Mouse Models Of Solid Tumors Research Articles

Abstract B42: Ibrutinib in combination with durvalumab (MEDI4736) in patients with relapsed or refractory HER2-positive or triple-negative breast cancer: A phase 1b/2 multicenter study

Abstract Purpose: HER2+ and triple-negative (TN) breast cancers (BC) are associated with an aggressive course and poor prognosis, with currently available treatments yielding low response rates and decreased progression-free survival (PFS) due to a high relapse rate, rapid disease progression, and development of resistance. Hence, novel agents with efficacy and a tolerable safety profile are needed for this challenging patient (pt) population. Ibrutinib is a first-in-class, oral inhibitor of Bruton's tyrosine kinase (BTK), which is a crucial signaling molecule in the B-cell receptor pathway. It has demonstrated robust clinical activity in B-cell malignancies. In preclinical studies, ibrutinib inhibited tyrosine phosphorylation of ErbB and ErbB2 in HER2- positive BC cell lines, thereby suppressing AKT and MAPK signaling (Elias, 2013; Grabinski, 2014). Programmed death-ligand 1 (PD-L1) is a molecule associated with inhibition of antitumor T cell immunity (Zou, 2008; Keir, 2008), and is highly expressed in TNBC (Tessari, 2014; Mittendorf, 2014). Durvalumab (MEDI4736) is a selective, high-affinity human IgG1 monoclonal antibody that blocks PD-L1 binding to PD-1 (IC50 of 0.1nM) and CD80/B7.1 (IC50 of 0.04 nM) (Ibrahim, 2015). Durvalumab has shown promising clinical activity with an acceptable safety profile across multiple solid tumors (Fury, 2014; Segal, 2014; Antonia, 2014). The combination of an anti–PD-L1 antibody and ibrutinib suppressed tumor growth in mouse models of solid tumors, and led to enhanced antitumor T-cell immune responses (Sagiv-Barfi, 2015). Based on these encouraging preclinical data, the PCYC-1135 trial (NCT02403271) was initiated to test the safety and efficacy of ibrutinib plus durvalumab in pts with relapsed/refractory (R/R) Stage III/IV BC (both HER2+ and TNBC), as well as non-small cell lung cancer (NSCLC), and pancreatic cancer. This abstract focuses on the BC cohort enrolling in the trial. Methods: A total of 130–160 pts (BC, NSCLC, and pancreatic) will be enrolled in this Phase 1b/2 study. Key eligibility criteria for the BC cohort include pathologically confirmed BC (HER2+ or TN), R/R disease (Stage III or IV) failing at least 2 prior therapies, measurable lesion by RECIST 1.1, and adequate hematologic, hepatic, and renal function. Key exclusion criteria include central nervous system involvement, antitumor therapy within 21 days of study initiation, prior treatment with ibrutinib or other BTK inhibitors, and/or anti-PD1, anti–PD-L1, anti–PD-L2, anti–CD137 or anti–CTLA-4 antibody, a history of allogeneic organ transplant, or treatment with a strong cytochrome P4503A inhibitor. The primary objectives are safety, tolerability, and efficacy as assessed by overall response rate. Secondary endpoints are disease control rate, duration of response, PFS, overall survival, and pharmacokinetics and pharmacodynamic assessments of the combination. The Phase 1b will assess dose-limiting toxicities (DLTs) and will determine the recommended phase 2 dose (RP2D) of ibrutinib plus durvalumab. The starting dose level of ibrutinib is 560 mg daily, with the potential for subsequent dose level reductions if DLTs occur, in combination with durvalumab 10 mg/kg IV every 2 weeks in 28-day cycles until DLT or disease progression. Enrollment in phase 2 will commence at the RP2D, accruing a total of 130–160 pts (Phase 1b + Phase 2). Ibrutinib and durvalumab will be administered until unacceptable toxicity or disease progression. Enrollment began in March 2015. Citation Format: Drew W. Rasco, Erkut Borazanci, Martin Guiterrez, David Hong, Ahmed Tawashi, Jennifer Lin, Isaiah W. Dimery, Mark Fosdale. Ibrutinib in combination with durvalumab (MEDI4736) in patients with relapsed or refractory HER2-positive or triple-negative breast cancer: A phase 1b/2 multicenter study. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Breast Cancer Research; Oct 17-20, 2015; Bellevue, WA. Philadelphia (PA): AACR; Mol Cancer Res 2016;14(2_Suppl):Abstract nr B42.

