Purpose
To provide guidance primarily for the academic researcher for the translation from research of novel ophthalmic drugs for improved patient treatment to early-stage development including clinical trials.
Methods
Based upon available guidelines and the authors’ extensive experience in developing novel products, the authors present the requirements for chemistry (both drug substance and formulated drug product), nonclinical (pharmacology, pharmacokinetics, and toxicology), clinical and regulatory development.
Conclusion
Development of successful novel ophthalmic products is a structured, sequential, and interactive scientific process.
B iomedical researchers want their research to be impactful in improving human health. This often means translating their basic research into a potential therapy for humans. Like basic research, this translation—product development—is a scientific process of testable hypotheses, experiments, modification of the hypotheses, and more experiments. However, compared to basic research, drug product development is typically longer, more costly, involves different skill sets, and requires compliance with regulations for treating humans. In this article, a “road map” is provided for the development of ophthalmic drug products that is directed primarily at the academic researcher for early-stage development. For regulatory requirements, guidance and guidelines by the U.S. Food and Drug Administration (FDA) and the International Council on Harmonisation (ICH) were selected as they are publicly available and a worldwide standard. However, there may be additional local or regional regulations that need to be considered for drug product development, for example, Europe, Japan, Australia, etc.
Development of ophthalmic products is similar to development of products for other therapeutics areas. However, consistent with the unique nature of ophthalmology, there are aspects to product development. Advantages include an implied benefit/risk by limiting exposure to the blood and, therefore, first-pass hepatic metabolism, relatively small amounts of drug required; and the ability to directly and noninvasively examine neural tissue (retina). Relative disadvantages of local ophthalmic products are the limited ability to measure drug at the target site (pharmacokinetics). This tends to limit data-driven selection of dose and dosing frequency for patient evaluation. Another undesirable consequence of limited pharmacokinetic data is the lack of pharmacokinetic/pharmacodynamic interactions (how much drug is required for how much efficacy). Much of the genetic variability in drug response is due to metabolism—which again is not often assessed with most ophthalmic products.
“Translational research” is a term frequently used but with a wide range of definitions. The explicit point at which translation from research to development happens is when the pharmaceutical firm (Sponsor/Applicant) applies to a regulatory agency to conduct human clinical trials with the investigational product. In the U.S., this is the Investigational New Drug (IND) application. This is a relatively unique regulatory application in that it is a notice to the FDA that the Sponsor will ship investigational drug product across a state line in 30 days for clinical investigation unless the FDA stops the transfer by objecting to the data contained in the IND (21 CFR 312). For the IND the application must include data to demonstrate that: (1) the drug product is well characterized, stable, and in the case of most ophthalmic products, sterile, (2) there is adequate nonclinical pharmacology, pharmacokinetics, and toxicology studies as to the safety of the drug product, and (3) the clinical study is well designed and the clinical investigator has appropriate training and experience to conduct the study. More simply stated, these are chemistry, nonclinical, and clinical areas.
Drug development is a “high-risk, high-reward” endeavor. In an effort to maximize the reward, firms aim to have the product sold worldwide. In the previous century, different countries had different requirements, which added time, costs, and uncertainty. Starting in 1990, in an effort to standardize these requirements to optimize drug development, an international group of pharmaceutical firms and regulators created the ICH. As a result, there are now over a score of guidance documents and guidelines for development ( www.ich.org ). Among these guidance are scientific and documentation standards—“GxP”—good practices for manufacturing (GMP), laboratory nonclinical studies (GLP), and clinical studies (GCP).
With that overview, a theoretical “road map” for ophthalmic product development is shown in Figure 1 and Table . As noted in the description of an IND, the three areas are chemistry, nonclinical, and clinical. Early-stage development activities are concerned primarily with the quality of the chemistry, and safety—including “off-target” (unintended) effects. This may seem counterintuitive to the basic science researcher who is focused on mechanisms and efficacy, that is, on-target biology.
