The camptothecins

NSC606985, a novel camptothecin analog, induces apoptosis and growth arrest in prostate tumor cells

PURPOSE

Prostate cancer is a major cause of cancer mortality in American males. Once prostate cancer has metastasized, there is currently no curative therapy available. The development of effective agents is therefore a continuing effort to combat this disease. In the present study, the effects and potential mechanisms of NSC606985 (NSC), a water-soluble camptothecin analog, in prostate cancer cells were investigated.

METHODS

Prostatic tumor cells, DU-145, LNCaP and PC-3, were used for the study. Cell proliferation, cell cycle, cell apoptosis and caspase 3/7 activity were determined in the presence or absence of NSC. The levels of Bax and Bak, and the release of cytochrome c from mitochondria were analyzed by Western blot.

RESULTS

Treatment with NSC at nanomolar concentrations produced a time- and dose-dependent decrease in viable cell numbers of multiple prostate cancer cells. In DU-145 cells, NSC produced a time-and dose-dependent induction of cell apoptosis and cell cycle arrest as evidenced by cell morphological changes, increases in S-phase and sub-G1 cell fractions, an elevation of caspase 3/7 activity, DNA fragmentation and apoptotic cells. NSC increased the levels of apoptotic proteins, Bax and Bak, and induced a release of cytochrome c from mitochondria to cytosol in DU-145 cells. Co-administration of Z-VAD-FMK, a pan-caspase inhibitor, blocked NSC-induced caspase 3/7 activity and cell apoptosis without affecting NSC-induced cell cycle arrest. In contrast, co-administration of a PKCdelta inhibitor, rottlerin, had no significant effect on NSC induction of caspase activity, and slightly potentiated NSC-induced cell death. Furthermore, like camptothecin, a mutation of topoisomerase 1 that prevents the binding of camptothecin to the enzyme completely abolished the NSC effect in DU-145 cells.

CONCLUSION

The data obtained suggest that NSC is able to decrease cell growth, induce cell apoptosis and cause growth arrest in prostatic tumor cells, which may involve an interaction with topoisomerase 1 and an activation of mitochondrial apoptotic pathway.

A randomized phase II trial of pemetrexed plus irinotecan (ALIRI) versus leucovorin-modulated 5-FU plus irinotecan (FOLFIRI) in first-line treatment of locally advanced or metastatic colorectal cancer

BACKGROUND

This multicenter, randomized trial compared overall response rate between pemetrexed plus irinotecan (ALIRI) and leucovorin-modulated 5-fluorouracil plus irinotecan (FOLFIRI) in patients with advanced colorectal cancer. Secondary objectives included overall and progression-free survival, duration of response, toxicities, and biomarkers.

PATIENTS AND METHODS

ALIRI patients received pemetrexed 500 mg/m(2) and irinotecan 350 mg/m(2) with vitamin supplementation on day 1 of each 21-day cycle. FOLFIRI patients received irinotecan 180 mg/m(2) on days 1, 15, 29; on days 1, 2, 15, 16, 29, 30, patients received leucovorin 200 mg/m(2), bolus 5-fluorouracil 400 mg/m(2), and 5-fluorouracil 600 mg/m(2) as 22-hour infusion.

RESULTS

Of 132 patients randomly assigned, 130 patients (64 = ALIRI, 66 = FOLFIRI) received > or =1 dose of treatment. Response rates (ALIRI = 20.0%, FOLFIRI = 33.3%) were not significantly different between arms (p = 0.095). Progression-free survival was 5.7 months for ALIRI and 7.7 months for FOLFIRI (p < 0.001). Neutropenia, fatigue, diarrhea, nausea, and vomiting were the major toxicities. There were 5 drug-related deaths (ALIRI = 4, FOLFIRI = 1). Biomarker analysis failed to reveal that any of the 18 preselected genes were clearly associated with tumor response.

CONCLUSIONS

Neither efficacy nor safety improved on the ALIRI arm compared to the FOLFIRI arm. Progression-free survival on FOLFIRI was significantly longer compared to ALIRI. Potential biomarkers capable of predicting response to either regimen in advanced or metastatic colorectal carcinoma need further characterization.

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.

Synthesis and bioevaluation of 22-hydroxyacuminatine analogs

A series of 22-hydroxyacuminatine analogs was prepared by using different Friedländer condensations. Several of the new compounds were tested for antiproliferative activity on cancer cell lines and for topoisomerase I inhibitory activity.

Topotecan in cervical cancer

Recurrent and advanced cervical cancers are associated with high mortality and a lack of effective treatment options, especially for women who are poor candidates for surgery or radiation therapy. The broad clinical effectiveness and manageable toxicity of topotecan in other human malignancies as well as promising recent study results suggest that it is highly effective in treating cervical tumors. We therefore conducted a systematic review on the studies using topotecan in cervical cancer. Seven phase I-III clinical trials using topotecan, both as a single agent and in combination with cisplatin or paclitaxel, in patients with recurrent or advanced carcinoma of the cervix were reviewed. Data from two studies in which topotecan was used in combination with radiotherapy for induction therapy were also evaluated. Although single-agent cisplatin-based chemoradiotherapy is the standard of care for high-risk or locally advanced cervical cancer, topotecan, when used concurrently with cisplatin and/or radiation therapy, produces high objective response rates and prolonged survival. Gynecologic Oncology Group (GOG) Protocol 179 for the first time showed significantly improved overall survival and progression-free survival in a combination therapy for advanced cervical cancer compared to cisplatin alone. Recent data suggest that topotecan, when used concurrently with cisplatin, may be the new standard of care for the management of recurrent or advanced cervical cancer. Ongoing phase III studies (GOG-204, AGO-Zervix-1) will compare this combination with other cisplatin-containing and cisplatin-free combinations. Moreover, further evaluation of topotecan appears to be warranted in conjunction with radiotherapy and in the neoadjuvant setting as well as in combination with novel biologic agents.

Phase I trial of poly-L-glutamate camptothecin (CT-2106) administered weekly in patients with advanced solid malignancies

PURPOSE

CT-2106 is a 20(S)-camptothecin poly-L-glutamate conjugate. This linkage stabilizes the active lactone form of camptothecin and enhances aqueous solubility. In addition, poly-L-glutamate is postulated to increase tumor delivery of the active compound through enhanced permeability and retention effect in tumor. We studied a weekly schedule of CT-2106 in patients with refractory solid tumor malignancies.

EXPERIMENTAL DESIGN

CT-2106 was infused (10 min i.v. infusion) on days 1, 8, and 15 of each 28-day cycle. Plasma and urine were analyzed for total and unconjugated camptothecin by high-performance liquid chromatography equipped with a fluorescence detector. Toxicity and response assessments were done with Common Toxicity Criteria for Adverse Events version 3 and Response Evaluation Criteria in Solid Tumors, respectively.