Evaluation of in vivo antitumor activity of cleistanthin B in Swiss albino mice

To evaluate the in vivo antitumor activity of cleistanthin B in Ehrlich's ascites carcinoma (EAC) and Dalton's ascites lymphoma (DAL) cell lines induced malignant ascites mouse models and DAL cell line induced solid tumor mouse model. All animals were injected with 2 × 106 EAC/DAL cells i.p./s.c. to induce malignant ascites and solid tumor and treated with 5-fluorouracil (5-FU) 20 mg/kg or cleistanthin B for 10 days. Cleistanthin B was given at three doses viz. 25, 50 and 100 mg/kg. The percentage increase in life span and the overall survival in malignant ascites animals and the tumor volume in solid tumor animals were measured. The haematological parameters were assessed in all animals before and 2 weeks after the treatment. Cleistanthin B 50 mg/kg and 5-FU significantly prolonged the life span (>25%) of malignant ascites tumor bearing animals. The overall survival was significantly improved by both. Only cleistanthin B 50 mg/kg significantly reduced the elevated WBC counts in EAC tumor bearing animals. Both 5-FU and cleistanthin B 50 mg/kg reversed the malignancy induced increase in neutrophils and platelet counts and decrease in lymphocyte counts but not to the normal range. Only 5-FU significantly reduced the solid tumor volume. None of the three doses of cleistanthin B was effective against the solid tumor. Cleistanthin B has antitumor activity against EAC and DAL tumor mice but it is not as effective as 5-FU. At 50 mg/kg dose cleistanthin B exerts significant antitumor activity compared to 25 and 100 mg/kg dose. Its effect on WBC count is higher and advantageous when compared to 5-FU. But cleistanthin B in the doses used is not effective against solid tumor.

MYC as therapeutic target in leukemia and lymphoma

MYC is a transcription factor that is involved in the expression of many genes. Deregulated MYC is found in about half of human tumors, being more prevalent in hematologi- cal neoplasms. Deregulation mechanisms include chromosomal translocation (particularly in lymphoma), amplification, and hyperactivation of MYC transcription. Here we review MYC involvement in the major types of leukemia and lymphoma. MYC rearrangements appear in all Burkitt lymphomas and are common in other lymphoma types, whereas in acute lymphoblastic leukemia, acute myeloid leukemia, lymphoproliferative, and myeloproferative diseases, they are less frequent. However, MYC overexpression is present in all types of hematological malignancies and often correlates with a worse prognosis. Data in leukemia-derived cells and in animal models of lymphomagenesis and leukemogenesis suggest that MYC would be a good therapeutic target. Several MYC-directed therapies have been assayed in preclinical settings and even in clinical trials. First, peptides and small molecules that interrupt the MYC-MAX interaction impair MYC- mediated tumorogenesis in several mouse models of solid tumors, although not yet in lymphoma and leukemia models. Second, there are a number of small molecules inhibiting the interaction of MYC-MAX heterodimers with DNA, still in the preclinical research phase. Third, inhibitors of MYC expression via the inhibition of BRD4 (a reader of acetylated histones) have been shown to control the growth of MYC-transformed leukemia and lymphoma cells and are being used in clinic trials. Finally, we review a number of promising MYC-mediated synthetic lethal approaches

413. Pre-Clinical Preparation and Validation of Tumor Cell-Based IL-12 Immunotherapy for Acute Myeloid Leukemia

Interleukin(IL)-12 is a potent pro-inflammatory cytokine that stimulates a variety of effector cells involved in anti-tumor immunity. Systemic administration of IL-12 has associated toxicities, however. Various strategies are being developed to reduce such toxicities by restricting IL-12 distribution. Options here include generating fusions with tumor-targeting molecules and directing gene delivery to specific cells. First – we used lentivirus vectors (LVs) to engineer expression of murine IL-12 in tumor cells ex vivo and subsequently infused such modified cells into recipient mice. This strategy restricts IL-12 to the local tumor microenvironment thereby promoting immune activation in the context of tumor-associated antigens (TAAs). Using mouse models of both leukemia and solid tumors, we found that this cell-based approach generated effective anti-tumor protection when as little as 1% of the tumor burden expressed IL-12 as long as threshold expression levels on a per cell basis were reached. Second – our groups showed that anti-tumor mechanisms here involve CD4+ killer T cells, dendritic cells, and direct cell-cell contact with effectors. Clinical translation of this cell-based IL-12 therapy is in progress in Toronto for AML using a novel LV to modify patients’ own blast cells. Patient AML cells collected to date (n = 21) were stratified based on in vivo growth kinetics and transduced with a near-GMP-grade bicistronic LV that encodes the human IL-12 cDNA as a p40-p70 fusion, as well as a mutant thymidylate kinase (tmpK) fused to the ectodomain of LNGFR (trLNGFR) as a suicide (cell-fate control) cassette. The trLNGFR/tmpK element allows selection and also selective ablation of transduced cells by administration of AZT. Furthermore, it also allows tracking of transduced cells and quantification of transduction frequencies/transgene expression levels. With our current protocol, functional transduction efficiencies of primary patient AML blasts ranged from 20% to 70% (n=17). Transduced AML cells displayed a strong correlation between vector copy number and trLNGFR/tmpK + IL-12 levels and dose-dependent sensitivity to AZT. In vitro immortalization (IVIM) assays determined that the near-GMP LV/IL-12 vector displayed minimal genotoxic risk in transduced lin- cells; insertion site analyses carried out on expanded clones displayed poly-to oligo-clonality patterns. Pre-clinical data on toxicity and scale-up considerations are being accumulated in preparation for a Clinical Trial Application to Health Canada targeting AML. This LV/IL-12 immunotherapy platform targeting tumor cells themselves thus holds potential to be effective against a wide variety of cancers.

