Near Infrared Fluorophore-Tagged Chloroquine in Plasmodium falciparum Diagnostic Imaging

Abstract

Chloroquine was among the first of several effective drug treatments against malaria until the onset of chloroquine resistance. In light of diminished clinical efficacy of chloroquine as an antimalarial therapeutic, there is potential in efforts to adapt chloroquine for other clinical applications, such as in combination therapies and in diagnostics. In this context, we designed and synthesized a novel asymmetrical squaraine dye coupled with chloroquine (SQR1-CQ). In this study, SQR1-CQ was used to label live Plasmodium falciparum (P. falciparum) parasite cultures of varying sensitivities towards chloroquine. SQR1-CQ positively stained ring, mature trophozoite and schizont stages of both chloroquine–sensitive and chloroquine–resistant P. falciparum strains. In addition, SQR1-CQ exhibited significantly higher fluorescence, when compared to the commercial chloroquine-BODIPY (borondipyrromethene) conjugate CQ-BODIPY. We also achieved successful SQR1-CQ labelling of P. falciparum directly on thin blood smear preparations. Drug efficacy experiments measuring half-maximal inhibitory concentration (IC50) showed lower concentration of effective inhibition against resistant strain K1 by SQR1-CQ compared to conventional chloroquine. Taken together, the versatile and highly fluorescent labelling capability of SQR1-CQ and promising preliminary IC50 findings makes it a great candidate for further development as diagnostic tool with drug efficacy against chloroquine-resistant P. falciparum.

Fluorescent Reporters for Drug Delivery Monitoring

“…There are some other classes of fluorescent reporters such as squaraines (a subclass of cyanines), fluoresceins, coumarins, 1,8‐naphthalimides, and BODIPY dyes that have also been proposed for drug delivery monitoring and other imaging applications.…”

“…[71] The cyanine probe IR780 iodide (Figure 3) introduced in folate-targeted liposome NPs was tested for near-infrared fluorescence image-guided surgery and photothermal therapy in ovarian cancer. [72] There are some other classes of fluorescent reporters such as squaraines (a subclass of cyanines), [73] fluoresceins, [74] coumarins, [75] 1,8-naphthalimides, [75] and BODIPY dyes [76] that have also been proposed for drug delivery monitoring and other imaging applications.…”

Squaraine probes for the bimodal staining of lipid droplets and endoplasmic reticulum imaging in live cells

“…This class of probes is a good candidate for fluorescence bioimaging owing to their ease of synthesis, superior photostability, high molar extinction coefficients, moderately high quantum yields, and large Stokes shift with emission in the far-red region. 23,24 Additionally, SQR probes possess a versatile structure, thus allowing facile modifications to exhibit phototherapeutic capability. [25][26][27][28][29][30][31] These probes (SQR22 (R = -C 4 H 9 ) and SQR23 (R = -C 9 H 19 )) can be embedded in a nanocarrier system such as bilayer functionalized phospholipid liposomes and safely delivered into cancer cells via endocytosis with high efficiency.…”

Intrinsic fluorescence properties of antimalarial pyrido[1,2-a]benzimidazoles facilitate subcellular accumulation and mechanistic studies in the human malaria parasite Plasmodium falciparum

“…In the absence of this property, extrinsic fluorescent dyes are attached to the compounds to allow for their fluorescent imaging. While most fluorescent imaging protocols have required the derivatization of the target compounds by attaching extrinsic fluorophores, 17,18 there have been growing concerns that the presence of these extrinsic fluorophores may change the MoA of the compounds under study and hence interfere with their subcellular accumulation in the parasite even when they retain antiplasmodium activity. Also, attaching external fluorophores requires the need for structure activity relationship studies to ascertain the most appropriate site for attachment and results in the need for additional synthetic steps.…”