Nearly 5 decades have passed since cisplatin was approved in the United States in 1978, and it remains one of the most widely used and effective anticancer drugs worldwide [1]. Cisplatin exerts potent antitumor effects primarily through the formation of DNA cross-links, thereby inhibiting DNA replication and transcription. However, because its cytotoxic activity is not selective for cancer cells, cisplatin damages normal tissues and causes adverse effects, such as myelosuppression, ototoxicity, neurotoxicity, and nephrotoxicity, which often limit its clinical use [2]. Among these toxicities, nephrotoxicity is particularly significant as it can result in both acute and chronic kidney injury [3]. Cisplatin-induced nephrotoxicity (CIN) reportedly occurs in approximately 30% of the patients receiving cisplatin-based chemotherapy [4,5].

Hydration therapy can reduce the intratubular concentration of cisplatin, thereby lowering renal toxicity, and it is recognized as the globally established preventive method for CIN [6,7]. Particularly, recently developed short hydration protocols have offered comparable protective effects to conventional hydration while reducing patient burden and improving safety [8,9]. In addition, magnesium supplementation is used for preventing hypomagnesemia and mitigating the subsequent aggravation of renal dysfunction [10,11]. Use of osmotic diuretics, such as mannitol, has also been reported as a preventive strategy; however, their use might increase risk of nausea, vomiting, and potential deterioration in renal function, particularly in patients with comorbid diabetes mellitus or hypertension [12]. Although emerging preclinical evidence in animal and in vitro studies suggests that antioxidant-based agents, including riociguat, JP4-039, and amentoflavone, exert renoprotective effects against CIN, robust clinical data supporting their efficacy and safety are still lacking [13-15]. Thus, in addition to preventive strategies such as hydration therapy and magnesium supplementation, the development of novel prophylactic approaches for CIN is warranted.

One proposed mechanism underlying CIN involves the formation of a highly reactive thiol-cisplatin complex catalyzed by cysteine conjugate-β lyase 1 (CCBL1) in renal tubular cells [16,17]. We previously reported that 2′,4′,6′-trihydroxyacetophenone, a CCBL1 inhibitor, dose dependently suppressed cisplatin-induced increases in blood urea nitrogen (BUN) and serum creatinine levels and tubular cell damage and apoptosis in a CIN mouse model [18]. Flopropione (2′,4′,6′-trihydroxypropiofenone), identified concurrently with 2′,4′,6′-trihydroxyacetophenone as a CCBL1 inhibitor, exhibits comparable inhibitory activity in renal tubular cells and animal models (Koseki, T, unpublished data, April 2022). Flopropione was approved in Japan in 1978 for its antispasmodic effects in hepatobiliary and pancreatic diseases and urinary calculi [19]. Given its known safety profile and potential to inhibit CCBL1, flopropione may also confer protective effects against CIN.

Therefore, for the first time, a phase 1 and 2a clinical trial has been designed for patients initiating cisplatin therapy to obtain proof of concept for the efficacy and safety of flopropione in preventing CIN.

This phase 1 and 2a clinical trial aims to primarily evaluate the safety of flopropione in patients receiving cisplatin-based chemotherapy while exploring preliminary efficacy and generating proof-of-concept evidence for its potential protective effect against CIN.

This is a single-center, randomized, open-label trial conducted at Fujita Health University Hospital (Toyoake, Japan) in patients undergoing cisplatin therapy.

Patients who meet all inclusion criteria and none of the exclusion criteria are eligible for enrollment (Textbox 1).

No predefined criteria are established for using preventive measures against CIN, including hydration, magnesium supplementation, or mannitol administration. However, at the participating institution, hydration is routinely implemented for managing patients undergoing cisplatin regimens at doses of 75 mg/m² or higher. In addition, magnesium supplementation and mannitol administration are implemented, involving many of the applicable regimens.

The schedule for informed consent, registration, randomization, observations, and assessments is presented in Table 1.

