Pharmacokinetics and safety of single doses of tabalumab in subjects with rheumatoid arthritis or systemic lupus erythematosus

AIMS

Two phase 1 studies evaluated the pharmacokinetics (PK), safety and biological activity of tabalumab, a human monoclonal antibody against B-cell activating factor (BAFF), administered intravenously (i.v.) or subcutaneously (s.c.) in subjects with rheumatoid arthritis (RA) or systemic lupus erythematosus (SLE).

METHODS

In study A, subjects with RA (n = 23) or SLE (n = 6) received a single i.v. dose of tabalumab (RA 0.01, 0.04, 0.125, 0.5, 2.0, and 8.0 mg kg(-1) and SLE 0.125 or 2.0 mg kg(-1) ) or placebo. In study B, subjects with RA received a single tabalumab dose i.v. (10 mg) (n = 12) or s.c. (20 mg) (n = 12). Serum tabalumab and CD20+ B cells were evaluated and safety was assessed throughout both studies.

RESULTS

Tabalumab PK were non-linear across the 0.01 to 8.0 mg kg(-1) dose range. Clearance (CL) decreased from 2.9 to 0.1 l day(-1) and terminal half-life (t1/2 ) increased from about 1.6 to 25 days. Subjects with RA or SLE had similar PK. After s.c. dosing, tabalumab time to maximal concentration (tmax ) was 5.5 days. Absolute bioavailability (F) was approximately 62%. Following tabalumab dosing, CD20+ B cells transiently increased from baseline followed by a progressive decrease below baseline.

CONCLUSION

A single tabalumab dose administered i.v. or s.c. was well tolerated and had non-linear CL over the dose range investigated in subjects with RA and SLE. The non-linearity likely reflects target-mediated CL due to binding to BAFF. Tabalumab showed biological activity based on changes in peripheral CD20+ lymphocyte numbers in both subjects with RA and SLE.

Abstract A161: Angiotensin II type 1 receptor antagonism suppresses tumor metastasis through inhibition of CCL2-CCR2 mediated monocyte recruitment

Purpose: Inflammatory monocytes have been shown to play key roles in cancer metastasis through promotion of tumor cell extravasation, seeding, growth, and angiogenesis, as well as suppression of anti-tumor immunity. Migration of inflammatory monocytes to sites of inflammation or tumor metastasis is mediated primarily via the action of the CCL2-CCR2 chemotactic axis. Thus, disruption of this axis through receptor or ligand blockade represents an attractive therapeutic target for the treatment of metastatic disease.

Methods: Losartan, an angiotensin II type 1 receptor (AT1R) antagonist, has been previously reported to suppress tumor growth through mechanisms associated with tumor angiogenesis and inhibition of TGF-β signaling. However, our studies also suggest an important contribution to the anti-tumor effects of losartan from monocyte migration inhibition. Therefore, we conducted studies in murine breast (4T1) and colon (CT26) carcinoma experimental pulmonary metastasis models, to determine the degree to which losartan's anti-metastatic effect was predominantly dependent on disruption of CCL2-CCR2 mediated monocyte recruitment to tumor metastases.

Results: We found that daily treatment with losartan prolonged survival, and significantly reduced metastatic burden, percentages of CD11b+/Ly6C+ lung monocytes, and tumor microvessel density in mice with 4T1 and CT26 pulmonary metastases. However, compared to pure CCR2 antagonists, our studies show that losartan does not act as a direct competitive antagonist to CCR2. Rather, in vitro assays and studies in CCR2 -\- mice indicated that losartan's anti-metastatic effect was primarily mediated via suppression of monocyte recruitment through indirect interruption of the CCL2-CCR2 axis. Importantly, losartan proved more effective at reducing monocyte recruitment and slowing CT26 pulmonary metastatic tumor growth compared to a specific CCR2 antagonist.

Conclusions: We conclude therefore that losartan exerts significant anti-metastatic activity in aggressive murine metastasis models, and that losartan's major anti-metastatic effect is mediated by blockade of CCL2-CCR2 dependent monocyte recruitment. Thus, by virtue of its myeloid cell activity, losartan, in combination with conventional cancer therapeutics, has potential for use as an anti-metastatic agent in animals and humans at high risk for tumor metastasis.

Citation Format: Daniel P. Regan, Amanda M. Guth, Ryan J. Hansen, Daniel L. Gustafson, Steven W. Dow. Angiotensin II type 1 receptor antagonism suppresses tumor metastasis through inhibition of CCL2-CCR2 mediated monocyte recruitment. [abstract]. In: Proceedings of the CRI-CIMT-EATI-AACR Inaugural International Cancer Immunotherapy Conference: Translating Science into Survival; September 16-19, 2015; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(1 Suppl):Abstract nr A161.

Limited sampling pharmacokinetics of subcutaneous ondansetron in healthy geriatric cats, cats with chronic kidney disease, and cats with liver disease

Ondansetron, a 5-HT3 receptor antagonist, is an effective anti-emetic in cats. The purpose of this study was to compare pharmacokinetics of subcutaneous (SQ) ondansetron in healthy geriatric cats to cats with chronic kidney disease (CKD) or liver disease using a limited sampling strategy. 60 cats participated; 20 per group. Blood was drawn 30 and 120 min following one 2 mg (mean 0.49 mg/kg, range 0.27-1.05 mg/kg) SQ dose of ondansetron. Ondansetron concentrations were measured by liquid chromatography coupled to tandem mass spectrometry. Drug exposure represented as area under the curve (AUC) was predicted using a limited sampling approach based on multiple linear regression analysis from previous full sampling studies, and clearance (CL/F) estimated using noncompartmental methods. Kruskal-Wallis anova was used to compare parameters between groups. Mean AUC (ng/mL·h) of subcutaneous ondansetron was 301.4 (geriatric), 415.2 (CKD), and 587.0 (liver). CL/F (L/h/kg) of SQ ondansetron was 1.157 (geriatric), 0.967 (CKD), and 0.795 (liver). AUC was significantly higher in liver and CKD cats when compared to geriatric cats (P < 0.05). CL/F in liver cats was significantly decreased (P < 0.05) compared to geriatric cats. In age-matched subset analysis, AUC and CL/F in liver cats remained significantly different from geriatric cats.

