LSD1 inhibition suppresses ASCL1 and de-represses YAP1 to drive potent activity against neuroendocrine prostate cancer

Lysine-specific demethylase 1 (LSD1 or KDM1A ) has emerged as a critical mediator of tumor progression in metastatic castration-resistant prostate cancer (mCRPC). Among mCRPC subtypes, neuroendocrine prostate cancer (NEPC) is an exceptionally aggressive variant driven by lineage plasticity, an adaptive resistance mechanism to androgen receptor axis-targeted therapies. Our study shows that LSD1 expression is elevated in NEPC and associated with unfavorable clinical outcomes. Using genetic approaches, we validated the on-target effects of LSD1 inhibition across various models. We investigated the therapeutic potential of bomedemstat, an orally bioavailable, irreversible LSD1 inhibitor with low nanomolar potency. Our findings demonstrate potent antitumor activity against CRPC models, including tumor regressions in NEPC patient-derived xenografts. Mechanistically, our study uncovers that LSD1 inhibition suppresses the neuronal transcriptional program by downregulating ASCL1 through disrupting LSD1:INSM1 interactions and de-repressing YAP1 silencing. Our data support the clinical development of LSD1 inhibitors for treating CRPC - especially the aggressive NE phenotype.

Statement of Significance

Neuroendocrine prostate cancer presents a clinical challenge due to the lack of effective treatments. Our research demonstrates that bomedemstat, a potent and selective LSD1 inhibitor, effectively combats neuroendocrine prostate cancer by downregulating the ASCL1- dependent NE transcriptional program and re-expressing YAP1.

Real-time feedback on nonverbal clinical communication. Theoretical framework and clinician acceptance of ambient visual design

INTRODUCTION

This article is part of the focus theme of Methods of Information in Medicine on "Pervasive Intelligent Technologies for Health".

BACKGROUND

Effective nonverbal communication between patients and clinicians fosters both the delivery of empathic patient-centered care and positive patient outcomes. Although nonverbal skill training is a recognized need, few efforts to enhance patient-clinician communication provide visual feedback on nonverbal aspects of the clinical encounter.

OBJECTIVES

We describe a novel approach that uses social signal processing technology (SSP) to capture nonverbal cues in real time and to display ambient visual feedback on control and affiliation--two primary, yet distinct dimensions of interpersonal nonverbal communication. To examine the design and clinician acceptance of ambient visual feedback on nonverbal communication, we 1) formulated a model of relational communication to ground SSP and 2) conducted a formative user study using mixed methods to explore the design of visual feedback.

METHODS

Based on a model of relational communication, we reviewed interpersonal communication research to map nonverbal cues to signals of affiliation and control evidenced in patient-clinician interaction. Corresponding with our formulation of this theoretical framework, we designed ambient real-time visualizations that reflect variations of affiliation and control. To explore clinicians' acceptance of this visual feedback, we conducted a lab study using the Wizard-of-Oz technique to simulate system use with 16 healthcare professionals. We followed up with seven of those participants through interviews to iterate on the design with a revised visualization that addressed emergent design considerations.

RESULTS

Ambient visual feedback on non- verbal communication provides a theoretically grounded and acceptable way to provide clinicians with awareness of their nonverbal communication style. We provide implications for the design of such visual feedback that encourages empathic patient-centered communication and include considerations of metaphor, color, size, position, and timing of feedback.

CONCLUSIONS

Ambient visual feedback from SSP holds promise as an acceptable means for facilitating empathic patient-centered nonverbal communication.

The effect of smoking on bone healing: A systematic review

Objectives

To review the systemic impact of smoking on bone healing as evidenced within the orthopaedic literature.

Methods

A protocol was established and studies were sourced from five electronic databases. Screening, data abstraction and quality assessment was conducted by two review authors. Prospective and retrospective clinical studies were included. The primary outcome measures were based on clinical and/or radiological indicators of bone healing. This review specifically focused on non-spinal orthopaedic studies.

Results

Nine tibia studies and eight other orthopaedic studies were considered for systematic review. Of these 17 studies, 13 concluded that smoking negatively influenced bone healing.

Conclusions

Smoking has a negative effect on bone healing, in terms of delayed union, nonunion and more complications.

