Evaluation of a Three Compartment In Vitro Gastrointestinal Simulator Dissolution Apparatus to Predict In Vivo Dissolution

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/109359/1/jps24112.pd

Formulation predictive dissolution (fPD) testing to advance oral drug product development: an introduction to the US FDA funded ‘21st Century BA/BE’ project

Over the past decade, formulation predictive dissolution (fPD) testing has gained increasing attention. Another mindset is pushed forward where scientists in our field are more confident to explore the in vivo behavior of an oral drug product by performing predictive in vitro dissolution studies. Similarly, there is an increasing interest in the application of modern computational fluid dynamics (CFD) frameworks and high-performance computing platforms to study the local processes underlying absorption within the gastrointestinal (GI) tract. In that way, CFD and computing platforms both can inform future PBPK-based in silico frameworks and determine the GI-motility-driven hydrodynamic impacts that should be incorporated into in vitro dissolution methods for in vivo relevance. Current compendial dissolution methods are not always reliable to predict the in vivo behavior, especially not for biopharmaceutics classification system (BCS) class 2/4 compounds suffering from a low aqueous solubility. Developing a predictive dissolution test will be more reliable, cost-effective and less time-consuming as long as the predictive power of the test is sufficiently strong. There is a need to develop a biorelevant, predictive dissolution method that can be applied by pharmaceutical drug companies to facilitate marketing access for generic and novel drug products. In 2014, Prof. Gordon L. Amidon and his team initiated a far-ranging research program designed to integrate (1) in vivo studies in humans in order to further improve the understanding of the intraluminal processing of oral dosage forms and dissolved drug along the gastrointestinal (GI) tract, (2) advancement of in vitro methodologies that incorporates higher levels of in vivo relevance and (3) computational experiments to study the local processes underlying dissolution, transport and absorption within the intestines performed with a new unique CFD based framework. Of particular importance is revealing the physiological variables determining the variability in in vivo dissolution and GI absorption from person to person in order to address (potential) in vivo BE failures. This paper provides an introduction to this multidisciplinary project, informs the reader about current achievements and outlines future directions

Floxuridine prodrug development: Transporter affinity and enzymatic activation.

The researches were conducted to determine the advantages of prodrug approach over a parent drug. 5'-dipeptide floxuridine prodrugs were synthesized and evaluated for their enzymatic stability in human plasma and cell homogenates and non-enzymatic stability in pH 7.4 buffer. Suitability as transporter substrates was assessed by their ability to inhibit [3H]Gly-Sar uptake into 3 different cells, Caco-2 cells, AsPC-1 cells, and Capan-2 cells. The transporter affinity and stability of 5'-dipeptide floxuridine prodrugs were also compared with 5'-mono ester floxuridine prodrugs. The 5'-dipeptide floxuridine prodrugs showed, higher affinity by inhibiting Gly-Sar uptake for transporters than the monoesters. All prodrugs were hydrolyzed to parent drug in all cell homogenates and human plasma. Two prodrugs, 5'-O-Valyl-Phenylalanyl-floxuridine and 5'-O-Phenylalanyl-Tyrosyl-floxuridine, were the most stable dipeptide prodrugs among them in three different cell lines, half life 62.90-83.18 min and 42.83-95.23 min, respectively. Mono amino acid/dipeptide ester prodrugs of floxuridine showed better tumor growth inhibition in two pancreatic cancer cells while the parent drug barely exhibited any tumor growth inhibition. All prodrugs showed good permeability in Capan-2 cells while the membrane permeability of floxuridine was not observed. This might be a faster metabolic pathway for FUdR and 5-FU due to enzyme upregulation. Therefore, the importance of prodrug stability cannot be emphasized enough. In prodrugs, time lag for growth inhibition of tumor cells was observed due to the various chemical/enzymatic stabilities of prodrugs. The result suggests that there are specific enzymes to activate prodrugs based on the prodrug stability and the enzyme locations in cells, in which all enzymes are well arranged in the cell compartments unlike cell homogenates. Thus, the stability of prodrugs in cell homogenates may lead to underestimation. Dipeptide prodrugs of floxuridine with improved transporter affinity and tumor growth inhibition were successfully synthesized. To design prodrugs for further investigations, not only the transporter affinity but also the stability and activation of prodrugs including enzyme substrate specificities have to be carefully considered and monitored.Ph.D.Health and Environmental SciencesPharmacologyUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/126307/2/3238099.pd

Potential Development of Tumor-Targeted Oral Anti-Cancer Prodrugs: Amino Acid and Dipeptide Monoester Prodrugs of Gemcitabine

One of the main obstacles for cancer therapies is to deliver medicines effectively to target sites. Since stroma cells are developed around tumors, chemotherapeutic agents have to go through stroma cells in order to reach tumors. As a method to improve drug delivery to the tumor site, a prodrug approach for gemcitabine was adopted. Amino acid and dipeptide monoester prodrugs of gemcitabine were synthesized and their chemical stability in buffers, resistance to thymidine phosphorylase and cytidine deaminase, antiproliferative activity, and uptake/permeability in HFF cells as a surrogate to stroma cells were determined and compared to their parent drug, gemcitabine. The activation of all gemcitabine prodrugs was faster in pancreatic cell homogenates than their hydrolysis in buffer, suggesting enzymatic action. All prodrugs exhibited great stability in HFF cell homogenate, enhanced resistance to glycosidic bond metabolism by thymidine phosphorylase, and deamination by cytidine deaminase compared to their parent drug. All gemcitabine prodrugs exhibited higher uptake in HFF cells and better permeability across HFF monolayers than gemcitabine, suggesting a better delivery to tumor sites. Cell antiproliferative assays in Panc-1 and Capan-2 pancreatic ductal cell lines indicated that the gemcitabine prodrugs were more potent than their parent drug gemcitabine. The transport and enzymatic profiles of gemcitabine prodrugs suggest their potential for delayed enzymatic bioconversion and enhanced resistance to metabolic enzymes, as well as for enhanced drug delivery to tumor sites, and cytotoxic activity in cancer cells. These attributes would facilitate the prolonged systemic circulation and improved therapeutic efficacy of gemcitabine prodrugs

Measuring the Impact of Gastrointestinal Variables on the Systemic Outcome of Two Suspensions of Posaconazole by a PBPK Model

For the last two decades, the application of physiologically based pharmacokinetic (PBPK) models has grown exponentially in the field of oral absorption and in a regulatory context. Although these models are widely used, their predictive power should be validated and optimized in order to rely on these models and to know exactly what is going on "under the hood". In this study, an automated sensitivity analysis (ASA) was performed for 11 gastrointestinal (GI) variables that are integrated into the PBPK software program Simcyp®. The model of interest was a previously validated workspace that was able to predict the intraluminal and systemic behavior of two different suspensions of posaconazole in the Simcyp® Simulator. The sensitivity of the following GI parameters was evaluated in this model: gastric and duodenal pH, gastric and duodenal bicarbonate concentrations (reflecting buffer capacity), duodenal bile salts concentration, gastric emptying, the interdigestive migrating motor complex (IMMC), small intestinal transit time (SITT), gastric and jejunal volumes, and permeability. The most sensitive parameters were gastric/duodenal pH and gastric emptying, for both suspensions. The outcome of the sensitivity analyses highlights the important GI variables that must be integrated into an in vivo predictive dissolution test to help and create a rational and scientific framework/design for product development of novel and generic drug products.status: publishe