The chemopreventive agent development process is a science in its infancy.
Developers of chemopreventive agents face the same regulatory hurdles as do therapeutic drug developers. As in all drug development, chemoprevention scientists must demonstrate both safety and efficacy for an agent to be ap- proved for marketing to the public. Historically, this has meant that developers must demonstrate reduced cancer incidence or mortality in order to show ef- fectiveness. Needless to say, this would be a lengthy process given the 20 to 30-year trajectory of carcinogenesis. This requirement has been modified in re- cent years. The notion of targeted prevention of cancer is now based on the discovery of surrogate endpoint biomarkers, signal transduction pathways, and the ability to promote or inhibit specific molecules in those pathways with new molecular entities (NME) or drugs (O'Shaughnessy, Kelloff et al. 2002).
In the United States and internationally, the development and manufacture of drug products is regulated by government entities in order to protect general populations as well as research participants. In the United States (U.S.), the Food and Drug Ad- ministration (FDA) has this regulatory responsibility, while in Europe and Japan, the responsibility falls to individual governments using standards established and main- tained by the International Conference of Harmonization (ICH). The regulatory agen- cies and the developers of drugs must balance the benefit of new drugs to the popula- tion as a whole against the risk to individuals participating in clinical trials and even- tually to the general public. In the development of chemopreventive agents, the risk must be very low and the benefit very high, as, in order to be effective, large at-risk populations would need to use the drug, possibly for life, in order for a drug to be ef- fective in preventing cancer (Anonymous 1999).
The process of developing chemopreventive agents consists of several systematic steps. First, NMEs are chosen based on basic science findings. Promising agents then undergo preclinical testing in animal models. Before human testing can begin, the science must be reviewed by the FDA or other regulatory agency. After the completion of clinical trials and prior to marketing, findings must be evaluated and communi- cated to the scientific community. This chapter outlines the process of developing che- mopreventive agents and the standards that guide such development.
Naja E. McKenzie
College of Medicine, University of Arizona, Tucson AZ 85724
Selecting New Molecular Entities for Development as Chemopreventive Agents
New molecular entities are the focus of scientific study in cancer therapeutics as well as cancer prevention programs across the world. However, the selection of new molec- ular entities (NMEs) for development is not a random or serendipitous process.
Rather, specific important criteria apply to the selection of NMEs for clinical develop- ment as potential chemopreventive agents. The major criteria include evidence of ac- tivity in preventing cancer at the target site, low toxicity to allow for potential use in large populations, the identification of the biomarkers associated with the effectiveness of the NME, and the availability of a pertinent population for clinical testing. The fo- cus of these criteria is the real feasibility of giving a drug prophylactically to large populations at risk for a particular type of cancer (Kelloff, Hawk et al. 1996).
There are significant precedents for the notion of developing drugs that lessen the risk for a disease or the recurrence of disease and that can be given on a large scale.
An example of such a precedent is the development and FDA approved marketing of lipid lowering drugs that aim to reduce the risk of cardiovascular disease. The process included research on cholesterol lowering and modulation of other markers. Lowering of cholesterol emerged as a definitive risk reduction marker and development of cho- lesterol lowering drugs followed. In the case of cancer chemopreventive agents, early associated biomarkers discovered by basic scientist must also form the basis for devel- opment. Examples of such markers are proliferation antigens [e.g., proliferating cell nuclear antigen (PCNA)], inhibition of growth factors [e.g., epidermal growth factor receptor (EGFR)] and apoptosis.
Discovery of related biomarkers is followed by research to demonstrate activity against proliferation of pre-cancer or intraepithelial neoplasias (IEN). Demonstration of activity is performed in vitro in cell lines and later in vivo in animal models. Satis- factory activity in both models can then be evaluated as justification for proceeding to clinical trials. In addition to peer review by other scientists, the FDA performs the function of approving clinical trials in humans using NMEs. The criteria used by the FDA to evaluate proposed drugs for development and marketing are safety and effec- tiveness viewed in a risk-benefit balancing framework.
An important requirement for chemoprevention agents is that while they must be highly effective, they must also be safe enough to be given to large populations at risk for a particular cancer. This is a marked departure from the usual thinking about therapeutic cancer drugs where the toxicity, unless major, is an expected fact that is mitigated by the effectiveness of the drug in treating the cancer. Therapeutic clinical trials, therefore, tend to seek the highest effective dose for which the toxicity can be justified by its effectiveness, while chemoprevention studies seek to find the highest safe dose that is also effective.
