Correspondence: Yao-Chi Chuang M.D., Department of Urology, Kaohsiung Chang Gung Memorial Hospital, Chang Gung University College of Medicine, 123 Ta-Pei Road, Niao Song Hsiang, Kaohsiung 833, Taiwan. Email: email@example.com
The bladder is a hollow organ that can be treated locally by transurethral catheter for intravesical drug instillation or cystoscopy for intravesical drug injection. With advancing technology, local organ-specific therapy and drug delivery is of expanding interest for treating dysfunctional bladder, including interstitial cystitis/bladder pain syndrome, overactive bladder and sterile hemorrhagic cystitis after chemotherapy or pelvic radiation. Intravesical therapy has shown varying degrees of efficacy and safety in treating interstitial cystitis/bladder pain syndrome, overactive bladder and hemorrhagic cystitis with new modalities being developed. Intravesical (regional) therapy has several advantages than oral (systemic) therapy, including high local concentration and less systemic toxicity. In recent years, intravesical delivery of biotechnological products including neurotoxins and immunosuppressive agents, and delivery platform including liposomes has shown promise for lower urinary tract symptoms. This review considers the current status of intravesical therapy in dysfunctional bladder including interstitial cystitis/bladder pain syndrome, overactive bladder and hemorrhagic cystitis with special attention to lipid based novel drug-delivery.
Intravesical therapy/drug delivery is widely used for delaying or preventing the recurrence of superficial bladder cancer after transurethral resection of bladder tumor.[1, 2] Given the success of this approach in oncology, it would be wise to apply the lessons learned over the decades to improve the treatment of dysfunctional bladder, such as IC/BPS, OAB and sterile HC, from chemotherapy and pelvic radiation. The concept of “applying the medicine directly where it hurts” is apt for promoting wider acceptance of this line of therapy for dysfunctional bladder. Instillation of drugs through a catheter into the bladder provides a high concentration of drugs locally at the disease site in the bladder without an increase in systemic levels, which can explain the low risk of systemic side-effects. However, drug delivery to bladder tissues by the intravesical route is hindered by the impermeability of urothelial cells with tight junction and umbrella cells on the apical surface, a short duration of action, and the need for frequent administration.[3-5] The intact urinary bladder lining has the most impermeable barrier in the human body. The present review of the literature describes the status of intravesical drug delivery with respect to specific diseases and novel drug delivery systems.
Bladder structure and function: A reservoir with impermeable urothelium
The structure of the bladder wall contains multiple layers of tissue. The layers from luminal to outer surface are: urothelium, detrusor muscle and adventitia. The urothelium is the inner layer within the bladder lumen and serves as a bladder permeability barrier. The structure of the urothelium from the detrusor side to the apical is composed of three different cells: basal cells, intermediate cells and umbrella cells. The barrier function of umbrella cells is established by the arrangement of uroplakins, tight junctional protein and further enhanced by a mucin layer composed of GAG on the luminal side. The GAG layer is hydrophilic, and forms an aqueous layer on umbrella cells, and has been suggested to prevent urine substances from adhering to the bladder lumen. The bladder wall is elastic and allows the bladder to store 400–600 mL of urine. The bladder urothelium is impermeable, and prevents urine and waste solute from penetrating into the submucosal layer.
