Pharma BD Deal Intelligence
A $2.5B all-cash bet on an engineered IL-2 immuno-oncology platform that Sanofi wrote off entirely: after weak Phase 2 efficacy triggered a ~$1.6B impairment in 2022, Sanofi terminated all remaining studies and dropped the lead molecule from its pipeline by Q4 2024.
Sanofi acquired Synthorx for $2.5B for IL-2 cancer immunotherapy.
Sanofi dropped its IL-2 candidate SAR444245 (THOR-707) Phase 2 3-week dosing schedule citing lower-than-projected efficacy; ~$1.6B impairment charge.
THOR-707/SAR444245 solid-tumor study NCT04009681: overall status TERMINATED — 'terminated as per Sponsor decision... not related to any safety concerns.'…
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Sanofi acquired San Diego-based Synthorx for $68/share, ~$2.5 billion in cash, to anchor its immuno-oncology pipeline under then-new CEO Paul Hudson. The deal (announced December 9, 2019; closed January 23, 2020) was built around THOR-707 / SAR444245 (tenxilvunakin), an engineered 'not-alpha' PEGylated IL-2 designed to bias signaling toward CD8+ T and NK cells while avoiding regulatory-T-cell activation. The thesis did not pan out. In October 2022 Sanofi halted the Phase 2 platform's every-3-week dosing after efficacy came in 'lower than projected' and booked a ~EUR1.6 billion (~$1.6B) impairment, then ran a Phase 1/2 dose-intensification salvage program. In the fourth quarter of 2024 Sanofi removed SAR444245 from its R&D pipeline entirely; the lead solid-tumor study (NCT04009681) and the Pegathor Lymphoma study (NCT05179603) are both terminated per a strategic sponsor decision (not safety-driven), as verified on ClinicalTrials.gov in December 2025. The $2.5B acquisition is effectively a write-off.
SAR444245 (THOR-707, tenxilvunakin) is a Phase 2 not-alpha PEGylated IL-2 variant biased toward CD8+ T/NK cells; it competes in a history-laden cytokine class against three IO MOA classes. Engineered IL-2/IL-15 cytokines (direct class): bempegaldesleukin (NKTR-214, Nektar/BMS) failed Phase 3 PIVOT IO-001 in melanoma 2022, freezing class enthusiasm; nemvaleukin alfa (ALKS 4230, Mural Oncology) in Phase 3 ARTISTRY-7 ovarian cancer; MDNA11 (Medicenna) Phase 1/2; NKTR-358 repurposed for autoimmunity. Legacy IL-2: Proleukin (aldesleukin, Iovance/Clinigen) FDA approved 1992, used sparingly in metastatic melanoma and RCC due to severe toxicity; Proleukin also required as lymphodepletion backbone with TIL therapy Amtagvi (lifileucel, Iovance, FDA-approved 2024). Anti-PD-(L)1 backbone (combination partner and gatekeeper): Keytruda (pembrolizumab, Merck, ~$25B), Opdivo (nivolumab, BMS, ~$9B), Tecentriq (atezolizumab, Roche) and Libtayo (cemiplimab, Regeneron) dominate 1L solid tumor IO; all IL-2 variants are positioning as PD-1 add-ons. TIL and TCR-T therapies: Amtagvi (lifileucel) FDA-approved 2024 in melanoma; afami-cel (afamitresgene autoleucel, Adaptimmune/Tecelra) approved synovial sarcoma 2024. Commercial threat: the IL-2 class is in reputational rehabilitation after bempegaldesleukin failure; SAR444245 must deliver randomized evidence of Keytruda-additive benefit in PD-1-refractory or cold tumors to justify development, and Sanofi has publicly de-prioritized the asset.
Sanofi completed $2.5B acquisition of Synthorx, gaining THOR-707, an engineered IL-2 variant for cancer immunotherapy designed to avoid Treg activation.
Oct 2022: Sanofi halted SAR444245 Phase 2 every-3-week dosing after efficacy came in lower than projected; took a ~EUR1.6B (~$1.6B) impairment and reset to a dose-intensification program.
Sanofi removed SAR444245 (THOR-707) from its R&D pipeline in Q4 2024 following the 2022 ~$1.6B impairment and a failed Phase 2/salvage Phase 1-2 program. Lead solid-tumor (NCT04009681) and lymphoma (NCT05179603) trials terminated per strategic sponsor decision; the $2.5B deal is a write-off.
Engineered IL-2 program failed to show sufficient efficacy, took a ~$1.6B impairment, and was removed from Sanofi's pipeline by Q4 2024. The $2.5B Synthorx acquisition yielded no marketed product.
| Deal | Year | Value | Outcome |
|---|---|---|---|
| Sanofi SA / Synthorx Inc. (this deal) | 2019 | $2.5B | 15 |
| Sanofi SA / Regeneron Pharmaceuticals, Inc. | 2007 | $1.0B | 97 |
| Sanofi SA / Synthelabo S.A. | 1998 | $11.0B | 84 |
| Sanofi SA / Genzyme Corporation | 2011 | $20.1B | 84 |
| Sanofi SA / Amunix Pharmaceuticals Inc. | 2021 | $1.2B | 76 |
| Sanofi SA / Genzyme Corporation | 2010 | $18.5B | 75 |
| Sanofi SA / Translate Bio Inc. | 2018 | $805M | 73 |
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