An important consideration for selecting a NME for development as a chemopre- ventive agent is the availability of the agent in quantities needed for all phases of test- ing. A supply can be assured by either synthesizing the drug, provided no patent rights are contravened, or acquired in bulk from the manufacturer or wholesaler of known compounds. Synthesis can be a computer assisted process in which a com- pound is simulated using enzymes that attach to the disease related target site on the cell membrane. Synthesis of a drug for research also requires attention to documenta-
tion of good laboratory practice (GLP). While formal GLP is not required for synthe- sis of drugs intended for laboratory use only, it becomes a consideration when apply- ing for FDA approval for testing in humans.
Acquisition can be a more efficient way of getting a supply of a new drug substance for testing. Many known compounds are available from chemical suppliers and even proprietary drugs may be available in sample quantities or by agreement from the manufacturers. Academic institutions can be highly effective and less costly than com- mercial laboratories in basic and preclinical science portions of drug development.
Such arrangements are usually managed by Materials Transfer Agreements (MTA).
The FDA may require that a compound that is to be used in clinical trials be manu- factured under current Good Manufacturing Practice (GMP). It may therefore be nec- essary for clinical researchers to limit drug development to the pre-clinical stage un- less a GMP supply of the study compound can be found.
Some promising chemopreventive compounds may have been tested in countries where laws are less restrictive. Drugs thus studied may be of interest to drug develop- ment researchers in FDA or ICH regulated countries and may enter their list of poten- tial drugs as a result of preclinical activity or safety and effectiveness in humans.
However, any human testing must be repeated under US regulatory requirements. Un- der new guidance for botanicals, clinical data obtained in non-US safety trials can be used to support later and larger trials provided the botanical used is the same. How- ever, the developer must be able to show bioequivalence. Likewise, agents may have been tested for other purposes and based on other activity and have subsequently yielded serendipitous findings. Repeating studies designed to explore those findings can lead to discovery of safety and effectiveness for those new indications. In all cases, scientifically sound animal testing must precede testing in humans in order to get a preliminary idea of what may be expected in regard to safety and effectiveness in hu- mans and to get information to guide dose setting in clinical trials. In summary, agents selected for clinical trials are those which have shown the most activity in pre- clinical testing and at the same time have shown the least toxicity at doses that can be tolerated by large elements of the population.
Regulatory Requirements and the US Food and Drug Administration
Details of the legislative basis of the drug development regulatory authority of the US Food and Drug Administration (FDA) and the requirements of the regulatory process are the basis for an understanding of the Investigational New Drug application (IND) and the accepted phases of clinical trials research. Good Clinical Practice considerations are essential for drug trials in human and the requirements for the protection of human subjects in clinical trials. Specifics of the regulatory requirements outlined here can be found in the current Code of Federal Regulations, Title 21, Parts 50, 54, 56, and 312.
The FDA, an agency within the Department of Health and Human Services (DHHS), is authorized to regulate drug development by a series of federal laws. These laws, enacted over the past 150 years, are authorized under the Interstate Commerce Clause of the US Constitution. The first law enacted, the Drug Importation Act of 1848, was written in response to the perception that excessive mortality during the Mexican War was caused by harmful drugs entering the country and that such sub- stances had to be regulated or prohibited. Virtually every subsequent law was passed
in response to an actual or perceived problem. The Biologics Control Act was passed in reaction to a diphtheria vaccine developed from horses with tetanus that caused the death of many children, especially in St. Louis. This Act was designed to ensure purity and safety of serums and vaccines and included annual licensing requirements and in- spections of manufacturing facilities (FDA 1999).
In 1906, the Pure Food and Drugs Act was passed as the foundation of modern food and drug law. It was, in large part, the creation of Harvey Washington Wiley, the chief chemist of the Bureau of Chemistry. The Act prohibited interstate commerce of mislabeled and adulterated drugs and food. The basic authorizing act of the FDA came in 1938 in the Federal Food, Drug and Cosmetic Act. Again, it was a reaction to an elixir of sulfonamide marketed by S.C. Massengill which used a solvent similar to antifreeze and caused the death of 107 people. It required new drugs, devices and cos- metics to be shown to be safe before they were brought to market. This Act required the filing of a New Drug Application (NDA) and adequate directions for safe use. Vari- ous refinements followed.
