The hair follicle and its stem cells as drug delivery targets

The hair follicle is a skin appendage with a complex structure containing many cell types that produce highly specialised proteins. The hair follicle is in a continuous cycle: anagen is the hair growth phase, catagen the involution phase and telogen is the resting phase. The follicle offers many potential therapeutic targets. Hoffman and colleagues have pioneered hair-follicle-specific targeting using liposomes to deliver small and large molecules, including genes. They have also pioneered ex vivo hair-follicle targeting with continued expression of the introduced gene following transplantation. Recently, it has been discovered that hair follicle stem cells are highly pluripotent and can form neurons, glial cells and other cell types, and this has suggested that hair follicle stem cells may serve as gene therapy targets for regenerative medicine.     

人参茎叶皂苷对毛囊间充质干细胞增殖的影响

目的:研究人参茎叶皂苷对毛囊间充质干细胞(hair follicle mesenchymal stem cell)的促增殖作用。方法:采用MTT法检测其是否增殖,筛选人参茎叶皂苷对毛囊间充质干细胞促增殖作用的有效浓度,流式细胞术研究加药后细胞周期。结果:当人参皂苷浓度为12.5μg/mL时对毛囊间充质干细胞的促增殖作用最强。结论:毛囊间充质干细胞是毛囊内发育成毛发的主要细胞之一,人参茎叶皂苷可能通过促进毛囊间充质干细胞增殖而促进毛发生长。     

Follicular transport route - Research progress and future perspectives

The important role of hair follicles as penetration pathways and reservoir structures for topically applied compounds has been validated in numerous animal models as well as in humans. Follicular penetration rates are modulated by regional variations in size and proportions and the functional status. Advances have especially been made in the targeting of hair follicle-associated cell populations including antigen-presenting cells and stem cells. Improved investigative methods based on differential stripping, spectrophotometry and confocal laser scanning microscopy have led to the determination of the penetration profiles and kinetics for a multiplicity of drugs and drug delivery systems. The observation that particulate delivery systems aggregate and remain in hair follicle openings and their penetration along the follicular duct occurs in a size-dependent manner, which has led to advanced concepts of targeted drug delivery of bioactive compounds in the field of solid particles, as well as semi-solid particles, such as liposomes. This review summarizes the recent progress in this field, and underlines the necessity for pilot studies in human volunteers to further the development of clinical applications for follicular targeting.     

Engineering the niche for hair regeneration — A critical review

Recent progress in hair follicle regeneration and alopecia treatment necessitates revisiting the concepts and approaches. In this sense, there is a need for shedding light on the clinical and surgical therapies benefitting from nanobiomedicine. From this perspective, this review attempts to recognize requirements upon which new hair therapies are grounded; to underline shortcomings and opportunities associated with recent advanced strategies for hair regeneration; and most critically to look over hair regeneration from nanomaterials and pluripotent stem cell standpoint. It is noteworthy that nanotechnology is able to illuminate a novel path for reprogramming cells and controlled differentiation to achieve the desired performance. Undoubtedly, this strategy needs further advancement and a lot of critical questions have yet to be answered. Herein, we introduce the salient features, the hurdles that must be overcome, the hopes, and practical constraints to engineer stem cell niches for hair follicle regeneration.     

Cutaneous applied nano-ZnO reduce the ability of hair follicle stem cells to differentiate

The ability of metal oxide nanoparticles to penetrate the skin has aroused a great deal of interest during the past decade due to concerns over the safety of topically applied sunscreens that contain physical UV-resistant metal particles, such as nano-Zinc oxide (nZnO). Previous studies demonstrate that metal oxide nanoparticles accumulate in skin furrows and hair follicles following topical application while little is known about the consequence of these nanoparticles on skin homeostasis. The current investigation tested the effects of nZnO (0.5?mg/day mouse) on hair follicle physiology. Topical application of Vaseline containing nZnO, bulk ZnO (bZnO), or ionized Zn to newborn mice vibrissa pad over a period of 7 consecutive days revealed that nZnO accumulated within hair follicles, and this induced the apoptosis of hair follicle stem cells (HFSCs). In vitro studies also indicated that nZnO exposure caused obvious DNA damage and induced apoptosis in HFSCs. Furthermore, it was found that nZnO exposure perturbed genes associated with HFSC apoptosis, cell communication, and differentiation. HFSCs transplantation assay demonstrated that the potential of HFSCs to differentiate was reduced. This investigation indicates a potential risk of topically applied ZnO nanoparticles on skin homeostasis.     

