We present the clinical course of a 4-year-old girl with neurofibromatosis type 1-associated, unresectable, symptomatic urinary bladder ganglioneuroma. She was initially trialed on sirolimus without response and subsequently responded to MEK inhibitor trametinib, with improvement clinically and radiographically over 10 months. This report broadens the repertoire of therapeutic strategies for MEK inhibition in diseases related to the MAPK pathway.

Oligodendrocytes (OLs) are differentiated from oligodendrocyte precursor cells (OPCs) in the central nervous system (CNS). Demyelination is a common feature of many neurological diseases such as multiple sclerosis (MS) and leukodystrophies. Although spontaneous remyelination can happen after myelin injury, nevertheless, it is often insufficient and may lead to aggravated neurodegeneration and neurological disabilities. Our previous study has discovered that MEK/ERK pathway negatively regulates OPC-to-OL differentiation and remyelination in mouse models. To facilitate possible clinical evaluation, here we investigate several MEK inhibitors which have been approved by FDA for cancer therapies in both mouse and human OPC-to-OL differentiation systems. Trametinib, the first FDA approved MEK inhibitor, displays the best effect in stimulating OL generation in vitro among the four MEK inhibitors examined. Trametinib also significantly enhances remyelination in both MOG-induced EAE model and LPC-induced focal demyelination model. More exciting, trametinib facilitates the generation of MBP+ OLs from human embryonic stem cells (ESCs)-derived OPCs. Mechanism study indicates that trametinib promotes OL generation by reducing E2F1 nuclear translocation and subsequent transcriptional activity. In summary, our studies indicate a similar inhibitory role of MEK/ERK in human and mouse OL generation. Targeting the MEK/ERK pathway might help to develop new therapies or repurpose existing drugs for demyelinating diseases.

BACKGROUND: Tunlametinib (HL-085) is a novel, highly selective MEK inhibitor with substantial clinical activities in patients with NRAS-mutant melanoma. This phase I study evaluated the safety and preliminary efficacy of tunlametinib plus vemurafenib in patients with advanced BRAF V600-mutant solid tumors.
METHODS: Patients with confirmed advanced BRAF V600-mutant solid tumors who had progressed on or shown intolerance or no available standard therapies were enrolled and received tunlametinib plus vemurafenib. This study consisted of a dose-escalation phase and a dose-expansion phase. Primary end points of this study were safety, the recommended phase II dose (RP2D), and preliminary efficacy.
RESULTS: From August 17, 2018 to April 19, 2022, 72 patients were enrolled. No dose-limiting toxicities occurred, and the maximum tolerated dose was not reached. The RP2D for BRAF V600-mutant non-small cell lung cancer (NSCLC) patients was tunlametinib 9 mg plus vemurafenib 720 mg, twice daily (BID, bis in die). Until the data cut-off date of December 15, 2023, of 33 NSCLC patients with evaluable disease, the objective response rate (ORR) was 60.6% (20/33; 95% confidence interval [CI], 42.1-77.1), the median progression free survival (PFS) was 10.5 months (95%CI, 5.6-14.5) and median duration of response (DoR) was 11.3 months (95%CI, 6.8-NE). At the RP2D, ORR was 60.0% (9/15; 95% CI, 32.3-83.7), the median PFS was 10.5 months (95%CI, 5.6 -NE) and median DoR was 11.3 months (95%CI, 3.9-NE). Of 24 colorectal cancer patients with evaluable disease, the ORR was 25.0% (6/24; 95% CI, 5.6-NE). All 72 patients had treatment-related adverse events (TRAEs), and the most common grade 3-4 TRAEs were anemia (n = 13, 18.1%) and blood creatine phosphokinase increased (n = 10, 13.9%). Tunlametinib was absorbed rapidly with Tmax of 0.5-1 h. Vemurafeinib did not influence the system exposure of tunlametinib and vice versa, indicating no drug-drug interaction for this combination.
CONCLUSIONS: Tunlametinib (HL-085) plus vemurafenib had a favorable safety profile and showed promising antitumor activity in patients with BRAF V600-mutant solid tumors. The RP2D for NSCLC was tunlametinib 9 mg BID plus vemurafeinib 720 mg BID.
BACKGROUND: ClinicalTrials.gov, NCT03781219.

