Abstract 5322: Bioluminescence, fluorescence, and biomarker mediated monitoring of an orthotopic model of colon cancer treated with VX-680

With 10% of all newly diagnosed cases per year, colon cancer ranks within the top 5 cancer types within the USA, and, with a similar figure of people succumbing to the disease, is a major cause of tumor-related deaths. Primary tumors may often be removed via surgery, but metastatic spread poses considerable difficulties and chemotherapeutic treatments are rarely curative. Novel drugs, and predictive pre-clinical model systems to better mimic human disease are therefore urgently needed.

Although subcutaneously implanted tumor cells have been used for pre-clinical drug testing for decades now, the predictive value of these models has recently become the subject of controversy. Orthotopically implanted cells reflect the human disease much better in that organo-typical tumor stromal interactions are enabled, and tumor cells spread to other sites with distribution patterns reflecting the human disease.

Orthotopical implantation requires sensitive imaging modalities, similar to the patient situation. Bioluminescence imaging (BLI) is a well established modality for pre-clinical models, but is not translatable to the clinic. Recently, fluorescence molecular tomography (FTM) imaging has been shown to offer good sensitivity and tissue penetration, and sensitive probes – that may be used in the clinic – have been developed.

A pre-clinical experiment was performed to compare the growth behaviour of orthotopically implanted, luciferase marked HCT116 wild-type and p53 KO human colon cancer cells and test their sensitivity towards the aurora-inhibitor VX-680. Growth of the tumors, and treatment effects were followed in vivo using BLI, and a final imaging analysis with integrisense, using FMT. The in vivo imaging data were validated with necropsy data, including sensitive luciferase assays to detect metastases in organs.

In vivo BLI suggested that p53 KO tumors grew much more aggressive, giving rise to larger, more fragmented signals than their wild-type counterparts. Imaging using integrisense confirmed the presence of much larger tumor masses in the p53 KO than in the wild-type group. VX-680 slightly reduced the BLI signals from both groups. Necropsy results confirmed the tumor size differences between wild-type and p53 KO tumors, also the VX-680 effect against wild-type tumors (−50%, SD 70%). However, the drug appeared ineffective against p53 KO tumors (+120%, SD 70%). Luciferase assays from potential target organs detected an increased metastasation in p53 KO tumor bearing animals compared to those with wild-type tumors. Interestingly, metastasation of the p53 KO tumors to the spleen was sensitive to VX-680 treatment (−90%, SD 20%). The effect of the drug could also be demonstrated in skin biopsies taken from the mice as a surrogate tissue.

This study represents a ‘high content’, partially translatable mouse model applicable also for the testing of other targeted therapies.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 5322. doi:10.1158/1538-7445.AM2011-5322

Abstract 2569: Combination of the albumin-binding prodrug of doxorubicin (INNO-206) and doxorubicin produces complete remissions in an ovarian A2780 xenograft model

INNO-206, the (6-maleimidocaproyl)hydrazone of doxorubicin (DOXO-EMCH) is an albumin-binding prodrug of doxorubicin with acid-sensitive properties that has demonstrated superior antitumor efficacy in eight murine tumor models compared to doxorubicin. After intravenous administration, INNO-206 rapidly binds to the cysteine-34 position of circulating albumin and accumulates in solid tumors due to passive targeting. It has shown objective responses in a phase I study, and phase II studies are planned for 2011 at the recommended dose of 260 mg/m2 i.e. an approximate 4-fold increase over the standard dose for doxorubicin.

Interestingly, in contrast to free doxorubicin, which primarily locates in the nucleus, INNO-206, mainly accumulates in the cytoplasm. Furthermore, the binding of INNO-206 to albumin and the resulting EPR-mediated accumulation and distribution in the tumor will differ from the distribution of free doxorubicin which will be mediated by diffusion. There might thus be a rationale to combine the two drug formulations for obtaining an optimal antitumor effect. Indeed, in cell culture experiments using A2780 cells, a moderate synergy was found at a 5:1 ratio of free Doxo : INNO-206.

