Biochemical Target-Based Hair-Growth Reduction

10.5.1 Patented Technologies on Hair-Growth Regulation

The hair follicle represents a complex structure that includes the undifferentiated, rapidly proliferating cells of the matrix region surrounding the dermal papilla, as well as the highly differentiated or keratinized hair fiber that emerges from the follicle. The matrix cells give rise to the hair shaft proper, as well as to the inner root sheath layers. The dermal papillas are enveloped by the matrix region, and are thought to be a primary regulator of the hair cycle as well as hair phenotype. Although the dermal papilla has been implicated in hair – growth regulation, no definite data has clearly implicated a single factor as a signal for controlling hair growth. This is due to the likely scenario where multiple and redundant factors are involved with hair cycle and hair-growth regulation. The structural and func­tional heterogeneity that exists within this skin appendage is interesting as it contains some of the most rapidly proliferating cells in the body, as well as the most differentiated. These properties, along with its ability to renew itself, provide unique characteristics that can be selectively exploited to control hair growth.

Pioneering work in the area of biochemical control processes for hair-growth regulation has been performed by researchers from the Gillette Company (now P&G). The research­ers used a rational biochemical and pharmacological approach that started with the identi­fication of key hair follicle growth biochemical pathways a based on biochemical/histological and molecular biology studies; next they identified and selected chemical molecules that could specifically alter the activity of an identified target pathway, and have the potential to penetrate skin stratum cornium after their topical application in dermatologically accept­able formulations. It was then demonstrated in in-vitro human hair follicle and/or hamster flank-organ models that the chemical agent is able to effectively inhibit hair growth in a dose-dependent manner parallel with the alteration of the target pathway activity in the fol­licle. The results of these investigations led to a series of patents in this field. A select list of awarded US patents on hair-growth control along with the metabolic pathway and select hair-growth inhibitors is shown in Table 10.2.