A new bispyrroloiminoquinone alkaloid, tsitsikammamine C (1), displayed potent in vitro antimalarial activity with IC50 values of 13 and 18 nM against chloroquine-sensitive (3D7) and ...chloroquine-resistant (Dd2) Plasmodium falciparum, respectively. Tsitsikammamine C (1) displayed selectivity indices of >200 against HEK293 cells and inhibited both ring and trophozoite stages of the malaria parasite life cycle. Previously reported compounds makaluvamines J (2), G (3), L (4), K (5) and damirones A (6) and B (7) were also isolated from the same marine sponge (Zyzzya sp.). Compounds 2–4 displayed potent growth inhibitory activity (IC50 < 100 nM) against both P. falciparum lines and only moderate cytotoxicity against HEK293 cells (IC50 = 1–4 μM). Makaluvamine G (3) was not toxic to mice and suppressed parasite growth in P. berghei infected mice following subcutaneous administration at 8 mg kg–1 day–1.
Drug therapy is the mainstay of antimalarial therapy, yet current drugs are threatened by the development of resistance. In an effort to identify new potential antimalarials, we have undertaken a ...lead optimization program around our previously identified triazolopyrimidine-based series of Plasmodium falciparum dihydroorotate dehydrogenase (PfDHODH) inhibitors. The X-ray structure of PfDHODH was used to inform the medicinal chemistry program allowing the identification of a potent and selective inhibitor (DSM265) that acts through DHODH inhibition to kill both sensitive and drug resistant strains of the parasite. This compound has similar potency to chloroquine in the humanized SCID mouse P. falciparum model, can be synthesized by a simple route, and rodent pharmacokinetic studies demonstrated it has excellent oral bioavailability, a long half-life and low clearance. These studies have identified the first candidate in the triazolopyrimidine series to meet previously established progression criteria for efficacy and ADME properties, justifying further development of this compound toward clinical candidate status.
Lipid-based delivery systems are finding increasing application in the oral delivery of poorly water-soluble, lipophilic drugs. Whilst lipidic dose forms may improve oral bioavailability via several ...mechanisms, enhancement of gastrointestinal solubilisation remains argueably the most important method of absorption enhancement. This review firstly describes the mechanistic rationale which underpins the use of lipid-based delivery systems to enhance drug solubilisation and briefly reviews the available literature describing increases in oral bioavailability after the administration of lipid solution, suspension and self-emulsifying formulations. The use of
in vitro methods including dispersion tests and more complex models of
in vitro lipolysis as indicators of potential
in vivo performace are subsequently described, with particular focus on recent data which suggests that the digestion of surfactants present in lipid-based formulations may impact on formulation performance. Finally, a series of seven guiding principles for formulation design of lipid-based delivery systems are suggested based on an analysis of recent data generated in our laboratories and elsewhere.
After oral administration, the majority of drug molecules are absorbed across the small intestine and enter the systemic circulation via the portal vein and the liver. For some highly lipophilic ...drugs (typically log
P
>
5, lipid solubility
>
50 mg/g), however, association with lymph lipoproteins in the enterocyte leads to transport to the systemic circulation via the intestinal lymph. The attendant delivery benefits associated with lymphatic drug transport include a reduction in first-pass metabolism and lymphatic exposure to drug concentrations orders of magnitude higher than that attained in systemic blood. In the current review we briefly describe the mechanisms by which drug molecules access the lymph and the formulation strategies that may be utilised to enhance lymphatic drug transport. Specific focus is directed toward recent advances in understanding regarding the impact of lipid source (both endogenous and exogenous) and intracellular lipid trafficking pathways on lymphatic drug transport and enterocyte-based first-pass metabolism.
Malaria is one of the leading causes of severe infectious disease worldwide; yet, our ability to maintain effective therapy to combat the illness is continually challenged by the emergence of drug ...resistance. We previously reported identification of a new class of triazolopyrimidine-based Plasmodium falciparum dihydroorotate dehydrogenase (PfDHODH) inhibitors with antimalarial activity, leading to the discovery of a new lead series and novel target for drug development. Active compounds from the series contained a triazolopyrimidine ring attached to an aromatic group through a bridging nitrogen atom. Herein, we describe systematic efforts to optimize the aromatic functionality with the goal of improving potency and in vivo properties of compounds from the series. These studies led to the identification of two new substituted aniline moieties (4-SF5-Ph and 3,5-Di-F-4-CF3-Ph), which, when coupled to the triazolopyrimidine ring, showed good plasma exposure and better efficacy in the Plasmodium berghei mouse model of the disease than previously reported compounds from the series.
