Synthesis of water-soluble (aminoalkyl)camptothecin analogues: inhibition of topoisomerase I and antitumor activity

Combined Directed Ortho Metalation/Cross-Coupling Strategies: Synthesis of the Tetracyclic A/B/C/D Ring Core of the Antitumor Agent Camptothecin

A convergent synthesis of the A/B/C/D ring fragment 5 of camptothecin using a combination of directed ortho metalation and Negishi cross-coupling is described. The key features of the synthetic sequence are an anionic ortho-Fries rearrangement (10 --> 12), a Negishi cross-coupling (7 --> 6), and a terminal modified von Braun reaction (16 --> 5) that leads to tetracyclic derivative 5 in 7 steps and 11% overall yield.

Synthesis and cytotoxicity of water soluble quaternary salt derivatives of camptothecin

In an effort to improve the water solubility of camptothecin, 16 water soluble 10-substituted quaternary ammonium salt derivatives of camptothecin were prepared. Their antitumor activity was evaluated on cancer cells in vitro. All of these salts possess lower cytotoxicities than CPT in comparison. The camptothecin salts 16, 20 showed similar cytotoxic activity to topotecan. Especially the salts 21 showed similar cytotoxic activity to CPT in vitro.

Palladium-Catalyzed Cyanation of Aryl Bromides Promoted by Low-Level Organotin Compounds

A novel method for palladium-catalyzed cyanation of aryl bromides promoted by low-level tri-n-butyltin chloride or cyanide is described. The method features low catalyst loading and mild reaction conditions. KCN is used as the cyanide source. Only trace levels of the tri-n-butyltin compound are required to achieve high conversion and yield in the cyanation of aryl bromides, iodides, and triflates.

BN80927

BN80927 belongs to a novel family of camptothecin analogs, the homocamptothecins, developed on the concept of topoisomerase I (Topo I) inhibition and characterized by a stable seven-membered beta-hydroxylactone ring. Preclinical data reported here show that BN80927 retains Topo I poisoning activity in cell-free assay (DNA relaxation) as well as in living cells, in which in vivo complexes of topoisomerase experiments and quantification of DNA-protein-complexes stabilization, have confirmed the higher potency of BN80927 as compared with the Topo I inhibitor SN38. In addition, BN80927 inhibits Topo II-mediated DNA relaxation in vitro but without cleavable-complex stabilization, thus indicating catalytic inhibition. Moreover, a Topo I-altered cell line (KBSTP2), resistant to SN38, remains sensitive to BN80927, suggesting that a part of the antiproliferative effects of BN80927 are mediated by a Topo I-independent pathway. This hypothesis is also supported by in vitro data showing an antiproliferative activity of BN80927 on a model of resistance related to the noncycling state of cells (G(0)-G(1) synchronized). In cell growth assays, BN80927 is a very potent antiproliferative agent as shown by IC(50) values consistently lower than those of SN38 in tumor cell lines as well as in their related drug-resistant lines. BN80927 shows high efficiency in vivo in tumor xenograft studies using human androgen-independent prostate tumors PC3 and DU145. Altogether, these data strongly support the clinical development of BN80927.

A phase I study with MAG-camptothecin intravenously administered weekly for 3 weeks in a 4-week cycle in adult patients with solid tumours

In MAG-camptothecin (MAG-CPT), the topoisomerase inhibitor camptothecin is linked to a water-soluble polymer. Preclinical experiments showed enhanced antitumour efficacy and limited toxicity compared to camptothecin alone. Prior phase I trials guided the regimen used in this study. The objectives were to determine the maximum tolerated dose, dose-limiting toxicities, safety profile, and pharmacokinetics of weekly MAG-CPT. Patients with solid tumours received MAG-CPT intravenously administered weekly for 3 weeks in 4-week cycles. At the starting dose level (80 mg x m(-2) week(-1)), no dose-limiting toxicities occurred during the first cycle (n=3). Subsequently, three patients were enrolled at the second dose level (120 mg x m(-2) week(-1)). Two of three patients at the 80 mg x m(-2) week(-1) cohort developed haemorrhagic cystitis (grade 1/3 dysuria and grade 2/3 haematuria) during the second and third cycles. Next, the 80 mg x m(-2) week(-1) cohort was enlarged to a total of six patients. One other patient at this dose level experienced grade 1 haematuria. At 120 mg x m(-2) week(-1), grade 1 bladder toxicity occurred in two of three patients. Dose escalation was stopped at 120 mg x m(-2) week(-1). Cumulative bladder toxicity was dose-limiting toxicity at 80 mg x m(-2) week(-1). Pharmacokinetics revealed highly variable urinary camptothecin excretion, associated with bladder toxicity. Due to cumulative bladder toxicity, weekly MAG-CPT is not a suitable regimen for treatment of patients with solid tumours.

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.

Synthesis of novel 2,3-dihydro-1,4-dioxino[2,3- g ]quinoline derivatives as potential antitumor agents

New dioxinoquinolines (1-8) have been synthesized and their antiproliferative properties have been tested against several cell lines. The treatment of the 6-acetamido-2,3-dihydro-1,4-benzodioxine (10) with phosphorous oxychloride in the presence of DMF leads to a mixture of linear and angular tricyclic compounds. The key intermediates were modified and cyclized giving the corresponding dioxinoquinolines. In general, these compounds have a moderate citotoxycity.

Current developments in the discovery and design of new drug candidates from plant natural product leads

This review article will emphasize recent research in the Natural Products Laboratory, School of Pharmacy, University of North Carolina at Chapel Hill, on various classes of plant-derived compounds that possess potent antitumor or anti-HIV activity. These compounds were obtained by bioactivity- and mechanism of action-directed isolation and characterization coupled with rational drug design-based modification and analogue synthesis. Structural modification, SAR, and mechanism of action studies are discussed.