To elicit a therapeutic effect after luminal delivery into the urinary bladder, drugs have to cross a watertight barrier. The urothelium is the tightest and most impermeable barrier in the body (Fig. 1). The urothelium, responsible for a multitude of physiological activities, is not only effective in blocking the entry of urine contents, but is also equally effective in blocking the entry of instilled drugs.[3, 4] It sits at the interface between the urine and underlying connective tissue, where it forms a barrier preventing the unregulated exchange of solutes, ions and toxic metabolites. The permeability to substances, such as water, ammonia and urea, which normally cross membranes relatively rapidly, is extremely low in the urothelium.[3, 4] It has exceptionally high transepithelial resistance ranging from 10 000 to >75 000 Ωcm2 owing to paracellular resistance of tight junctions pooled with apical plasma membrane transcellular resistance.[10, 11] Urothelial tight junctions are comprised of a dense network of cytoplasmic proteins (zonula occludens-1), cytoskeletal elements and transmembrane proteins (occludin and claudins), and have the highest recorded paracellular resistance of all epithelia measured to date. In addition, the apical plasma membrane of the urothelium contains specific proteins, uroplakins, which account for the transcellular resistance. Electron microscopy of umbrella cells lying at the luminal surface of the urothelium showed a hexagonal arrangement of uroplakins, where six subunits of each particle are tightly joined together to form a complete hexagonal ring, with lipids contained in the central cavity. The low permeability of the urothelial barrier is believed to result from the peculiar protein array and tight junctions between umbrella cells. The urothelial barrier restricts the movement of drugs after intravesical administration, and also restricts the action of the active drug fraction in the urine. Hence, many drugs fail to reach the bladder at desired therapeutic levels, and ultimately lack pharmacological effects.[13, 14]
Rationale for intravesical delivery
Oral drug therapy for dysfunctional bladder is commonly used and might require large doses, because only a small fraction is actually absorbed and reaches the bladder. Biodistribution throughout the whole body is undesired, with risks of increased side-effects. Hence, the per oral route often fails to have a sufficient effect at the disease site. The urinary bladder is a hollow organ with a natural conduit (urethra) to drain out the urine, and allows relatively uncomplicated access and manipulation with a catheter, and hence localized treatment options have therapeutic benefits. Delivery of a bladder agent directly into the wounded or dysfunctional bladder greatly improves the exposure of the affected bladder lining to the agent, and this is of even greater significance in the case of drug-resistant targets that require a much-higher dose of the drug.[15, 16]
Limitations to current intravesical delivery
There are several limitations to intravesical drug delivery, including dilution of the instilled drug to fill the bladder reduces drug concentration and voiding washes out instilled drug solutions. To overcome the unstable drug concentration in the bladder, strategies such as emptying the bladder before drug instillation, suppressing the rate of urine production by the kidneys, and regulating fluid intake before and after drug administration have been utilized. Recent studies for intravesical mitomycin have shown that eliminating the residual volume, overnight fasting, doubling the mitomycin concentration to 40 mg in 20 mL and urinary alkalinization using oral bicarbonate resulted in a doubling of the durable tumor-free rate at 5 years. Acidic urinary pH has been suggested as a limiting factor in intravesical epirubicin and doxorubicin therapy. Another important variable is the drug's lipophilicity, which allows membrane incorporation and penetration through cell membranes. Paclitaxel, a highly lipophilic compound, achieves greater intraurothelial concentrations than either mitomycin or doxorubicin.
Intravesical formulation and drug delivery
Because of the limited permeability of the bladder wall and undesired side-effects of chemical enhancers, the intravesical drug delivery approach is amenable to modulating the release and absorption characteristics of instilled drugs through coupling them to novel carriers, such as liposomes, microspheres, nanoparticles and so forth. Strategies involving nanoparticles and in situ gels for intravesical drug delivery are shown in Figure 1.
Liposomes are lipid vesicles composed of synthetic or natural phospholipids that self-assemble to form bilayers surrounding an aqueous core (Fig. 2). They can incorporate small drug molecules, both hydrophilic and hydrophobic, macromolecules and even plasmids, and show greater uptake into cells through endocytosis. Intravesical liposomes, even without drugs, have therapeutic effects on IC/BPS patients, mainly because of their ability to form a protective lipid film on the urothelial surface. Fraser et al. examined the effect of intravesically administered liposomes of L-α-phosphatidylcholine: cholesterol at 2:1 in a rat model of hyperactive bladder. PS was used to mimic IC/BPS, followed by a KCl and acetic acid infusion to serve as an irritant. The cystometrographic results showed that the hyperactivity induced by PS/KCl was partially reversed by treatment with liposomes/KCl, showing a significant change in the ICI from 15.8 ± 1.4 min with the control KCl solution to 2.7 ± 1.0 min with PS/KCl, and finally an increase to 4.4 ± 1.2 min with liposome treatment. Similarly, the irritant effect induced by acetic acid was reduced by liposome treatment, with ICI values changing from 2.4 ± 0.5 min with acetic acid to 6.7 ± 1.5 min with the liposome formulation.
The possible mechanism of action of liposomes is the formation of a lipid film on the urothelium that protects it from penetration by irritants. Additionally, liposomes can augment the barrier properties of the urothelium by stabilizing neuromembranes of damaged nerves and reducing their hyperexcitability. In addition, liposomes composed of phospholipids can exert anti-inflammatory effects by initiating local lipid signaling and affecting mast cell activity.
