ-7706621 and to mitoxantrone; (b) human embryonic kidney-293 cells transfected with ABCG2 were resistant to both JNJ-7706621 and mitoxantrone; and (c) resistant cells that were removed from the drug for 12 weeks and reverted to susceptibility to JNJ-7706621 showed near-normal ABCG2 RNA levels. ABCG2 is likely to limit the bioavailability of JNJ-7706621 because oral administration of JNJ-7706621 to Bcrp (the murine homologue of ABCG2) knockout mice resulted in an increase in the plasma concentration of JNJ-7706621 compared with wild-type mice. These findings indicate that ABCG2 mediates the resistance to JNJ-7706621 and alters the absorption of the compound following administration.

Intelligent hydrogels for the oral delivery of chemotherapeutics

A novel approach toward improvements of oral chemotherapeutic formulations has evolved, which combines solubilisation (molecular dispersion) of the hydrophobic anticancer drugs in micelles attached to large macromolecules or microparticles. The large size of the macromolecules or microgels prevents the gel components from being transported into the systemic circulation. The discussed gels comprise copolymers of poly(acrylic acid) (PAA) and Pluronic surfactants, linked via C-C bonds. The Pluronic-PAA copolymers are non-irritating when administered orally. The micelles formed in the Pluronic-PAA solutions and in crosslinked microgels can be loaded with chemotherapeutic drugs and then released in contact with the intestine. The microgels are collapsed at the acidic pH of the stomach and expand, thus releasing the loaded drugs at the pH of the lower gastrointestinal tract. Yet the microgels are mucoadhesive and enable longer retention time and prolonged release in the colon. Ease of preparation and formulation of the drugs with the Pluronic-PAA polymers and gels may enable the wider use of oral chemotherapy, resulting in a better patient compliance and improved quality of life of the patients.

Dose-Finding Phase I Clinical and Pharmacokinetic Study of Orally Administered Irinotecan in Patients with Advanced Solid Tumors

PURPOSE

The aim of this study was to determine the daily maximum tolerated dose (MTD) and the dose-limiting toxicity for the following administration schedules: oral irinotecan given over 14 days every 3 weeks (part I) and oral irinotecan administered concomitantly with capecitabine over 14 days every 3 weeks (part II). In total, 42 patients (17 male and 25 female) with solid tumors refractory to standard therapy entered the study.

EXPERIMENTAL DESIGN

Treatment in part I consisted of irinotecan administered orally as semisolid matrix capsules at doses of 25, 30, and 35 mg/m(2) once daily to confirm the MTD of our earlier study. In part II treatment, dose levels for irinotecan combined with capecitabine were 20/1,600, 25/1,600, 30/1,600, and 30/2,000 mg/m(2)/d.

RESULTS

The median number of cycles administered per patient was 2.0 (range, 1-12) in part I and 2.0 (range, 1-13) in study part II. Gastrointestinal toxicities (grade 3 nausea, grades 3 and 4 vomiting, and grades 3 and 4 diarrhea) were dose limiting in both parts of the study. There were no grade 3 or 4 hematologic toxicities. The MTD was 30 mg/m(2)/d for irinotecan single agent and 30/1,600 mg/m(2)/d for the combination with capecitabine. Absorption of irinotecan was rapid, and peak concentrations of irinotecan and metabolite SN-38 were reached within 0 to 3 and 1.5 to 4.0 hours, respectively.

CONCLUSIONS

In conclusion, oral irinotecan and capecitabine is feasible and well tolerated, and the recommended dose for phase II studies is 30/1,600 mg/m(2)/d administered daily for 14 days every 3 weeks.

