Two deals for antibody-drug conjugates inked since May between Merck & Co. Inc. and Sichuan Kelun-Biotech Pharmaceutical Co. Ltd. have blossomed eight months later into the year’s biggest agreement, one that could bring Kelun-Biotech up to $9.3 billion in development, regulatory and sales milestones. The exclusive license and collaboration deal has Merck paying an up-front $175 million to Kelun-Biotech plus promising to make an equity investment in the Sichuan, China-based company.