Identification of novel ROCK inhibitors with anti-migratory and anti-invasive activities

ROCK1 and ROCK2 mediate important processes such as cell migration, invasion and metastasis; making them good targets for the development of antitumor agents. Recently, using a fragment-based approach and X-ray crystallography, we reported on the design and synthesis of novel Rho-kinase inhibitors (RKIs). Here, we selected a pair of RKIs, the closely-related structural analogues RKI-18 (potent; IC₅₀ values of 397 nM (ROCK1) and 349 nM (ROCK2)) and RKI-11 (weak/inactive; IC₅₀ values of 38 µM (ROCK1) and 45 µM (ROCK2), as chemical probes and determined their effects on cytoskeleton organization, signaling, apoptosis, anchorage-dependent and –independent growth, migration and invasion. RKI-18 but not RKI-11 suppresses potently the phosphorylation of the ROCK substrate MLC2 in intact human breast, lung, colon and prostate cancer cells. Furthermore, RKI-18 is highly selective at decreasing the levels of P-MLC2 over those of P-Akt, P-S6 and P-Erk ½. RKI-18 suppresses ROCK-mediated actin fiber formation following stimulation with LPA as well as PAK-mediated lamelipodia and filopodia formation following bradykinin or PDGF stimulation. Furthermore, RKI-18 but not RKI-11 inhibits migration, invasion and anchorage-independent growth of human breast cancer cells. The fact that the active ROCK inhibitor RKI-18 but not the inactive closely related structural analogue RKI-11 is effective at suppressing malignant transformation suggests that inhibition of ROCK with RKI-18 results in preventing migration, invasion and anchorage-independent growth. The potential of this class of RKIs as anti tumor agents warrants further advanced preclinical studies.

Design, synthesis, and biological evaluation of triazolopiperazine-based β-amino amides as potent, orally active dipeptidyl peptidase IV (DPP-4) inhibitors

Various beta-amino amides containing triazolopiperazine heterocycles have been prepared and evaluated as potent, selective, orally active dipeptidyl peptidase IV (DPP-4) inhibitors. These compounds display excellent oral bioavailability and good overall pharmacokinetic profiles in preclinical species. Moreover, in vivo efficacy in an oral glucose tolerance test in lean mice is demonstrated.

Imidazopiperidine amides as dipeptidyl peptidase IV inhibitors for the treatment of diabetes

A series of substituted imidazopiperidine amides has been prepared and evaluated for inhibition of dipeptidyl peptidase IV (DPP-4). Substitution at the 1- and 3-positions produced increased selectivity for DPP-4 relative to DPP-8 and DPP-9. Compounds in this series had IC(50) values as low as 5.8 nM for inhibition of DPP-4.

4-Arylcyclohexylalanine analogs as potent, selective, and orally active inhibitors of dipeptidyl peptidase IV

A novel series of 4-arylcyclohexylalanine DPP-4 inhibitors was synthesized and tested for inhibitory activity as well as selectivity over the related proline-specific enzymes DPP-8 and DPP-9. Optimization of this series led to 28 (DPP-4 IC(50)=4.8 nM), which showed an excellent pharmacokinetic profile across several preclinical species. Evaluation of 28 in an oral glucose tolerance test demonstrated that this compound effectively reduced glucose excursion in lean mice.

Discovery of 3-aminopiperidines as potent, selective, and orally bioavailable dipeptidyl peptidase IV inhibitors

Substituted 3-aminopiperidines 3 were evaluated as DPP-4 inhibitors. The inhibitors showed good DPP-4 potency with superb selectivity over other peptidases (QPP, DPP8, and DPP9). Selected DPP-4 inhibitors were further evaluated for their hERG potassium channel, calcium channel, Cyp2D6, and pharmacokinetic profiles.

Triazolopiperazine-amides as dipeptidyl peptidase IV inhibitors: Close analogs of JANUVIA™ (sitagliptin phosphate)

A series of beta-aminoamides bearing triazolopiperazines has been prepared and evaluated as potent, selective, orally active dipeptidyl peptidase IV (DPP-4) inhibitors. Efforts at optimization of the beta-aminoamide series, which ultimately led to the discovery of JANUVIA (sitagliptin phosphate, compound 1), are described.

4-Aminophenylalanine and 4-aminocyclohexylalanine derivatives as potent, selective, and orally bioavailable inhibitors of dipeptidyl peptidase IV

A novel series of 4-aminophenylalanine and 4-aminocyclohexylalanine derivatives were designed and evaluated as inhibitors of dipeptidyl peptidase IV (DPP-4). The phenylalanine series afforded compounds such as 10 that were potent and selective (DPP-4, IC(50)=28nM), but exhibited limited oral bioavailability. The corresponding cyclohexylalanine derivatives such as 25 afforded improved PK exposure and efficacy in a murine OGTT experiment. The X-ray crystal structure of 25 bound to the DPP-4 active site is presented.

