Merck & Co. is continuing to tinker with its antibody-drug conjugate (ADC) alliance with Kelun-Biotech, agreeing (PDF) to pay $37.5 million to take up its option on one candidate while returning the rights to another asset.
The Big Pharma entered into a series of agreements with China’s Kelun in 2021 and 2022. In that period, Merck exercised its option on a TROP2-directed ADC, paid $35 million for rights to a second candidate and then went big by handing Kelun $175 million in return for licenses and options on a smorgasbord of assets. However, Merck axed one license and one option from the pact in 2023.
Now, Kelun has revealed further changes to the scope of the agreement. Merck has taken up its option on SKB571, a bispecific ADC that Kelun sees primarily as a treatment of solid tumors such as lung cancer and gastrointestinal tumors.
Kelun is yet to disclose the targets of the ADC but has shared information about its design decisions. The goal was to enhance tumor targeting and help overcome tumor heterogeneity—an objective that Kelun tried to achieve through its selection of the target combination and the design of the bispecific molecule. Kelun used its high hydrophilicity drug-linker strategy to ensure a uniform drug-antibody ratio.
Kelun said SKB571 showed promising anti-tumor efficacy and a good safety profile in preclinical tests, putting the candidate on the cusp of a filing for testing in humans. The biotech is retaining the rights to SKB571 in mainland China, Hong Kong and Macau.
Merck took up its option on SKB571 while cutting its ties to another asset. The drugmaker returned the global rights to the CLDN18.2-directed ADC SKB315. Kelun began a phase 1 trial of the candidate in China in 2022 and, in its statement about Merck’s actions, said the early-stage data show positive efficacy and acceptable safety in gastric cancer with high expression of CLDN18.2.
Kelun, which plans to share the clinical data at upcoming conferences, said the significant population of gastric cancer patients in China gives it confidence about the market prospects of SKB315 in its home country. The biotech said it will “explore suitable expansion into overseas markets.”
Merck’s action removes one big name from the congested CLDN18.2 space. Astellas Pharma received a complete response letter for its anti-CLDN18.2 antibody in January but is still in pole position to become the first seller of a drug against the target in the U.S. The drugmaker’s antibody is trailed by CLDN18.2 ADCs, bispecifics and mRNA cancer vaccines in development at a long list of companies.