Design and synthesis of a series of bioavailable fatty acid synthase (FASN) KR domain inhibitors for cancer therapy.

We designed and synthesized a new series of fatty acid synthase (FASN) inhibitors with potential utility for the treatment of cancer. Extensive SAR studies led to highly active FASN inhibitors with good cellular activity and oral bioavailability, exemplified by compound 34. Compound 34 is a potent inhibitor of human FASN (IC50 = 28 nM) that effectively inhibits proliferation of A2780 ovarian cells (IC50 = 13 nM) in lipid-reduced serum (LRS). This cellular activity can be rescued by addition of palmitate, consistent with an on-target effect. Compound 34 is also active in many other cell types, including PC3M (IC50 = 25 nM) and LnCaP-Vancouver prostate cells (IC50 = 66 nM), and is highly bioavailable (F 61%) with good exposure after oral administration. In a pharmacodynamics study in H460 lung xenograft-bearing mice, oral treatment with compound 34 results in elevated tumor levels of malonyl-CoA and decreased tumor levels of palmitate, fully consistent with the desired target engagement.

Thin SnOx films for surface plasmon resonance enhanced ellipsometric gas sensing (SPREE).

Background: Gas sensors are very important in several fields like gas monitoring, safety and environmental applications. In this approach, a new gas sensing concept is investigated which combines the powerful adsorption probability of metal oxide conductive sensors (MOS) with an optical ellipsometric readout. This concept shows promising results to solve the problems of cross sensitivity of the MOS concept. Results: Undoped tin oxide (SnOx) and iron doped tin oxide (Fe:SnOx) thin add-on films were prepared by magnetron sputtering on the top of the actual surface plasmon resonance (SPR) sensing gold layer. The films were tested for their sensitivity to several gas species in the surface plasmon resonance enhanced (SPREE) gas measurement. It was found that the undoped tin oxide (SnOx) shows higher sensitivities to propane (C3H8) then to carbon monoxide (CO). By using Fe:SnOx, this relation is inverted. This behavior was explained by a change of the amount of binding sites for CO in the layer due to this iron doping. For hydrogen (H2) no such relation was found but the sensing ability was identical for both layer materials. This observation was related to a different sensing mechanism for H2 which is driven by the diffusion into the layer instead of adsorption on the surface. Conclusion: The gas sensing selectivity can be enhanced by tuning the properties of the thin film overcoating. A relation of the binding sites in the doped and undoped SnOx films and the gas sensing abilities for CO and C3H8 was found. This could open the path for optimized gas sensing devices with different coated SPREE sensors.

Efficacy of sequential treatment with sunitinib-everolimus in an orthotopic mouse model of renal cell carcinoma.

BACKGROUND/AIM: Sequential treatment with targeted agents is standard of care for patients with metastatic renal cell carcinoma (mRCC). However, clinical data directly comparing treatment outcomes with a mammalian target of rapamycin inhibitor or a vascular endothelial growth factor-targeted agent in the second-line setting are lacking. We evaluated sequential treatment in a syngeneic, orthotopic mouse model of mRCC. MATERIALS AND METHODS: BALB/c mice were orthotopically implanted with murine RCC (RENCA) cells expressing luciferase and randomized to vehicle, sunitinib, sunitinib followed by sorafenib, or sunitinib followed by everolimus. Tumor growth and metastases were assessed by in vivo (whole body) and ex vivo (primary tumor, lung, liver) luciferase activity and necropsies, performed on day 20 or 46 for vehicle and treatment groups, respectively. RESULTS: Sunitinib followed by everolimus was associated with reduced luciferase activity and primary tumor weight and volume compared with sunitinib, and sunitinib followed by sorafenib. CONCLUSION: Sequential therapy with sunitinib followed by everolimus demonstrated significant antitumor and anti-metastatic effects.

Generation of a conditionally transformed murine embryonic fibroblast cell line using doxycycline-dependent IGF-1R overexpression.