Eligibility will be confirmed within 28 days before cisplatin initiation. Baseline characteristics, including age, sex, height, weight, and comorbidities, will be recorded at registration.

After confirming eligibility, registration and randomization will be performed through an electronic data capture system, assigning participants in a 5:2 ratio (flopropione:control) within each cohort.

Flopropione (80 mg per tablet) will be administered orally 30 minutes before cisplatin initiation. Doses are as follows: 80 mg in cohort 1, 160 mg in cohort 2, and 240 mg in cohort 3. A second dose of the same amount will be given at least 4 hours later on day 1, followed by 80 mg 3 times daily on day 2 at intervals of at least 4 hours.

Blood and urine samples will be collected at the time points defined as the secondary and exploratory end points. The details of each test item are summarized in Table 2.

The collected urine samples will be centrifuged at 400×g or higher for 5 minutes. Thereafter, the supernatants will be stored at –80 °C until analysis. The samples will be sent to LSI Medience Corporation for N-GAL, L-FABP, KIM-1, NAG, β2-microglobulin, and α1-microglobulin measurement. N-GAL will be measured by a chemiluminescent immunoassay; L-FABP, β2-microglobulin, and α1-microglobulin will be measured by latex agglutination turbidimetry; KIM-1 will be measured by an enzyme-linked immunosorbent assay; NAG will be measured by the artificial substrate MPT method.

All adverse events, including abnormal laboratory findings, will be collected and recorded in the electronic medical records with information on severity, seriousness, outcome, and the presence or absence of a causal relationship. The seriousness criteria for serious adverse events are (1) death, (2) life-threatening complication, (3) patient requires inpatient hospitalization or prolongation of hospitalization, (4) persistent or significant disability or incapacity, (5) risk of persistent or significant disability or incapacity, (6) congenital anomaly or birth defect, (7) and important medical event.

The planned sample size includes 21 participants: 5 (24%) each in the 80 mg, 160 mg, and 240 mg flopropione cohorts and 6 (29%) in the control group. On the basis of the number of eligible patients in the previous year, anticipated consent rate, and screening dropouts, 21 participants are considered feasible to complete enrollment within 1 to 1.5 years.

Given the early-phase pilot nature of this study, the sample size is selected to balance between exploratory evaluation of potential dose-response trends, safety assessment, ethical considerations, and feasibility. Although not powered for statistical significance, 5 participants per dose level is considered appropriate for an initial exploration of a proof-of-concept study. Participants assigned to the control group will be enrolled among all cohorts and pooled for assessment, providing a common reference group for comparisons with each dose level. This approach allows for efficient use of control data while minimizing unnecessary patient exposure to the investigational intervention.

The data will be collected using an electronic data capture system. All data and materials obtained in this study will be managed under the responsibility of the principal investigator. Digital data will be encrypted with passwords, and paper-based materials will be securely stored in locked cabinets. Data will be retained for 5 years following the completion of this clinical study. Upon disposal, all materials will be destroyed in an irreversible manner through methods such as shredding or incineration to ensure destruction.

This study will be conducted in accordance with Japan’s Clinical Trials Act and the Declaration of Helsinki. The protocol was reviewed and approved by the clinical research review board of Fujita Health University (CR22-002). At Fujita Health University Hospital, the principal investigator or subinvestigator will screen patients under their care to identify those who may meet the eligibility criteria for participation in this study. Written informed consent will be obtained from eligible patients by the principal investigator or subinvestigator using an explanatory document approved by the clinical research review board, within 28 days before cisplatin administration. All participant data will be deidentified and maintained confidentially. Data will be stored securely with restricted access. Data will be retained for 5 years after study completion. For adverse events, the principal investigator or subinvestigator will provide appropriate medical treatment. For severe adverse events, clinical research insurance will provide appropriate compensation to participants.

