2.1 Introduction In the first instance, the primary sources of anticancer agents were natural sources, plant extracts, sea molluscs and other such life forms or parts thereof, which were on some occasions initially used in traditional medicines and preparations, or were discovered though extensive screening of materials from such sources on cancer cell lines for the identification of active ingredients as a first generation agents. These were subsequently chemically manipulated to improve their anticancer or pharmaceutical properties. However, as chemical and technological developments were progressing, it became possible to synthesize, using automated solid-phase or solution-phase synthetic techniques, vast libraries of de novo compounds that could be tested against cancer cell lines or particular targets of interest to generate high affinity and selectivity agents with appropriate desirable properties. A number of combinatorial techniques are currently available, ranging in application from the preparation of small organic compounds to the synthesis of the latest biologics that seem to currently dominate the market in terms of FDA approvals and sales in the past few years. Some of the combinatorial techniques currently available and widely used in anticancer drug design will be presented in this chapter.
2.2 Combinatorial Approaches for Small Molecule Drug Design The increasing demand for new therapeutics, or compounds that could be screened in biological assays for the identification of novel leads, has pushed development of technological and chemical methodologies in drug design. Combinatorial chemistry or automated medicinal chemistry approaches for the development of novel inhibitors from libraries of organic molecules has been the focus of large pharmaceutical industries perhaps for the past 10-20 years, but a decade ago it remained the source of frustration, originally failing to fulfill its promise. This was partly due to the limitations of the robust chemical protocols and synthetic reactions available for automation; the fact that methodologies available often resulted in mixtures of compounds, for which few or no purification methods were available, resulting in poor quality control and thus frustrating screening results and difficulties in identifying the active ingredients. However, as synthetic approaches and technological developments have been progressing, combinatorial chemistry, coupled with traditional chemistry and in silico drug design, is expected to lead to a number of new drug molecules in the future.
2.3 Display Technologies 2.3.1 Phage display technology As mentioned before, peptides have been at the intersection between small molecule therapeutics and their larger proteinic counterparts, antibodies. Furthermore, peptides have some advantages over antibodies, in that they have lower manufacturing costs, higher activity per mass, better tumor penetration, increased stability and reduced immunogenicity. Fur- thermore, they have the advantage of increased specificity over small molecule therapeutics, which makes them interesting modalities for the pharmaceutical industry (Ladner et al., 2004). Although synthetic approaches to peptide libraries have been described for over 45 years, the greatest boost of combinatorial approaches to selection of peptides from vast libraries came with the development of the phage display technology by Smith in 1985. Subsequently, this was improved upon and it was reported that a filamentous phage was used to display a random oligopeptide on the N-terminus of the viral PIII coat protein, by inserting a stretch of random deoxyoligonucleotide into the pill gene of filamentous phage (Smith, 1985; Parmley and Smith, 1988), thus initiating a process that has resulted in a number of modern therapeutics. The phage display technique is very effective in producing large numbers (up to 10^9) of diverse peptides and proteins and isolating molecules that perform particular functions.
Key Takeaways
- Natural sources were initially used for anticancer agents, but combinatorial chemistry has become a focus in recent years.
- Combinatorial approaches allow the synthesis of vast libraries of compounds that can be tested against cancer cell lines or specific targets.
- Phage display technology is an effective method for selecting peptides with high affinity and specificity to protein targets.
Practical Tips
- Utilize combinatorial chemistry techniques to generate diverse compound libraries for drug discovery.
- Apply phage display technology to select peptides that bind specifically to oncological targets.
- Incorporate in silico modeling to predict the properties of potential anticancer agents before synthesis.
Warnings & Risks
- Ensure robust chemical protocols and purification methods are available when synthesizing compound libraries.
- Be cautious about the limitations of phage display technology, such as gene deletion or plasmid instability.
Modern Application
While this chapter focuses on historical drug discovery techniques for anticancer agents, many principles remain relevant today. The use of combinatorial chemistry and in silico modeling continues to be crucial in modern pharmaceutical research. However, advancements in technology have improved the efficiency and accuracy of these methods, reducing some of the initial frustrations mentioned.
Frequently Asked Questions
Q: What are the primary sources for anticancer agents according to this chapter?
The primary sources for anticancer agents were natural sources such as plant extracts, sea molluscs, and other life forms or parts thereof. These materials were initially used in traditional medicines and preparations.
Q: How has combinatorial chemistry evolved over time?
Combinatorial chemistry was initially a source of frustration due to limitations in robust chemical protocols and purification methods. However, with advancements in synthetic approaches and technological developments, it is now expected to lead to the discovery of new drug molecules.
Q: What advantages do peptides have over antibodies according to this chapter?
Peptides offer lower manufacturing costs, higher activity per mass, better tumor penetration, increased stability, reduced immunogenicity, and greater specificity compared to small molecule therapeutics. These properties make them interesting modalities for the pharmaceutical industry.