Animal models for studying the action of topoisomerase I targeted drugs

Liposomal Irinotecan Shows a Larger Therapeutic Index than Non-liposomal Irinotecan in Patient-Derived Xenograft Models of Pancreatic Cancer

INTRODUCTION

Liposomal irinotecan promotes controlled sustained release of irinotecan (CPT-11), therefore, we hypothesize that the therapeutic index (quantitative measurement of the relative efficacy/safety ratio of a drug) will be higher for liposomal than non-liposomal irinotecan.

METHODS

We compared the therapeutic indexes of liposomal and non-liposomal irinotecan in mice bearing subcutaneous patient-derived xenograft (PDX) pancreatic tumors under dosing regimens approximating the clinical setting. Following preliminary drug sensitivity/antitumor activity analyses on three PDX tumor models, one model was selected for analyses of efficacy, biomarker, toxicology, pharmacokinetics in mice receiving liposomal irinotecan (2.5, 10, 50 mg/kg/week) or non-liposomal irinotecan (10, 25, 50 mg/kg/week). The maximum tolerated dose (MTD) for each treatment was 50 mg/kg/week.

RESULTS

Using the selected IM-PAN-001 model at the MTD (both treatments, 50 mg/kg/week), antitumor activity, phospho-histone gamma-H2AX protein staining in cancer cell nuclei, histological tumor regression, and plasma levels of CPT-11 and its active metabolite SN-38 after 24 h were greater with liposomal than non-liposomal irinotecan, but tumor SN-38 levels were similar. At the lowest doses assessed, antitumor activity, histological tumor regression, and jejunum and bone marrow toxicity were similar. Based on these findings, liposomal and non-liposomal irinotecan had therapeutic indexes of 20 and 5, respectively.

CONCLUSION

This non-clinical study showed a fourfold broader therapeutic index with liposomal than non-liposomal irinotecan in mice bearing IM-PAN-001 PDX pancreatic tumors, even at optimal dosing for the two drugs. These findings support the clinical benefit observed with liposomal irinotecan in patients with pancreatic cancer.

Application status and future prospects of the PDX model in lung cancer

Lung cancer is one of the most prevalent, fatal, and highly heterogeneous diseases that, seriously threaten human health. Lung cancer is primarily caused by the aberrant expression of multiple genes in the cells. Lung cancer treatment options include surgery, radiation, chemotherapy, targeted therapy, and immunotherapy. In recent decades, significant progress has been made in developing therapeutic agents for lung cancer as well as a biomarker for its early diagnosis. Nonetheless, the alternative applications of traditional pre-clinical models (cell line models) for diagnosis and prognosis prediction are constrained by several factors, including the lack of microenvironment components necessary to affect cancer biology and drug response, and the differences between laboratory and clinical results. The leading reason is that substantial shifts accrued to cell biological behaviors, such as cell proliferative, metastatic, invasive, and gene expression capabilities of different cancer cells after decades of growing indefinitely in vitro. Moreover, the introduction of individualized treatment has prompted the development of appropriate experimental models. In recent years, preclinical research on lung cancer has primarily relied on the patient-derived tumor xenograft (PDX) model. The PDX provides stable models with recapitulate characteristics of the parental tumor such as the histopathology and genetic blueprint. Additionally, PDXs offer valuable models for efficacy screening of new cancer drugs, thus, advancing the understanding of tumor biology. Concurrently, with the heightened interest in the PDX models, potential shortcomings have gradually emerged. This review summarizes the significant advantages of PDXs over the previous models, their benefits, potential future uses and interrogating open issues.

Comparative study on the efficacy and exposure of molecular target agents in non-small cell lung cancer PDX models with driver genetic alterations

