Tovorafenib: A novel B‑RAF inhibitor for the treatment of pediatric low‑grade glioma (Review)

1. Introduction

Pediatric low-grade glioma (pLGG) is the most common type of brain tumor among children. It is characterized by slow-growing tumors that are often curable with complete surgical removal (1-3). Of note, ~2,000 patients suffer from this type of cancer annually in the USA. Symptoms vary depending on the location of the tumor, but can include headaches, vision problems, seizures and balance issues. Treatment options may involve surgery, chemotherapy, or targeted therapy, and the optimal treatment approach is selected based on factors, such as the location of the tumor, molecular characteristics and the possibility of complete surgical removal (4). Common treatments include a combination of thioguanine + procarbazine + CCNU + vincristine (TPCV) and vincristine + carboplatin. Trametinib in combination with dabrafenib is used for the treatment of pediatric patients who are ≥1 year of age with pLGG and with a BRAF V600E mutation who require systemic therapy (1).

The B-RAF signaling pathway is a key component of the RAS-RAF-MEK-ERK [mitogen-activated protein kinase (MAPK)] cascade, one of the most critical intracellular signaling networks regulating cell growth, proliferation, differentiation and survival (Fig. 1). Typically signaling begins at the cell surface receptor, such as a receptor tyrosine kinase (RTK) [e.g., epidermal growth factor receptor (EGFR), fibroblast growth factor receptor (FGFR) and platelet-derived growth factor receptor (PDGFR)]. Upon ligand binding (e.g., growth factors), RTKs undergo dimerization and auto phosphorylation. Growth factor receptor-bound protein 2 (GRB2) and son of sevenless (SOS) are key adaptor proteins that link activated RTKs. GRB2 SH2 binds phospho-tyrosines on RTK and SH3 domains of GRB2 recruit SOS (4-6). GRB2 is a 25-kDa adaptor protein. GRB2/SOS also play roles in activating downstream phosphatidylinositol 3-kinase (PI3K), leading to AKR mouse thymoma (AKT) activation for survival and growth. SOS promotes the guanosine diphosphate (GDP)-guanosine triphosphate (GTP) exchange on rat sarcoma virus (RAS). This recruits and activates RAS, a small GTPase that acts as a molecular switch: RAS-GDP → inactive; RAS-GTP → active. The GDP-GTP exchange is a critical molecular switch mechanism that activates G-proteins (or GTPases) in cell signaling, turning them from an ‘off’ (GDP-bound) to an ‘on’ (GTP-bound) state. Guanine nucleotide exchange factors catalyze this process by releasing bound GDP, allowing the more abundant cellular GTP to bind, which triggers conformational changes that initiate cellular responses (7).

Figure 1 RAF signaling pathway. RAF, rapidly accelerated fibrosarcoma; RTK, receptor tyrosine kinase; GRB2, growth factor receptor-bound protein 2; SOS, son of sevenless; PI3K, phosphatidylinositol 3-kinase; GDP, guanosine diphosphate; GTP, guanosine triphosphate; PIP2, phosphatidylinositol 4,5-bisphosphate; PIP3, phosphatidylinositol 3,4,5-trisphosphate; AKT, AKR mouse thymoma; ERK, extracellular signal-regulated kinase; mTOR, mammalian target of rapamycin.

Active RAS-GTP recruits rapidly accelerated fibrosarcoma (RAF) kinases (A-RAF, B-RAF and C-RAF/RAF-1) to the plasma membrane. B-RAF is the most potent activator of the downstream pathway due to its higher basal kinase activity and stronger interaction with MEK1/2. Inactive B-RAF is autoinhibited (the N-terminal regulatory region suppresses kinase activity). Upon binding the of RAS-GTP, conformational changes relieve inhibition. B-RAF can form homo (BRAF-BRAF)- or heterodimers (particularly with C-RAF), leading to MEK phosphorylation. MEK phosphorylates extracellular signal-regulated kinase (ERK). The dysregulation of this pathway, often through mutations in BRAF, is a hallmark of several types of cancer, including melanoma, thyroid, brain cancer and colorectal cancers. Although the majority of driver events are MAPK pathway alterations (BRAF fusions/mutations and NF1), the PI3K/AKT/mammalian target of rapamycin (mTOR) activation is common as a co-operating pathway (PTEN loss or promoter methylation, occasional PIK3CA mutations, upstream RTK activation) (3). PI3K/mTOR activation can influence the progression and treatment resistance of pLGG (5). Tovorafenib is a small-molecule kinase inhibitor, specifically a type II pan-RAF inhibitor. It is orally bioavailable anpenetrates the central nervous system (CNS), which is relevant for its use in brain tumors (8-10). Tovorafenib was approved by the US FDA on April 23, 2024 in patients ≥6 months of age with relapsed or refractory pLGG harboring a BRAF fusion or rearrangement or BRAF V600 mutation (9).