Encouraged by the efficacy of empty liposomes as a therapeutic agent for intravesical therapy of IC/BPS, Chuang et al. recently published information on the clinical safety and efficacy of liposomes in IC/BPS patients. In an open labeled prospective study of 24 IC/BPS patients, the effect of intravesical liposomes (80 mg/40 cc distilled water) once weekly was compared with oral pentosan polysulfate sodium (100 mg) three times daily for 4 weeks each. Statistically significant decreases in pain, urgency and the O'Leary–Sant symptom were observed in the liposome group. None of the patients reported urinary incontinence, retention or infection as a result of liposome instillation. Intravesical instillation of liposomes was found to be safe for IC/BPS, with potential improvement after one course of therapy for up to 8 weeks. Furthermore, Lee et al. reported that intravesical liposome twice weekly has a better effect than once weekly. Intravesical liposomes appear to be a promising new treatment for IC/BPS, and future large-scale placebo-controlled studies are required to verify the results of the pilot study.
A study carried out by the authors' laboratory evaluated the potential of liposomes as a vehicle for the intravesical delivery of the neurotoxin, capsaicin, for treating IC/BPS. Capsaicin is a water-insoluble hydrophobic drug, so its instillation requires the use of ethanolic saline to enhance urothelial penetration, but this can damage bladder tissues. The efficacy of liposome-encapsulated capsaicin was evaluated by measuring the micturition reflex in normal rats under urethane anesthesia. The cystometrogram tracings showed that liposomes were able to deliver capsaicin with an efficacy similar to ethanolic saline. Tissue histological and morphological studies, however, showed that toxicity to the bladder was drastically reduced. In the context of toxins instilled in the bladder, fat-soluble neurotoxins, such as capsaicin, can be integrated into the phospholipid bilayer, and water-soluble neurotoxins, such as botulinum, can be protected. Liposomes can co-opt the native vesicular traffic ongoing in the bladder, necessary for periodic expansion of the bladder lining during urine storage phases, which might provide a favorable environment for drug delivery. Liposomes can mimic these vesicles and thereby aid in improving the delivery of cargo across the bladder permeability barrier. Formulation of botulinum toxin with liposomes protected it from urinary degradation without compromising the efficacy in a rat model. Immunohistochemical detection confirmed the liposome-mediated transport of botulinum toxin into the urothelium. Animal studies indicate that liposomes can restrict botulinum toxin delivery to the detrusor muscle, and avoid the risk of retention and incomplete bladder emptying.
Polymer-based nanoparticles offer a variety of compositions with variable degrees of drug loading, and release by changing the parameters of the chemical nature and cross-linking reactions involved. The encapsulated drug is released in a controlled manner by either diffusion, erosion or a combination of both. Chang et al. studied poly(ethyl-2-cyanoacrylate) EPI-NP against bladder cancer cell lines (T24 and RT4). The nanoparticles greatly improved the penetration of epirubicin into the bladder wall, as commercial aqueous formulations of EPI have very low efficacy. Histological staining showed that the formulation caused no structural damage to the urothelium. Tissue analyses also showed higher penetration and accumulation of the EPI-NP formulation in tissues compared with those of the free drug.
Nanoparticles developed using magnetic compounds have potential as targeted drug carriers and for diagnostic imaging. Magnetic nanoparticles can be used as contrast agents to visualize diseased regions of the bladder, by targeting specific regions of the bladder utilizing a magnetic field to localize drug-loaded magnetic particles.[31, 32] The core of these nanoparticles can be coated with an organic or inorganic shell to allow drug adsorption or for ligand attachment to their surface. However, the size and properties of these particles need to be optimized for intravesical delivery. A recent study by Leakakos et al. used MTC (with particle sizes of 0.5–5 μm) to deliver the anticancer drug, doxorubicin, into the bladder wall. The MTC contained an iron component to allow targeting by a magnet, and an activated carbon component to adsorb the drug. Magnetic guiding of such particles might provide site-specific intravesical delivery of drugs.
