First-in-Human Phase I Clinical Trial of SLC-391, a Novel and Selective AXL Inhibitor, in Patients with Advanced Solid Tumours

<b>Background/Objectives:</b> AXL, a receptor tyrosine kinase of the TAM family, has emerged as a key target in cancer therapy due to its role in tumour growth, metastasis, immune evasion, and therapy resistance. SLC-391, a novel, orally bioavailable and selective AXL inhibitor, has demonstrated potent anti-tumour effects in preclinical studies. This first-in-human, open-label, multi-centre Phase I clinical trial (NCT03990454) was conducted to evaluate the safety, tolerability, pharmacokinetics (PK), and preliminary efficacy of SLC-391 in patients with advanced solid tumours. <b>Methods:</b> Using a 3 + 3 design, SLC-391 was administered orally, either once daily (from 25 mg up to 175 mg QD) or twice daily (from 75 mg to 200 mg BID) in 21-day cycles. <b>Results:</b> Following single and repeated dosing, SLC-391 was generally well tolerated by subjects. The maximum tolerated dose (MTD) was not reached in this study. A total of 34/35 subjects experienced at least one TEAE. Three (8.6%) subjects experienced Grade 3 TRAEs that were considered related to SLC-391. Eight SAEs were reported in five (14.3%) subjects (seven Grade 3 SAEs and one Grade 2 SAE), in 150 mg QD (3/6, 50%), 175 mg QD (1/2, 50%), and 110 mg BID (1/3, 33.3%) cohorts. Four SAEs in three (8.6%) subjects led to dose interruption, drug withdrawal, or study discontinuation. Three DLTs were reported in two subjects: one subject experienced Grade 3 hematochezia (SUSAR/DLT) at 175 mg QD, and another subject experienced Grade 3 thrombocytopenia associated with Grade 1 hematuria at 200 mg BID. The median T_max was 2.0 h. Plasma concentrations following multiple doses generally increased with higher doses and appeared to reach steady state by Day 21 and were generally dose-proportional. Twelve (12) out of 35 subjects with solid tumours achieved stable disease according to RECIST or mRECIST (mesothelioma), with durations of stable disease lasting up to 318 days on SLC-391 monotherapy. The clinical benefit rate was 34.3%. <b>Conclusions:</b> This first study of SLC-391 in adult subjects with advanced solid tumours demonstrated that a total daily dose of 300 mg (150 mg BID) of SLC-391 monotherapy was generally well tolerated, with no DLTs or SAEs observed at this dose. The drug's promising safety profile, along with stable disease reported for several subjects with advanced solid tumours, provides a strong rationale for the phase 1b/2a clinical investigation of SLC-391 in combination with pembrolizumab in subjects with advanced or metastatic non-small cell lung cancer (NSCLC) (NCT05860296).