A-RAF is the least well-characterized member of the RAF family and generally exhibits a lower basal kinase activity compared with other isoforms. Structurally, as with all RAF kinases, it contains conserved regions (CR1-CR3), including the Ras-binding domain and kinase domain; however, its regulatory regions confer weaker activation efficiency (10).

B-RAF is the most catalytically active RAF isoform and a driver of MAPK signaling. Its structure favors activation as it possesses constitutive phosphorylation-mimicking residues in its activation segment, reducing dependence on upstream priming events. Upon binding to active Ras, B-RAF readily forms dimers and efficiently phosphorylates MEK. Functionally, B-RAF is a dominant activator of the MAPK cascade, particularly in proliferative signaling. Notably, oncogenic mutations (e.g., V600E) render B-RAF constitutively active, constituting it a major therapeutic target in cancer (9).

C-RAF (also known as RAF-1) has intermediate kinase activity; however, it plays a central regulatory role in RAF signaling. Its activation is more tightly controlled and requires multiple steps: Recruitment by Ras, dephosphorylation of inhibitory sites, phosphorylation at activating residues and dimerization (often with B-RAF). Beyond MEK phosphorylation, C-RAF also has kinase-independent roles, including the regulation of apoptosis through interactions with mitochondrial proteins. This makes it functionally more versatile than B-RAF (9).

pLGGs are frequently driven by BRAF alterations (~50-85% of cases), most commonly the KIAA1549-BRAF fusion and BRAF V600E mutation, which constitutively activate the RAS/MAPK pathway to drive tumor growth. The pathway activates downstream MEK and ERK kinases, promoting cell proliferation and survival (2). Some distinct features are summarized in Table I.

Table I Some Features of A-RAF, B-RAF, and C-RAF.

Table I

Some Features of A-RAF, B-RAF, and C-RAF.

Feature	A-RAF	B-RAF	C-RAF (RAF1)
Kinase activity	Low	Highest	Intermediate
Activation dependence on Ras	High	Moderate	High
Key structural traits	Standard RAF domains; weaker regulatory efficiency	Activation segment mimics phosphorylation; primed for activity	Multiple regulatory phosphorylation sites; tightly controlled
Dimerization	Required but less efficient	Strong dimerization; can activate partners	Frequently heterodimerizes (e.g., with B-RAF)
Primary function in MAPK pathway	Modest/auxiliary signaling	Dominant MEK activation	Regulatory and signaling integration
Non-canonical roles	Limited/less defined	Mostly kinase-dependent signaling	Apoptosis regulation, mitochondrial functions
Oncogenic relevance	Rare	Very high (e.g., V600E)	Moderate

2. Physicochemical properties of tovorafenib

The chemical name of tovorafenib is 6-amino-5-chloro-N-((1R)-1-(5-(((5-chloro-4-(trifluoromethyl)-2-pyridinyl)amino)carbonyl)-2-thiazolyl)ethyl)-4-pyrimidinecarboxamide (; its molecular formula is C17H12Cl2F3N7O2S. It has a molecular weight of 506.29; LogD (pH 7.4) of 2.79; a polar surface area of 164 Ų; a hydrogen bond donor count of 3; a hydrogen bond acceptor count of 11; a freely rotating bond count of 5; a heavy atom count of 32; and a number of ring count 3(10).

Lipinski's Rule of Five dicts that compounds with a molecular weight <500 Da, <5 hydrogen bond donors, <10 hydrogen bond acceptors, and a LogP value <5 are more likely to exhibit favorable oral absorption and bioavailability. Tovorafenib is considered to generally comply with Lipinski's Rule of Five, with physicochemical properties consistent with oral bioavailability. Its balance of molecular weight, polarity and lipophilicity supports adequate membrane permeability and gastrointestinal absorption, which aligns with its clinical use as an orally administered targeted therapy (11).