Patient-derived xenografts (PDXs) can adequately reflect clinical drug efficacy. However, the methods for evaluating drug efficacy are not fully established. We selected five non-small cell lung cancer (NSCLC) PDXs with genetic alterations from established PDXs and the corresponding molecular targeted therapy was administered orally for 21 consecutive days. Genetic analysis, measurement of drug concentrations in blood and tumors using liquid chromatography and tandem mass spectrometry, and analysis of drug distribution in tumors using matrix-assisted laser desorption/ionization mass spectrometry were performed. Fifteen (20%) PDXs were established using samples collected from 76 NSCLC patients with genetic alterations. The genetic alterations observed in original patients were largely maintained in PDXs. We compared the drug efficacy in original patients and PDX models; the efficacies against certain PDXs correlated with the clinical effects, while those against the others did not. We determined blood and intratumor concentrations in the PDX model, but both concentrations were low, and no evident correlation with the drug efficacy could be observed. The intratumoral spatial distribution of the drugs was both homogeneous and heterogeneous for each drug, and the distribution was independent of the expression of the target protein. The evaluation of drug efficacy in PDXs enabled partial reproduction of the therapeutic effect in original patients. A more detailed analysis of systemic and intratumoral pharmacokinetics may help clarify the mode of action of drugs. Further development of evaluation methods and indices to improve the prediction accuracy of clinical efficacy is warranted.

Mechanisms underlying synergy between DNA topoisomerase I-targeted drugs and mTOR kinase inhibitors in NF1-associated malignant peripheral nerve sheath tumors

Malignant peripheral nerve sheath tumors (MPNSTs) are soft-tissue sarcomas that frequently arise in patients with neurofibromatosis type 1 (NF1). Most of these tumors are unresectable at diagnosis and minimally responsive to conventional treatment, lending urgency to the identification of new pathway dependencies and drugs with potent antitumor activities. We therefore examined a series of candidate agents for their ability to induce apoptosis in MPNST cells arising in nf1/tp53-deficient zebrafish. In this study, we found that DNA topoisomerase I-targeted drugs and mTOR kinase inhibitors were the most effective single agents in eliminating MPNST cells without prohibitive toxicity. In addition, three members of these classes of drugs, either AZD2014 or INK128 in combination with irinotecan, acted synergistically to induce apoptosis both in vitro and in vivo. In mechanistic studies, irinotecan not only induces apoptosis by eliciting a DNA damage response, but also acts synergistically with AZD2014 to potentiate the hypophosphorylation of 4E-BP1, a downstream target of mTORC1. Profound hypophosphorylation of 4E-BP1 induced by this drug combination causes an arrest of protein synthesis, which potently induces tumor cell apoptosis. Our findings provide a compelling rationale for further in vivo evaluation of the combination of DNA topoisomerase I-targeted drugs and mTOR kinase inhibitors against these aggressive nerve sheath tumors.

Patient-derived xenografts effectively capture responses to oncology therapy in a heterogeneous cohort of patients with solid tumors

Background

While patient-derived xenografts (PDXs) offer a powerful modality for translational cancer research, a precise evaluation of how accurately patient responses correlate with matching PDXs in a large, heterogeneous population is needed for assessing the utility of this platform for preclinical drug-testing and personalized patient cancer treatment.

Patients and methods

Tumors obtained from surgical or biopsy procedures from 237 cancer patients with a variety of solid tumors were implanted into immunodeficient mice and whole-exome sequencing was carried out. For 92 patients, responses to anticancer therapies were compared with that of their corresponding PDX models.

Results

We compared whole-exome sequencing of 237 PDX models with equivalent information in The Cancer Genome Atlas database, demonstrating that tumorgrafts faithfully conserve genetic patterns of the primary tumors. We next screened PDXs established for 92 patients with various solid cancers against the same 129 treatments that were administered clinically and correlated patient outcomes with the responses in corresponding models. Our analysis demonstrates that PDXs accurately replicate patients' clinical outcomes, even as patients undergo several additional cycles of therapy over time, indicating the capacity of these models to correctly guide an oncologist to treatments that are most likely to be of clinical benefit.

Conclusions

Integration of PDX models as a preclinical platform for assessment of drug efficacy may allow a higher success-rate in critical end points of clinical benefit.

Patient-derived xenografts as tools in pharmaceutical development

Successful drug development in oncology is grossly suboptimal, manifested by the very low percentage of new agents being developed that ultimately succeed in clinical approval. This poor success is in part due to the inability of standard cell-line xenograft models to accurately predict clinical success and to tailor chemotherapy specifically to a group of patients more likely to benefit from the therapy. Patient-derived xenografts (PDXs) maintain the histopathological architecture and molecular features of human tumors, and offer a potential solution to maximize drug development success and ultimately generate better outcomes for patients. Although imperfect in mimicking all aspects of human cancer, PDXs are a more predictable platform for preclinical evaluation of treatment effect and in selected cases can guide therapeutic decision making in the clinic. This article summarizes the current status of PDX models, challenges associated with modeling human cancer, and various approaches that have been applied to overcome these challenges and improve the clinical relevance of PDX cancer models.