The insulin-like growth factor I receptor (IGF1-R) system has long been implicated in cancer and is a promising target for tumor therapy. Besides in vitro screening assays, the discovery of specific inhibitors against IGF-1R requires relevant cellular models, ideally applicable to both in vitro and in vivo studies. With this aim in mind, the authors generated an inducible cell line using the tetracycline-responsive gene expression system to mimic the effects of therapeutic inhibition of the IGF-1R both in vitro and on established tumors in vivo. Inducible overexpression of IGF-1R in murine embryonic fibroblasts was achieved and resulted in the transformation of the cells as verified by their ability to grow in soft agar and in nude mice. Continuous repression of exogenous IGF-1R expression completely prevented outgrowth of the tumors. Furthermore, induced repression of IGF-1R expression in established tumors resulted in regression of the tumors. Interestingly, however, IGF-1R-independent relapse of tumor growth was observed upon prolonged IGF-1R repression. The IGF-1R cell line generated using this approach was successfully employed to test reference small-molecule inhibitors in vitro and an IGF-1R-specific inhibitory antibody, EM164, in vivo. Besides efficacy as a read-out, phospho-AKT could be identified as a pharmacodynamic biomarker, establishing this cell line as a valuable tool for the preclinical development of IGF-1R inhibitors.

Delayed cell death associated with mitotic catastrophe in γ-irradiated stem-like glioma cells.

BACKGROUND AND PURPOSE: Stem-like tumor cells are regarded as highly resistant to ionizing radiation (IR). Previous studies have focused on apoptosis early after irradiation, and the apoptosis resistance observed has been attributed to reduced DNA damage or enhanced DNA repair compared to non-stem tumor cells. Here, early and late radioresponse of patient-derived stem-like glioma cells (SLGCs) and differentiated cells directly derived from them were examined for cell death mode and the influence of stem cell-specific growth factors. MATERIALS AND METHODS: Primary SLGCs were propagated in serum-free medium with the stem-cell mitogens epidermal growth factor (EGF) and fibroblast growth factor-2 (FGF-2). Differentiation was induced by serum-containing medium without EGF and FGF. Radiation sensitivity was evaluated by assessing proliferation, clonogenic survival, apoptosis, and mitotic catastrophe. DNA damage-associated γH2AX as well as p53 and p21 expression were determined by Western blots. RESULTS: SLGCs failed to apoptose in the first 4 days after irradiation even at high single doses up to 10 Gy, but we observed substantial cell death later than 4 days postirradiation in 3 of 6 SLGC lines treated with 5 or 10 Gy. This delayed cell death was observed in 3 of the 4 SLGC lines with nonfunctional p53, was associated with mitotic catastrophe and occurred via apoptosis. The early apoptosis resistance of the SLGCs was associated with lower γH2AX compared to differentiated cells, but we found that the stem-cell culture cytokines EGF plus FGF-2 strongly reduce γH2AX levels. Nonetheless, in two p53-deficient SLGC lines examined γIR-induced apoptosis even correlated with EGF/FGF-induced proliferation and mitotic catastrophe. In a line containing CD133-positive and -negative stem-like cells, the CD133-positive cells proliferated faster and underwent more γIR-induced mitotic catastrophe. CONCLUSIONS: Our results suggest the importance of delayed apoptosis, associated mitotic catastrophe, and cellular proliferation for γIR-induced death of p53-deficient SLGCs. This may have therapeutic implications. We further show that the stem-cell culture cytokines EGF plus FGF-2 activate DNA repair and thus confound in vitro comparisons of DNA damage repair between stem-like and more differentiated tumor cells.

Gamma-secretase inhibitor treatment promotes VEGF-A-driven blood vessel growth and vascular leakage but disrupts neovascular perfusion.

The Notch signaling pathway is essential for normal development due to its role in control of cell differentiation, proliferation and survival. It is also critically involved in tumorigenesis and cancer progression. A key enzyme in the activation of Notch signaling is the gamma-secretase protein complex and therefore, gamma-secretase inhibitors (GSIs)--originally developed for Alzheimer's disease--are now being evaluated in clinical trials for human malignancies. It is also clear that Notch plays an important role in angiogenesis driven by Vascular Endothelial Growth Factor A (VEGF-A)--a process instrumental for tumor growth and metastasis. The effect of GSIs on tumor vasculature has not been conclusively determined. Here we report that Compound X (CX), a GSI previously reported to potently inhibit Notch signaling in vitro and in vivo, promotes angiogenic sprouting in vitro and during developmental angiogenesis in mice. Furthermore, CX treatment suppresses tumor growth in a mouse model of renal carcinoma, leads to the formation of abnormal vessels and an increased tumor vascular density. Using a rabbit model of VEGF-A-driven angiogenesis in skeletal muscle, we demonstrate that CX treatment promotes abnormal blood vessel growth characterized by vessel occlusion, disrupted blood flow, and increased vascular leakage. Based on these findings, we propose a model for how GSIs and other Notch inhibitors disrupt tumor blood vessel perfusion, which might be useful for understanding this new class of anti-cancer agents.

