Mersana takes IPO plunge, seeking $75M to push its antibody-drug conjugates

Company plans to list on the Nasdaq under the symbol MRSN

Mersana Therapeutics is capitalizing on a buoyant period with its filing for a $75 million IPO to advance its antibody-drug conjugates (ADCs) for cancer into the clinic.

The Nasdaq filing comes after a very quiet 2016 for biotech IPOs, and lends weight to the view that after a slow first quarter, 2017 might show something of a rebound.

It also speaks to the momentum gathering behind Mersana under the stewardship of CEO Anna Protopapas, who joined the company from Takeda unit Millennium in March 2015 and since then has led the company though a $33 million third-round financing and an expanded, transformative partnership with Takeda worth upwards of $1 billion.


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IPO specialist Renaissance Capital says Mersana filed the IPO confidentially in March and JP Morgan, Cowen & Co, Leerink Partners and Wedbush PacGrow are the joint book-runners on the deal. As yet pricing details have not been disclosed.

Mersana's bagged FDA approval to start trials of its lead ADC candidate XMT-1522 last October, winning a $20 million milestone for Takeda. The company is convinced the HER2-targeting drug is a step up from current HER2 therapies because it has improved potency but—hypothetically at least—improved tolerability.

The biotech thinks XMT-1522 has the potential to extend HER2-targeted therapy beyond the current 'HER2-positive' populations into patients with lower levels of HER2 expression, including breast, gastric and non-small cell lung cancers.

Following after is preclinical candidate XMT-1536, an ADC targeting NaPi2b that is expressed on NSCLC and ovarian cancers, amongst other tumor types, that in preclinical testing achieved "complete and durable regressions in patient-derived lung cancer models," according to Mersana.  Clinical trials are due to start in the latter half of this year.

Mersana is benefitting from a resurgence in interest in ADC drugs after the first drug in the category, Pfizer's Mylotarg, was pulled off the market in 2010 because of safety issues.

There are now a handful of ADCs on the market—notably Roche's HER2-targeting breast cancer therapy Kadcyla, Seattle Genetics' Adcetris for classical Hodgkin lymphoma and Spectrum Pharma's non-Hodgkin lymphoma (NHL) drug Zevalin—and well upwards of 200 candidates in clinical development.

Mersana's lead drug has been pitted against $800m-plus brand Kadcyla in animal models and shown durable tumor regressions where Roche's drug is inactive, according to the company.

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