Substituent Effects in CH Hydrogen Bond Interactions: Linear Free Energy Relationships and Influence of Anions

Aryl CH hydrogen bonds (HBs) are now commonly recognized as important factors in a number of fields, including molecular biology, stereoselective catalysis, and anion supramolecular chemistry. As the utility of CH HBs has grown, so to has the need to understand the structure-activity relationship for tuning both their strength and selectivity. Although there has been significant computational effort in this area, an experimental study of the substituent effects on CH HBs has not been previously undertaken. Herein we disclose a systematic study of a single CH HB by using traditional urea donors as directing groups in a supramolecular binding cavity. Experimentally determined association constants are examined by a combination of computational (electrostatic potential) and empirical (σm and σp) values for substituent effects. The dominance of electrostatic parameters, as observed in a computational DFT study, is consistent with current CH HB theory; however, a novel anion dependence of the substituent effects is revealed in solution.

Proteolytic cleavage of antigen extends the durability of an anti-PCSK9 monoclonal antibody

Lilly PCSK9 antibody LY3015014 (LY) is a monoclonal antibody (mAb) that neutralizes proprotein convertase subtilisin-kexin type 9 (PCSK9). LY decreases LDL cholesterol in monkeys and, unlike other PCSK9 mAbs, does not cause an accumulation of intact PCSK9 in serum. Comparing the epitope of LY with other clinically tested PCSK9 mAbs, it was noted that the LY epitope excludes the furin cleavage site in PCSK9, whereas other mAbs span this site. In vitro exposure of PCSK9 to furin resulted in degradation of PCSK9 bound to LY, whereas cleavage was blocked by other mAbs. These other mAbs caused a significant accumulation of serum PCSK9 and displayed a shorter duration of LDL-cholesterol lowering than LY when administered to mice expressing the WT human PCSK9. In mice expressing a noncleavable variant of human PCSK9, LY behaved like a cleavage-blocking mAb, in that it caused significant PCSK9 accumulation, its duration of LDL lowering was reduced, and its clearance (CL) from serum was accelerated. Thus, LY neutralizes PCSK9 and allows its proteolytic degradation to proceed, which limits PCSK9 accumulation, reduces the CL rate of LY, and extends its duration of action. PCSK9 mAbs with this property are likely to achieve longer durability and require lower doses than mAbs that cause antigen to accumulate.

Abstract 538: A PCSK9 Antibody that Blocks Binding to LDLR while Allowing Normal PCSK9 Inactivation by Furin is Afforded a Reduced Clearance Rate and a Longer Duration of Effect in Mice

Introduction: Monoclonal antibodies (Mabs) that neutralize proprotein convertase subtilisin-kexin type 9 (PCSK9) have been shown to lower LDL-C in human trials. It is known that PCSK9 is cleaved by furin at Arg218 and that the cleaved PCSK9 is inactive in modulating LDLR. Antibodies whose epitopes are near the EGFA binding domain are more efficacious in increasing LDLR but may interfere with furin cleavage and thus normal PCSK9 clearance. Here we describe a unique antibody (LY) that both lowers LDL-C and allows for normal PCSK9 cleavage by furin.

Hypothesis: An antibody with an epitope that permits furin cleavage of PCSK9 will show more durable LDL lowering compared to one with an epitope that interferes with cleavage.

Methods: Furin cleavage of recombinant PCSK9 was evaluated by electrophoresis in the presence of antibodies. Antibodies were studied in mice expressing wild-type or a non-cleavable variant of human PCSK9.

Results: We determined that LY3015014 (LY) permits furin cleavage of PCSK9 while Mab A, which shares the epitope of a Mab tested in humans, does not. LY’s epitope is completely N-terminal of the cleavage site, while the conformational epitope of Mab A spans the Arg218 cleavage site. To assess the impact of PCSK9 cleavage on antibody efficacy in vivo, we generated two human PCSK9 overexpressing mouse models; one with WT PCSK9 and one with a non-cleavable variant (R215A, R218A). In mice expressing WT human PCSK9, LY showed a longer duration of LDL lowering and a slower clearance rate than Mab A. Additionally, we found that PCSK9 did not accumulate in the serum of mice given LY, likely due to cleavage and release from the antibody. In mice expressing the non-cleavable variant PCSK9, the clearance and LDL durability benefits of LY compared to Mab A were lost. Additionally, in the non-cleavable model, PCSK9 accumulated in the serum of mice given LY, presumably due to lack of furin cleavage.

Conclusions: LY allows normal cleavage and inactivation of bound PCSK9 while maintaining LDL-C lowering. This proteolysis reduces the antibody’s clearance rate and extends the therapeutic durability of LY in mice relative to Mab A which interferes with proteolytic degradation. We have shown that cleavage is the mechanism of durability through the use of non-cleavable PCSK9.

Comparative pharmacokinetic properties and antitumor activity of the marine HDACi Largazole and Largazole peptide isostere

PURPOSE

Largazole is a potent class I-selective HDACi natural product isolated from the marine cyanobacteria Symploca sp. The purpose of this study was to test synthetic analogs of Largazole to identify potential scaffold structural modifications that would improve the drug-like properties of this clinically relevant natural product.

METHODS

The impact of Largazole scaffold replacements on in vitro growth inhibition, cell cycle arrest, induction of apoptosis, pharmacokinetic properties, and in vivo activity using a xenograft model was investigated.