RESULTS

Twenty-six patients were enrolled. Median age was 58 years (range, 36-83) and median number of doses was 6 (range, 1-9). The most frequent tumor type (50%) was melanoma. Dose limiting toxicities were thrombocytopenia and fatigue. A weekly dose of 25 mg/m2 given every 3 of 4 weeks was the maximum tolerated dose. The majority of grade 3 and 4 toxicities were hematologic. The pharmacokinetic profile of conjugated and unconjugated camptothecin showed a polyexponential decline with similar terminal half life (t1/2 range was 44-63 and 31-48 h for conjugated and unconjugated, respectively). Pharmacokinetics of conjugated and unconjugated camptothecin were dose and time independent in the tested dose range. Urinary excretion of conjugated and unconjugated camptothecin accounted for about 30% and 4% of the administered dose, respectively.

CONCLUSIONS

CT-2106 has a more manageable toxicity profile compared with unconjugated camptothecin. The maximum tolerated dose is 25 mg/m2 weekly given 3 of 4 weeks. This compound results in prolonged release of unconjugated camptothecin.

Batracylin (NSC 320846), a dual inhibitor of DNA topoisomerases I and II induces histone gamma-H2AX as a biomarker of DNA damage

Batracylin (8-aminoisoindolo [1,2-b]quinazolin-10(12H)-one; NSC320846) is an investigational clinical anticancer agent. Previous animal studies showed activity against solid tumors and Adriamycin-resistant leukemia. We initially sought to test the proposed Top2-mediated DNA cleavage activity of batracylin and identify potential biomarkers for activity. COMPARE analysis in the NCI-60 cell lines showed batracylin activity to be most closely related to the class of Top2 inhibitors. The 50% growth inhibition (GI50) value for batracylin in HT29 colon carcinoma cells was 10 micromol/L. DNA-protein cross-links, consistent with Top2 targeting, were measured by alkaline elution. DNA single-strand breaks were also detected and found to be protein associated. However, only a weak induction of DNA double-strand breaks was observed. Because batracylin induced almost exclusively DNA single-strand breaks, we tested batracylin as a Top1 inhibitor. Batracylin exhibited both Top1- and Top2alpha/beta-mediated DNA cleavage in vitro and in cells. The phosphorylation of histone (gamma-H2AX) was tested to measure the extent of DNA damage. Kinetics of gamma-H2AX "foci" showed early activation with low micromol/L concentrations, thus presenting a useful early biomarker of DNA damage. The half-life of gamma-H2AX signal reversal after drug removal was consistent with reversal of DNA-protein cross-links. The persistence of the DNA-protein complexes induced by batracylin was markedly longer than by etoposide or camptothecin. The phosphorylated DNA damage-responsive kinase, ataxia telangiectasia mutated, was also found activated at sites of gamma-H2AX. The cell cycle checkpoint kinase, Chk2, was only weakly phosphorylated. Thus, batracylin is a dual Top1 and Top2 inhibitor and gamma-H2AX could be considered a biomarker in the ongoing clinical trials.

Therapeutic efficacy of NSC606985, a novel camptothecin analog, in a mouse model of acute promyelocytic leukemia

Nanomolar concentrations of NSC606985, a novel camptothecin (CPT) analog, effectively induces apoptosis in vitro in acute myeloid leukemic (AML) cells. Here we investigated the potential therapeutic effects of NSC606985 on the mice model with acute promyelocytic leukaemia (APL), a unique subtype of AML. The results showed that NSC606985 at single dose rapidly eliminated the infiltration with apoptosis induction of leukemic cells in peripheral blood and tissues. Treatment of NSC606985 with two regimens, continuous monotherapy and intermittent long-term therapy, significantly prolonged the survival of leukemic mice with tumor regression. These results propose that NSC606985 warrants further preclinical and clinical investigations for AML treatment.

Irinotecan fluorouracil plus leucovorin is not superior to fluorouracil plus leucovorin alone as adjuvant treatment for stage III colon cancer: results of CALGB 89803

PURPOSE

Randomized studies have shown that irinotecan (CPT-11) extends survival in metastatic colorectal cancer patients when administered in second-line and when added to fluorouracil (FU) plus leucovorin (LV) in first-line therapy of metastatic colorectal cancer. When this study was initiated, FU plus LV was standard adjuvant treatment for stage III colon cancer. We evaluated the efficacy and safety of weekly bolus CPT-11 plus FU plus LV in the treatment of patients with completely resected stage III colon cancer.

METHODS

A total of 1,264 patients were randomly assigned to receive either standard weekly bolus FU plus LV regimen or weekly bolus CPT-11 plus FU plus LV. The primary end points of the study were overall survival (OS) and disease-free survival (DFS).

RESULTS

Treatment arms were well-balanced for patient characteristics and prognostic variables. There were no differences in either DFS or OS between the two treatment arms. Toxicity, including lethal toxicity, was significantly higher on the CPT-11 plus FU plus LV arm.

CONCLUSION

The addition of CPT-11 to weekly bolus FU plus LV did not result in improvement in DFS or OS in stage III disease, but did increase both lethal and nonlethal toxicity. This trial demonstrates that advances in the treatment of metastatic disease do not necessarily translate into advances in adjuvant treatment, and it reinforces the need for randomized controlled adjuvant studies.

Irinotecan Toxicity to Human Blood Cells in vitro: Relationship between Various Biomarkers

Toxic effects of the antineoplastic drug irinotecan on human blood cells at concentrations of 9.0 microg/ml and 4.6 microg/ml were evaluated in vitro. Using the alkaline and neutral comet assay significantly increased levels of primary DNA damage in lymphocytes were detected. The induction of apoptosis/necrosis, as determined by a fluorescent assay, was also notably increased. Cytogenetic outcomes of the treatment were assessed by the analysis of structural chromosome aberrations and fluorescence in situ hybridization. A significantly higher incidence of chromatid breaks and complex quadriradials was observed. Painted chromosomes 1, 2 and 4 were equally involved in translocations, but only the chromosome 1 was involved in the formation of quadriradials. Sister chromatid exchange analysis was performed in parallel with the analysis of lymphocyte proliferation kinetics. The higher concentration of irinotecan caused almost seven-time increase, while the lower one caused a five-time increase of the basal sister chromatid exchange frequency, accompanied with significant lowering of the lymphocyte proliferation index. Using the cytokinesis-block micronucleus assay, a dose-dependent increase in micronucleus frequency along with the formation of nuclear buds and nucleoplasmic bridges was noticed. Inhibitory effects of irinotecan on enzyme acetylcholinesterase (AChE) were studied in erythrocytes. An IC(50) value of 5.0 x 10(-7) was established. Irinotecan was found to be strong inhibitor of the acetylcholine hydrolysis and to cause a continuous decrease of catalytic activity of AChE. The results obtained on a single donor may contribute to the understanding of irinotecan toxicity, but further in vitro and in vivo studies are essential in order to clarify remaining issues, especially on possible inter-individual variability in genotoxic responses to the drug.