Drug delivery to hair follicles

Introduction: The optimization of drug delivery to and via the hair follicles is gaining more and more importance as it has been recognized that the hair follicles are an interesting target site for topical applications. They are closely surrounded by capillaries and antigen-presenting cells, are associated with the sebaceous glands and are the host of stem cells in the bulge region of the hair follicle.

Areas covered: The present review shortly summarizes the complexity of the structure, biology and functions of the hair follicle and presents the models and methods suitable to investigate follicular penetration. Drug delivery to hair follicles was clearly shown to be dependent on the physicochemical properties of the applied substances and vehicles as well as on the activity status, size and density of the hair follicles. Especially particulate substances were demonstrated to be proficient drug carriers into the hair follicles, whereas dependent data for transfollicular penetration into the deeper viable skin layers could only be found for non-particulate substances which then, however, received rapid access to the circulation when the follicular pathway was accessible.

Expert opinion: Promising concepts to optimize hair follicle delivery and to beneficially utilize particulate substances for efficient follicular drug delivery are the application of external or internal stimuli for controlled drug release from the particles such as the combined application with protease or the usage of gold nanoparticles in combination with near-infrared irradiation.     

Androgenetic alopecia: combing the hair follicle signaling pathways for new therapeutic targets and more effective treatment options

ABSTRACT

Introduction: In the past 30 years, only two drugs have received FDA approval for the treatment of androgenetic alopecia reflecting a lack of success in unraveling novel targets for pharmacological intervention. However, as our knowledge of hair biology improves, new signaling pathways and organogenesis processes are being uncovered which have the potential to yield more effective therapeutic modalities.

Areas covered: This review focuses on potential targets for drug development to treat hair loss. The physiological processes underlying the promise of regenerative medicine to recreate new functional hair follicles in bald scalp are also examined.

Expert opinion: The discovery of promising new targets may soon enable treatment options that modulate the hair cycle to preserve or extend the growth phase of the hair follicle. These new targets could also be leveraged to stimulate progenitor cells and morphogenic pathways to reactivate miniaturized follicles in bald scalp or to harness the potential of wound healing and embryogenic development as an emerging paradigm to generate new hair follicles in barren skin.     

Regeneration and replacement in the vertebrate inner ear

Deafness affects more than 40 million people in the UK and the USA, and many more world-wide. The primary cause of hearing loss is damage to or death of the sensory receptor cells in the inner ear, the hair cells. Birds can readily regenerate their cochlear hair cells but the mammalian cochlea has shown no ability to regenerate after damage. Current research efforts are focusing on gene manipulation, gene therapy and stem cell transplantation for repairing or replacing damaged mammalian cochlear hair cells, which could lead to therapies for treating deafness in humans.     

Characterization of multipotent cells from human adult hair follicles.

Recent works demonstrated the presence of a multipotent epithelial cell population in the bulge region of adult human hair follicles. These cells can be cultured in vitro, thus leading to the preparation of dermal-epidermal substitutes which are applicable in the treatment of burns and ulcers. We evaluated the main marker expression in cells obtained from stripped human hair follicles. A pool of hair follicles were incubated at 37 degrees C and 5% CO(2) in a growth medium. The cells were then labelled with antibodies (anti-CD34, anti-CD38, anti-CD45, anti-CD90, anti-CD133, anti-CD146) and analysed by cytometry. We also used hair follicles for immunohistochemical studies, employing antibodies such as CD34, Actin Smooth Muscle, Filaggrin, Desmin, Vimentin, Glial Fibrillary Acidic Protein, Ki-67, PanCytokeratin, CK15, CK19. The cytometry results revealed that a part of bulge cells were CD34+ (1-2%). CD34+ population comprises both large, CD45-, CD133-, CD146- cells and small, CD45+, CD133+, CD146+ cells. Thus, a part of CD34+ cells present a mature endothelial marker (CD146). An expression of the proliferation marker Ki-67 and the stem cell marker CD34 is present in the follicle bulge region. In conclusion, we observed that the stripped hair follicle has the same multipotent cell population as adult and fetal scalp hair follicles.     