3. Synthesis of tovorafenib

The synthesis of tovorafenib begins from compound 1 (Fig. 2). Compound 1 is converted into acid chloride using oxalyl chloride conditions and it is then coupled with compound 3 to provide compound 4. Compound 4 reacts with hydroxylamine to yield oxime, compound 5. Compound 5 is converted into primary amine using Zn/AcOH conditions. The chiral resolution of compound 6 using D-ditoluoyl tartaric acid in isopropanol followed by sodium carbonate basification provides chiral amine, compound 7. Compound 7 is coupled with compound 8 using amide coupling agents to afford the final compound 9, tovorafenib (11,12).

Figure 2 Synthesis of tovorafenib: Reagents and conditions: (a) Oxalyl chloride, DMF, DME, r. t., 2 h; (b) pyridine, CH3CN, 10˚C to r. t., 96%; (c) NH2OH, 45˚C, 5 h, 98%; (d) Zn, AcOH, 0˚C to 30˚C, 77%; (e) D-di-p-toluoyl tartaric acid, isopropanaol, Na2CO3, H2O, 53˚C to r. t., 88%; (f) EDC, HOBt, DIEA, DMF, r. t., 84%.

4. Dosage and administration, and mechanisms of action of tovorafenib

The dosage of tovorafenib based on body surface area is 380 mg/m2 orally once weekly (the maximum dosage is 600 mg orally once weekly) with or without food (13).

Mechanism of action of tovorafenib

Tovorafenib binds to RAF kinases in their inactive (DFG-out) conformation, which means it stabilizes RAF in a form that cannot signal downstream. It inhibits multiple forms of RAF including mutants BRAF V600E and V600D, wild-type BRAF, and wild-type CRAF. It has demonstrated antitumor activity in cells and xenograft tumor models harboring BRAF mutations and BRAF fusion. The efficacy of tovorafenib was assessed in a multicenter, open-label, single-arm clinical trial (FIREFLY-1; NCT04775485) in patients with a relapsed or refractory pediatric low-grade glioma harboring an activating BRAF alteration. The overall response rate was 51% and the median duration of response was 13.8 months (14-18). In biochemical kinase assays, IC50 values of tovorafenib are 7.1, 10.1 and 0.7 nM for the BRAF V600E mutant, wild-type BRAF, and wild-type CRAF, respectively (14).

Tovorafenib (DAY101) is a type II pan-RAF inhibitor designed to target aberrant MAPK signaling across multiple RAF isoforms, A-RAF, B-RAF and C-RAF (RAF-1), with activity against both monomeric and dimeric RAF configurations. This is particularly relevant in pLGG, where signaling is often driven by BRAF fusions (e.g., KIAA1549-BRAF) or activating mutations (10). A structured comparison of the efficacy of tovorafenib across RAF forms is presented in Table II.

Table II Comparative activity of tovorafenib across RAF configurations.

Table II

Comparative activity of tovorafenib across RAF configurations.

RAF isoform	Activation context	Monomer vs. dimer	Sensitivity to tovorafenib	Mechanistic notes	Relevance in pLGG
A-RAF	Less frequently mutated; low basal kinase activity	Mostly monomeric	Moderate	Lower intrinsic kinase activity; inhibited but not primary driver	Limited direct role
B-RAF (V600E)	Constitutively active mutation	Monomer-driven	High sensitivity	Tovorafenib stabilizes inactive conformation; strong MAPK suppression	Present in subset of pLGG
B-RAF (fusion, e.g., KIAA1549–BRAF)	Constitutive dimerization due to fusion	Dimer-driven	High sensitivity	Designed to inhibit RAF dimers without paradoxical activation
C-RAF (RAF-1)	Activated downstream of RAS or via dimerization	Dimer-dependent	Moderate-high	Tovorafenib disrupts RAF dimer signaling; prevents transactivation	Contributes to pathway amplification
RAF heterodimers (B-RAF/C-RAF)	RAS activation or fusion-driven signaling	Obligate dimers	High sensitivity	Key advantage: avoids paradoxical ERK activation seen with type I inhibitors	Highly relevant in fusion-driven pLGG
RAF homodimers (B-RAF/B-RAF)	Fusion or overexpression	Dimeric	High sensitivity	Effective inhibition of both protomers in dimer	Common in pLGG

[i] pLGG, pediatric low-grade glioma.

pLGG is characterized in the majority of cases by the constitutive activation of the RAS/RAF/MEK/ERK signaling cascade, most commonly through KIAA1549-BRAF fusion, BRAF V600E mutation, FGFR1 alterations, or NF1-associated pathway dysregulation. As tovorafenib is a selective, orally bioavailable, type II pan-RAF inhibitor, its therapeutic relevance in pLGG lies in its ability to directly suppress aberrant RAF signaling across multiple oncogenic contexts, while avoiding paradoxical MAPK activation often associated with first-generation BRAF inhibitors (4).