Surface-modified silica nanoparticles for tumor-targeted delivery of camptothecin and its biological evaluation

Here we report the design, synthesis and biological evaluation of surface-modified silica nanoparticles (SNP) for the delivery of camptothecin (CPT). Drug has been covalently linked to the nanoparticle through an ester bond with the 20-hydroxy moiety, in order to stabilize its lactone ring and to avoid unspecific release of the drug. The obtained material is highly stable in plasma, with low release of the cargo at physiological pH. Cell internalization and in vitro efficacy assays demonstrated that nanoparticles carrying CPT (SNP-CPT) entered cells via endocytosis and the intracellular release of the cargo induced cell death with half maximal inhibitory concentration (IC₅₀) values and cell cycle distribution profiles similar to those observed for the naked drug. Further, in vivo biodistribution, therapeutic efficacy and biocompatibility of the SNP-CPT were evaluated in human colorectal cancer xenografts using in vivo fluorescence or bioluminescence optical imaging. In vivo tumor-accumulation and whole-body tissue distribution were carried out based on the acquisition of fluorescence emission of a fluorophore (Cy5.5) conjugated to the SNP-CPT, as well as by HPLC quantification of tissue CPT levels. The results showed that, although SNP-CPT tended to accumulate in organs of the reticulo-endothelial system, nanoparticles boost CPT concentration in tumor vs administration of the free drug. Accordingly, SNP-CPT treatment delayed the growth of subcutaneous tumors while significantly reducing the systemic toxicity associated with CPT administration. These results indicate that the SNP-CPT could be used as a robust drug delivery system for antitumoral treatments based on CPT.

Phase I and pharmacokinetic study of gimatecan given orally once a week for 3 of 4 weeks in patients with advanced solid tumors

PURPOSE

A phase I study was conducted to determine the dose-limiting toxicities (DLT) and maximum tolerated dose (MTD) of gimatecan, a lipophilic camptothecin analogue, administered orally once a week for 3 weeks.

EXPERIMENTAL DESIGN

Adult patients with advanced solid tumors with good performance status and adequate hematologic, hepatic, and renal function were eligible for the study. The plasma pharmacokinetics of the drug was characterized during the initial 28-day cycle.

RESULTS

A total of 33 patients were evaluated at 7 dose levels ranging from 0.27 to 3.20 mg/m(2)/wk. Anemia, fatigue, neutropenia, nausea, and vomiting were the principal toxicities. DLTs experienced by 3 of 7 patients in dose level 7 (3.20 mg/m(2)) were grade 2 hyperbilirubinemia and grade 3 to 4 fatigue. DLT (anorexia and nausea) occurred in only 1 of 11 patients evaluated at the MTD of 2.40 mg/m(2). There were no objective responses, although disease stabilization was observed in 4 patients. Gimatecan has a very long apparent biological half-life (mean +/- SD, 77 +/- 37 h) and exists in plasma almost entirely as the pharmacologically active intact lactone form. At the MTD, mean peak concentrations of the drug in plasma ranged from 67 to 82 ng/mL for the 3 weekly doses and the mean concentration 7 days after dosing was 15 +/- 18 ng/mL.

CONCLUSIONS

Administration of gimatecan orally once a week at doses that are well tolerated provides continuous exposure to potentially effective plasma concentrations of the biologically active form of the drug. This regimen deserves further evaluation to define its antitumor activity in specific tumor types either alone or in combination with other agents.

Reducing irinotecan-associated diarrhea in children

Irinotecan is increasingly being used in pediatric oncology. Amelioration of diarrhea associated with protracted irinotecan administration may reduce morbidity and improve dose intensity. In this review, we discuss what is known about the pathogenesis of this toxicity as well as potential predisposing genetic factors. We comprehensively summarize the literature regarding available prevention and treatment strategies, and report data on the use of cephalosporin prophylaxis in 51 patients treated on various pediatric trials. This approach is feasible in children and allows for tolerance of higher doses of protracted irinotecan.