RESULTS

In vitro studies in colon, lung, and pancreatic cancer cell lines showed that pyridyl-substituted Largazole analogs had low-nanomolar/high-picomolar antiproliferative activity, and induced apoptosis and cell cycle arrest at concentrations equivalent to or lower than the parent compound Largazole. Using IV bolus delivery at 5 mg/kg, two compartmental pharmacokinetic modeling on the peptide isostere analog of Largazole indicated improved pharmacokinetic parameters. In an A549 non-small cell lung carcinoma xenograft model using a dosage of 5 mg/kg administered intraperitoneally every other day, Largazole, Largazole thiol, and Largazole peptide isostere demonstrated tumor growth inhibition (TGI%) of 32, 44, and 66%, respectively. Largazole peptide isostere treatment was statistically superior to control (p = 0.002) and to Largazole (p = 0.006). Surprisingly, tumor growth inhibition was not observed with the potent pyridyl-based analogs.

CONCLUSIONS

These results establish that replacing the depsipeptide linkage in Largazole with an amide may impart pharmacokinetic and therapeutic advantage and that alternative prodrug forms of Largazole are feasible.

Abstract B48: Subcutaneous delivery of docetaxel and carboplatin accumulate preferentially in lymphatic circulation as compared to intravenous delivery in rats with surgically created lymph and venous fistulae

Purpose: Intravenous delivery of chemotherapy is an indisputable pillar of cancer therapy, but associated with unfavorable systemic toxicity. Locally delivered chemotherapy – via subcutaneous, surgical placement, or intracavitary routes – is effective in animal models of breast cancer and in client-owned dogs receiving treatment for bone tumors. There are unexplained beneficial effects of chemotherapy delivered via nontraditional routes resulting in decreased systemic toxicity and positive tumor control at dosages less than traditionally given. One role of the lymphatic system is to return large particulate matter and proteins in the interstitial space to the vascular system which cannot be absorbed by adjacent blood capillaries. This unidirectional circulatory pathway for particles deposited in areas outside of blood capillaries has not been characterized to date for nontraditionally delivered chemotherapy agents.

Experimental Design: In this study the pharmacokinetics of docetaxel and carboplatin in the blood and lymph following subcutaneous (SQ) versus intravenous (IV) delivery was determined in a surgical lymphatic and hemovascular cannulated rat model. In anesthetized adult male Sprague Dawley rats, fixed length polyurethane catheters were surgically placed simultaneously into a jugular vein and the lymphatic thoracic duct in each animal. Either docetaxel (5 mg/kg) or carboplatin (14 or 28 mg/kg) were delivered IV via tail vein catheter or SQ into the mammary fat pad. Rats were permitted free movement and access to water and food ad libitum. Paired blood and lymph samples were serially collected in animals at 0, ½, 1, 2, 3, 4, 12, and 24 hrs. Drug levels were determined via LC/MS/MS or ICP/MS for docetaxel and carboplatin, respectively. Pharmacokinetic parameters were determined via noncompartmental analysis.

Results: The maximum concentration measured (Cmax) and the area under the time-concentration curve (AUC0-24hr) in the plasma and lymph for docetaxel delivered IV were 2.86 µg/ml and 1160 hr*ng/ml, and 172 ng/ml and 1020 hr*ng/m, respectively. When administered SQ, the Cmax and AUC0-24hr were 0.644 µg/ml and 815 hr*ng/ml, and 107 ng/ml and 1650 hr*ng/ml, for plasma and lymph respectively, which demonstrates preferential lymphatic accumulation when delivered SQ. The terminal half-life (t1/2) in lymph for docetaxel is greater with either IV or SQ delivery (18.3 hr and 22.6 hr, respectively) as compared to t1/2 in blood for docetaxel with either IV or SQ delivery (9.6 hr and 6.0 hr, respectively), possibly suggesting lipophilic docetaxel resides in the lymph for longer periods.

The Cmax and AUC0-24hr in the plasma and lymph for total platinum following delivery of carboplatin (14 mg/kg) IV were 23.0 µg/ml and 28.8 hr*µg/ml, and 16.4 µg/ml and 36.1 hr*µg/m, respectively. When delivered SQ, the Cmax and AUC0-24hr for the plasma and lymph were 6.99 µg/ml and 16.6 hr*µg/ml, and 9.39 µg/ml and 24.3 hr*µg/ml, respectively. While a dose response was observed in the plasma regardless of route of administration with the Cmax in the plasma following carboplatin (28 mg/kg) of 40.0 µg total platinum/ml when given IV and 12.9 µg total platinum/ml when given SQ, the AUC0-24hr did not when administered IV.

Additionally, the AUC0-24hr in the lymph was 31.0 hr*µg/ml following IV dosing at 28 mg/kg which is similar to that observed in the plasma. However, when dosed SQ at 28 mg/kg, the Cmax and AUC0-24hr for total platinum in the lymph responded in a dose dependent manner with 17.3 µg/ml and 76.7 hr*µg/ml, respectively. This demonstrates preferential lymphatic accumulation of carboplatin delivered SQ and that there is a dose response with regards to the level of total platinum in the lymph when delivered SQ.

Conclusions: Nontraditional SQ delivery of docetaxel and carboplatin achieves targeted lymphatic accumulation greater than with traditional IV delivery. This study has broad implication for dosing strategies of chemotherapeutics for cancers metastasizing predominantly via lymphatic pathways and for cancer patients susceptible to toxicity resulting from peak maximum hemovascular concentrations that may be lessened via SQ delivery.