Discovery of potent, selective, and orally bioavailable oxadiazole-based dipeptidyl peptidase IV inhibitors

A novel series of oxadiazole based amides have been shown to be potent DPP-4 inhibitors. The optimized compound 43 exhibited excellent selectivity over a variety of DPP-4 homologs.

(2S,3S)-3-Amino-4-(3,3-difluoropyrrolidin-1-yl)-N,N-dimethyl-4-oxo-2-(4-[1,2,4]triazolo[1,5-a]-pyridin-6-ylphenyl)butanamide: a selective alpha-amino amide dipeptidyl peptidase IV inhibitor for the treatment of type 2 diabetes

A series of beta-substituted biarylphenylalanine amides were synthesized and evaluated as inhibitors of dipeptidyl peptidase IV (DPP-4) for the treatment of type 2 diabetes. Optimization of the metabolic profile of early analogues led to the discovery of (2S,3S)-3-amino-4-(3,3-difluoropyrrolidin-1-yl)-N,N-dimethyl-4-oxo-2-(4-[1,2,4]triazolo[1,5-a]pyridin-6-ylphenyl)butanamide (6), a potent, orally active DPP-4 inhibitor (IC(50) = 6.3 nM) with excellent selectivity, oral bioavailability in preclinical species, and in vivo efficacy in animal models. Compound 6 was selected for further characterization as a potential new treatment for type 2 diabetes.

Discovery of potent, selective, and orally bioavailable pyridone-based dipeptidyl peptidase-4 inhibitors

anti-Substituted beta-methylphenylalanine derived amides have been shown to be potent DPP-IV inhibitors exhibiting excellent selectivity over both DPP8 and DPP9. The optimized compound exhibited good pharmacokinetic profiles in three preclinical species.

Dipeptidyl peptidase IV inhibition for the treatment of type 2 diabetes: potential importance of selectivity over dipeptidyl peptidases 8 and 9

Dipeptidyl peptidase (DPP)-IV inhibitors are a new approach to the treatment of type 2 diabetes. DPP-IV is a member of a family of serine peptidases that includes quiescent cell proline dipeptidase (QPP), DPP8, and DPP9; DPP-IV is a key regulator of incretin hormones, but the functions of other family members are unknown. To determine the importance of selective DPP-IV inhibition for the treatment of diabetes, we tested selective inhibitors of DPP-IV, DPP8/DPP9, or QPP in 2-week rat toxicity studies and in acute dog tolerability studies. In rats, the DPP8/9 inhibitor produced alopecia, thrombocytopenia, reticulocytopenia, enlarged spleen, multiorgan histopathological changes, and mortality. In dogs, the DPP8/9 inhibitor produced gastrointestinal toxicity. The QPP inhibitor produced reticulocytopenia in rats only, and no toxicities were noted in either species for the selective DPP-IV inhibitor. The DPP8/9 inhibitor was also shown to attenuate T-cell activation in human in vitro models; a selective DPP-IV inhibitor was inactive in these assays. Moreover, we found DPP-IV inhibitors that were previously reported to be active in models of immune function to be more potent inhibitors of DPP8/9. These results suggest that assessment of selectivity of potential clinical candidates may be important to an optimal safety profile for this new class of antihyperglycemic agents.

Discovery of potent and selective orally bioavailable β-substituted phenylalanine derived dipeptidyl peptidase IV inhibitors

anti-Substituted biaryl beta-methylphenylalanine derived amides have been shown to be potent DPP-IV inhibitors that suffer from suboptimal selectivity and pharmacokinetics. This letter describes the substitution of the beta-methyl substituent with beta-polar substituents, culminating in the discovery of a beta-dimethylamide substituted phenylalanine derivative with an excellent potency, selectivity, and pharmacokinetic profile.

Discovery of potent and selective phenylalanine based dipeptidyl peptidase IV inhibitors

anti-Substituted beta-methylphenylalanine derived amides have been shown to be potent DPP-IV inhibitors exhibiting excellent selectivity over both DPP8 and DPP9. These are among the most potent compounds reported to date lacking an electrophilic trap. The most potent compound among these is 5-oxo-1,2,4-oxadiazole 44, which is a 3 nM DPP-IV inhibitor.