The results will be disseminated through peer-reviewed publications, conference presentations, and the Japan Registry of Clinical Trials (jRCTs041220021).

On-site monitoring will be performed to ensure compliance with the study protocol, participant safety, and data accuracy. No formal audit is planned.

This trial was registered in the Japan Registry of Clinical Trials (jRCTs041220021).

CIN is a critical concern about initiating or continuing cisplatin-based chemotherapy. Although hydration therapy is widely implemented, its preventive effects against CIN remain limited. Various pharmacological agents have been investigated for potential protective effects; however, none have yet been successfully translated into clinical practice, and an unmet medical need persists [22]. In addition to currently recommended preventive strategies, such as hydration, the development of mechanism-based pharmacological interventions targeting the pathogenesis of CIN not only reduces the incidence and severity of CIN but also enables cisplatin therapy continuation, potentially leading to improved overall treatment outcomes. Therefore, we designed a clinical trial to evaluate the safety of flopropione, a CCBL1 inhibitor, and obtain proof of concept for its preventive effect against CIN. If proof of concept for the preventive effect of flopropione can be demonstrated in this study, subsequent clinical trials would be able to further verify its efficacy. Such evidence would support the potential of flopropione as an adjunctive therapy to existing preventive strategies, including hydration, with the expectation of achieving greater suppression of CIN incidence compared with those currently available. Furthermore, if its clinical benefit is confirmed, future studies should also consider comparative trials against hydration-based protocols to evaluate whether flopropione could serve as a simpler and more convenient alternative preventive approach to CIN.

In designing this study, several measures are implemented to ensure participant safety while obtaining proof of concept. No previous studies have evaluated the concomitant use of flopropione with cisplatin; therefore, a step-up dosing approach was adopted in the participants who were hospitalized. This design allows for sequential confirmation of safety across cohorts while gradually increasing the flopropione dose. Given that hydration may reduce plasma concentrations of orally administered drugs, we have set the maximum single dose of flopropione on cisplatin administration day 1 at 240 mg, consistent with the previously reported dose administered to healthy adults [19].

N-GAL, L-FABP, and KIM-1 were selected as urinary biomarkers for detecting early renal injury. All have been reported as useful indicators for early detection of CIN [23-25]. Furthermore, urinary KIM-1 levels reportedly continue to rise for up to 10 days after the initial administration of cisplatin [26]. Therefore, urinary biomarkers will be measured at 24 hours, 48 hours, and 1 week after cisplatin initiation.

This study has several limitations. First, it is an open-label study using a nontreated control group rather than a placebo control. Although the primary focus is on safety and biomarker evaluation, the potential for participant- or investigator-related bias cannot be completely eliminated. Therefore, a future pivotal study should adopt a randomized, double-blind, placebo-controlled design. Second, this study does not assess the impact of flopropione on cisplatin efficacy. Because this is the first clinical investigation of flopropione used in combination with cisplatin, it is limited to the first cisplatin administration (cycle 1) with an observation period of 1 week. Evaluation of potential effects on antitumor efficacy will require a longer observation period. Third, several studies have suggested that nephrotoxicity develops in a cumulative, dose-dependent manner [27,28]. Therefore, CIN may not necessarily occur after a single cisplatin administration. Accordingly, future studies involving multiple cycles of cisplatin and repeated treatment of flopropione will be necessary for comprehensively assessing its safety and preventive efficacy.

Cisplatin continues to be one of the most important anticancer agents. However, prevention of CIN is crucial for expanding therapeutic options in patients with cancer and enhancing treatment sustainability. This study is a proof-of-concept trial designed to evaluate flopropione, a CCBL1 inhibitor, with a focus on the pathophysiological mechanisms underlying CIN. It occupies an important position in generating evidence that will inform subsequent clinical trials. Through this study and the following clinical trials, we aim to demonstrate the preventive efficacy of flopropione against CIN and establish it as a prophylactic agent capable of further reducing the incidence of CIN.