Tumor, tissue, and plasma pharmacokinetic studies and antitumor response studies of docetaxel in combination with 9-nitrocamptothecin in mice bearing SKOV-3 human ovarian xenografts

PURPOSE

We evaluated the antitumor activity of two different schedules of docetaxel and 9-nitrocamptothecin (9NC) in mice bearing human SKOV-3 ovarian carcinoma xenografts and evaluated the plasma, tissue, and tumor disposition of each agent alone and in combination.

EXPERIMENTAL DESIGN

The following treatment groups were evaluated: (1) docetaxel 10 mg/kg IV on days 0 and 7; (2) 9NC 0.67 mg/kg PO qdx5dx2wk; (3) 9NC 0.67 mg/kg PO qdx5dx2wk in combination with docetaxel 10 mg/kg IV on days 0 and 7; and (4) 9NC 0.67 mg/kg PO qdx5dx2wk in combination with docetaxel 10 mg/kg IV on days 4 and 11; (5) vehicle controls for each agent; and (6) no treatment controls.

RESULTS

All treatment regimens produced significant antitumor activity as compared with control groups (P < 0.05). Docetaxel administered on days 0 and 7 or on days 4 and 11 in combination with 9NC resulted in similar antitumor activity (P > 0.05). High docetaxel concentrations in tumor were maintained at late time points as compared with plasma and tissues with the retention of docetaxel at 24 h being 132-fold and 15-fold higher in tumor than in plasma and liver, respectively. After administration of 9NC alone, the ratio of the 9-aminocamptothecin (9AC) area under the concentration versus time curve (AUC) to 9NC AUC in plasma and tumor was 0.15 and 1.34, respectively.

CONCLUSIONS

The combination of docetaxel and 9NC was effective against SKOV-3 xenografts. The lack of a difference in sequence-dependent antitumor activity may reflect the sensitivity of the SKOV-3 xenograft to 9NC. The factors associated with tumor-specific retention of docetaxel and the ratio of 9NC to 9AC in tumors is unknown.

Mathematical modeling of topotecan pharmacokinetics and toxicodynamics in mice

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

Primary lymphocytes as predictors for species differences in cytotoxic drug sensitivity

Several in vitro methods have been suggested to predict drug-induced haematotoxicity and species differences; the most commonly used being the clonogenic CFU-GM assay. The aim of the current study was to evaluate whether primary lymphocytes from peripheral blood, assayed with a short-term non-clonogenic assay, could be used to detect species differences in drug sensitivity, and offer an alternative to the CFU-GM assay. The effect of 17 different cytotoxic drugs on lymphocytes from human, dog, rat and mouse was evaluated. A higher sensitivity of human than mouse lymphocytes was seen for topotecan and for 3 of 5 antimetabolites tested. Clear species specificity was also seen for the proteasome inhibitor bortezomib where rodent cells were 50-300 times less sensitive than human cells. Good agreement between our data and published CFU-GM data was observed, suggesting that primary lymphocytes may be a useful model for species difference screening in drug development.

The mighty mouse: genetically engineered mouse models in cancer drug development

Deficiencies in the standard preclinical methods for evaluating potential anticancer drugs,such as xenograft mouse models, have been highlighted as a key obstacle in the translation of the major advances in basic cancer research into meaningful clinical benefits. In this article, we discuss the established uses and limitations of xenograft mouse models for cancer drug development, and then describe the opportunities and challenges in the application of novel genetically engineered mouse models that more faithfully mimic the genetic and biological evolution of human cancers. Greater use of such models in target validation, assessment of tumour response, investigation of pharmacodynamic markers of drug action, modelling resistance and understanding toxicity has the potential to markedly improve the success of cancer drug development.

Relationship between plasma exposure of 9-nitrocamptothecin and its 9-aminocamptothecin metabolite and antitumor response in mice bearing human colon carcinoma xenografts