Delivery of nucleic acid therapeutics by genetically engineered hematopoietic stem cells

Several populations of adult human stem cells have been identified, but only a few of these are in routine clinical use. The hematopoietic stem cell (HSC) is arguably the most well characterized and the most routinely transplanted adult stem cell. Although details regarding several aspects of this cell's phenotype are not well understood, transplant of HSCs has advanced to become the standard of care for the treatment of a range of monogenic diseases and several types of cancer. It has also proven to be an excellent target for genetic manipulation, and clinical trials have already demonstrated the usefulness of targeting this cell as a means of delivering nucleic acid therapeutics for the treatment of several previously incurable diseases. It is anticipated that additional clinical trials will soon follow, such as genetically engineering HSCs with vectors to treat monogenic diseases such as hemophilia A. In addition to the direct targeting of HSCs, induced pluripotent stem (iPS) cells have the potential to replace virtually any engineered stem cell therapeutic, including HSCs. We now know that for the broad use of genetically modified HSCs for the treatment of non-lethal diseases, e.g. hemophilia A, we must be able to regulate the introduction of nucleic acid sequences into these target cells. We can begin to refine transduction protocols to provide safer approaches to genetically manipulate HSCs and strategies are being developed to improve the overall safety of gene transfer. This review focuses on recent advances in the systemic delivery of nucleic acid therapeutics using genetically modified stem cells, specifically focusing on i) the use of retroviral vectors to genetically modify HSCs, ii) the expression of fVIII from hematopoietic stem cells for the treatment of hemophilia A, and iii) the use of genetically engineered hematopoietic cells generated from iPS cells as treatment for disorders of hematopoiesis.     

Metastatic cancer stem cells: new molecular targets for cancer therapy

The cancer stem cell (CSC) hypothesis, predicts that a small subpopulation of cancer cells that possess "stem-like" characteristics, are responsible for initiating and maintaining cancer growth. According to the CSC model the many cell populations found in a tumour might represent diverse stages of differentiation. From the cellular point of view metastasis is considered a highly inefficient process and only a subset of tumour cells is capable of successfully traversing the entire metastatic cascade and eventually re-initiates tumour growth at distant sites. Some similar features of both normal and malignant stem cells suggest that CSCs are not only responsible for tumorigenesis, but also for metastases. The CSC theory proposes that the ability of a tumour to metastasize is an inherent property of a subset of CSCs. The similar biological characteristics shared by normal stem cells (NSCs) and CSCs mainly implicate self-renewal and differentiation potential, survival ability, niche-specific microenvironment requirements and specific homing to metastatic sites and may have important implications in terms of new approaches to cancer therapy in the metastatic setting. There are several agents targeting many of these CSC features that have shown to be effective both in vitro and in vivo. Although clinical trials results are still preliminary and continue under investigation, these new therapies are very promising. The identification of new therapeutic targets and drugs based on CSC model constitutes a great challenge.     

Cancer stem cells in hematological disorders: current and possible new therapeutic approaches

An increasing body of evidence has shown that hematologic malignancies, alike normal hematopoiesis, has a hierarchical structure including a stem cell compartment with self renewal capability, endowed in a neoplastic niche bearing resemblance to its normal hematopoietic counterpart. According to experimental data on NOD-SCID mice, leukemic stem cells are characterized by a CD34+/CD38- surface profile and account for 1 in 10(3) to 1 in 10(6) of the total amount of leukemic cells. The available knowledge about leukemic stem cells (LSC) has arisen the question as to whether some targeting of LSC is achieved by current treatments; the answer is dubitative at best, with the possible exception of arsenic trioxide in promyelocytic leukemia. On the other side, the unsatisfactory results in the treatment of many hematological neoplasms has prompted many research groups to find out whether direct targeting of LSC, possibly in its niche, would result in an improvement in cure rates. This approach implies the identification of LSC specific markers, clearly distinct from their normal counterpart in order to spare normal hematopoietic stem cells. Adhesion/surface antigens, metabolic pathways involved in LSC survival and renewal, telomerase, commonly mutated genes and epigenetic phenomena have been investigated as candidate targets for newer therapeutic strategies. So far, most of the possibly effective agents have been studied in experimental models only. FLT-3 inhibitors account for a notable exception since they have resulted effective in vivo in AML with mutated, but not over expressed, FLT-3. A main task for the future is to find out whether some common LSC specific markers would be identifiable in a substantial proportion of AML cases, or whether each AML case shows a unique fingerprint of markers. In the latter event, targeting of LSC could result in an arduous task.     