Potent Effects Of The Vascular Disrupting Agent, ASA404 (DMXAA) On The Marrow Microenvironment In Preclinical Human Leukemia and Lymphoma Models

BackgroundTumor vascular disrupting agents (VDAs) represent a novel class of anti-cancer therapeutics with the unique ability to rapidly destroy established tumor vasculature and induce ischemic necrosis. In contrast to most VDAs which are derivatives of anti-tubulin agents, ASA404 (5,6-dimethylxanthenone-4-acetic acid, DMXAA) is an unique non-steroidal anti-inflammatory VDA which induces potent host immune responses and disrupts tumor vasculature in solid tumor mouse models. MethodsThe overall aim of these studies was to examine the effects of ASA404 treatment on tumor growth in preclinical human acute myeloid leukemia (HEL, HL60) and lymphoma (Raji) xenograft models. We specifically investigated the effects of drug treatment on host immune and inflammatory responses, marrow vasculature, and initial tumor engraftment. Disease progression in vivo was measured using small animal magnetic resonance imaging and bioluminescent imaging of luciferase-transfected human tumor cells. Host cytokine and chemokine levels in the plasma and other tissues (marrow, spleen, liver) were determined by multiplex flow cytometric assays. ResultsIn local acute myeloid leukemia (HEL-luciferase) xenografts, a single dose of ASA404 (25 mg/kg) markedly enhanced tumor vascular permeability, as determined by magnetic resonance imaging at 4 hours. This was followed by vascular disruption and central necrosis at 24 hours, as determined by immunohistochemistry. In systemic leukemia xenografts, a single dose of ASA404 enhanced marrow vascular permeability and induced several-fold elevations in host chemokine levels (G-CSF, IL-6, MCP-1, KC) in circulating plasma as well as bone marrow and spleen cells (MIG, G-CSF, MIP-1alpha, IP-10). Administration of ASA404 4-24 hours prior to inoculation of human acute myeloid leukemia (HEL) or lymphoma (Raji) cells in immunodeficient mice delayed disease progression and prolonged overall survival. Continuous ASA404 treatment (20 mg/kg twice weekly) for up to three weeks in established systemic leukemia and lymphoma xenografts resulted in marrow vascular disruption and significant inhibition of tumor growth. Prolonged ASA404 treatment was associated with elevations in circulating host TNF-a levels and increased numbers of macrophages within the leukemic marrow microenvironment. Combination ASA404 and doxorubicin therapy further improved the overall survival of HEL and Raji-engrafted mice as compared with AS404 or doxorubicin alone. Quantification of doxorubicin levels by HPLC in local tumor xenografts and leukemic marrow samples revealed several-fold higher doxorubicin levels following ASA404 vs. vehicle (PBS) treatment, consistent with ASA404-mediated improvements in leukemia drug delivery. Preliminary data suggest a therapeutic benefit of combination ASA404 and cytarabine therapy in the same xenograft models. ConclusionsOur results demonstrate that ASA404 exerts anti-tumor activity in human acute myeloid leukemia and lymphoma xenografts via myriad unique effects on the marrow microenvironment. Single dose administration of ASA404 results in rapid and marked alterations in multiple host cytokine/chemokine levels in association with enhanced tumor vascular permeability and impaired in vivo leukemia cell engraftment. Prolonged drug administration leads to pronounced vascular disrupting effects and inhibition of tumor growth. Combination regimens of ASA404 with anthracycline or cytarabine lead to further improvements in anti-tumor activity and overall survival in leukemia-bearing mice. These data suggest that ASA404/DMXAA may be worthy of further clinical investigation for the treatment of aggressive hematological malignancies. Disclosures:No relevant conflicts of interest to declare.