9-Nitrocamptothecin has completed phase III studies in patients with newly diagnosed and refractory pancreatic cancer; however, the optimal 9-nitrocamptothecin treatment regimen is unclear. We used an intermittent schedule of 9-nitrocamptothecin to evaluate the relationship between plasma exposure of 9-nitrocamptothecin and its 9-aminocamptothecin metabolite and antitumor response in mice bearing human colon carcinoma xenografts. 9-Nitrocamptothecin was given orally at 0.44, 0.67, or 1.0 mg/kg/d qd x 5d x 2 weeks repeated q 4 weeks for two cycles to female C.B-17 SCID mice bearing HT29 or ELC2 human colon xenografts. Pharmacokinetic studies were done after oral administration of 0.67 mg/kg x 1. Serial samples were obtained and 9-nitrocamptothecin and 9-aminocamptothecin lactone concentrations in plasma were determined by high-performance liquid chromatography analysis with fluorescence detection. The areas under plasma concentration versus time curve (AUC) from 0 to infinity for 9-nitrocamptothecin and 9-aminocamptothecin were calculated. The antitumor activity of 9-nitrocamptothecin was dose-dependent in both colon xenografts. At all doses, 9-nitrocamptothecin treatment resulted in significant antitumor activity in both xenografts compared with vehicle-treated and control groups and achieved levels of tumor regression that met criteria (minimum %T/C < or = 40%) for antitumor activity. In mice bearing HT29 xenografts, the 9-nitrocamptothecin and 9-aminocamptothecin lactone AUCs after administration of 9-nitrocamptothecin at 0.67 mg/kg were 41.3 and 5.7 ng/mL h, respectively. The responses seen in these xenograft models occurred at systemic exposures that are tolerable in adult patients. These results suggest that the intermittent schedule of 9-nitrocamptothecin may be an active regimen in patients with colorectal carcinoma.

Topotecan Combination Chemotherapy in Two New Rodent Models of Retinoblastoma

Chemotherapy combined with laser therapy and cryotherapy has improved the ocular salvage rate for children with bilateral retinoblastoma. However, children with late-stage disease often experience recurrence shortly after treatment. To improve the vision salvage rate in advanced bilateral retinoblastoma, we have developed and characterized two new rodent models of retinoblastoma for screening chemotherapeutic drug combinations. The first model is an orthotopic xenograft model in which green fluorescent protein- or luciferase-labeled human retinoblastoma cells are injected into the eyes of newborn rats. The second model uses a replication-incompetent retrovirus (LIA-E(E1A)) encoding the E1A oncogene. Clonal, focal tumors arise from mouse retinal progenitor cells when LIA-E(E1A) is injected into the eyes of newborn p53-/- mice. Using these two models combined with pharmacokinetic studies and cell culture experiments, we have tested the efficacy of topotecan combined with carboplatin and of topotecan combined with vincristine for the treatment of retinoblastoma. The combination of topotecan and carboplatin most effectively halted retinoblastoma progression in our rodent models and was superior to the current triple drug therapy using vincristine, carboplatin, and etoposide. Vincristine had the lowest LC50 in culture but did not reduce tumor growth in our preclinical retinoblastoma models. Taken together, these data suggest that topotecan may be a suitable replacement for etoposide in combination chemotherapy for the treatment of retinoblastoma.

The novel highly lipophilic topoisomerase I inhibitor DB67 is effective in the treatment of liver metastases of murine CT-26 colon carcinoma

Colorectal carcinoma occurs in 1 of 20 individuals in most developed countries. The relapse after resection with metastatic liver disease is a major cause of death. 7-t-Butyldimethylsilyl-10-hydroxycamptothecin (DB67) has been incorporated into liposomes allowing for intravenous (i.v.) administration. A preclinical efficacy study of liposomal DB67 was performed using the colon carcinoma CT-26 cell line. The therapeutic dose for DB67 and liposomal DB67 was found to be 7 mg/kg per day using the qdx5/1 schedule. The results are compared with those obtained with irinotecan. The treatment with liposomal DB67 administered intravenously was more effective in reducing the weight and volume of primary spleen tumors and the weight and extent of liver metastases than free DB67 or liposomal DB67 administered intraperitoneally, but less effective than irinotecan. When the primary tumor was resected, treatment with liposomal DB67 administered intravenously was more effective in reducing the weight and extent of liver metastases than DB67 or liposomal DB67 administered intraperitoneally, and irinotecan. DB67 showed a higher accumulation in spleen and liver after its i.v. administration in liposomal form compared with its free or liposomal form administered intraperitoneally. DB67 and liposomal DB67 are more effective than irinotecan in the treatment of liver metastases after resection of the primary tumor.