From a tumor-specific pharmacodynamic perspective, tovorafenib inhibits RAF dimer and monomer signaling, thereby reducing the downstream phosphorylation of MEK and ERK in pLGG cells harboring BRAF fusions or activating RAF alterations. This is particularly important in BRAF fusion-positive pLGG, where constitutive RAF dimerization drives chronic ERK activation and tumor proliferation. By stabilizing RAF in an inactive conformation, tovorafenib can suppress mitogenic signaling, decrease cyclin D1 expression, induce cell-cycle arrest and limit tumor cell proliferation. In preclinical glioma mouse models, sustained ERK pathway suppression has also been associated with reduced tumor growth and enhanced differentiation of neoplastic glial cells (18).

In BRAF V600E-mutant pLGG, tovorafenib may provide an advantage over selective BRAF V600 inhibitors as it targets both monomeric mutant BRAF and compensatory RAF dimers that frequently emerge as resistance mechanisms. This broader RAF blockade may delay pathway reactivation and improve durability of response. Furthermore, intermittent or adaptive dosing strategies may help maintain pathway suppression while reducing toxicity in pediatric patients requiring prolonged treatment (15).

Tovorafenib demonstrates robust, mechanistically consistent inhibition across RAF isoforms and dimer states, with particularly strong efficacy in dimer-driven BRAF fusion contexts, rendering it highly suitable for pLGG. Its pan-RAF and anti-dimer profile represents a significant advancement over earlier RAF inhibitors that were limited by paradoxical activation and poor dimer inhibition (16,17).

5. Binding mode

Tovorafenib is a highly selective, type II, pan-RAF inhibitor that stabilizes RAF kinases in their inactive (DFG-out) conformation (19). Unlike type I BRAF inhibitors (vemurafenib and dabrafenib) that bind the active conformation, the type II profile of tovorafenib results in a distinct binding mode that contributes to its activity against BRAF fusions and BRAF V600 as well as wild-type RAF dimers. From the high resolution BRAF-tovorafenib co-crystal structure (PDB: 8F7O), the bi-substituted pyrimidine ring of tovorafenib (the portion mimicking the ATP site) forms two hydrogen bonds with the hinge region of the kinase, one H-bond with the backbone amide of residue Cys532, and another H-bond with the backbone carbonyl of Cys532 (Fig. 3). On the left-hand side of the molecule, the amide nitrogen forms a H-bonding interaction with the side-chain of Thr529. The central thiazole ring of tovorafenib stays between Thr529 and the catalytic lysine (Lys483), although that is more a positional/steric placement than a hydrogen bond. A carbonyl oxygen (adjacent to the central ring) of tovorafenib forms a hydrogen bonding interaction with the backbone amide of Asp594, a residue in the DFG motif. On the right-hand side of the molecule, an amide nitrogen forms a hydrogen bond with the side-chain of Glu501 located on the αC-helix (19,20).

Figure 3 Hydrogen bonding networks of tovorafenib with BRAF.

Therefore, tovorafenib engages BRAF through a network of 4-5 hydrogen bonds and locks BRAF into an inactive DFG-out/αC-in. The trifluoromethyl-substituted pyridine ring of tovorafenib sits a hydrophobic pocket created by the displaced DFG phenylalanine (Phe595), the DFG-out flip opens this pocket, and the trifluoromethyl pyridine moiety nestles deeply there, contributing via hydrophobic interactions (19).

The overall inhibitor spans the ATP-binding cleft, leveraging both hinge binding (via the pyrimidine) and extension into the DFG-out hydrophobic pocket; this dual anchoring (hinge + DFG-pocket) is typical of type II inhibitors and is critical for potency and selectivity. By forming the H-bond with Glu501 (on the αC-helix), tovorafenib helps stabilize αC-in a conformation incompatible with kinase activation. This contributes to its ability to inhibit BRAF both as a monomer and in a dimer (19).