Pharmacokinetic and pharmacodynamic evaluation of a novel in situ forming poly(ethylene glycol)-based hydrogel for the controlled delivery of the camptothecins

Inadequate drug delivery, due to problems associated with achieving constant therapeutic blood levels, has hampered the use of anticancer agents of the camptothecin (CPT) class. The objective of the current studies was to develop a depot delivery system for the water-soluble analog of CPT, topotecan (TPT). In this study, a 2-phase drug depot consisting of TPT-loaded liposomes entrapped in a poly(ethylene glycol) hydrogel was designed. Physically entrapped unaltered TPT displayed a rapid release rate from the hydrogel. Controlled release was demonstrated in vitro and in vivo from the 2-phase system with constant blood levels being achieved for several days in rats. Cytotoxicity and antitumor activity were also evaluated in rats inoculated with syngeneic MAT B III breast cancer cells. Rats treated with the liposome-loaded hydrogel displayed significantly longer tumor growth suppression and did not exhibit body weight loss compared to those treated with other delivery modes. These experiments constitute a proof-of-principle of the 2-phase depot concept and its potential value for enhancing safety and efficacy in chemotherapy.

The role of the human ABCG2 multidrug transporter and its variants in cancer therapy and toxicology

The human multidrug resistance ABC transporters provide a protective function in our body against a large number of toxic compounds. These proteins, residing in the plasma membrane, perform an active, ATP-dependent extrusion of such xenobiotics. However, the same proteins are also used by the tumor cells to fight various anticancer agents. ABCG2 is an important member of the multidrug resistance proteins, an 'ABC half transporter', which functions as a homodimer in the cell membrane. In this review, we provide a basic overview of ABCG2 function in physiology and drug metabolism, but concentrate on the discussion of mutations and polymorphisms discovered in this protein. Interestingly, a single nucleotide mutation, changing amino acid 482 from arginine to threonine or glycine in ABCG2, results in a major increase in the catalytic activity and a wider drug recognition by this protein. Still, this mutation proved to be an in vitro artifact, produced only in heavily drug-selected cell lines. In contrast, at least two, but possibly more polymorphic variants of ABCG2 were found to be present in large human populations with different ethnic background. However, currently available experimental data regarding the cellular expression, localization and function of these ABCG2 variants are strongly contradictory. Since, the proteins produced by these variant alleles may differently modulate cancer treatment, general drug absorption and toxicity, may represent risk factors in fetal toxicity, or alter the differentiation of stem cells, their exact characterization is a major challenge in this field.

Sequential prolonged oral topotecan and prolonged oral etoposide as second-line therapy in ovarian or peritoneal carcinoma: a phase I Gynecologic Oncology Group study

OBJECTIVE

Preclinical models suggest synergy when topoisomerase I and II inhibitors are given sequentially, but not simultaneously. A phase I study was conducted in previously treated ovarian or peritoneal carcinoma to determine the tolerability (maximum number of days) of sequential oral topotecan and oral etoposide.

METHODS

Topotecan (0.8 mg/m(2)) was administered daily (days 1-5) followed by etoposide (50 mg/m(2)) administered daily for up to 5 days (days 8-12). Patients on dose levels 3 and 4 repeated topotecan for up to 5 days starting on day 15 after the initial topotecan and etoposide sequence. Cycles were repeated every 28 days. Dose-limiting toxicities (DLT) were defined as: neutrophils <1000/microl or platelets <50,000/microl before completing administration of etoposide or topotecan; neutropenic fever; platelets <20,000/microl; or a delay greater than 2 weeks in starting cycle 2 due to hematologic toxicity (ANC <1500/microl or platelets <100,000/microl on scheduled day of treatment).

RESULTS

Nineteen patients were entered into this trial, and a total of 54 cycles (range 1-10) of therapy were administered. Dose-limiting toxicities, principally neutropenia, occurred when therapy was administered for 3 of 4 weeks.

CONCLUSION

Oral topotecan and oral etoposide administered at these doses daily for 5 days sequentially for a maximum of three (out of every four) weeks of therapy are tolerable. In some cases, it may be necessary to hold therapy the third week. Based on the activity seen in this patient population, it is planned to take this regimen into a phase II setting.

Use of P-glycoprotein and BCRP inhibitors to improve oral bioavailability and CNS penetration of anticancer drugs

P-glycoprotein (ABCB1) and breast cancer resistance protein [BCRP (also known as ABCG2)] are drug efflux transporters of the ATP binding cassette (ABC) family of proteins. Both P-glycoprotein and BCRP are located in the apical membrane of epithelial cells (e.g. in the intestinal wall and blood-brain barrier), where they can actively extrude a variety of structurally diverse drugs and drug metabolites. Consequently, the oral uptake and CNS penetration of substrate drugs can be low and variable. Inhibition of P-glycoprotein and/or BCRP is therefore a logical strategy to improve oral absorption, CNS penetration and delivery of anticancer agents to brain tumors or CNS metastases. As outlined in this review, this concept of improved oral pharmacokinetics has been demonstrated extensively for the anticancer drugs paclitaxel and topotecan both in preclinical models and in patients, and improved CNS penetration has been shown for paclitaxel, docetaxel and imatinib in preclinical models.

