The preclinical to clinical transition is one of the most critical and high-stakes moments in drug development strategy. It marks the point where laboratory and animal data must convince regulators that a compound is safe enough to test in humans for the first time. Getting this transition right determines whether a program advances efficiently or stalls for months while waiting on additional studies, revised submissions, or regulatory feedback.
What happens at the preclinical to clinical transition?
The preclinical to clinical transition is the regulatory and scientific process through which a drug candidate moves from laboratory and animal studies into first-in-human trials. It requires compiling a complete preclinical data package, submitting an Investigational New Drug application (IND) in the US or a Clinical Trial Application (CTA) in the EU, and receiving regulatory clearance before any human dosing begins.
During this phase, a sponsor must demonstrate that the compound has been adequately characterized, that toxicology studies support the proposed starting dose, and that manufacturing processes are sufficiently controlled to produce a consistent clinical supply. Regulators review these data to assess whether the risk to trial participants is justified by the potential benefit. In practice, this means the transition is not just a filing exercise. It is a scientific and strategic alignment between what the data show and what the regulatory framework requires.
What preclinical data do regulators require before clinical trials?
Before approving a first-in-human study, regulators require preclinical data covering pharmacology, toxicology, and chemistry, manufacturing, and controls (CMC). At minimum, this includes in vitro and in vivo pharmacodynamic studies, single and repeat-dose toxicology studies in at least one rodent and one non-rodent species, genotoxicity assessments, and pharmacokinetic data that support dose selection.
The specific data package depends on the compound type, the intended patient population, and the duration of the proposed clinical trial. For biologics and biotechnology-derived products, additional immunogenicity and species-selection justification studies are typically expected. For oncology programs targeting seriously ill patients, regulators may accept a more limited preclinical package in exchange for a tighter initial dose escalation design. The ICH guidelines, particularly ICH M3(R2), S6, and S9, provide the international framework that most major regulators follow, though regional requirements in the EU and US can differ in important ways.
Why do so many drugs fail at this transition stage?
Many drug candidates fail at the preclinical to clinical transition because the preclinical data package is incomplete, misaligned with regulatory expectations, or does not adequately justify the proposed clinical protocol. Common failure points include insufficient toxicology study design, poor characterization of the drug substance, and a starting dose that regulators consider inadequately justified.
Beyond data gaps, failure often stems from a lack of early regulatory engagement. Sponsors who develop their preclinical programs without consulting regulatory strategy early frequently discover late that key studies were conducted in the wrong species, at the wrong dose levels, or under conditions that do not meet current guideline expectations. This forces costly repeat studies and delays the entire program. Another underappreciated reason for failure is the disconnect between the CMC readiness of the drug and the ambition of the clinical protocol. A compound that is not yet manufactured consistently enough for clinical use cannot advance, regardless of how strong the efficacy data look.
How does regulatory strategy affect the transition timeline?
Regulatory strategy directly shapes how quickly and smoothly a program reaches first-in-human trials. A well-planned strategy aligns preclinical study design with the specific requirements of the target regulatory agency, identifies potential data gaps early, and sequences studies to avoid critical path delays. Without it, programs routinely encounter avoidable hold requests or deficiency letters that add months to the timeline.
One of the most effective tools available to sponsors is the pre-IND or scientific advice meeting with regulators. These interactions, available from the FDA, EMA, and national competent authorities, allow sponsors to confirm their proposed preclinical package before committing to expensive studies. Regulators provide written feedback that can be used to design studies with confidence. Sponsors who use these meetings strategically tend to submit stronger applications and receive fewer questions. In contrast, sponsors who skip early regulatory dialogue often find themselves redesigning studies after the fact, which is far more expensive and time-consuming than getting the design right the first time.
What are the biggest CMC challenges during this transition?
The biggest CMC challenges at the preclinical to clinical transition involve demonstrating that the drug substance and drug product are manufactured with sufficient consistency, quality, and characterization to support human use. Regulators expect a defined manufacturing process, validated analytical methods, and stability data that support the proposed shelf life of clinical trial material.
Drug substance characterization
For small molecules, this means providing a complete structural characterization and controlling impurities to levels justified by toxicology data. For biologics, the challenge is substantially greater because the molecule itself is more complex, more sensitive to manufacturing conditions, and harder to fully characterize. Sponsors frequently underestimate how much analytical development work is needed before regulators will accept a biologics CMC package for clinical use.
Manufacturing process control
Clinical trial material must be produced under conditions that are reproducible and documented in a way that regulators can evaluate. Early-phase programs often rely on contract manufacturing organizations, which introduces the additional complexity of technology transfer and quality oversight. Ensuring the CMC section of an IND or CTA accurately reflects the actual manufacturing process, including any planned changes between preclinical batches and clinical batches, is a common area where applications attract regulatory questions.
When should a company engage a regulatory consultant for this transition?
A company should engage a regulatory consultant as early as the lead candidate selection stage, well before preclinical studies are finalized. The earlier regulatory expertise is integrated into program planning, the more influence it can have on study design, data package strategy, and manufacturing readiness. Waiting until the IND or CTA is nearly ready to submit is one of the most common and costly mistakes in early drug development.
Regulatory consultants add the most value at three specific points: when designing the preclinical program to ensure it meets regulatory expectations, when preparing for pre-IND or scientific advice meetings with regulators, and when drafting and reviewing the submission itself. For startup founders and early-stage companies operating with lean teams, external regulatory expertise fills a critical gap that is difficult and expensive to build in-house at an early stage. It also provides access to experience across multiple programs and regulatory agencies, which is difficult to replicate internally when a company is running its first or second asset through development. To understand the full scope of support available, it is worth reviewing our regulatory services before committing to a development plan.
How Starodub Supports the Preclinical to Clinical Transition
We work with biopharmaceutical companies at every stage of the preclinical to clinical transition, from early regulatory strategy through IND and CTA preparation and submission. Our team brings hands-on experience across small molecules, biologics, and biotechnology-derived products, and we understand the CMC, nonclinical, and clinical requirements that regulators expect at this critical inflection point.
Here is what working with us looks like in practice:
- Regulatory gap analysis: We review your existing preclinical data package and identify gaps before you engage with regulators, so there are no surprises at submission.
- Pre-IND and scientific advice meeting preparation: We prepare briefing documents, formulate the right questions, and help you interpret regulatory feedback to inform study design decisions.
- IND and CTA preparation: We draft, review, and coordinate all sections of your submission, including the CMC, nonclinical, and clinical sections, ensuring consistency and regulatory alignment throughout.
- CMC regulatory support: We provide expert guidance on drug substance and drug product characterization, analytical method requirements, and stability data expectations for clinical trial material.
- Regulatory strategy development: We build a transition roadmap that sequences your preclinical activities efficiently and positions your program for a clean, timely submission.
With over 400 completed projects and more than 300 clients supported, we have the depth of experience to guide your program through this transition efficiently. If you are approaching the preclinical to clinical stage and want to make sure your regulatory strategy is sound, contact us today to discuss how we can support your program.
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This content was generated with the help of AI and it may contain mistakes
