Daiichi Sankyo has reported positive initial findings from the dose escalation phase of the first-in-human Phase I trial of its investigational antibody-drug conjugate (ADC) DS-9606 for treating advanced solid tumours.

Developed in collaboration with the Tokyo University of Pharmacy and Life Sciences, DS-9606 is designed using Daiichi Sankyo’s second ADC technology platform.

The drug comprises a humanised Claudin-6 (CLDN6) monoclonal antibody linked to a modified PBD payload.

The latest findings indicated promising clinical activity in patients with advanced solid tumours expressing CLDN6.  

DS-9606, a modified pyrrolobenzodiazepine (PBD) ADC, targets CLDN6, a protein found in several tumour types, including endometrial, ovarian, and gastric cancers, germ cell tumours, and non-small cell lung cancer.

The Phase I trial involved 53 heavily pretreated patients with various cancers. These patients had already undergone a median of four prior therapies.

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The safety and tolerability of DS-9606 were assessed across doses ranging from 0.016 mg/kg to 0.225 mg/kg. No dose-limiting toxicities were observed, and no patients withdrew due to treatment-related adverse events.

The most common treatment-emergent adverse events (TEAEs) included nausea, fatigue, and anaemia, with Grade 3 or higher TEAEs occurring in 30.2% of patients.

Daiichi Sankyo said that preliminary efficacy results showed four confirmed objective responses at doses greater than or equal to 0.072mg/kg.

Notably, two responses were observed in patients with germ cell tumours, and one response each in patients with gastric / esophageal cancer and non-small cell lung cancer.

Seven patients with germ cell tumours showed significant tumour marker reductions, with two maintaining treatment response for over six months.

As of the data cutoff on 14 June 2024, 21 patients continue to receive DS-9606 treatment.

The ongoing Phase I trial is evaluating the drug’s safety, tolerability, and efficacy in adult patients with CLDN6-expressing advanced solid tumours in Europe and North America.

The trial’s next steps include determining the maximum tolerated dose and the recommended dose for expansion, followed by further evaluation in dose expansion cohorts.

Daiichi Sankyo R&D global head Ken Takeshita said: “While these results provide preliminary proof-of-concept for DS-9606, further clinical evaluation is warranted across different tumour types that are known to express CLDN6.

“We continue to apply our science and technology expertise to DS-9606, which has been developed from our second antibody-drug conjugate platform in order to create potentially new and innovative treatments for certain patients with cancer.”