In a next step, we therefore tested whether a combination of suboptimal doses of INNO-206 with doxorubicin improved the therapeutic efficacy of INNO-206 or doxorubicin at their respective maximum tolerated doses (MTDs) in the mouse model. We treated nude mice with subcutaneously growing ovarian A2780 xenografts on a weekly schedule with 2 × 8 mg/kg doxorubicin (MTD), 3 × 24 mg/kg INNO-206 (doxorubicin equivalents) (MTD) and a combination of 3 × 12 mg/kg INNO-206 (doxorubicin equivalents) and 3 × 4 mg/kg doxorubicin. In the combination protocol, INNO-206 was administered 6 h prior to doxorubicin treatment. Doxorubicin showed a very moderate effect and a body weight loss of -21 %, whereas INNO-206 and also the combination produced complete remissions. The combination, however, was much better tolerated causing a body weight loss of -12 % compared to -31 % for INNO-206. The surprising result of this experiment is that the doses used in the combination regimen were able to induce complete remission and the best tolerability considering that when dosed individually at these doses, neither doxorubicin or INNO-206 would have produced such an impressive antitumor response. This work is an impetus for investigating further combinations of albumin-binding prodrugs with clinically established anticancer agents.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2569. doi:10.1158/1538-7445.AM2011-2569

Abstract 3502: Activity of combinations of anticancer agents in pancreatic carcinoma cell lines

Long term and successful treatment of pancreatic cancer remains a considerable challenge, and there is an urgent need to develop new therapeutic strategies that improve the response rate and overall survival of this disease that responds poorly to monotherapy with anticancer agents such as gemcitabine or 5-fluorouracil. Instead of combining drugs at their respective maximum tolerated doses, a number of recent studies have shown that the “more is better” paradigm may not be the optimal strategy for maximizing the clinical outcome for combination therapy and rather synergistic effects can be achieved if the drugs are dosed at a defined ratio. Such an approach is currently being investigated clinically with liposomal formulations which contain irinotecan and floxuridine at a 1:1 ratio or cytarabine and daunorubicin at a 5:1 ratio. We therefore tested a number of combinations of chemotherapeutic agents using defined ratios ranging from 10:1 to 1:10 for their efficacy against a luciferase transduced pancreatic cell line, MIAPaCa2 ELN, using a 72 h Luciferase proliferation assay. Using this assay, a combination of camptothecin with gemcitabine showed synergy at a ratio of 1:5 over a cell survival range of 10-80% with combination indexes (CIs) between 0.36 and 0.71.

In addition, a synergy was found at a 1:10 ratio for methotrexate with doxorubicin with CI values from 0.36 to 0.32 over a 20-90% cell survival range. A third synergistic combination was observed between cytarabine and gemcitabine at a 1:5 ratio with CIs from 0.16 to 0.21 over a 20-90% cell survival range. None of the other combinations tested, including campthotecin with methotrexate, camptotecin with doxorubicin, or cytarabine with daunorubicin showed synergistic effects at ratios from 5:1 to 1:5.

These in vitro results show that the ratio of the respective drug combination is a decisive factor for inducing additive, synergistic or even antagonistic effects.

We are currently testing the most promising combinations in additional pancreatic carcinoma cell lines in order to elucidate whether the synergistic effects of these combinations and specific ratios apply to pancreatic cancer cells in general.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 3502. doi:10.1158/1538-7445.AM2011-3502

A direct ELISA assay for quantitative determination of the inhibitory potency of small molecules inhibitors for JNK3

The c-jun N-terminal kinase 3 (JNK3) is a promising drug target for the treatment of neurological disorders. Here we report a direct ELISA including the optimization of a nonradioactive immunosorbent JNK3 activity assay to determine inhibitory potency of small-molecule inhibitors. Based on our previous JNK3 assay and our recently optimized p38α mitogen activated protein kinase (MAPK) protocol for monitoring the phosphorylation of activating-transcription factor 2 (ATF-2), we present a rapid and straightforward alternative to conventional radioactive and indirect ELISA kinase assays. To validate the assay with the optimized assay conditions we used reference compounds and achieved well comparable IC(50) results to published data. The use of a linked monoclonal antibody increased the specificity and the sensitivity of the assay, reducing the required antibody concentration by approximately 100-fold. The novel protocol is an accurate, easy-to-handle and robust screening assay for JNK3 and the assay performance was reduced from 7.5 to 3h.

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.