Metastasizing, Luciferase Transduced MAT­Lu Rat Prostate Cancer Models: Follow up of Bolus and Metronomic Therapy with Doxorubicin as Model Drug.

The most fatal outcomes of prostate carcinoma (PCa) result from hormone-refractory variants of the tumor, especially from metastatic spread rather than from primary tumor burden. The goal of the study was to establish and apply rat MAT-Lu prostate cancer tumor models for improved non-invasive live follow up of tumor growth and metastasis by in vivo bioluminescence. We established luciferase transduced MAT-Lu rat PCa cells and studied tumor growth and metastatic processes in an ectopic as well as orthotopic setting. An intravenous bolus treatment with doxorubicin was used to demonstrate the basic applicability of in vivo imaging to follow up therapeutic intervention in these models. In vitro analysis of tissue homogenates confirmed major metastatic spread of subcutaneous tumors into the lung. Our sensitive method, however, for the first time detects metastasis also in lymph node (11/24), spleen (3/24), kidney (4/24), liver (5/24), and bone tissue (femur or spinal cord - 5/20 and 12/20, respectively). Preliminary data of orthotopic implantation (three animals) showed metastatic invasion to investigated organs in all animals but with varying preference (e.g., to lymph nodes). Intravenous bolus treatment of MAT-Lu PCa with doxorubicin reduced subcutaneous tumor growth by about 50% and the number of animals affected by metastatic lesions in lymph nodes (0/4), lung (3/6) or lumbar spine (0/2), as determined by in vivo imaging and in vitro analysis. Additionally, the possible applicability of the luciferase transduced MAT-Lu model(s) to study basic principles of metronomic therapies via jugular vein catheter, using newly established active microport pumping systems, is presented.

Non-invasive in vivo imaging of tumor-associated CD133/prominin.

BACKGROUND: Cancer stem cells are thought to play a pivotal role in tumor maintenance, metastasis, tumor therapy resistance and relapse. Hence, the development of methods for non-invasive in vivo detection of cancer stem cells is of great importance. METHODOLOGY/PRINCIPAL FINDINGS: Here, we describe successful in vivo detection of CD133/prominin, a cancer stem cell surface marker for a variety of tumor entities. The CD133-specific monoclonal antibody AC133.1 was used for quantitative fluorescence-based optical imaging of mouse xenograft models based on isogenic pairs of CD133 positive and negative cell lines. A first set consisted of wild-type U251 glioblastoma cells, which do not express CD133, and lentivirally transduced CD133-overexpressing U251 cells. A second set made use of HCT116 colon carcinoma cells, which uniformly express CD133 at levels comparable to primary glioblastoma stem cells, and a CD133-negative HCT116 derivative. Not surprisingly, visualization and quantification of CD133 in overexpressing U251 xenografts was successful; more importantly, however, significant differences were also found in matched HCT116 xenograft pairs, despite the lower CD133 expression levels. The binding of i.v.-injected AC133.1 antibodies to CD133 positive, but not negative, tumor cells isolated from xenografts was confirmed by flow cytometry. CONCLUSIONS/SIGNIFICANCE: Taken together, our results show that non-invasive antibody-based in vivo imaging of tumor-associated CD133 is feasible and that CD133 antibody-based tumor targeting is efficient. This should facilitate developing clinically applicable cancer stem cell imaging methods and CD133 antibody-based therapeutics.

Development of a novel prodrug of paclitaxel that is cleaved by prostate-specific antigen: an in vitro and in vivo evaluation study.