Dendrimers are core-shell macromolecules made up of highly organized layers of monomers that make up branches surrounding a core. Dendrimers have a narrow size distribution, highly ordered structures, availability of a large number of functional groups for attachment of targeting ligands and drug molecules, and a high degree of control over drug-release properties.[35-38] Recently, Francois et al. evaluated ALA-loaded dendrimers to decrease the photobleaching of the fluorophore, PpIX, and to improve the visualization and specificity during cystoscopy. In vitro experiments showed that there was prolonged and sustained PpIX synthesis with reduced photobleaching compared with ALA-induced PpIX.
A previous study investigated the effect of nanocrystalline silver in experimental bladder inflammation. Nanocrystalline silver or phosphate-buffered saline was introduced intravesically to rat bladders for 20 min followed by vehicle or protamine sulfate and lipopolysaccharide. Nanocrystalline silver was not effective at <1%. Intravesical administration of nanocrystalline silver (1%) decreased urine histamine, bladder tumor necrosis factor-α and mast cell activation with no toxic effects. The effects were apparent even 4 days later and night be useful for IC/BPS.
Hydrogels have been considered as a vehicle for sustained intravesical drug delivery, avoiding drugs being washed out with urination. Large varieties of biocompatible, bioactive polymeric hydrogels are available. Tyagi et al. reported in vivo evaluation of a FITC- and misoprostol-loaded thermosensitive polymeric hydrogel in a rat model. Thermosensitive polymers can be used to first inject the hydrogel in its liquid form, which then forms a gel in situ inside the bladder cavity at an elevated body temperature. Results showed that the injected gel did not obstruct urine outflow, proving that it attached itself as a thin layer onto the bladder wall. The prolonged excretion (over 24 h) of FITC in the urine suggested that the hydrogel did not get washed off during urine voiding. Efficacy studies showed that the misoprostol, a synthetic PGE1 analog, trapped in the hydrogel maintained its biological activity, and successfully reduced incontinence and bladder damage in a cyclophosphamide-induced cystitis model in rats. A number of challenges remain for human trials including gels that must form a uniform thin layer inside the bladder, and mechanical properties of the gels should also allow them to resist detachment by shear forces of urine flow and stretching of the bladder wall.
Mucoadhesive formulations can be used to coat and protect damaged tissue surfaces or even to increase penetration of therapeutic agents into the cell lining. Mucoadhesive formulations should rapidly adhere to the bladder wall, not obstruct the flow of urine and remain attached to the affected site even after urine is voided. A number of biomolecules, such as chitosan, carbomers and cellulose derivatives, were identified as having mucoadhesive properties, among which chitosan is widely used for permeability enhancement of drug solutions through the urothelium. Chitosan has many properties advantageous for intravesical delivery, as it is biodegradable, biocompatible and polycationic, and has reactive amine and alcohol groups. Derivatives of chitosan are used to treat IC/BPS using sulfated form sNOCC to encapsulate and transport 5-ASA into the rat bladder wall. The inflammation and urinary frequency was found to be reduced using a combination of 3% sNOCC with 5-ASA. The sNOCC coats the wall of the bladder, where chitosan enhances permeation of the anti-inflammatory agent into the bladder lining. In a recent study, TGA nanoparticles were evaluated as carriers for intravesical delivery. Because of its thiol groups and disulfide bonds, chitosan-TGA nanoparticles showed greater stability, superior mucoadhesion, and more-sustained and controlled release than the corresponding unmodified chitosan particles. Release studies showed more-sustained release from covalently cross-linked particles compared with unmodified chitosan nanoparticles over a period of 3 h in artificial urine at 37°C.
EMDA has been explored to increase the penetration of drugs instilled into the bladder. In a recent study, patients suffering from urge syndrome with and without urge incontinence (25.6% OAB wet, 20.0% OAB dry and 54.4% mixed urinary incontinence) and non-responding to oral anticholinergic drugs underwent EMDA therapy carried out once every 4 weeks for a period of 3 months. EMDA significantly improved urodynamic parameters, the quality of life as evaluated with the Kings Health Questionnaire, and pad usage in patients with urge syndrome and therapy-resistant idiopathic detrusor overactivity as evident from a micturition chart over 48 h.
Dysfunctional bladder diseases amicable to local therapy
IC/BPS is a chronic disease characterized by suprapubic/bladder discomfort, which usually corresponds to progressive filling of the bladder, and decreases with the completion of voiding. It is accompanied by urinary frequency, urgency or nocturia in the absence of infection or other pathological conditions.