A galactomannan polysaccharide from Punica granatum imparts in vitro and in vivo anticancer activity

Galactomannan polysaccharide (PSP001) was isolated from the fruit rind of Punica granatum and was previously reported to have excellent antioxidant and immunomodulatory properties. The cytotoxicity of PSP001 was evaluated in the human cancer cell lines A375, HCT116, and HepG2 as well as the murine cancer cell lines DLA and EAC over a wide range of concentrations. PSP001 exhibited significant cytotoxicity against cancer cells through the induction of apoptosis with no in vivo toxicity up to a concentration of 2000mg/kg body weight when assessed in BALB/c mice. The antitumor efficacy of PSP001 was tested in DLA and EAC murine ascites and EAC solid tumor mouse models. PSP001 alone and in combination with doxorubicin produced a significant reduction in the tumor burden and increased life span in both models compared to the controls. The results suggest that PSP001 has the potential to be developed as an anticancer agent either alone or as an adjuvant to chemotherapy.

Abstract 962: Prolonged antiangiogenic therapy with oral metronomic topotecan and pazopanib in pediatric solid tumor mouse model.

Abstract Background: We have previously observed that the combination of daily oral Low Dose Metronomic (LDM) Topotecan (TP) and Pazopanib (PZ) significantly delayed the tumor growth and enhanced the survival in neuroblastoma (NB) mouse models (Kumar et al, 2011). However, this combination (TP+PZ) did not stop tumor growth and the animals eventually died due to disease during the course of therapy. Therefore, we planned to investigate the factors contributing to resistance to this antiangiogenic therapy in NB mouse model. Objectives: To investigate the effect of prolonged TP+PZ therapy on angiogenesis by testing the effect of therapy at different durations in NB mice xenograft model. Methods: Mice bearing subcutaneous SK-N-BE(2) NB xenografts were treated with either of the four regimens, daily, orally: vehicle (untreated), PZ (150 mg pazopanib), TP (1.0 mg/Kg topotecan), TP+PZ (combination of topotecan and pazopanib, same doses as single agents). Durations of treatment planned for each regimen were 28 days, 56 days and 80 days. Animals were sacrificed after these durations or upon end point, whichever was earlier. The criteria for end point are tumor sizes exceeding 2.0 cms in diameter or animals showing signs of morbidity. Results: The animals in control, PZ, TP reached the end point after 23d, 28d and 46d respectively. TP+PZ halted the tumor growth for up to 40 days, after which gradual growth was observed. The mean tumor diameters in the third TP+PZ group reached 1.8 cms at the day 80. CD31 immunofluorescence revealed that all the three durations of TP+PZ significantly lowered microvessel densities compared to the control (P= 0.02, 0.04 and 0.009 respectively for 28, 56 and 80 days respectively). However the ratio of CD31 to α- smooth muscle actin (pericyte marker) stained areas were significantly higher in animals treated with TP+PZ for 56 and 80days, compared to control (P=0.0006; 56d and 0.004; 80d) indicating higher pericyte coverage. TP+PZ (28d) showed signs of necrosis and cell cycle arrest (Ki67 staining), which were not observed in later durations (56 and 80 days) with TP+PZ. Long-term TP+PZ therapy also increased the levels of HIF-1 alpha, VEGF and Oct-4 within the tumor tissue. Conclusion: This study indicates that even though prolonged TP+PZ therapy demonstrates sustained antiangiogenic activity, it encounters resistance in NB, potentially mediated by pericyte coverage. Long-term TP+PZ therapy may also increase tumor stemness. Citation Format: Sushil Kumar, Reza Bayat Mokhtari, Syed Islam, Herman Yeger, Sylvain Baruchel. Prolonged antiangiogenic therapy with oral metronomic topotecan and pazopanib in pediatric solid tumor mouse model. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 962. doi:10.1158/1538-7445.AM2013-962

NG, a novel PABA/NO-based oleanolic acid derivative, induces Human hepatoma cell apoptosis via a ROS/MAPK-dependent mitochondrial pathway