In developed countries, prostate cancer is the third most common cause of death from cancer in men. Unfortunately, whilst accumulating clinical data have suggested that taxanes may prolong the survival in a subset of men with prostate carcinoma, the dose and duration of administration of these drugs are limited by their significant systemic toxicities due to a lack of tumour selectivity. In an attempt to improve both the water solubility and tumour-targeting properties of paclitaxel (Taxol®), we set out to develop a water soluble paclitaxel prodrug that is activated specifically by prostate-specific antigen (PSA) which is almost exclusively expressed in prostate tissue and prostate carcinoma making it an ideal molecular target for prodrug strategies. Using albumin as a drug carrier, we describe a novel albumin-binding prodrug of paclitaxel, EMC-Arg-Ser-Ser-Tyr-Tyr-Ser-Leu-PABC-paclitaxel [EMC: ε-maleimidocaproyl; PABC: p-aminobenzyloxycarbonyl] that was synthesised by reacting EMC-Arg-Ser-Ser-Tyr-Tyr-Ser-OH with H-Leu-PABC-paclitaxel. This prodrug was water soluble and was bound to endogenous and exogenous albumin. Moreover, incubation studies with PSA demonstrated that the albumin-bound form of the prodrug was cleaved rapidly at the P1-P1' scissile bond releasing the paclitaxel-dipeptide H-Ser-Leu-PABC-paclitaxel. Last but not least, due to the incorporation of a PABC self-eliminating linker, this dipeptide was rapidly degraded to liberate paclitaxel as a final cleavage product within a few hours in prostate tumour tissue homogenates. Of note was that the albumin-bound form of the prodrug was approximately three-fold more active in killing PSA-positive LNCaP cells than paclitaxel. In addition, orientating toxicity studies in mice showed that the maximum tolerated dose of the novel paclitaxel prodrug was twice that of conventional paclitaxel. When tested in vivo in an orthotopic mouse model of human prostate cancer using luciferase-transduced LNCaP LLN cells, both paclitaxel and the new paclitaxel prodrug showed distinct antitumour efficacy on the primary tumour and metastases that was significantly better than the effect of doxorubicin which was used as a comparison and showed no antitumour efficacy. The new paclitaxel prodrug (3 × 24 mg paclitaxel equivalents) showed comparable antitumour activity on the primary tumour to paclitaxel at its maximum-tolerated dose (3 × 12mg/kg), reduced circulating PSA levels and demonstrated a better antitumour effect on lung metastases but not on bone metastases.

Anti-tumor effects of AMT in the renal cell carcinoma model.

Auron-Misheil-Therapy (AMT) is a defined but unique combination of approved pharmaceuticals. It consists of insulin, chlorpheniramine and an aqueous camomile extract, and it has been successfully applied clinically in late-stage cancer patients. The purpose of this study was to elucidate the anti-tumor efficacy of AMT in a validated murine renal cell carcinoma animal model (RENCA). There were two independent studies; each animal group consisted of 16 mice. During a 6-week pretreatment period, vehicle (group A) and AMT (1.6 mg/kg/d) (group B) were administered once daily in a 5 days/week schedule either intramuscularly or subcutaneously. Tumor challenge at day 0 was followed by a 3-week treatment period (either vehicle or AMT once daily intramuscularly for 21 days consecutively). In study 2 the AMT dosage was increased up to 4-fold by doubling individual doses and switching to a twice daily schedule. The injections were all intramuscular. With the exception of group D, a six-week pretreatment period preceded the tumor challenge at day 0. Tumor challenge was followed by a 3-week treatment period (vehicle, AMT at either 3.2 mg/kg/d) (group A) or 6.4 mg/kg/d (group B), or AMT0, an AMT preparation which does not stimulate IL-6 secretion (6.4 mg/kg/d, group C) continuously for 21 days. AMT administration for group D (6.4 mg/kg/d) was limited to the treatment period from day 1 to 21. All mice were sacrificed 21 days after tumour transplantation. AMT administration was safe and well tolerated, and significantly reduced primary tumor volume in pretreated animals. The effective route of application was intramuscular, with dose escalation resulting in an improved anti-tumor effect. This is the first demonstration of a significant anti-tumorigenic effect of AMT in a validated tumor model.

Anti-metastatic effects of liposomal gemcitabine in a human orthotopic LNCaP prostate cancer xenograft model.