Topotecan Dosing Guidelines in Ovarian Cancer: Reduction and Management of Hematologic Toxicity

Topotecan dosing considerations and alternative dosing schedules to reduce and manage myelosuppression during the treatment of relapsed ovarian cancer were reviewed. The myelosuppression patterns from phase I, II, and III clinical trials were analyzed to evaluate the degree of hematologic toxicity and to determine risk factors predictive of myelosuppression. Additionally, recent publications of alternative topotecan doses and schedules were examined. Extent of prior therapy, prior platinum therapy (particularly carboplatin), advanced age, impaired renal function, and prior radiation therapy were identified as potential risk factors for greater hematologic toxicity after topotecan therapy. Reducing the starting topotecan dose to 1.0 or 1.25 mg/m2/day is recommended to reduce the incidence of severe myelosuppression in high-risk individuals receiving topotecan for 5 consecutive days. Hematopoietic growth factors, transfusion therapy, and schedule adjustments may also help manage myelosuppression. Alternative schedules of 3-day or weekly dosing appear to have less myelotoxicity and are currently under evaluation. The clinical aspects of topotecan-related myelosuppression and results from clinical trials indicate that the dose, and possibly the dosing schedule, of topotecan can be modified to reduce hematologic toxicity and improve tolerance without compromising efficacy. Prospective individualization of topotecan dosing may prevent or minimize dose-limiting myelosuppression and allow patients to achieve the maximum topotecan benefit by improving their ability to complete therapy with fewer treatment delays. Ongoing clinical trials evaluating alternative dosing schedules with superior hematologic tolerability may facilitate the inclusion of topotecan in combination regimens for patients with ovarian cancer. Proposed topotecan dosing guidelines to reduce and manage myelosuppression are outlined.

Water-Soluble Camptothecin Derivatives that Are Intrinsic Topoisomerase I Poisons

[structure: see text] In an effort to improve the water solubility of camptothecin, four 20-O-phosphate and phosphonate analogues have been prepared. These analogues are freely water soluble, stable at physiological pH, and stabilize the human topoisomerase I-DNA covalent binary complex with the same sequence selectivity as camptothecin itself. All four compounds inhibited the growth of yeast expressing human topoisomerase I in an enzyme-dependent fashion.

Ex vivo analysis of topotecan: advancing the application of laboratory-based clinical therapeutics

Topotecan is currently approved for relapsed small-cell lung cancer and ovarian cancer. Topotecan's efficacy in the second-line setting and novel mechanism of action suggest broad antitumour activity. We utilised a clinically validated, cell-death, ex vivo assay in human tumour explants to examine the activity profile of topotecan alone and in combination with other antitumour agents. Serial dilutions of topotecan alone and in combination with other cytotoxic agents were applied to biopsy specimens of non-small-cell lung cancer (NSCLC) and breast, colon, and prostate cancers. Dose-response curves were interpolated to provide 50% lethal concentrations (LC(50)). The degree of synergy (by median effect) and normalised Z-scores (raw scores converted to relative activity distributed around the mean) were then computed. Single-agent activity was observed for topotecan in all four tumour types. In 57 chemotherapy-naive specimens, NSCLC revealed the highest activity, demonstrated by the lowest LC(50) value (0.26+/-0.06 microg ml(-1); P=0.002). Overall, previously treated and chemotherapy-naive specimens revealed no significant differences in mean LC(50)'s. Synergy was observed for several combinations, including topotecan plus cisplatin in prostate and for topotecan plus 5-fluorouracil in breast cancers. The Z-score analyses conducted suggest activity for previously unexplored drug regimens, including topotecan plus 5-fluorouracil, vinorelbine, and mitomycin-C in NSCLC and breast cancer. Phase II studies are underway to determine the degree to which these ex vivo findings will translate into improved clinical results.

A new multidrug reinduction protocol with topotecan, vinorelbine, thiotepa, dexamethasone, and gemcitabine for relapsed or refractory acute leukemia

We report the results of a phase 2 nonrandomized single-arm trial of a combination therapy for relapsed or refractory leukemia. From January 1999 to June 2002, 28 patients with multiple relapsed or refractory acute leukemia received a combination of topotecan, vinorelbine, thiotepa, dexamethasone, and, for patients with an M3 marrow on day 7, gemcitabine. A total of 14 patients had pre-B-ALL (acute lymphoblastic leukemia), three had T-cell leukemia, nine acute myeloblastic leukemia (AML), and two biphenotypic leukemia. In all, 13 patients achieved a significant response (10 complete responses and three partial responses). Among the responders, five had pre-B-ALL, two had T-cell leukemias, five had AML, and one had biphenotypic leukemia. In total, 10 of these patients subsequently underwent hematopoietic stem cell transplantation, and four are alive without disease. One patient died, while in remission, of complications resulting from an episode of sepsis and pneumonia that occurred during topotecan, vinorelbine, thiotepa, dexamethasone, and gemcitabine (TVTG) reinduction. Other toxicities included grade 4 neutropenia in all patients and transient grade 2 hepatotoxicity in 10 patients (36%). In summary, we report that 47% of heavily pretreated pediatric patients with multiply relapsed or refractory leukemia achieved a significant response after therapy on the TVTG protocol. Further studies are warranted to evaluate the role of the TVTG combination in the treatment of leukemia.

Oral topotecan for refractory and relapsed neuroblastoma: a retrospective analysis

PURPOSE

Among patients with multiply relapsed neuroblastoma refractory to conventional chemotherapy, oral topotecan has often been used for palliation. Although toxicity was generally thought to be mild, the efficacy of such an approach remains unproven.

METHODS

The authors retrospectively analyzed patients with multiply relapsed or refractory neuroblastoma who were treated with oral topotecan for palliation. Each course was generally 1 mg/m2/d in two divided doses, for 21 consecutive days, repeated after a 1-week rest in patients without symptoms of progressive disease. Disease status was assessed by radiographic studies, urine catecholamine levels, and multiple bone marrow aspirations and biopsies.