Phase-I study of a new schedule based on increasing days of topotecan administration associated with dose individualisation

BACKGROUND

The most commonly prescribed schedule of topotecan administration is daily for five days, every 21 days. Both pre-clinical and clinical studies suggest that a more protracted schedule may increase its therapeutic index. The current study was undertaken to determine the maximum tolerated number of days with 30-minute i.v. infusion of topotecan daily at fixed area under the plasma concentration-time curve (AUC) (i.e., 35 microg/Lxh).

PATIENTS AND METHODS

Topotecan was administered i.v. over 30 min. The planned levels of number of days of administration were: 7, 10, 13, 15 and 17. The dose was individualized according to the patient's individual topotecan clearance observed after the first infusion of each cycle.

RESULTS

Twenty-three patients were enrolled and received 71 cycles of therapy. The 13-day level was defined as the maximum number of days of administration. The main side effects were thrombocytopenia and anaemia, whereas neutropenia was infrequent. The mean (coefficient of variation) observed AUC was 34.6 (21%), and 33.4 (19%) microg/Lxh, for the last day of cycle 1, and of cycle 2, respectively. Confirmed partial responses were observed in one patient with metastatic desmoplastic tumour and in two patients with small round metastatic endocrine carcinoma.

CONCLUSION

The recommended number of topotecan administration is 10 days. Beyond the potential clinical interest of topotecan administered for a 10-day period, this is the first trial showing the feasibility of a phase-I study exploring a number of administrations of daily AUC rather than a total dose in mg/m(2).

Phase I and pharmacokinetic study of Bay 38-3441, a camptothecin glycoconjugate, administered as a 30-minute infusion daily for five days every 3 weeks in patients with advanced solid malignancies

Bay 38-3441 is a camptothecin glycoconjugate which stabilizes the active lactone form of camptothecin and allows selective uptake into tumor cells. We conducted a phase I study of Bay 38-3441 administered as a 30-minute infusion daily for five consecutive days every 21 days. Thirty-one patients were enrolled at 8 dose levels. Most common nonhematologic side effects were diarrhea (29%), vomiting (19%), nausea (19%), lethargy (13%), and abdominal pain (10%). The main hematologic toxicity was prolonged neutropenia. Nine patients had a best response of stable disease with a median duration of 2.7 months (range: 2.3-20.6 months). The study was closed without reaching the maximum tolerated dose (MTD) due to excessive toxicity in a companion trial resulting in termination of development of this agent. Bay 38-3441 was well tolerated in this study with granulocytopenia as the main hematologic toxicity. This study showed that glycoconjugation is a feasible delivery technique for camptothecin.

Pharmacogenomics of the human ABC transporter ABCG2: from functional evaluation to drug molecular design

In the post-genome-sequencing era, emerging genomic technologies are shifting the paradigm for drug discovery and development. Nevertheless, drug discovery and development still remain high-risk and high-stakes ventures with long and costly timelines. Indeed, the attrition of drug candidates in preclinical and development stages is a major problem in drug design. For at least 30% of the candidates, this attrition is due to poor pharmacokinetics and toxicity. Thus, pharmaceutical companies have begun to seriously re-evaluate their current strategies of drug discovery and development. In that light, we propose that a transport mechanism-based design might help to create new, pharmacokinetically advantageous drugs, and as such should be considered an important component of drug design strategy. Performing enzyme- and/or cell-based drug transporter, interaction tests may greatly facilitate drug development and allow the prediction of drug-drug interactions. We recently developed methods for high-speed functional screening and quantitative structure-activity relationship analysis to study the substrate specificity of ABC transporters and to evaluate the effect of genetic polymorphisms on their function. These methods would provide a practical tool to screen synthetic and natural compounds, and these data can be applied to the molecular design of new drugs. In this review article, we present an overview on the genetic polymorphisms of human ABC transporter ABCG2 and new camptothecin analogues that can circumvent AGCG2-associated multidrug resistance of cancer.