Fatal outcomes of prostate carcinoma (PCa) mostly result from metastatic spread rather than from primary tumor burden. Here, we monitored growth and metastatic spread of an orthotopic luciferase/GFP-expressing LNCaP PCa xenograft model in SCID mice by in vivo imaging and in vitro luciferase assay of tissues homogenates. Although the metastatic spread generally shows a significant correlation to primary tumor volumes, the susceptibility of various tissues to metastatic invasion was different in the number of affected animals as well as in absolute metastatic burden in the individual tissues. Using this xenograft model we showed that treatment with liposomal gemcitabine (GemLip) inhibited growth of the primary tumors (83.9 +/- 6.4%; P = 0.009) as well as metastatic burden in lymph nodes (95.6 +/- 24.0%; P = 0.047), lung (86.5 +/- 10.5%; P = 0.015), kidney (88.4 +/- 9.2%; P = 0.045) and stomach (79.5 +/- 6.6%; P = 0.036) already at very low efficient concentrations (8 mg/kg) as compared to conventional gemcitabine (360 mg/kg). Our data show that this orthotopic LNCaP xenograft PCa model seems to reflect the clinical situation characterized by the fact that at time of diagnosis, prostate neoplasms are biologically heterogeneous and thus, it is a useful model to investigate new anti-metastatic therapies.

Liposomal gemcitabine (GemLip)-efficient drug against hormone-refractory Du145 and PC-3 prostate cancer xenografts.

BACKGROUND: Gemcitabine (Gemc) is an efficient chemotherapeutic drug in various cancer types (e.g., pancreas) but has only limited effects on hormone-refractory prostate cancer (HRPCa). Since HRPCa cells are highly sensitive to even low doses of Gemc in vitro, the lack of clinical effects might be due to rapid degradation of Gemc by deaminases combined with impaired accumulation in tumor tissue and PCa cells. Liposomal formulation (GemLip) is expected to protect the entrapped cytotoxic substance from enzymatic degradation and furthermore augment its accumulation within tumor tissues due to an enhanced permeability of the tumor vessels. METHODS: Anti-tumoral and anti-metastatic activity of GemLip and Gemc were investigated in two luciferase-expressing, human hormone-refractory PC-3 and Du145 HRPCa xenograft models in immunodeficient mice. Tumor growth was monitored by in vivo luminescence imaging (orthotopic) or callipering (subcutaneous). Anti-metastatic effects of treatment were determined by in vitro luciferase assay of the tissues. RESULTS: Tumor growth of subcutaneous Du145 xenografts was significantly inhibited only by GemLip (8 mg/kg: P = 0.014 and 6 mg/kg: P = 0.011) but not by conventional Gemc (360 mg/kg). In contrast, growth of orthotopic PC-3 xenografts was significantly inhibited by both, GemLip (P = 0.041) and Gemc (P = 0.002). The drugs furthermore strongly reduced spleen and liver metastases in this model. CONCLUSIONS: As shown by the very low efficient concentration of GemLip, liposomal entrapment of Gemc greatly enhances its activity. GemLip has, even at very low doses, a significant anti-tumoral and anti-metastatic therapeutic effect in HRPCa xenografts in vivo and was beneficial even when the conventional Gemc failed.

Antimetastatic effects of liposomal gemcitabine and empty liposomes in an orthotopic mouse model of pancreatic cancer.

OBJECTIVES: Test the efficacy of liposomal gemcitabine (GemLip) on primary tumor and metastases using the pancreatic tumor cell line AsPC1 implanted orthotopically into nude mice. METHODS: The efficacy of gemcitabine and GemLip cells was tested on luciferase-transduced AsPC1 cells in vitro as well as implanted orthotopically into the pancreata of nude mice. RESULTS: In vitro, the IC50s for GemLip and gemcitabine were 20 nM and 140 nM, respectively. However, when applied against established tumors, GemLip (8 mg/kg) blocked tumor growth for 5 consecutive weeks according to bioluminescence measurements in vivo. Gemcitabine (240 mg/kg) had no effect on luciferase-monitored tumor growth. When analyzed at the time of necropsy, GemLip strongly reduced tumor size (-64% +/- [SD] 27%; ***P < 0.0001), whereas gemcitabine only weakly (-36% +/- 37%) affected tumor size. Empty liposomes had no effect on the tumor size. GemLip and empty liposomes both significantly interfered with the metastatic spread to the liver, as measured using luciferase assays (GemLip, *P = 0.01; empty liposomes, *P = 0.036). In addition, they showed effects against spleen, as well as peritoneal metastases. CONCLUSIONS: GemLip presents an effective new formulation of gemcitabine, combining the targeting and protective features of the liposomes with their antimetastatic effects to target pancreatic cancer.