RESULTS

Twenty patients between the ages of 3 and 34 (median 13 years) received 1 (n = 7), 2 (n = 3), 3 (n = 4), 4 (n = 2), 6 (n = 2), and 12 courses (n = 2). Prior treatments included multiple cycles of high-dose alkylator-based chemotherapy (n = 20), high-dose intravenous topotecan (n = 8), myeloablative chemotherapy or radioimmunotherapy (n = 10), or experimental biologic agents (n = 16). Anti-neuroblastoma effects were seen in five patients lasting 6 to 12 months; two additional patients remained stable for 4 months. Thirteen patients had progressive disease (11 after one or two cycles). Toxicity included diarrhea (n = 12) requiring a dose adjustment in three patients and discontinuation of the drug in a fourth, and myelosuppression (n = 11) requiring transfusion and/or granulocyte-colony stimulating factor support.

CONCLUSIONS

Oral topotecan therapy has antitumor activity in a small percentage of patients with relapsed or refractory neuroblastoma. Toxicities, including diarrhea and myelosuppression, may necessitate a dose adjustment in this patient population. Low-dose oral topotecan may have utility in the treatment of neuroblastoma.

Pharmacology of intraperitoneal CPT-11

CPT-11 is clearly one of the most important new anticancer drugs developed in the last few decades, and CPT-11 combined with 5-fluorouracil (5-FU) and leucovorin is considered as reference first-line chemotherapy in the treatment of metastatic colorectal cancer. CPT-11 has a complex pharmacologic profile in vivo, and it needs caboxylesterase-mediated biotransformation to SN-38 before production of its cytotoxic effect. Intraperitoneal administration of CPT-11 has been studied recently in murine models and presented some potential advantage over the intravenous (i.v.) route. Intraperitoneal administration of CPT-11 may be more effective than i.v. administration not only for peritoneal seeding but also for liver metastases. Also, these effects may occur with less toxicity by intraperitoneal administration. Intraperitoneal chemotherapy containing CPT-11 might be an essential option for prevention and treatment of cancerous dissemination of gastrointestinal malignancy.

The camptothecins

Supported by detailed understanding of their mechanism of action, and facilitated by chemical manipulations that have amplified their solubility, the camptothecins have advanced to the forefront of several areas of therapeutic and developmental chemotherapy. Additive and synergistic laboratory interactions with other cytotoxic drugs have been exploited to allow development of camptothecin-based multidrug regimens, which are showing important activity in several malignancies. Topotecan and irinotecan are already in widespread use in clinical practice, and newer agents with promising preclinical activity are in various stages of clinical assessment. As knowledge of molecular and biochemical mechanisms of action and resistance continues to expand, newer and better camptothecin-based strategies for treatment of malignant disease are likely to evolve.

Camptothecin analogs in malignant gliomas: comparative analysis and characterization

OBJECT

The authors compared and characterized several new classes of camptothecin (CPT) analogs (a total of 22 drugs) directed against human and murine glioma cell lines in vitro, trying to identify CPT analogs that can be used for local therapy in future clinical trials. Camptothecin is a naturally occurring alkaloid that inhibits the DNA-replicating enzyme topoisomerase I. Moreover, CPT and its analogs have shown promising antitumor activity against both systemic and intracranial neoplasms. Because the CPTs have poor bioavailability and are unable to cross the blood-brain barrier, they may best be delivered to the central nervous system by polymers. The authors have previously shown that local delivery of Na-CPT by implantable polymers prolongs survival in a rat intracranial glioma model. In recent years, a number of newly synthesized CPT analogs have been developed that exhibit more potency and stability than Na-CPT.

METHODS

Cytotoxicities of the drugs were tested using modified clonogenic and monotetrazolium assays in three glioma cell lines. A potassium chloride-sodium dodecyl sulfate coprecipitation assay was used to determine the frequency of drug-stabilized cleavable complexes. Of the CPT analogs analyzed, the 10,11-methylenedioxy (MD) class consistently demonstrated the greatest cytotoxicity. Three of these analogs, 10,11-MD-20(RS)-CPT, 10,11-MD-20(S)-CPT-glycinate ester (Gly).HCl, and 9-amino-10,11-MD-20(S)-CPT-Gly, exhibit significantly greater antiproliferative activities than CPT, Na-CPT, or 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) against all three glioma cell lines. In addition, the 10,11-MD-20(RS)-CPT analog induces more cleavable complexes than Na-CPT at every concentration.

CONCLUSIONS

The increased potency and greater stability of CPT analogs hold promise for more effective local antitumor treatments against malignant intracranial brain tumors. The greater cytotoxicity of 10,11-MD CPTs in comparison with other CPT analogs as well as CPT, BCNU, or Na-CPT, may present an ideal candidate drug class for development against both primary and metastatic brain tumors.

Maleimide-oligo(ethylene glycol) derivatives of camptothecin as albumin-binding prodrugs: synthesis and antitumor efficacy

In situ binding of thiol-reactive prodrugs to the cysteine-34 position of circulating albumin is a new approach in drug delivery. Therefore, five maleimide-bearing derivatives of the anticancer drug camptothecin (CPT) were developed as albumin-binding prodrugs. These compounds were synthesized by reacting heterobifunctional cross-linkers based on oligo(ethylene glycols) [3-6 (O-CH(2)-CH(2)) units] bearing a maleimide group on one end and a carboxylic acid group on the other with camptothecin 20-O-glycinate. Incorporating oligo(ethylene glycol) chains into the prodrugs enhanced their water-solubility when compared to the parent compound (up to 27-fold). HPLC studies showed that the prodrugs react almost quantitatively with the cysteine-34 position of endogenous albumin within a few minutes after incubation of the CPT derivatives with human blood plasma. The therapeutic potential of two of the prodrugs was assessed in nude mice bearing a colon xenograft (HT-29). Both albumin-binding derivatives of camptothecin were well-tolerated and showed enhanced antitumor efficacy when compared to CPT.

Selective phenolic acylation of 10-hydroxycamptothecin using poly (ethylene glycol) carboxylic acid

Selective acylation of the phenolic hydroxyl group of 10-hydroxycamptothecin has been accomplished using phenyl dichlorophosphate. Additional modification of the 10-OH as an ether permits a 20-acyl derivative to be synthesized. This result along with data from a 6-hydroxyquinoline model strongly suggests that powerful intermolecular hydrogen bonding exists in the parent molecule.