The DFG-out stabilization (via D594 backbone H-bond + hydrophobic insertion into the DFG-pocket) locks the activation loop in an inactive conformation, blocking access to ATP and preventing catalytic activity. As both protomers of BRAF dimer can bind tovorafenib (full occupancy), this helps explain the potency of the inhibitor even against BRAF dimers, which are relevant in a number of oncogenic contexts (e.g. BRAF fusions, RAS-driven dimerization) (20).

6. Pharmacokinetics

Tovorafenib is an orally available pan-RAF kinase inhibitor. The pharmacokinetic parameters described below are typically reported for the tablet or oral-suspension formulations used in clinical trials.

Absorption and bioavailability

Following a single oral dose, the median time to reach the peak plasma concentration (Tmax) is 3 h (range, 1.5-4 h). The tovorafenib steady state maximum concentration (Cmax) is 6.9 µg/ml (23%) and the area under the concentration-time curve (AUC) is 508 µg·h/ml (31%). The time to reach a steady state of tovorafenib is 12 days (33%). Tovorafenib exposure increases in a dose-proportional manner. No clinically significant tovorafenib accumulation occurs (13).

Based on a phase 1 study (QSC205140), the relative bioavailability of the tovorafenib powder for oral suspension (PfOS) compared to the tablet formulation is high, with bioequivalence confirmed between the two formulations. The quantitative pharmacokinetic data on the bioavailability of tovorafenib across formulations are summarized as follows:

i) Relative bioavailability (suspension vs. tablet); PfOS vs. tablet geometric mean ratios: The geometric mean ratios (90% confidence interval) of dose-corrected peak plasma concentration (Cmax/D) and area under the plasma concentration-time curve from time zero to the last measurable concentration (AUCo-last/D) indicate that the suspension is comparable to the tablet: Cmax/D: 96% (83-111%), AUC0-last/D: 104% (95-115%) (13).

ii) Bioavailability: Both formulations exhibit peak plasma concentrations at a median of 3 h, with a range of 1.5 to 4 h. When taken with a high-fat meal, there is no clinically significant change in overall exposure (Cmax or AUC), although Tmax may be delayed (~6.5 h vs. ~3 h fasted). In formulations studied (tablet vs. suspension), bioavailability is comparable (13). Plasma exposure increases roughly in a dose-proportional manner across studied dose ranges.

Distribution

The apparent volume of distribution of tovorafenib is 60 l/m2, indicating moderate distribution beyond plasma. Tovorafenib is highly protein bound, ~97.5% bound to human plasma proteins in vitro. The drug has been reported to cross the blood-brain barrier (13).

Metabolism and elimination

The primary metabolic pathways (in vitro) are through aldehyde oxidase and CYP2C8. Minor metabolism occurs through CYP3A, CYP2C9 and CYP2C19. Following a single radiolabeled oral dose, 65% of radioactivity is recovered via feces (8.6% unchanged drug) and 27% via urine (0.2% unchanged). This suggests that hepatic/biliary excretion is the major route, with only minimal renal elimination. In plasma after dosing, unchanged tovorafenib remains the major circulating moiety and metabolites represent a minor fraction (<10%) of total plasma radioactivity exposure (13,16).

Half-life, clearance, accumulation and steady state

The terminal elimination half-life (T1/2) of tovorafenib is ~56 h. Apparent clearance is 0.7 l/h/m2. Steady state is reached in ~12 days. Notably, when used on a once-weekly (QW) regimen, there is minimal to no significant accumulation; but more frequent dosing (e.g., every 2 days in early trials) has been associated with a 2.5-fold accumulation over 21 days (13).

7. Adverse reactions

From clinical trials, some treatment-related adverse events in patients have been observed, including rash, dry skin, hair color changes, fatigue, vomiting, nausea and headaches. All are manageable and below grade 3 in severity (10).

8. Comparison of tovorafenib with vemurafenib, dabrafenic and encorafenib

Tovorafenib is a type-II pan-RAF inhibitor (binds inactive RAF conformation and exhibits potent activity against CRAF and BRAF and RAF dimers), whereas vemurafenib, dabrafenib and encorafenib are type-I BRAF V600 selective inhibitors that bind the active monomeric mutant BRAF (Table III). This difference explains i) why tovorafenib may be active against tumors with BRAF fusions/rearrangements (common in pediatric LGG); and ii) why it may overcome some resistance mechanisms tied to RAF dimerization (20). Tovorafenib was developed with CNS penetration and has shown responses in pLGG; dabrafenib (particularly when combined with trametinib) also exhibits evidence of intracranial activity for V600E gliomas. Vemurafenib and encorafenib are less commonly used for BRAF-fusion gliomas. In cell free, biochemical assays, tovorafenib inhibits all RAF isoforms and vemurafenib, dabrafenib, encorafenic are more selective BRAF V600 mutant inhibitors (21,22). From clinical trial tovorafenib exhibits greater efficacy compared to other RAF inhibitors (10). The long half-life of tovorafenib helps to lower the dosing interval.