O2-(2,4-dinitro-5-{[2-(12-en-28-β–D- galactopyranosyl-oleanolate-3-yl) -oxy-2-oxoethyl]amino}phenyl)1-(N-hydroxyethylmethylamino)diazen-1-ium-1,2- diolate (NG), a novel PABA/NO-based derivative of oleanolic acid (OA), has been found to show potent antitumor activity both in vivo and in vitro. In the present study, NG could significantly reduce tumor volume and weight in the H22 solid tumor mouse model. Meanwhile, NG showed selective effects on the HepG2 cells including NO generation, cytotoxic effect and apoptosis, which were prevented by hemoglobin (NO scavenger). Moreover, NG-induced apoptosis of HepG2 cells was characteristic of intracellular reactive oxygen species (ROS) generation, loss of mitochondrial membrane potential (Δψm) and enhanced Bax-to-Bcl-2 ratio. The release of apoptotic inducing factor (AIF) and cytochrome c (Cyt c) from mitochondria and the activation of caspase-3, 9 were also detected, indicating that NG may induce apoptosis through a mitochondrial-mediated pathway. Simultaneously, NG treatment could lead to the activation of the phosphorylation of c-Jun N-terminal kinase (JNK) and p38 MAPK but not ERK1/2. Treatment with SP600125 (an inhibitor of JNK) and SB203580 (an inhibitor of p38) prior to NG was found to reverse NG-induced apoptosis. Moreover, it was found that antioxidant N-acetylcysteine (NAC) blocked the induction of apoptosis and partly reversed the activation of JNK and p38, up-regulation of Bax, down-regulation of Bcl-2 and the activation of caspase-3 in NG-treated cells. Taking together, these findings suggest that NO can be released from NG, which induces apoptosis through a ROS/MAPK-mediated mitochondrial pathway.

Dosimetric evaluation of nanotargeted 188Re-liposome with the MIRDOSE3 and OLINDA/EXM programs

The OLINDA/EXM computer code was created as a replacement for the widely used MIRDOSE3 code for radiation dosimetry in nuclear medicine. A dosimetric analysis with these codes was performed to evaluate nanoliposomes as carriers of radionuclides ((188)Re-liposomes) in colon carcinoma-bearing mice. Pharmacokinetic data for (188)Re-N, N-bis (2-mercaptoethyl)-N',N'-diethylethylenediamine ((188)Re-BMEDA) and (188)Re-liposome were obtained for estimation of absorbed doses in normal organs. Radiation dose estimates for normal tissues were calculated using the MIRDOSE3 and OLINDA/EXM programs for a colon carcinoma solid tumor mouse model. Mean absorbed doses derived from(188)Re-BMEDA and (188)Re-liposome in normal tissues were generally similar as calculated by MIRDOSE3 and OLINDA/EXM programs. One notable exception to this was red marrow, wherein MIRDOSE3 resulted in higher absorbed doses than OLINDA/EXM (1.53- and 1.60-fold for (188)Re-BMEDA and (188)Re-liposome, respectively). MIRDOSE3 and OLINDA have very similar residence times and organ doses. Bone marrow doses were estimated by designating cortical bone rather than bone marrow as a source organ. The bone marrow doses calculated by MIRDOSE3 are higher than those by OLINDA. If the bone marrow is designated as a source organ, the doses estimated by MIRDOSE3 and OLINDA programs will be very similar.

Improved intratumoral delivery of PEG-coated siRNA-lipoplexes by combination with metronomic S-1 dosing in a murine solid tumor model.

Efficient systemic siRNA delivery to cells in the target tissue is a current critical challenge in the drug delivery field. Several studies have demonstrated that nanoparticles such as polyethylene glycol (PEG)-coated siRNA-lipoplexes may enhance the systemic delivery of siRNA to tumor. However, the disordered tumor microenvironment still poses a potential impediment with respect to the efficient delivery of PEG-coated siRNA-lipoplexes. Recently, we showed that metronomic S-1 dosing (daily oral administration) enhanced the accumulation of PEG-coated siBcl-2-lipoplex in DLD-1 solid tumor mouse model. In this study, to extend our work, we investigated the effect of metronomic S-1 dosing on the intratumoral accumulation and, thereby, therapeutic efficacy of PEG-coated siAgo2-lipoplex in Lewis lung carcinoma cells (LLCC) solid tumor mouse model. Also, we tried to elucidate the probable mechanism of the enhanced intratumoral accumulation of PEG-coated siRNA-lipoplexes induced by S-1 combination therapy. Results showed that metronomic S-1 dosing improved systemic delivery of intravenously injected PEG-coated siAgo2-lipoplexes into a LLCC solid tumor. In addition, the combined therapy of S-1 and PEG-coated siRNA-lipoplexes resulted in potent tumor growth suppression. These findings offer proof-of-concept for the improved systemic delivery of PEG-coated siRNA-lipoplexes by metronomic S-1 dosing in whatever tumor model used, and this may pose a promising therapeutic strategy to conquer cancer progression.

