Ocular Tissue Conversion and Activity Profile of QLS-101, a Novel Topical IOP-Lowering Therapeutic

Abstract

Purpose : QLS-101, a water-soluble phosphate ester prodrug of an ATP-sensitive potassium channel opener in preclinical development, has shown potent IOP reduction in multiple normotensive and glaucomatous animal models. The purpose of this study was to determine the conversion profile and activity of QLS-101 and its active moiety (QLS-100) using human tissue.

Methods : Conversion of QLS-101 (200 μM-5.0 mM) was examined by LC/MS-MS following incubation at pH 7.4 with either human alkaline phosphatase (ALP), acid phosphatase, or 5’-nucleotidase (2.0 nM-1.0 μM) for up to 2h. Further dose- and time-dependent analysis of QLS-101 (0.01-40.0 mM) conversion to QLS-100 was determined following incubation with human ALP (0.0002-0.2 U/μl) for up to 72h. Tissue-specific conversion of QLS-101 was assessed in fresh human ocular tissues and fluids over 24h. To quantify channel activity, HEK-293 cells stably expressing human Kir6.2/SUR2B ATP-sensitive potassium channel subunits were incubated with increasing concentrations (0.003-100 µM) of either QLS-101 or QLS-100. Pinacidil (100 μM), a commercially-available ATP-sensitive potassium channel opener, was used as a positive control. Cell membrane potential was measured on a FLIPR fluorescence plate reader.

Results : Human ALP, but not acid phosphatase or 5’-nucleotidase, converted QLS-101 to QLS-100 in vitro, with Km and kcat values of 630 uM and 15 min(-1), respectively. In a separate study at a fixed QLS-101 concentration, approximately 21% of QLS-101 was converted by ALP in a concentration-dependent manner. Similarly, ALP at a fixed concentration converted QLS-101 to QLS-100 in a QLS-101 inverse concentration-dependent manner. In human ocular tissues, 24h conversion of QLS-101 was most robust in samples of iris, ciliary body, trabecular meshwork, and sclera. Treatment of HEK-Kir6.2/SUR2B cells with QLS-100 resulted in a concentration-dependent hyperpolarization of the cell membrane, with a mean EC₅₀ value of 0.53 µM ± 0.05, consistent with pinacidil (EC₅₀ = 5.49 µM ± 0.99). In contrast, application of QLS-101 did not result in any significant hyperpolarization, confirming QLS-101 as an inactive prodrug.

Conclusions : QLS-101 is activated by human ALP to QLS-100, which promotes cell membrane hyperpolarization through ATP-sensitive potassium channels composed of Kir6.2/SUR2B.

This is a 2021 ARVO Annual Meeting abstract.