It was proposed that a dysfunctional epithelium allows the transepithelial migration of solutes, such as potassium, which is highly concentrated in the urine, and can depolarize subepithelial afferent nerves and provoke sensory symptoms (Fig. 3). In addition, an increased amount of activated mast cells in the bladder and dysfunction of the superficial layer of the extracellular matrix of the GAG layer was shown to be related to IC/BPS.[48, 49] Pain-sensing C-fibers are located within the uroepithelium and submucosa of the bladder, and can be activated by toxic solute leaking into the defective urothelium or release of histamine by mast cells. Because of the multifactorial nature of the disease, improved therapeutic outcomes can be achieved with multimodal treatment through intravesical approaches acting through different mechanisms.
According to the International Continence Society, OAB is defined as a symptom complex comprised of urinary urgency, with or without urgency incontinence, usually with frequency and nocturia. It has been estimated that the prevalence of OAB was 10.7% in the worldwide population in 2008, and will increase to 20.1% in 2018. Urologists from around the world are familiar with oral pharmacotherapy for OAB. Oral antimuscarinics are the mainstay of pharmaceutical management of OAB, competitively inhibiting either all muscarinic receptors (oxybutynin) or selectively the M3 receptor (darifenacin and solifenacin).[52, 53]
An oral beta3 adrenergic receptor agonist, mirabegron, has been evaluated and is now approved for OAB by the regulatory authorities in most developed countries. The rationale for intravesical therapy for OAB is less well known, but the application of intravesical botulinum toxin might benefit patients with oral drug therapy refractory OAB.
In OAB, the release of acetylcholine from the urothelium during the storage phase of micturition can activate muscarinic receptors in the urothelium. Activated muscarinic receptors trigger the release of urothelial adenosine triphosphate leading to activation of the afferent pathway.[54, 55] Thus, blockade of urothelial muscarinic receptors could indirectly act to reduce afferent nerve activation and therefore decrease OAB symptoms.
Hemorrhagic cystitis is a potentially fatal condition, which is encountered in patients receiving one or both of two specific chemotherapeutic agents (cyclophosphamide and ifosfamide) or pelvic radiation. The more severe occurrences involve massive bleeding, as well as clot formations that require evacuation. The most severe cases require surgical intervention (e.g. urinary diversion or cystectomy). There is no adequate pharmacotherapy treatment for hemorrhagic cystitis. There is a reported 5.35% incidence of sterile hemorrhagic cystitis in patients treated with cyclophosphamide and ifosphamide, and a lower incidence of hemorrhagic cystitis requiring therapy from radiation. The prevalence estimation for hemorrhagic cystitis is estimated at less than 80 000 in the USA. Table 1 lists the current and future therapies for hemorrhagic cystitis.
Table 1. Current and future therapies for hemorrhagic cystitis
Interventional fulguration of bleeding sites, which rarely works and exposes sick, frail patients to surgical risks
Aminocaprotic acid instillation, which might lead to dangerous clots
Intravesical silver nitrate, which can cause bladder perforation or kidney failure
Treatment with formalin instillation, which significantly reduces bladder functionality and causes pain
Up to 30 sessions of hyperbaric oxygen therapy
Cystectomy with significant morbidity and is clearly an option of last resort
Intravesical liposomal tacrolimus -based therapy
Intravesical therapeutics for dysfunctional bladder
GAG analogs for IC/BPS
Intravesical delivery of GAG analogs, such as HA, heparin and CS, restores the barrier function lost as a result of epithelial dysfunction in interstitial cystitis (Table 2). HA is an important component of the urothelium, and sodium hyaluronate is used to replenish bladder GAG when treating IC/PBS. Hyaluronic acid inhibits leukocyte aggregation and migration, and adherence of immune complexes to polymorphonuclear cells.[57, 58] From a clinical study involving 48 patients, it was evident that intravesical heparin (104 units/10 mL sterile water, three times a week for 3 months) controlled symptoms of IC/BPS with continued improvement even after 1 year of therapy. When used in conjunction with hydrodistention therapy, both HA and heparin prolonged the beneficial effects of hydrodistention in patients with a small functional bladder capacity. HA was found to be more effective compared with heparin. In contrast to no improvement in the control group, there was a significantly higher rate of improvement at 6 and 9 months in the HA group relative to the heparin group (50% vs 20%, P < 0.05). Improvements in the number of times of voiding per day (−1.8 ± 2.5, P < 0.01), a visual analog scale (−0.9 ± 1.1, P < 0.01) and bladder capacity (16 ± 18 mL, P < 0.01) were more significant in the HA group at 9 months relative to no improvement in the heparin group. Hauser et al. investigated CS binding to the bladder urothelium in a mouse model of urothelial acid damage. CS was labeled with Texas red, and the efficacy of restoring the barrier function was determined using intravesically instilled 45Rb, a potassium ion mimetic, through the urothelium into the bloodstream. The results showed that CS preferentially binds to damaged urothelium and restores the impermeability barrier. Maximum efficacy was achieved with a dose of 400 mg CS per instillation.