Metronomic Oral Topotecan with Pazopanib Is an Active Antiangiogenic Regimen in Mouse Models of Aggressive Pediatric Solid Tumor

Low dose metronomic (LDM) chemotherapy, combined with VEGF signaling pathway inhibitors, is a highly effective strategy to coordinately inhibit angiogenesis and tumor growth in many adult preclinical cancer models. We have tested the efficacies of daily oral LDM topotecan alone and in combination with pazopanib, a VEGF receptor inhibitor, in three pediatric extracranial solid tumor mouse models. In vitro dose-response study of topotecan and pazopanib was conducted on several neuroblastoma, osteosarcoma, and rhabdomyosarcoma cell lines. In vivo antitumor efficacies of the LDM topotecan and pazopanib as single agents and in combination were tested on 4 subcutaneous xenograft models and on 2 neuroblastoma metastatic models. Circulating angiogenic factors such as circulating endothelial cells (CEC), circulating endothelial pro genitor cells (CEP), and microvessel densities were used as surrogate biomarker markers of antiangiogenic activity. In vitro, topotecan caused a dose-dependent decrease in viabilities of all cell lines, while pazopanib did not. In vivo, combination of topotecan + pazopanib (TP + PZ) showed significant antitumor activity and significant enhancement in survival compared with the respective single agents in all models. Reductions in viable CEP and/or CEC levels and tumor microvessel density were correlated with tumor response and therefore confirmed the antiangiogenic activity of the regimens. Pharmacokinetic studies of both drugs did not reveal any drug-drug interaction. Metronomic administration of TP + PZ showed a statistically significant antitumor activity compared with respective single agents in pediatric tumor mouse models and represent a valid option as a maintenance therapy in aggressive pediatric solid tumors.

ZL11n is a novel nitric oxide-releasing derivative of farnesylthiosalicylic acid that induces apoptosis in human hepatoma HepG2 cells via MAPK/mitochondrial pathways

ZL11n is a novel furoxan-based nitric oxide (NO)-releasing derivative of farnesylthiosalicylic acid. In this study, we examined the anticancer effects and the potential mechanism of action of ZL11n in vitro and in vivo. It was found that ZL11n exhibited a favorable, selective cytotoxic effect in the HepG2 cell line. The yield of NO in the ZL11n treated HepG2 cells was much higher than in the control group and the normal human liver L-02 cells. Furthermore, the NO concentration was correlated to the degree of cytotoxicity observed. The ZL11n-induced apoptosis was assessed by Annexin V-FITC/propidium iodide flow cytometry assay. ZL11n triggered the mitochondrial/caspase apoptotic pathway by decreasing mitochondrial membrane potential, cytochrome c release from mitochondrial, and reducing the Bcl-2-to-Bax ratio, in addition to activating the caspase cascade. Simultaneously, we found that ZL11n treatment led to an increase in JNK and ERK1/2 phosphorylation. Furthermore, treatment with SP600125 (a JNK inhibitor) and PD98059 (an ERK1/2 inhibitor) prior to ZL11n treatment was found to significantly reverse ZL11n-induced apoptosis. The in vivo findings also revealed that ZL11n significantly reduced tumor volume and weight in the H22 solid tumor mouse model examined. In short, our findings suggest that ZL11n induced apoptosis through the coordination of the mitochondrial apoptotic pathway (activated by NO) and MAPKs signaling pathway (triggered by JNK or ERK).

Targeting fibroblast activation protein inhibits tumor stromagenesis and growth in mice

Membrane-bound proteases have recently emerged as critical mediators of tumorigenesis, angiogenesis, and metastasis. However, the mechanisms by which they regulate these processes remain unknown. As the cell surface serine protease fibroblast activation protein (FAP) is selectively expressed on tumor-associated fibroblasts and pericytes in epithelial tumors, we set out to investigate the role of FAP in mouse models of epithelial-derived solid tumors. In this study, we demonstrate that genetic deletion and pharmacologic inhibition of FAP inhibited tumor growth in both an endogenous mouse model of lung cancer driven by the K-rasG12D mutant and a mouse model of colon cancer, in which CT26 mouse colon cancer cells were transplanted into immune competent syngeneic mice. Interestingly, growth of only the K-rasG12D-driven lung tumors was also attenuated by inhibition of the closely related protease dipeptidyl peptidase IV (DPPIV). Our results indicate that FAP depletion inhibits tumor cell proliferation indirectly, increases accumulation of collagen, decreases myofibroblast content, and decreases blood vessel density in tumors. These data provide proof of principle that targeting stromal cell-mediated modifications of the tumor microenvironment may be an effective approach to treating epithelial-derived solid tumors.

