Glucuronides: From biological waste to bio-nanomedical applications

Label-free turn-on electrochemiluminescence assay of β-glucuronidase at single-electrode

Electrochemiluminescence (ECL) has achieved significant commercial success over the past few decades across various fields, particularly in the healthcare industry. The measurement scheme oftentimes involves target recognition elements (e.g. catching antibodies) labeled with a suitable ECL luminophore (e.g. tris(2,2'-bipyridine)ruthenium(II))). While this approach realizes the ultrasensitive detection of various biomarkers, it is somewhat complicated strategy for certain targets such as enzymes. In this study, β-glucuronidase (B-GLU), a promising biomarker and a common water/foodstuff safety indicator, was quantified by measuring the ECL signal of fluorescent product generated from non-fluorescent substrate by the B-GLU enzyme. To this end, hot electron-induced ECL of three luminophores (fluorescein, 4-methylumbelliferyl and resorufin) that are used as building blocks to synthesize various commercially available non-fluorescent substrates was compared for the first time. To increase the appeal and practicality of this approach, the common multi-well assay format was adapted to the present type ECL by carrying out the ECL reactions at single carbon black/polystyrene electrode. In this electrochemical setup, multiple cells were fabricated on the surface of a poorly conducting substrate by attaching Teflon tape with multiple holes to the substrates surface. Sample throughput time decreases considerable as target, blank and sample signals can be simultaneously obtained from the electrochemical cells when voltage is applied across the single electrode. The detection limit for B-GLU after 2 h of incubation was 0.07 U L-1 when 4-methylumbelliferyl-β-D-glucuronide was used as the fluorogenic substrate and Br- was used as the co-reactant. B-GLU recovery rates from diluted saliva with the present ECL approach were adequate (93-103 %) and similar to those obtained with the fluorescence technique.

Comparative Study on Covalent and Noncovalent Endogenous Albumin-Binding β-Glucuronidase-Activated SN38 Prodrugs for Antitumor Efficacy

Albumin-binding prodrugs have been explored to overcome the limitations of small-molecule anticancer chemotherapy agents, such as inadequate physiological and pharmaceutical compatibility, as well as rapid renal clearance. Herein, we investigated two endogenous albumin-binding prodrugs, M-g-SN38 and S-g-SN38, forming macromolecular conjugates. Both prodrugs exhibited robust stability in murine and human plasma, crucial for their therapeutic potential. Selective activation by β-glucuronidase ensures minimal toxicity in their inactive state. Notably, M-g-SN38 exhibited higher cellular uptake, a longer circulation half-life, and enhanced tumor accumulation compared to S-g-SN38, suggesting its greater potential for improved antitumor efficacy. In vivo, M-g-SN38 exhibited significant antitumor activity, leading to profound tumor reduction and, in many cases, marked depletion and complete eradication in all treated mice in the HCT116 xenograft model. Furthermore, M-g-SN38 also demonstrated pronounced antitumor efficacy in the BxPC-3 xenograft model. Together, these findings provide new insights for the development of albumin-binding prodrugs.

Engineering stable and non-immunogenic immunoenzymes for cancer therapy via in situ generated prodrugs

Engineering human enzymes for therapeutic applications is attractive but introducing new amino acids may adversely affect enzyme stability and immunogenicity. Here we used a mammalian membrane-tethered screening system (ECSTASY) to evolve human lysosomal beta-glucuronidase (hBG) to hydrolyze a glucuronide metabolite (SN-38G) of the anticancer drug irinotecan (CPT-11). Three human beta-glucuronidase variants (hBG3, hBG10 and hBG19) with 3, 10 and 19 amino acid substitutions were identified that display up to 40-fold enhanced enzymatic activity, higher stability than E. coli beta-glucuronidase in human serum, and similar pharmacokinetics in mice as wild-type hBG. The hBG variants were two to three orders of magnitude less immunogenic than E. coli beta-glucuronidase in hBG transgenic mice. Intravenous administration of an immunoenzyme (hcc49-hBG10) targeting a sialyl-Tn tumor-associated antigen to mice bearing human colon xenografts significantly enhanced the anticancer activity of CPT-11 as measured by tumor suppression and mouse survival. Our results suggest that genetically-modified human enzymes represent a good alternative to microbially-derived enzymes for therapeutic applications.

Induced-volatolomics for the design of tumour activated therapy

The discovery of tumour-associated markers is of major interest for the development of selective cancer chemotherapy. Within this framework, we introduced the concept of induced-volatolomics enabling to monitor simultaneously the dysregulation of several tumour-associated enzymes in living mice or biopsies. This approach relies on the use of a cocktail of volatile organic compound (VOC)-based probes that are activated enzymatically for releasing the corresponding VOCs. Exogenous VOCs can then be detected in the breath of mice or in the headspace above solid biopsies as specific tracers of enzyme activities. Our induced-volatolomics modality highlighted that the up-regulation of N-acetylglucosaminidase was a hallmark of several solid tumours. Having identified this glycosidase as a potential target for cancer therapy, we designed an enzyme-responsive albumin-binding prodrug of the potent monomethyl auristatin E programmed for the selective release of the drug in the tumour microenvironment. This tumour activated therapy produced a remarkable therapeutic efficacy on orthotopic triple-negative mammary xenografts in mice, leading to the disappearance of tumours in 66% of treated animals. Thus, this study shows the potential of induced-volatolomics for the exploration of biological processes as well as the discovery of novel therapeutic strategies.