Pharmacokinetics, pharmacodynamics and adherence to oral topotecan in myelodysplastic syndromes: a Cancer and Leukemia Group B study

OBJECTIVE

To evaluate medication adherence, pharmacokinetics and exposure versus response relationships in patients with myelodysplastic syndromes (MDS).

METHODS

Ninety adult patients with MDS received oral topotecan (1.2 mg/m2) either once a day for 10 days or twice a day for 5 days every 21 days for up to six cycles. Dosing histories were collected using electronic monitoring devices fitted to medication vials. Topotecan plasma concentrations were measured, and exposure was determined by a sparse sampling approach and Bayesian estimation methods. Relationships between exposure and clinical response and toxicity were evaluated using logistic regression.

RESULTS

Overall adherence was excellent with 90% of patients taking the prescribed number of doses in cycle 1. Adherence did not differ between the two regimens. Topotecan pharmacokinetics were described using a one compartment open model with first order absorption and elimination. Pharmacokinetic parameter estimates did not differ between the once a day and twice a day dosing groups. While topotecan exposure was greater in the twice a day arm compared to the once a day arm due to drug accumulation, exposure did not correlate with clinical response. However, the probability of needing a platelet transfusion in the twice a day arm was significantly increased (by 35%) as a result of greater steady-state plasma topotecan concentrations.

CONCLUSIONS

Adherence is high in patients with MDS receiving oral topotecan, whether the drug is prescribed once or twice daily. The optimal schedule cannot be determined from this study, as there was no evident relationship between any pharmacokinetic parameter and clinical response.

Effects of dihydropyridines and pyridines on multidrug resistance mediated by breast cancer resistance protein: in vitro and in vivo studies

Breast cancer resistance protein (BCRP, ABCG2) is a recently identified member of the ATP-binding cassette family of cell surface transport proteins. This study was conducted to investigate the effect of a series of newly synthesized 1,4-dihydropyridines and pyridines, designed as potent P-glycoprotein inhibitors, on BCRP-mediated drug efflux both in vitro and in vivo. The effects of 25 synthesized dihydropyridines and corresponding pyridines along with 4 commercially available dihydropyridines (niguldipine, nicardipine, nifedipine, and nitrendipine) on the intracellular accumulation of the BCRP substrate mitoxantrone were evaluated in BCRP-expressing human breast cancer MCF-7/MX100 and human non-small cell lung cancer H460/MX20 cells. At a 2.5 microM concentration, 24 of 25 newly synthesized dihydropyridines and pyridines produced a significant increase of mitoxantrone accumulation in both cell lines. The most potent compound was able to enhance mitoxantrone accumulation approximately 4.5-fold, greater than that obtained with 10 microM fumitremorgin C, which is a specific BCRP inhibitor. The results from the two cell lines showed good correlation (r(2) = 0.71, p < 0.01). Niguldipine, nicardipine, and nitrendipine also demonstrated potent BCRP inhibition, whereas nifedipine had no effect. The effects of the dihydropyridine and pyridine compounds on mitoxantrone cytotoxicity paralleled their effects on mitoxantrone accumulation. Coadministration of a selected dihydropyridine compound, I(m) [DHP-014; 3-(3-(4,4-diphenylpiperidin-1-yl)propyl) 5-methyl 4-(3,4-dimethoxyphenyl)-2,6-dimethyl-1,4-dihydropyridine-3,5-dicarboxylate)] with topotecan, a good BCRP substrate and a moderate to poor P-glycoprotein substrate, resulted in significant increases in the systemic exposure and peak concentration of topotecan in Sprague-Dawley rats when oral topotecan (2 mg/kg) was combined with 20 mg/kg DHP-014. The observed increase of topotecan exposure provides proof-of-concept for in vivo inhibition of BCRP by these agents.

