Navigating Solid State Chemistry and Accelerating Drug Development

The pharmaceutical research landscape continues to evolve, fueled by exponential scientific progress in chemistry, biotechnology, genetics, and cell biology. Alongside the increasing exploration of complex biologics and cell and gene therapies, small molecule research remains fundamental. Advancements in small molecule chemistry and design are pushing boundaries, with work now focusing on disease mechanism targets that were deemed “undruggable” until recently (1, 2).

Precision medicine, with innovations such as PROTACs (PROteolysis TArgeting Chimeras) and molecular glue targeted protein degraders (3), is revolutionizing drug development. A critical driver of these developments is solid state chemistry, which will continue to be pivotal in optimizing the therapeutic potential of drug candidates, particularly through polymorph, salt, and co-crystal screening (4, 5, 6).

Designing and testing the chemical structure of a new chemical entity (NCE) in high-throughput receptor screens effectively explores its binding capacity. However, as solid-state properties become crucial in later stages, from candidate selection and preclinical testing to clinical formulation and manufacturing, they can ultimately determine the product's success in reaching the market. Synthesis and crystallization processes dictate solid state chemistry, resulting in specific forms like polymorphs, hydrates, solvates, co-crystals, salts, or amorphous solids (7). Solid state chemistry can change because of amorphization or solid-solid conversions triggered by drug product processing stress, including precipitation, granulation, drying, coating, milling, desolvation, roller compaction, and compression (8).

During the critical phase between drug discovery and clinical trials, numerous research activities occur concurrently, progressively enhancing the understanding of solid state chemistry. However, overlooking even a single unfavorable solid state characteristic, whether in early or late-stage development, can lead to substantial setbacks and delays. Issues stemming from a poor understanding of solid state chemistry have plagued many drug development programs, resulting in unnecessary complications, delays and even withdrawals (9). To mitigate such risks, the EMA and FDA mandate the investigation of solid state properties and clinical form selection early in development, along with a comprehensive polymorph screening and mechanistic understanding upon submission (10).

Solid state chemistry and solid form screens are crucial aspects of drug candidate selection, impacting stability, purity, bioavailability, processing, and essential particle characteristics for drug delivery. Rapidly generating knowledge about diverse solid state properties and rationally selecting the optimal solid form is vital for advancing proof-of-concept studies (11). This is particularly true for new drugs under expedited development and review pathways, which represent a significant portion of new drug launches. Identifying and manufacturing specific physical forms with unique performance attributes is not only essential for drug development but also crucial for securing intellectual property (IP) rights, safeguarding against early generic competition, and maximizing market potential.

Challenges in solid state chemistry and polymorph screens
 

Extensive research has clarified solid state properties and processes, enabling the analysis and systematic screening of solid state change risks during drug development (12). However, polymorph screens remain labor-intensive and time-consuming, necessitating specialized and costly analytical procedures. Consequently, as with other resource-intensive processes, industry capacity can quickly become strained when numerous promising drug candidates progress from discovery to clinical phases.

Modern drug development faces an additional growing challenge because of the increasing complexity of new chemical structures. This is exemplified by the rapid emergence of kinase inhibitors in oncology, which are now being explored for immunological diseases, such as rheumatoid arthritis (13). Additionally, the constant demand for novel antiviral compounds to combat drug resistance and emerging viral infections (14) places significant pressure on development timelines, as these compounds often possess intricate chemistry and are driven by urgent clinical needs.

To adhere to stringent timelines, maintaining flexibility through strategic outsourcing of targeted activities, particularly capacity-limited ones like solid state chemistry, is crucial. Solid-state chemistry plays a pivotal role in decision making during three key development phases. Initially, polymorph screens and selection occur between drug discovery and preclinical stages. Subsequently, a comprehensive screen and final polymorph selection take place during phase II, alongside market formulation development. Finally, an extensive screen in phase III consolidates polymorph selection, supporting regulatory filings and ensuring product robustness in the market.

Overcoming the challenges
 

Partnering with outsourcing companies during drug development is one strategy drug developers can take to overcome the challenges in solid state chemistry. However, several important aspects of any partnership or collaboration should be considered when outsourcing solid state chemistry and polymorph screens to accelerate the development program or increase R&D efficiency, including:

• Accessibility. To address urgent, on-demand needs, project timelines should be prioritized over contracting and administrative processes. Streamlined, project-focused collaboration agreements expedite service delivery and ensure efficient execution.
• Capacity. A complete analytical infrastructure, encompassing both personnel and equipment, must be readily accessible and aligned with project requirements and timelines. For instance, a comprehensive solid-state toolbox should include techniques such as high-throughput XRPD, single crystal XRD, DSC, TGA, DVS, ¹H-NMR, LC-MS and solubility studies, including dissolution rate determinations.
• Phase appropriateness. The workflow should be tailored to the specific goals, milestones, and overall objectives of each project phase. An initial enabling screen is advisable before preclinical development to identify potential solid forms. During phase II, a comprehensive screen and selection of the final polymorph are crucial for formulation development. Lastly, an extensive screen in phase III is essential to solidify IP protection and ensure product robustness before launch.
• Efficiency. The workflow should prioritize efficiency, enabling rapid screening with minimal material and short timelines. For instance, an initial polymorph screen to identify a preliminary stable form should be achievable with 2g of compound within a 6-week timeframe, including reporting. For a comprehensive polymorph screen, 3-6g of compound and a 6-8 week timeline are typically required.
• Flexibility. The overall work and workflow must remain adaptable to both project and corporate needs, ensuring timely delivery of milestones and deliverables. The project scope should be flexible enough to integrate new scientific insights as they emerge during the research process.

While outsourcing relies on trust and competence, the pharmaceutical industry's rigid formalities often overshadow these factors in contract awards. The rapid pace of medical and pharmaceutical advancements necessitates a shift in outsourcing strategies towards greater flexibility. Smaller, specialized providers can offer swifter access to specialized expertise and analytical capabilities crucial for complex development work, particularly in areas such as solid state chemistry and solid form screens, where research indicates their efficiency advantage (15).

The accelerating pace of drug discovery and development, fueled by advancements in in vitro and in silico methods, presents new challenges for the pharmaceutical industry. While these methods enable the exploration of novel clinical targets, they also strain resources and often lead to capacity bottlenecks, particularly in the demanding areas of solid state chemistry and polymorph screening.

Implementing streamlined contract systems, short-term resource planning, and efficient allocation can foster collaboration and alleviate these challenges. Additionally, established, adaptable workflows, coupled with transparent communication and a continuous exchange of information, empower developers and enhance the flexibility needed to achieve project goals.