Daiichi and Merck’s drug, like the others in its class, use an antibody to home in on a protein expressed on tumor cells and then release a toxic chemical directly to diseased cells. The first ADCs were in blood cancers, but more and more drugmakers are developing them for solid tumors like those of the breast and bladder.
Their development has been helped along by Daiichi, which discovered the breast cancer ADC Enhertu — one of the most successful drugs in the class. Enhertu, which AstraZeneca helps market, had sales of $1.8 billion through the first six months of the year.
The Japan-based drugmaker has a total of six ADCs using the deruxtecan chemotherapy. Those include Enhertu, another agent partnered with AstraZeneca, an additional two drugs partnered with Merck and one Daiichi is developing alone.
The Merck deal saw the New Jersey-based drugmaker pledge up to $22 billion, including $3 billion on the deal’s signing last October. Merck is seeking to boost its pipeline as it faces a potential loss of revenue later in the decade when key patents for its immunotherapy Keytruda begin to expire.
The type of lung cancer patritumab deruxtecan is being tested in is usually treated first with EGFR-blocking small molecule drugs like AstraZeneca’s Tagrisso. The cancer typically becomes resistant to those agents over time and, once that happens, people have a poor outlook and few effective drug options.
In the Phase 2 trial Daiichi reported last year, people who received patritumab deruxtecan went a median of six months before their disease progressed again, and three in 10 people who received it had their tumors shrink or disappear.