Gimatecan, a novel camptothecin with a promising preclinical profile

The realization that position 7 of camptothecin allows several options in chemical manipulation of the drug has stimulated a systematic investigation of a variety of substituents in this position. These efforts resulted in the identification of a novel series of 7-oxyiminomethyl derivatives. Among compounds of this series we have selected a promising lipophilic derivative, gimatecan, for further development. The relevant features of gimatecan are: (i) marked cytotoxic potency, likely related to multiple factors, including a potent inhibition of topoisomerase I, a persistent stabilization of the cleavable complex, an increased intracellular accumulation and a peculiar subcellular localization; (ii) lack of recognition by known resistance-related transport systems; (iii) increased lactone stability and favorable pharmacokinetics; (iv) good oral bioavailability; and (v) an impressive antitumor efficacy in a large panel of human tumor xenografts, with various treatment schedules. Phase I clinical studies with oral administration support the preclinical results of the novel camptothecin. Using different schedules and dosing durations, gimatecan exhibited an acceptable toxicity profile, with myelotoxicity being the dose-limiting toxic effect. An appreciable number of tumor responses was achieved and favorable pharmacokinetics with a very long terminal half-life was observed. The clinical development of gimatecan is currently ongoing, with phase II studies in diverse tumor types (colon, lung, breast carcinoma and pediatric tumors).

Phase I and Pharmacologic Study of Intermittently Administered 9-Nitrocamptothecin in Patients with Advanced Solid Tumors

PURPOSE

9-Nitrocamptothecin (9NC) is an oral camptothecin analogue currently administered at 1.5 mg/m(2)/day x 5 days/week in Phase III studies for pancreatic carcinoma. In an effort to increase the dose administered per day and determine whether the daily dose or number of days of treatment influence toxicity, we performed a Phase I study of 9NC using intermittent schedules of administration.

EXPERIMENTAL DESIGN

On schedule A, 9NC was administered orally daily x 5 days for 2 weeks every 4 weeks (one cycle). On schedule B, 9NC was administered orally daily x 14 days every 4 weeks (one cycle). Dose levels were determined by adaptive dose finding. Serial blood samples were obtained on day 1 of each schedule for pharmacokinetic studies of 9NC and its 9-aminocamptothecin (9AC) metabolite, and lactone forms were measured by high-performance liquid chromatography.

RESULTS

The recommended Phase II doses for schedules A and B were 2.43 and 1.70 mg/m(2)/day, respectively, each providing the same dose intensity (i.e., 24 mg/m(2)/cycle). The primary toxicities on schedules A and B were neutropenia, thrombocytopenia, and diarrhea. On schedule A, two patients with gastric cancer and two patients with pancreatic cancer had stable disease for more than six cycles. On schedule B, one patient with pancreatic cancer had stable disease for more than six cycles, and a patient with pancreatic cancer had a partial response. There was significant interpatient variability in the disposition of 9NC and 9AC. Most of the drug remained in the 9NC form with a ratio of 9NC to 9AC of approximately 4 to 1.

CONCLUSIONS

These studies suggest that 9NC administered on an intermittent schedule is tolerable and may be an active regimen in patients with gastric or pancreatic cancers. Dosing 9NC on a mg/m(2) basis does not reduce pharmacokinetic variability.

Oral RDP58 Allows CPT-11 Dose Intensification for Enhanced Tumor Response by Decreasing Gastrointestinal Toxicity

Cancer patients undergoing triple therapy (CPT-11, 5-fluorouracil, and leucovorin) often present with severe delayed diarrhea as a result of chemotherapy-induced gastrointestinal (GI) toxicity and inflammation. RDP58 is a novel, anti-inflammatory, D-amino acid decapeptide that inhibits the production of tumor necrosis factor alpha, IFN-gamma, and interleukin 12, and has been shown to effectively inhibit clinical symptoms and intestinal inflammation in several rodent models of chemically induced colitis, nonhuman primates with spontaneous colitis, and humans with mild to moderate ulcerative colitis. We evaluated RDP58 as a potential protective agent in chemotherapy-induced GI inflammation. Oral administration of RDP58 significantly decreased the incidence of diarrhea and improved the survival rates of mice treated with toxic doses of CPT-11 or 5-fluorouracil. Histological analysis showed that RDP58 significantly reduced the destruction of the intestinal mucosa by inhibiting local overproduction of tumor necrosis factor alpha, IFN-gamma, and interleukin 12 in vivo. Furthermore, RDP58 administration allowed the maximum tolerated dose of CPT-11 to be doubled in tumor-bearing mice resulting in significantly enhanced primary tumor responses and prolongation of time to relapse without a concomitant increase in GI toxicity. Our results suggest that RDP58 may have clinical utility in cancer therapy by preventing treatment-associated GI toxicity and potentially increasing the effectiveness of chemotherapy.