Rationale: The response rate to the MEK inhibitor trametinib in BRAF-mutated melanoma patients is less than 30%, and drug resistance develops rapidly, but the mechanism is still unclear. Yes1-associated transcriptional regulator (YAP1) is highly expressed in melanoma and may be related to MEK inhibitor resistance. The purpose of this study was to investigate the mechanism of YAP1 in MEK inhibitor resistance in melanoma and to screen YAP1 inhibitors to further determine whether YAP1 inhibition reverses MEK inhibitor resistance. Methods: On the one hand, we analyzed paired melanoma and adjacent tissue samples using RNA-seq and found that the Hippo-YAP1 signaling pathway was the top upregulated pathway. On the other hand, we evaluated the transcriptomes of melanoma samples from patients before and after trametinib treatment and investigated the correlation between YAP1 expression and trametinib resistance. Then, we screened for inhibitors that repress YAP1 expression and investigated the mechanisms. Finally, we investigated the antitumor effect of YAP1 inhibition combined with MEK inhibition both in vitro and in vivo. Results: We found that YAP1 expression levels upon trametinib treatment in melanoma patients were correlated with resistance to trametinib. YAP1 was translocated into the nucleus after trametinib treatment in melanoma cells, which could render resistance to MEK inhibition. Thus, we screened for inhibitors that repress YAP1 expression and identified multiple bromodomain and extra-terminal (BET) inhibitors, including NHWD-870, as hits. BET inhibition repressed YAP1 expression by decreasing BRD4 binding to the YAP1 promoter. Consistently, YAP1 overexpression was sufficient to reverse the proliferation defect caused by BRD4 depletion. In addition, the BET inhibitor NHWD-870 acted synergistically with trametinib to suppress melanoma growth in vitro and in vivo. Conclusions: We identified a new vulnerability for MEK inhibitor-resistant melanomas, which activated Hippo pathway due to elevated YAP1 activity. Inhibition of BRD4 using BET inhibitors suppressed YAP1 expression and led to blunted melanoma growth when combined with treatment with the MEK inhibitor trametinib.

UNASSIGNED: Non-small cell lung cancer (NSCLC) has a poor prognosis and usually presents resistance against radiotherapy. MEK inhibitors have been proven to possess a radiosensitization effect. The compound KZ-001 as a particular MEK inhibitor is superior to the listed MEK inhibitor AZD6244.
UNASSIGNED: To investigate whether KZ-001 could enhance the radiosensitivity of NSCLC cell lines in vitro.
UNASSIGNED: MTT and colony formation assay were used to evaluate the radiosensitivity effect of KZ-001. Immunofluorescence, cell cycle, apoptosis staining, and western blot experiments were used to explore the radiosensitivity mechanism.
UNASSIGNED: KZ-001 significantly decreased A549 cell viability at 6 Gy and 8 Gy radiation doses and caused the radiosensitivity at 1 Gy, 4 Gy, and 6 Gy in colony formation experiments. The A549 apoptosis ratio induced by irradiation (IR) combined with KZ-001 increased significantly in comparison with that by IR monotherapy (10.57% vs. 6.23%, P = 0.0055). The anti-apoptosis marker Bcl-XL was found downregulated in KZ-001 and IR-treated A549/H460 cells, but apoptosis marker Bax was downregulated in H460. Extracellular regulated protein kinases (ERK1/2) phosphorylation of H460 cells could be blocked both by IR alone and IR combined with KZ-001. IR combined with KZ-001 is able to inhibit ERK activation of A549 cells apparently. KZ-001 increased the proportion of G2 phase in irradiated cells from 21.24% to 32.22%. KZ-001 could also significantly increase the double-strand break damage cell ratio to more than 30% compared to the irradiation alone group.
UNASSIGNED: MEK1/2 inhibitor KZ-001 is a potential radiosensitizer for clinical applications.

