Company: DAWN
Filing Date: 2025-02-25
Form Type: 10-K
Source: 0000950170-25-026654
Chunk: 71

Company: Day One Biopharmaceuticals, Inc.
Filing Date: 2025-02-25
Form: 10-K
Item: Item 1
Chunk 71
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 of BRAF has important consequences: the resultant novel oncogene is both aberrantly expressed and it also exhibits constitutive, or always-on, activation of the kinase domain. This kinase activity can result in the activation of downstream oncogenic signaling, exacerbating tumor growth. BRAF gene fusions have been observed in patients with prostate cancer, melanoma, radiation-induced thyroid cancer, and pLGG.

Three BRAF inhibitors have been approved by the FDA for the treatment of certain solid tumors containing only BRAF V600E or V600K mutations, including melanoma, non-small cell lung cancer, anaplastic thyroid cancer, and colorectal cancer. These first-generation BRAF inhibitors, known more generally as type I RAF inhibitors, are vemurafenib, marketed as Zelboraf® by Genentech; dabrafenib, marketed as Tafinlar® by Novartis; and encorafenib, marketed as Braftovi® by Pfizer. However, despite initial clinical responses to monotherapy type 1 RAF inhibitors, most patients relapse within one year following the initiation of treatment.

One way by which resistance develops to type I RAF inhibitors is related to the mechanism of normal RAF activation in cells. In contrast to the constitutively active V600E or V600K variant, which is active as a monomer, normal RAF function requires formation of dimers of RAF. Approved inhibitors of V600E/K BRAF do not block the activity of RAF dimers or other non-V600 BRAF mutations. In fact, the binding of some of these inhibitors to V600E/K BRAF can stimulate the formation of dimers, thereby causing paradoxical activation (undesired increases 

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in MAP kinase signaling) in RAF wild-type cells – a phenomenon which could potentially lead to renewed tumor growth. Paradoxical activation of wild-type RAF also occurs in non-tumor tissue. This leads to a common adverse event associated with these agents—the development of proliferative pre-malignant and malignant skin lesions. In order to avoid resistance and paradoxical activation, in many instances type I RAF inhibitors need to be given in combination with MEK inhibitors, but again only to patients with BRAF V600E/K mutations.

Figure 2. Schema showing the effect of different RAF inhibitors on monomeric RAF kinases (i.e., BRAF V600E; top section) or dimeric RAF kinases (bottom section). ERK activation is strongly activated downstream of BRAF V600E, even