Citation Format: Deanna R. Worley, Ryan J. Hansen, Laura S. Chubb, Daniel L. Gustafson. Subcutaneous delivery of docetaxel and carboplatin accumulate preferentially in lymphatic circulation as compared to intravenous delivery in rats with surgically created lymph and venous fistulae. [abstract]. In: Proceedings of the AACR Special Conference: The Translational Impact of Model Organisms in Cancer; Nov 5-8, 2013; San Diego, CA. Philadelphia (PA): AACR; Mol Cancer Res 2014;12(11 Suppl):Abstract nr B48.

Abstract A37: Role of autophagy inhibition in metastatic disease utilizing mouse models

Modification of autophagy to enhance cancer treatment is being aggressively pursued in the laboratory and clinic; however, it remains to be seen if inhibition or induction of autophagy is going to result in better outcomes. In addition, the advantages of autophagic modification with neoadjuvant chemotherapy vs. surgical adjuvant chemotherapy have yet to be reported. The 4T1-luc metastatic mammary mouse cell line modified to express luciferase was used to induce lung metastases, both from orthotopic growth of primary tumors or experimentally induced via tail vein injection. Both pharmacologic inhibition (chloroquine (CQ) administered 60 mg/kg daily to mice) and genetic knockdown of a key protein necessary for autophagy alone (4T1-luc-shBeclin-1 cells) did not alter time to metastasis (as determined by luciferase positive lungs) when 4T1-luc cells were injected via tail vein. In addition, inhibiting autophagy in 4T1-luc cells with CQ in vitro prior to injection via the tail did not alter time to metastasis. Similar results were observed with pharmacologic inhibition on experimentally induce lung metastases using the metastatic mouse melanoma B16-F10 cell line. In vitro work, by us and others, has lead us to conclude that pharmacologic inhibition plus cisplatin leads to greater growth inhibition and cell kill in vitro than either alone. Effect of autophagy inhibition in combination with cisplatin on metastatic formation in a neoadjuvant setting was tested by treating mice with daily with CQ and cisplatin (q14d) one day post tumor cell injection in the mammary fat pad. Additional experiments were conducted to determine if autophagy inhibition plus cisplatin in a surgical adjuvant setting delays metastasis formation. In each instance, primary tumors were removed at ~100mm3 and mice were followed until luciferase positive lungs were observed. From these results we conclude that autophagy inhibition, using CQ, does not alter metastatic growth alone and appears to slightly enhance the efficacy of cisplatin on treating metastases. It remains to be seen if autophagy inhibition with other compounds would alter results.

Citation Format: Rebecca Barnard, Ryan J. Hansen, Paola Maycotte, Andrew Thorburn, Daniel L. Gustafson. Role of autophagy inhibition in metastatic disease utilizing mouse models. [abstract]. In: Proceedings of the AACR Special Conference: The Translational Impact of Model Organisms in Cancer; Nov 5-8, 2013; San Diego, CA. Philadelphia (PA): AACR; Mol Cancer Res 2014;12(11 Suppl):Abstract nr A37.

Pharmacokinetics and pharmacodynamics of propofol with or without 2% benzyl alcohol following a single induction dose administered intravenously in cats

OBJECTIVE

To compare the pharmacokinetics and pharmacodynamics of propofol with or without 2% benzyl alcohol administered intravenously (IV) as a single induction dose in cats.

STUDY DESIGN

Prospective experimental study.

ANIMALS

Six healthy adult cats, three female intact, three male castrated, weighing 4.8 ± 1.8 kg.

METHODS

Cats received 8 mg kg(-1) IV of propofol (P) or propofol with 2% benzyl alcohol (P28) using a randomized crossover design. Venous blood samples were collected at predetermined time points to 24 hours after drug administration to determine drug plasma concentrations. Physiologic and behavioral variables were also recorded. Propofol and benzyl alcohol concentrations were determined using high pressure liquid chromatography with fluorescence detection. Pharmacokinetic parameters were described using a 2-compartment model. Pharmacokinetic and pharmacodynamic parameters were analyzed using repeated measures anova (p < 0.05).

RESULTS

Plasma concentrations of benzyl alcohol were below the lower limits of quantification (LLOQ) at all time points for two of the six cats (33%), and by 30 minutes for the remaining four cats. Propofol pharmacokinetics, with or without 2% benzyl alcohol, were characterized by rapid distribution, a long elimination phase, and a large volume of distribution. No differences were noted between treatments with the exception of clearance from the second compartment (CLD2), which was 23.6 and 38.8 mL kg(-1)  minute(-1) in the P and P28 treatments, respectively. Physiologic and behavioral variables were not different between treatments with the exception of heart rate at 4 hours post administration.

CONCLUSIONS AND CLINICAL RELEVANCE

The addition of 2% benzyl alcohol as a preservative minimally altered the pharmacokinetics and pharmacodynamics of propofol 1% emulsion when administered as a single IV bolus in this group of cats. These data support the cautious use of propofol with 2% benzyl alcohol for induction of anesthesia in healthy cats.

Pharmacokinetics of sustained-release analgesics in mice

Buprenorphine and carprofen, 2 of the most commonly used analgesics in mice, must be administered every 8 to 12 h to provide sustained analgesia. Sustained-release (SR) formulations of analgesics maintain plasma levels that should be sufficient to provide sustained analgesia yet require less frequent dosing and thus less handling of and stress to the animals. The pharmacokinetics of SR formulations of buprenorphine (Bup-SR), butorphanol (Butp-SR), fentanyl (Fent-SR), carprofen (Carp-SR), and meloxicam (Melox-SR) were evaluated in mice over 72 h and compared with those of traditional, nonSR formulations. Bup-SR provided plasma drug levels greater than the therapeutic level for the first 24 to 48 h after administration, but plasma levels of Bup-HCl fell below the therapeutic level by 4 h. Fent-SR maintained plasma levels greater than reported therapeutic levels for 12 h. Therapeutic levels of the remaining drugs are unknown, but Carp-SR provided plasma drug levels similar to those of Carp for the first 24 h after administration, whereas Melox-SR had greater plasma levels than did Melox for the first 8 h. Butp-SR provided detectable plasma drug levels for the first 24 h, with a dramatic decrease over the first 4 h. These results indicate that Bup-SR provides a stable plasma drug level adequate for analgesia for 24 to 48 h after administration, whereas Carp-SR, Melox-SR, Fent-SR, and Butp-SR would require additional doses to provide analgesic plasma levels beyond 24 h in mice.

