Camptothecins

Antitumor efficacy of colon-specific HPMA copolymer/9-aminocamptothecin conjugates in mice bearing human-colon carcinoma xenografts

The antitumor activity of a colon-specific N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer - 9-aminocamptothecin (9-AC) conjugate (P-9-AC) was assessed in orthotopic and subcutaneous animal (HT29 xenograft) tumor models. P-9-AC treatment of mice bearing orthotopic colon tumors, with a dose of 3 mg/kg of 9-AC equivalent every other day for 6 weeks, resulted in regression of tumors in 9 of 10 mice. A lower dose of P-9-AC (1.25 mg/kg of 9-AC equivalent) every other day for 8 weeks inhibited subcutaneous tumor growth in all mice. No liver metastases were observed. Colon-specific release of 9-AC from polymer conjugates enhanced antitumor activity and minimized the systemic toxicity.

UGT1A1 genotyping: a predictor of irinotecan-associated side effects and drug efficacy?

Irinotecan [Camptosar (CPT-11), Pfizer Pharmaceuticals, New York, USA] is one of the most effective chemotherapeutic agents in the treatment of metastatic colorectal cancer. In vivo, the prodrug CPT-11 is biotransformed by carboxylesterase into its active metabolite SN-38. SN-38 is inactivated by uridine disphosphate glucuronosyl transferase 1 (UGT1A1) into the inactive compound SN-38G, which is excreted with the bile.This review concentrates on a critical evaluation of UGT1A1 gene polymorphism as a predictor of toxicity and treatment efficacy in patients who received irinotecan for metastatic colorectal cancer. Irinotecan is explained with its main toxicities as well as the underlying mechanisms. The enzyme UGT1A1 is shown in the context of other metabolic pathways and different UGT enzymes involved. We will review in detail the controversy of the current literature with regard to the significance of identifying patients carrying the homozygous genotype UGT1A1 28. Racial differences concerning UGT enzymes have to be considered when discussing a pragmatic approach to determine gene polymorphisms as a predictor of treatment efficacy and outcome in patients receiving irinotecan-based chemotherapy. Dose dependency of toxicity and the clinical relevance of various UGT1 enzymes and single nucleotide polymorphisms in different alternative metabolic pathways are clarified to put UGT1A1 genotyping in a broad context with additional and competing strategies of patient-tailored therapy.

UGT1A1 gene polymorphism: Impact on toxicity and efficacy of irinotecan-based regimens in metastatic colorectal cancer

AIM: To investigate the correlation between uridine diphosphate glucuronosyl transferase 1A1 (UGT1A1) gene polymorphisms and irinotecan-associated side effects and parameters of drug efficacy in patients with metastatic colorectal cancer (mCRC) receiving a low-dose weekly irinotecan chemotherapeutic regimen.

METHODS: Genotypes were retrospectively evaluated by gene scan analysis on the ABI 310 sequencer of the TATAA box in the promoter region of the UGT1A1 gene in blood samples from 105 patients who had received 1st line irinotecan-based chemotherapy for mCRC.

RESULTS: The distribution of the genotypes was as follows: wild type genotype (WT) (6/6) 39.0%, heterozygous genotype (6/7) 49.5%, and homozygous genotype (7/7) 9.5%. The overall response rate (OR) was similar between patients carrying the (6/7, 7/7) or the WT genotype (6/6) (44.3% vs 43.2%, P = 0.75). Neither time to progression [(TTP) 8.1 vs 8.2 mo, P = 0.97] nor overall survival [(OS) 21.2 vs 18.9 mo, P = 0.73] differed significantly in patients who carried the (6/6) when compared to the (6/7, 7/7) genotype. No significant differences in toxicity were observed: Grade 3 and 4 delayed diarrhoea [(6/7, 7/7) vs (6/6); 13.0% vs 6.2%, P = 0.08], treatment delays [(6/7, 7/7) vs (6/6); 25.1% vs 19.3%, P =0.24] or dose reductions [(6/7, 7/7) vs (6/6); 21.5% vs 27.2%, P = 0.07].

CONCLUSION: This analysis demonstrates the non-significant influence of the UGT1A1 gene polymorphism on efficacy and rate of irinotecan-associated toxicity in mCRC patients receiving low-dose irinotecan based chemotherapy.

Mechanistic studies of the modulation of cleavage activity of topoisomerase I by DNA adducts of mono- and bi-functional PtII complexes

Using electrophoresis and replication mapping, we show that the presence of DNA adducts of bifunctional antitumor cisplatin or monodentate [PtCl(dien)]Cl (dien = diethylenetriamine) in the substrate DNA inhibits eukaryotic topoisomerase 1 (top1) action, the adducts of cisplatin being more effective. The presence of camptothecin in the samples of platinated DNA markedly enhances effects of Pt–DNA adducts on top1 activity. Interestingly, the effects of Pt–DNA adducts on the catalytic activity of top1 in the presence of camptothecin differ depending on the sequence context. A multiple metallation of the short nucleotide sequences on the scissile strand, immediately downstream of the cleavage site impedes the cleavage by top1. On the other hand, DNA cleavage by top1 at some cleavage sites which were not platinated in their close proximity is notably enhanced as a consequence of global platination of DNA. We suggest that this enhancement of DNA cleavage by top1 may consist in its inability to bind to other cleavage sites platinated in their close neighborhood; thus, more molecules of top1 may become available for cleavage at the sites where top1 normally cleaves and where platination does not interfere.

