First-in-Class ERK 1 / 2 Inhibitor Ulixertinib ( BVD-523 ) in Patients with MAPK Mutant Advanced Solid Tumors : Results of a Phase I Dose-Escalation and Expansion Study

Ryan J. Sullivan1, Jeffrey R. Infante2, Filip Janku3, Deborah Jean Lee Wong4, Jeffrey A. Sosman5, Vicki Keedy5, Manish R. Patel6, Geoffrey I. Shapiro7, James W. Mier8, Anthony W. Tolcher9, Andrea Wang-Gillam10, Mario Sznol11, Keith Flaherty1, Elizabeth Buchbinder7, Richard D. Carvajal12, Anna M. Varghese12, Mario E. Lacouture12, Antoni Ribas4, Sapna P. Patel3, Gary A. DeCrescenzo13, Caroline M. Emery13, Anna L. Groover13, Saurabh Saha13, Mary Varterasian13, Dean J. Welsch13, David M. Hyman12, and Bob T. Li12 ReseaRch aRticle

Precedence for targeting the MAPK/ERK pathway has been established for treatment of BRAF V600-mutant melanoma and lung cancers, where combined BRAF and MEK inhibition is now standard of care following FDA approval of dabrafenib plus trametinib (16,17) and vemurafenib plus cobimetinib (18).Furthermore, favorable phase III data have been described for encorafenib plus binimetinib (19).Initially, BRAF inhibitor monotherapy was shown to be effective (20), yet the addition of MEK inhibition not only attenuated BRAF inhibitor-associated toxicities but also improved overall response rates (ORR), progression-free survival (PFS), and overall survival (OS; refs.[16][17][18].The combination of BRAF/ MEK inhibitor therapy now has been studied in a number of BRAF V600E-mutant solid-tumor malignancies with varying results, ranging from melanoma-like outcomes in lung cancer Research. on January 13, 2018.© 2017 American Association for Cancer cancerdiscovery.aacrjournals.orgDownloaded from Published OnlineFirst December 15, 2017; DOI: 10.1158/2159-8290.CD-17-1119 (17) to only rare responses in colorectal cancer (21), and intermediate results in thyroid cancer (22).Additionally, although it has been demonstrated that BRAF/MEK inhibitor-targeted combination therapy provides significant additional benefit beyond single-agent options in melanoma and other cancers, the majority of patients eventually develop resistance and disease progression after approximately 12 months (16,23,24).Several mechanisms of acquired resistance following either single-agent or combination therapies have been identified, including, but not limited to, the generation of BRAF splicing variants, BRAF amplification, NRAS or MEK mutations, and upregulation of bypass pathways (25)(26)(27)(28)(29)(30)(31).Central to these mechanisms of resistance is the reactivation of ERK signaling, which enables the rapid recovery of MAPK pathway signaling and escape of tumor cells from single-agent BRAF inhibitors or combination BRAF/MEK inhibitor therapies (32,33).Therefore, ERK inhibition may provide the opportunity to avoid or overcome resistance from upstream mechanisms, as it is the most distal master kinase of this signaling pathway.This is supported by preclinical evidence that inhibition of ERK by small-molecule inhibitors acted to both inhibit the emergence of resistance and overcome acquired resistance to BRAF and MEK inhibitors (34)(35)(36)(37)(38)(39).
Ulixertinib (BVD-523) is a highly potent, selective, reversible, ATP-competitive ERK1/2 inhibitor that has been shown to reduce tumor growth and induce tumor regression in BRAF-and RAS-mutant xenograft models.Furthermore, single-agent ulixertinib was found to inhibit tumor growth in human xenograft models that were cross-resistant to both BRAF and MEK inhibitors (38).Therefore, we undertook an open-label, first-in-human study (Clinicaltrials.govidentifier: NCT01781429) of oral ulixertinib to identify both the maximum tolerated dose (MTD) and the recommended phase II dose (RP2D).Study aims also included assessment of the pharmacokinetic and pharmacodynamic properties of ulixertinib as well as preliminary efficacy in patients with genetic aberrations in BRAF, both at V600 and non-V600 positions, NRAS, and MEK.

