USA – Mersana Therapeutics Inc has announced a research collaboration and license agreement with Janssen Biotech Inc, a subsidiary of Johnson & Johnson, to discover antibody-drug conjugates (ADCs) for three targets.

The Janssen unit is paying US$40 million up front and up to US$1 billion in potential milestone payments for ADCs across three targets.

During preclinical development, the two will collaborate to research target candidates. J&J’s biotech unit will supply proprietary antibodies, and Mersana will contribute its Dolasynthen platform to aid in the discovery of new ADC product candidates.

Janssen will handle clinical development and commercialization of the therapies after preclinical work is completed.

Mersana will receive royalties ranging from the mid-single digits to the low-double digits on global sales if any of them reach the market.

Janssen will take over and manage the therapies’ clinical development and commercialization after the preclinical work is completed.

Mersana will receive mid-single-digit to low-double-digit percentage royalties on global sales if any of them make it to market.

Anna Protopapas, Mersana’s President and CEO, said in a statement that the transaction strengthens the biotech’s financial position, as it has a wholly owned pipeline of ADCs.

Mersana stated in November 2021 that the Cambridge, Massachusetts-based company had US$192 million in cash and equivalents as of the most recent quarter.

Mersana’s lead ADC, upifitamab rilsodotin, is currently being tested as a maintenance therapy for recurrent, platinum-sensitive ovarian cancer in a phase 3 trial.

It’s also being tested in platinum-resistant ovarian tumors in a single-arm pivotal trial, as well as in an early-stage umbrella trial in combination with other ovarian cancer treatments.

Mersana’s ADC collaboration with Synaffix was expanded a few months before the Janssen agreement.

Mersana could pay more than US$1 billion in that deal in exchange for access to the Dutch biotech’s site-specific platform for six additional ADC targets. The original US$295 million deal included a single target date in 2019.

Meanwhile, Synaffix also struck a US$415 million biobucks deal with Genmab last month.

Mersana’s previously failed collabo

Mersana’s previous collaboration with a Big Pharma did not go well. Takeda came on board for a similar partnership in 2016, with a US$40 million upfront payment and a US$1 billion-plus in milestone payments, drawn to the biotech’s most advanced platform tech, dubbed Dolaflexin, which used a unique linker technology to connect an antibody with as many as 12 to 15 drugs.

The significant increase from the usual three to four drugs per payload promised higher efficacy and the ability to reach cancer patients that other ADCs at the time couldn’t.

However, once in the clinic, its lead compound, a HER2-targeted ADC, raised serious safety concerns, prompting a partial clinical hold.

Mersana quickly devised a strategy to exclude high-risk patients from trials and test alternative dosing regimens, but it was too late: Takeda decided to terminate their agreement, and the competitive environment for HER2-targeted therapies forced Mersana to discontinue its lead drug.

Since then, Mersana’s newer ADC platforms have taken center stage, including the core platform featured in the J&J deal, known as Dolasynthen.

While retaining the desirable elements of Dolaflexin, Dolasynthen improves on it by producing ADCs with improved physicochemical and pharmacokinetic properties, including the ability to manufacture them more consistently, according to the company.

In comparison to 2016, Mersana will face a much larger field of ADC enthusiasts. As the class gains traction both clinically and commercially, an endless stream of drug developers is placing bets.

For instance, AstraZeneca and Daiichi Sankyo are claiming the big HER2 drug Enhertu, Gilead promoting Immunomedics’ Trodelvy, and Roche, Seagen, and ADC Therapeutics beefing up their pipelines.

 Not to mention the plethora of startups springing up all over the world.

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