(Adds background, details of U.S. sales of drug, share move)

Sept 13 (Reuters) – AbbVie and Regenxbio Inc entered a partnership to develop and commercialize RGX-314, a gene therapy candidate for the treatment of chronic retinal diseases, which would give the latter an upfront payment of $370 million.

Shares of Regenxbio rose 18% to $39.18 in premarket trade.

Regenxbio may also potentially receive up to $1.38 billion in milestone payments, the pharmaceutical companies said on Monday.

AbbVie has been trying to strengthen its portfolio of drugs as it prepares for the loss of U.S. patent protection for its top-selling arthritis treatment Humira in 2023.

RGX-314 is currently in a key trial for the treatment of wet age-related macular degeneration (AMD), an eye disorder causing blurred vision or a blind spot in the visual field. The trial is testing RGX-314 injected under the retina.

It is also being studied in patients with wet AMD and diabetic retinopathy in two separate mid-stage clinical trials using a different type of delivery.

AbbVie markets a range of eye disease drugs in the United States, including Acular and Acuvail, which are used to treat inflammation following cataract surgery, and Durysta to reduce eye pressure in patients with glaucoma.

Regenxbio will be responsible for the completion of the ongoing studies of RGX-314. Both companies will share the costs of additional trials of RGX-314, they said.

AbbVie will lead the clinical development and commercialization of RGX-314 globally.

The companies said they would equally split the profit from net sales of RGX-314 in the United States, and that AbbVie would pay Regenxbio tiered royalties on net sales of RGX-314 outside the country. (Reporting by Amruta Khandekar; Editing by Amy Caren Daniel)

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