BACKGROUND: There are no standard third-line treatment options for metastatic pancreatic ductal adenocarcinoma (mPDAC). Trametinib in combination with hydroxychloroquine (HCQ) or CDK4/6 inhibitors for pancreatic adenocarcinoma showed promising efficacy in preclinical studies. However, the regimens have not been well examined in patients with mPDAC.
METHODS: Patients with mPDAC who received the combination of trametinib and HCQ or CDK4/6 inhibitors as third- or later-line therapy were reviewed. The efficacy and prognosis were further analyzed.
RESULTS: A total of 13 mPDAC patients were enrolled, of whom 8 and 5 patients were treated with trametinib plus HCQ or a CDK4/6 inhibitor (palbociclib or abemaciclib), respectively. All enrolled patients had either KRAS G12D or G12V mutations and had received a median of 3 prior lines of therapy (range, 2-6). The median trametinib treatment duration was 1.4 months. Of the 10 patients with measurable disease, only 1 patient achieved stable disease, and the remaining patients had progressive disease. Moreover, in patients treated with trametinib plus HCQ and a CDK4/6 inhibitor, the median progression-free survival was 2.0 and 2.8 months, respectively, and the median overall survival was 4.2 and 4.7 months, respectively. Moreover, 5 (50%) patients experienced grade 3-4 adverse events in 10 patients with available safety data.
CONCLUSIONS: The combination of trametinib and HCQ or CDK4/6 inhibitors may not be an effective later-line treatment for mPDAC, and the current preliminary findings need to be confirmed by other studies with larger sample sizes.

Background: Aberrant activation of RAS-RAF-MEK-ERK signaling pathway has been implicated in more than one-third of all malignancies. MEK inhibitors are promising therapeutic approaches to target this signaling pathway. Though four MEK inhibitors have been approved by FDA, these compounds possess either limited efficacy or unfavorable PK profiles with toxicity issues, hindering their broadly application in clinic. Our efforts were focused on the design and development of a novel MEK inhibitor, which subsequently led to the discovery of tunlametinib. Methods: This study verified the superiority of tunlametinib over the current MEK inhibitors in preclinical studies. The protein kinase selectivity activity of tunlametinib was evaluated against 77 kinases. Anti-proliferation activity was analyzed using the 3-(4,5-dimethylthiazole-2-yl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) or (3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium) (MTS) assay. ERK and phospho-ERK levels were evaluated by Western blot analysis. Flow cytometry analysis was employed to investigate cell cycle and arrest. Cell-derived xenograft (CDX) and Patient-derived xenograft (PDX) models were used to evaluate the tumor growth inhibition. The efficacy of tunlametinib as monotherapy treatment was evaluated in KRAS/BRAF mutant or wild type xenograft model. Furthermore, the combination studies of tunlametinib with BRAF/KRASG12C/SHP2 inhibitors or chemotherapeutic agent were conducted by using the cell proliferation assay in vitro and xenograft models in vivo. Results: In vitro, tunlametinib demonstrated high selectivity with approximately 19-fold greater potency against MEK kinase than MEK162, and nearly 10-100-fold greater potency against RAS/RAF mutant cell lines than AZD6244. In vivo, tunlametinib resulted in dramatic tumor suppression and profound inhibition of ERK phosphorylation in tumor tissue. Mechanistic study revealed that tunlametinib induced cell cycle arrest at G0/G1 phase and apoptosis of cells in a dose-proportional manner. In addition, tunlametinib demonstrated a favorable pharmacokinetic profile with dose-proportionality and good oral bioavailability, with minimal drug exposure accumulation. Furthermore, tunlametinib combined with BRAF/KRASG12C/SHP2 inhibitors or docetaxel showed synergistically enhanced response and marked tumor inhibition. Conclusion: Tunlametinib exhibited a promising approach for treating RAS/RAF mutant cancers alone or as combination therapies, supporting the evaluation in clinical trials. Currently, the first-in-human phase 1 study and pivotal clinical trial of tunlametinib as monotherapy have been completed and pivotal trials as combination therapy are ongoing.

Colorectal cancer (CRC) is a common malignant tumor with a high incidence and mortality worldwide. Preoperative chemoradiotherapy is a common treatment for patients with metastatic colorectal cancer (mCRC) as it reduces colostomy and local recurrence. The RAS (rat sarcoma)-RAF (extracellular signal-regulated kinase)-MEK (mitogen-activated protein kinase)-ERK (extracellular signal-regulated kinase) pathway regulates important cellular processes in the CRC. Abnormal ERK activation stimulates cell growth and provides a survival advantage. Our group has previously reported that the compound KZ02 has a stronger ability to inhibit tumor growth than AZD6244 (a MEK inhibitor). In this study, we evaluated the antitumor activity of KZ02 in combination with ionizing radiation (IR) and investigated its mechanism of action in BRAF-mutated colorectal cancer. Our results showed that this combination kills tumor cells better than either radiation or drugs alone, both in vivo and in vitro. Furthermore, studies have shown that KZ02 inhibits ERK overactivation. The combination resulted in a G1 phase arrest, a reduction in the radioresistant S phase, and aggravating DNA damage. It can also inhibit Pim-1 (Moloney murine leukemia virus-1), p-BAD (Bcl-2 associated agonist of cell death), Bcl-2 (B-cell lymphoma 2) and Bcl-XL (B-cell lymphoma-extra large) levels and promote apoptosis when combined with radiation. Our results suggest that KZ02 significantly increases the radiosensitivity of BRAF-mutated CRC cells by perturbing the cell cycle, increasing DNA damage, and promoting tumor apoptosis.