STAT3-mediated autophagy dependence identifies subtypes of breast cancer where autophagy inhibition can be efficacious

Autophagy is a protein and organelle degradation pathway that is involved in diverse diseases, including cancer. Recent evidence suggests that autophagy is a cell survival mechanism in tumor cells and that its inhibition, especially in combination with other therapy, could be beneficial but it remains unclear if all cancer cells behave the same way when autophagy is inhibited. We inhibited autophagy in a panel of breast cancer cell lines and found that some of them are dependent on autophagy for survival even in nutrient rich conditions without any additional stress, whereas others need autophagy only when stressed. Survival under unstressed conditions is due to cell type-specific autophagy regulation of STAT3 activity and this phenotype is enriched in triple-negative cell lines. This autophagy-dependency affects response to therapy because autophagy inhibition reduced tumor growth in vivo in autophagy-dependent but not in autophagy-independent breast tumors, whereas combination treatment with autophagy inhibitors and other agent was preferentially synergistic in autophagy-dependent cells. These results imply that autophagy-dependence represents a tumor cell-specific characteristic where autophagy inhibition will be more effective. Moreover, our results suggest that autophagy inhibition might be a potential therapeutic strategy for triple-negative breast cancers, which currently lack an effective targeted treatment.

A phase I dose-finding study of silybin phosphatidylcholine (milk thistle) in patients with advanced hepatocellular carcinoma

PURPOSE

To determine the maximum tolerated dose per day of silybin phosphatidylcholine (Siliphos) in patients with advanced hepatocellular carcinoma (HCC) and hepatic dysfunction.

EXPERIMENTAL DESIGN

Patients with advanced HCC not eligible for other therapies based on poor hepatic function were enrolled in a phase I study of silybin phosphatidylcholine. A standard phase I design was used with 4 planned cohorts, dose escalating from 2, 4, 8, to 12 g per day in divided doses for 12 weeks.

RESULTS

Three participants enrolled in this single institution trial. All enrolled subjects consumed 2 g per day of study agent in divided doses. Serum concentrations of silibinin and silibinin glucuronide increased within 1 to 3 weeks. In all 3 patients, liver function abnormalities and tumor marker α-fetoprotein progressed, but after day 56 the third patient showed some improvement in liver function abnormalities and inflammatory biomarkers. All 3 participants died within 23 to 69 days of enrolling into the trial, likely from hepatic failure, but it could not be ruled out that deaths were possibly due to the study drug.

CONCLUSION

Short-term administration of silybin phosphatidylcholine in patients with advanced HCC resulted in detectable increases in silibinin and its metabolite, silibinin glucuronide. The maximum tolerated dose could not be established. Since patients died soon after enrollment, this patient population may have been too ill to benefit from an intervention designed to improve liver function tests.

Oral, subcutaneous, and intravenous pharmacokinetics of ondansetron in healthy cats

Ondansetron is a 5-HT3 receptor antagonist that is an effective anti-emetic in cats. The purpose of this study was to evaluate the pharmacokinetics of ondansetron in healthy cats. Six cats with normal complete blood count, serum biochemistry, and urinalysis received 2 mg oral (mean 0.43 mg/kg), subcutaneous (mean 0.4 mg/kg), and intravenous (mean 0.4 mg/kg) ondansetron in a cross-over manner with a 5-day wash out. Serum was collected prior to, and at 0.25, 0.5, 1, 2, 4, 8, 12, 18, and 24 h after administration of ondansetron. Ondansetron concentrations were measured using liquid chromatography coupled to tandem mass spectrometry. Noncompartmental pharmacokinetic modeling and dose interval modeling were performed. Repeated measures anova was used to compare parameters between administration routes. Bioavailability of ondansetron was 32% (oral) and 75% (subcutaneous). Calculated elimination half-life of ondansetron was 1.84 ± 0.58 h (intravenous), 1.18 ± 0.27 h (oral) and 3.17 ± 0.53 h (subcutaneous). The calculated elimination half-life of subcutaneous ondansetron was significantly longer (P < 0.05) than oral or intravenous administration. Subcutaneous administration of ondansetron to healthy cats is more bioavailable and results in a more prolonged exposure than oral administration. This information will aid management of emesis in feline patients.

Structure-activity relationships for biodistribution, pharmacokinetics, and excretion of atomically precise nanoclusters in a murine model

The absorption, distribution, metabolism and excretion (ADME) and pharmacokinetic (PK) properties of inorganic nanoparticles with hydrodynamic diameters between 2 and 20 nm are presently unpredictable. It is unclear whether unpredictable in vivo properties and effects arise from a subset of molecules in a nanomaterials preparation, or if the ADME/PK properties are ensemble properties of an entire preparation. Here we characterize the ADME/PK properties of atomically precise preparations of ligand protected gold nanoclusters in a murine model system. We constructed atomistic models and tested in vivo properties for five well defined compounds, based on crystallographically resolved Au25(SR)18 and Au102(SR)44 nanoclusters with different (SR) ligand shells. To rationalize unexpected distribution and excretion properties observed for several clusters in this study and others, we defined a set of atomistic structure-activity relationships (SAR) for nanoparticles, which includes previously investigated parameters such as particle hydrodynamic diameter and net charge, and new parameters such as hydrophobic surface area and surface charge density. Overall we find that small changes in particle formulation can provoke dramatic yet potentially predictable changes in ADME/PK.