Modulation of orphan nuclear receptor Nur77-mediated apoptotic pathway by acetylshikonin and analogues

Shikonin derivatives, which are the active components of the medicinal plant Lithospermum erythrorhizon, exhibit many biological effects including apoptosis induction through undefined mechanisms. We recently discovered that orphan nuclear receptor Nur77 migrates from the nucleus to the mitochondria, where it binds to Bcl-2 to induce apoptosis. Here, we report that certain shikonin derivatives could modulate the Nur77/Bcl-2 apoptotic pathway by increasing levels of Nur77 protein and promoting its mitochondrial targeting in cancer cells. Structural modification of acetylshikonin resulted in the identification of a derivative 5,8-diacetoxyl-6-(1'-acetoxyl-4'-methyl-3'-pentenyl)-1,4-naphthaquinones (SK07) that exhibited improved efficacy and specificity in activating the pathway. Unlike other Nur77 modulators, shikonins increased the levels of Nur77 protein through their posttranscriptional regulation. The apoptotic effect of SK07 was impaired in Nur77 knockout cells and suppressed by cotreatment with leptomycin B that inhibited Nur77 cytoplasmic localization. Furthermore, SK07 induced apoptosis in cells expressing the COOH-terminal half of Nur77 protein but not its NH(2)-terminal region. Our data also showed that SK07-induced apoptosis was associated with a Bcl-2 conformational change and Bax activation. Together, our results show that certain shikonin derivatives act as modulators of the Nur77-mediated apoptotic pathway and identify a new shikonin-based lead that targets Nur77 for apoptosis induction.

Phase II study of 9-aminocamptothecin in previously treated lymphomas: results of Cancer and Leukemia Group B 9551

PURPOSE

To evaluate the efficacy and toxicity of the topoisomerase I inhibitor, 9-aminocamptothecin (9-AC), in patients with relapsed lymphoma and to correlate 9-AC plasma concentrations with response and toxicity.

METHODS

Eligible patients had relapsed Hodgkin lymphoma (HL) treated with one or two prior regimens, low grade non-Hodgkin's lymphoma (NHL) treated with one or two prior regimens, or aggressive NHL treated with one prior regimen. The first nine patients received 9-AC dimethylacetamide 0.85 mg/m(2) per day intravenously over 72 h every 2 weeks and the remaining 27 patients received 9-AC/colloidal dispersion 1.1 mg/m(2) per day. Patients received a minimum of three cycles unless progression or intolerable toxicity occurred. Responding patients received two cycles past best response with a minimum of six cycles.

RESULTS

CALGB 9551 accrued 37 patients from April 1996 through October 2000; one patient with HD, 18 patients with indolent lymphoma, and 17 patients with aggressive lymphoma. The overall response rate was 17%, with response rates of 11% (2 partial responses) in patients with indolent histologies and 23% (1 complete response, 3 partial responses) in patients with aggressive histologies. The patient with HD did not respond. Response rates were similar for both drug formulations. The median remission duration for the six responders was 6.5 months, with one remission lasting longer than 12 months. Significant grade 3 and 4 toxicities included neutropenia (66%), anemia (31%), and thrombocytopenia (36%), with 20% of patients experiencing grade 3 or 4 infection. No treatment related deaths occurred. Steady state serum concentrations did not correlate with patient response or toxicity.

CONCLUSION

Single agent 9-AC has modest activity in aggressive non-Hodgkin's lymphomas.

Potential oral delivery of 7-ethyl-10-hydroxy-camptothecin (SN-38) using poly(amidoamine) dendrimers

PURPOSE

To investigate potential application of poly(amidoamine) (PAMAM) dendrimers for improving the delivery of SN-38.

METHODS

Complexes of SN-38 with generation 4 amine terminated PAMAM dendrimers were synthesized with varying amounts of drug. Stability of the complexes as well as influence of complexation on permeability across and cellular uptake by Caco-2 cells was evaluated.

RESULTS

The complexes were stable at pH 7.4 and drug was released at pH 5. A tenfold increase in permeability and more than hundredfold increase in cellular uptake of the complexes with respect to free SN-38 was observed.

CONCLUSIONS

Studies suggest that complexation with PAMAM dendrimers has the potential to improve the oral bioavailability of SN-38.

Freeze drying of double emulsions to prepare topotecan-entrapping liposomes featuring controlled release

Topotecan-entrapping liposomes were prepared by freeze drying double emulsions with hydrogenated soy phosphatidylcholine, N-(carbonyl-methoxypolyethyleneglycol2000)-1,2-distearoyl-sn-glycero-3-phosphoethanolamine, and cholesterol. Different inner aqueous phases of different pH values containing topotecan together with different chemicals, such as citrate and sulfate, were used to modify the physicochemical state of the drug to prepare W1/O/W2 double emulsions that were then freeze dried to obtain dry products. Upon rehydration, the dry products, which were stable for at least 6 months, formed into unilamellar liposomes with a high encapsulation efficiency of up to 80% and a mean diameter below 200 nm. The in vitro release experiments demonstrated that different formulations displayed different drug release properties. Thus, stable submicron unilamellar topotecan-entrapping liposomes can be prepared by freeze drying double emulsions, and the drug release can be successfully controlled by altering the physicochemical state of the incorporated drug.

Liposomal delivery of hydrophobic weak acids: enhancement of drug retention using a high intraliposomal pH

Clinical development of highly potent lipophilic neutral camptothecins has been impeded by the poor solubility, stability, and nonspecific toxicity of these compounds. Liposomal encapsulation offers a promising formulation route for tumor site-specific delivery of these novel drug candidates. However, the development of formulation strategies for liposomal loading and retention of hydrophobic drugs such as the neutral camptothecins has been lacking. In the studies presented here, we explored the potential of a trans-bilayer pH gradient strategy for prolonging the liposome retention of DB-67, a novel lipophilic camptothecin that can undergo lactone ring-opening to form a hydrophobic weak acid. The liposome membrane permeability of DB-67 was obtained as a function of pH in aqueous buffers. A permeability model was developed and liposome membrane permeability was shown to be controlled by the fraction of unbound neutral lactone entrapped in the vesicles. Liposome membrane permeability of DB-67 was also studied under physiological conditions. The high membrane partitioning of DB-67 in the intraliposomal microenvironment was found to shift the equilibrium between lactone and carboxylate towards the lactone species resulting in a faster than desired drug release under physiological conditions. The effectiveness of the pH gradient strategy was further reduced under physiological conditions by the rapid loss of trans-membrane pH gradients due to CO(2) uptake. Simulations were conducted to explore the role of membrane binding, intravesicular pH, and carbonate buffer concentration in successful utilization of the pH gradient strategy for hydrophobic weak acids.