A Phase II Study of Topotecan in Patients with Relapsed Small-Cell Lung Cancer

An early phase II study of topotecan produced favorable results in a small number of untreated and previously treated patients with small-cell lung cancer (SCLC). This multicenter study was conducted in patients with relapsed SCLC at 19 medical institutions in Japan. Topotecan 1.0 mg/m2/day was administered for 5 consecutive days every 3 weeks. Fifty-three patients were enrolled in the study. One patient was withdrawn before the commencement of study treatment, and 2 patients were unable to continue study treatment due to an interruption in the supply of study medication. The response rate was 26.0% in 13 of the 50 evaluable patients who were eligible and completed protocol-specified treatment and procedures. The median time to progression and overall survival were 133 days and 262 days, respectively. The most frequently reported toxicity was reversible myelosuppression, such as leukopenia, neutropenia, anemia (decreased hemoglobin), and thrombocytopenia. Nonhematological toxicity was also reported but the incidence of grade 3/4 symptoms was low. The results of this study indicate that topotecan is effective against relapsed SCLC with good tolerability.

Alternate dosing schedules for topotecan in the treatment of recurrent ovarian cancer

Topotecan has demonstrated efficacy in the treatment of both platinum-sensitive and platinum-resistant recurrent ovarian cancer. However, the optimal dosing for topotecan has not been established. The standard dosing regimen is 1.5 mg/m(2)/day on days 1-5 of a 21-day cycle, with response rates ranging from 13%-33%. Although the resulting hematologic toxicities are reversible and noncumulative, this schedule is associated with significant myelosuppression. Ongoing clinical phase I and II trials have evaluated alternative dosing schedules such as the 21-day 24-hour continuous intravenous (c.i.v.), the 3-day i.v. bolus, the weekly 72-hour c.i.v., the weekly 24-hour c.i.v., and the weekly bolus i.v. regimens. Prolonged exposure to topotecan has been shown to increase the efficacy of topotecan, whereas shorter regimens decrease exposure to the drug and therefore decrease toxicity. Preliminary studies investigating the weekly bolus i.v. regimen have demonstrated response rates comparable with those achieved with the standard dosing regimen, with a lower frequency of severe toxicity. Although randomized, controlled comparative trials are necessary to determine relative efficacy, results from studies utilizing other alternative regimens are less encouraging, especially for lower-risk patients with platinum-sensitive ovarian cancer who are likely to tolerate higher doses of topotecan. Optimizing the dosing regimen will also increase the quality of life for the patient through increased efficacy, decreased toxicity, and increased convenience of administration. Continued investigation of the weekly i.v. bolus is needed to fully elucidate the contribution of this regimen to the current armamentarium used in the treatment of patients with relapsed ovarian cancer.

Prolonged infusional topotecan and accelerated hyperfractionated 3d-conformal radiation in patients with newly diagnosed glioblastoma--a phase I study

PURPOSE

Topotecan has demonstrated exceptional central nervous system penetration as well as radiosensitizing properties in glioblastoma xenografts [Chastagner et al., Int J Radiat Oncol Biol Phy 50: 777-782, 2001]. This phase I trial was performed to determine the maximum tolerated dose and the recommended dose of topotecan continuous infusion administered together with concomitant radiotherapy in patients with glioblastoma.

PATIENTS AND METHODS

A total of 20 patients were treated in this trial. Twenty one day topotecan continuous infusion was escalated from 0.3 mg/m2/d in increments of 0.1 mg/m2/d and cohorts of 3-6 patients until maximum tolerated dose was reached; Three-dimensional (3d) conformal radiotherapy was applied concurrently twice daily with a fraction size of 1.75 Gy up to 57.75 Gy total dose. Three additional cycles of maintenance topotecan chemotherapy were scheduled.

RESULTS

Fifty-three courses were performed in 5 dose levels (0.3 mg/m2/d: 12 cycles, 0.4 mg/m2/d: 6 cycles, 0.5 mg/m2/d: 10 cycles, 0.6 mg/m2/d: 6 cycles, 0.7 mg/m2/d: 19 cycles). Maximum tolerated dose was reached at dose level 5 (0.7 mg/m2/d), because 3/7 patients suffered from dose limiting toxicity. These were febrile sinusitis, bacterial sepsis and grade 4 thrombocytopenia. Neutropenia of grade 4 was encountered in 2 cycles (0.5 and 0.7 mg/m2/d). Response data were available in 17 patients, 3 of which (18%) achieved partial remission, 12 (71%) stable disease throughout the observation period and 2 (11%) progressive disease.

CONCLUSION

The recommended dose for further trials will be 0.6 mg/m2/d topotecan administered as 21 days continuous infusion in combination with accelerated 3d conformal radiation.

Camptothecin delivery methods

Camptothecin has shown significant antitumor activity to lung, ovarian, breast, pancreas, and stomach cancers. Camptothecin, however, like a number of other potent anticancer agents such as paclitaxel, is extremely water insoluble. Furthermore, pharmacology studies have determined that prolonged schedules of administration given continuously are required. Thus, this insolubility has restricted its clinical application. For these reasons, a number of water-soluble analogs have been synthesized and a number of different formulation approaches have been investigated. In this review, we examine each of these approaches and discuss their advantages and limitations.

A phase I and pharmacokinetic study of MAG-CPT, a water-soluble polymer conjugate of camptothecin

Polymeric drug conjugates are a new and experimental class of drug delivery systems with pharmacokinetic promises. The antineoplastic drug camptothecin was linked to a water-soluble polymeric backbone (MAG-CPT) and administrated as a 30 min infusion over 3 consecutive days every 4 weeks to patients with malignant solid tumours. The objectives of our study were to determine the maximal tolerated dose, the dose-limiting toxicities, and the plasma and urine pharmacokinetics of MAG-CPT, and to document anti-tumour activity. The starting dose was 17 mg m(-2) day(-1). Sixteen patients received 39 courses at seven dose levels. Maximal tolerated dose was at 68 mg m(-2) day(-1) and dose-limiting toxicities consisted of cumulative bladder toxicity. MAG-CPT and free camptothecin were accumulated during days 1-3 and considerable amounts of MAG-CPT could still be retrieved in plasma and urine after 4-5 weeks. The half-lives of bound and free camptothecin were equal indicating that the kinetics of free camptothecin were release rate dependent. In summary, the pharmacokinetics of camptothecin were dramatically changed, showing controlled prolonged exposure of camptothecin. Haematological toxicity was relatively mild, but serious bladder toxicity was encountered which is typical for camptothecin and was found dose limiting.