Control of Mycosphaerella graminicola on wheat seedlings by medical drugs known to modulate the activity of ATP-binding cassette transporters

Medical drugs known to modulate the activity of human ATP-binding cassette (ABC) transporter proteins (modulators) were tested for the ability to potentiate the activity of the azole fungicide cyproconazole against in vitro growth of Mycosphaerella graminicola and to control disease development due to this pathogen on wheat seedlings. In vitro modulation of cyproconazole activity could be demonstrated in paper disk bioassays. Some of the active modulators (amitriptyline, flavanone, and phenothiazines) increased the accumulation of cyproconazole in M. graminicola, suggesting that they reversed cyproconazole efflux. However, synergism between cyproconazole and modulators against M. graminicola on wheat seedlings could not be shown. Despite their low in vitro toxicity to M. graminicola, some modulators (amitriptyline, loperamide, and promazine) did show significant intrinsic disease control activity in preventive and curative foliar spray tests with wheat seedlings. The results suggest that these compounds have indirect disease control activity based on modulation of fungal ABC transporters essential for virulence and constitute a new class of disease control agents.

Preclinical antitumor activity of the oral platinum analog satraplatin

PURPOSE

Satraplatin is an orally available platinum analog. The purpose of this study was to better characterize satraplatin's preclinical antitumor efficacy in a variety of sensitive and resistant human tumor cell lines and in a prostate cancer xenograft model and to evaluate the effect of satraplatin on PSA expression and/or secretion in a prostate cancer cell line.

METHODS

Satraplatin and its primary metabolite JM-118 were preclinically tested for their cytotoxic activity in a range of cancer cells including: human prostate, those forming the NCI drug screening panel, and those resistant to anti-cancer drugs. Also, the antiproliferative efficacy of satraplatin was tested in vivo in a human prostate cancer model. The effect of satraplatin and JM-118 on PSA transcription was measured by quantitative real time PCR.

RESULTS

Satraplatin and JM-118 inhibited in vitro and in vivo the growth of prostate cancer cells in a dose-dependent fashion. The IC50 cytotoxicity values for satraplatin ranged from 1 to 3 microM for androgen-insensitive cells and was 11 microM for the androgen-sensitive cell line. Interestingly, JM-118 was up to 16-fold more potent than satraplatin. Oral administration of satraplatin to nude mouse PC-3 xenograft models inhibited the growth of these human tumors. Satraplatin had no direct effect on PSA transcription and the observed decrease in secreted PSA correlated with a decrease in cell number. When evaluated in the NCI drug-screening panel, satraplatin was most active in leukemia and small cell lung cancer cell lines. Both satraplatin and JM-118 were tested on cells resistant to chemotherapeutic agents. Satraplatin and JM-118 were equally active in the cisplatin-resistant A129cp80 ovarian carcinoma cell line, with activity comparable to that observed in the parent line. Neither expression of MDR1, BCRP, MRP1, nor altered tubulin or topoisomerase I were found to mediate resistance to satraplatin or JM-118. Although these resistance mechanisms contribute to drug resistance for a number of chemotherapeutics, they do not appear to play a role in satraplatin resistance.

CONCLUSIONS

These results demonstrate that satraplatin and JM-118 have preclinical antitumor activity in human prostate cancer and other tumor types as well, including several cell lines displaying drug resistance to cisplatin, docetaxel and mitoxantrone. In addition, the results suggest that PSA should be further evaluated as a relevant marker of clinical response in patients with prostate cancer treated with satraplatin.

A Phase I dose-finding study using an innovative sequential biweekly schedule of irinotecan followed 24 hours later by capecitabine

BACKGROUND

Irinotecan and capecitabine have a broad spectrum of activity in human malignancy and are synergistic in an animal model when irinotecan precedes capecitabine.

PATIENTS AND METHODS

A Phase I design of the combination of irinotecan IV Day 1 with capecitabine on Days 2-8 every 2 weeks was evaluated in 27 adult patients with solid tumors. Two sequential schema were used: Arm A fixed the dose of irinotecan at 100 mg/m(2) and escalated capecitabine in cohorts, and arm B fixed the dose of capecitabine at 750 mg/m(2) PO BID and escalated the dosage of irinotecan.

RESULTS

Neutropenia was dose limiting with nausea and diarrhea as the most common nonhematological toxicities. Significant interpatient variation in toxicity occurred despite uniform dosing. No Grade IV toxicities were encountered. Grade III toxicity occurred in first cycle in 15 percent (3/20) patients in arm A and 29 percent (2/7) of patients in arm B. All toxicities were reversible. Repetitive dosing was feasible with prolonged disease stabilization in 8 patients.

CONCLUSIONS

The suggested Phase II dose of this combination and schedule is irinotecan 100 mg/m(2) and capecitabine 1000 mg/m(2) BID. Some patients tolerated a capecitabine dose as high as 1250 mg/m(2) BID.

Inhibition of topoisomerase I cleavage activity by thiol-reactive compounds: importance of vicinal cysteines 504 and 505

DNA topoisomerase I (Top1) is a nuclear enzyme that plays a crucial role in the removal of DNA supercoiling associated with replication and transcription. It is also the target of the anticancer agent, camptothecin (CPT). Top1 contains eight cysteines, including two vicinal residues (504 and 505), which are highly conserved across species. In this study, we show that thiol-reactive compounds such as N-ethylmaleimide and phenylarsine oxide can impair Top1 catalytic activity. We demonstrate that in contrast to CPT, which inhibits Top1-catalyzed religation, thiolation of Top1 inhibited the DNA cleavage step of the reaction. This inhibition was more pronounced when Top1 was preincubated with the thiol-reactive compound and could be reversed in the presence of dithiothreitol. We also established that phenylarsine oxide-mediated inhibition of Top1 cleavage involved the two vicinal cysteines 504 and 505, as this effect was suppressed when cysteines were mutated to alanines. Interestingly, mutation of Cys-505 also altered Top1 sensitivity to CPT, even in the context of the double Cys-504 to Cys-505 mutant, which relaxed supercoiled DNA with a comparable efficiency to that of wild-type Top1. This indicates that cysteine 505, which is located in the lower Lip domain of human Top1, is critical for optimal poisoning of the enzyme by CPT and its analogs. Altogether, our results suggest that conserved vicinal cysteines 504 and 505 of human Top1 play a critical role in enzyme catalytic activity and are the target of thiol-reactive compounds, which may be developed as efficient Top1 catalytic inhibitors.