Cellular bases of the antitumor activity of a 7-substituted camptothecin in hormone-refractory human prostate carcinoma models

ST1481, a lead compound of a novel potent 7-substituted lipophilic camptothecin series, is able to overcome several mechanisms of drug resistance and was selected for clinical development. This study was designed to examine the antitumor activity of ST1481 in the treatment of preclinical models of human p53-defective hormone-refractory prostate carcinoma (DU145, PC3, and JCA-1) and to explore the cellular bases of the efficacy of camptothecins. A cellular pharmacology study (cytotoxicity, apoptosis, cellular drug accumulation, DNA damage, and cell cycle perturbation) was performed in DU145 and PC3 cells, characterized by a different cell cycle checkpoint status. The introduction of wild-type p53 in PC3 cells appreciably decreased the drug sensitivity. The 7-substituted camptothecins exhibited a high cytotoxic potency that paralleled their relative ability to induce DNA damage and a substantially increased cellular accumulation as compared to topotecan. The cytotoxic effect of camptothecins in DU145 cells was associated with arrest in S phase and early activation of apoptosis, whereas PC3 cells responded to drugs by a persistent block in G2 phase with a cytostatic effect and a late apoptosis. The efficiency of S phase checkpoint in DU145 cells was supported by a time-dependent decrease of DNA synthesis following treatment. In spite of an apparent cytostatic response and apoptosis resistance, the PC3 tumor was more responsive to in vivo treatment with camptothecins than the DU145 model. Indeed, the therapeutic outcome did not reflect the cell susceptibility to early activation of apoptosis. We suggest that cell death in PC3 cells is a delayed event consequent to persistent arrest in G2 and insufficient repair of DNA damage. ST1481 was appreciably more effective than topotecan in all tested tumors. In conclusion, the results indicated a relevant efficacy of camptothecins against human prostate carcinoma models, in spite of p53 alterations. Although p53 status could influence DNA damage and cell cycle checkpoints, p53 mutation was not a determinant of resistance. The results support that, in addition to the extent and persistence of topoisomerase I-mediated DNA damage, cell cycle checkpoints and DNA damage signaling pathways are critical determinants of tumor responsiveness to camptothecins. A role of cell cycle checkpoints activated by DNA damage in cell response is supported by the modulation of transcriptional profile.

Cellular, pharmacokinetic, and pharmacodynamic aspects of response to camptothecins: can we improve it?

The camptothecins provide a novel class of effective anticancer agents that exert their action against DNA topoisomerase I. Members of the camptothecins include topotecan, irinotecan, 9-aminocamptothecin, and 9-nitrocamptothecin, which are analogs of the plant alkaloid 20(S)-camptothecin. These agents vary in their antitumor efficacy and toxicity. Several pharmacokinetic and pharmacodynamic factors including cellular efflux, modulation of topoisomerases I and II, lactone stability, alterations in metabolism, and drug-drug interactions, influence the antitumor response and toxicity of these agents. Preclinical studies suggest that protracted schedules of administration produce greater antitumor effect than bolus administration. However, the optimal treatment regimens and administration schedules of these agents have yet to be established in clinical studies.

9-Nitrocamptothecin liposome aerosol treatment of human cancer subcutaneous xenografts and pulmonary cancer metastases in mice