Table 2. Summary of current intravesical agents
Clinical testing in progress
Clinical testing in progress
Clinical testing in progress
Clinical testing in progress
Clinical testing in progress
Clinical testing in progress
Clinical testing in progress
Clinical testing in progress
Clinical testing in progress
DMSO for IC/BPS
A 50% aqueous solution of DMSO (RIMSO-50) is widely used to treat IC/BPS because of its analgesic, anti-inflammatory and muscle-relaxant properties. DMSO might influence conduction and neurotransmission in sensory nerves.[63-66] DMSO has been recommended for relieving symptoms or urgency and pain in IC/BPS. Intravesical instillation of DMSO in animal models showed direct correlations of the drug concentration and contact time with the bladder with the anti-inflammatory effects without a change in the bladder capacity or systemic toxicity. DMSO can penetrate tissues without damaging them and is used to enhance the transport of chemotherapeutic drugs, such as cisplatin, doxorubicin and pirarubicin into bladder tumors.
Drug cocktails for IC/BPS
Because of the multifactorial nature of IC/BPS, combination therapy utilizing drugs with different mechanisms of action is a reasonable approach. Parsons et al. showed the effect of mixing different ratios of heparin with lidocaine in drug cocktails for patients with IC/BPS. Relief from symptoms 2 weeks after treatment suggested that the efficacy was retained beyond the duration of the local anesthetic activity of lidocaine. With the recent outbreak of fungal infection from compounding pharmacy in the USA, caution should be practiced in mixing up our drug compound in a doctor's own office or in a compounding pharmacy when not regulated by state or federal drug regulatory agencies.
Vanilloids for IC/BPS
Compounds related to capsaicin and an ultrapotent analogue, RTX, collectively referred to as vanilloids, interact at a specific membrane recognition site (the vanilloid receptor) expressed almost exclusively by primary sensory neurons involved in nociception and neurogenic inflammation. Vanilloids are used to downregulate sensory nerves in the bladder, thereby mitigating the pain response. RTX is an ultrapotent analog of capsaicin that might have improved tolerability and enhanced efficacy compared with capsaicin. RTX resulted in a more favorable ratio of desensitization to initial excitation compared with capsaicin in animal models of pain behavior. In a rat model, intravesical RTX (0.01 μmol/L) reversibly desensitized bladder afferents for 3 weeks, and a 0.1-μmol/L dose resulted in sustained desensitization for at least 4 weeks. In patients with neurogenic bladder, intravesical RTX and capsaicin both showed efficacy, with RTX better tolerated. Unfortunately, randomized clinical trials did not show a benefit of RTX for IC/BPS, and instillation pain was bothersome and commercial development has been stopped.[72, 73]
Intravesical antimuscarinics for OAB
Recent reports showed that intravesically administered anticholinergic agents, apart from blocking muscarinic receptors in the bladder, might also act by blocking the bladder-cooling reflex mediated by C-fibers with an incomplete neurogenic lesion and detrusor overactivity. Intravesical oxybutynin (1.25 mg/5 mL, twice a day) was shown to be a relatively safe and effective therapeutic option for children with neurogenic bladders who experienced intolerable side-effects or were unresponsive to oral antimuscranics. Intravesical delivery of oxybutynin was proven to be suitable for patients who have an overactive bladder and suffer from side-effects of the metabolite, N-desethyl-oxybutynin, after per-oral administration.[76, 77]
Botulinum toxin for OAB and IC/BPS
The use of botulinum neurotoxin to treat lower urinary tract dysfunction has expanded in recent years, and the off-license usage list includes IC/BPS, neurogenic detrusor overactivity, idiopathic detrusor overactivity and lower urinary tract symptoms resulting from bladder outflow obstruction. There are several commonly used preparations of botulinum toxins (Table 3). Onabotulinumtoxin A, the most commonly used toxin, clinically acts by cleaving the soluble N-ethylmaleimide-sensitive fusion attachment protein receptor protein, SNAP-25, and inhibiting release of various neurotransmitters at the presynaptic vesicle by binding to the synaptic vesicle protein, SV2, during neurotransmitter exocytosis. Botulinum toxin was successfully used to treat IC/BPS and OAB through a cystoscopically-guided injection. However, instillation of this high-molecular-weight toxin has to be localized, because any systemic absorption can prove fatal. Pretreatment of the urothelium with protamine sulfate to improve the permeability to botulinum toxin was attempted in rats. The cationic protamine sulfate interacts with the anionic GAG layer, leading to a slight increase in permeability of the urothelium. Instillation of neurotoxins into the bladder, especially with liposomal formulation, is an exciting approach to achieving chemical neuromodulation of neurotransmission underlying IC/BPS and OAB.