Dipeptidyl peptidase IV inhibitors derived from β-aminoacylpiperidines bearing a fused thiazole, oxazole, isoxazole, or pyrazole

A series of beta-aminoacylpiperidines bearing various fused five-membered heterocyclic rings was synthesized as dipeptidyl peptidase IV inhibitors. Potent and relatively selective inhibition could be obtained, depending on choice of heterocycle, regioisomerism, and substitution. In particular, one analog (74, DPP-IV IC50=26 nM) exhibited good oral bioavailability and acceptable half-life in the rat, albeit with rather high clearance.

(2R)-4-oxo-4-[3-(trifluoromethyl)-5,6-dihydro[1,2,4]triazolo[4,3-a]pyrazin-7(8H)-yl]-1-(2,4,5-trifluorophenyl)butan-2-amine: a potent, orally active dipeptidyl peptidase IV inhibitor for the treatment of type 2 diabetes

A novel series of beta-amino amides incorporating fused heterocycles, i.e., triazolopiperazines, were synthesized and evaluated as inhibitors of dipeptidyl peptidase IV (DPP-IV) for the treatment of type 2 diabetes. (2R)-4-Oxo-4-[3-(trifluoromethyl)-5,6-dihydro[1,2,4]triazolo[4,3-a]pyrazin-7(8H)-yl]-1-(2,4,5-trifluorophenyl)butan-2-amine (1) is a potent, orally active DPP-IV inhibitor (IC(50) = 18 nM) with excellent selectivity over other proline-selective peptidases, oral bioavailability in preclinical species, and in vivo efficacy in animal models. MK-0431, the phosphate salt of compound 1, was selected for development as a potential new treatment for type 2 diabetes.

Potent and selective proline derived dipeptidyl peptidase IV inhibitors

In-house screening of the Merck sample collection identified proline derived homophenylalanine 3 as a DPP-IV inhibitor with modest potency (DPP-IV IC50=1.9 microM). Optimization of 3 led to compound 37, which is among the most potent and selective DPP-IV inhibitors discovered to date.

Substituted piperazines as novel dipeptidyl peptidase IV inhibitors

Incorporation of a fluorophenyl beta-amino amide moiety into piperazine screening lead 2 has resulted in the discovery of a structurally novel series of potent and selective DP-IV inhibitors. Simplification of the molecule and incorporation of multiple fluorine atoms on the phenyl ring has provided low molecular weight analogs such as compound 32, which is a 19nM DP-IV inhibitor with >4000-fold selectivity over QPP.

Discovery of potent and selective β-homophenylalanine based dipeptidyl peptidase IV inhibitors

Modification of in-house screening lead beta-aminoacyl proline 8 gave an equipotent thiazolidide 9. Extensive SAR studies on the phenyl ring of 9 led to the discovery of a novel series of potent and selective DP-IV inhibitors. Introduction of a fluorine at the 2-position proved to be crucial for the potency of this series. The 2,5-difluoro (22q) and 2,4,5-trifluoro (22t) analogues were potent inhibitors of DP-IV (IC(50)=270, 119nM, respectively).

Fluoropyrrolidine amides as dipeptidyl peptidase IV inhibitors

Amides derived from fluorinated pyrrolidines and 4-substituted cyclohexylglycine analogues have been prepared and evaluated as inhibitors of dipeptidyl dipeptidase IV (DP-IV). Analogues which incorporated (S)-3-fluoropyrrolidine showed good selectivity for DP-IV over quiescent cell proline dipeptidase (QPP). Compound 48 had good pharmacokinetic properties and was orally active in an oral glucose tolerance test in lean mice.

Diastereoselective synthesis and configuration-dependent activity of (3-substituted-cycloalkyl)glycine pyrrolidides and thiazolidides as dipeptidyl peptidase IV inhibitors

A diastereoselective synthesis was used to prepare a series of (3-substituted-cyclopentyl and -cyclohexyl)glycine pyrrolidides and thiazolidides. The three chiral centers were generated in an unambiguous, stereochemically defined manner. Inhibitory activity was dependent on the configuration at each stereocenter and on the nature of the 3-substituent. In the cyclopentylglycine pyrrolidide series, high potency against dipeptidyl peptidase IV and good selectivity could be achieved.