Antitumor and antiangiogenic activity of cediranib in a preclinical model of renal cell carcinoma.

Cediranib is a highly potent and selective vascular endothelial growth factor (VEGF) signaling inhibitor with activity against all three VEGF receptors (VEGFRs) that inhibits angiogenesis and growth of human tumor xenografts in vivo. The present study evaluated the antitumor and antiangiogenic activity of cediranib in the clinically relevant, murine renal cell carcinoma (RENCA) model and its biological response using VEGF and sVEGFR-2 as biomarkers. Mice were treated with cediranib (5 mg/kg/d p.o.) or vehicle for 2, 8 or 12 days and tumor volumes, microvessel density (MVD) and VEGF and sVEGFR-2 plasma concentrations were determined. Cediranib treatment (8 and 12 days) led to a significant reduction in tumor size (42-50%) and a highly significant reduction in MVD (30-55%) versus controls. After 12 days' treatment, VEGF plasma concentration increased significantly in both cediranib-treated and control animals and this increase correlated with tumor size; the cediranib group showed a more pronounced increase in VEGF but a reduced tumor volume compared with control animals. Plasma concentrations of VEGF reached a plateau in the cediranib group after 17-21 days' treatment. sVEGFR-2 concentrations significantly decreased over 12 days in controls, whereas they remained stable in cediranib-treated mice. sVEGFR-2 did not correlate with tumor volume in controls; mice treated with cediranib had lower relative VEGFR-2 plasma concentrations and tumor burdens. In conclusion, cediranib showed potent antitumor and antiangiogenic efficacy in the RENCA model. sVEGFR-2 plasma concentrations can act as a surrogate marker for antitumor activity of VEGFR signaling inhibitors.

Mode-of-action, efficacy, and safety of a homologous multi-epitope vaccine in a murine model for adjuvant treatment of renal cell carcinoma.

BACKGROUND AND OBJECTIVE: In a phase-III trial it was recently shown that an adjuvant renal cell carcinoma (RCC) vaccine (Reniale) reduces the risk of tumour progression following nephrectomy. This clinical trial focused on efficacy and did not investigate end-points relating to mode-of-action of the vaccine. In a murine model we investigated mode-of-action, efficacy, and safety of a homologous RENCA cell-based vaccine. DESIGN, SETTING, AND PARTICIPANTS: Six groups with 12 BALB/c mice per group received five vaccinations (lysate of 1x10(6)-1x10(7) RENCA cells, manufactured with or without prior IFN-gamma incubation) at 3-wk intervals before tumour transplantation and one vaccination 14 d afterwards. Controls (12 mice) received only solvent. All mice were sacrificed 21 d after tumour transplantation. MEASUREMENTS: Animal welfare, tumour growth, number of metastases, and the presence of cytotoxic T-lymphocytes as determined by a (51)chromium-release assay. Adoptive immune transfer experiments (vaccination of nine mice with the RENCA vaccine or saline and transfer of serum, spleen cells, and CD4 and/or CD8 depleted spleen cells into five recipient mice each) were carried out to demonstrate involvement of different immune mechanisms. RESULTS: All controls developed a renal tumour, compared to 7/72 animals (9.7%) in the vaccine groups. The mean number of lung metastases was 100 (range 3-750) in controls and 4 (range 0-196) in the vaccine groups, respectively. Tumour uptake and number of metastases were not related to the vaccine dose. The (51)chromium-release assay confirmed a significant tumour-specific cytolytic activity and marginally increased NK activity of splenocytes from vaccinated mice against RENCA cells compared to controls. Adoptive immune transfer experiments showed that the antitumoural effective immune mechanisms are cell-based. CONCLUSIONS: We could demonstrate the mode-of-action, efficacy, and safety of a homologous tumour vaccine in a RENCA model. These findings support the positive results from a phase-III trial with Reniale.

Antitumoral and antiangiogenic efficacy of bisphosphonates in vitro and in a murine RENCA model.