Table 3. Currently marketed botulinum toxins
-Myobloc is the brand name in the USA, Canada and Korea. Neurobioc is the brand name in the European Union, Iceland and Norway.
Tacrolimus (FK506) is a potent hydrophobic immunosuppressive agent that hinders interleukin-2-dependent T cell activation by inhibiting calcineurin phosphatase. Tacrolimus has a direct inhibitory effect on cell-mediated immunity, but its systemic administration is limited by the high incidence of severe adverse effects, including nephrotoxicity and hypertension. Site-specific tacrolimus treatment was shown to have efficacy as an ointment or lotion formulation against inflammatory skin conditions without systemic side-effects.
The restriction of immune response mechanisms to the targeted site or organ by topical therapy of potent immunosuppressive drugs prompted us to investigate the bladder instillation of tacrolimus in the treatment of sterile hemorrhagic cystitis. Delivery of tacrolimus in the bladder faces hindrance because of its poor aqueous solubility. Liposomes were used in the past as pharmaceutical nanocarriers to deliver poorly water-soluble drugs. Liposomes are vesicles composed of concentric phospholipid bilayers separated by aqueous compartments. Liposomes can serve as vehicles for drug and gene delivery, because they adsorb to cell surfaces and fuse with cells. The ability of liposomes to form a molecular film on cell surfaces has encouraged their use in the healing of wounds and injured uroepithelium.[6, 23]
We have shown that intravesical lipo-tacrolimus treatment attenuated hemorrhage, inflammatory reaction and overactive micturition pattern in CYP-induced hemorrhagic cystitis. Subsequently, we observed that although tacrolimus after bladder instillation showed a higher drug exposure in the serum, the liposomal tacrolimus inversed this phenomenon in favor of increased drug concentration in the urine and bladder tissue. Reduced systemic exposure caused by liposome encapsulation is also evident from the 2.5-fold lower serum levels at 1 h in the lipo-tacrolimus group. Tissue pharmacokinetics showed that tacrolimus was retained in the bladder tissue up to 24 h in all groups without any significant difference in the area under the curve values. Reduced infiltration of mononuclear inflammatory cells in histopathology of normal rats after instillation of lipo-tacrolimus further shows the superior tissue safety afforded by liposomes over alcoholic solution of tacrolimus. Contrary to alcohol, liposomes do not irritate the epithelial surfaces and do not induce inflammatory reaction. Intravesical lipo-tacrolimus possess the desirable attributes of higher residence in bladder, retention in urine, and significantly reduced systemic exposure of instilled tacrolimus and its resultant toxicity. Intravesical liposomal delivery of tacrolimus significantly inhibited CYP-induced inflammatory hemorrhagic cystitis in rats, and is a promising approach toward orphan drug indication for hemorrhagic cystitis as a result of chemotherapy and radiation.
Future research and development of novel drug delivery systems as a delivery platform for intravesical administration of drugs can improve the efficacy and safety of pharmacotherapy for dysfunctional bladder. The recent promising results in the field of nanotechnology bring this mode of therapy to the forefront as a new hope for disease management in the lower urinary tract.
Conflict of interest
Y-C Chuang is a consultant for Allergan, Lipella and Pfizer. MB Chancellor is a consultant for Allergan, Astellas, Cook, Lipella, Merck, Pfizer and Targacept.