Phenotyping of Gprc6a KO mice has shown that this promiscuous class C G protein coupled receptor is variously involved in regulation of metabolism, inflammation and endocrine function. Such effects ...are described as mediated by extracellular calcium, L-amino acids, the bone-derived peptide osteocalcin (OCN) and the male hormone testosterone, introducing the concept of a bone-energy-metabolism-reproduction functional crosstalk mediated by GPRC6A. However, whilst the calcium and L-amino acid-sensing properties of GPRC6A are well established, verification of activity of osteocalcin at both human and mouse GPRC6A in vitro has proven somewhat elusive. This study characterises the in vitro pharmacology of mouse GPRC6A in response to its putative ligands in both recombinant and endogenous GPRC6A-expressing cells. Using cell signalling, and glucagon-like peptide (GLP)-1 and insulin release assays, our results confirm that basic L-amino acids act as agonists of the murine GPRC6A receptor in both recombinant cells and immortalised entero-endocrine and pancreatic β-cells. In contrast, our studies do not support a role for OCN as a direct ligand for mouse GPRC6A, suggesting that the reported in vivo effects of OCN that require GPRC6A may be indirect, rather than via direct activation of the receptor.
Background and Purpose
Strontium ranelate, a drug approved and until recently used for the treatment of osteoporosis, mediates its effects on bone at least in part via the calcium‐sensing (CaS) ...receptor. However, it is not known whether bone‐targeted CaS receptor positive allosteric modulators (PAMs; calcimimetics) represent an alternative (or adjunctive) therapy to strontium (Sr2+o).
Experimental Approach
We assessed three structurally distinct calcimimetics cinacalcet, AC‐265347 and a benzothiazole tri‐substituted urea (BTU‐compound 13), alone and in combination with extracellular calcium (Ca2+o) or Sr2+o, in G protein‐dependent signalling assays and trafficking experiments in HEK293 cells and their effects on cell differentiation, tartrate‐resistant acid phosphatase (TRAP) activity and hydroxyapatite resorption assays in human blood‐derived osteoclasts.
Key Results
Sr2+o activated CaS receptor‐dependent signalling in HEK293 cells in a similar manner to Ca2+o, and inhibited the maturation, TRAP expression and hydroxyapatite resorption capacity of human osteoclasts. Calcimimetics potentiated Ca2+o‐ and Sr2+o‐mediated CaS receptor signalling in HEK293 cells with distinct biased profiles, and only cinacalcet chaperoned an endoplasmic reticulum‐retained CaS mutant receptor to the cell surface in HEK293 cells, indicative of a conformational state different from that engendered by AC‐265347 and BTU‐compound 13. Intriguingly, only cinacalcet modulated human osteoclast function, reducing TRAP activity and profoundly inhibiting resorption.
Conclusion and Implications
Although AC‐265347 and BTU‐compound 13 potentiated Ca2+o‐ and Sr2+o‐induced CaS receptor activation, they neither replicated nor potentiated the ability of Sr2+o to inhibit human osteoclast function. In contrast, the FDA‐approved calcimimetic, cinacalcet, inhibited osteoclast TRAP activity and hydroxyapatite resorption, which may contribute to its clinical effects on bone mineral density
Linked Articles
This article is part of a themed section on Molecular Pharmacology of GPCRs. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v175.21/issuetoc
Drug repurposing is promoted as a cost- and time-effective mechanism for providing new medicines. Often, however, there is insufficient consideration by academic researchers of the processes required ...to ensure that a repurposed drug can be used for a new indication. This may explain the inability of drug repurposing to fulfill its promise. Important aspects, often overlooked, include financial and intellectual property considerations, the clinical and regulatory path, and clinical equipoise, which provides ethical justification for randomized controlled trials. The goal of drug repurposing is to obtain a new regulator-approved label for an existing drug, and so, the trajectory for drug repurposing and traditional drug development is similar. Here, we discuss factors critical for a successful repurposed medicine to help academic investigators better identify drug repurposing opportunities.
Plasmodium falciparum causes 1−2 million deaths annually. Yet current drug therapies are compromised by resistance. We previously described potent and selective triazolopyrimidine-based inhibitors of ...P. falciparum dihydroorotate dehydrogenase (PfDHODH) that inhibited parasite growth in vitro; however, they showed no activity in vivo. Here we show that lack of efficacy against P. berghei in mice resulted from a combination of poor plasma exposure and reduced potency against P. berghei DHODH. For compounds containing naphthyl (DSM1) or anthracenyl (DSM2), plasma exposure was reduced upon repeated dosing. Phenyl-substituted triazolopyrimidines were synthesized leading to identification of analogs with low predicted metabolism in human liver microsomes and which showed prolonged exposure in mice. Compound 21 (DSM74), containing p-trifluoromethylphenyl, suppressed growth of P. berghei in mice after oral administration. This study provides the first proof of concept that DHODH inhibitors can suppress Plasmodium growth in vivo, validating DHODH as a new target for antimalarial chemotherapy.
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