Development of selective colorimetric probes for hydrogen sulfide based on nucleophilic aromatic substitution

Hydrogen sulfide is an important biological signaling molecule and an important environmental target for detection. A major challenge in developing H2S detection methods is separating the often similar reactivity of thiols and other nucleophiles from H2S. To address this need, the nucleophilic aromatic substitution (SNAr) reaction of H2S with electron-poor aromatic electrophiles was developed as a strategy to separate H2S and thiol reactivity. Treatment of aqueous solutions of nitrobenzofurazan (7-nitro-1,2,3-benzoxadiazole, NBD) thioethers with H2S resulted in thiol extrusion and formation of nitrobenzofurazan thiol (λmax = 534 nm). This reactivity allows for unwanted thioether products to be converted to the desired nitrobenzofurazan thiol upon reaction with H2S. The scope of the reaction was investigated using a Hammett linear free energy relationship study, and the determined ρ = +0.34 is consistent with the proposed SN2Ar reaction mechanism. The efficacy of the developed probes was demonstrated in buffer and in serum with associated submicromolar detection limits as low as 190 nM (buffer) and 380 nM (serum). Furthermore, the sigmoidal response of nitrobenzofurazan electrophiles with H2S can be fit to accurately quantify H2S. The developed detection strategy offers a manifold for H2S detection that we foresee being applied in various future applications.

Rational combination of a MEK inhibitor, selumetinib, and the Wnt/calcium pathway modulator, cyclosporin A, in preclinical models of colorectal cancer

PURPOSE

The mitogen-activated protein kinase (MAPK) pathway is a crucial regulator of cell proliferation, survival, and resistance to apoptosis. MEK inhibitors are being explored as a treatment option for patients with KRAS-mutant colorectal cancer who are not candidates for EGFR-directed therapies. Initial clinical results of MEK inhibitors have yielded limited single-agent activity in colorectal cancer, indicating that rational combination strategies are needed.

EXPERIMENTAL DESIGN

In this study, we conducted unbiased gene set enrichment analysis and synthetic lethality screens with selumetinib, which identified the noncanonical Wnt/Ca++ signaling pathway as a potential mediator of resistance to the MEK1/2 inhibitor selumetinib. To test this, we used shRNA constructs against relevant WNT receptors and ligands resulting in increased responsiveness to selumetinib in colorectal cancer cell lines. Further, we evaluated the rational combination of selumetinib and WNT pathway modulators and showed synergistic antiproliferative effects in in vitro and in vivo models of colorectal cancer.

RESULTS

Importantly, this combination not only showed tumor growth inhibition but also tumor regression in the more clinically relevant patient-derived tumor explant (PDTX) models of colorectal cancer. In mechanistic studies, we observed a trend toward increased markers of apoptosis in response to the combination of MEK and WntCa(++) inhibitors, which may explain the observed synergistic antitumor effects.

CONCLUSIONS

These results strengthen the hypothesis that targeting both the MEK and Wnt pathways may be a clinically effective rational combination strategy for patients with metastatic colorectal cancer.

Effects of intratumoral administration of a hyaluronan-cisplatin nanoconjugate to five dogs with soft tissue sarcomas

OBJECTIVE

To determine the effects of intratumoral injection of a hyaluronan-cisplatin nanoconjugate on local and systemic platinum concentrations and systemic toxicosis.

ANIMALS

5 dogs with spontaneous soft tissue sarcomas (STSs).

PROCEDURES

For each dog, approximately 1.5 mL of hyaluronan nanocarrier conjugated with 20 mg of cisplatin was injected into an external STS. Blood samples were collected immediately before (0 hours) and at 0.5, 1, 2, 3, 4, 24, and 96 hours after hyaluronan-cisplatin injection for pharmacokinetic analyses. Urine samples were obtained at 0 and at 96 hours after hyaluronan-cisplatin injection for urinalysis. Each treated STS and its sentinel lymph nodes were surgically removed 96 hours after the hyaluronan-cisplatin injection. Inductively coupled plasma mass spectrometry was used to measure platinum concentrations in blood samples, tumors, and lymph nodes.

RESULTS

No tissue reactions were detected 96 hours after hyaluronan-cisplatin injection. Mean ± SD area under the curve, peak concentration, and terminal half-life for unbound (plasma) and total (serum) platinum were 774.6 ± 221.1 ng•h/mL and 3,562.1 ± 2,031.1 ng•h/mL, 56.5 ± 20.9 ng/mL and 81.6 ± 40.4 ng/mL, and 33.6 ± 16.1 hours and 51.2 ± 29.1 hours, respectively. Platinum concentrations ranged from 3,325 to 8,229 ng/g in STSs and 130 to 6,066 ng/g in STS-associated lymph nodes.

CONCLUSIONS AND CLINICAL RELEVANCE

Intratumoral injection of the hyaluronan-cisplatin nanoconjugate was well tolerated in treated dogs. Following intratumoral hyaluronan-cisplatin injection, platinum concentration was 1,000-fold and 100-fold greater within treated tumors and tumor-draining lymphatics, respectively, compared with that in plasma.

Abstract 1863: Differing sensitivity to stage-specific autophagy inhibition

Background: Autophagy is an intracellular process that involves the sequestration of cytosolic proteins and organelles into double-membraned vesicles called autophagosomes and their subsequent degradation in the lysosome. This process is induced during cellular stress and is crucial for maintaining proper homeostasis. Recently, autophagy has been identified as a potential mechanism of chemoresistance. Thus, autophagy inhibition has become an attractive anti-cancer therapy. However, autophagy is a multi-step process and it is still unclear if blocking autophagy at one particular stage is more advantageous than another. Therefore, we inhibited autophagy at various points in the pathway using genetic and pharmacologic means in multiple cancer models.