Treatment options for relapsed small-cell lung cancer

Small-cell lung cancer is a chemo-sensitive disease with a response rate ranging from 70 to 90% for first-line treatment; however, relapses are very common and as a result long-term survival is poor. Chemotherapy has demonstrated a benefit over the best supportive care, even in patients who have relapsed after initial treatment with a platinum-based regimen. Agents currently being used in salvage therapy include topotecan, cyclophosphamide, doxorubicin and vincristine regimen. In the last 5 years, several drugs have shown promise in initial evaluation; however, randomized phase III trials would be needed to answer this question. Our understanding of the biology of small-cell lung cancer has improved dramatically over the past few years and this has translated into the developments of new therapeutic targets for this disease. Agents affecting several targets, including bcl-2, matrix metalloproteinases, epidermal growth factors and angiogenesis, are being studied currently and have the potential to change the treatment paradigms of this otherwise fatal malignancy. This review focuses on the various current and future options, including cytoxic and targeted agents, for salvage therapy in patients with this disease.

Vitamin E analogues as a novel group of mitocans: anti-cancer agents that act by targeting mitochondria

Mitochondria have recently emerged as new and promising targets for cancer prevention and therapy. One of the reasons for this is that mitochondria are instrumental to many types of cell death and often lie downstream from the initial actions of anti-cancer drugs. Unlike the tumour suppressor gene encoding p53 that is notoriously prone to inactivating mutations but whose function is essential for induction of apoptosis by DNA-targeting agents (such as doxorubicin or 5-fluorouracil), mitochondria present targets that are not so compromised by genetic mutation and whose targeting overcomes problems with mutations of upstream targets such as p53. We have recently proposed a novel class of anti-cancer agents, mitocans that exert their anti-cancer activity by destabilising mitochondria, promoting the selective induction of apoptotic death in tumour cells. In this communication, we review recent findings on mitocans and propose a common basis for their mode of action in inducing apoptosis of cancer cells. We use as an example the analogues of vitamin E that are proving to be cancer cell-specific and may soon be developed into efficient anti-cancer drugs.

Thermal behavior and thermal decarboxylation of 10-hydroxycamptothecin in the solid state

In order to investigate the thermal-related properties and thermal stability of 10-hydroxycamptothecin (10-HCPT) in the solid state, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and Fourier transform infrared (FT-IR) microspectroscopy were used. A novel combination of FT-IR microspectroscopy with thermal analyzer was applied simultaneously to monitor the dehydration and rehydration processes of the 10-HCPT sample. The thermal-induced decomposition of the 10-HCPT sample was also determined by using electrospray-ion trap mass spectrometry (ES-ITMS). The results indicated that the 10-HCPT sample used in this study was a monohydrate in structure, this form that can dehydrate to an anhydrate form if the temperature goes beyond 90 degrees C. The 10-HCPT anhydrate was first suggested to have two polymorphs, in which the form I might transform to form II when the 110 degrees C-preheated sample was cooled to 30 degrees C. The polymorphic transformation temperature was shown within 90-120 degrees C with 10.46 kcal/mol of enthalpy. The peak at 1723 cm(-1) found in the IR spectrum of 10-HCPT monohydrate might correspond to the hydrogen-bonded CO stretching vibration of lactone, which shifted to 1750 cm(-1) assigned to a free CO group of lactone after the destruction of hydrogen bonding via dehydration. This suggests that monohydrate seems to interact intramolecularly with 10-HCPT by hydrogen bonding. However, the rehydration process of the 10-HCPT anhydrate might cause it to return to being a monohydrate, depending on the storage condition. In addition, the thermal-induced decarboxylation of the solid-state 10-HCPT when the temperature is beyond 226 degrees C was proven by the appearance of a new IR peak at 1701 cm(-1) and one major mass spectral peak at m/z 321. This unique IR spectral peak at 1701 cm(-1) was due to the conjugated carbonyl group in the degraded product of 10-HCPT. The m/z 321 assigned to the decarboxylation of 10-HCPT was equal to the molecular weight loss of 44 from mass spectra; which was consistent with the weight loss of 11.9% (molecular weight of 43.3) from TGA curve of 10-HCPT anhydrate.

Sequential doxorubicin and topotecan in relapsed/refractory aggressive non-Hodgkin's lymphoma: results of CALGB 59906

Topoisomerase enzymes are critical components of genomic replication and function to minimize torsional stress on DNA. Sequential administration of a topoisomerase II inhibitor followed by a topoisomerase I inhibitor is potentially synergistic due to increased target enzyme levels. Patients with relapsed or refractory aggressive non-Hodgkin's lymphomas (NHL) were eligible for this phase II study of doxorubicin 25 mg/m2 intravenous (IV) on day 1 and topotecan 1.75 mg/m2/day IV on days 3 - 5, every 21 days. The trial objectives included the overall response rate, progression-free survival, and toxicity. Twenty-six patients were enrolled and 25 patients are assessable for toxicity and response. The median age was 58 (range 23 - 74) years. The patients had received a median of two (range one to five) prior regimens, including five patients with a prior stem cell transplant. Five patients (20%, 95% confidence interval 0.07, 0.42) responded with two (8%) complete remissions and three (12%) partial remissions; an additional four (16%) patients had stable disease. Both patients achieving a complete remission had Burkitt's lymphoma. There were no treatment-related deaths. In conclusion, the combination of doxorubicin and topotecan is well tolerated and has modest activity in relapsed/refractory NHL, with occasional patients having a prolonged remission. The activity in Burkitt's lymphoma should be investigated further.