The Selective Proteasome Inhibitor Carfilzomib Is Well Tolerated in Experimental Animals with Dose Intensive Administration

Carfilzomib (CFZ) is a selective inhibitor of the chymotrypsin-like (CT-L) activity of the proteasome. Phase I trials have demonstrated that doses of carfilzomib from 11 – 20 mg/m2 were well tolerated, inhibited blood CT-L activity by ≥80%, and resulted in objective anti-tumor responses in patients with multiple myeloma (MM) and non-Hodgkin's lymphoma (NHL) (Blood 110:409 & 411). In order to further characterize the safety profile of CFZ, studies in mice, rats and monkeys were conducted to assess the toxicologic consequences of acute and chronic administration. In both rats and monkeys, a single dose of CFZ (equivalent to 24 mg/m2) resulted in > 80% inhibition of CT-L activity in blood and tissues with recovery occurring in most tissues with a t1/2 of 24 hr. At this dose, monkeys developed a pre-renal azotemia within 24 hr, which was characterized by increases in serum creatinine, blood urea nitrogen (BUN) levels and urine specific gravity. These changes resolved in 72 hr, were not associated with histologic changes in the kidney, and were not exacerbated by consecutive daily administrations, suggesting that CFZ may not have a direct nephrotoxic effect. A single dose in either rats or monkeys induced a transient drop in platelets within 48 hr that resolved within 7 days and neither the level of nor recovery from this thrombocytopenia were affected by consecutive daily administration. This phenomenon has also been noted with bortezomib (BTZ), and is observed clinically with both compounds, suggesting that thrombocytopenia is a hallmark of inhibition of proteasome CT-L activity. However, in contrast to BTZ, which has been reported to induce both lymphopenia and neutropenia in animals, CFZ treatment in both rats and monkeys resulted in acute increases in circulating neutrophils and monocytes which rose within 24 hr of a single dose and returned to baseline in 3 – 4 days. We were unable to detect a significant induction of cytokines or chemokines capable of mediating leukocyte fluxes. However, since the acute phase proteins fibrinogen and C-reactive protein were elevated during the same time period of leukocyte flux, cytokines may play a role in this response. In chronic studies, CFZ was administered on Days 1, 2, 8, 9, 15, and 16 of a 28-day cycle to rats and monkeys for 6 and 9 cycles, respectively. This dosing schedule results in anti-tumor activity in mouse models of MM, NHL and solid tumors and is currently being utilized in Phase 2 studies in MM and solid tumors. In these chronic studies, transient pre-renal azotemia and increases in circulating neutrophils were manifest in monkeys at 24 mg/m2 following the first dose of both the first and last cycles of treatment. However, no histologic signs of nephropathy were seen in the kidneys of rats receiving 6 cycles of treatment. In addition, chronic administration of CFZ at doses equivalent to those currently administered in the clinic did not impact on the neurobehavioral function of rats and monkeys. There was no severe degeneration in the dorsal root ganglion or in the sciatic, sural, and peroneal nerves of CFZ treated rats. The data with CFZ are in distinct contrast to the axonal swelling, demyelination and severe neural degeneration that is induced by BTZ in rodents and monkeys. In the clinic, peripheral neuropathy associated with CFZ treatment appears to be less severe and possibly less frequent than what is seen with BTZ. Overall, studies in rodents and monkeys have been largely predictive of the clinical experience to date with CFZ. Together with anti-tumor activity in human tumor xenograft models, the toxicologic data support that CFZ administered at therapeutic doses is well tolerated and prolonged treatment of patients with this agent will be feasible.

Pharmacokinetics, Pharmacodynamics and Anti-Tumor Efficacy of PR-171, a Novel Inhibitor of the 20S Proteasome.