In vivo evaluation of a novel albumin-binding prodrug of doxorubicin in an orthotopic mouse model of prostate cancer (LNCaP)

PSA, which is overexpressed in prostate carcinoma, represents a molecular target for selectively releasing an anticancer agent from a prodrug formulation. In this study, we report on the in vivo antitumor efficacy of an efficacious albumin-binding prodrug of doxorubicin (PSA9) that incorporates p-aminobenzyloxycarbonyl (PABC) as a self-immolative spacer in addition to the heptapeptide, Arg-Ser-Ser-Tyr-Tyr-Ser-Leu, which serves as a substrate for PSA. The prodrug is cleaved very efficiently by PSA releasing H-Ser-Leu-PABC-doxorubicin and subsequently doxorubicin in PSA-positive cell lysates and prostate tumor homogenates as the final cleavage product. PSA9 at 3 × 6 mg kg(-1) doxorubicin equivalents (intravenous) was compared with conventional doxorubicin at equitoxic doses (at 3 × 3 mg kg(-1); intravenous) in an orthotopic mouse model of prostate cancer using LNCaP lentiviral luciferase-neomycin cells transduced with luciferase. Whereas doxorubicin did not show any efficacy against the primary tumor or metastases, the prodrug reduced the primary tumor by 30-50% and circulating PSA levels, and in addition, showed a pronounced reduction in lung and bone metastases by ∼77% and ∼96%, respectively, and a positive trend regarding the activity against liver and lymph-node metastases compared with control and doxorubicin-treated animals. The incorporation of PABC as a self-immolative spacer together with a PSA substrate demonstrates superior antitumor effects over doxorubicin attributed to an efficient cleavage by PSA releasing doxorubicin as the final active agent in prostate tumor homogenates. Using this approach for developing effective prodrugs against prostate cancer, is worthy of further preclinical optimization.

Optimization of an albumin-binding prodrug of Doxorubicin that is cleaved by prostate-specific antigen

We have developed a novel albumin-binding prodrug of doxorubicin that incorporates p-aminobenzyloxycarbonyl (PABC) as a 1,6 self-immolative spacer in addition to the heptapeptide, Arg-Ser-Ser-Tyr-Tyr-Ser-Leu, as a substrate for the prostate-specific antigen (PSA) that is overexpressed in prostate carcinoma and represents a molecular target for selectively releasing an anticancer agent from a prodrug formulation. The prodrug exhibited good water solubility and was bound rapidly to the cysteine-34 position of human serum albumin. Incubation studies with PSA demonstrated that the albumin-bound form of the prodrug was cleaved rapidly at the P1-P1' scissile bond, releasing H-Ser-Leu-PABC-DOXO, which was further degraded to release doxorubicin as a final cleavage product within a few hours in prostate tumor tissue homogenates as well as in PSA-positive LNCaP LN cell lysates. Moreover, our prodrug exhibited antiproliferative activity in a low micromolar range against a PSA-expressing prostate cancer cell line (LNCaP).

Abstract 4665: A combined IHC/Western method to measure phosphorylated histone H3 in skin biopsies as potential biomarker for anticancer drug action

In recent years there has been a rapid increase in targeted tumor therapy approaches. Hand in hand with these novel approaches, the need has arisen to monitor specific target inhibition by the drug. In contrast to classic chemotherapy, which non-specifically targets proliferating cells, these novel approaches attempt to specifically interfere with some process thought to be crucial for the tumor cell survival. Nevertheless, despite extensive validation, an immediate effect of target interference on tumor growth may not necessarily be expected. Thus, in order to demonstrate activity of anti-cancer drugs, a marker known to be modified upon inhibition of the target may serve as a surrogate to tumor inhibition. Ideally, tumor biopsies would be analysed for monitoring of drug-induced effects. However, taking in consideration the difficulties to perform sequential tumor biopsies, the use of surrogate tissues like blood or skin is being explored instead. Blood is relatively easily accessible, but unlike skin tissue, blood may not reflect the fact that drugs have to penetrate multiple layers of tissue in order to reach their target in the tumor. Also, to monitor the effects of anti-mitotic drugs, the investigated specimen must exhibit proliferating features, which is given only in a very poor manner blood samples, as peripheral blood cells have typically exited the cell cycle. However cells in the dermis still proliferate, albeit to a small percentage.

