RXi Pharmaceuticals has signed an exclusive option agreement giving it until April 5, 2017, to acquire MirImmune—a deal that would expand the buyer’s pipeline into immuno-oncology.

The option agreement allows RXi to acquire all outstanding capital stock of MirImmune for 19.99% of the then outstanding shares of common stock of Rxi, plus additional payments tied to MirImmune achieving undisclosed milestones.

The stock portion of the agreement would equal about 13 million shares, based on the total 65,349,121 shares reported by the company as of March 15, according to its Form 10-K annual report for 2015. At yesterday’s closing share price of $1.69, the stock portion would have a value of $21.97 million, not counting the milestone payments.

The option agreement comes a year and a half after MirImmune signed an exclusive license agreement for RXi's novel and proprietary sd-rxRNA technology for use in developing cell-based cancer immunotherapies.

Since then, RXi said, MirImmune has filed intellectual property that covers the use of RNA interference (RNAi) compounds for use in cell therapy—and has shown the effectiveness of RXi’s sd-rxRNA platform for cell therapy by:

  • Selecting six lead sd-rxRNA compounds against six different extracellular and intracellular immune check points
  • Generating preclinical data showing the silencing of all six targets in vitro, alone and in combinations
  • Demonstrating efficient and long-lasting knockdown of immune checkpoints in vivo
  • Showing through additional preclinical data that mesothelin-targeted chimeric antigen receptor (CAR) T cells modified with the anti-programmed death-1 (PD1)-targeted sd-rxRNA significantly slowed in vivo tumor growth in a human ovarian cancer model in mice
  • Generating promising results in ex vivo testing on melanoma cells obtained from a patient-donor, using sd-rxRNA reduction of PD1 in tumor-infiltrating lymphocytes (TILs) resulting in destruction of those melanoma cells

“We treat therapeutic immune cells with RNAi compounds ex vivo to knock down immune checkpoints, such as PD-1, LAG-3 [lymphocyte activating 3], and others. This treatment boosts the antitumor activity of the cells when they are subsequently administered to the patients,” MirImmune CEO Alexey Eliseev, Ph.D., said in a statement. “Our plan is to develop sd-rxRNA as a more safe and effective alternative to gene editing of the immune cells or checkpoint blockade with monoclonal antibodies.”

RXi said MirImmune’s progress in cell therapy using RXi's RNAi technology “forms a strong foundation for therapeutic development in the immuno-oncology space.”

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