Drug Delivery to the Malaria Parasite Using an Arterolane‐Like Scaffold

Abstract

The antimalarial agents artemisinin and arterolane act via initial reduction of a peroxide bond in a process likely mediated by ferrous iron sources in the parasite. Here, we report the synthesis and antiplasmodial activity of arterolane-like 1,2,4-trioxolanes specifically designed to release a tethered drug species within the malaria parasite. Compared to our earlier drug delivery scaffolds, these new arterolane-inspired systems are of significantly reduced molecular weight and possess superior metabolic stability. We also demonstrate the use of the aminonucleoside antibiotic puromycin as a chemo/biomarker to validate successful drug release in live P. falciparum parasites.

A reactivity-based probe of the intracellular labile ferrous iron pool

“…2b ). While the reason(s) for this are unclear, we have observed similarly accelerated rates of intracellular retro-Michael reaction of trioxolane conjugates in malaria parasites 33 , 35 , suggesting a common feature of both environments may enhance the rate of the β-elimination. Consistent with the analysis by Western blotting, U-2 OS cells treated with non-peroxidic control 4 showed negligible immunofluorescence signal in the high-content assay, further confirming that puromycin release from 3 is peroxide dependent ( Fig.…”

“…Significantly, the α-amino group of puromycin ( 2 ) required for incorporation in peptides is carbamoylated in conjugate 3 and thus puromycin incorporation from 3 is precluded prior to reaction with Fe(II). As an important negative control we prepared the bioisosteric but non-peroxidic dioxolane conjugate 4 35 , which is unreactive with Fe(II) ( Fig. 2a , Supplementary Note ).…”

“…While we judged simple organic peroxides too reactive for such purposes, the 1,2,4-trioxolane ring embedded in the antimalarial agents arterolane 25 , 26 , 27 and artefenomel 28 combines good chemical stability with finely-tuned Fe(II)-dependent reactivity 29 – 32 . Accordingly, we re-engineered the arterolane scaffold so that Fenton reaction of the endoperoxide bond is mechanistically coupled to traceless release of amine-tethered payloads 33 – 35 . For detection of labile iron pools, we imagined employing this scaffold for the Fe(II)-dependent unmasking of either fluorescent moieties or cell-active compounds such as puromycin, an aminonucleoside that leaves a permanent mark on the cell that can be detected with α-puromycin antibodies.…”

A Novel Tumor-Activated Prodrug Strategy Targeting Ferrous Iron Is Effective in Multiple Preclinical Cancer Models

“…17,20 Given that labile Fe(II) promotes Fenton chemistry, we sought to develop a tumor-targeting strategy in which Fenton reaction of a peroxidic prodrug was coupled to release of drug payloads. Recognizing that antimalarial agents such as arterolane 21−24 exhibit finely tuned iron(II) reactivity, 25−28 we subsequently developed 29,30 an arterolane-inspired small molecule platform (denoted TRX herein) for Fe(II)-dependent drug delivery. These TRX-drug conjugates function via initial Fe(II)-promoted fragmentation of a 1,2,4-trioxolane ring to afford a cyclohexanone intermediate, followed by spontaneous β-elminiation and decarboxylation to release the drug payload (Figure 1 and Supporting Information Figure S1).…”

Trioxolane-Mediated Delivery of Mefloquine Limits Brain Exposure in a Mouse Model of Malaria

“…In recent years, our group and others have sought to exploit the intrinsic reactivity of endoperoxide antimalarials as platforms for targeted drug delivery. [5][6][7][8][9] Our designs in particular involve embedding a masked retro-Michael linker in an arterolane-like scaffold. [6][7][8] Intra-parasitic reduction of the endoperoxide bond in such systems (e.g., 3) serves to unmask a ketone and reveal the competent retro-Michael substrate 4, which then undergoes traceless release of a 3"-carbamate-tethered payload (Scheme 1).…”