Simple and efficient liposomal encapsulation of topotecan by ammonium sulfate gradient: stability, pharmacokinetic and therapeutic evaluation

Topotecan (TPT), a topoisomerase I inhibitor, is presently undergoing clinical evaluation worldwide. Previous studies have shown that entrapping TPT within multi-lamellar vesicle liposome can stabilize the lactone moiety, which is structurally important for biological activity. However, low drug:lipid ratios due to the amphipathic character and small entrapment volume in the unilamellar vesicle limits the development of pharmaceutically acceptable liposomal formulation. With an aim to improve on this drawback, we herein describe a method that utilizes the ammonium sulfate gradient to entrap TPT into liposomes. By this method, the encapsulation efficiency was over 90% and a drug:lipid molar ratio as high as 1:5.4 was reached. In comparison with free drug, liposome-encapsulated TPT is more stable in physiological conditions and shows higher in vitro cytotoxicity. Because of increased blood circulation time, the initial plasma concentration and area under the plasma concentration of liposomal drugs were 14 and 40 times, respectively, of those of free drug. Furthermore, liposome encapsulation enhanced the antitumor activity of TPT in syngeneic murine C-26 and human HTB-9 xenograft models in vivo. At a dose of 5 mg/kg, the tumor growth delay of liposomal formulation was significantly than that of free TPT. Based on these results, we believe that this liposomal TPT formulation is worthy of further clinical study.

An efficient synthesis of the new benzo[c]pyrido[2,3,4-kl]acridine skeleton

A series of molecules of therapeutic interest, possessing the new skeleton of 1H-benzo[c]pyrido[2,3,4-kl]acridine with acyl or aminoacyl and methoxy or aminoalkoxy substituents on the aromatic homocycles were synthesized by means of a Friedländer-type reaction. The requisite 5-aminodihydroquinoline-4-ones 1, whose preparation is described, were reacted with the appropriate alpha-tetralones 2 using an acidic catalyst (PPTS) under azeotropic conditions. Optimized reaction time and yield depend on temperature, which must not be below 90 degrees C.

Novel camptothecin derivatives. Part 1: oxyalkanoic acid esters of camptothecin and their in vitro and in vivo antitumor activity

A series of oxyalkanoic acid esters of (20S)-camptothecin derivatives was prepared by the method of acylation. Their antitumor activity was evaluated on cancer cells in vitro by the colony formation assay and in vivo. These newly synthesized derivatives show a dramatically higher chemotherapeutic activity in killing human cancer cells than the parent drug, camptothecin, and clinically available drugs, irinotecan and taxol.

Protracted intermittent schedule of topotecan in children with refractory acute leukemia: a pediatric oncology group study

PURPOSE

To determine dose-limiting toxicity (DLT) and maximum-tolerated dose (MTD) of a protracted, intermittent schedule of daily 30-minute infusions of topotecan (TPT) for up to 12 consecutive days, every 3 weeks, in children with refractory leukemia.

PATIENTS AND METHODS

Forty-nine children were enrolled onto this phase I trial (24 with acute nonlymphoblastic leukemia [ANLL] and 25 with acute lymphoblastic leukemia [ALL]). TPT dosage was escalated from 2.0 to 5.2 mg/m(2)/d for 5 days and 2.4 mg/m(2)/d from 7 days to the same dose for 9 and 12 days in cohorts of three to six patients when no DLT was identified. TPT pharmacokinetics were studied in 33 children once or twice (first and last doses in patients who received TPT for > 7 days).

RESULTS

Seventy assessable courses of TPT were administered to 49 children who had refractory leukemia. DLTs were typhlitis, diarrhea, and mucositis, and the MTD was 2.4 mg/m(2)/d for 9 days in this group of heavily pretreated children. In 33 patients, the median TPT lactone clearance after the first dose was 19.2 L/h/m(2) (range, 9.4 to 45.9 L/h/m(2)) and did not change during the course. There were significant responses (one complete response [CR] and four partial responses [PR] in patients with ANLL and one CR and two PRs in patients with ALL), and all but one were at dosages of TPT given for at least 9 days.

CONCLUSION

The MTD was 2.4 mg/m(2)/d for 9 days. Further testing is warranted of TPT's schedule dependence in children with leukemia.

Antitumoral effect of irinotecan (CPT-11) on an experimental model of malignant neuroectodermal tumor

Irinotecan (CPT-11) is a topoisomerase I inhibitor with antitumor activity on a wide variety of neoplasms in several preclinical studies, but it showed poor efficacy in patients with nervous system tumors. We have carried out an experimental study in order to evaluate the effect of CPT-11 on the growth of a subcutaneously implanted malignant neuroectodermal tumor, after administration by different routes. The results showed that CPT-11 administration by intraperitoneal injections (at dose 10 mg/kg, 5 days per week, for 2 weeks, followed by 7-days rest period--one course--to a total of two courses) had no significant antitumor effect. Nevertheless, continuous infusion by intraperitoneal osmotic minipump over 28 days (at an infusion rate of 4.4 microg/h) showed a significant delay in tumor growth in 4 weeks of the implantation. The best antitumor effects were observed after CPT-11 intratumoral administration (at dose of 5 mg/kg, 5 days per week, for 2 weeks, followed by 7-days rest period, to a total of three courses) reaching tumor regression in the treated animals. These results suggest the utility of CPT-11, by means of intralesional administration, on malignant tumors of the nervous system.