Therefore, considering these issues, we set out to develop a method to analyse drug effects in skin biopsies. Traditionally, most analyses of skin biopsies have relied on immunohistochemistry (IHC) studies. However, the quantification of such results is time-consuming and error-prone. Western Blot analyses are easier to quantify, but require a considerable amount of protein lysate of sufficient concentration. We developed a protocol that reproducibly allows the detection and quantification of phosphorylated histone H3 in Western Blots from a single half of a skin biopsy. For normalization, the total amount of histone H3 present in the lysate is determined. The other half of the skin biopsy may be used for IHC analysis of phosphorylated histone H3, allowing the comparison to other studies relying solely on IHC.

We will present data on the measurement of phosphorylated histone H3 via Western Blots and IHC from skin biopsies of healthy donors.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4665.

Abstract LB-37: In vitro and in vivo studies of novel acid-sensitive prodrugs derived from dendritic polyglycerol

Research in the development of tumor-specific nanocarriers is currently one of the major sources of innovation for improved anticancer chemotherapy. Due to their low degree of molecular weight dispersity, their flexible design and their biocompatible nature, dendritic polyglycerols (PGs) have a broad range of potential applications in medicine and pharmacology. Recently, we demonstrated that drugs could be bound to the thiolated hyperbranched polymers incorporating enzymatically cleavable spacers that were efficiently released by the target enzyme cathepsin B. These initially developed dug carriers with PGs, however, did not have an optimal molecular weight for EPR-mediated tumor targeting and remaining amino groups on the surface of the dendritic scaffold showed acute toxicity properties.

As a consequence, we set out to improve the conjugation method and fine-tune the architecture of the polyglycerol drug conjugates for optimal tumor targeting. A logically consistent option was to mask remaining and potentially toxic amino groups with the polymer polyethylene glycol which would have the additional advantage of increasing the molecular weight of drug polyglycerol conjugate to > 40 kDa which is a pre-requisite for passive targeting. Thus, we developed a macromolecular prodrug derived from hyperbranched amino-bearing polyglycerol that in a first step was partially thiolated with iminothiolane followed by a Michael addition to the maleimide group of the acid-sensitive 6-maleimidocaproyl(hydrazone) derivative of doxorubicin, and in a second step the maleimide group of 2 and 5 kDa PEG chains were reacted with the remaining sulfhydryl groups. Thus, the drug was covalently attached to the hyperbranched polyglycerol core and surrounded by a “shell” of long, solubilizing PEG chains which radiate from the core. By varying the amount of iminothiolane, of doxorubicin prodrug and of PEG-maleimide, drug PG conjugates with different drug loading (1 to 10) were isolated. Analysis by dynamic light scattering measurements (DLS) and z-potential showed that average diameters were in the range of 12 to 16 nm and the conjugates showed a slightly negative surface charge. The in vitro release studies showed that the release of doxorubicin was minimal at pH 7.4 after 22 h (less than 10%), while at acidic pH half-lives were below 4 h. Although free doxorubicin was more active than the PG doxorubicin conjugates against A2780 ovarian carcinoma cells, in the respective xenograft model the pegylated PG doxorubicin conjugates with 5 to 10 bound molecules of doxorubicin showed a distinct increase in tolerability and antitumor efficacy in comparison to the parent drug producing excellent antitumor effects with complete and transient tumor remissions (at 24 mg/kg doxorubicin equivalents). Doxorubicin treated animals only showed a moderate antitumor effect at its optimal dose of 2 × 8 mg/kg.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr LB-37.

Abstract LB-39: Development of a novel water-soluble prodrug of paclitaxel that is cleaved by prostate-specific antigen (PSA): In vitro and in vivo evaluation