The next reactive legislation came about due to the thalidomide tragedy. Senator Estes Kefauver was holding hearings pertaining to the manufacturing of antibiotics and other development practices. An NDA was submitted for Kevadon, the brand of thalidomide that the William Merrell Company hoped to market in the U.S. Despite ongoing pressure from the firm, the FDA's medical officer, Dr. Frances Kelsey, refused to allow the NDA to become effective because of insufficient safety data. By 1962, tha- lidomide's horrifying effects on newborns became known. Even though Kevadon was never approved for marketing, Merrell had distributed over two million tablets for in- vestigational use, use which the contemporary law and regulations left mostly un- checked. Once thalidomide's deleterious effects became known, namely major birth defects, the agency moved quickly to recover the supply from physicians, pharmacists, and patients. Henceforth, drug developers are required to provide sufficient preclinical data that a drug is safe to give to humans before commencing clinical trials. For her efforts, Dr. Kelsey received the President's Distinguished Federal Civilian Service Award in 1962, the highest civilian honor available to government employees.
Current regulations are contained in a series of laws including the FDA Moderniza- tion Act of 1997, renewed in 2002. Today, the FDA is responsible for the review of new products, keeping watch over the safety of the drug supply, developing standards and regulations, and correcting or preventing problems through regulatory compliance programs. Drug regulatory efforts are handled by the Center for Drug Evaluation and Research (CDER). The main areas of focus are safety, effectiveness and availability (FDA 1999).
The Investigational NewDrug Application
An Investigational New Drug Application is required by anyone planning to test a new molecular entity in humans. An IND actually allows a developer to proceed by permit- ting the shipment of drug for the purpose of conducting clinical trials. The provisions of the Code of Federal Regulations (CFR) that pertain to INDs are found in Title 21 Section 312 [21 CFR Part 312 (1999)]. An IND is not needed to study a legally mar- keted drug, unless the studies will deal with new indications, new delivery methods or new labeling claims. This section is a global review of this process and is not in-
tended to provide comprehensive information for drug developers to file an IND. For more specific details, please consult the CFR.
The FDA's primary IND review objective is to protect human subjects involved in initial clinical trials. In later phases of investigation, the FDA also reviews IND sub- missions for scientific rigor to permit assurance of effectiveness. In addition to infor- mation about the applicant's identity and qualifications, the IND must contain the fol- lowing information:
A general investigational plan An investigator's brochure
Protocol for planned studies (Nestle, Alijagic et al.) Chemistry, manufacturing and control information Pharmacology and toxicology information Summary of previous human experience.
In a general investigational plan a developer provides background information on the drug to be tested and the rationale for testing it in the manner and for the duration proposed. The developer also indicates the number of research participants to be en- rolled over the course of the development of the drug. Most importantly, the developer summarizes the likelihood and severity of risks anticipated in humans based on the results of testing in animals.
The investigators brochure (IB) is a set of documentation that provides detailed infor- mation to investigators who will be performing the clinical trials. The IB includes infor- mation on the drug substance and how it is formulated. It summarizes pharmacological and toxicological effects and pharmacokinetics of the drug as tested in animals and dis- closes any such findings available in humans and concludes with a discussion of antici- pated risks, special precautions and monitoring needed in the clinical trial.
Protocols must contain the objectives of each proposed study with specific attention to the indications studied and desired endpoints. Protocols must be specific in detail- ing the number and characteristics of study participants to be recruited and those to be excluded for safety reasons. The design of the study must be described in detail and must be appropriate to the type of trial envisioned. In particular, details pertain- ing to randomization, blinding and control are specified in the protocol. Finally, the protocol must describe what the actual data will look like and how they will be ana- lyzed and reported. The data collected must include specific measurements pertaining to the safety of study participants, so that adverse events related to the administration of the drug can be reported and evaluated.
