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Novel ADC payloads are the scarce asset, and 23 independent developers remain
Novartis agreed to pay up to $1.5 billion for Myricx Bio’s antibody-drug conjugate (ADC) payload platform, whose lead drugs are still preclinical. That’s how scarce new payload chemistry has become: Sleuth’s July 2026 map finds only 23 independent developers still building ADCs with novel payloads, meaning chemistries outside the topoisomerase-1, auristatin and maytansinoid classes behind most approved ADCs, and five look like clean buys. The next ADC deal will turn on the warhead, not the antibody or the target.
Novartis announced the agreement in July 2026, with $1.1 billion upfront. Myricx’s payload is an N-myristoyltransferase inhibitor (NMTi), and its lead ADCs are directed at B7-H3 and HER2.
The first ADC wave bought revenue, and buyers have claimed most of it
Pfizer acquired Seagen for $43 billion, and Daiichi Sankyo partnered its deruxtecan ADCs with AstraZeneca and Merck. Most of that wave is now owned, and topoisomerase-1 copies crowd the most sought-after antigens, HER2 and TROP2.
With the leading targets crowded and the dominant payload classes taken, a differentiated payload is the part of an ADC a buyer can still own outright. Sleuth’s ADC Intelligence Report, Q3 2026 traces the same shift toward payload and linker engineering.
Most novel-payload developers are preclinical or in Phase 1
Sleuth identified 30 novel-payload developers in July 2026. Twenty-three qualified as independent, and seven were excluded as acquired or locked to an exclusive platform partner. By chemistry, the 23 are 10 other novel payload developers, 5 degrader or degrader-antibody conjugate (DAC) developers, 4 dual-payload developers, 3 immune-agonist developers and 1 amanitin developer, Heidelberg Pharma.
Eighteen are preclinical, IND-enabling or in Phase 1. Only five have reached Phase 1/2 or Phase 2: Tallac, MacroGenics and Helix in Phase 2, and SOTIO and Heidelberg Pharma in Phase 1/2. Ten of the 23 are fully independent, seven work with non-exclusive partners and six are optioned or carry verification risk.
With Myricx’s NMTi class off the board, Sleuth sees the open ground in immune-agonist ADCs and clinical-stage cytotoxic payloads, and a buyer who wants clinical data on a novel payload has only a handful of options.
Five developers look like clean buys, but most of the field needs diligence
Sleuth’s July 2026 acquisition shortlist has five names: Jacobio (immune agonist, preclinical), Mersana (immune agonist, Phase 1; now part of Day One Biopharmaceuticals), Callio (dual payload, Phase 1), Adcentrx (other novel, Phase 1) and MacroGenics (other novel, Phase 2). Adcentrx’s Nectin-4 ADC is unpartnered.
Across the full set, 19 of the 23 developers carry at least one diligence flag: an undisclosed target or payload, a partnership exclusivity or an ambiguous stage. The chemistry exists. Owning it outright is the harder question.
How Sleuth built this analysis
Which developers count
The map covers developers whose lead novel-payload assets sit between preclinical and Phase 2. A developer counts as independent unless it has been acquired or is locked to an exclusive platform partner.
A caveat on the shortlist
Sleuth’s July 2026 count and shortlist still include Mersana, but Day One completed its acquisition of Mersana in January 2026. Mersana’s HER2-directed STING-agonist ADC, which became available again when GSK ended its partnership in April 2026, would now be bought or licensed from Day One.
Developer counts, independence classes and stages are as of July 2026, and the Myricx terms and expected second-half 2026 closing are as Novartis announced them in July 2026. Mersana’s ownership is as of January 2026. This page is a dated snapshot.
Frequently asked questions about novel ADC payloads
What counts as a novel ADC payload?
In Sleuth’s July 2026 analysis, a novel payload is any chemistry other than topoisomerase-1 inhibitors, auristatins or maytansinoids, the classes behind most approved ADCs.
How many independent novel-payload ADC developers are there?
Sleuth counted 23 as of July 2026, out of 30 developers identified with lead assets between preclinical and Phase 2. Seven were excluded as acquired or locked to an exclusive platform partner, and 19 of the 23 carry at least one diligence flag.
What did Novartis buy with Myricx Bio?
Novartis agreed in July 2026 to acquire Myricx Bio for up to $1.5 billion, including $1.1 billion upfront, for its N-myristoyltransferase inhibitor payload platform. Myricx’s lead ADCs, against B7-H3 and HER2, are preclinical, and the deal was expected to close in the second half of 2026.
Which novel-payload ADC developers look acquisition-ready?
Sleuth’s July 2026 shortlist names Jacobio, Mersana, Callio, Adcentrx and MacroGenics. Mersana has been part of Day One Biopharmaceuticals since January 2026, so its assets would now come through Day One.