2-(3-Fluorophenyl)-6-methoxyl-4-oxo-1,4-dihydroquinoline-3-carboxylic acid (YJC-1) induces mitotic phase arrest in A549 cells

A 2-phenyl-4-quinolone (2-PQ) derivative, 2-(3-fluorophenyl)-6-methoxyl-4-oxo-1,4-dihydroquinoline-3-carboxylic acid (YJC-1), was synthesized in our laboratory. In this study, we delineated the growth-inhibitory effect of YJC-1 in human lung carcinoma A549 cells. YJC-1 inhibited cell growth with an IC(50) value of about 4.8 microM via microtubule polymerization, causing growth arrest in the mitotic phase. Immunoblotting analysis revealed a dramatic induction of cyclin-dependent kinase (CDK) inhibitor p21(Cip1/Waf1) and down-regulation of Cdc25C phosphatase to inhibit the protein expression of cyclin B1 and CDK1. We also found that YJC-1 induced a profound time-dependent elevation in p21(Cip1/Waf1) gene expression in comparison with the negative control. In vivo, we also found that YJC-1 significantly suppressed tumor growth in mice inoculated with A549 cells. These findings suggest that YJC-1 can suppress A549 cell growth via mitotic phase arrest.

A Phase I and Pharmacokinetic Study of Pemetrexed Plus Irinotecan in Patients with Advanced Solid Malignancies

PURPOSE

The main objectives of this phase I and pharmacokinetic, open-label study were to characterize the principal toxicities and determine the maximum tolerated dose of the multitargeted antifolate pemetrexed administered in combination with irinotecan. The study also sought to detect major pharmacokinetic drug-drug interactions between these agents and preliminary evidence of antitumor activity in patients with advanced solid malignancies.

EXPERIMENTAL DESIGN

Pemetrexed was administered as a 10-min i.v. infusion followed by irinotecan given i.v. over 90 min every 3 weeks to patients with advanced solid malignancies. The study objectives were first pursued in heavily pretreated patients and then in lightly pretreated patients who also received vitamin supplementation.

RESULTS

Twenty-three heavily pretreated patients enrolled in the first stage of the study, and the maximum tolerated dose level of pemetrexed/irinotecan without vitamin supplementation was 400/250 mg/m(2); further dose escalation was precluded by severe neutropenia that was protracted and/or associated with fever. In the second stage of the study, 28 lightly pretreated patients were administered pemetrexed/irinotecan with vitamin supplementation; these patients tolerated pemetrexed/irinotecan at a dose level of 500/350 mg/m(2), which reflected clinically relevant single-agent doses of both agents. No major pharmacokinetic interactions between the agents were evident. Four patients, two patients each with colorectal cancer refractory to fluoropyrimidines and advanced mesothelioma, had partial responses.

CONCLUSIONS

The pemetrexed/irinotecan regimen is well tolerated in patients with advanced solid malignancies at clinically relevant single-agent doses. The recommended dose level of pemetrexed/irinotecan for subsequent disease-directed evaluations involving lightly pretreated patients is 500/350 mg/m(2) every 3 weeks with vitamin supplementation.

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.

Increased expression and activity of repair genes TDP1 and XPF in non-small cell lung cancer

Resistance to camptothecin (CPT), a topoisomerase I (Top1) inhibitor, is frequently encountered in non-small cell lung cancer (NSCLC) and CPT resistance is linked with TDP1, an enzyme capable of cleaving the covalent linkage between stabilized Top1 with DNA. The aim of this study is to evaluate the in vivo expression level of TDP1, as well as parallel repair pathway components XPF and MUS81, in primary NSCLC. We collected 30 un-matched and 4 NSCLC samples matched with normal lung tissue and 8 samples of non-neoplastic lung tissue from patients with and without lung cancer, and determined the protein expression of these three genes using Western blot and TDP1 activity by a specific enzymatic assay. Both TDP1 and XPF were overexpressed in over 50% of NSCLC tissues, with wide ranges of expression levels. MUS81 did not exhibit alteration in expression. Overexpression of TDP1 and XPF is common in NSCLC, and is therefore of interest as a possible contributor to drug resistance in NSCLC.

Drugs, their targets and the nature and number of drug targets

What is a drug target? And how many such targets are there? Here, we consider the nature of drug targets, and by classifying known drug substances on the basis of the discussed principles we provide an estimation of the total number of current drug targets.

Rubitecan

The only approved camptothecins for use in patients to date (topotecan and irinotecan) are delivered intravenously. Thus, an oral camptothecin analogue that would provide the convenience of oral delivery with the flexibility for a variety of prolonged treatment schedules would be advantageous. Rubitecan is an orally available camptothecin analogue that also has potential for delivery transdermally or by inhalation. Like all of the camptothecins, its antitumour activity is mediated through the inhibition of DNA topoisomerase I, which is involved in relaxing supercoiled DNA, which is important for the process of DNA replication and RNA transcription. Rubitecan exists in equilibrium as 9-nitro-camptothecin (9-NC) and 9-amino-camptothecin (9-AC), a metabolite that is thought to be active although it failed in clinical trials. Both 9-NC and 9-AC contain a lactone ring that is required for optimal activity with the carboxylic acid (open ring) forms being significantly less active or inactive. A more acidic environment favours the lactone ring structure, whereas neutral or basic conditions favour the conversion to the carboxylic acid form. In addition to issues of lactone ring stability at physiological pH (true for all of the camptothecin analogues), there is pharmacokinetic variability that has had to be dealt with during the development of rubitecan. Preclinically, rubitecan has shown activity against a broad spectrum of tumour types in in vitro and in vivo human tumour xenograft models. Frustratingly, the level of activity of an agent in preclinical models has not always translated into similar activity against human tumours in clinical trials. To date, with the exception of pancreatic and possibly ovarian cancer, rubitecan has had disappointing activity against a number of other solid tumours in relatively small Phase I/II trials; however, it has shown sufficient activity against pancreatic cancer, a malignancy that remains difficult to treat, to continue to be evaluated in clinical trials for this indication. Results of clinical trials in the next few years should determine whether rubitecan can find a role in cancer therapy.

Targeting atypical trypanosomatid DNA topoisomerase I

Tropical diseases produced by kinetoplastid protozoa are among humanity's costliest banes, owing to high mortality and the economic burden resulting from morbidity. Drug resistant strains of parasites, together with insecticide-resistant vectors, are contributing to their increased prevalence in the developing world. Their extension now threatens industrialized countries because of opportunistic infections in immuno-compromised individuals. Current chemotherapy is expensive, has undesirable side effects and, in many patients, is only marginally effective. Based on the clinical success of camptothecin derivatives as anticancer agents, DNA topoisomerases have been identified as targets for drug development. The substantial differences in homology between trypanosome and leishmania DNA topoisomerase IB compared with the human form provides a new lead in the study of the structural determinants that can be targeted.

