NBCD Pharmacokinetics and Bioanalytical Methods to Measure Drug Release

Current state of nanomedicine drug products: An industry perspective

Nanomedicine drug products have reached an unprecedented high in terms of global commercial acceptance and media exposure with the approvals of the mRNA COVID-19 vaccines in 2021. In this paper, we examine the current state of the art for nanomedicine technologies as applied for pharmaceutical products and compare those trends with results from a recent IQ Consortium industry survey on nanomedicine drug products. We find that 1) industry companies continue to push the envelope in terms of new technologies for characterizing their specific drug products, 2) new analytical technologies continue to be utilized by industry to characterize the increasingly complex nanomedicine drug products and 3) alignment and communication are key between industry and regulatory authorities to better understand the regulatory filings that are being submitted. There are many CMC challenges that a company must overcome to successfully file a nanomedicine drug product. In 2022, the FDA Guidance on Drug Products containing Nanomaterials was published, and it provides a roadmap for submission of a nanomedicine drug product. We propose that our paper serves as a complimentary guide providing knowledge on specific CMC issues such as quality attributes, physicochemical characterization methods, excipients, and stability.

A reanalysis of nanoparticle tumor delivery using classical pharmacokinetic metrics

Nanoparticle (NP) delivery to solid tumors has recently been questioned. To better understand the magnitude of NP tumor delivery, we reanalyzed published murine NP tumor pharmacokinetic (PK) data used in the Wilhelm et al. study. Studies included in their analysis reporting matched tumor and blood concentration versus time data were evaluated using classical PK endpoints and compared to the unestablished percent injected dose (%ID) in tumor metric from the Wilhelm et al. study. The %ID in tumor was poorly correlated with standard PK metrics that describe NP tumor delivery (AUC_tumor/AUC_blood ratio) and only moderately associated with maximal tumor concentration. The relative tumor delivery of NPs was ~100-fold greater as assessed by the standard AUC_tumor/AUC_blood ratio than by %ID in tumor. These results strongly suggest that PK metrics and calculations can influence the interpretation of NP tumor delivery and stress the need to properly validate novel PK metrics against traditional approaches.

Distinguishing Pharmacokinetics of Marketed Nanomedicine Formulations Using a Stable Isotope Tracer Assay

The pharmacokinetics of nanomedicines are complicated by the unique dispositional characteristics of the drug carrier. Most simplistically, the carrier could be a solubilizing platform that allows administration of a hydrophobic drug. Alternatively, the carrier could be stable and release the drug in a controlled manner, allowing for distribution of the carrier to influence distribution of the encapsulated drug. A third potential dispositional mechanism is carriers that are not stably complexed to the drug, but rather bind the drug in a dynamic equilibrium, similar to the binding of unbound drug to protein; since the nanocarrier has distributional and binding characteristics unlike plasma proteins, the equilibrium binding of drug to a nanocarrier can affect pharmacokinetics in unexpected ways, diverging from classical protein binding paradigms. The recently developed stable isotope tracer ultrafiltration assay (SITUA) for nanomedicine fractionation is uniquely suited for distinguishing and comparing these carrier/drug interactions. Here we present the the encapsulated, unencapsulated, and unbound drug fraction pharmacokinetic profiles in rats for marketed nanomedicines, representing examples of controlled release (doxorubicin liposomes, Doxil; and doxorubicin HCl liposome generic), equilibrium binding (paclitaxel cremophor micelle solution, Taxol generic), and solubilizing (paclitaxel albumin nanoparticle, Abraxane; and paclitaxel polylactic acid micelle, Genexol-PM) nanomedicine formulations. The utility of the SITUA method in differentiating these unique pharmacokinetic profiles and its potential for use in establishing generic nanomedicine bioequivalence are discussed.

Report of the AAPS Guidance Forum on the FDA Draft Guidance for Industry: "Drug Products, Including Biological Products, that Contain Nanomaterials"

To guide developers of innovative and generic drug products that contain nanomaterials, the U.S. Food and Drug Administration issued the draft guidance for industry titled: "Drug Products, Including Biological Products, that Contain Nanomaterials" in December 2017. During the AAPS Guidance Forum on September 11, 2018, participants from industry, academia, and regulatory bodies discussed this draft guidance in an open setting. Two questions raised by the AAPS membership were discussed in more detail: what is the appropriate regulatory pathway for approval of drug products containing nanomaterials, and how to determine critical quality attributes (CQAs) for nanomaterials? During the meeting, clarification was provided on how the new FDA center-led guidance relates to older, specific nanomaterial class, or specific product-related guidances. The lively discussions concluded with some clear observations and recommendations: (I) Important lessons can be learned from how CQAs were determined for, e.g., biologics. (II) Publication of ongoing scientific discussions on strategies and studies determining CQAs of drug products containing nanomaterials will significantly strengthen the science base on this topic. Furthermore, (III) alignment on a global level on how to address new questions regarding nanomedicine development protocols will add to efficient development and approval of these much needed candidate nanomedicines (innovative and generic). Public meetings such as the AAPS Guidance Forum may serve as the place to have these discussions.