Clinical studies using the boronic acid-based proteasome inhibitor bortezomib (VelcadeTM) have validated the proteasome as a therapeutic intervention point for the treatment of multiple myeloma and non-Hodgkin's Lymphoma. Despite encouraging clinical response rates with this drug, significant toxicities, including neutropenia, thrombocytopenia and peripheral neuropathy have restricted the intensity of bortezomib dosing. PR-171 is a novel peptide epoxyketone inhibitor that selectively and irreversibly inhibits the chymotryptic subunit of the 20S proteasome. We have characterized the pharmacokinetics, pharmacodynamics and anti-tumor efficacy of PR-171 in rodents and non-human primates. PR-171 is rapidly cleared from the plasma compartment following intravenous bolus administration, with a terminal half-life in rats and monkeys of 15 and 7.2 min, respectively. Despite this rapid clearance, PR-171 administration results in a prolonged dose-dependent inhibition of the 20S proteasome in all tissues examined with the exception of brain. Single doses of PR-171 that are tolerated in mice, rats and monkeys result in greater than 90% inhibition of proteasome activity in blood and many tissues. Recovery of proteasome activity following exposure to PR-171 is dependent upon synthesis of new proteasome subunits and occurs with a t1/2 of ~ 24 hr in nucleated cells. Recovery of proteasome activity in erythrocytes is dependent upon red blood cell turnover and occurs more slowly in animals. The safety of PR-171 has been assessed in rodents using multiple dosing schedules including weekly, biweekly, daily and BID administration. In rats, daily administration of PR-171 at doses that resulted in >80% inhibition of proteasome activity in whole blood and selected tissues were well tolerated. Recovery of proteasome activity following repeated daily administrations was unchanged from that seen after a single dose. PR-171 was also well tolerated when administered daily to monkeys at equivalent doses on a body surface area comparison. A transient thrombocytopenia was noted in both rats and monkeys but neutrophil and lymphocyte counts were not decreased in response to PR-171 administration. PR-171 induced a significant anti-tumor response in beige-nu-xid (BNX) triple immunodeficient mice bearing established HS-Sultan Burkitt's lymphoma tumors and in Balb/c mice challenged with A20 lymphoma cells. We have also demonstrated anti-tumor activity of PR-171 in several mouse models of solid tumors including syngeneic and human tumor xenograft models of colorectal cancer. These studies demonstrate the tolerability, anti-tumor activity and dosing flexibility of PR-171 and provide validation for the clinical testing of PR-171 in the treatment of hematologic malignancies utilizing dose intensive schedules.

High Resolution Crystal Structure of a Human Tumor Necrosis Factor-α Mutant with Low Systemic Toxicity

A human tumor necrosis factor-alpha (TNF-alpha) mutant (M3S) with low systemic toxicity in vivo was designed, and its structures in two different crystal packings were determined crystallographically at 1.8 and 2.15-A resolution, respectively, to explain altered biological activities of the mutant. M3S contains four changes: a hydrophilic substitution of L29S, two hydrophobic substitutions of S52I and Y56F, and a deletion of the N-terminal seven amino acids that is disordered in the structure of wild-type TNF-alpha. Compared with wild-type TNF-alpha, it exhibits 11- and 71-fold lower binding affinities for the human TNF-R55 and TNF-R75 receptors, respectively, and in vitro cytotoxic effect and in vivo systemic toxicity of M3S are 20 and 10 times lower, respectively. However, in a transplanted solid tumor mouse model, M3S suppresses tumor growth more efficiently than wild-type TNF-alpha. M3S is highly resistant to proteolysis by trypsin, and it exhibits increased thermal stability and a prolonged half-life in vivo. The L29S mutation causes substantial restructuring of the loop containing residues 29-36 into a rigid segment as a consequence of induced formation of intra- and intersubunit interactions, explaining the altered receptor binding affinity and thermal stability. A mass spectrometric analysis identified major proteolytic cleavage sites located on this loop, and thus the increased resistance of M3S to the proteolysis is consistent with the increased rigidity of the loop. The S52I and Y56F mutations do not induce a noticeable conformational change. The side chain of Phe56 projects into a hydrophobic cavity, while Ile52 is exposed to the bulk solvent. Ile52 should be involved in hydrophobic interactions with the receptors, since a mutant containing the same mutations as in M3S except for the L29S mutation exhibits an increased receptor binding affinity. The low systemic toxicity of M3S appears to be the effect of the reduced and selective binding affinities for the TNF receptors, and the superior tumor-suppression of M3S appears to be the effect of its weak but longer antitumoral activity in vivo compared with wild-type TNF-alpha. It is also expected that the 1.8-A resolution structure will serve as an accurate model for explaining the structure-function relationship of wild-type TNF-alpha and many TNF-alpha mutants reported previously and for the design of new TNF-alpha mutants.

Serum 1-methyladenosine and pseudouridine as tumor markers in tumor-bearing mice

It is known that in cancer patients elevated levels of modified nucleosides originated from RNA are excreted in the urine. Modified nucleosides in the serum are thought to be more useful than those in the urine as tumor markers because they are not influenced by other factors. However the determination of these nucleosides is difficult because of their low amounts. To examine the efficacy of the modified nucleosides in the serum as tumor markers, ascites and solid tumor mouse models were prepared, and the amounts of 1-methyladenosine and pseudouridine in the serum were determined. Along with the growth of ascites tumor, the amounts of 1-methyladenosine and pseudouridine in the serum increased. The modified nucleosides in the serum in a solid tumor model also increased. This is the first report on the variation in the amount of 1-methyladenosine in the serum of tumor models, and the results suggest the usefulness of measuring the amounts of 1-methyladenosine and pseudouridine in the serum as tumor markers.