| Activity |
|---|
| Chemistry (Module 3) |
| Drug substance (active pharmaceutical ingredient) |
| Manufacture |
| Control |
| Stability |
| Drug product |
| Manufacture |
| Control |
| Stability |
| Nonclinical (Module 2) |
| Pharmacology |
| Primary pharmacodynamics |
| Secondary pharmacodynamics |
| Pharmacokinetics |
| Bioanalytical methods |
| Absorption |
| Distribution |
| Metabolism |
| Excretion |
| Toxicology |
| Single dose |
| Multiple dose |
| Genotoxicity |
| Carcinogenicity |
| Reproductive and developmental toxicity |
| Local Tolerance |
| Clinical (Module 5) |
| Biopharmaceutic studies |
| Bioanalytical methods |
| Plasma protein binding |
| Pharmacokinetic studies |
| Human pharmacodynamic studies |
| Efficacy and safety studies |
| Controlled studies |
| Uncontrolled studies |
| Other (eg, literature) |
With respect to chemistry, the first step is to translate the basic research into selection of the lead drug molecule—the “Drug Substance” or “Active Pharmaceutical Ingredient” (API) that would be taken further into development. This is typically an iterative process whereby the researcher evaluates various molecules—either existing approved molecules or those synthesized de novo (new chemical entity). If the selected molecule is a new chemical entity, then a chemistry manufacturing vendor(s) must be identified that can synthesize the substance in sufficient quantities to a high standard, eventually to GMP standards, for use in clinical trials and manufacturing for commercialization. The synthetized molecule is subjected to analytical tests for purity, as well as stability over time in a range of physical conditions. With availability of the API, then the drug product formulation for clinical delivery must be developed. For ophthalmic products, this is a challenging early-stage task. Nearly all local ophthalmic products are given as liquids. There is a truism in drug development that the most active molecules are those with low water solubility. The researcher may have used extemporaneous formulations in the lab, for example, phosphate-buffered saline or dimethyl sulfoxide. However, although the latter is not a preferred pharmaceutically acceptable excipient (inactive), it is used in some drug product formulations for other routes of administration, and in early drug development assays (in vitro). Note that there is a list of these in the FDA’s “Inactive Ingredient Database.” However, this list has errors in both inclusion and exclusion. A better option is to review approved ophthalmic drugs whether a drug that is administered topically or by ocular injection. Unfortunately, the concentration of these excipients is confidential. This is another situation where working with experienced vendors, in this case, ophthalmic formulators is key. Another key decision that is best made early is the use of a preservative such as benzalkonium chloride, as preservatives may affect ocular bioavailability.
Both the API and the Drug Product must adhere to a Specification. Specifications are a list of test methods and acceptance criteria. Each batch will be tested against this specification. For ophthalmic products, guidance on specifications is provided by the United States Pharmacopeia (USP) in General Chapter <771> Ophthalmic Products—Quality Tests. Additional quality tests outside of this General Chapter may be required based on the type of formulation. For instance, a sterile aqueous solution would require the testing described in USP <771> but would also require sterility testing and subvisible particulate testing. Specifications must be included in the IND. However, throughout development, it is expected that the specifications be further refined, such as acceptance criteria tightened and additional characterization or specialty tests added as they are developed. It is typical, for instance, that a cell and gene therapy product may not have an exact Potency test in early-stages of development; however, this test must be in place prior to filing the Biological License Application.
There is an FDA regulation that requires some method for protection from contamination of these sterile products (21 CFR 200.50) whether the drug is administered as single-use as for intravitreal products or for most products for ocular surface diseases. Preserved multidose container/closure systems or specialized nonpreserved multidose products add another level of complexity in the development of a drug product formulation. In general, ophthalmic formulations should be near neutral pH and isotonic. However, some products (eg, artificial tears) may be hypotonic by design. For other products, pH may be adjusted for stability purposes. Typically, an acceptable pH range is 4.5 to 7.4. The formulation must be stable either as a frozen/lyophilized formulation, a refrigerated formulation, or at room temperature. Stability must be assured through testing at routine intervals, ideally as prescribed by ICH, but some flexibility is allowable at early-stages of development. Ideally, the drug product is stable at room temperatures. Products that require refrigeration or freezing make the distribution process more complicated and costly.
Once formulated, the ocular tolerability of the highest possible concentration of the drug product should be assessed in preclinical animal models. Typically, single and repeated ocular dosing in a New Zealand White (albino) or a Dutch-belted (pigmented) rabbit are used although other nonrodent species are often used, for example, monkey, dog, and minipig.
If this formulation is not tolerated at the maximum concentration, then lower concentrations would be evaluated until a concentration is found which is tolerated. Before proceeding too far with the animal study, a “paper” calculation should be undertaken to determine if this maximal tolerated formulation concentration is sufficient to achieve the desired pharmacological effect. It is best exemplified for an intravitreal treatment. Using 50 μL as the maximum volume for a dose, multiplying by the maximum tolerated concentration divided by the approximate volume of the human vitreous cavity. The concentration is then compared to the potency of the molecule from in vitro pharmacology studies. A conservative estimate is that one needs 5 times the IC 50 or K d at the time of maximum concentration in order to have a chance for a therapeutic effect. A further consideration is the duration of the exposure (to be covered below in pharmacokinetics). If it does not appear that delivery of the maximum volume of the maximum tolerated dose will achieve a potential therapeutic effect, then it is unlikely that this molecule will be effective, and an alternative molecule should probably be selected. This also exemplifies a basic premise in drug development, that is, if a drug is to fail for clinical development, it should fail early before the expenditure of resources.