Camptothecins

Camptothecin analogues and derivatives appear to exert their antitumour activity by binding to topoisomerase I and have shown significant activity against a broad range of tumours. In general, camptothecins are not substrates for either the multidrug-resistance P-glycoprotein or the multidrug-resistance-associated protein (MRP). Because of manageable toxicity and encouraging activity against solid tumours, camptothecins offer promise in the clinical management of human tumours. This review illustrates the proposed mechanism(s) of action of camptothecins and presents a concise overview of current camptothecin therapy, including irinotecan and topotecan, and novel analogues undergoing clinical trails, such as exatecan (DX-8951f), IDEC-132 (9-aminocamptothecin), rubitecan (9-nitrocamptothecin), lurtotecan (GI-147211C), and the recently developed homocamptothecins diflomotecan (BN-80915) and BN-80927.

Separation methods for camptothecin and related compounds

This paper reviews working procedures for the analytical determination of camptothecin and analogues. We give an overview of aspects such as the chemistry, structure-activity relationships, stability and mechanism of action of these antitumor compounds. The main body of the review describes separation techniques. Sample treatment and factors influencing high-performance liquid chromatography development are delineated. Published high-performance liquid chromatographic methods are summarized to demonstrate the variability and versatility of separation techniques and a critical evaluation of separation efficiency, detection sensitivity and specificity of these methods is reported.

Design and optimization of 20-O-linked camptothecin glycoconjugates as anticancer agents

To improve the biological profile of 20(S)-camptothecin, a novel class of 20-O-linked camptothecin glycoconjugates has been designed for preferential cellular uptake into tumor cells by an active transport mechanism. Such conjugates have been optimized for enhanced solubility, stabilization of the camptothecin lactone ring, sufficient hydrolytic and proteolytic stability, and for an overall improvement in tumor selectivity. The constitution of the peptide spacer has a major impact on stability and biological activity of the conjugates both in vitro and in vivo. Glycoconjugates 17-22 with valine residues at the linkage position to camptothecin are sufficiently stable and show good antitumor activity in vitro against HT29 and other tumor cell lines. Fluorescence microscopy and flow cytometry experiments indicate that glycoconjugates such as 19 are taken up into lysosomal compartments of the tumor cell line HT29 by an active transport mechanism. The steric configuration of the particular amino acid residues linked to the camptothecin moiety has a major impact on the in vivo activity of the corresponding glycoconjugates in the breast cancer xenograft MX-1 model. Inhibiting tumor growth by >96%, the glycoconjugates 19 and 21 show the best activity in this particular model and have been investigated more extensively. The glycoconjugate 19 compares favorably to topotecan 4 and glycoconjugate 21 with respect to toxicity against hematopoietic stem cells and hepatocytes. Based on its profile, 19 has been selected for clinical trials.

Improved therapeutic index of lower dose topotecan chemotherapy in recurrent ovarian cancer

OBJECTIVE

Topotecan (1.5 mg/m(2)) administered daily for 5 consecutive days of a 21-day cycle is an established chemotherapeutic regimen in recurrent ovarian cancer. However, noncumulative myelosuppression has limited its use by many clinicians. We sought to determine whether a lower dose of topotecan could provide comparable tumor activity and higher tolerability in pretreated ovarian cancer patients.

METHODS

A retrospective chart review was conducted on recurrent ovarian, peritoneal, or fallopian tube cancer patients with measurable disease or elevated cancer antigen 125 levels (evaluable disease). Patients were treated with topotecan (1.0 mg/m(2)) given by 30-min intravenous infusion for 5 consecutive days every 21 days until disease progression or unacceptable toxicity.

RESULTS

Treatment records from 37 women who had been treated with a median of 3 courses (range, 1 to 17) of lower dose topotecan were evaluated; all were evaluable for tolerability and 36 were evaluable for response. Patients had received a median of 3 (range, 1 to 6) previous treatments. The overall response rate was 22% (8/36); the response rates for patients with evaluable disease and measurable disease were 35.7 (5/14) and 13.6% (3/22), respectively. An additional 8 patients (22%) achieved stable disease. Grade 4 neutropenia, thrombocytopenia, and anemia occurred in 48.6, 5.4, and 5.4% of patients, respectively. Granulocyte colony-stimulating factor support was used in 37% of patients, including 5 who experienced febrile neutropenia.

CONCLUSION

Topotecan at 1.0 mg/m(2) x 5 days every 21 days is active in platinum- and paclitaxel-resistant ovarian cancer, with significant improvements in hematologic toxicity. In heavily pretreated patients-topotecan can be safely given at reduced doses without apparent loss of efficacy.

A phase I and pharmacokinetic study of intraperitoneal topotecan

PURPOSE

To evaluate the feasibility and pharmacology of intraperitoneal (IP) topotecan.

PATIENTS AND METHODS

Fifteen patients with recurrent ovarian cancer in a phase I trial were treated with escalating IP topotecan doses (5-30 mg/m(2)) for pharmacokinetic analysis.

RESULTS

Dose limiting toxicity (DLT) was acute hypotension, chills and fever at the 30 mg/m(2) dose level. Haematological toxicity and abdominal pain were mild for all dose levels studied.

PHARMACOKINETICS

Peak plasma levels of total topotecan were reached at 2.7 +/- 1.1 h after IP instillation. The apparent V(ss) was 69.9 +/- 25.4 L/m(2), plasma clearance 13.4 +/- 2.5 L/h/m(2) and plasma T1/2 3.7 +/- 1.3 h. The plasma AUC was correlated with the dose (R = 0.95, P < 0.01). The plasma AUC ratio of lactone versus total topotecan (lactone + carboxy-forms) increased with the dose from 16% to 55%, (R = 0.84, P < 0.01). Peritoneal total topotecan was cleared from the peritoneal cavity at 0.4 +/- 0.3 L/h.m(2) with a T1/2 = 2.7 +/- 1.7 h. The mean peritoneal/plasma AUC ratio for total topotecan was 54 +/- 34.

CONCLUSION

A substantial dose of topotecan can be delivered by the IP route, achieving cytotoxic plasma levels of topotecan, with acceptable toxicity. The recommended dose for further phase II trials is 20 mg/m(2) IP, which enables combination with active doses of other cytotoxic drugs, in view of its limited myelotoxicity when given by this route.

