Can a Nektar rival make it on Nasdaq with a $100M IPO? Synthorx is giving it a shot

After all the hubbub around Nektar’s second-gen take on a pegylated IL-2, is Nasdaq ready for a rival that believes it can do the whole field one better?

Synthorx, a preclinical biotech with primate data that was set up by Avalon, has filed for a $100 million IPO — hoping to catch a wave of excitement that has propelled scores of S-1s this year for early-stage companies.

Like Nektar, Synthorx started out with the knowledge that Proleukin never lived up to its incredible initial promise in cancer, largely because of a bad tox profile highlighted by vascular leak syndrome. And the little biotech has been working on its own alternative under the guidance of CEO Laura Shawver, an experienced biotech vet.

Here’s the relevant section from the S-1 filed with the SEC:

Using our Expanded Genetic Alphabet platform technology, we site-specifically pegylated IL-2 to invent THOR-707 for immuno-oncology, or IO. We have designed THOR-707 to kill tumor cells by increasing CD8+ T and NK cells without causing VLS (vascular leak syndrome) that has been observed with aldesleukin. In our non-human primate…preclinical studies THOR-707 at doses ten times higher than the doses observed to maximally expand CD8+ T cells in NHP did not result in signs of VLS, as measured by increases in eosinophil count and lung and liver weight. Published preclinical literature shows that combining IL-2 treatment with PD-1 inhibitors could have synergistic effects in enhancing CD8+ T cell responses. As a result, we believe that THOR-707 in combination with immune checkpoint inhibitors may have greater anti-tumor effects than PD-1 inhibitors alone without the VLS observed with aldesleukin.

There’s also another IL-2 program that works in reverse, promoting regulatory T cells that suppress the immune system to the advantage of patients suffering from autoimmune disease.

Nektar’s NKTR-214 is spotlighted as the biggest rival in the clinic. But the S-1 also cites Roche’s RO6874281, which spurred 3 objective responses in an early study. That drug, they say, is similar to their own. And there is also Alkermes’ ALKS-4230, “where a portion of the alpha receptor is attached to IL-2, which disables alpha binding. In a Phase I study of advanced solid tumors, no responses were observed in 24 patients.”

Jay Lichter’s Avalon still controls the largest batch of stock, with 32%, with Peter Kolchinsky at RA Capital in for 28.2% and OrbiMed holding 21.5%. Those are the big 3. Shawver herself has a slight 1% of the equity. Tighe Reardon, the CFO at Avalon, has 6.5% of the shares.

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Research Scientist - Immunology
Recursion Pharmaceuticals Salt Lake City, UT
Director of Operations
Atlas Venture Cambridge, MA

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