Development and clinical advancement of small molecules for ex vivo expansion of hematopoietic stem cell

Hematopoietic stem cell (HSC) transplantation is the only curative therapy for many diseases. HSCs from umbilical cord blood (UCB) source have many advantages over from bone marrow. However, limited HSC dose in a single CB unit restrict its widespread use. Over the past two decades, ex vivo HSC expansion with small molecules has been an effective approach for obtaining adequate HSCs. Till now, several small-molecule compounds have entered the phase I/II trials, showing safe and favorable pharmacological profiles. As HSC expansion has become a hot topic over recent years, many newly identified small molecules along with novel biological mechanisms for HSC expansion would help solve this challenging issue. Here, we will give an overview of HSC biology, discovery and medicinal chemistry development of small molecules, natural products targeting for HSC expansion, and their recent clinical progresses, as well as potential protein targets for HSC expansion.     

Lipogenic enzymes as therapeutic targets for obesity and diabetes

Since storage of excess fat in peripheral tissues is a contributing factor leading to obesity and type II diabetes, many investigators are studying the key lipid metabolizing enzymes found in adipose tissue as drug targets to reduce excess fat. The availability of cultured cell lines and primary stem cells, preadipocyetes, and adipocytes has facilitated therapeutic approaches aimed at targeting fat storage. This includes developing inhibitors for enzymes regulating lipogenesis in these cells, such as acetyl-CoA carboxylase, fatty acid synthase, diacylgycerol acyl transferase, and stearoyl CoA desaturase. High level expression of each protein is often used to confirm stem cells have undergone adipogenesis. Inhibition of these enzymes often leads to reduced fat cell fat differentiation and lipid synthesis and may also contribute to increased fat oxidation and energy expenditure. This article reviews developments in pharmaceutical research on these enzymes, with particular emphasis on the role of the enzymes in adipose tissue metabolism.     

New therapy options for amyotrophic lateral sclerosis

Introduction: Amyotrophic lateral sclerosis (ALS) is a rapidly progressing neurodegenerative disease leading almost irrevocably to paralysis and death within 5 years after the first symptoms. Since the approval of riluzole, all other therapeutic trials have been negative, including many that followed hopeful preclinical and early clinical data. New approaches are needed to uncover effective treatments for this still-devastating disease.

Areas covered: The review summarizes the current approaches to clinical drug development in ALS. It focuses on several new trials listed on PubMed Central or the National Institutes of Health online trial registry. New targets for therapeutic intervention in ALS include skeletal muscle, energetic metabolism and cell replacement. Two different approaches are directed at muscle: interventions that influence proteins near the neuromuscular junction such as Nogo-A; in contrast to drugs pointed toward disease physiology, therapies that directly increase strength. Other trials are evaluating nutritional interventions. Current cell therapy strategies utilize various types of stem cells to study disease pathophysiology, support neurons or surrounding cells through gene therapy or release of neurotrophic factors, or directly replace cells. The review includes a section on known genetic influences in ALS and future directions for the field.

Expert opinion: These new interventions have important implications for the direction of ALS research. Investigators are focusing less on physiological mechanisms inside the neuron, a process that has proved unfruitful for nearly two decades, and more on concepts that have not been examined previously. These studies will surely add to the overall understanding of ALS. Future research will test ways to reduce gene expression in those with known mutations, as well as means to reduce the spread of aggregated protein.     

Targeting RNA with small molecules

Therapeutic targeting of RNA is not as well-developed as with DNA and proteins, and the many structures and functions of RNA suggest that it is an underutilized target. As with DNA, RNA has heterocyclic bases and base pairs with a highly anionic backbone, but as with proteins, RNA can fold into complex tertiary structures that create unique binding pockets for small molecules. Aminoglycoside targeting of ribosomal RNA is a well-known success story, and mRNAs and tRNAs have also served as therapeutic targets as well as model systems for understanding RNA-ligand interactions. The unique, species-specific structures and chemistry involved in splicing and ribozyme activity makes this RNA function an attractive target, and inhibitors of ribozyme activity have been discovered. The numerous serious human diseases caused by RNA viruses highlight the importance of developing new compounds that can target RNA structures in viral genomes. Considerable effort has been directed at finding compounds that target HIV-1 RNAs that control viral replication and frameshifting. As part of these efforts very useful new assays have been developed for small molecule-RNA interactions. The assays have led to the discovery of new inhibitors for different steps in viral replication. The next phase of research in RNA targeting will not only focus on the discovery of new compounds, but also on how to develop small molecules with high affinity and selectively for RNA that can penetrate effectively into a wide array of cell types.     