The purpose of this study was to test the anticancer properties of the water-insoluble derivative of camptothecin, 9-nitrocamptothecin (9NC), administered in a liposome formulation (L-9NC) in aerosol to mice with subcutaneous xenografts of three human cancers and in mice with murine melanoma and human osteosarcoma pulmonary metastases. The drug was formulated with dilauroylphosphatidylcholine and nebulized in particle sizes of 1.2-1.6 microns mass median aerodynamic diameter and a geometric standard deviation of 2.0. The aerosol was generated with the nebulizer flowing at 10 l/min and delivered to mice in sealed plastic cages or in a nose-only exposure chamber. Aerosol was administered for 15 min to 2 hr daily, delivering deposited doses in the respiratory tract of 8.1-306.7 micrograms of 9NC/kg. With subcutaneous tumors, growth was greatly inhibited or tumors were undetectable after several weeks of treatment. We also showed that oral dosage with L-9NC had no detectable effect on cancer growth, and thus the benefit from aerosol treatment was due to pulmonary deposition and not the larger fraction of drug deposited in the nose of mice during aerosol treatment which is promptly swallowed. Intramuscular L-9NC in slightly larger doses than given in the aerosol had detectable anticancer activity, but it was significantly less than in mice receiving the drug by aerosol. With metastatic pulmonary cancers, treated animals showed highly significantly less cancer growth than control animals. L-9NC aerosol showed a major therapeutic benefit in the treatment of subcutaneous human cancer xenografts in nude mice, suggesting that cancers at systemic sites might be responsive to this treatment. In addition, the strong anticancer effect of L-9NC aerosol on pulmonary metastases offers a therapeutic approach for treatment of pulmonary cancers. Thus, L-9NC aerosol may have applicability in the treatment of cancers throughout the body.

Up-front window trial of topotecan in previously untreated children and adolescents with metastatic rhabdomyosarcoma: an intergroup rhabdomyosarcoma study

PURPOSE

To investigate the antitumor activity and toxicity of topotecan, used alone and in combination with conventional therapy, in patients with metastatic rhabdomyosarcoma (RMS).

PATIENTS AND METHODS

Forty-eight patients younger than 21 years of age with newly diagnosed metastatic RMS received 2.0 to 2.4 mg/m(2) of topotecan intravenously daily for 5 days every 21 days before standard therapy. Two courses were given in the absence of progressive disease or excessive toxicity and response was assessed. Patients with at least a partial response (PR) to topotecan proceeded to therapy with alternating courses of vincristine 1.5 mg/m(2), dactinomycin 1.5 mg/m(2), and cyclophosphamide 2.2 g/m(2) (VAC) and vincristine 1.5 mg/m(2), topotecan 0.75 mg/m(2) daily x 5, and cyclophosphamide 250 mg/m(2) daily x 5. Patients who did not respond to topotecan received continuation therapy with VAC alone.

RESULTS

The overall response rate to topotecan was 46% (complete response, 4%; partial response 42%). Unexpectedly, patients with alveolar RMS had a higher rate of response (65%) than those with embryonal RMS (28%; P: = .08). The most common grade 3 or 4 toxicities were neutropenia (67%), anemia (33%), thrombocytopenia (25%), and infection (21%). Two-year failure-free survival and survival estimates were 24% and 46%, respectively. Response to window therapy did not correlate with survival.

CONCLUSION

The high response rate and acceptable toxicity profile of topotecan in children with advanced RMS support further evaluation of this agent in phase III trials. The superior responses in alveolar RMS are of interest.

Direct translation of a protracted irinotecan schedule from a xenograft model to a phase I trial in children

PURPOSE

In a preclinical model of neuroblastoma, administration of irinotecan daily 5 days per week for 2 consecutive weeks ([qd x 5] x 2) resulted in greater antitumor activity than did a single 5-day course with the same total dose. We evaluated this protracted schedule in children.

PATIENTS AND METHODS

Twenty-three children with refractory solid tumors were enrolled onto a phase I study. Cohorts received irinotecan by 1-hour intravenous infusion at 20, 24, or 29 mg/m(2) (qd x 5) x 2 every 21 days.

RESULTS

The 23 children (median age, 14.1 years; median prior regimens, two) received 84 courses. Predominant diagnoses were neuroblastoma (n = 5), osteosarcoma (n = 5), and rhabdomyosarcoma (n = 4). The dose-limiting toxicity was grade 3/4 diarrhea and/or abdominal cramps in six of 12 patients treated at 24 mg/m(2), despite aggressive use of loperamide. The maximum-tolerated dose (MTD) on this schedule was 20 mg/m(2)/d. Five patients had partial responses and 16 had disease stabilization. On day 1, the median systemic exposure to SN-38 (the active metabolite of irinotecan) at the MTD was 106 ng-h/mL (range, 41 to 421 ng-h/mL).

CONCLUSION

This protracted schedule is well tolerated in children. The absence of significant myelosuppression and encouraging clinical responses suggest compellingly that irinotecan be further evaluated in children using the (qd x 5) x 2 schedule, beginning at a dose of 20 mg/m(2). These results imply that data obtained from xenograft models can be effectively integrated into the design of clinical trials.