Chemistry, manufacturing and control (CMC) information includes relatively com- plex information about the composition, manufacture and quality control of the drug substance (raw drug) and drug product (drug as formulated for use in humans). Iden- tity, quality, purity and strength of the drug must be supplied to the FDA as well as the methods for validating each parameter. The FDA must be assured by the manufac- turer that these parameters will remain stable over time and can be maintained from one batch to the next. As the scope of investigations increases, the FDA requires that new information pertaining to CMC be submitted in detail.
Pharmacology and toxicology information is very important in the IND as this is the basis for concluding that the drug can be reasonably assumed to be safe to study in humans. Pharmacology information includes the effects and mechanism (Nestle,
Alijagic et al.) of action of the drug in animals. To the extent known, the absorption, distribution, metabolism and excretion of the drug are included in this section. Toxi- cology information consists of an integrated summary of toxicological testing in ani- mals. Specifically, results of acute, sub-acute and chronic toxicity testing in animals are reported as are reproductive or developmental effects of the drug. Full tabulations of data, not summaries, must be provided to the FDA.
If previous human studies have been performed with the drug, for example, by an- other route or for different indications, such data are to be summarized in the IND as should any human trials experience from other countries. Any published papers can be included in the submission. Certainly, if the drug to be studied is marketed or has previously been marketed in another country, experience from that population should also be included in the application. Finally, for drugs that are believed to have abuse potential, are radioactive or are to be studied in a pediatric population, submission of additional information illuminating those characteristics, as applicable, is required.
Phases of Clinical Research
The Phases of Investigation are a set of conventions the FDA requires developers to use when planning and reporting clinical trials. There are four phases of investigation, of which the first three are most commonly used. Phase I represents the first use of a given drug in humans. This kind of study is usually performed in a small sample, in the range of 20 to 80, and with normal volunteers, but it can also be done with patients. In this phase of study, the drug is tested in humans to establish a measure of safety and to pro- vide enough information about metabolism and the pharmacokinetics of the drug to de- sign a well-controlled, scientifically valid Phase II study. Phase I studies are typically closely monitored, especially if no previous experience in humans exists.
Phase II studies include studies to evaluate effectiveness for a particular indication in patients with the disease as well as continuing the evaluation of safety. Phase IIa studies are usually small and fairly short in duration, typically three months, and are designed to evaluate dose-response on both pharmacological and intermediate endpoints. Phase II b studies are randomized, placebo-controlled, double-blinded trials in a larger group of patients, perhaps 75 to 100. In this phase, participants usually receive the same dose, possibly with dose-reduction provided for in the event of adverse study related effects.
The investigational treatment may also be compared to standard treatment in this phase.
Endpoints of Phase II trials in chemoprevention studies would include the biomarkers and pathways found to be affected in pre-clinical and animal studies.
Phase II studies are larger trials of more than 100 participants. This phase of study is specifically aimed at determining whether the new drug is more effective and/or safer than the standard treatment. Frequently, Phase III trials are conducted in multiple set- tings and locations across the country in order to supply evidence for effectiveness in a more heterogeneous population. Generally, participants are randomized to an investi- gational group, which receives the test agent, or a control group, which receives the stan- dard treatment. Phase III trials data are the centerpiece of the New Drug Application (NDA) submitted to the FDA to obtain permission to market the new drug.
Phase IV studies are undertaken after approval of the NDA and marketing of the drug.
These studies, which are not as common as Phase I through III trials, can be requested by the FDA as non-essential to the approval of the drug, but useful in providing additional
information that could, for example, change the prescribing information or labeling of a drug. If requested, manufacturers commit to do such studies at the time of the approval of the NDA. The design of Phase IV studies depends on the research question. They gen- erally resemble Phase III studies but participants come from a more defined population in order to support specific use of the drug. Phase IV studies can also be undertaken voluntarily by manufacturers to extend the marketing potential of the drug.
Good Clinical Practice
The term Good Clinical Practice (GCP) refers to a standard for the design, conduct, performance, monitoring, auditing, recording, analyses, and reporting of clinical trials that provides assurance that the data and reported results are credible and accurate, and that the rights, integrity and confidentiality of trial subjects are protected (ICH 1994). Developed by the International Conference on Harmonisation (ICH), GCP guidelines follow a set of fundamental principles for the ethical conduct clinical trials involving human subjects. These principles were formulated in the World Medical As- sociation's Declaration of Helsinki in 1964 and revised in 1989 (WMA 1989). The principles cover the manner of conducting clinical trials as follows:
Clinical trials should be conducted according to ethical principles based on the De- claration of Helsinki.
