Pharmacokinetic modeling of doxorubicin pharmacokinetics in dogs deficient in ABCB1 drug transporters

MDR1 Inhibition Reverses Doxorubicin-Resistance in Six Doxorubicin-Resistant Canine Prostate and Bladder Cancer Cell Lines

Acquired chemoresistance during chemotherapy, often accompanied by cross- and multi-resistance, limits therapeutic outcomes and leads to recurrence. In order to create in vitro model systems to understand acquired doxorubicin-resistance, we generated doxorubicin-resistant sublines of canine prostate adenocarcinoma and urothelial cell carcinoma cell lines. Chemoresistance to doxorubicin, cross-resistance to carboplatin, and the reversibility of the acquired resistance by the specific MDR1-inhibitor tariquidar were quantified in metabolic assays. Resistance mechanisms were characterized by expression of the efflux transporters MDR1 and RALBP1, as well as the molecular target of doxorubicin, TOP2A, with qPCR and Western blotting. Six out of nine cell lines established stable resistance to 2 µM doxorubicin. Drug efflux via massive MDR1 overexpression was identified as common, driving resistance mechanism in all sublines. MDR1 inhibition with tariquidar extensively reduced or reversed the acquired, and also partly the parental resistance. Three cell lines developed additional, non-MDR1-dependent resistance. RALBP1 was upregulated in one resistant subline at the protein level, while TOP2A expression was not altered. Combination therapies aiming to inhibit MDR1 activity can now be screened for synergistic effects using our resistant sublines. Nevertheless, detailed resistance mechanisms and maintained molecular target expression in the resistant sublines are still to be examined.

Vinblastine pharmacokinetics in mouse, dog, and human in the context of a physiologically based model incorporating tissue-specific drug binding, transport, and metabolism

Vinblastine (VBL) is a vinca alkaloid-class cytotoxic chemotherapeutic that causes microtubule disruption and is typically used to treat hematologic malignancies. VBL is characterized by a narrow therapeutic index, with key dose-limiting toxicities being myelosuppression and neurotoxicity. Pharmacokinetics (PK) of VBL is primarily driven by ABCB1-mediated efflux and CYP3A4 metabolism, creating potential for drug-drug interaction. To characterize sources of variability in VBL PK, we developed a physiologically based pharmacokinetic (PBPK) model in Mdr1a/b(-/-) knockout and wild-type mice by incorporating key drivers of PK, including ABCB1 efflux, CYP3A4 metabolism, and tissue-specific tubulin binding, and scaled this model to accurately simulate VBL PK in humans and pet dogs. To investigate the capability of the model to capture interindividual variability in clinical data, virtual populations of humans and pet dogs were generated through Monte Carlo simulation of physiologic and biochemical parameters and compared to the clinical PK data. This model provides a foundation for predictive modeling of VBL PK. The base PBPK model can be further improved with supplemental experimental data identifying drug-drug interactions, ABCB1 polymorphisms and expression, and other sources of physiologic or metabolic variability.

Sorafenib and Doxorubicin Show Synergistic Effects in Human and Canine Osteosarcoma Cell Lines

Osteosarcoma (OSA) is the most common bone tumor in both humans and dogs and has a nearly ten-fold higher incidence in dogs than humans. Despite advances in the treatment of other cancers, the overall survival rates for OSA have stagnated for the past four decades. Therefore, there is a great need to identify novel and effective treatments. We screened a series of tyrosine kinase inhibitors and selected sorafenib, a multi-kinase inhibitor, for further evaluation alone and in combination with cisplatin, carboplatin, and doxorubicin on canine and human OSA cell lines. Our data point to synergistic effects when sorafenib is combined with doxorubicin, but not when combined with cisplatin or carboplatin, in both human and canine OSA. Based on current findings, clinical trials using a combination of doxorubicin and sorafenib in proof-of-concept studies in dogs are warranted. These studies can be carried out relatively quickly in dogs where case load is high and, in turn, provide useful data for the initiation of clinical trials in humans.