Effect of phospholipid composition on characterization of liposomes containing 9-nitrocamptothecin

9-Nitrocamptothecin (9-NC), a newly developed camptothecin derivative, had poor solubility in any pharmaceutically acceptable solvents. One way of improving the solubility is to formulate the drug into liposomes. However, 9-NC has low affinity to lipid membranes resulting in a very low drug-to-liposome entrapment. We developed a novel liposome-based 9-NC formulation which was composed of soybean phosphatidylcholine (SPC), hydrogenated soybean phosphatidylcholine (HSPC), and cholesterol. Compared with conventional liposomes composed of only SPC and cholesterol, 9-NC/lipid molar ratio increased from 1:72 to 1:18 while incorporation efficiency was still maintained about 80%. In addition, after 9-NC was encapsulated into novel liposomes, pharmacokinetic results revealed an increase in area under the plasma concentration-time curve (AUC) and a decrease in distribution volume of 9-NC following intravenous administration to rats. Increased stability in plasma may account for the improved pharmacokinetic behavior of the novel liposomes. Effect of HSPC/SPC molar ratio on characterization of the novel liposomes was also investigated. Except for drug/lipid molar ratio and encapsulation efficiency, HSPC/SPC molar ratio had only a little effect on other properties of novel liposomes. In conclusion, the study suggests that the novel liposomes can act as promising carriers for hydrophobic substances such as 9-NC.

Phase II NCCTG trial of oral topotecan and paclitaxel with G-CSF (filgrastim) support in patients with previously untreated extensive-stage small cell lung cancer

OBJECTIVE

To determine the efficacy and toxicity of oral topotecan and paclitaxel in untreated patients with extensive stage small cell lung cancer (SCLC).

PATIENTS AND METHODS

Thirty-eight patients received 1.75 mg/m2 of oral topotecan days 1 to 5 and 175 mg/m2 paclitaxel IV over 3 hours on day 5 (after topotecan) every 4 weeks for 6 cycles. Subcutaneous G-CSF at a dose of 5 microg/kg was then given 24 to 48 hours after the last dose of chemotherapy and daily for 10 days.

RESULTS

All 38 patients were available for toxicity and response analysis. A median of 5 treatment cycles was given, with a range of 1 to 7 cycles. Seventeen (45%) patients received at least 6 cycles of treatment. The most common severe adverse events were neutropenia (42.1%), leukopenia (34.2%), thrombocytopenia (18.4%), nausea (18.4%), diarrhea (13.2%), and fatigue (13.2%). Two grade 5 treatment-related evens were seen. The median overall survival was 9.1 month (95% CI: 7.5-13.0 months), with a 1-year survival estimate of 44.7% (95% CI: 31.4-63.7%) and a 2-year survival rate of 5.3% (95% CI: 1.4-20.3%). The median time to progression was 5.0 months (95% CI: 3.8-6.6 months), with a 1-year progression-free rate of 5.8% (95% CI: 1.5-22.2%) and a 2-year progression-free rate of 2.9% (95% CI: 0.4-19.9%). The estimated confirmed response rate was 52.9%.

CONCLUSION

This regimen has shown similar antitumor activity to that achieved with standard therapy. Because of unacceptable toxicity and cost, we do not recommend this regimen in a palliative setting.

Total and semisynthesis and in vitro studies of both enantiomers of 20-fluorocamptothecin

Both enantiomers of 20-fluorocamptothecin and the racemate have been prepared by total synthesis. The (R)-enantiomer is essentially inactive in a topoisomerase-I/DNA assay, while the (S)-enantiomer is much less active than (20S)-camptothecin. The lactone ring of 20-fluorocamptothecin hydrolyzes more rapidly than that of camptothecin in PBS. The results provide insight into the role of the 20-hydroxy group in the binding of camptothecin to topoisomerase-I and DNA.

Phase I dose-finding study and a pharmacokinetic/pharmacodynamic analysis of the neutropenic response of intravenous diflomotecan in patients with advanced malignant tumours

PURPOSE

To determine the maximum tolerated dose (MTD) of intravenous (iv) diflomotecan administered once every 3 weeks, and to characterize the relationship between pharmacokinetics and neutropenic effect, using a semi-mechanistic pharmacokinetic/pharmacodynamic (PK/PD) model.

EXPERIMENTAL DESIGN

Twenty-four patients received a total of 75 cycles of iv diflomotecan that was administered as 20-min infusion, once every 3 weeks at escalating doses of 2, 4, 5, and 6 mg/m2. Haematological and non-haematological toxicities were evaluated. Plasma concentrations of diflomotecan were measured after the first drug administration.

RESULTS

Dose limiting toxicity (DLT) following the first cycle occurred in 12 patients and a total of 16 patients experienced DLT at some point in the trial. During the first cycle of treatment the number of patients in the 5 and 6 mg/m2 dose groups that experienced DLT was 3 of 4, and 3 of 3, respectively. Therefore, the dose of 5 mg/m2 was considered the MTD and the dose of 4 mg/m2 the recommended dose (RD). During the first cycle, 12 patients experienced DLT, six had either infection of haematological toxicity and eight complained of fatigue. The best response was a partial response in one patient treated at the 6 mg/m2 dose level. Disease stabilization was observed in seven patients (four patients treated at 4 mg/m2 and one patient at each dose level of 2, 5, and 6 mg/m2). The remaining patients had all progressive disease. The median time to progression for all patients was 5.9 weeks. Pharmacokinetics of diflomotecan was described with a three-compartmental model. Mean population parameter estimates of the apparent volume of distribution of the central compartment (V c) increased linearly with body surface area (BSA) as: V c (L) = 41.5 x (BSA/1.85), and the mean population estimate of the apparent volume of distribution of the shallow compartment was lower in females (29.5 vs 48.8 L). Computer simulations showed the lack of clinical significance of these covariates. The time course of the neutropenic response was adequately described by a semi-mechanistic model that includes cellular processes and drug effects.

