A snake toxin as a theranostic agent for the type 2 vasopressin receptor

Abstract

Rationale: MQ1, a snake toxin which targets with high nanomolar affinity and absolute selectivity for the type 2 vasopressin receptor (V2R), is a drug candidate for renal diseases and a molecular probe for imaging cells or organs expressing V2R. Methods: MQ1's pharmacological properties were characterized and applied to a rat model of hyponatremia. Its PK/PD parameters were determined as well as its therapeutic index. Fluorescently and radioactively labeled MQ1 were chemically synthesized and associated with moderate loss of affinity. MQ1's dynamic biodistribution was monitored by positron emission tomography. Confocal imaging was used to observe the labeling of three cancer cell lines. Results: The inverse agonist property of MQ1 very efficiently prevented dDAVP-induced hyponatremia in rats with low nanomolar/kg doses and with a very large therapeutic index. PK (plasma MQ1 concentrations) and PD (diuresis) exhibited a parallel biphasic decrease. The dynamic biodistribution showed that MQ1 targets the kidneys and then exhibits a blood and kidney biphasic decrease. Whatever the approach used, we found a T1/2α between 0.9 and 3.8 h and a T1/2β between 25 and 46 h and demonstrated that the kidneys were able to retain MQ1. Finally, the presence of functional V2R expressed at the membrane of cancer cells was, for the first time, demonstrated with a specific fluorescent ligand. Conclusion: As the most selective V2 binder, MQ1 is a new promising drug for aquaresis-related diseases and a molecular probe to visualize in vitro and in vivo V2R expressed physiologically or under pathological conditions.

A new Kunitz-type snake toxin family associated with an original mode of interaction with the vasopressin 2 receptor.

“…To explain this discrepancy between human and rat V2R, we measured the affinity of MQ1 and MQ1-K39A for rat V2R. As published, MQ1 displays the same affinity for both species (K i of 5.3 and 6.13 nM for human and rat V2R, Droctové et al, 2020). On its side, MQ1-K39A displayed similar affinity for rat V2R (K i = 7.73 nM, pK i = 8.37 ± 0.74, Fig.…”

“…MQ1 displays the same nanomolar affinity for rat and human V2R (Droctové et al, 2020) but no interaction with V1aR, V1bR or OTR (Ciolek et al, 2017). The figure 6 shows a sequence alignment between the 3 external loops (ELs) of the vasopressin-sensitive receptors.…”

“…3 H-AVP was purchased from PerkinElmer (Courtaboeuf, France). Binding experiments on self-prepared CHO cells overexpressing vasopressin hV2R subtype or HEK cells transfected with a plasmid coding for the rat V2R, were performed as described (Ciolek et al, 2017;Droctové et al, 2020). Briefly, 1.5 nM 3 H-AVP in a 100 μL reaction mixture at room temperature in buffer composed of 50 mM Tris-HCl, pH 7.4, 10 mM MgCl 2 , 1 g/L BSA was incubated with increasing concentrations of competitors for 3 hours.…”

“…Up to now, it is the sole Kunitz peptide known to be active on a GPCR. We furthermore validated MQ1 as a therapeutic solution to hyponatremia and polycystic kidney diseases and as a diagnostic agent to detect V2R in vivo (Ciolek et al, 2017, Droctové et al, 2020.…”

Structural and Functional Diversity of Animal Toxins Interacting With GPCRs

“…By functional tests, MQ1 displays a pure antagonist effect against AVP (Ciolek et al, 2017). In addition, MQ1 acts as an inverse agonist on the V2R/Gαs pathway (Droctové et al, 2020).…”