Patient Characteristics
Between April 4, 2013, and March 6, 2017, a total of 135 patients at 12 sites were consented and enrolled into this study; 27 patients were enrolled in the dose-escalation por-tion and 108 patients enrolled in the cohort expansion portion (Fig. 1).All patients received at least one dose of study drug.Baseline demographics and disease characteristics are presented in Table 1.The median patient age across the study was 62 years.Fifty-two percent (14/27) and 64% (69/108) of patients were male, and 59% (16/27) and 68% (73/108) had an Eastern Cooperative Oncology Group performance status (ECOG PS) of 1 for the dose-escalation and cohort expansion phases of the study, respectively.Patients who had previously received BRAF and/or MEK therapy represented 41% (11/27)  In cohort expansion, 108 patients were enrolled to six cohorts: patients without prior MAPK-targeted therapy who had BRAFmutant colorectal (17 enrolled/11 evaluable), lung (16/12), or other cancers (24/21), NRAS-mutant melanoma (22/18), or any tumor type with a MEK mutation (8/4), and patients with melanoma who had received prior BRAF and/or MEK inhibitor treatment and who were refractory to, intolerant of, or progressed on these treatments (21/15).A variety of specific BRAF and NRAS mutations were included, as were a number of different tumor types (Supplementary Table S1).Collectively, 91 patients with tumors harboring mutations in BRAF, 24 with NRAS, 9 with MEK, 5 with no mutation identified, and 6 with other mutations (5 KRAS and 1 GNAS) were enrolled.

Dose Escalation, Dose-Limiting Toxicities, MTD, and RP2D
Per protocol, 5 single-patient cohorts (from 10 through 150 mg twice daily) proceeded without evidence of a doselimiting toxicity (DLT).The 300-mg twice daily cohort was expanded to more fully characterize ulixertinib exposures.One of 6 patients given 600 mg twice daily experienced a DLT of grade 3 rash.The 900-mg twice daily dose exceeded the MTD, with 1 patient experiencing grade 3 pruritus, grade 3 elevated aspartate aminotransferase, and grade 3 elevated alanine aminotransferase, and another patient experiencing grade 3 diarrhea, grade 3 vomiting, grade 3 dehydration, and grade 3 elevated creatinine (Supplementary Table S2).The subsequent intermediate dose of 750 mg twice daily also exceeded the MTD, with DLTs of grade 3 rash and grade 2 diarrhea in 1 patient and grade 2 hypotension, grade 2 anemia, and grade 1 elevated creatinine in another patient, which delayed cycle 2 dosing.Therefore, the MTD and RP2D were determined to be 600 mg twice daily.

Pharmacokinetics and Pharmacodynamics
Pharmacokinetic analyses of ulixertinib following a single dose and after achieving steady state in dose escalation are summarized in Fig. 2A and B. Generally, orally administered ulixertinib (taken without food) was slowly absorbed, reaching maximum concentration (C max ) at approximately 2 to 4 hours, and then declining slowly thereafter.Plasma drug concentrations were measured as a function of time through a single dosing period (12 hours).As such, it was not possible to calculate an effective or terminal phase elimination rate.Ulixertinib pharmacokinetics were linear and dose proportional in terms of both C max (Supplementary Table S3) and area under the curve (AUC) when administered up to 600 mg twice daily on day 1 and at steady state (Fig. 2C and D, respectively).A further increase in exposure was not observed as the dose increased from 600 to 900 mg twice daily, although only a limited number of patients were treated at the higher dose levels.Minimal plasma accumulation of ulixertinib and its metabolites was observed at steady state at the lower (<75 mg twice daily) dose levels, whereas accumulation ranged from approximately 1.3-to 4.0-fold for the higher dose levels.The degree of interpatient variability in plasma exposure to ulixertinib and its metabolites was moderate and considered clinically manageable.Urinary excretion of ulixertinib on day 1 and at steady state was negligible (<0.2% of the dose) and not dose-related within this very low percentage range.Individual renal clearance values ranged from 0.128 to 0.0895 L/hour (where n = 1 patient per dose level) and mean values ranged from 0.0149 to 0.0300 L/hour (where n ≥3 patients).
of ERK activity was observed throughout the entire dosing period at RP2D.Ulixertinib exposures in cohort-expansion patients dosed at the RP2D were C max 1.15 and 2.12 μg/mL and AUC 0-12 8.07 and 19.93 μg*h/mL after the first dose and at steady state, respectively (Fig. 2F).

Antitumor Effects
Tumor response to ulixertinib was assessed in 25 and 81 evaluable patients from the dose-escalation and expansion cohorts, respectively, using Response Evaluation Criteria in Solid Tumors version 1.1 (RECIST v1.1).Per protocol, evaluable patients were defined as those who completed two cycles of treatment.Although no patient achieved a complete response, 14 partial responses were observed in 101 evaluable patients who were dosed at 600 mg twice daily or greater (3 in dose escalation and 11 in cohort expansion).