BACKGROUND: Bisphosphonates have shown direct antitumoral activity in vitro, in vivo and even in clinical studies, but the exact mechanism for this has not yet been elucidated. In this study the antiangiogenic potency of zoledronic acid and clodronate were evaluated. MATERIALS AND METHODS: The effects of zoledronic acid and clodronate on the proliferation of endothelial cells and different tumor cells, and on the activity of protein kinases were investigated. Furthermore in vitro experiments were performed to evaluate the underlying antiangiogenic mechanism of action. Both bisphosphonates were examined in vivo at different doses and in daily subcutaneous application in a murine renal cell carcinoma model (RENCA). The antiangiogenic activity was evaluated by immunohistochemical staining (CD31) and by determination of mouse vascular endothelial growth factor (VEGF) serum concentration. RESULTS: Zoledronic acid and clodronate inhibited proliferation of endothelial cells at lower concentrations than the different tumor cell lines did. This effect was more pronounced for zoledronic acid. The activity of almost all tested kinases was inhibited by zoledronic acid, whereas clodronate showed no effect. In the RENCA model, a significant effect of zoledronic acid on the primary tumor in a bell-shaped dose response curve with the highest efficacy between 100 Bg/kg 2xd and 200 Bg/kg 1xd, was observed. The mean vessel density (MVD) was significantly reduced by both bisphosphonates at different concentrations. This is the first report on increased mouse VEGF serum concentrations in the RENCA model. CONCLUSION: The results indicate that these bisphosphonates, particularly zoledronic acid, possess antitumoral and antiangiogenic activity.

Synthesis and biological evaluation of an albumin-binding prodrug of doxorubicin that is cleaved by prostate-specific antigen (PSA) in a PSA-positive orthotopic prostate carcinoma model (LNCaP).

The prostate-specific antigen (PSA) is a serine protease that is over-expressed in prostate carcinoma and represents a molecular target for selectively releasing an anticancer agent from a prodrug formulation. We have recently investigated a macromolecular prodrug strategy for improved cancer chemotherapy based on 2 features: (i) rapid and selective binding of thiol-reactive prodrugs to the cysteine-34 position of endogenous albumin after intravenous administration, and (ii) enzymatic release of the albumin-bound drug at the tumor site (Mansour et al., Cancer Res 2003, 63, 4062-4066). In this work, we describe an albumin-binding prodrug, EMC-Arg-Ser-Ser-Tyr-Tyr--Ser-Arg-DOXO [EMC: epsilon-Maleimidocaproic acid; DOXO = doxorubicin; X = amino acid] that is cleaved by PSA. Because of the incorporation of 2 arginine residues, the prodrug exhibited excellent water-solubility and was rapidly and selectively bound to endogenous albumin. Incubation studies with PSA and tumor homogenates from PSA-positive tumors (LNCaP) demonstrated that the albumin-bound form of the prodrug was efficiently cleaved by PSA at the P(1)-P' (1) scissile bond releasing the doxorubicin dipeptide H-Ser-Arg-DOXO, which was further degraded to doxorubicin as the final cleavage product. In cell culture experiments, the prodrug was approximately 100-fold less active against LNCaP cells than the free drug. In contrast, in a mouse model of human prostate cancer using luciferase transduced LNCaP cells orthotopically implanted in SCID mice, the prodrug showed enhanced antitumor efficacy when compared to doxorubicin. Doxorubicin treatment at a dose of 2 x 4 mg/kg caused significant weight loss and mortality (-25%), and did not result in a significant antitumor response at the end of the experiment. The prodrug at 3 x 12 mg/kg doxorubicin equivalents, however, was well tolerated and induced a significant reduction in tumor size of 62% (+/-25%, **p = 0.003) as well as a decrease of the metastatic burden in the lungs as detected in luciferase assays (-50%, SD +/- 115%, *p = 0.038).

Antiangiogenic potency of various chemotherapeutic drugs for metronomic chemotherapy.