CONCLUSIONS

The MTD and RD after a 20-min iv infusion of diflomotecan every 3 weeks are 4 and 5 mg/m2, respectively. Diflomotecan showed linear pharmacokinetic behaviour and the selected PK/PD model described adequately the time course of neutropenia. The mean model predicted values of nadir and time to nadir after a 20-min iv infusion of 4 mg/m2 of diflomotecan was 0.86 x 10(9) /L neutrophil cell counts and 11 days, respectively.

Cell cycle effects of topotecan alone and in combination with irradiation

BACKGROUND AND PURPOSE

To elucidate the role of TP53 on differential effects of topoisomerase I inhibitor topotecan (Hycamtin on radiation sensitivity.

MATERIALS AND METHODS

Cell cycle distribution and protein expression of TP53, p21(WAF1/CIP1) and cyclin B was studied in CCD32 lung fibroblasts, glioblastoma cell lines U118 (mutant TP53), and U87 (wildtype TP53) after treatment with topotecan (0.05 and 1 microM) and/or ionizing radiation (2 Gy).

RESULTS

Cell cycle effects varied with topotecan concentration, resulting in G1 arrest (1 microM), or S/G2/M arrest (0.05 microM), and was modified differentially in fibroblasts and in glioblastoma cells in combination with irradiation. Phosphorylation of TP53 and expression of p21(WAF1/CIP1) was induced by IR and/or topotecan in CCD32 cells, and in U118 cells after topotecan treatment, accompanied by cyclin B degradation. In U87 cells only 1 microM topotecan generated phosphorylation of TP53 and p21(WAF1/CIP1) expression; 0.05 microM caused stabilization of cyclin B.

CONCLUSIONS

The antagonistic effect of combined topotecan/irradiation treatment in fibroblasts was most likely due to an immediate radiation induced G1 arrest, but was not observed in p53 wildtype glioblastoma cells. Thus, the impact of TP53 on the topotecan response remains indistinct, and is obviously influenced by other genomic alterations acquired by tumor cells.

Sequence-selective DNA recognition: natural products and nature's lessons

Biologically active, therapeutically useful, DNA binding natural products continue to reveal new paradigms for sequence-selective recognition, to enlist beautiful mechanisms of in situ activation for DNA modification, to define new therapeutic targets, to exploit new mechanisms to achieve cellular selectivity, and to provide a rich source of new drugs. These attributes arise in compact structures of complex integrated function.

Rotenone-induced caspase 9/3-independent and -dependent cell death in undifferentiated and differentiated human neural stem cells

We used human neural stem cells (hNSCs) and their differentiated cultures as a model system to evaluate the mechanism(s) involved in rotenone (RO)- and camptothecin (CA)-induced cytotoxicity. Results from ultrastructural damage and terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) staining indicated that RO-induced cytotoxicity resembled CA-induced apoptosis more than H(2)O(2)-induced necrosis. However, unlike CA-induced, caspase 9/3-dependent apoptosis, there was no increased activity in caspase 9, caspase 3 or poly (ADP-ribose) polymerase (PARP) cleavage in RO-induced cytotoxicity, in spite of time-dependent release of cytochrome c and apoptosis-inducing factor (AIF) following mitochondrial membrane depolarization and a significant increase in reactive oxygen species generation. Equal doses of RO and CA used in hNSCs induced caspase 9/3-dependent apoptosis in differentiated cultures. Time-dependent ATP depletion occurred earlier and to a greater extent in RO-treated hNSCs than in CA-treated hNSCs, or differentiated cultures treated with RO or CA. In conclusion, these results represent a unique ultrastructural and molecular characterization of RO- and CA-induced cytotoxicity in hNSCs and their differentiated cultures. Intracellular ATP levels may play an important role in determining whether neural progenitors or their differentiated cells follow a caspase 9/3-dependent or -independent pathway in response to acute insults from neuronal toxicants.

Phase II trial of oral rubitecan in previously treated pancreatic cancer patients

BACKGROUND

Additional systemic treatments for locally advanced or metastatic pancreatic cancer are needed, as current treatment options produce only modest survival benefits. Rubitecan (Orathecin; Supergen Inc., Dublin, CA, http://www.supergen.com) is an orally active camptothecin derivative with demonstrated responses in patients with pancreatic cancer in early clinical trials. This phase II, open-label trial was developed to assess the safety and efficacy of rubitecan in patients with locally advanced or metastatic pancreatic cancer refractory to conventional chemotherapy.

METHODS

Fifty-eight patients with failed or relapsed advanced pancreatic cancer after receiving at least one prior chemotherapy regimen were enrolled to receive eight consecutive weeks of treatment with rubitecan at a dose of 1.5 mg/m2 orally on five consecutive days per week, followed by 2 days off therapy, repeatedly. The primary end point was response rate. Time to progression, overall survival, changes in CA19-9 levels, and the composite measure of clinical benefit response were evaluated as secondary end points.

RESULTS

Among 43 patients with measurable disease, 7% (3/43) achieved partial responses and 16% (7/43) had disease stabilization for an overall response and disease stabilization rate of 23%. All responses were confirmed by independent radiology review. Median survival was longer in responding patients than in the overall study cohort (10 months versus 3 months). Gastrointestinal and hematologic toxicities were the most commonly reported adverse events.

CONCLUSION

Oral rubitecan produced responses and was well tolerated by heavily pretreated patients with refractory pancreatic cancer. The overall risk-benefit profile of oral rubitecan appears promising, supporting further evaluation in phase III trials in patients with refractory and chemotherapy-naive pancreatic cancer.