Material and Methods: Murine cell lines used were 4T1, mammary carcinoma, B16-F10, melanoma, DLM8, osteosarcoma, and A20, lymphoma. Autophagy was inhibited by multiple methods. The first method was pharmacologic inhibition using 10uM chloroquine (CQ) or 1nM bafilomycin A1 (Baf A1), doses sufficient to inhibit autophagy. The second method was genetic knockdown by decreasing expression of critical autophagy proteins Beclin-1 (Bcn-1) or Atg7 by shRNA lentiviral delivery. Cells were assessed for protein knockdown by western blot and qPCR analysis. Proliferation of cells in the presence or absence of active autophagy was assessed using an Alamar Blue assay. For cell cycle analysis, cells were grown for 48h, stained with propidium iodine and analyzed by flow cytometry.

Results and Conclusions: A significant decrease in expression of Bcn-1 and Atg7 was observed after lentiviral transduction. Autophagy was also successfully inhibited as indicated by a failure to induce elevations in autophagy marker LC3 after serum starvation, a positive autophagy control. CQ and Baf A1, which inhibit late stage autophagy, had little effect on the 4T1 cells, but CQ did inhibit the other three lines. Bcn-1 knockdown, preventing nucleation of the autophagosome, was able to inhibit proliferation in all lines at a level that was even more pronounced than CQ inhibition. In addition, the percentage of cells in G1 significantly increased in the Bcn-1 knockdown cells. Continued study with the Atg7 cells and Baf A1 will reveal if the effects of CQ and Bcn-1 knockdown are merely off target effects or truly autophagy inhibition. The inclusion of Vps 34 inhibitors and late stage mediator knockdown lines will also be useful in determining if the early, nucleation stage of autophagy is the critical step(s) to target. Lastly, it will be important to determine if these effects differ when cells experience stress, such as the presence of chemotherapy. These studies suggest that the sensitivity toward autophagy inhibition may depend on the stage of the pathway that is targeted and cancer type.

Acknowledgements:

Role of Autophagy in Tumor Cell Death

National Cancer Institute 1R01CA150925

Citation Format: Rebecca A. Barnard, Paola Maycotte, Ryan J. Hansen, Daniel L. Gustafson, Andrew Thorburn. Differing sensitivity to stage-specific autophagy inhibition. [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 1863. doi:10.1158/1538-7445.AM2013-1863

Issues, challenges, and opportunities in model-based drug development for monoclonal antibodies

Over the last two decades, there has been a simultaneous explosion in the levels of activity and capability in both monoclonal antibody (mAb) drug development and in the use of quantitative pharmacologic models to facilitate drug development. Both of these topics are currently areas of great interest to academia, the pharmaceutical and biotechnology industries, and to regulatory authorities. In this article, we summarize convergence of these two areas and discuss some of the current and historical applications of the use of mathematical-model-based techniques to facilitate the discovery and development of mAb therapeutics. We also consider some of the current issues and limitations in model-based antibody discovery/development and highlight areas of further opportunity.

Qualification of a free ligand assay in the presence of anti-ligand antibody Fab fragments

The aim of this work was to develop and characterize an ELISA to measure free ligand concentrations in rat serum in the presence of a Fab to the same ligand. A variety of experiments were conducted to understand optimal assay conditions and to verify that only free ligand was detected. The parameters explored included sample incubation time on plate, the initial concentrations of Fab and ligand, and the pre-incubation time required for the Fab-ligand complex concentrations to reach equilibrium. We found the optimal experimental conditions to include a 10-minute on-plate incubation of ligand-containing samples, with a 24-hour pre-incubation time for test samples of Fab and ligand to reach equilibrium. An alternative approach, involving removal of Fab-ligand complexes from the solution prior to measuring concentrations of the ligand, was also used to verify that the assay only measured free ligand. Rats were dosed subcutaneously with Fab and the assay was used to demonstrate dose-dependent suppression of endogenous free ligand levels in vivo.

Abstract C19: The effect of autophagy inhibition on anchorage-independent cell growth

Background: Autophagy is an intracellular process that involves the sequestration of cytosolic proteins and organelles into double-membraned vesicles called autophagosomes and their subsequent degradation in the lysosome. This process is induced during cellular stress and is crucial for maintaining proper homeostasis. Autophagy has also been shown to play a role in tumorigenesis, yet the role of autophagy in metastasis progression is poorly understood. Some of the key steps in metastasis progression are the ability of tumor cells to detach from the extracellular matrix, enter circulation, and seed a distal site. Non-tumorigenic cells undergo apoptosis upon detachment, referred to as anoikis. Some evidence suggests that autophagy is induced after detachment and facilitates anchorage independent growth and anoikis evasion. Therefore, we studied the effect of autophagy inhibition on anchorage independent growth using multiple cancer models both in vitro and in vivo.

Material and Methods: Murine cell lines used were 4T1, mammary carcinoma, B16-F10, melanoma, and DLM8, osteosarcoma. Autophagy was inhibited by multiple methods. The first method was pharmacologic inhibition using 10uM chloroquine (CQ) or 1nM bafilomycin A1 (BafA1). The second method was genetic knockdown by decreasing expression of critical autophagy proteins Beclin-1 (Bcn-1) or Atg7 by shRNA lentiviral delivery. Cells were assessed for Bcn-1 or Atg7 knockdown by western blot and qPCR analysis. Proliferation of cells in the presence or absence of active autophagy was assessed using an Alamar Blue assay. To determine anchorage independent proliferation, PolyHEMA coated plates were used to prevent attachment. For cell cycle analysis, cells were grown for 48h, stained with propidium iodine and analyzed by flow cytometry. For the in vivo model, mice were pretreated with CQ for 72h at 60mg/kg daily IP, allowing for systemic autophagy inhibition. 4T1 cells transfected with a luciferase reporter, or B16-F10 cells were injected via the tail vein of syngeneic Balb/c or C57Bl/6J mice. Mice continued to receive CQ or vehicle daily and were monitored thrice weekly until the development of luciferase positive metastases or 10% weight loss. Blood and liver samples were also collected to assess autophagy inhibition by measuring LC3 expression as determined by flow cytometry or Western blot.