Alternative administration of camptothecin analogues

In order to improve the therapeutic index of camptothecin (CPT) analogues, alternative administration of CPT analogues is being evaluated. Topotecan, irinotecan, rubitecan, lurtotecan and 9-aminocamptothecin have been administered orally with response rates equivalent to that seen after intravenous administration, where applicable. Oral availability and administration of some of the newer CPT analogues, including diflomotecan (BN80915) and grimatecan (ST1481), have also shown promising results. Aerosolisation of liposomal 9-nitrocamptothecin has been studied in patients with advanced malignancies involving the lung, demonstrating systemic antitumour activity. Intrathecal administration of topotecan has been studied in children with refractory neoplastic meningitis. It is well tolerated and associated with some antitumour activity. Intraperitoneal administration of topotecan as consolidation therapy in patients with ovarian cancer has shown promising results. Transdermal administration of rubitecan has been studied in mice. So far, no CPT has been approved for an alternative route of administration.

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

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

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.

Oral topotecan in children with recurrent or progressive high-grade glioma: a Phase I/II study by the German Society for Pediatric Oncology and Hematology

BACKGROUND

Continuous oral treatment with topotecan may be more effective than the typical 1-day and 5-day treatment schedules. In previous studies of continuous treatment with topotecan, increased intestinal side effects were reported in adult patients; however, the experience in pediatric patients and patients with high-grade glioma is quite limited.

METHODS

Thirty-two pediatric patients with recurrent high-grade glioma (16 females and 16 males; median age, 9.5 years) were enrolled in the current Phase I/II study. Tumor locations included the cerebral cortex (n = 5), pons (n = 18), and other sites (n = 9). An injectable formulation of topotecan was administered orally, in ice-cold orange juice, once daily. The starting dose of 0.4 mg/m(2) per day was escalated on a patient-by-patient basis. At each patient's maximum dose, blood samples were obtained for the determination of plasma hydroxytopotecan and topotecan lactone concentrations and for the calculation of pharmacokinetic quantities.

RESULTS

The toxicity criteria for a maximum tolerated topotecan dose were met in only 19 patients. The primary toxicity type was hematologic. The median maximum tolerated dose was 0.9 mg/m(2) per day (n = 19). The calculated maximum total plasma topotecan concentration was 3.8 ng/mL (n = 7), with an area under the concentration-time curve of 38.4 ng. hours/mL and a half-life of 4.1 hours, which would result in the complete disappearance of topotecan from the plasma after 12 hours. Objective responses were observed in 2 of 13 evaluable patients and lasted for 2.5 and 9 months, respectively (continuous clinical remission, 1 of 14 patients; partial response, 2 of 14 patients; stable disease, 7 of 14 patients; progressive disease, 4 of 14 patients).

CONCLUSIONS

Oral topotecan (median dose, 0.9 mg/m(2) per day) administered once daily was well tolerated and somewhat effective in children with recurrent high-grade glioma. A schedule in which the daily dose is split so that dosing is performed twice daily may be superior to the current schedule.

Membrane transport of camptothecin: facilitation by human P-glycoprotein (ABCB1) and multidrug resistance protein 2 (ABCC2)

BACKGROUND

The purpose of the present study was to continue the investigation of the membrane transport mechanisms of 20-(S)-camptothecin (CPT) in order to understand the possible role of membrane transporters on its oral bioavailability and disposition.

METHODS

The intestinal transport kinetics of CPT were characterized using Caco-2 cells, MDCKII wild-type cells and MDCKII cells transfected with human P-glycoprotein (PGP) (ABCB1) or human multidrug resistance protein 2 (MRP2) (ABCC2). The effects of drug concentration, inhibitors and temperature on CPT directional permeability were determined.

