Fig. 4: Anti-leukaemic agents used in the treatment of CLL are substrates for UGT-dependent glucuronidation.

MS analysis indicated the formation of one or two glucuronidated products named according to their order of elution G1 and G2. Glucuronidation assays using pooled human liver microsomes enriched in UGT enzymes led to the formation of polar G derivatives confirmed by their fragmentation patterns assessed by mass spectrometry (MS), namely a loss of the GlcA moiety corresponding to a m/z shift of 176 Da. Masses of the protonated drug-glucuronide [M + H]⁺ and parent drug [M-G + H]⁺ are shown and were in accordance with the masses of the parent drug and of GlcA (176 Da). The metabolite of bendamustine HP2 was glucuronidated. The HP2 metabolite has hydroxyl groups in place of chlorine atoms in bendamustine. Chlorambucil undergoes a similar process, generating a dechlorinated metabolite subsequently conjugated. Venetoclax is an orally available, selective, small molecule inhibitor of BCL2 approved by the US Food and Drug Administration for the treatment of patients with CLL. Acalabrutinib is an orally available, irreversible Bruton’s tyrosine kinase (BTK) inhibitor in development designed to be more selective than ibrutinib.¹⁰ Cerdulatinib (PRT062070) is an investigational oral, dual spleen tyrosine kinase (Syk), janus kinase (JAK1/3) and tyrosine kinase 2 (TYK2) inhibitor for the treatment of haematological malignancies and approved for the treatment of peripheral T-cell lymphoma.⁹ Duvelisib is an oral, dual small molecule inhibitor of phosphatidylinositol 3-kinase (PI3K) δ and γ, approved for the treatment of relapsed or refractory CLL.⁷ A second set of experiments identified the UGT enzyme(s) involved, revealing a predominant role for UGT2B17 and UGT1A4.