FCN-159 is a novel, oral, potent, selective MEK1/2 inhibitor in clinical development for the treatment of NRAS-mutant advanced melanoma and neurofibromatosis type 1. We investigated the effect of food on the pharmacokinetics (PK), safety, and tolerability of FCN-159.
In this single-center, open-label, phase 1 study with a three-period, three-sequence, crossover design, healthy Chinese male subjects (n = 24) were randomized (1:1:1) to receive a single, oral 8 mg dose of FCN-159 in the fasted state (overnight, > 10 h), and with a low-fat and a high-fat meal, separated by a 10-day washout. PK parameters including time to maximum plasma concentration (Cmax) and area under the concentration-time curve (AUC) were compared using geometric least-squares mean ratios (GLSMR), with the fasted state as the reference. A 90% CI for the GLSMR within 80-125% indicated no significant food effect.
A low-fat meal (n = 23) did not affect the PK profile of FCN-159: G LSMR for AUC from time 0 to t (AUC0-t), 106.9% (90% CI 99.9-114.4%); AUC from time 0 to infinity (AUC0-∞), 106.8% (90% CI 100.0-114.0%); Cmax, 96.4% (90% CI 83.9-110.8%). A high-fat meal (n = 24) did not affect exposure to FCN-159 (GLSMR for AUC0-t, 99.4%; 90% CI 99.0-106.3%; AUC0-∞, 99.5 5%; 90% CI 93.2-106.1%), but modestly reduced Cmax by 15% (GLSMR 84.9%; 90% CI 74.0-97.3%). Both the low-fat and high-fat meals slightly prolonged the median time to Cmax by 0.5 h (90% CI 0.5-1.0 h). FCN-159 was generally well tolerated, with a lower incidence of treatment-emergent adverse events following administration in the fasted state than with a low-fat or high-fat meal (20.8%, 39.1%, and 37.5%, respectively).
Food did not affect the PK profile of FCN-159 to a clinically meaningful extent compared with administration in the fasted state.

HL-085 is a selective, orally administered MEK1/2 inhibitor. We aimed to evaluate the safety and efficacy of HL-085 in patients with advanced melanoma harboring NRAS mutations.
This was a multicenter phase 1 study. HL-085 was administered twice daily in a standard 3 + 3 dose-escalation design (10 dose cohorts; 0.5-18 mg twice daily), followed by dose expansion at the recommended phase II dose (RP2D). The primary endpoints included tolerability, dose-limiting toxicity (DLT), maximum tolerated dose (MTD) and RP2D.
Between September 13, 2017, and January 18, 2021, 42 patients were enrolled (dose escalation phase: n = 30; dose expansion phase: n = 12). No DLT was reported during dose escalation and MTD was not reached with HL-085 doses up to 18 mg twice daily. The RP2D was 12 mg twice daily. The most common all-grade drug-related adverse events (AEs) across all dose levels were rash (61.9%), increased creatine phosphokinase (CK, 59.5%), face edema (50.0%), increased aspartate aminotransferase (47.6%), peripheral edema (40.5%), diarrhea (33.3%), alanine aminotransferase (33.3%), and paronychia (19.0%), most of which were grade 1 and 2. Most frequency of grade ≥ 3 AEs were CK (14.2%), asthenia (7.1%), peripheral edema (4.8%), and acneiform dermatitis (4.8%). In the cohort of 12 mg twice daily dose (15 patients), confirmed objective response rate was 26.7%; disease control rate was 86.7%; median duration of response was 2.9 months; median progression-free survival was 3.6 months.
The HL-085 showed acceptable tolerability and substantial clinical activity in patients with advanced melanoma harboring NRAS mutations.
Trial registration ClinicalTrials.gov number: NCT03973151.