At this point, there are several concurrent development activities being conducted in parallel. In chemistry, there is ongoing stability of both drug substance and drug product. In nonclinical pharmacology, one might repeat the primary pharmacology, for example, animal model of disease, with the properly formulated drug product. Secondary pharmacology studies with in vitro receptor binding assays are more frequently being conducted for the IND to evaluate for the potential of off-target effects. In clinical, the conceptual ideas of the inventor as to how the molecule might treat disease need to be refined into testable hypotheses. An in-depth understanding of the disease is required. As to clinical study design, this is typically both a “top-down” approach—that is, what aspects of the disease process (signs and/or symptoms) in which patients might be ameliorated by this treatment—and a “bottom-up” approach—that is, who are the first human subjects to whom one administers the drug.
Once the drug product formulation is developed, nonclinical studies are initiated. A majority of the nonclinical studies need to conducted in compliance with GLP regulations, primarily those considered to be pivotal studies (IND-enabling). Pivotal nonclinical studies are those that the Sponsor and regulatory authorities would use for decisions of safety in order for a Sponsor to enter into clinical trials. Prior to initiating the pivotal nonclinical (toxicology) studies, range-finding studies may be necessary for dose selection for the pivotal studies. The range-finding studies are most often not conducted in compliance with GLP regulations.
Prior to initiating any pivotal toxicology study, bioanalytical assays for the drug in blood (serum/plasma) would be necessary. These assays do not specifically require to be conducted by GLP regulations. However, the sample analysis from the pivotal studies do need to be conducted in compliance with GLP regulations. Hence, it is best to validate the bioanalytical method per GLP regulations.
Dose formulation analysis, also to be conducted in compliance with GLP regulations are not often done for ocular toxicology programs as the toxicologist relies on the Sponsor to provide data demonstrating stability, concentration, and homogeneity of the formulations, and that characterization needs conducted in compliance with GLP or GMP regulations. Furthermore, Sponsors often provide dosing formulations that are ready to use.
A guiding principle for undertaking nonclinical (toxicology) studies is a knowledge of the duration of the planned clinical study, the frequency of administration (regimen) and the anticipated dose to be used. The latter principle was discussed above. The duration of a clinical trial and the regimen of administration will guide the duration and regimen of the toxicology study. The duration of the toxicology must mirror or exceed the duration of the clinical study. Also, the doses to be used in the toxicology study should provide a sufficient margin of safety (MOS) compared to the clinical dose.
The toxicology studies would be conducted in two species, a rodent and nonrodent species. Although useful for early development and understanding the pharmacology of the drug molecule, rodents are not considered a viable animal model for evaluation of ocular toxicity for entry into a clinical study. Most often, two nonrodent species are used for the toxicology studies. Those species used are the rabbit, dog, minipig and monkey. The species selected should be a pharmacologically-relevant species, that is, the ocular target of the drug would result in a similar outcome in humans and the animal model. It is plausible to justify the use of a single nonrodent species but requires a robust scientific justification for the regulatory authority to agree. The following discussion assumes that two nonrodent species are to be used in the pivotal (GLP, IND-enabling) toxicology studies.
As noted above, the duration of the initial toxicology study will be a duration that mirrors or exceeds the duration of the clinical study. This initial study is often 28 days in duration with daily administration (topical indication) or at least weekly injection (intravitreal indication). There are variations on the regimen from multiple daily topical administration to monthly injection and the regimen is dependent on the pharmacokinetic profile of the drug including ocular tissue distribution, the pharmacological activity of the drug, and the disease indication. In addition, the parameters for evaluation of toxicity are many even beyond the typical standard toxicological endpoints. Short has reviewed some of the more critical endpoints to be included in an ocular toxicity study. Also noted is the article by Pruimboom-Brees et al specifically focusing on the development of intravitreal drugs.
Ocular tissue distribution studies are becoming more commonplace during Phase 1 clinical studies or before. These studies assist Sponsors in demonstrating that the drug distributes to the target tissue, for example, retina. Metabolism studies, either in vitro or in vivo, may start at this time, cognizant of the limited cytochrome P450 levels in the eye. It is recognized, however, that the activity of CYP450 and other metabolic enzymes in the eye have not been well studied.