Table III Some features of tovorafenib, vemurafenib, dabrafenib, and encorafenib.

Table III

Some features of tovorafenib, vemurafenib, dabrafenib, and encorafenib.

Parameter	Tovorafenib	Vemurafenib	Dabrafenib	Encorafenib
Type	Type-II pan-RAF inhibitor	Type-I BRAF inhibitor	Type-I BRAF inhibitor	Type-I BRAF inhibitor
Target	Monomeric and dimeric BRAF, BRAF fusion, CRAF	BRAF V600E	BRAF V600E/K	BRAF V600E/K
Medical use	Pediatric low-grade glioma (use alone)	Melanoma	Melanoma, non-small cell lung cancer, thyroid cancer, low-grade glioma (with trametinib)	Melanoma, colorectal cancer, non-small cell lung cancer (with binimetinib)
Resistance	Designed to target RAF dimers and CRAF activity, a known resistance to type I inhibitor	Resistance via MAPK reactivation	Similar resistance, combination with MEK inhibitor overcome resistance	Combination strategies aim to delay resistance
Potential toxicity concern	Risk of paradoxical MAPK activation (lower than type I inhibitors)	Increased risk of paradoxical MAPK activation; higher rates of skin toxicities	Higher rates of skin toxicities	Higher rates of increased aminotransferase, serous retinopathy, and left ventricular dysfunction (when combined with a MEK inhibitor)
Cell-free assays
IC50 in nM CRAF (wild-type)	0.7	16	5	8
BRAF (wild-type)	10.1	39	3.2	0.47
ARAF	55	29	Not reported	Not reported
BRAFV600E (mutant)	7.1	8	0.5	0.35
Clinical results (human)
Dose	380 mg/m2 orally once weekly	1920 mg orally per day	300 mg orally per day	450 mg per day
Half-life (h)	88	57	8	3.5
Overall response rate	53%	53%	46%	63%
Median duration of response	16.6 months	6.7 months	5.6 months	16.6 months
Median progression-free survival (PFS)	16.6 months	6.8 months	5.1 months	14.9 months
Overall survival (OS)	42.6 months	15.9 months	18.7 months	33.6 months
Central nervous system penetration	Yes	No	Yes	No

9. Resistance mechanisms to tovorafenib and Pan-RAF inhibition

Tovorafenib represents a critical step forward over first-generation type I BRAF inhibitors; however, acquired and intrinsic resistance remain major clinical challenges, particularly in the long-term treatment of pLGGs. The resistance mechanism to RAF inhibition primarily involves the reactivation of alternative survival pathways.

One common mechanism involves the reactivation of the MAPK pathway independent of RAF inhibition, driven by enhanced MEK or ERK signaling. This can occur through the upregulation of RTKs, such as FGFR, PDGFR or EGFR, which are frequently expressed in gliomas and can drive RAS activation in the upstream of RAF. Increased RAS-GTP levels may promote RAF dimerization and stabilize signaling complexes, thereby partially reducing the effectiveness of inhibitors, even for type II pan-RAF inhibitors (23).

Another key escape route is the activation of compensatory PI3K/AKT/mTOR signaling, commonly observed in pLGG due to PTEN loss, epigenetic silencing, or upstream RTK activation. This pathway provides an alternative proliferative and survival signal when MAPK signaling is suppressed, contributing to disease stabilization rather than durable tumor regression (24).

Compared to type I BRAF inhibitors, tovorafenib is less likely to cause unwanted MAPK activation in wild-type cells, as it inhibits RAF dimers and CRAF activity. However, this benefit may only delay adaptive resistance mechanisms driven by pathway rewiring and tumor heterogeneity, rather than completely stop them (14).

10. Combination therapy strategies involving tovorafenib

Given the flexible nature of MAPK signaling and the long treatment times required for pediatric glioma, combination therapy is a sensible approach to improve the durability of response to tovorafenib. Several combination strategies have strong biological support and increasing clinical or preclinical evidence.