Topoisomerase I amino acid substitutions, Gly185Arg and Asp325Glu, confer camptothecin resistance in Leishmania donovani

The antitumor compound camptothecin (CPT) is also recognized for its specific activity against Leishmania donovani topoisomerase I (Topo-I). In consequence, defining CPT resistance mechanisms represents an important strategic tool in the acquisition of a better understanding of its mode of action. In the present study, we selected a single highly resistant L. donovani strain termed LdRCPT.160 by stepwise exposure to CPT. Gene sequencing revealed two single nucleotide mutations in the LdRCPT.160 LdTOP1A gene, resulting in two amino acid substitutions (Gly185Arg and Asp325Glu) in the protein. Moreover, these two substitutions observed in the LdTOP1A protein were correlated with a decreased Topo-I DNA relaxation activity in these resistant parasites. Nevertheless, there was no change in the LdTOP1A gene expression level. Interestingly, transfection studies of the LdRCPT.160 LdTOP1A gene in its wild-type counterpart showed that it induced CPT resistance. Site-directed mutagenesis studies demonstrated that, despite a substantial level of resistance conferred by the Gly185Arg and Asp325Glu substitutions separately, both were essential to reach a high-resistance phenotype. Of interest, the amino acid substitutions observed in LdRCPT.160 LdTOP1A protein occurred near the amino acids previously predicted to interact with CPT, providing new insight into the mechanism of CPT molecular action.

Structures of three classes of anticancer agents bound to the human topoisomerase I-DNA covalent complex

Human topoisomerase I (top1) is the molecular target of a diverse set of anticancer compounds, including the camptothecins, indolocarbazoles, and indenoisoquinolines. These compounds bind to a transient top1-DNA covalent complex and inhibit the resealing of a single-strand nick that the enzyme creates to relieve superhelical tension in duplex DNA. (Hertzberg, R. P.; et al. Biochem. 1989, 28, 4629-4638. Hsiang, Y. H.; et al. J. Biol. Chem 1985, 260, 14873-14878. Champoux, J. J. Annu. Rev. Biochem. 2001, 70, 369-413. Stewart, L.; et al. Science 1998, 729, 1534-1541.) We report the X-ray crystal structures of the human top1-DNA complex bound with camptothecin and representative members of the indenoisoquinoline and indolocarbazole classes of top1 poisons. The planar nature of all three structurally diverse classes allows them to intercalate between DNA base pairs at the site of single-strand cleavage. All three classes of compounds have a free electron pair near Arg364, a residue that if mutated confers resistance to all three classes of drugs. The common intercalative binding mode is augmented by unexpected chemotype-specific contacts with amino acid residues Asn352 and Glu356, which adopt alternative side-chain conformations to accommodate the bound compounds. These new X-ray structures explain how very different molecules can stabilize top1-DNA covalent complexes and will aid the rational design of completely novel structural classes of anticancer drugs.

Phase-I dose escalation and sequencing study of docetaxel and continuous infusion topotecan in patients with advanced malignancies

PURPOSE

Anti-tumor activity can often be enhanced with combination therapy in managing patients with metastatic cancer. However, dose sequence and schedule of delivery can alter the pharmacokinetics, toxicity, and anti-tumor response. Therefore, attention to drug-drug interactions which may be sequence or schedule-dependent are necessary. Docetaxel and topotecan are non-cross-resistance cytotoxic agents with activity in a variety of malignancies. The goal of this study was to determine the maximum tolerated dose of docetaxel and continuous infusion topotecan using two sequences of administration.

EXPERIMENTAL DESIGN

Patients were randomized to schedule A or B and enrolled in four escalating-dose cohorts. On schedule A, docetaxel was administered over 1 h and followed by topotecan administered over 72 h. On schedule B, topotecan was given as a 72 h continuous infusion followed by a 1 h infusion of docetaxel. While the doses for the docetaxel and topotecan were the same for schedule A and schedule B, the toxicities, and thus the determination of maximum tolerated dose (MTD), were assessed independently. The plasma pharmacokinetic disposition of topotecan and docetaxel were evaluated during the first cycle of each sequence to assess drug interactions.

RESULTS

Thirty patients, 20 males and 10 females were evaluable for toxicity and response. Four patients were chemonaive. Mean number cycles given were 3. Grade 3/4 thrombocytopenia and neutropenia were comparable on both schedules, as was the dose-limiting toxicity (DLT) for both schedules. There were no apparent differences in absolute neutrophil count or platelet nadirs between schedules A and B for three of the four cohorts. The principal non-hematologic toxicity was nausea and vomiting. The time of overlap of topotecan lactone or total concentrations and docetaxel concentrations were greater on schedule A as compared with schedule B and was associated with reduced clearance of docetaxel on schedule A as compared to schedule B. However, the mean clearance for docetaxel (18 for all 16 L h(-1) m(-2) and 29 for all 28 L h(-1) m(-2) on schedules A and B, respectively, and topotecan 16 for all 10 L h(-1) m(-2) and 7 for all 6 L h(-1) m(-2) on schedules A and B, respectively) were not statistically different (P > 0.05).

CONCLUSIONS

The observed toxicity was not sequence-dependent, despite the observed change in kinetics. Docetaxel and topotecan can be administered with acceptable toxicity at the recommended phase-II dose of docetaxel 60 mg m(-2) and topotecan 0.85 mg m(-2) day(-1)x3 days.

Natural products to drugs: natural product derived compounds in clinical trials

Natural product and natural product-derived compounds that are being evaluated in clinical trials or in registration (current 31 December 2004) have been reviewed. Natural product derived drugs launched in the United States of America, Europe and Japan since 1998 and new natural product templates discovered since 1990 are discussed.

Synthesis of 14-Azacamptothecin, a Water-Soluble Topoisomerase I Poison

14-Azacamptothecin, a potent, water-soluble analogue of the antitumor agent camptothecin, has been prepared by a convergent synthesis. The key condensation of the AB and DE rings with concomitant formation of ring C of 14-aza CPT was carried out in two stages, the latter of which involved a radical cyclization strategy. [structure: see text]

UGT1A7 and UGT1A9 Polymorphisms Predict Response and Toxicity in Colorectal Cancer Patients Treated with Capecitabine/Irinotecan

Purpose: Capecitabine and irinotecan are commonly used in the treatment of metastatic colorectal cancer (CRC). We hypothesized that germline polymorphisms within genes related to drug target (thymidylate synthase) or metabolizing enzymes (UDP-glucuronosyltransferase, UGT) would impact response and toxicity to the combination of capecitabine plus irinotecan (CPT-11).