RU 58841-myristate--prodrug development for topical treatment of acne and androgenetic alopecia

Acne and androgenetic alopecia are linked to androgen effects and therefore should improve following topical application of antiandrogens. We present a new antiandrogen prodrug, RU 58841-myristate (RUM) for topical therapy. Almost devoid of affinity to the androgen receptor, as derived from investigations in the mouse fibroblast cell line 29 +/GR +, RUM is rapidly metabolised to the potent antiandrogen RU 58841 by cultured human foreskin fibroblasts and keratinocytes, male occipital scalp skin dermal papilla cells, and by cells of the sebaceous gland cell line SZ95. In order to improve a specific targeting of the hair follicle, RUM was loaded on solid lipid nanoparticles (SLN), which are already known to support dermal targeting effects. Physically stable RUM loaded SLN were produced by hot homogenization. Penetration/permeation studies carried out using the Franz diffusion cell proved only negligible permeation of reconstructed epidermis and excised porcine skin within 6 h, implying a more topical action of the drug. Targeting to the hair follicle using SLN was visualised by fluorescence microscopy, following the application of Nile Red labelled SLN to human scalp skin. Transmission electron microscopy (TEM) allowed to detect intact silver labelled SLN in porcine hair follicles of preparations applied to the skin for 24 h. RUM loaded SLN should be considered for topical antiandrogen therapy of acne and androgenetic alopecia.     

Can nanomedicines kill cancer stem cells?

Most tumors are heterogeneous and many cancers contain small population of highly tumorigenic and intrinsically drug resistant cancer stem cells (CSCs). Like normal stem cell, CSCs have the ability to self-renew and differentiate to other tumor cell types. They are believed to be a source for drug resistance, tumor recurrence and metastasis. CSCs often overexpress drug efflux transporters, spend most of their time in non-dividing G₀ cell cycle state, and therefore, can escape the conventional chemotherapies. Thus, targeting CSCs is essential for developing novel therapies to prevent cancer relapse and emerging of drug resistance. Nanocarrier-based therapeutic agents (nanomedicines) have been used to achieve longer circulation times, better stability and bioavailability over current therapeutics. Recently, some groups have successfully applied nanomedicines to target CSCs to eliminate the tumor and prevent its recurrence. These approaches include 1) delivery of therapeutic agents (small molecules, siRNA, antibodies) that affect embryonic signaling pathways implicated in self-renewal and differentiation in CSCs, 2) inhibiting drug efflux transporters in an attempt to sensitize CSCs to therapy, 3) targeting metabolism in CSCs through nanoformulated chemicals and field-responsive magnetic nanoparticles and carbon nanotubes, and 4) disruption of multiple pathways in drug resistant cells using combination of chemotherapeutic drugs with amphiphilic Pluronic block copolymers. Despite clear progress of these studies the challenges of targeting CSCs by nanomedicines still exist and leave plenty of room for improvement and development. This review summarizes biological processes that are related to CSCs, overviews the current state of anti-CSCs therapies, and discusses state-of-the-art nanomedicine approaches developed to kill CSCs.     

Hair Growth Promotion by δ-Opioid Receptor Activation

Literature has revealed that the delta opioid receptor (DOR) exhibited diverse pharmacological effects on neuron and skin. In the present study, we have investigated whether the activation of DOR has hair-growth promotion effects. Compared with other opioid receptor, DOR was highly expressed in epidermal component of hair follicle in human and rodents. The expression of DOR was high in the anagen phase, but it was low in the catagen and telogen phases during mouse hair cycle. Topical application of UFP-512, a specific DOR agonist, significantly accelerated the induction of the anagen in C₃H mice. Topical application of UFP-512 also increased the hair length in hair organ cultures and promoted the proliferation and the migration of outer root sheath (ORS) cells. Similarly, pharmacological inhibition of DOR by naltrindole significantly inhibited the anagen transition process and decreased hair length in hair organ cultures. Thus, we further examined whether Wnt/β-catenin pathway was related to the effects of DOR on hair growth. We found that Wnt/β-catenin pathway was activated by UFP-512 and siRNA for β-catenin attenuated the UFP-512 induced proliferation and migration of ORS cells. Collectively, result established that DOR was involved in hair cycle regulation, and that DOR agonists such as UFP-512 should be developed for novel hair-loss treatment.