Defective Mre11-dependent activation of Chk2 by ataxia telangiectasia mutated in colorectal carcinoma cells in response to replication-dependent DNA double strand breaks

The Mre11.Rad50.Nbs1 (MRN) complex binds DNA double strand breaks to repair DNA and activate checkpoints. We report MRN deficiency in three of seven colon carcinoma cell lines of the NCI Anticancer Drug Screen. To study the involvement of MRN in replication-mediated DNA double strand breaks, we examined checkpoint responses to camptothecin, which induces replication-mediated DNA double strand breaks after replication forks collide with topoisomerase I cleavage complexes. MRN-deficient cells were deficient for Chk2 activation, whereas Chk1 activation was independent of MRN. Chk2 activation was ataxia telangiectasia mutated (ATM)-dependent and associated with phosphorylation of Mre11 and Nbs1. Mre11 complementation in MRN-deficient HCT116 cells restored Chk2 activation as well as Rad50 and Nbs1 levels. Conversely, Mre11 down-regulation by small interference RNA (siRNA) in HT29 cells inhibited Chk2 activation and down-regulated Nbs1 and Rad50. Proteasome inhibition also restored Rad50 and Nbs1 levels in HCT116 cells suggesting that Mre11 stabilizes Rad50 and Nbs1. Chk2 activation was also defective in three of four MRN-proficient colorectal cell lines because of low Chk2 levels. Thus, six of seven colon carcinoma cell lines from the NCI Anticancer Drug Screen are functionally Chk2-deficient in response to replication-mediated DNA double strand breaks. We propose that Mre11 stabilizes Nbs1 and Rad50 and that MRN activates Chk2 downstream from ATM in response to replication-mediated DNA double strand breaks. Chk2 deficiency in HCT116 is associated with defective S-phase checkpoint, prolonged G2 arrest, and hypersensitivity to camptothecin. The high frequency of MRN and Chk2 deficiencies may contribute to genomic instability and therapeutic response to camptothecins in colorectal cancers.

Synthesis and activity of a folate peptide camptothecin prodrug

A folate receptor targeted camptothecin prodrug was synthesized using a hydrophilic peptide spacer linked to folate via a releasable disulfide carbonate linker. The conjugate was found to possess high affinity for folate receptor-expressing cells and inhibited cell proliferation in human KB cells with an IC(50) of 10nM. Activity of the prodrug was completely blocked by excess folic acid, demonstrating receptor-mediated uptake.

Evaluation of the toxic potentials of a new camptothecin anticancer agent CKD-602 on fertility and early embryonic development in rats

This study examined the potential adverse effects of a new camptothecin anticancer agent, CKD-602, on the fertility and early embryonic development of Sprague-Dawley rats. Ninety-six rats of each gender were divided into four groups: three treatment groups and a control group. CKD-602 was administered intravenously to male rats at 0, 4.7, 14, and 42 microg/kg from 63 days prior to mating until the end of the mating period, and to female rats from 14 days before mating until day 6 of gestation. All the males were sacrificed after the end of the 14-day mating period, while all the females were subjected to a caesarean section on day 15 of gestation. In the high dose group, a high incidence of hair loss was observed in both genders. A decrease in the level of food consumption, followed by a decrease in body weight gain was also observed in both genders. At the scheduled necropsy, the gross postmortem examinations revealed an increase in the incidence of thymic atrophy, paleness of the thoracic and abdominal organs in both genders and an increase in the serum testosterone concentration. In addition, there was a decrease in the thymus weight of the males and an increase in the liver, spleen, kidneys, lung, and heart weights of the females. There was an increase in the number of fetal deaths and post-implantation losses as well as a decrease in the litter size found at the caesarean section of the dams. No treatment-related effect on the histopathological findings, sexual cycle, pre-coital time, mating index, fertility index, pregnancy index, and sperm parameters was observed. There were no adverse effects on the general findings and reproductive performance of the parent animals and early embryonic development in the low and medium dose groups. Overall, the no-observed-adverse-effect levels (NOAELs) of CKD-602 are believed to be 14 microg/kg for both general toxicity and early embryonic development, and more than 42 microg/kg for the reproductive performance of the parent animals.

Reproductive toxicity evaluation of a new camptothecin anticancer agent, CKD-602, in pregnant/lactating female rats and their offspring

CKD-602 is a camptothecin anticancer agent that was recently developed by the Chong Kun Dang Pharmaceutical Co. (Seoul, Korea). This study examined the potential adverse effects of CKD-602 on pregnancy, delivery, and lactation in female Sprague-Dawley rats as well as on the pre- and postnatal development of their offspring. One hundred pregnant females were divided into four groups: three treatment groups and a control group. CKD-602 was administered once daily by intravenous bolus injection to female rats at doses of 0, 5.7, 17, or 51 microg/kg/day from gestational day 6, through to parturition and throughout the period of lactation up to weaning [lactational day (LD) 21]. All the dams were sacrificed on LD 22 after weaning. The clinical signs, mortality, body weight change, food consumption, physical development, and behavioral function were evaluated in their progeny. When the exposed offspring reached maturity (postnatal day 70), their reproductive performance was assessed. In the high-dose group, suppressed body weight and a decrease in the amount of food consumption were observed in the dams during both the gestation and lactation periods. An increase in the incidence of thymic atrophy, decreased liver and ovary weight, and an increase in the weight of the spleen were also observed in the dams at the scheduled necropsy. In addition, an increase in the number of stillborn and postnatal mortality, a decrease in the live litter size, and a delay in physical development were observed in the F1 offspring. Teratological examinations showed an increase in the incidence of congenital anomalies in both the F1 offspring and F2 fetuses. In the medium dose group, only slight maternal toxicity including suppressed body weight and decreased food consumption was observed. There were no treatment-related effects on the maternal function and pre- and postnatal development in the low dose group. The no-observed-adverse-effect level (NOAEL) of CKD-602 for the dams are considered to be 5.7 microg/kg/day, however, the NOAEL for their offspring are estimated to be 17 microg/kg/day.

St. John's wort attenuates irinotecan-induced diarrhea via down-regulation of intestinal pro-inflammatory cytokines and inhibition of intestinal epithelial apoptosis

Diarrhea is a common dose-limiting toxicity associated with cancer chemotherapy, in particular for drugs such as irinotecan (CPT-11), 5-fluouracil, oxaliplatin, capecitabine and raltitrexed. St. John's wort (Hypericum perforatum, SJW) has anti-inflammatory activity, and our preliminary study in the rat and a pilot study in cancer patients found that treatment of SJW alleviated irinotecan-induced diarrhea. In the present study, we investigated whether SJW modulated various pro-inflammatory cytokines including interleukins (IL-1beta, IL-2, IL-6), interferon (IFN-gamma) and tumor necrosis factor-alpha (TNF-alpha) and intestinal epithelium apoptosis in rats. The rats were treated with irinotecan at 60 mg/kg for 4 days in combination with oral SJW or SJW-free control vehicle at 400 mg/kg for 8 days. Diarrhea, tissue damage, body weight loss, various cytokines including IL-1beta, IL-2, IL-6, IFN-gamma and TNF-alpha and intestinal epithelial apoptosis were monitored over 11 days. Our studies demonstrated that combined SJW markedly reduced CPT-11-induced diarrhea and intestinal lesions. The production of pro-inflammatory cytokines such as IL-1beta, IFN-gamma and TNF-alpha was significantly up-regulated in intestine. In the mean time, combined SJW significantly suppressed the intestinal epithelial apoptosis induced by CPT-11 over days 5-11. In particular, combination of SJW significantly inhibited the expression of TNF-alpha mRNA in the intestine over days 5-11. In conclusion, inhibition of pro-inflammatory cytokines and intestinal epithelium apoptosis partly explained the protective effect of SJW against the intestinal toxicities induced by irinotecan. Further studies are warranted to explore the potential for STW as an agent in combination with chemotherapeutic drugs to lower their dose-limiting toxicities.

