Pharmaceutical Forced Degradation (Stress Testing) Endpoints: A Scientific Rationale and Industry Perspective.

Forced degradation (i.e., stress testing) of small molecule drug substances and products is a critical part of the drug development process, providing insight into the intrinsic stability of a drug that is foundational to the development and validation of stability-indicating analytical methods. There is a lack of clarity in the scientific literature and regulatory guidance as to what constitutes an "appropriate" endpoint to a set of stress experiments. That is, there is no clear agreement regarding how to determine if a sample has been sufficiently stressed. Notably, it is unclear what represents a suitable justification for declaring a drug substance (DS) or drug product (DP) "stable" to a specific forced degradation condition. To address these concerns and to ensure all pharmaceutically-relevant, potential degradation pathways have been suitably evaluated, we introduce a two-endpoint classification designation supported by experimental data. These two endpoints are 1) a % total degradation target outcome (e.g., for "reactive" drugs) or, 2) a specified amount of stress, even in the absence of any degradation (e.g., for "stable" drugs). These recommended endpoints are based on a review of the scientific literature, regulatory guidance, and a forced degradation data set from ten global pharmaceutical companies. The experimental data set, derived from the Campbell et al. (2022) benchmarking study,1 provides justification for the recommendations. Herein we provide a single source reference for small molecule DS and DP forced degradation stress conditions and endpoint best practices to support regulatory submissions (e.g., marketing applications). Application of these forced degradation conditions and endpoints, as part of a well-designed, comprehensive and a sufficiently rigorous study plan that includes both the DS and DP, provides comprehensive coverage of pharmaceutically-relevant degradation and avoids unreasonably extreme stress conditions and drastic endpoint recommendations sometimes found in the literature.

Discovery of a Potent and Orally Bioavailable Zwitterionic Series of Selective Estrogen Receptor Degrader-Antagonists.

Herein, we report the optimization of a meta-substituted series of selective estrogen receptor degrader (SERD) antagonists for the treatment of ER+ breast cancer. Structure-based design together with the use of modeling and NMR to favor the bioactive conformation led to a highly potent series of basic SERDs with promising physicochemical properties. Issues with hERG activity resulted in a strategy of zwitterion formation and ultimately in the identification of 38. This compound was shown to be a highly potent SERD capable of effectively degrading ERα in both MCF-7 and CAMA-1 cell lines. The low lipophilicity and zwitterionic nature led to a SERD with a clean secondary pharmacology profile and no hERG activity. Favorable physicochemical properties resulted in good oral bioavailability in preclinical species and potent in vivo activity in a mouse xenograft model.

Assessing the Relevance of Solution Phase Stress Testing of Solid Dosage Form Drug Products: A Cross-Industry Benchmarking Study.

Stress testing (also known as forced degradation) of pharmaceutical products has long been recognized as a critical part of the drug development process, providing foundational information related to intrinsic stability characteristics and to the development of stability-indicating analytical methods. A benchmarking study was undertaken by nine pharmaceutical companies and the Brazilian Health Regulatory Agency (Agência Nacional de Vigilância Sanitária, or ANVISA) with a goal of understanding the utility of various stress testing conditions for producing pharmaceutically-relevant chemical degradation of drugs. Special consideration was given to determining whether solution phase stress testing of solid drug products produced degradation products that were both unique when compared to other stress conditions and relevant to the formal drug product stability data. The results from studies of 62 solid dosage form drug products were compiled.  A total of 387 degradation products were reported as being observed in stress testing studies, along with 173 degradation products observed in accelerated and/or long-term stability studies for the 62 drug products.  Among these, 25 of the stress testing degradation products were unique to the solution phase stress testing of the drug products; however, none of these unique degradation products were relevant to the formal stability data. The relevant degradation products were sufficiently accounted for by stress testing studies that included only drug substance stressing (in solution and in the solid state) and drug product stressing (in the solid state). Based on these results, it is the opinion of the authors that for solid dosage form drug products, well-designed stress testing studies need not include solution phase stress testing of the drug product in order to be comprehensive.

Experimental design, development and evaluation of extended release subcutaneous thermo-responsive in situ gels for small molecules in drug discovery.

The objective of this work is to develop extended release subcutaneous thermo-responsive in situ gel-forming delivery systems using the following commercially available triblock polymers: poly (lactic-co-glycolic acid)-poly (ethylene glycol)-poly (lactic-co-glycolic acid) (PLGA-PEG-PLGA, copolymer A & B) and poly (lactide-co-caprolactone)-poly (ethylene glycol)-poly (lactide-co-caprolactone) (PLCL-PEG-PLCL, copolymer C). Performance of two optimized formulations containing ketoprofen as a model compound, was assessed by comparing in vitro drug release profiles with in vivo performance following subcutaneous administration in rats. This work employs a Design of Experiment (DoE) approach to explore first, the relationship between copolymer composition, concentration, and gelation temperature (GT), and second, to identify the optimal copolymer composition and drug loading in the thermo-responsive formulation. Furthermore, this work discusses the disconnect observed between in vitro drug release and in vivo pharmacokinetic (PK) profiles. In vitro, both formulations showed extended-release profiles for 5-9 days, while PK parameters and plasma profiles were similar in vivo without extended release observed. In conclusion, a clear disconnection is observed between in vitro ketoprofen drug release and in vivo performance from the two thermogel formulations tested. This finding highlights a remaining challenge for thermogel formulation development, that is, being able to accurately predict in vivo behavior from in vitro results.

Discovery of AZD9833, a Potent and Orally Bioavailable Selective Estrogen Receptor Degrader and Antagonist.

Herein we report the optimization of a series of tricyclic indazoles as selective estrogen receptor degraders (SERD) and antagonists for the treatment of ER+ breast cancer. Structure based design together with systematic investigation of each region of the molecular architecture led to the identification of N-[1-(3-fluoropropyl)azetidin-3-yl]-6-[(6S,8R)-8-methyl-7-(2,2,2-trifluoroethyl)-6,7,8,9-tetrahydro-3H-pyrazolo[4,3-f]isoquinolin-6-yl]pyridin-3-amine (28). This compound was demonstrated to be a highly potent SERD that showed a pharmacological profile comparable to fulvestrant in its ability to degrade ERα in both MCF-7 and CAMA-1 cell lines. A stringent control of lipophilicity ensured that 28 had favorable physicochemical and preclinical pharmacokinetic properties for oral administration. This, combined with demonstration of potent in vivo activity in mouse xenograft models, resulted in progression of this compound, also known as AZD9833, into clinical trials.

Discovery and Optimization of Pyrrolopyrimidine Inhibitors of Interleukin-1 Receptor Associated Kinase 4 (IRAK4) for the Treatment of Mutant MYD88L265P Diffuse Large B-Cell Lymphoma.

Herein we report the optimization of a series of pyrrolopyrimidine inhibitors of interleukin-1 receptor associated kinase 4 (IRAK4) using X-ray crystal structures and structure based design to identify and optimize our scaffold. Compound 28 demonstrated a favorable physicochemical and kinase selectivity profile and was identified as a promising in vivo tool with which to explore the role of IRAK4 inhibition in the treatment of mutant MYD88L265P diffuse large B-cell lymphoma (DLBCL). Compound 28 was shown to be capable of demonstrating inhibition of NF-κB activation and growth of the ABC subtype of DLBCL cell lines in vitro at high concentrations but showed greater effects in combination with a BTK inhibitor at lower concentrations. In vivo, the combination of compound 28 and ibrutinib led to tumor regression in an ABC-DLBCL mouse model.