Seattle Genetics has secured global rights to Immunomedics’ antibody-drug conjugate IMMU-132 (sacituzumab govitecan), currently in late-stage trials for triple-negative metastatic breast cancer.
Immunomedics could receive up to $2 billion if the drug succeeds, paid out as $250 million upfront, up to $1.7 billion in milestone payments and tiered double-digit royalties.
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According to Clay Siegall, CEO of Seattle Genetics, the milestones stretch out for many years and are contingent upon approvals in different jurisdictions and in indications beyond breast cancer.
“I honestly, would love to pay out all the milestone payments,” Siegall said in a phone interview, in reference to the long-term potential of the drug.
IMMU-132 is an antibody-drug conjugate (ADC), comprised of a targeted antibody, a linker molecule and a highly potent ‘payload.’ In this instance, the antibody targets a signaling molecule called Trop-2, guiding the complex to this receptor and delivering its cytotoxic punch.
Siegall said Trop-2 is overexpressed on virtually all triple-negative breast cancers (TNBCs), which are resistant to standard hormone treatments and HER2.
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“The thought here is that they would not need a diagnostic tool because literally, everyone has the expression.”
Prior research by Amgen suggests Trop-2 is also expressed in healthy tissues, but Seattle Genetics is evidently comfortable with the trade-off.
“Almost every target that you look at that is overexpressed on tumors at very high amounts has some expression on normal tissue,” Siegall said. “We have a lot of human safety data on this drug.”
IMMU-132 was granted an FDA breakthrough therapy designation in early 2016 for patients with metastatic TNBC that have failed previous therapies. To date, no targeted antibody therapies have been approved for this type of cancer.
“We think that going after the last-stage patients first and trying to get accelerated approval makes sense,” Siegall explained. “Then you go earlier lines of therapy, whether it’s single agent or combinations with some of the standard care.”
IMMU-132 is not restricted to breast cancer, however. The agency has also granted the drug fast track designation for patients with small-cell lung cancer (SCLC) or non-small-cell lung cancer (NSCLC), along with orphan drug status for SCLC and pancreatic cancer.
Given the freshness of the deal, Siegall wouldn’t provide guidance on when the company would submit its FDA biologics license application (BLA) for TNBC. But with solid Phase 1/2 data and a recognized unmet need in this patient population, commercialization could come soon.
In 85 patients with a metastatic form of the disease, IMMU-132 showed an objective response rate of 29 percent and a median duration of response of 10.8 months. For all 89 patients in the intent-to-treat population, the estimated median overall survival was 18.8 months.
“When we started looking at this a long time ago, what caught our attention was durability,” Siegall stated.
If approved, it could be the first drug targeting Trop-2. It also marks an important milestone for the company.
“Seattle Genetics is in the process of changing and maturing,” he said. “In a way we’re emerging as a company that’s no longer a hem-onc company, but now a company that has drugs in hematology as well as drugs that target solid tumors.”
In the next year or two, it could well have drugs to treat both cancer forms in its global supply chain.
Photo: John Slater, Getty Images