Results and Conclusions: A significant decrease in expression of Bcn-1 and Atg7 was observed after lentiviral transduction. Autophagy was also successfully inhibited as indicated by a failure to induce elevations in autophagy marker LC3 after serum starvation, a positive autophagy control. Pharmacologic inhibition had no significant effect on 4T1 proliferation under any culture condition and failed to delay metastasis development in vivo. However, CQ did inhibit proliferation for B16-F10 and DLM8 cells, and this effect was more pronounced in B16-F10 cells grown in suspension. To demonstrate if a similar affect can be seen in vivo, mice will also be challenged with B16-F10 cells and treated with CQ. Conversely, Bcn-1 knockdown was able to significantly inhibit proliferation for all cell types and under all culture conditions, but there was no difference whether cells were attached or suspended. Further study with the Atg7 cells and BafA1 will reveal if this effect is merely an off target effect of Bcn-1 or truly autophagy inhibition. These studies suggest that the role autophagy plays in anchorage independent growth and survival of tumor cells is context dependent and thus broad use of autophagy inhibitors in cancer treatment is a questionable strategy.

Acknowledgements: Role of Autophagy in Tumor Cell Death. National Cancer Institute 1R01CA150925

Citation Format: Rebecca A. Barnard, Paola Maycotte, Ryan J. Hansen, Daniel L. Gustafson, Andrew Thorburn. The effect of autophagy inhibition on anchorage-independent cell growth. [abstract]. In: Proceedings of the AACR Special Conference on Tumor Invasion and Metastasis; Jan 20-23, 2013; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2013;73(3 Suppl):Abstract nr C19.

Neuroprotective efficacy and pharmacokinetic behavior of novel anti-inflammatory para-phenyl substituted diindolylmethanes in a mouse model of Parkinson's disease

There are currently no registered drugs that slow the progression of neurodegenerative diseases, in part because translation from animal models to the clinic has been hampered by poor distribution to the brain. The present studies examined a selected series of para-phenyl-substituted diindolylmethane (C-DIM) compounds that display anti-inflammatory and neuroprotective efficacy in vitro. We postulated that the pharmacokinetic behavior of C-DIM compounds after oral administration would correlate with neuroprotective efficacy in vivo in a mouse model of Parkinson's disease. Pharmacokinetics and metabolism of 1,1-bis(3'-indolyl)-1-(p-methoxyphenyl)methane (C-DIM5), 1,1-bis(3'-indolyl)-1-(phenyl)methane, 1,1-bis(3'-indolyl)-1-(p-hydroxyphenyl)methane (C-DIM8), and 1,1-bis(3'-indolyl)-1-(p-chlorophenyl)methane (C-DIM12) were determined in plasma and brain of C57Bl/6 mice after oral and intravenous administration at 10 and 1 mg/Kg, respectively. Putative metabolites were measured in plasma, liver, and urine. C-DIM compounds given orally displayed the highest area under the curve, Cmax, and Tmax levels, and C-DIM12 exhibited the most favorable pharmacokinetics of the compounds tested. Oral bioavailability of each compound ranged from 6% (C-DIM8) to 42% (C-DIM12). After pharmacokinetic studies, the neuroprotective efficacy of C-DIM5, C-DIM8, and C-DIM12 (50 mg/Kg per oral) was examined in mice exposed to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and probenecid for 14 days, a model of progressive neurodegeneration with a strong neuroinflammatory component. C-DIM5 and C-DIM12 given orally once daily after one week of exposure to MPTP and probenecid prevented further loss of dopaminergic neurons in the substantia nigra pars compacta and striatal dopamine terminals, indicating that these compounds could be effective therapeutic agents to prevent neurodegeneration.

Optimized dosing of a CCR2 antagonist for amplification of vaccine immunity

We have recently discovered that inflammatory monocytes recruited to lymph nodes in response to vaccine-induced inflammation can function as potent negative regulators of both humoral and cell-mediated immune responses to vaccination. Monocyte depletion or migration blockade can significantly amplify both antibody titers and cellular immune responses to vaccination with several different antigens in mouse models. Thus, we hypothesized that the use of small molecule CCR2 inhibitors to block monocyte migration into lymph nodes may represent a broadly effective means of amplifying vaccine immunity. To address this question, the role of CCR2 in monocyte recruitment to vaccine draining lymph nodes was initially explored in CCR2-/- mice. Next, a small molecule antagonist of CCR2 (RS102895) was evaluated in mouse vaccination models. Initial studies revealed that a single intraperitoneal dose of RS102895 failed to effectively block monocyte recruitment following vaccination. Pharmacokinetic analysis of RS102895 revealed a short half-life (approximately 1h), and suggested that a multi-dose treatment regimen would be more effective. We found that administration of RS102895 every 6 h resulted in consistent plasma levels of 20 ng/ml or greater, which effectively blocked monocyte migration to lymph nodes following vaccination. Moreover, administration of RS102895 with concurrent vaccination markedly enhanced vaccine responses following immunization against the influenza antigen HA1. We concluded that administration of small molecule CCR2 antagonists such as RS102895 in the immediate post-vaccine period could be used as a novel means of significantly enhancing vaccine immunity.