Design, synthesis, and biological evaluation of N-(4-substituted)-3-phenylisoxazolo[5,4-d]pyrimidin-4-amine derivatives as apoptosis-inducing cytotoxic agents

Selective isoxazolopyrimidine PAT1 (SLC26A6) inhibitors for therapy of intestinal disorders

A loss of prosecretory Cl- channel CFTR activity in the intestine is considered as the key cause of gastrointestinal problems in cystic fibrosis (CF): meconium ileus, distal intestinal obstruction syndrome (DIOS) and constipation. Since CFTR modulators have minimal effects on gastrointestinal symptoms, there is an unmet need for novel treatments for CF-associated gastrointestinal disorders. Meconium ileus and DIOS mainly affect the ileum (distal small intestine). SLC26A6 (putative anion transporter 1, PAT1) is a Cl-/HCO3- exchanger at the luminal membrane of small intestinal epithelial cells which facilitates Cl- and fluid absorption. We recently identified first-in-class PAT1 inhibitors by high-throughput screening. Isoxazolopyrimidine PAT1inh-A01 was a hit compound, which had low potency (IC50 5.2 μM) for SLC26A6 inhibition precluding further preclinical development. Here we performed structure-activity relationship studies to optimize isoxazolopyrimidine SLC26A6 inhibitors and tested a potent inhibitor in mouse models of intestinal fluid absorption. Structure-activity studies of 377 isoxazolopyrimidine analogs identified PAT1inh-A0030 (ethyl 4-(benzyl(methyl)amino)-3-methylisoxazolo[5,4-d]pyrimidine-6-carboxylate) as the most potent SLC26A6 inhibitor with a 1.0 μM IC50. Selectivity studies showed that PAT1inh-A030 has no activity on relevant ion transporters/channels (SLC26A3, SLC26A4, SLC26A9, CFTR, TMEM16A). In a closed-loop model of intestinal fluid absorption, intraluminal PAT1inh-A0030 treatment inhibited fluid absorption in the ileum of wild-type and CF mice (CftrdelF508/delF508) with >90% prevention of a decrease in loop fluid volume and loop weight/length ratio at 30 minutes. These results suggest that SLC26A6 is the key transporter mediating Cl- and fluid absorption in the ileum and SLC26A6 inhibitors are novel drug candidates for treatment of CF-associated small intestinal disorders.

Quality by Design steered Development of Niclosamide Loaded Liposomal Thermogel for Melanoma: In vitro and Ex vivo Evaluation

Melanoma is the most malignant form of skin cancer across the globe. Conventional therapies are currently ineffective which could be attributed to the rampant chemo-resistance, metastasis, inability to cross the skin barriers and accumulate within the tumor microenvironment. This advent brings in the principles of drug repurposing by repositioning Niclosamide (NIC), an anthelmintic drug for skin cancer. Incorporation into the liposomes facilitated enhanced melanoma cell uptake and apoptosis. Cytotoxicity studies revealed 1.756-fold enhancement in SK-MEL-28 cytotoxicity by NIC-loaded liposomes compared to free drug. Qualitative and quantitative cell internalization indicated greater drug uptake within the melanoma cells illustrating the efficacy of liposomes as efficient carrier systems. Nuclear staining showed blebbing and membrane shrinkage. Elevated ROS levels and apoptosis shown by DCFDA and acridine orange-ethidium bromide staining revealed greater melanoma cell death by liposomes compared to free drug. Incorporating NIC liposomes into the thermogel system restricted the liposomes as a depot onto the upper skin layers. Sustained zero order release up to 48 h with liposomes and 23.58-fold increase in viscosity led to the sol-to-gel transition at 33℃ was observed with liposomal thermogel. Ex vivo gel permeation studies revealed that C-6 loaded liposomes incorporated within the thermogel successfully formed a depot over the upper skin layer for 6 h to prevent transdermal delivery and systemic adverse effects. Thus, it could be concluded that NIC loaded liposomal thermogel system could be an efficacious therapeutic alternative for the management of melanoma.

An Overview of the Biological Evaluation of Selected Nitrogen-Containing Heterocycle Medicinal Chemistry Compounds

Heterocyclic compounds are a class of compounds of natural origin with favorable properties and hence have major pharmaceutical significance. They have an exceptional adroitness favoring their use as diverse smart biomimetics, in addition to possessing an active pharmacophore in a complex structure. This has made them an indispensable motif in the drug discovery field. Heterocyclic compounds are usually classified according to the ring size, type, and the number of heteroatoms present in the ring. Among different heterocyclic ring systems, nitrogen heterocyclic compounds are more abundant in nature. They also have considerable pharmacological significance. This review highlights recent pioneering studies in the biological assessment of nitrogen-containing compounds, namely: triazoles, tetrazoles, imidazole/benzimidazoles, pyrimidines, and quinolines. It explores publications between April 2020 and February 2022 and will benefit researchers in medicinal chemistry and pharmacology. The present work is organized based on the size of the heterocyclic ring.