Quantitative structure-antitumor activity relationships of camptothecin analogues: cluster analysis and genetic algorithm-based studies

Topoisomerase 1 (top1) inhibitors are proving useful against a range of refractory tumors, and there is considerable interest in the development of additional top1 agents. Despite crystallographic studies, the binding site and ligand properties that lead to activity are poorly understood. Here we report a unique approach to quantitative structure-activity relationship (QSAR) analysis based on the National Cancer Institute's (NCI) drug databases. In 1990, the NCI established a drug discovery program in which compounds are tested for their ability to inhibit the growth of 60 different human cancer cell lines in culture. More than 70 000 compounds have been screened, and patterns of activity against the 60 cell lines have been found to encode rich information on mechanisms of drug action and drug resistance. Here, we use hierarchical clustering to define antitumor activity patterns in a data set of 167 tested camptothecins (CPTs) in the NCI drug database. The average pairwise Pearson correlation coefficient between activity patterns for the CPT set was 0.70. Coherence between chemical structures and their activity patterns was observed. QSAR studies were carried out using the mean 50% growth inhibitory concentrations (GI(50)) for 60 cell lines as the dependent variables. Different statistical methods, including stepwise linear regression, principal component regression (PCR), partial least-squares regression (PLS), and fully cross-validated genetic function approximation (GFA) were applied to construct quantitative structure-antitumor relationship models. For our data set, the GFA method performed better in terms of correlation coefficients and cross-validation analysis. A number of molecular descriptors were identified as being correlated with antitumor activity. Included were partial atomic charges and three interatomic distances that define the relative spatial dispositions of three significant atoms (the hydroxyl hydrogen of the E-ring, the lactone carbonyl oxygen of the E-ring, and the carbonyl oxygen of the D-ring). The cross-validated r(2) for the final GFA model was 0.783, indicating a predictive QSAR model.

Sequence-specific trapping of topoisomerase I by DNA binding polyamide-camptothecin conjugates

Hairpin pyrrole-imidazole polyamides are synthetic ligands that bind in the minor groove of DNA with affinities and specificities comparable to those of DNA binding proteins. Three polyamide-camptothecin conjugates 1-3 with linkers varying in length between 7, 13, and 18 atoms were synthesized to trap the enzyme Topoisomerase I and induce cleavage at predetermined DNA sites. One of these, polyamide-camptothecin conjugate 3 at nanomolar concentration (50 nM) in the presence of Topo I (37 degrees C), induces DNA cleavage between three and four base pairs from the polyamide binding site in high yield (77%).

A phase I trial of topotecan and gemcitabine administered weekly for 3 consecutive weeks to patients with advanced tumors

BACKGROUND

The complementary action of gemcitabine and topotecan on DNA metabolism suggested the potential for their use in combination chemotherapy. Gemcitabine, a synthetic cytidine analogue chain terminator, and topotecan, a topoisomerase-1 inhibitor, have been reported to have broad antitumor activity and are approved for clinical use.

METHODS

The cytotoxicity of the combination in various models in vitro was additive. In the current study, the authors conducted a Phase I study to determine the recommended Phase II doses and toxicity profile of gemcitabine and topotecan when administered weekly in combination. Gemcitabine (400--1000 mg/m(2)) was given intravenously over 30 minutes followed by a 15-minute infusion of topotecan (0.75--2.5 mg/m(2)) weekly for 3 consecutive weeks in a 4-week treatment cycle. Thirty-eight patients with advanced refractory solid tumors and good performance status were treated.

RESULTS

Myelosuppression in the form of granulocytopenia and thrombocytopenia were the major dose-limiting toxicities. Other toxic effects included anemia, nausea, and elevated hepatic transaminases. Partial responses were observed in two patients (one with nonsmall cell lung carcinoma and one with pancreatic carcinoma). Disease stabilization occurred in five patients (three with pancreatic carcinoma, one with rectal carcinoma, and one with metastatic carcinoma of an unknown primary site). Gemcitabine, 1000 mg/m(2), and topotecan, 2.5 mg/m(2), were the maximum tolerated doses for this combination.

CONCLUSIONS

The results of the current study showed that the combination of weekly gemcitabine and topotecan for 3 weeks in a 4-week cycle schedule appeared to be well tolerated and was associated with clinical activity. Therefore, this combination is recommended for a further Phase II evaluation.

The highly lipophilic DNA topoisomerase I inhibitor DB-67 displays elevated lactone levels in human blood and potent anticancer activity

The novel silatecan 7-t-butyldimethylsilyl-10-hydroxycamptothecin (DB-67) is 25- to 50-times more lipophilic than camptothecin and readily incorporates into lipid bilayers. Using the method of fluorescence anisotropy titration, we determined that DB-67 bound to small unilamellar vesicles composed of dilaurylphosphatidylcholine (DLPC) with an association constant (K value) of 5000 M(-1). This association constant is significantly higher than the K(DLPC) value observed for camptothecin (K(DLPC) value of 110 M(-1)). Using HPLC methods, we demonstrated that the presence of liposomal membranes readily stabilize the lactone form of DB-67. At drug and lipid concentrations of 10 microM and 0.3 mM, respectively, the lactone form of DB-67 persisted in liposome suspension after 3 h of incubation at 37 degrees C. Thus an advantage of a liposomal formulation of DB-67 is that the presence of lipid bilayers assists with stabilizing the key pharmacophore of the agent. The highly lipophilic character of DB-67, in combination with its 10-hydroxy moiety (which functions to enhance lactone stability in the presence of human serum albumin), results in DB-67 having superior stability in human blood with a percent lactone at equilibrium value of 30 [Cancer Res. 59 (1999) 4898; J. Med. Chem. 43 (2000) 3970]. Potent cytotoxicities against a broad range of cancer cells were observed for DB-67, indicating that DB-67 is of comparable potency to camptothecin. The impressive human blood stability and cytotoxicity profiles for DB-67 indicate it is an excellent candidate for comprehensive in vivo pharmacological and efficacy studies. Based on these promising attributes, DB-67 is currently being developed under the NCI RAID program. Due to its potent anti-topoisomerase I activity and its intrinsic blood stability, DB-67 appears as an attractive novel camptothecin for clinical development.