In developed countries, prostate cancer is the second most frequently diagnosed cancer, and the third most common cause of death from cancer in men. Unfortunately, while accumulating clinical data have suggested that the 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 tumor selectivity. Besides prostate cancer, paclitaxel (Taxol®) is currently showing a promising antitumor activity against a variety of human tumors. In an attempt to improve both the water solubility and tumor targeting properties of paclitaxel, we set out to develop a water soluble paclitaxel prodrug that is activated specifically by prostate-specific antigen (PSA) which is solely expressed in prostate tissue and prostate carcinoma with high levels up to mg/g present in human prostate carcinoma. Using albumin as an efficient carrier for drug delivery, we describe a novel albumin-binding prodrug of paclitaxel, EMC-Arg-Ser-Ser-Tyr-Tyr-Ser-Leu-PABC-Paclitaxel [EMC: -maleimidocaproyl; PABC: p-aminobenzyloxycarbonyl] that was synthesized by reacting EMC-Arg-Ser-Ser-Tyr-Tyr-Ser-OH with H-Leu-PABC-Paclitaxel. This prodrug exhibited excellent water-solubility and was bound rapidly to the cysteine-34 position of endogenous and exogenous albumin. Moreover, incubation studies with PSA demonstrated that the albumin-bound form of the prodrug was cleaved rapidly at the P1-P‘1 scissile bond releasing the paclitaxel-dipeptide H-Ser-Leu-PABC-Paclitaxel. Above all, 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 tumor tissue homogenates. Of note was that the albumin-bound form of the prodrug was approximately 4-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. Therefore, the in vivo efficacy of the prodrug (24 mg/kg paclitaxel equivalents) in comparison to free paclitaxel (12 mg/kg) is currently being evaluated in a mouse model of human prostate cancer using luciferase transduced LNCaP LN cells orthotopically implanted in SCID mice.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr LB-39.

Abstract LB-38: Evaluation of a PSA cleavable doxorubicin prodrug in the in vitro and in vivo LNCaP LN model

The goal of this work was to investigate the biological activity of a doxorubicin prodrug that is efficiently cleaved by prostate specific antigen (PSA) rapidly liberating doxorubicin as the final cleavage product. For this purpose we have developed an albumin-binding prodrug of doxorubicin, EMC-Arg-Ser-Ser-Tyr-Tyr-Ser-Leu-PABC-DOXO [EMC: ε-maleimidocaproyl; PABC: p-aminobenzyloxycarbonyl; DOXO: doxorubicin]. The incorporation of the PABC self-eliminating linker between the peptide sequence and doxorubicin enhanced the enzymatic cleavage rate and improved the cleavage profile. PSA cleavage produced the metabolite H-Ser-Leu-PABC-DOXO which was further degraded to release doxorubicin as a final cleavage product within a few hours in prostate tumor tissue homogenates as well as in PSA-positive LNCaP LN cell lysates. In the cell culture experiments, our prodrug exhibited antiproliferative activity in the low micromolar range with an IC50 value of ∼1 μM against a PSA-expressing prostate cancer cell line with a stably integrated Luciferase-Neomycin (LN) resistance fusion gene cassette (LNCaP LN). Moreover, H-Ser-Leu-PABC-DOXO showed comparable in vitro activity to doxorubicin (∼0.2 μM). Orientating toxicity studies in mice showed that the maximum tolerated dose of our novel prodrug was twice that of conventional doxorubicin. Consequently, the in vivo efficacy of the prodrug (6 mg/kg doxorubicin equivalents) is currently being compared to free doxorubicin (3 mg/kg) in a mouse model of human prostate cancer using luciferase transduced LNCaP cells orthotopically implanted in SCID mice.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr LB-38.

Abstract C187: Antitumoral efficacy of the novel thrombin inhibitor Revasc©/Desirudin in an orthotopic metastatic AsPC-1 pancreas tumor model

Background: Thrombo-embolism is one of the most common secondary diseases in cancer patients and is the second leading cause of death of these patients. In pancreatic cancer patients, thrombosis occurs more frequently than in other cancer patients. Thus anticoagulants are widely used in cancer therapies mainly to prevent the development of thrombo-embolisms. However there is increasing evidence that anticoagulants have also antitumoral and anti-angiogenic effects. The aim of this study was to evaluate the anti-tumoral, anti-metastatic and anti-angiogenic efficacy of the novel anticoagulant Revasc© a recombinant hirudin and direct thrombin inhibitor, in an orthotopic mouse model of pancreatic cancer.

Material and Methods: To evaluate the anti-tumoral, anti-metastatic and anti-angogenic efficacy of Revasc©, luciferase labeled pancreatic AsPC-1-tumor cells were orthotopically implanted into the pancreas of NMRI nude mice. After onset of tumor growth, mice were randomized into six groups. Group 1 received vehicle control (0.9% NaCl) twice daily, Group 2 received Gemcitabine (240 mg/kg) once weekly; Group 3 received Revasc at a concentration of 1 mg/kg twice daily, Group 4 received Revasc© at a concentration of 3 mg/kg twice daily, Group 5 received Revasc© at a concentration of 10 mg/kg daily and Group 6 received a combination therapy of twice daily 10 mg/kg Revasc© plus a weekly dose of 240 mg/kg Gemcitabine. At the end of the study, tumor weight and volume were determined and luciferase activity was monitored in the primary tumor and selected organs (spleen, liver, stomach, intestine, lung and inguinal lymph nodes). In addition, microvessel densities and vessel maturation was determined by immunohistochemisty.