Improved Ultrafiltration Method to Measure Drug Release from Nanomedicines Utilizing a Stable Isotope Tracer

An important step in the early development of a nanomedicine formulation is the evaluation of stability and drug release in biological matrices. Additionally, the measurement of encapsulated and unencapsulated nanomedicine drug fractions is important for the determination of bioequivalence (pharmacokinetic equivalence) of generic nanomedicines. Unfortunately, current methods to measure drug release in plasma are limited, and all have fundamental disadvantages including non-equilibrium conditions and process-induced artifacts. The primary limitation of current ultrafiltration (and equilibrium dialysis) methods for separation of encapsulated and unencapsulated drug and determination of drug release is the difficulty in accurately differentiating protein bound and encapsulated drug. Since the protein binding of most drugs is high (>70%) and can change in a concentration- and time-dependent manner, it is very difficult to accurately account for the fraction of non-filterable drug that is encapsulated within the nanomedicine and how much is bound to protein. The method in this chapter is an improvement of existing ultrafiltration protocols for nanomedicine fractionation in plasma, in which a stable isotope tracer is spiked into a nanomedicine containing plasma sample in order to precisely measure the degree of plasma protein binding. Determination of protein binding then allows for accurate calculation of encapsulated and unencapsulated nanomedicine drug fractions, as well as free and protein-bound fractions.

Equivalence of complex drug products: advances in and challenges for current regulatory frameworks

Biotechnology and nanotechnology provide a growing number of innovator-driven complex drug products and their copy versions. Biologics exemplify one category of complex drugs, but there are also nonbiological complex drug products, including many nanomedicines, such as iron-carbohydrate complexes, drug-carrying liposomes or emulsions, and glatiramoids. In this white paper, which stems from a 1-day conference at the New York Academy of Sciences, we discuss regulatory frameworks in use worldwide (e.g., the U.S. Food and Drug Administration, the European Medicines Agency, the World Health Organization) to approve these complex drug products and their follow-on versions. One of the key questions remains how to assess equivalence of these complex products. We identify a number of points for which consensus was found among the stakeholders who were present: scientists from innovator and generic/follow-on companies, academia, and regulatory bodies from different parts of the world. A number of topics requiring follow-up were identified: (1) assessment of critical attributes to establish equivalence for follow-on versions, (2) the need to publish scientific findings in the public domain to further progress in the field, (3) the necessity to develop worldwide consensus regarding nomenclature and labeling of these complex products, and (4) regulatory actions when substandard complex drug products are identified.

When Is It Important to Measure Unbound Drug in Evaluating Nanomedicine Pharmacokinetics?

Nanoformulations have become important tools for modifying drug disposition, be it from the perspective of enabling prolonged drug release, protecting the drug molecule from metabolism, or achieving targeted delivery. When examining the in vivo pharmacokinetic properties of these formulations, most investigations either focus on systemic concentrations of total (encapsulated plus unencapsulated) drug, or concentrations of encapsulated and unencapsulated drug. However, it is rare to find studies that differentiate between protein-bound and unbound (free) forms of the unencapsulated drug. In light of the unique attributes of these formulations, we cannot simply assume it appropriate to rely upon the protein-binding properties of the traditionally formulated or legacy drug when trying to define the pharmacokinetic or pharmacokinetic/pharmacodynamic characteristics of these nanoformulations. Therefore, this commentary explores reasons why it is important to consider not only unencapsulated drug, but also the portion of unencapsulated drug that is not bound to plasma proteins. Specifically, we highlight those situations when it may be necessary to include measurement of unencapsulated, unbound drug concentrations as part of the nanoformulation pharmacokinetic evaluation.

Early Development Challenges for Drug Products Containing Nanomaterials

The vast majority of drug product candidates in early development fail to progress to clinics. This is true for products containing nanomaterials just as for other types of pharmaceuticals. Early development pathways should therefore place high priority on experiments that help candidates fail faster and less expensively. Nanomedicines fail for many reasons, but some are more avoidable than others. Some of the points of failure are not considerations in the development of small molecules or biopharmaceuticals, and so may be unexpected, even to those with previous experience bringing drug products to the clinic. This article reviews experiments that have proven useful in providing "go/no-go" decision-making data for nanomedicines in early preclinical development. Of course, the specifics depend on the particulars of the drug product and the nanomaterial type, and not every product shares the same development pathway or the same potential points of failure. Here, we focus on challenges that differ from those in the development of traditional small molecule therapeutics, and on experiments that reveal deficiencies that can only be corrected by essentially starting over-altering the nanomedicine to an extent that all previous characterization and proof-of-concept testing must be repeated. Conducting these experiments early in the development process can save significant resources and time and allow developers to focus on derisked candidates with a greater likelihood of ultimate success.