Synthesis and biological evaluation of novel A-ring modified hexacyclic camptothecin analogues

Eleven A-ring modified hexacyclic analogues of camptothecin (CPT) containing a 1,4-oxazine ring were synthesized from 10-hydroxycamptothecin (11a) and 7-ethyl-10-hydroxycamptothecin (3) (SN-38) in four to five steps and were subjected to the biological tests such as cytotoxicity, topoisomerase I (Topo I) inhibitory activity, acetylcholinesterase (AChE) inhibition, and stability in human plasma. Four compounds 15a, 15b, 16a, and 16c were about 2-fold more potent than topotecan and as potent as CPT toward human cancer cell lines A549, H128, WiDr, MKN45, SK-OV-3, and SK-BR-3 in vitro, even though the most active compound 15b was slightly less potent than SN-38. The potency of Topo I inhibition of these compounds showed relatively good correlation with their cytotoxicity. Most of the compounds exhibited AChE inhibitory activity weaker (9 +/- 2 to 20 +/- 3%) than CPT (23 +/- 5%) or topotecan (20 +/- 4%) and similar to SN-38 (13 +/- 2%), indicating that they might have little effect on causing early diarrhea. The stability of lactone forms of these compounds in human plasma seemed to be much higher than that of CPT and similar to that of topotecan but lower than that of SN-38. Among the new hexacyclic CPT analogues, compound 15b showed higher antitumor activity against human tumor xenograft, WiDr, in nude mice compared to that of SN-38. The most promising compound 15b has been selected for further development.

Determination of topotecan by ELISA

A highly sensitive ELISA for the determination of (s)-9-dimethylaminomethyl-10-hydroxy-camptothecin (topotecan) capable of measuring as low as 80 pg/ml was developed. Anti-topotecan antibody was obtained by immunizing rabbits with topotecan conjugated with bovine serum albumin using diazotized m-aminobenzoic acid as a cross-linker. Enzyme labeling of topotecan with beta-D-galactosidase was performed by utilizing another cross-linker, N-(4-diazophenyl)maleimide. The specificity of this ELISA appears to be primarily toward the lactone moiety of topotecan, showing a very slight cross-reactivity with the lactone opened-ring of topotecan. The values for the topotecan concentrations detected using this assay were comparable with those detected using HPLC. There was a good correlation between the values determined by the two methods. These findings suggest that this ELISA can detect the natural amounts of the lactone form. Using this assay, drug levels were easily determined in the blood and urine of rats for 5 h after i.v. administration of topotecan at a single dose of 1 mg/kg. The sensitivity and specificity of the ELISA should provide a useful tool for developing pharmacokinetic and pharmacodynamic studies of topotecan.

Camptothecins as probes of the microenvironments of topoisomerase I--DNA complexes

By uncoupling the cleavage and ligation reactions of DNA oligonucleotides mediated by topoisomerase I, it has been possible to demonstrate modification of DNA oligonucleotide structure by the enzyme. These modifications indicate an unusual flexibility inherent in the behavior of topoisomerase I and may reflect some of the cellular roles played by the enzyme. The ability of individual camptothecin analogues to inhibit these modification processes differentially provides insight into the relative nature of the microenvironments present. To the extent that these enzyme-mediated structural modifications do constitute models of cellular roles for the enzyme, the observed differential inhibition also provides a potential strategy for assessing the function and importance of such modifications.

Structure-activity relationship of alkyl camptothecin esters

The cytotoxicity of camptothecin (CPT) esters 1-6 was measured. Like parental camptothecin, esters 2 and 3, but not 1, 4, 5, and 6, inhibited proliferation of human leukemia cells in culture and induced programmed cell death as assessed by flow cytometry studies. Exhibition of similar levels of antiproliferative activities of CPT 2 and 3 required different incubation time periods in cell cultures, with CPT and 3 requiring the shortest and longest periods, respectively. Both 2 and 3 were inactive against cells resistant to the semisynthetic CPT derivative 9-nitrocamptothecin and unable to stabilize DNA-topoisomerase I (Topo I) "cleavable complexes" in a cell-free system, suggesting that Topo I activity was required but insufficient for the mechanism of action of 2 and 3. Mouse liver homogenate converted esters to parental CPT, but the conversion rates were different with different esters. Of four tested esters in this experiment, ester 2 had the fastest conversion rate. In vivo studies showed that ester 2 had an exceptional lack of toxicity in nude mice, even at enormous doses, and demonstrated extensive activity against human breast and colon tumors grown as xenografts in immunodeficient nude mice, whereas no antitumor activity was observed for the other esters. In conclusion, ester 2 is a prodrug of the antitumor compound CPT, and it can be administered at very high doses in mice with no appearance of toxicity. This study provides a basis for further evaluation of CPT ester 2 as an investigational anticancer agent.

Pharmacology of camptothecin esters

An intact lactone ring of camptothecins is a structural requirement for their anticancer activity. Propionate esters of camptothecin (CPT) and 9-nitrocamptothecin (9NC), CZ48 and CZ112, respectively, have been synthesized as derivatives resistant to lactone hydrolysis and are chemotherapeutically active. In this study, we have examined the mechanism of action of CZ48 and CZ112 and their distribution, metabolism, and toxicity. CZ112 incubated in human plasma retained its lactone structure longer than 9NC (t1/2: 10.5 and < 1 hr for CZ112 and 9NC, respectively). This resistance to lactone hydrolysis was also observed in mouse plasma or albumin solutions. Neither CZ48 nor CZ112 inhibit topoisomerase I and thus are prodrugs dependent on hydrolysis to CPT or 9NC, respectively. Rates of hydrolysis of CZ48 to CPT are higher by homogenates of mouse liver, spleen, lung, and kidney than by plasma. Rates of hydrolysis by tumor cells in culture vary and were higher by breast cancer and melanoma cells than by colon cancer cells. On the basis of these and other data, it is proposed that CZ48 and CZ112 may act as anticancer agents by resisting hydrolysis to camptothecins while in circulation. Hydrolysis in tissues may release intact lactone in target tissues.