Results: In general, Revasc© was very well tolerated. The primary tumor weight was significantly reduced in the groups receiving Revasc© at a concentration of 3 mg/kg and 10 mg/kg as well as in the control group treated with Gemcitabine. The combination of Gemcitabine and Revasc©, however, did not show any additive effect. No significant reduction of metastasis could be observed in the Revasc© Groups, whereas Gemcitabine efficiently inhibited metastasis into the lung. However, Revasc© showed a significant anti-angiogenic potential at the lowest concentration of 1mg/kg, corroborating findings of other groups showing that thrombin inhibition acts anti-angiogenic.

Conclusion: Taken together the study showed that Revasc© has an anti-tumoral and a mild anti-angiogenic effect. The data suggest that Revasc© has a potential to be used for the treatment of patients with pancreatic cancers; primarily to prevent thromboembolism but secondarly also to inhibit tumor growth. It remains to be shown if Revasc will lead to a solid anti-tumoral effect in patients and if the relatively short mean elimination half life of Revasc© (2–3 h) will allow to identify a convenient dosing scheme. Alternatively a pegylated hirudin derivative (PEG-hirudin) which has a longer half life and which has proven to have a very efficient antitumoral activity could be of high therapeutic interest.

Citation Information: Mol Cancer Ther 2009;8(12 Suppl):C187.

Abstract C183: Antitumor efficacy of PEG-Hirudin (LU 87981), administered three times weekly, in an orthotopic AsPC-1 pancreas carcinoma model

Background: Since anticoagulants could be shown as promising novel therapeutics in oncology, direct thrombin inhibitors like recombinant Hirudin (Revasc©/desirudin) were assessed in a preclinical orthotopic AsPC-1 mouse model in vivo. The challenges of desirudin for the treatment of cancer are its complex pharmacodynamics and a short half life (mean elimination half-life of 2–3h), requiring at least twice daily subcutaneous administration of the drug. PEG-Hirudin, the conjugate of recombinant Hirudin with two molecules of polyethylene glycol (PEG)-5000 represents a potential alternative to Revasc© with a longer half-life and more stable plasma levels. In order to test this compound, the pancreatic cancer cell line, AsPC-1 was chosen, for which preliminary results with Revasc© were available. AsPC-1 cells implanted orthotopically into the mouse pancreas reflect hallmarks of the human disease such as early invasion of the surrounding pancreatic tissue and the formation of metastases in the spleen and liver as well as the peritoneum.

Material and Methods: Luciferase expressing AsPC-1 cells were orthotopically implanted into mouse pancrei. The growth of the tumors was followed via bioluminescence measurements (whole body imaging). 13 days after surgery, 12 animals each were randomized into 5 treatment groups according to their bioluminescence signal. Group 1 served as vehicle control receiving 100µl saline solution three times weekly s.c. from day 15 to day 38. The application scheme was comparable to treatment groups receiving 1mg/kg (group 3), 3 mg/kg (group 4) and 0.3mg/kg (group 5) PEG-Hirudin three times weekly s.c. starting at day 15. The animals of group 2 received Gemcitabin at 240mg/kg administered i.v. once weekly starting at day 15. At the end of the study tumor weight and volume were determined and luciferase activity was monitored in the primary tumor and selected organs (spleen, liver, stomach, intestine, lung and inguinal lymph nodes).

Results: PEG-Hirudin was well tolerated, no bleeding at the injection site or other side effects could be observed. Only one animal of group 4 was found dead during the study, all other animals reached the end of the study. Gemcitabin, did not affect tumor growth according to in vivo bioluminescence imaging, whereas PEG-Hirudin at 1 and 3 mg reduced the increase of the bioluminescence signal during the treatment period significantly. Once the animals were sacrificed and tumor sizes measured, treatment with PEG-Hirudin at 1 and 3 mg/kg showed significant reduction of the average primary tumor size (Group 3: *p= 0.0129, Group 4:**p=0.0015). The positive control, Gemcitabin showed as well a significant antitumor efficacy (***p=0.0002). The differing results of in vivo imaging and primary tumor sizes are reflecting the different efficacy of the test items on primary tumor and peritoneal metastases.