In toxicology, in vitro genotoxicity studies may be conducted to assure that the molecule is not mutagenic or clastogenic. In vivo genotoxicity studies are usually done during Phase 1 clinical studies and completed prior to Phase 2. A “positive” in the in vitro studies, that is, the API is mutagenic or clastogenic, would lead to additional studies as outlined in recent FDA guidance. If the drug substance is “positive” in the mutagenicity study, this molecule tends to be eliminated from further consideration for an ocular indication, however.
With ocular administration, systemic exposure tends to be limited. Thus, systemic toxicology studies should be undertaken prior to the initial clinical study to provide possible guidance to clinicians on potential adverse effects that may be seen in the clinic. A key step in determining the type and number of systemic toxicology studies required is the systemic exposure to the parent molecule and metabolites after maximal ocular dosing. The initial systemic toxicity studies would utilize a route of administration that ensures systemic exposure and may include intravenous, oral, etc. As the duration of the nonclinical safety studies at various stages of clinical development must support the intended clinical dosing duration, it is important at this point for the clinical development scientists to be in communication with the nonclinical development scientists to plan the correct nonclinical safety studies. At a minimum, however, an initial systemic toxicity study would be 28 days in duration (GLP compliant), and these studies can utilize a rodent species, most often the rat. Also, a systemic route of administration is necessary to undertake safety pharmacology studies as outlined in ICH S7A and S7B. These studies consist of evaluation of the effects in the central nervous system, respiratory system, and cardiovascular system, organ systems that are considered core to safety pharmacology. The design and execution of these safety pharmacology studies are beyond the scope of this manuscript although numerous studies have been published regarding the conduct of the studies. The reader should review the ICH guideline and the cited references for those details.
Once all of the studies have been completed and reported, the sponsor would accumulate all of the nonclinical reports in preparation for submission to the regulatory authority. It is recommended that the pivotal toxicology studies not be conducted until there is an agreement with the authority on the design and scope of the studies as described below.
At this point, firms typically will want FDA feedback on the intended development plan. This is called a “Pre-IND meeting”, which is technically a “Type B” meeting. The lead time for this meeting is typically 3 months after request, and a briefing document (∼100 pages) due 30 days before the meeting. It is strongly recommended that the meeting not be requested until that briefing document is substantially complete.
At this meeting, the Sponsor presents their development plan to the FDA. As much of the work (eg, GLP toxicology studies) may not yet be complete, FDA’s response is of a subjunctive nature (the firm says “we are planning 3-month ocular toxicology studies in two species to support clinical dosing of 3-months duration,” and FDA answers “assuming there is no safety risk to subjects (toxicity), you should be able to proceed”). At a minimum, the firm should understand what FDA will expect in chemistry and nonclinical safety to conduct the initial (IND opening) clinical study. Optionally, the firm may also propose the late-phase planning required for a New Drug Application—in particular the primary efficacy measure and the duration and number of subjects required for safety evaluation.
The firm considers the FDA recommendation and modifies the development plan accordingly. Assuming the firm has the funding, it then proceeds to execute the chemistry and nonclinical safety studies. From a chemistry perspective, the work includes manufacturing increasingly higher quality lots of drug substance and drug product to GMP quality for use in clinical studies under the IND. From a nonclinical perspective, this includes drug product (GMP-like) quality ocular and systemic safety studies, as well as other possible genotoxicity studies and safety pharmacology studies for the evaluation of “off-target” respiratory, cardiovascular, and central nervous system. From a clinical perspective, a GCP quality clinical protocol is required for the IND opening study, as well as identification and qualification of clinical study sites. Small firms without an experience clinical operations group will need to select a Contract Research Organization in order to conduct the study consistent with GCP.
In the 1990s, the FDA, European Medicines Agency, and Ministry of Health, Labor and Welfare in Japan also developed the Common Technical Document (CTD). The CTD, now prepared in an electronic form (eCTD), standardizes the numbering of information to aid the Sponsor and regulatory reviewers. Shown in Figure 2 is the “eCTD pyramid.” The base of the pyramid is chemistry for the API and the drug product (Module 3), nonclinical studies (Module 4), and clinical studies (Module 5). Sitting on top of this base are summaries for each of these area (Module 2). Modules 2 through 5 are similar for all countries. Module 1 is specific for each country depending upon forms and regulatory requirements. Sponsors and regulators come to know the jargon for these module numbers well. For example, stability data on the drug product is located in Module 3.2.P.8.3, and published references to support nonclinical studies is located in Module 4.3. We make the analogy of a review article for a journal on a topic. The author first searches the literature, then writes the review. For the nonclinical section of the IND, the articles would be placed in Module 4, whereas the review itself would go into Modules 2.4 and/or 2.6.