4-Amino cyclohexylglycine analogues as potent dipeptidyl peptidase IV inhibitors

Substituted 4-amino cyclohexylglycine analogues were evaluated for DP-IV inhibitory properties. Bis-sulfonamide 15e was an extremely potent 2.6 nM inhibitor of the enzyme with excellent selectivity over all counterscreens. 2,4-difluorobenzenesulfonamide 15b and 1-naphthyl amide 16b, however, combined an acceptable in vitro profile with good pharmacokinetic properties in the rat, and 15b was orally efficacious at 3 mpk in an OGTT in lean mice.

Catalytic properties and inhibition of proline-specific dipeptidyl peptidases II, IV and VII

There is currently intense interest in the emerging group of proline-specific dipeptidases, and their roles in the regulation of biological processes. Dipeptidyl peptidase IV (DPP-IV) is involved in glucose metabolism by contributing to the regulation of glucagon family peptides and has emerged as a potential target for the treatment of metabolic diseases. Two other proline-specific dipeptidases, DPP-VII (also known as quiescent cell proline dipeptidase) and DPP-II, have unknown functions and have recently been suggested to be identical proteases based on a sequence comparison of human DPP-VII and rat DPP-II (78% identity) [Araki, Li, Yamamoto, Haneda, Nishi, Kikkawa and Ohkubo (2001) J. Biochem. 129, 279-288; Fukasawa, Fukasawa, Higaki, Shiina, Ohno, Ito, Otogoto and Ota (2001) Biochem. J. 353, 283-290]. To facilitate the identification of selective substrates and inhibitors for these enzymes, a complete biochemical profile of these enzymes was obtained. The pH profiles, substrate specificities as determined by positional scanning, Michaelis-Menten constants and inhibition profiles for DPP-VII and DPP-II were shown to be virtually identical, strongly supporting the hypothesis that they are the same protease. In addition, substrate specificities, catalytic constants and IC(50) values were shown to be markedly different from those of DPP-IV. Selective DPP-IV and DPP-VII substrates were identified and they can be used to design selective inhibitors and probe further into the biology of these enzymes.

Hypersensitivity pneumonitis: patterns on high-resolution CT

Hypersensitivity pneumonitis, also known as extrinsic allergic alveolitis, is caused by inhalation of specific environmental organic antigens. This disease may have typical high-resolution CT findings that, in the appropriate clinical setting, can be sufficiently characteristic to allow a confident diagnosis without the need for a lung biopsy. In this pictorial essay, the high-resolution CT patterns of hypersensitivity pneumonitis are illustrated. The authors emphasize the correlation among the radiologic presentation, functional abnormalities, and pathologic findings.

Helical CT for the evaluation of suspected acute pulmonary embolism: diagnostic pitfalls

Helical CT is being increasingly utilized for the evaluation of suspected pulmonary embolism (PE). Proper scan interpretation depends on the awareness of several diagnostic pitfalls that may simulate PE, including normal bronchovascular structures such as pulmonary veins, bronchi, and lymph nodes, technical considerations such as improper bolus timing and streak artifacts, and patient-related factors such as motion artifacts, pulmonary arterial catheters, and vascular shunts. An understanding of these pitfalls facilitates accurate diagnosis.

Preliminary experience with use of a selective 5HT3 receptor antagonist (ondansetron) to prevent high dose chemotherapy induced emesis

Ondansetron was used as an antiemetic along with dexamethasone during 16 cycles of highly or moderately ematogenic chemotherapy. There was major control in two cycles and complete control in the remaining 14. Side effects were minor and did not require discontinuation of the drug. This combination, therefore, appears to be safe and effective in preventing chemotherapy induced emesis.

Insulin stimulates phosphatidylinositol 3-kinase activity in rat neuronal primary cultures

We investigated the effect of insulin on phosphatidylinositol (PtdIns) 3-kinase (PtdIns 3-kinase) activity in neuronal cultures to determine if this enzyme is involved with the neurotrophic actions of insulin. Insulin caused a concentration-dependent increase in PtdIns 3-kinase activity in anti-phosphotyrosine immunoprecipitates. The kinase activity was able to phosphorylate PtdIns, PtdIns 4-phosphate, and PtdIns 4,5-bisphosphate. In intact neurons, a 10-min 1 mM insulin treatment in the presence of [32P]orthophosphate increased the levels of both 3-[32P]PtdIns phosphate and 3,4-[32P]PtdIns bisphosphate by 55 and 193%, respectively. This increase was associated with an increase in neurite outgrowth mediated by insulin. Our results indicate that insulin treatment of neuronal cells in primary culture increases PtdIns 3-kinase activity and the formation of the unique D-3-phosphorylated phosphoinositides, suggesting that growth factor-mediated neuronal growth may include the formation of novel phosphoinositide 3-phosphate phospholipids.