RESULTS

The absorptive (apical to basolateral) and secretory (basolateral to apical) permeabilities of CPT were found to be saturable. Reduced secretory CPT permeabilities with decreasing temperatures suggests the involvement of an active, transporter-mediated secretory pathway. In the presence of etoposide, the CPT secretory permeability decreased 25.6%. However, inhibition was greater in the presence of PGP and of the breast cancer resistant protein inhibitor, GF120918 (52.5%). The involvement of additional secretory transporters was suggested since the basolateral to apical permeability of CPT was not further reduced in the presence of increasing concentrations of GF120918. To investigate the involvement of specific apically-located secretory membrane transporters, CPT transport studies were conducted using MDCKII/PGP cells and MDCKII/MRP2 cells. CPT carrier-mediated permeability was approximately twofold greater in MDCKII/PGP cells and MDCKII/MRP2 cells than in MDCKII/wild-type cells, while the apparent Km values were comparable in all three cell lines. The efflux ratio of CPT in MDCKII/PGP in the presence of 0.2 microM GF120918 was not completely reversed (3.36 to 1.49). However, the decrease in the efflux ratio of CPT in MDCKII/MRP2 cells (2.31 to 1.03) suggests that CPT efflux was completely inhibited by MK571, a potent inhibitor of the Multidrug Resistance Protein transporter family.

CONCLUSIONS

The current results provide evidence that PGP and MRP2 mediate the secretory transport of CPT in vitro. However, the involvement of other transporters cannot be ruled out based on these studies. Since these transporters are expressed in the intestine, liver and kidney variations in their expression levels and/or regulation may be responsible for the erratic oral absorption and biliary excretion of CPT observed in human subjects.

Phase I and pharmacokinetic study of topotecan administered orally once daily for 5 days for 2 consecutive weeks to pediatric patients with refractory solid tumors

PURPOSE

We conducted a phase I trial of the injectable formulation of topotecan given orally once daily for 5 days for 2 consecutive weeks (qd x 5 x 2) in pediatric patients with refractory solid tumors.

PATIENTS AND METHODS

Cohorts of two to six patients received oral topotecan at 0.8, 1.1, 1.4, 1.8, and 2.3 mg/m(2)/d every 28 days for a maximum of six courses. Twenty patients (median age, 10.6 years) received a total of 51 courses. Eight patients received topotecan capsules during course 2 only.

RESULTS

Dose-limiting toxicity occurred at 2.3 mg/m(2)/d and consisted of prolonged grade 4 neutropenia (n = 2), grade 3 stomatitis as a result of radiation recall (n = 1), grade 3 hemorrhage (epistaxis) in the presence of grade 4 thrombocytopenia (n = 1), and grade 3 diarrhea in the presence of Clostridium difficile infection (n = 1). Dose-limiting, prolonged grade 4 neutropenia and thrombocytopenia occurred in one patient at 1.4 mg/m(2)/d. Infrequent toxicities were mild nausea, vomiting, elevated liver ALT or AST, and rash. The maximum-tolerated dosage was 1.8 mg/m(2)/d; the mean (+/- standard deviation) area under the plasma concentration-time curve for topotecan lactone at this dosage was 20.9 +/- 8.4 ng/mL. h. The population mean (+/- standard error) oral bioavailability of the injectable formulation was 0.27 +/- 0.03; that of capsules was 0.36 +/- 0.06 (P =.16). Disease stabilized in nine of 19 assessable patients for 1.5 to 6 months.

CONCLUSION

Oral topotecan (1.8 mg/m(2)/d) on a qd x 5 x 2 schedule is well tolerated and warrants additional testing in pediatric patients.

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.

Impact of drug transporter studies on drug discovery and development

Drug transporters are expressed in many tissues such as the intestine, liver, kidney, and brain, and play key roles in drug absorption, distribution, and excretion. The information on the functional characteristics of drug transporters provides important information to allow improvements in drug delivery or drug design by targeting specific transporter proteins. In this article we summarize the significant role played by drug transporters in drug disposition, focusing particularly on their potential use during the drug discovery and development process. The use of transporter function offers the possibility of delivering a drug to the target organ, avoiding distribution to other organs (thereby reducing the chance of toxic side effects), controlling the elimination process, and/or improving oral bioavailability. It is useful to select a lead compound that may or may not interact with transporters, depending on whether such an interaction is desirable. The expression system of transporters is an efficient tool for screening the activity of individual transport processes. The changes in pharmacokinetics due to genetic polymorphisms and drug-drug interactions involving transporters can often have a direct and adverse effect on the therapeutic safety and efficacy of many important drugs. To obtain detailed information about these interindividual differences, the contribution made by transporters to drug absorption, distribution, and excretion needs to be taken into account throughout the drug discovery and development process.