From previous preclinical findings continuous low dose (metronomic) chemotherapy is thought to inhibit tumor angiogenesis. This suggests that activated endothelial cells may be more sensitive to chemotherapeutic drugs than tumor cells. Therefore, we assessed the IC50 for several relevant chemotherapeutic drugs in different endothelial and tumor cell lines to identify optimal compounds to be used for metronomic therapy in a murine renal cell carcinoma model. Adriamycin, idarubicin, 5-fluorouracil, paclitaxel and etoposide were chosen for our studies because of their oral availability in patients or previous reports on metronomic potential. IC50s were determined by BrdU cell growth assay after short time as well as long term exposure of the following cell lines: human endothelial cells (HdmVEC/HUVEC), human breast cancer (Mcf-7), melanoma (Skmel), liver cancer (Huh7/Alexander), lung cancer (A549/LXFL), colon cancer (Dld) and murine renal cell carcinoma (RENCA). In addition, FACS analysis was performed to determine the effect on cell cycle. In vivo, doses of 2x12 mg/kg, 2x1.2 mg/kg and 10x0.24 mg/kg adriamycin were applied to 12 RENCA mice each and antitumor as well as antiangiogenic effects were assessed 21 days after tumor cell application. Independent of the exposure time, all chemotherapeutic drugs were more active against the endothelial cell lines. IC50s were significantly lower in endothelial cells (4.02E-06 to 6.16E-14 M) as compared to tumor cells (7.44E-02 to 1.9E-11 M). Cell cycle analysis of all chemotherapeutic drugs revealed a G1-arrest in endothelial cells. Adriamycin applied in metronomic doses of 10x0.24 mg/kg showed significant antiangiogenic activity whereas, in contrast, the application of 2x12 mg/kg significantly increased the vessel density in primary tumors. In summary, all chemotherapeutic agents were more active against endothelial cells in comparison to tumor cells. The hypothesis of an antiangiogenic active metronomic therapy could be confirmed in vivo by the use of adriamycin in RENCA.

Inhibition of tumor growth and angiogenesis by soluble EphB4.

EphB receptors and their ephrinB ligands play a key role in the formation of a regular vascular system. Recent studies have also shown the involvement of Eph/ephrin interactions in malignant tumor progression and angiogenesis. We have generated soluble monomeric EphB4 (sEphB4)-expressing A375 melanoma cells to study the effect of dominant negatively acting sEphB4 on tumor growth and angiogenesis. Soluble EphB4-expressing A375 tumors grown subcutaneously in nude mice show dramatically reduced tumor growth compared to control tumors. The proliferative capacity of sEphB4-expressing cells in monolayer culture is not altered. Yet, sEphB4-expressing A375 cells cannot establish proper cell-cell contacts in three-dimensional spheroids. However, sEphB4 transfectants have reduced proliferation and apoptosis rates when grown in three-dimensional culture in vitro or in subcutaneous tumors in vivo. Analysis of the vascular phenotype of the tumors revealed a reduction of intratumoral microvessel density in sEphB4-expressing tumors. Corresponding to these mouse experiments, a matched pair analysis of EphB4 and ephrinB2 expression in human colon carcinomas revealed significantly upregulated levels of EphB4 expression compared to adjacent normal tissue. Taken together, the data identify dual effects of sEphB4 on the tumor and the vascular compartment that collectively inhibit tumor growth.

A new approach for the treatment of malignant melanoma: enhanced antitumor efficacy of an albumin-binding doxorubicin prodrug that is cleaved by matrix metalloproteinase 2.

The progression of malignant melanoma is characterized by overexpression of a number of matrix metalloproteinases (MMPs), especially MMP-2, which play a critical role in the degradation of basement membranes and the extracellular matrix. Consequently, we assessed a drug targeting strategy in which the protease activity of MMP-2 is exploited to release an anticancer agent from a macromolecular carrier, i.e., circulating albumin. For this purpose, a water-soluble maleimide derivative of doxorubicin (1) incorporating a MMP-2 specific peptide sequence (Gly-Pro-Leu-Gly-Ile-Ala-Gly-Gln) was developed that binds rapidly and selectively to the cysteine-34 position of circulating albumin. The albumin-bound form of 1 was efficiently and specifically cleaved by MMP-2 liberating a doxorubicin tetrapeptide (Ile-Ala-Gly-Gln-DOXO) and subsequently doxorubicin. In vivo, 1 was superior to the parent compound doxorubicin in the A375 human melanoma xenograft, which is characterized by a high expression of MMP-2.