# Flopropione, a Cysteine Conjugate β-Lyase 1 Inhibitor, for Prevention of Cisplatin-Induced Nephrotoxicity: Protocol for a Randomized, Open-Label, Proof-of-Concept Phase 1 and 2a Trial

## TL;DR

This clinical trial tests if flopropione, a drug that blocks a specific enzyme, can prevent kidney damage caused by cisplatin chemotherapy.

## Contribution

This is the first clinical trial to investigate the use of a cysteine conjugate β-lyase 1 inhibitor to prevent cisplatin-induced nephrotoxicity.

## Key findings

- Flopropione inhibits the formation of thiol-cisplatin conjugates, potentially reducing kidney injury.
- The trial will assess safety and biomarker changes to evaluate flopropione's efficacy in preventing CIN.
- Results may provide evidence for a new preventive strategy for cisplatin-induced nephrotoxicity.

## Abstract

Cisplatin-induced nephrotoxicity (CIN) is a major dose-limiting adverse event that can lead to both acute and chronic kidney injury. The formation of thiol-cisplatin conjugates within renal tubular cells has been implicated as a key mechanism underlying CIN. Flopropione is an inhibitor of cysteine conjugate β-lyase 1, an enzyme that catalyzes the formation of the thiol-cisplatin conjugate, which might prevent CIN.

We designed a clinical trial to evaluate the safety of flopropione in patients receiving cisplatin-based chemotherapy and explore its efficacy in preventing CIN.

This is a phase 1 and 2a, single-center, randomized, open-label trial conducted in patients undergoing cisplatin therapy. Participants are randomized in a 5:2 ratio per cohort to receive either flopropione or no treatment. On the day of cisplatin administration, the flopropione group receives oral flopropione twice daily (80 mg in cohort 1, 160 mg in cohort 2, and 240 mg in cohort 3). On the following day, all cohorts receive 3 doses of 80 mg of oral flopropione. A step-up dose escalation design is adopted, progressing from cohort 1 to 3 after confirming safety at each level. The primary end point is the safety of flopropione use in combination with cisplatin; the secondary end points include changes in the levels of urinary biomarkers of nephrotoxicity such as neutrophil gelatinase-associated lipocalin, liver-type fatty acid-binding protein, and kidney injury molecule-1. Blood and urine samples are collected within 48 hours before cisplatin administration and at 24 hours, 48 hours, and 1 week after its initiation for safety and efficacy assessments.

The first participant was registered in July 2024. As of January 2026, participant registration is ongoing. The final participant will complete the study by March 2026. Publication of results is expected by March 2027.

This study is expected to contribute to advances in preventive strategies for CIN by providing evidence that inhibition of cysteine conjugate β-lyase 1 by flopropione may attenuate CIN.

Japan Registry of Clinical Trials jRCTs041220021; https://jrct.mhlw.go.jp/en-latest-detail/jRCTs041220021

DERR1-10.2196/87907