One approach is vertical pathway inhibition. In pLGG, the MAPK pathway can be disrupted at several points, leading to increased cell growth, survival and tumor formation. Combination therapies that include BRAF V600E inhibitors (vemurafenib, dabrafenib), MEK inhibitors (trametinib, pimasertib and selumetinib), and ERK inhibitors (ulixertinib) targeting these alterations have shown promising results in pLGG (25).

Another promising approach is horizontal pathway inhibition, combining tovorafenib with PI3K/AKT/mTOR pathway inhibitors. In pLGG, PI3K signaling is frequently coactivated. Dual inhibition may prevent compensatory survival signaling and enhance tumor control. Preclinical studies suggest that RAF inhibition sensitizes tumors to PI3K or mTOR blockade, providing a strong mechanistic rationale for this approach (26).

11. Conclusion and future perspectives

Tovorafenib is a next-generation, highly selective, CNS-penetrant type II RAF inhibitor that provides a meaningful therapeutic advance for pLGG driven by BRAF alterations, particularly BRAF fusions and rearrangements. By stabilizing RAF in its inactive conformation and avoiding paradoxical MAPK pathway activation, it provides more durable and safer pathway suppression than first-generation BRAF inhibitors. Its once-weekly oral dosing, favorable tolerability profile and clinically significant, durable responses position it as a valuable targeted therapy for children with recurrent or progressive BRAF-altered LGG. Continued research will clarify its role in combination strategies, long-term outcomes and potential applications in broader RAF- or MAPK-activated other tumors (27,28).

Positioning tovorafenib within the treatment landscape of pLGG benefits from a side-by-side comparison with current standards, followed by a clear proposal for how it could be integrated into evolving care algorithms (Table IV).

Table IV Comparative landscape: Tovorafenib vs. standard-of-care in pLGG.

Table IV

Comparative landscape: Tovorafenib vs. standard-of-care in pLGG.

Therapy class	Representative drugs	Mechanism of action	Molecular context	Clinical activity	Key limitation
Conventional chemotherapy	Carboplatin + vincristine	Cytotoxic (DNA damage, mitotic arrest)	Broad, non-selective	Disease stabilization, modest shrinkage	Toxicity, prolonged treatment, limited durability
MEK Inhibitors	Selumetinib, trametinib	Inhibit MEK1/2 downstream of RAF	MAPK-driven tumors (BRAF fusion/mutation)	High response rates in pLGG	Resistance via pathway reactivation or PI3K escape
First-generation BRAF inhibitors	Vemurafenib, dabrafenib	Selective BRAF V600E inhibition (monomers)	BRAF V600E mutant tumors	Strong responses in V600E	Paradoxical activation in WT/fusion RAF; limited in fusions
BRAF + MEK combinations	Dabrafenib + trametinib	Dual MAPK blockade	BRAF V600E tumors	Improved durability vs. monotherapy	Still limited in RAF fusions; resistance emerge
mTOR inhibitors	Everolimus	Inhibit mTORC1 signaling	PI3K/AKT/mTOR-driven or NF1-associated	Modest activity	Cytostatic, not curative
Pan-RAF inhibitor	Tovorafenib	Type II RAF inhibition (monomers + dimers)	BRAF fusions, V600E, RAF dimers	Strong responses, especially in fusion-driven pLGG	Adaptive resistance (e.g., PI3K/AKT activation)

[i] pLGG, pediatric low-grade glioma; mTOR, mammalian target of rapamycin; RAF, rapidly accelerated fibrosarcoma; PI3K, phosphatidylinositol 3-kinase.

Acknowledgements

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Funding

Funding: No funding was received.

Availability of data and materials

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Authors' contributions

HM was involved in the curation and investigation of data from the literature, data validation, visualization, and in the writing of the original draft. SKD contributed to the conceptualization of the study, in the investigation of data from the literature, in the editing of the manuscript, and also supervised the study. Both authors have read and approved the final manuscript. Data authentication is not applicable.

Ethics approval and consent to participate

Not applicable.

Patient consent for publication

Not applicable.

Competing interests

The authors declare that they have no competing interests.

Use of artificial intelligence tools

During the preparation of this work, AI tools were used to improve the readability and language of the manuscript or to generate images, and subsequently, the authors revised and edited the content produced by the AI tools as necessary, taking full responsibility for the ultimate content of the present manuscript.

References