Risks should be weighed against potential benefits prior to starting a trial.
The rights, safety and well-being of study participants are primary considerations.
All available clinical and non-clinical information should be presented for evalua- tion of a proposed trial.
Trials should be scientifically sound and clearly described in a detailed protocol.
Protocol should be approved by an ethics board and should be followed exactly as approved.
Any medical care given to study participants should be performed by or under the direct authority of a qualified physician.
Individuals involved in conduction clinical trials should be qualified by education, training and experience to perform their study tasks.
Freely given informed consent should be obtained from every study participant.
All trial information should be documented and stored in a way that assures accu- rate reporting, interpretation and verification.
Investigational products should be manufactured, handled and stored according to approved standards.
Quality assurance systems must be in place to assure quality of data.
Adherence to the principles of GCP is the responsibility of the sponsor, the principal in- vestigator, and all study staff. Compliance is monitored by the FDA's Bioresearch mon- itoring department (BIMO). In the U.S., penalties for non-compliance can range from voluntary correction of deficiencies to fines and imprisonment in cases of deliberate fraud.
The NewDrug Application
The New Drug Application (NDA) is submitted when all phases of investigation have been concluded. The NDA requires all the documentation necessary to present a com-
plete picture of how the drug is made, formulated and checked for quality, how the drug performed in clinical testing, how the drug was tested in animals, and what hap- pens to the drug in the body. The NDA also must include the proposed labeling so the FDA can ascertain that the claims made on the label do not exceed what can be reasonably supported by the clinical trials. Actual data and reports are part of the NDA so conclusions can be validated. The primary purpose of review is to evaluate safety and effectiveness in the context of the data presented and the claims made in the proposed marketing materials. The experiences gained in clinical trials provide the basis for telling health care providers how they should prescribe the drug. All this information is summarized on what becomes the package insert. If the documentation submitted to the FDA for review as an NDA is deemed insufficient, the application will be declined (FDA 1999). The company can then resubmit when the deficiencies have been addressed. Pharmaceutical companies pay a fee for the review of their NDA. In- stituting this fee has shortened review times considerably and consequently has les- sened the time it takes for new drugs to reach the consumer.
Clinical trials serve to promote safe and effective drugs and to eliminate those that turn out to be ineffective or too risky for the benefit they provide. Of the drugs tested for safety in Phase I, about 70% are successful. Of those, only about 33% successfully clear the effectiveness requirements of Phase 2. Of the drugs that successfully make it through Phase II, only about 25% make it through Phase III. In all, only about 20% of all INDs submitted are approved for marketing.
Conclusion
In this chapter we have reviewed the steps that are taken to develop a chemopreven- tive agent, from bench to market. While chemopreventive agents differ from therapeu- tic agents in their scope and intent, their development requires the same stringent ad- herence to laws, regulations and principles.
References
Anonymous (1999). ªPrevention of cancer in the next millennium: Report of the Chemopre- vention Working Group to the American Association for Cancer Research.º Cancer Re- search 59(19): 4743±4758.
FDA (1999). From test tube to patient: Improving health through human drugs. Rockville, MD, Food and Drug Administration, Center for Drug Evaluation and Research.
ICH (1994). International Conference on Harmonisation of Technical Requirements for Regis- tration of Pharmaceuticals for Human Use. Geneva, ICH Secretariat.
Kelloff, G. J., E.T. Hawk, et al. (1996). ªStrategies for identification and clinical evaluation of promising chemopreventive agents.º Oncology (Huntington) 10(10): 1471±1484; discus- sion 1484±1488.
Nestle, F.O., S. Alijagic, et al. (1998). ªVaccination of melanoma patients with peptide- or tu- mor lysate-pulsed dendritic cells.º Nature Medicine 4: 328±332.
O'Shaughnessy, J.A., G.J. Kelloff, et al. (2002). ªTreatment and prevention of intraepithelial neoplasia: an important target for accelerated new agent development [comment].º Clinical Cancer Research 8(2): 314±346.
WMA (1989) World Medical Association Declaration of Helsinki, World Medical Association.