Drug Exposure to Establish Pharmacokinetic-Response Relationships in Oncology

In the oncology field, understanding the relationship between the dose administered and the exerted effect is particularly important because of the narrow therapeutic index associated with anti-cancer drugs and the high interpatient variability. Therefore, in this review, we provide a critical perspective of the different methods of characterising treatment exposure in the oncology setting. The increasing number of modelling applications in oncology reflects the applicability and the impact of pharmacometrics on all phases of the drug development process and patient management as well. Pharmacometric modelling is a worthy component within the current paradigm of model-based drug development, but pharmacometric modelling techniques are also accessible for the clinician in the optimisation of current oncology therapies. Consequently, the application of population models in a hospital setting by generating close collaborations between physicians and pharmacometricians is highly recommended, providing a systematic means of developing and assessing model-based metrics as 'drivers' for various responses to treatments, which can then be evaluated as predictors for treatment success. Characterising the key determinants of variability in exposure is of particular importance for anticancer agents, as efficacy and toxicity are associated with exposure. We present the different strategies to describe and predict drug exposure that can be applied depending on the data available, with the objective of obtaining the most useful information in the patients' favour throughout the full drug cycle. Therefore, the objective of the present article is to review the different approaches used to characterise a patient's exposure to oncology drugs, which will result in a better understanding of the time course of the response and the magnitude of interpatient variability.

Molecular pathology in the cancer clinic - where are we now and where are we headed?

Molecular pathology is a developing sub-microscopic discipline of pathology that studies the effects of molecular variations and mutations on disease processes. The ultimate goal of molecular pathology in cancer is to predict risk, facilitate diagnosis and improve prognostication based on a complete understanding of the biological impact of specific molecular variations, mutations and dysregulations. This knowledge will provide the basis for customised cancer treatment, so-called precision medicine. Rapid developments in genomics have placed this field at the forefront of clinical molecular pathology and there are already a number of well-established genetic tests available for clinical use including PCR of antigen receptor rearrangement and KIT mutational analysis. Moving beyond tests assessing a single gene, there are significant research efforts utilising genomics to predict cancer risk, forecast aggressive behaviour and identify druggable mutations and therapeutic biomarkers. Researchers are also investigating the use of circulating cells and nucleic acid for clinically useful low morbidity genomic assessments. If we are to realise the full potential of molecular pathology and precision medicine there are a number of challenges to overcome. These include developing our understanding of the underlying biology (in particular intra-tumoural heterogeneity), methodological standardisation of assays, provision of adequate infrastructure and production of novel therapeutics backed by high-quality clinical data supporting the precision medicine approach. The era of molecular pathology holds the potential to revolutionise veterinary cancer care, but its impact on clinical practice will depend upon the extent to which the inherent challenges can be overcome.

Biodynamic signatures from ex vivo bone marrow aspirates are associated with chemotherapy-induced neutropenia in cancer-bearing dogs

Background

Neutropenia is the most common dose‐limiting side effect of cytotoxic chemotherapy in cancer‐bearing dogs. Biodynamic imaging (BDI) is a functional imaging technology that measures dynamic light scattering from living, three‐dimensional tissues to characterize intracellular motion within those tissues. Previous studies have associated BDI biomarkers with tumour sensitivity to chemotherapy agents in dogs with naturally occurring cancer. We hypothesized that BDI, performed ex vivo on bone marrow aspirate samples, would identify dynamic biomarkers associated with the occurrence of specific degrees of neutropenia in tumour‐bearing dogs receiving doxorubicin chemotherapy.

Materials and Methods

Bone marrow aspirates were collected from 10 dogs with naturally occurring cancers prior to initiation of doxorubicin treatment. BDI was performed on bone marrow samples treated ex vivo with doxorubicin at 0.1, 1, 10 and 100 μM along with 0.1% DMSO as a control. Dogs then were treated with doxorubicin (30 mg/m², intravenously). Peripheral blood neutrophil counts were obtained on the day of treatment and again 7 days later. Receiver operating characteristic curves identified provisional breakpoints for BDI biomarkers that correlated with specific changes in neutrophil counts between the two time points.