Experimental Design: Sixty-seven patients with measurable CRC were treated with irinotecan i.v. (100 or 125 mg/m2) on days 1 and 8 and capecitabine orally (900 or 1,000 mg/m2, twice daily) on days 2 through 15 of each 3-week cycle. Genomic DNA was extracted from peripheral blood and genotyped using Pyrosequencing, GeneScan, and direct sequencing (Big Dye terminator) technologies.

Results: The overall objective response rate was 45% with 21 patients (31%) exhibiting grade 3 or 4 diarrhea and 3 patients (4.5%) demonstrating grade 3 or 4 neutropenia in the first two cycles. Low enzyme activity UGT1A7 genotypes, UGT1A7*2/*2 (six patients) and UGT1A7*3/*3 (seven patients), were significantly associated with antitumor response (p = 0.013) and lack of severe gastrointestinal toxicity (p = 0.003). In addition, the UGT1A9 −118 (dT)9/9 genotype was significantly associated with reduced toxicity (p = 0.002) and increased response (p = 0.047). There were no statistically significant associations between UGT1A1, UGT1A6, or thymidylate synthase genotypes and toxicity or tumor response.

Conclusions: These data strongly suggest that UGT1A7 and/or UGT1A9 genotypes may be predictors of response and toxicity in CRC patients treated with capecitabine plus irinotecan. Specifically, patients with genotypes conferring low UGT1A7 activity and/or the UGT1A9 (dT)9/9 genotype may be particularly likely to exhibit greater antitumor response with little toxicity.

On the role of E-ring oxygen atoms in the binding of camptothecin to the topoisomerase I–DNA covalent binary complex

A recent X-ray crystallographic analysis of the binding of a water soluble camptothecin analogue to the human topoisomerase I-DNA covalent binary complex has suggested the existence of some novel features in the way that camptothecin is bound to the binary complex. Four additional models based on chemical and biochemical data have also been proposed. Presently we describe S-containing analogues of camptothecin prepared on the basis of these models, and report their ability to form stable ternary complexes with human topoisomerase I, and to mediate cytotoxicity at the locus of topoisomerase I. The results indicate that replacement of the 20-OH group of CPT with a SH functionality results in diminution of the potency of CPT as a topoisomerase I poison, while replacement of the O atoms at positions 20 and 21 with S atoms results in essentially complete loss of topoisomerase I inhibitory activity.

14-Azacamptothecin: A Potent Water-Soluble Topoisomerase I Poison

On the basis of an analysis of luotonin A and its D-ring deaza analogue as topoisomerase I poisons and topoisomerase I-dependent cytotoxic agents, a novel analogue of the structurally related antitumor antibiotic camptothecin (CPT) was prepared. 14-Azacamptothecin was found to have much greater aqueous solubility than CPT, to inhibit topoisomerase I-mediated DNA relaxation more efficiently than CPT, and to stabilize the covalent binary complex to almost the same extent. 14-Aza CPT was found to be slightly less active than CPT in mediating cytotoxicity toward yeast expressing human topoisomerase I, possibly as a consequence of its greater off-rate from the CPT-topoisomerase I-DNA ternary complex.

Synthesis and topoisomerase I inhibitory properties of luotonin A analogues

Luotonin A, a naturally occurring pyrroloquinazolinoquinoline alkaloid, has been previously demonstrated to be a topoisomerase I poison. A number of luotonin A derivatives have now been prepared through the condensation of anthranilic acid derivatives and 1,2-dihydropyrrolo[3,4-b]quinoline-3-one in the presence of phosphorus oxychloride. When dichloromethane was used as solvent the reaction proceeded to a single product. In contrast when the reaction was carried out in tetrahydrofuran or in phosphorus oxychloride, an additional isomeric product was obtained. The luotonin A analogues were evaluated for their ability to effect stabilization of the covalent binary complex formed between human topoisomerase I and DNA, and for cytotoxicity toward a yeast strain expressing the human topoisomerase I.

Camptothecin: current perspectives

This review provides a detailed discussion of recent advances in the medicinal chemistry of camptothecin, a potent antitumor antibiotic. Two camptothecin analogues are presently approved for use in the clinic as antitumor agents and several others are in clinical trials. Camptothecin possesses a novel mechanism of action involving the inhibition of DNA relaxation by DNA topoisomerase I, and more specifically the stabilization of a covalent binary complex formed between topoisomerase I and DNA. This review summarizes the current status of studies of the mechanism of action of camptothecin, including topoisomerase I inhibition and additional cellular responses. Modern synthetic approaches to camptothecin and several of the semi-synthetic methods are also discussed. Finally, a systematic evaluation of novel and important analogues of camptothecin and their contribution to the current structure-activity profile are considered.

A phase I clinical and pharmacokinetic study of the camptothecin glycoconjugate, BAY 38-3441, as a daily infusion in patients with advanced solid tumors

BACKGROUND

The aim of this study was to define the maximum tolerated dose (MTD), dose-limiting toxicity (DLT) and pharmacokinetics of the camptothecin glycoconjugate BAY 38-3441, administered as an infusion for 30 min on two separate schedules every 3 weeks.

PATIENTS AND METHODS

A total of 81 patients with advanced solid tumors were treated with BAY 38-3441 either at doses of 20, 40, 67, 100, 140, 210, 315, 470 and 600 mg/m2/day for 1 day every 3 weeks (single-dose schedule), or at doses of 126, 189, 246, 320 and 416 mg/m2/day once daily for three consecutive days every 3 weeks (3-day schedule). Plasma sampling was performed to characterize the pharmacokinetics of BAY 38-3441 and camptothecin with these schedules.