Conclusion: The results presented here suggest a promising anti-tumoral efficacy of the PEG-Hirudin compound. Due to its extended half-life and the resulting relaxation of the application scheme, PEG-Hirudin is a promising alternative to Revasc© (desirudin) in oncology.

Citation Information: Mol Cancer Ther 2009;8(12 Suppl):C183.

Abstract A132: Development of efficient macromolecular prodrugs derived from dendritic polyglycerol

Introduction: Utilizing the Enhanced Permeation Retention Effect (EPR) for passive targeting is one of the novel approaches for tumor-selective drug delivery. Polymer-based nanocarriers, especially those of dendritic architecture, have gained increasing interest for encapsulating or coupling diagnostic or therapeutic agents. Chemical conjugation to a dendritic scaffold, thereby exploiting the high multivalency, allows for the covalent attachment of different kinds of bioactive molecules (imaging agents, drugs, targeting moieties, or biocompatible molecules) in a controlled ratio. (1) Hyperbranched polyglycerol is a potent alternative to perfect dendrimers for biomedical applications because of its ease of preparation, non-immunogenicity, tuneable molecular weight, high water-solubility and structural flexibility through end group modification. (2)

Here we present a comprehensive study for the development of macromolecular doxorubicin-polyglycerol prodrugs. The effects of the conjugation approach, the polymeric architecture, the cleavable linker and the drug loading over the final properties are analyzed.

Results and Discussion: Hyperbranched polyglycerols partially modified with azido, propargyl, amine or polyethylene glycol were prepared with overall yields higher than 60%. Different reactions, e.g click coupling and Michael addition, were evaluated for the conjugation of several doxorubicin derivates to the polyglycerol scaffolds. UV-Visible, 1H-NMR, GPC and HPLC were used to demonstrate the obtention of macromolecular prodrugs with several molecular weights, architectures and different cleavable linkers. The conjugates showed rapid and selective release of doxorubicin after being triggered by a change in pH or in presence of enzymes, accordingly to the nature of conjugated prodrugs.

The antiproliferative activity assessed against two human tumor cell lines AsPC1 LN (pancreatic carcinoma) and MDA-MB-231 LN (mamma carcinoma) showed less (2- to 10-fold) cytotoxicity than the corresponding free drugs. Cellular uptake was confirmed by fluorescence microscopy. In all cases, the conjugates showed to be active in the low micromolar range that is relevant for further preclinical studies of anticancer prodrugs.

The in vivo efficacy was tested in ovarian carcinoma A2780 xenograft model. With respect to antitumor efficacy, some of the conjugates manifested excellent antitumor effects with complete tumor remissions up to day 30. No significant changes in body weight were observed even after administration of 3-fold the maximal tolerated dose for free doxorubicin.

Citation Information: Mol Cancer Ther 2009;8(12 Suppl):A132.

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.

INNO-206, the (6-maleimidocaproyl hydrazone derivative of doxorubicin), shows superior antitumor efficacy compared to doxorubicin in different tumor xenograft models and in an orthotopic pancreas carcinoma model

The (6-maleimidocaproyl)hydrazone derivative of doxorubicin (INNO-206) is an albumin-binding prodrug of doxorubicin with acid-sensitive properties that is being assessed clinically. The prodrug binds rapidly to circulating serum albumin and releases doxorubicin selectively at the tumor site. This novel mechanism may provide enhanced antitumor activity of doxorubicin while improving the overall toxicity profile. Preclinically, INNO-206 has shown superior activity over doxorubicin in a murine renal cell carcinoma model and in breast carcinoma xenograft models. In this work, we compared the antitumor activity of INNO-206 and doxorubicin at their respective maximum tolerated doses in three additional xenograft models (breast carcinoma 3366, ovarian carcinoma A2780, and small cell lung cancer H209) as well as in an orthotopic pancreas carcinoma model (AsPC-1). INNO-206 showed more potent antitumor efficacy than free doxorubicin in all tumor models and is thus a promising clinical candidate for treating a broad range of solid tumors.