Epstein-Barr virus infectivity of Raji and Molt 4 cells: differences in cellular membrane lipids and apparent microviscosity

Infection of lymphocytes by the Epstein-Barr virus (EBV) is initiated by attachment of the major virus glycoprotein gp350/220 to a cell surface glycoprotein, known as CR2 (CD21). In a productive infection the virus envelope fuses with host cell membranes either at the cell surface or within endocytic vesicles. To investigate the relevance of host cell membrane properties in the fusion process, we used the lymphoblastoid cell lines Raji and Molt 4. Both cell lines express CR2 and bind EBV; however, only the Raji cell supports virus-cell fusion. Lipid analysis of the two cell lines indicated that Raji cells had a significantly lower cholesterol to phospholipid molar ratio due to a greater membrane content of phospholipid relative to protein. Determination of cell membrane fluid dynamics by fluorescence polarization indicated that the apparent membrane microviscosity of Molt 4 cells was significantly greater than that of Raji. Increasing Raji cell membrane apparent microviscosity to values similar to those of Molt 4 cells by incubation with cholesteryl-hemisuccinate caused a reduction in EBV fusion with Raji cells. However, experiments designed to allow EBV infection of Molt 4 cells whose plasma membranes had been fluidized were unsuccessful. These studies suggest that the lipid composition and other as yet unidentified factors are involved in entry of EBV into cells.

Bayesian forecasting of serum lithium concentrations. Comparison with traditional methods

Twelve pharmacokinetic methods of estimating lithium maintenance dosage requirements were compared in 21 patients with bipolar illness. Methods which were compared included the single- and multiple-point methods of Perry, 4 non-linear regression and 6 Bayesian methods. The REVOL algorithm was employed for converging on to estimates of clearance and apparent volume of distribution for the non-linear regression and Bayesian methods. Data analysis was based on an evaluation of prediction error as a measure of bias, and absolute prediction error as a measure of precision. In a direct comparison, there were no statistically significant differences in bias or precision between any of the methods.

Comparison of pharmacokinetic procedures for dosing lithium based on analysis of prediction error

Five pharmacokinetic methods for estimating maintenance dosage requirements of lithium carbonate were compared retrospectively in 20 inpatients with acute bipolar illness. Specific pharmacokinetic methods tested included the method of Cooper, the multiple-point method of Perry, the single-point method of Perry, the method of Zetin, and the method of Pepin. Data analysis was based on evaluation of prediction error or the difference between the predicted steady-state lithium concentration and the measured steady-state lithium concentration at equivalent daily doses. Each dosing method was assessed in regard to accuracy and bias of predicted steady-state serum lithium concentrations. Bias was assessed by comparison of the median value of the prediction error with zero. The dosing recommendation based on the Cooper nomogram resulted in a significant positive bias (p less than or equal to 0.05). Intermethod accuracy was assessed by comparison of the absolute prediction errors of each dosing method. Significant differences in accuracy were observed between the method of Pepin when compared with the single-point method of Perry (p less than or equal to 0.05, k-sample sign test). All other comparisons were nonsignificant.

Transdermal delivery of isoproterenol HCl: an investigation of stability, solubility, partition coefficient, and vehicle effects

Effects of solubility, partition coefficient, and selected adjuvants (propylene glycol and Azone) on percutaneous penetration of isoproterenol HCl have been investigated using human cadaver skin. Isoproterenol was found to be stable (less than 1% decomposition) for 24 hr at 22 +/- 0.5 degrees C in the pH range 1 to 7 in the following solvents: water, normal saline, propylene glycol and a series of propylene glycol-water mixtures (10, 20, 40, and 60%; v/v); however, decomposition was significant beyond pH 8. In normal saline, the rate of decomposition increased significantly with an increase in temperature to 37 degrees C. The solubility of isoproterenol HCl decreased and its skin/vehicle partition coefficient increased with increasing proportions of propylene glycol in the vehicle, while the product of the solubility and partition coefficient appeared to plateau at 20% propylene glycol in water. Optimal penetration enhancing effects of Azone were seen when incorporated at a concentration of 1% (v/v) in the 20% (v/v) propylene glycol-water blend and, more significantly, when skin was pretreated with pure Azone for 60 min prior to application of the drug formulation.