RESULTS

DLTs included renal toxicity, granulocytopenia and thrombocytopenia on the single-day schedule at doses > or = 470 mg/m2/day, and diarrhea and thrombocytopenia on the 3-day schedule at doses > or = 320 mg/m2/day. Other non-DLTs were gastrointestinal, dermatological and hematological. Pharmacokinetics of BAY 38-3441 and camptothecin appear to be dose-dependent, but not linear.

CONCLUSIONS

Renal toxicity was dose-limiting for BAY 38-3441 using 30-min infusions on the single-dose schedule. Dose escalation to 470 mg/m2/day is feasible using a 2-h infusion. However, because of the superior safety profile, we recommend the 3-day schedule for BAY 38-3441 at a dose of 320 mg/m2/day as 30-min infusions for further phase II studies.

Topoisomerases of kinetoplastid parasites as potential chemotherapeutic targets

The protozoan parasites Trypanosoma, Leishmania and Crithidia, which belong to the order kinetoplastidae, emerge from the most ancient eukaryotic lineages. The diversity found in the life cycle of these organisms must be directed by genetic events, wherein topoisomerases play an important role in cellular processes affecting the topology and organization of intracellular DNA. Topoisomerases are valuable as potential drug targets because they have indispensable function in cell biology. This review summarizes what is known about topoisomerase genes and proteins of kinetoplastid parasites and the roles of these enzymes as targets for therapeutic agents.

Novel vitamin E analogue and 9-nitro-camptothecin administered as liposome aerosols decrease syngeneic mouse mammary tumor burden and inhibit metastasis

PURPOSE

To test the anticancer properties of a nonhydrolyzable ether-linked acetic acid analogue of vitamin E, 2,5,7,8-tetramethyl-2R-(4R,8R, 12-trimethyltridecyl)chroman-6-yloxyacetic acid (alpha-TEA), and a derivative of camptothecin, 9-nitrocamptothecin (9-NC)singly and in combination against mouse mammary tumor cells (line 66 clone 4 stably transfected with green fluorescent protein; 66cl-4-GFP) cultured in vitro or transplanted subcutaneously into the inguinal region of female BALB/c mice to form established tumors.

METHODS

Following in vitro treatment of 66cl-4-GFP cells with alpha-TEA and suboptimal concentrations of 9-NC, singly or in combination, apoptosis was measured by morphological evaluation of nuclei stained with 4',6-diamidino-2-phenylindole (DAPI), and DNA synthesis arrest was measured by tritiated thymidine uptake. For in vivo analyses alpha-TEA and 9-NC, both water-insoluble compounds, were formulated into liposomes using dil-auroylphosphatidylcholine and administered by aerosol to deliver doses calculated to be 36 and 0.4 microg/mouse per day, respectively, (singly or each separately for combined treatments) 7 days per week.

RESULTS

Treatment of 66cl-4-GFP cells in culture for 3 days with a combination of alpha-TEA (10 microg/ml; singly produces 38% apoptosis), and suboptimal concentrations of 9-NC(15.6, 31.3, 62.5, or 125 ng/ml; singly produce 2-7% apoptosis), produced 47%, 58%, 64%, and 69% apoptosis. Likewise, combinations of alpha-TEA 9-NC inhibited DNA synthesis more than either agent administered singly. A significant reduction (P< 0.001)in growth of subcutaneous transplanted tumors was observed with liposome-formulated and aerosolized delivery of alpha-TEA + 9-NC to BALB/c mice. The incidence of macroscopic lung metastasis was 83% in control vs 8 % in alpha-TEA-, 9-NC-, or combination-treated mice. Fluorescence microscopic examination of lungs and axillary and brachial lymph nodes showed a statistically significant decrease in metastasis observed in alpha-TEA-,9-NC-, and combination- vs control-treated animals. Analyses of primary tumor tissue for proliferation and apoptosis showed treatment groups to have lower Ki-67 and higher terminal deoxynucleotidyl transferase-mediated nick end labeling, respectively. Treatments showed no measurable effects on two angiogenesis parameters,namely intratumoral blood volume as assessed by hemoglobin content and intratumoral blood vessel density as assessed with CD31 staining.

CONCLUSIONS

Combination treatments enhanced antiproliferative and proapoptotic activities in cell culture, and when formulated in liposomes and delivered via aerosolization to treat an aggressive and metastatic syngeneic murine mammary tumor, the combination treatment showed a significant reduction in tumor volume in comparison to either treatment alone. Mechanistically, it appears that neither enhanced apoptosis, reduced cell proliferation,nor reduced blood vessel density can fully account for the enhanced effects of the combination treatment.

An evaluation of transmembrane ion gradient-mediated encapsulation of topotecan within liposomes

Topotecan can be encapsulated in liposomes, however little is known about the role encapsulated counter ions play in drug loading efficiency and drug release. Using 1,2-distearoyl-sn-glycero-3 phosphatidylcholine and cholesterol liposomes (55:45 mole ratio), encapsulation was achieved using manganese ion gradients (MnSO(4) or MnCl(2)), with the addition of A23187, a divalent cation/proton exchanger, to maintain a pH gradient. This methodology was compared to procedures where the pH gradient was generated by use of encapsulated (NH(4))(2)SO(4) or citrate (300 mM, pH 3.5). All methods facilitated topotecan encapsulation. Liposomes prepared in the presence of the citrate and MnCl(2) (+A23187) exhibited reduced loading capacities. Liposomes prepared in the presence of (NH(4))(2)SO(4) and MnSO(4) (+A23187) could be used to generate liposomes exhibiting a drug-to-lipid ratio of 0.3 (wt/wt) with an encapsulation efficiency of >90%. In vitro drug release data suggested that the (NH(4))(2)SO(4) and MnSO(4) (+A23187) formulations released drug at a reduced rate. For these formulations, the drug release rates decreased as the drug-to-lipid ratio (wt/wt) increased from 0.1 to 0.2. Cryo-electron micrographs indicated that encapsulated topotecan precipitated as linear particles within liposomes. The stability of topotecan loaded liposomes appeared to be dependent on the presence of both a pH gradient and encapsulated sulfate.