Multicenter phase II study of fixed sequences of capecitabine combined with oxaliplatin or irinotecan in patients with previously untreated metastatic colorectal cancer

PURPOSE

The purpose of this study was to evaluate the antitumor activity and toxicity of fixed sequences of capecitabine/oxaliplatin followed by capecitabine/irinotecan in patients with previously untreated metastatic colorectal cancer.

PATIENTS AND METHODS

Adult patients with histologically confirmed, previously untreated, nonresectable, locally advanced or metastatic colorectal adenocarcinoma were enrolled in the study. Patients were treated as follows: capecitabine (1000 mg/m2 orally twice daily) on days 1-14 and oxaliplatin (130 mg/m2 2-hour intravenous infusion) on day 1, followed by capecitabine (1000 mg/m2 twice daily) on days 1-14 and irinotecan (240 mg/m2 1.5-hour intravenous infusion) on day 1. Each combination was administered every 21 days during 4 consecutive cycles followed by the alternating sequence to a maximum of 16 cycles.

RESULTS

A total of 35 eligible patients have been included in this ongoing study. Response rate (complete responses plus partial responses) was 37.1%. With a median follow-up of 9.5 months, the median time to disease progression and overall survival were 7.4 months and 16.4 months, respectively. Treatment was well tolerated, with only 6% of the patients developing grade 3/4 neurotoxicity. However, the low number of patients treated beyond 4 cycles limits the interpretation of the data.

CONCLUSION

The preliminary results from this ongoing study suggest the feasibility of this strategy, which resulted in promising antitumor activity with less neurotoxicity.

A Mechanistic Study on Reduced Toxicity of Irinotecan by Coadministered Thalidomide, a Tumor Necrosis Factor-α Inhibitor

Dose-limiting diarrhea and myelosuppression compromise the success of irinotecan (7-ethyl-10-[4-[1-piperidino]-1-piperidino]carbonyloxycamptothecin) (CPT-11)-based chemotherapy. A recent pilot study indicates that thalidomide attenuates the toxicity of CPT-11 in cancer patients. This study aimed to investigate whether coadministered thalidomide modulated the toxicities of CPT-11 and the underlying mechanisms using several in vivo and in vitro models. Diarrhea, intestinal lesions, cytokine expression, and intestinal epithelial apoptosis were monitored. Coadministered thalidomide (100 mg/kg i.p. for 8 days) significantly attenuated body weight loss, myelosuppression, diarrhea, and intestinal histological lesions caused by CPT-11 (60 mg/kg i.v. for 4 days). This was accompanied by inhibition of tumor necrosis factor-alpha, interleukins 1 and 6 and interferon-gamma, and intestinal epithelial apoptosis. Coadministered thalidomide also significantly increased the systemic exposure of CPT-11 but decreased that of SN-38 (7-ethyl-10-hydroxycampothecin). It significantly reduced the biliary excretion and cecal exposure of CPT-11, SN-38, and SN-38 glucuronide. Thalidomide hydrolytic products inhibited hydrolysis of CPT-11 in rat liver microsomes but not in primary rat hepatocytes. In addition, thalidomide and its major hydrolytic products, such as phthaloyl glutamic acid (PGA), increased the intracellular accumulation of CPT-11 and SN-38 in primary rat hepatocytes. They also significantly decreased the transport of CPT-11 and SN-38 in Caco-2 and parental MDCKII cells. Thalidomide and PGA also significantly inhibited P-glycoprotein (PgP/MDR1), multidrug resistance-associated protein (MRP1)- and MRP2-mediated CPT-11 and SN-38 transport in MDCKII cells. These results provide insights into the pharmacodynamic and pharmacokinetic mechanisms for the protective effects of thalidomide against CPT-11-induced intestinal toxicity.

Multiple binding modes of the camptothecin family to DNA oligomers

The binding constants of camptothecin, topotecan and its lactone ring-opened carboxylate derivative to DNA octamers were measured by UV and NMR spectroscopy. The self-association of topotecan (TPT) was also measured. The carboxylate form of TPT binds in the same way as the lactone, but more weakly. Titration of TPT into d(GCGATCGC)2 shows a preferred location stacked onto the terminal G1 base. However, the intermolecular NOEs cannot be reconciled with a single conformation of the complex, and suggest a model of a limited number of conformations in fast exchange. MD calculations on four pairs of starting structures with TPT stacked onto the G1-C8 base pair in different orientations were therefore performed. The use of selected experimental "docking" restraints yielded ten MD trajectories covering a wide conformational space. From a combination of calculated free energies, NOEs and chemical shifts, some of the structures produced could be eliminated, and it is concluded that the data are consistent with two major families of conformations in fast exchange. One of these is the conformation found in a crystal of a TPT/DNA/topoisomerase I ternary complex [Proc. Natl. Acad. Sci. USA 2002, 99, 15 387-15 392].

A novel norindenoisoquinoline structure reveals a common interfacial inhibitor paradigm for ternary trapping of the topoisomerase I-DNA covalent complex

We show that five topoisomerase I inhibitors (two indenoisoquinolines, two camptothecins, and one indolocarbazole) each intercalate between the base pairs flanking the cleavage site generated during the topoisomerase I catalytic cycle and are further stabilized by a network of hydrogen bonds with topoisomerase I. The interfacial inhibition paradigm described for topoisomerase I inhibitors can be generalized to a variety of natural products that trap macromolecular complexes as they undergo catalytic conformational changes that create hotspots for drug binding. Stabilization of such conformational states results in uncompetitive inhibition and exemplifies the relevance of screening for ligands and drugs that stabilize ("trap") these macromolecular complexes.

Triterpenoids and ellagic acid derivatives from in vitro cultures of Camptotheca acuminata Decaisne

The metabolic profile of secondary products in calli and cell suspension cultures of Camptotheca acuminata Decaisne was investigated and compared to that of the leaves and roots taken from the plant. Neither in vitro system produced the anticancer quinoline alkaloid camptothecin (CPT); they accumulated discrete quantities of polyhydroxylated triterpenoids, different from those found in the plant organs, and ellagic acid derivatives. Nine ellagic acid derivatives (1a-1d and 2a-2e) and eight triterpenoid acids (3a-3e and 4a-4c) were isolated and characterised. All the identified triterpenes were related to ursane- or oleanane-type skeletons and their concentrations rose to 4.5% in suspended cells.

