Merck pays $400 million upfront for a SciBrunch KRAS G12D drug tested only in cells and mice

SPR2015's best-known efficacy figure counts mouse tumor models, not patients. In a head-to-head study, SciBrunch dosed the drug orally at 100 mg/kg once daily across more than 15 colorectal cell-derived or patient-derived xenograft models. It reported a 64.7% objective response rate and a 94.1% disease control rate as monotherapy ^[3]. Those percentages match 11 and 16 of 17 models, the smallest count above 15 that produces both ^[19]. The comparator was an unnamed G12D (ON) inhibitor ^[3], so outsiders cannot check the claim of significantly superior efficacy against a known drug.

The compound is a molecular glue built to inhibit the ON form of KRAS G12D, and SciBrunch is developing it for colorectal, lung and pancreatic cancers ^[5]. The mutation swaps glycine for aspartate at position 12. That change leaves KRAS active and continuously signaling for cell proliferation and survival, SciBrunch said ^[16]. The xenograft results were presented at the 2026 AACR Annual Meeting by a team that included founder and chief executive Tao Hu ^[2].

Other G12D drugs already have human data. Revolution Medicines reported in May that zoldonrasib produced a 52% confirmed objective response rate and 93% disease control in 27 efficacy-evaluable, previously treated patients with G12D lung cancer ^[10]. Beside SPR2015's mouse figures those numbers look close. They count different things: patients against mouse models, and lung tumors against colorectal ones ^[3][10]. In June, Verastem reported that 13 of 14 heavily pretreated metastatic pancreatic cancer patients taking 900 mg of VS-7375 once daily had a fall of more than 50% in the tumor marker CA19-9 ^[11]. A marker reading is a different endpoint from an objective response.

Sreyashi Paul, a business analyst with Lucidquest Ventures, cited both programs. "The diligence question is whether those properties survive translation into humans strongly enough to compensate for SPR2015's later start," Paul wrote on the firm's website ^[9].

Of the $2.13 billion headline, $400 million is upfront. The other $1.73 billion is tied to development, commercial and other milestones across several indications ^[12][17]. The upfront is about 19% of the total ^[18]. "Evidence continues to accumulate for the therapeutic potential of targeting the KRAS pathway, a well-characterized factor in tumor cell growth," said George Addona, senior vice president for discovery, preclinical development and translational medicine at Merck Research Laboratories ^[15].

Hu spoke for the seller. "This agreement with Merck not only validates the R&D strength of our platform but also underscores the potential of SPR2015 in addressing longstanding unmet medical needs in oncology," Hu said ^[14].