Results

Provisional breakpoints for several BDI biomarkers were identified, specifying dogs with the largest proportionate change in neutrophils and with neutropenia that was grade 2 or higher following doxorubicin treatment.

Conclusions

Biodynamic imaging of bone marrow aspirates may identify those dogs at greater risk for neutropenia following doxorubicin chemotherapy. This approach may be useful for pre‐emptively modifying chemotherapy dosing in dogs to avoid unacceptable side effects.

Drug dose and drug choice: Optimizing medical therapy for veterinary cancer

Although novel agents hold great promise for the treatment of animal neoplasia, there may be room for significant improvement in the use of currently available agents. These improvements include altered dosing schemes, novel combinations, and patient-specific dosing or selection of agents. Previous studies have identified surrogates for "individualized dose intensity,", for example, patient size, development of adverse effects, and pharmacokinetic parameters, as potential indicators of treatment efficacy in canine lymphoma, and strategies for patient-specific dose escalation are discussed. Strategies for treatment selection in individual patients include conventional histopathology, protein-based target assessment (eg, flow cytometry, immunohistochemistry, and mass spectrometry), and gene-based target assessment (gene expression profiling and targeted or global sequencing strategies). Currently available data in animal cancer evaluating these strategies are reviewed, as well as ongoing studies and suggestions for future directions.

Pre-clinical evaluation of proteasome inhibitors for canine and human osteosarcoma

Osteosarcoma, a common malignancy in large dog breeds, typically metastasises from long bones to lungs and is usually fatal within 1 to 2 years of diagnosis. Better therapies are needed for canine patients and their human counterparts, a third of whom die within 5 years of diagnosis. We compared the in vitro sensitivity of canine osteosarcoma cells derived from 4 tumours to the currently used chemotherapy drugs doxorubicin and carboplatin, and 4 new anti-cancer drugs. Agents targeting histone deacetylases or PARP were ineffective. Two of the 4 cell lines were somewhat sensitive to the BH3-mimetic navitoclax. The proteasome inhibitor bortezomib potently induced caspase-dependent apoptosis, at concentrations substantially lower than levels detected in the bones and lungs of treated rodents. Co-treatment with bortezomib and either doxorubicin or carboplatin was more toxic to canine osteosarcoma cells than each agent alone. Newer proteasome inhibitors carfilzomib, ixazomib, oprozomib and delanzomib manifested similar activities to bortezomib. Human osteosarcoma cells were as sensitive to bortezomib as the canine cells, but slightly less sensitive to the newer drugs. Human osteoblasts were less sensitive to proteasome inhibition than osteosarcoma cells, but physiologically relevant concentrations were toxic. Such toxicity, if replicated in vivo, may impair bone growth and strength in adolescent human osteosarcoma patients, but may be tolerated by canine patients, which are usually diagnosed later in life. Proteasome inhibitors such as bortezomib may be useful for treating canine osteosarcoma, and ultimately may improve outcomes for human patients if their osteoblasts survive exposure in vivo, or if osteoblast toxicity can be managed.

A Multiscale Physiologically-Based Pharmacokinetic Model for Doxorubicin to Explore its Mechanisms of Cytotoxicity and Cardiotoxicity in Human Physiological Contexts

PURPOSE

The mechanisms underlying doxorubicin cytotoxicity and cardiotoxicity were broadly explored but remain incompletely understood. A multiscale physiologically-based pharmacokinetic (PBPK) model was developed to assess doxorubicin dispositions at levels of system, tissue interstitial, cell, and cellular organelles. This model was adopted to explore the mechanisms-of-action/toxicity of doxorubicin in humans.

METHODS

The PBPK model was developed by analyzing data from mice and the model was verified by scaling up to predict doxorubicin multiscale dispositions in rats and humans. The multiscale dispositions of doxorubicin in human heart and tumors were explicitly simulated to elucidate the potential mechanisms of its cytotoxicity and cardiotoxicity.

