Several Principles for Successful Steroid Hormone Hapten Design and Synthesis
The natural steroid hormones are generally synthesized from cholesterol in the gonads and adrenal glands while numerous artificial types have been contrived by advanced synthetic techniques. Steroid hormones, regardless of their source, are helpful in controlling metabolism, inflammation, immune functions, salt, and water balance as well as in the development of sexual characteristics and the ability to withstand injury and illness.
To detect hormones in biological fluids, or to exploit their therapeutic applications in tumor therapy, scientists have enabled the formation of anti-hapten antibodies on the basis of thoughtful steroid hormone hapten design and synthesis. After years of practice, the key points for successful hapten design and synthesis are summarized as follows:
The linker site on the steroid molecule
Antibodies can recognize a part of the hapten molecule with specific characteristics. Hence, similar physicochemical properties are supposed to appear in designed haptens. Particularly, the linker group should be carefully allocated due to its prominent influence on the specificity of antibodies
The chemical nature of the bridge connecting hapten and carrier
An active group is expected to show presence at the terminal of the linker, otherwise the hapten should be redesigned until it can be directly coupled with a carrier. For instance, -COOH or -NH is frequently introduced to the hapten for the connection between haptens and carriers.
The nature of the selected carrier
Carriers must go through elaborate selection as they can impact the intensity of immune response. Nowadays, plenty carrier macromolecules like albumins, thyroglobulins, haemocyanins, and polylysine provide a broad range of choices for researchers which, from another perspective, pose higher requirements for determining the appropriate one in varying situations.
The number of steroid residues attached to each carrier molecule
More than one steroid residue (hapten) is likely to be attached to the same carrier protein, leading to the emergence of polyclonal antibodies that can recognize more than one compound at a time. Therefore, it is necessary to control the number of steroid residues attached if antibodies of high specificity are required.
Beyond the above four principles, scientists also find that designing strategies must vary in line with disparate demands on haptens. When the class-specific haptens are required, it is desirable to choose D ring (the critical difference among steroid hormones) as the modification site so that the final antibodies can recognize similar structures with broad-spectrum reaction.
However, scientists are sometimes in pursuit of compound-specific haptens to form antibodies with high affinity. In this case, A and B ring modification is certainly more viable since the characteristic structure of individual steroids will be more easily exposed on the surface of the artificial antigen.
The principles discussed offer general guidelines for steroid hormone hapten design and synthesis. Although they seem demanding and complicated, researchers can benefit a lot if following them judiciously.
