We have previously evaluated and reported numerous classes of linear and cyclic peptides containing hydrophobic and hydrophilic segments for intracellular delivery of multiple molecular cargos. Herein, a combination of histidine and tryptophan amino acids were designed and evaluated for their efficiency in intracellular delivery of cell-impermeable phosphopeptides and the anti-HIV drug, emtricitabine. Two new decapeptides, with linear and cyclic natures, both containing alternate tryptophan and histidine residues, were synthesized using Fmoc/tBu solid-phase chemistry. The peptides were characterized and purified by using matrix-assisted laser desorption/ionization (MALDI) spectroscopy and high-performance liquid chromatography (HPLC), respectively. These peptides did not show significant toxicity up to 100 µM in ovarian cancer (SK-OV-3) and leukemia cancer (CCRF-CEM) cells. Furthermore, the cellular uptake of a fluorescence (F’)-labeled cell-impermeable phosphopeptide (F’-GpYEEI) was enhanced in the presence of linear (WH)₅ and cyclic [WH]₅ by 2- and 8-fold, respectively, compared to the uptake of the phosphopeptide alone. The cellular uptake was not significantly changed in the presence of endocytosis inhibitors. Furthermore, the intracellular uptake of the fluorescently-labeled anti-HIV drug, emtricitabine (F’-FTC), by linear (WH)₅ and cyclic [WH]₅ in SK-OV-3 cancer cell lines was found to be enhanced by 3.5- and 9-fold, respectively, compared to that of the drug alone. Fluorescent uptake experiments confirmed the localization of F’-GpYEEI-loaded cyclic [WH]₅ intracellularly in the SK-OV-3 cancer cell line after 3 h of incubation. Thus, these data demonstrated that [WH]₅ containing tryptophan and histidine enhanced the cellular uptake of F’-GpYEEI and emtricitabine.

Obstructive airway diseases, including asthma and chronic obstructive pulmonary disease (COPD), evoke significant global health concerns manifested by airway inflammation and obstruction. Despite their differing origins, shared pathophysiological features and responses to therapeutic interventions highlight common molecular mechanisms. Standard treatments include inhaled bronchodilators, with combination therapies offering enhanced symptom control. Cyclic AMP (cAMP) plays a crucial role in airway relaxation. Phosphodiesterase (PDE) decreases cAMP levels, thereby attenuating the relaxation of airway smooth muscle, making it a promising therapeutic target. The balance between cAMP production and degradation is essential for regulating airway tone and function. PDE inhibitors for the treatment of obstructive airway diseases have suffered challenges, with adverse side effects of prospective inhibitors causing clinical failures. Efforts to develop PDE inhibitors with an improved safety profile could prove to be beneficial as an add-on treatment for severe asthma and COPD. The recent FDA approval of Ensifentrine, a dual PDE3/4 inhibitor, can significantly advance COPD management by improving bronchodilation, reducing inflammation, and lowering exacerbation rates with favorable safety outcomes.

Sympathetic stimulation produces beneficial changes in cardiac function through β-adrenergic receptor (βAR) production of cAMP and subsequent alteration of electrical and mechanical activity. Long term activation of cAMP production also contributes to cardiac remodeling and detrimental changes associated with heart failure. However, sympathetic responses are mediated by the endogenous neurotransmitter norepinephrine (NE), which is also a potent α ₁ -adrenergic receptor (α ₁ AR) agonist, and α ₁ AR activation can produce significant effects on the heart as well. What is less clear is how α ₁ - and β-adrenergic responses interact with one another. Previous studies have demonstrated that α ₁ AR activation can inhibit β-adrenergic regulation of electrical and mechanical activity of cardiac myocytes, although the signaling mechanisms involved were not previously known. In the present study, we used FRET-based biosensors in adult rat ventricular myocytes to demonstrate that this crosstalk effect involves inhibition of cAMP production by nuclear α _1A ARs acting on βARs found on the plasma membrane. Furthermore, we established that this inside-out signaling mechanism involves a mitogen-activated protein kinase (MAPK) pathway that uncouples βARs from downstream signaling in a G protein coupled receptor kinase (GRK)/arrestin-dependent manner. These results reveal a novel, non-canonical signaling mechanism contributing to α ₁ AR responses in the heart, and that this effect limits βAR production of cAMP by NE. This mechanism may contribute to the cardioprotective effect previously ascribed to α _1A AR activation. These findings also clearly demonstrate the importance of considering the contributions of α ₁ and βARs together when studying the influence of the sympathetic nervous system on the heart.