RESULTS

The developed PBPK model was able to adequately describe doxorubicin dispositions in mice, rats and humans. In humans, prolonged infusion, a dosing regimen with less cardiotoxicity, was predicted with substantially reduced free doxorubicin concentrations at human heart interstitium, which were lower than the concentrations associated with oxidative stress. However, prolonged infusion did not reduce doxorubicin-DNA adduct at tumor nucleus, consistent with clinical observations that prolonged infusion did not compromise anti-tumor effect, indicating that one primary anti-tumor mechanism was DNA torsion.

CONCLUSIONS

A multiscale PBPK model for doxorubicin was developed and further applied to explore its cytotoxic and cardiotoxic mechanisms.

Utility of physiologically based pharmacokinetic (PBPK) modeling in oncology drug development and its accuracy: a systematic review

PURPOSE

Physiologically based pharmacokinetic (PBPK) modeling, a mathematical modeling approach which uses a pharmacokinetic model to mimick human physiology to predict drug concentration-time profiles, has been used for the discover and development of drugs in various fields, including oncology, since 2000. There have been a few general review articles on the utilization of PBPK in the development of oncology drugs, but these do not include an evaluation of model prediction accuracy. We therefore conducted a systematic review to define the accuracy of PBPK model prediction and its utility throughout all the developmental phases of oncology drugs.

METHODS

A systematic search was performed in the PubMed, PubMed Central and Cochrane Library databases from 1980 to February 2017 for articles (1) written in English, (2) focused on oncology or antineoplastic or anticancer drugs, tumor or cancer or anticancer drugs listed in the U.S. National Institutes of Health and (3) involving a PBPK model. The absolute-average-folding-errors (AAFEs) of the area under the curve (AUC) between predicted and observed values in each article were calculated to assess model prediction accuracy.

RESULTS

Of the 2341 articles initially identified by our search of the databases, 40 were included in the review analysis. These articles reported on six types of studies, i.e. in vivo (n = 4), first-in-human (n = 5), phase II/III clinical trials (n = 9), organ impairment (n = 3), pediatrics (n = 4) and drug-drug interactions (n = 15). AAFEs of the predicted AUC for all groups of studies were within 1.3-fold of each other despite variations in experimental methodologies.

CONCLUSION

PBPK modeling is a potential tool which can be effectively applied throughout all phases of oncology drug development. The number of experimental animals and human participants enrolled in the studies can be reduced using PBPK modeling and PBPK-population-PK modeling. The limited number of publications of unsuccessful model application to date may contribute to bias toward the usefulness of modeling.

A novel canine histiocytic sarcoma cell line: initial characterization and utilization for drug screening studies

BACKGROUND

Histiocytic sarcoma is a rare disorder in humans, however it is seen with appreciable frequency in certain breeds of dogs, such as Bernese mountain dog. The purpose of this study was to fully characterize a novel canine histiocytic sarcoma cell line, and utilize it as a tool to screen for potential therapeutic drugs.

METHODS

The histiocytic sarcoma cell line was characterized by expression of cellular markers as determined by immunohistochemistry and flow cytometry techniques. The neoplastic cells were also evaluated for their capability of phagocytizing beads particles, and their potential to grow as xenograft in an immunodeficient mouse. We investigated the in vitro cytotoxic activity of a panel of thirteen compounds using the MTS proliferation assay. Inhibitory effects of different drugs were compared using one-way ANOVA, and multiple means were compared using Tukey's test.

RESULTS

Neoplastic cells expressed CD11c, CD14, CD18, CD45, CD172a, CD204, MHC I, and vimentin. Expression of MHC II was upregulated after exposure to LPS. Furthermore, the established cell line clearly demonstrated phagocytic activity similar to positive controls of macrophage cell line. The xenograft mouse developed a palpable subcutaneous soft tissue mass after 29 days of inoculation, which histologically resembled the primary neoplasm. Dasatinib, a tyrosine kinase pan-inhibitor, significantly inhibited the growth of the cells in vitro within a clinically achievable and tolerable plasma concentration. The inhibitory response to dasatinib was augmented when combined with doxorubicin.