Phase II study of rubitecan, an oral camptothecin in patients with advanced colorectal cancer who have failed previous 5-fluorouracil based chemotherapy

BACKGROUND

Rubitecan (RFS-2000, 9NC, Orathecin) is an orally bioavailable camptothecin analogue, with evidence of preclinical activity in colon cancer cell lines. We evaluated oral rubitecan (5 days on, 2 days rest per week) on a continuous schedule, in patients with advanced colorectal cancer (CRC), who progressed after 5-fluorouracil based chemotherapy.

PATIENTS AND RESULTS

Fourteen eligible patients were treated with rubitecan at 1.5 mg/m2/day on a 5 day/week continuous schedule. Therapy was well tolerated with most adverse events in the mild to moderate category. Grade 3/4 toxicity consisting of anemia, diarrhea and elevated bilirubin was seen in 4 patients. No responses were seen in 13 evaluable patients. Overall median survival (95% confidence interval) was 10.1 (range 3.1-12.6) months, and median time to progression was 2.1 months.

CONCLUSIONS

Administration of rubitecan was well tolerated, but this schedule does not appear to have clinical activity in patients with advanced previously treated CRC.

Sensitization to gimatecan-induced apoptosis by tumor necrosis factor-related apoptosis inducing ligand in prostate carcinoma cells

Since the intrinsic resistance of prostate carcinoma likely reflects a low susceptibility to drug-induced apoptosis, in this study we explored the possibility of sensitizing prostate carcinoma cells to apoptosis by combination of TRAIL with camptothecins. Indeed, these agents are known to activate different pathways of apoptosis. Topotecan- and gimatecan induced moderate up-regulation of TRAIL-R1 and -R2 which resulted in a different cell response to the combination in androgen-independent cells (DU-145 and PC-3). In DU-145 cells apoptosis was increased by lower TRAIL concentrations and was earlier than in PC-3 cells, as shown using Annexin V-binding assay. The relative resistance of PC-3 cells to drug-induced apoptosis was associated with constitutive Akt activation, higher levels of cFLIP-L and Bcl-2, and lower levels of Bax. The different expression/activation of apoptosis-related factors appears to influence the sensitization of prostate carcinoma cells by TRAIL. Potentiation of camptothecin-induced apoptosis by TRAIL appears dependent on cooperation between extrinsic and intrinsic pathways, as documented by loss of the sensitization to apoptosis following reduction of caspase 8 after small interfering RNA transfection. The efficacy of the approach may be critically dependent on the intrinsic susceptibility to apoptosis of different tumors. These observations support that the activation of multiple signals could enhance apoptotic response and suggest the therapeutic interest of the TRAIL/camptothecin combination.

DNA topoisomerase I from parasitic protozoa: A potential target for chemotherapy

The growing occurrence of drug resistant strains of unicellular prokaryotic parasites, along with insecticide-resistant vectors, are the factors contributing to the increased prevalence of tropical diseases in underdeveloped and developing countries, where they are endemic. Malaria, cryptosporidiosis, African and American trypanosomiasis and leishmaniasis threaten human beings, both for the high mortality rates involved and the economic loss resulting from morbidity. Due to the fact that effective immunoprophylaxis is not available at present; preventive sanitary measures and pharmacological approaches are the only sources to control the undesirable effects of such diseases. Current anti-parasitic chemotherapy is expensive, has undesirable side effects or, in many patients, is only marginally effective. Under this point of view molecular biology techniques and drug discovery must walk together in order to find new targets for chemotherapy intervention. The identification of DNA topoisomerases as a promising drug target is based on the clinical success of camptothecin derivatives as anticancer agents. The recent detection of substantial differences between trypanosome and leishmania DNA topoisomerase IB with respect to their homologues in mammals has provided a new lead in the study of the structural determinants that can be effectively targeted. The present report is an up to date review of the new findings on type IB DNA topoisomerase in unicellular parasites and the role of these enzymes as targets for therapeutic agents.

Cetuximab and irinotecan interact synergistically to inhibit the growth of orthotopic anaplastic thyroid carcinoma xenografts in nude mice

PURPOSE

Anaplastic thyroid carcinoma (ATC) remains one of the most lethal known human cancers. Targeted molecular therapy with cetuximab, a monoclonal antibody against epidermal growth factor receptor, offers new treatment potentials for patient with ATC. Cetuximab has also been reported to have synergistic effects when combined with irinotecan, a topoisomerase inhibitor. Therefore, we hypothesized that cetuximab and irinotecan would be effective in inhibiting the growth and progression of ATC in a murine orthotopic model.

EXPERIMENTAL DESIGN

The in vitro antiproliferative effects of cetuximab and irinotecan on ATC cell line ARO were examined. We also studied the in vivo effects of cetuximab and irinotecan on the growth, invasion, and metastasis of orthotopic ATC tumors in nude mice. The in vivo antitumor efficacy of cetuximab/irinotecan combination was also compared with that of doxorubicin.

RESULTS

Cetuximab alone did not show any antiproliferative or proapoptotic effect on this cell line. However, when combined with irinotecan, cetuximab potentiated the in vitro antiproliferative and proapoptotic effect of irinotecan. Cetuximab, irinotecan, and cetuximab/irinotecan combination resulted in 77%, 79%, and 93% in vivo inhibition of tumor growth, respectively. Incidences of lymph node metastasis, laryngeal invasion, and tumor microvessel density were also significantly decreased in these treatment groups. Furthermore, the cetuximab/irinotecan combination was significantly more effective than doxorubicin in inhibiting the growth of orthotopic ATC xenografts.

CONCLUSIONS

Combination therapy with cetuximab/irinotecan inhibits the growth and progression of orthotopic ATC xenografts in nude mice. Given the lack of curative options for patients with ATC, combination therapy with cetuximab and irinotecan treatment warrants further study.

Phase II study of irinotecan and docetaxel in patients with previously treated non-small cell lung cancer: an Alpe-Adria Thoracic Oncology Multidisciplinary group study (ATOM 007)

This study was designed to evaluate the activity and tolerability of irinotecan and docetaxel in patients with previously treated non-small cell lung cancer (NSCLC). Eligibility included recurrent or progressive NSCLC, previous chemotherapy, age > or = 18 years, ECOG PS < or = 2. Treatment consisted of irinotecan (160 mg/m2 i.v.), followed by docetaxel (65 mg/m2 i.v.) on day 1 of a 21-day cycle, for a maximum of 6 cycles. Forty patients were enrolled. Median age was 60 years and median ECOG PS was 1. All patients were evaluable for toxicity and 31 (78%) were evaluable for response. A total of 125 cycles was administered (median, 3; range, 1-6). Most common grade 3-4 toxicities were neutropenia (62%), neutropenic fever (22%), and diarrhea (32%). Response rate was 10%; a further 40% of patients achieved stable disease. All responses were observed in patients with ECOG PS < or = 1, age <70 years, and who had received only one prior chemotherapy regimen. Median time to progression was 2.8 months and median survival was 7.4 months. Because of significant toxicity and limited activity, further investigation of irinotecan plus docetaxel in second line NSCLC is not recommended.