CONCLUSIONS

In the present study we demonstrated that a novel canine histiocytic sarcoma cell line presents a valuable tool to evaluate novel treatment approaches. The neoplastic cell line favorably responded to dasatinib, which represents a promising anticancer strategy for the treatment of this malignancy in dogs and similar disorders in humans.

Comparison of chemotherapeutic drug resistance in cells transfected with canine ABCG2 or feline ABCG2

ABCG2 (ATP binding cassette subfamily G, member 2) mediates resistance to a variety of cytotoxic agents. Although human ABCG2 is well characterized, the function of canine ABCG2 has not been studied previously. Feline ABCG2 has an amino acid substitution in the adenosine triphosphate-binding domain that decreases its transport capacity relative to human ABCG2. Our goal was to compare canine ABCG2-mediated chemotherapeutic drug resistance to feline ABCG2-mediated chemotherapeutic drug resistance. HEK-293 cells stably transfected with plasmid containing canine ABCG2, feline ABCG2 or no ABCG2 were exposed to carboplatin, doxorubicin, mitoxantrone, toceranib or vincristine, and cell survival was subsequently determined. Canine ABCG2 conferred a greater degree of chemotherapy resistance than feline ABCG2 for mitoxantrone. Neither canine nor feline ABCG2 conferred resistance to doxorubicin, vincristine or toceranib. Canine, but not feline, ABCG2 conferred resistance to carboplatin, a drug that is not reported to be a substrate for ABCG2 in other species.

Use of a Monte Carlo analysis within a physiologically based pharmacokinetic model to predict doxycycline residue withdrawal time in edible tissues in swine

The pharmacokinetics of doxycycline were studied following a single intravenous (I.V.) and intramuscular (I.M.) injection of 10 mg/kg into eight healthy pigs. The steady-state tissue/plasma partition coefficients were obtained via a 3-h constant rate infusion (CRI) in four pigs. Based on the results of in vivo studies and the parameters derived from published work, a physiologically based pharmacokinetic (PBPK) model was developed to predict the drug concentration in edible tissues. The predicted values were then compared with those derived from a previous study. To account for individual differences in the processes of drug metabolism and/or diffusion, a Monte Carlo (MC) run of 1000 simulations was incorporated into the PBPK model to predict the doxycycline residue withdrawal times in edible tissues in swine. The withdrawal periods were compared with those derived from linear regression analysis. The PBPK model presented here provided accurate predictions of the observed concentrations in all tissues except for the injection site. The withdrawal times in all edible tissues derived from the MC analysis were longer than those from linear regression analysis. Based on the residues in the injection site and muscle tissue, the MC analysis predicted a withdrawal time of 33 days. Here, we illustrate that MC analysis can be incorporated into the PBPK model to accurately predict doxycycline residue withdrawal time in edible tissues in swine.

Bisphosphonates significantly increase the activity of doxorubicin or vincristine against canine malignant histiocytosis cells

Canine malignant histiocytosis (MH) is an aggressive neoplasm of macrophages and dendritic cells. It carries a poor prognosis because of the development of widespread metastasis and poor sensitivity to chemotherapy. Thus, there is a large need for new treatments for MH. We hypothesized that bisphosphonates might be useful to increase the effectiveness of cytotoxic chemotherapy against MH. To address this question, we conducted in vitro screening studies using MH cell lines and a panel of 6 chemotherapy and 5 bisphosphonate drugs. The combination of clodronate with vincristine was found to elicit synergistic killing which was associated with a significant increase in cell cycle arrest. Second, zoledronate combined with doxorubicin also significantly increased cell killing. Zoledronate significantly increased the uptake of doxorubicin by MH cells. On the basis of these findings, we conclude that certain bisphosphonate drugs may increase the overall effectiveness of chemotherapy for MH in dogs.