Synergistic effects of protein tyrosine kinase inhibitor genistein with camptothecins against three cell lines in vitro

Genistein, a natural isoflavone product has been shown to induce cellular death and increase the apoptotic cell death induced by several DNA-damaging stimuli. We have explored the combined effect of genistein and camptothecins against three cell lines, HeLa (cervical cancer), OAW-42 (ovarian cancer) and L929 (normal fibroblasts). Combined effect was estimated in 96-well plates using the SRB method and median-effect analysis. Addition of genistein synergistically increased the antiproliferative affect of camptothecins, inhibiting the camptothecin-induced G2/M arrest and increasing the apoptotic cell population. In HeLa cells, genistein inhibited CDK1 phosphorylation after irinotecan treatment. Thus, abrogation of the G2/M checkpoint control by genistein may be a useful maneuver to increase cytotoxicity of agents that damage DNA and inhibit cell-cycle progression in the G2/M boundary.

Recent data with anti-epidermal growth factor receptor antibodies and irinotecan in colon cancer

The epidermal growth factor receptor (EGFR) is overexpressed in the majority of colorectal cancers. It is the target for a class of agents at the forefront of development for the treatment of colorectal cancer, ie, the anti-EGFR monoclonal antibodies, which include cetuximab, panitumumab, and matuzumab. At present, cetuximab is the furthest along in terms of established efficacy in the treatment of metastatic or inoperable disease and is licensed for the treatment of patients with irinotecan-refractory colorectal cancer. This article reviews the recent evidence supporting the combination of these anti-EGFR agents with the cytotoxic chemotherapeutic agent irinotecan.

Novel, efficient total synthesis of natural 20(S)-camptothecin

Enantiopure 20(S)-camptothecin has been prepared from a known hydroxypyridone through a novel approach that involves a Claisen rearrangement, an asymmetric nucleophilic ethylation, a Heck coupling and a Friedländer condensation as the key transformations.

Concise synthesis of 22-hydroxyacuminatine, cytotoxic camptothecinoid from Camptotheca acuminata, by pyridone benzannulation

A short, efficient synthesis of 22-hydroxyacuminatine, starting from a readily accessible hydroxy pyridone, is presented; key steps include a Heck coupling with methyl pentadienoate, a flash vacuum pyrolytic cyclization, and a Friedländer condensation.

Phosphorylation of BLM, dissociation from topoisomerase IIIalpha, and colocalization with gamma-H2AX after topoisomerase I-induced replication damage

Topoisomerase I-associated DNA single-strand breaks selectively trapped by camptothecins are lethal after being converted to double-strand breaks by replication fork collisions. BLM (Bloom's syndrome protein), a RecQ DNA helicase, and topoisomerase IIIalpha (Top3alpha) appear essential for the resolution of stalled replication forks (Holliday junctions). We investigated the involvement of BLM in the signaling response to Top1-mediated replication DNA damage. In BLM-complemented cells, BLM colocalized with promyelocytic leukemia protein (PML) nuclear bodies and Top3alpha. Fibroblasts without BLM showed an increased sensitivity to camptothecin, enhanced formation of Top1-DNA complexes, and delayed histone H2AX phosphorylation (gamma-H2AX). Camptothecin also induced nuclear relocalization of BLM, Top3alpha, and PML protein and replication-dependent phosphorylation of BLM on threonine 99 (T99p-BLM). T99p-BLM was also observed following replication stress induced by hydroxyurea. Ataxia telangiectasia mutated (ATM) protein and AT- and Rad9-related protein kinases, but not DNA-dependent protein kinase, appeared to play a redundant role in phosphorylating BLM. Following camptothecin treatment, T99p-BLM colocalized with gamma-H2AX but not with Top3alpha or PML. Thus, BLM appears to dissociate from Top3alpha and PML following its phosphorylation and facilitates H2AX phosphorylation in response to replication double-strand breaks induced by Top1. A defect in gamma-H2AX signaling in response to unrepaired replication-mediated double-strand breaks might, at least in part, explain the camptothecin-sensitivity of BLM-deficient cells.

Pharmacogenetics of irinotecan metabolism and transport: an update

The anticancer agent irinotecan (CPT-11) is converted to SN-38, which is approximately 100 to 1,000-fold more cytotoxic than the parent drug. The pharmacokinetics of irinotecan are extremely complex and have been the subject of intensive investigation in recent years. Irinotecan is subject to extensive metabolism by various polymorphic enzymes, including CES2 to form SN-38, members of the UGT1A subfamily, and CYP3A4 and CYP3A5, which form several pharmacologically inactive oxidation products. Elimination of irinotecan is also dependent on drug-transporting proteins, notably ABCB1 (P-glycoprotein), ABCC2 (cMOAT) and ABCG2 (BCRP), present on the bile canalicular membrane. The various processes mediating drug elimination, either through metabolic breakdown or excretion, likely impact substantially on interindividual variability in drug handling. This report provides an update on current strategies to individualize irinotecan chemotherapy based on each patient's genetic constitution, which may ultimately lead to more selective use of this agent.

Phase I/II Dose-Escalation Study of Pemetrexed plus Irinotecan in Patients with Advanced Colorectal Cancer

BACKGROUND

Pemetrexed and irinotecan have demonstrated antitumor activity as single agents in lung, pancreatic, breast, and colorectal cancer (CRC). The distinct mechanisms of action and patterns of resistance displayed by pemetrexed and irinotecan make them attractive agents for combination therapy.

PATIENTS AND METHODS

This phase I/II, nonrandomized, open-labeled, single-arm study was composed of 3 segments. The initial phase II portion of the study enrolled 23 patients with advanced CRC who had received 1 previous dose of 5-fluorouracil (5-FU)-based chemotherapy for advanced disease. Because of poorer than anticipated efficacy, a phase I dose-escalation study using vitamin supplementation (n = 12) was added to the original protocol. The phase II dose-escalation portion of the study enrolled 36 patients (64% with previous oxaliplatin-based therapy) who received pemetrexed 500 mg/m2 followed by irinotecan 300 mg/m2 on day 1, every 21 days.

RESULTS

For the 35 evaluable patients in the phase II dose-escalation study, the objective response rate was 11.4% (95% confidence interval, 3.2%-26.7%); there was 1 patient with a complete response, 3 with partial responses, and 17 with stable disease. Three of four responders had received previous oxaliplatin-based combination therapy. Grade 3/4 hematologic toxicities included leukopenia (5.6%), anemia (2.8%), and thrombocytopenia (2.8%). Grade 3/4 nonhematologic toxicities included diarrhea (11.1%), increased aminotransferase levels (8.3%), nausea (8.3%), febrile neutropenia (5.6%), vomiting (5.6%), and reduced creatinine clearance (2.8%).

CONCLUSION

Pemetrexed plus irinotecan appears to be at least as active as FOLFIRI (leucovorin/5-FU/irinotecan) for second-line therapy of CRC following 5-FU-based combination chemotherapy. Further studies are warranted.

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.