Dose-Escalation Cohorts
In dose escalation, 3 of 25 (12%) evaluable patients (all with melanoma harboring BRAF V600 mutations) achieved partial responses (PR).These 3 patients, who were BRAF/MEK therapy naïve, intolerant, or refractory, had response durations of 4.2, 12.4, and 24.9 months, respectively (Fig. 3A and B). Figure 3C shows computed tomography (CT) scans of one of the responders, who had progressed on prior vemurafenib and subsequent dabrafenib treatment and maintained a PR for 24.9 months.Noteworthy, this patient's PR was first observed after 13.5 months of treatment, whereas total time on study exceeded 38.4 months (ongoing at data cutoff).
Additionally, 6 patients had stable disease for more than 6 months.Figure 3B depicts the time to PR and the duration of response in this study population.One patient with bronchioloalveolar non-small cell lung cancer (not enough tissue for molecular profiling) was on treatment for >26.2 months with stable disease.Twenty-six of 27 patients (96%) discontinued treatment due to progressive disease (85%, 23/27) or other reasons (11%, 3/27; 1 drug-related and 2 unrelated AEs).The mean duration of ulixertinib treatment before discontinuation was 6.6 months.

Dose-Expansion Cohorts
In dose expansion, the tumor response and duration on study for each cohort are depicted in Fig. 4A and B, respectively.PRs were seen in 11 of 81 (14%) evaluable patients, including 3 of 18 with NRAS-mutant melanoma, 3 of 12 with BRAFmutant lung cancer (2 with V600E and 1 with L597Q), 1 of 15 with BRAF/MEK inhibitor-refractory BRAF V600E-mutant melanoma, and 4 of 21 with other BRAF-mutant cancers.These include one each of BRAF L485W gallbladder cancer (Fig. 5A), BRAF V600E glioblastoma multiforme (Fig. 5B), BRAF G469A head and neck cancer, and BRAF G469A small-bowel cancer.Of these patients, two of the responses lasted greater than 4.9 months.The maximal tumor responses for patients with BRAF non-V600 mutations (n = 28) are shown in Fig. 4C and are classified by their kinase activity (12,40).Of note, central nervous system (CNS) responses were seen in a patient with BRAF V600E-mutant lung cancer with metastases, and another with BRAF V600E-mutant glioblastoma mulitforme.
Based on the preclinical data, it was expected that ulixertinib would have activity in patients with melanoma harboring mutations in the MAPK pathway (39).In all (including dose escalation and expansion), 53 patients with melanoma were treated with ulixertinib, and 40 were eligible for response evaluation per RECIST v1.1.In 19 such patients with BRAFmutant melanoma previously treated with a BRAF and/or MEK inhibitor, 3 (15%) achieved a PR, 6 had stable disease, and 10 had progressive disease as a best response.In the patients with a PR, the time from last MAPK-targeted therapy was 21, 26, and 169 days, respectively.In patients with stable disease, this number ranged from 19 to 713 days; however, all but one commenced therapy within 6 weeks of the last dose of these targeted therapies.Seventeen patients with NRAS-mutated melanoma were evaluable for response.Three patients (18%) achieved a PR, 6 had stable disease, and 8 had disease progression as best response.Additionally, 3 other patients with melanoma harboring BRAF mutations, who had not received prior targeted therapy, were treated.One of 2 patients with a BRAF V600 mutation responded, and the 1 patient with a BRAF fusion had stable disease.

DiscUssiON
We report results from a first-in-human study evaluating the safety, pharmacokinetics, pharmacodynamics, and preliminary efficacy of ulixertinib in 135 patients with advanced solid tumors.In the dose-escalation portion of this study,     oral treatment with ulixertinib resulted in both radiographic responses by RECIST v1.1 (3 PRs) and prolonged disease stabilization in some patients, many with tumor alterations consistent with MAPK activation (BRAF, KRAS, NRAS).Drug exposures increased linearly with increasing doses up to 600 mg twice daily, which provided near-complete 24/7 inhibition of ERK substrate (RSK1) phosphorylation in an ex vivo whole-blood assay.Furthermore, toxicities associated with ulixertinib were consistent with preclinical models and were manageable when administered up to its MTD and RP2D, determined to be 600 mg twice daily.

Research
Ulixertinib was successfully administered in six cohorts of patients with NRAS, BRAF, and MEK mutations at the RP2D, which demonstrated unique and encouraging clinical activity.Tumor regression and/or stabilization of disease was seen in every dose cohort, and partial responses were seen in patients with a variety of solid-tumor malignancies with mutations in BRAF V600E/K, non-V600 BRAF, and NRAS.In particular, non-V600 BRAF mutations, including L485W, L597Q, and G469A across a variety of solid tumors, were shown to be clinically actionable for the first time, with durable objective responses.This study provides the first clinical evidence that dimer-dependent atypical BRAF non-V600 mutations may be actionable by downstream ERK inhibition, highlighting an important new therapeutic target for future drug development in solid tumors.Furthermore, the CNS activity of ulixertinib was clinically demonstrated by the objective responses achieved in glioblastoma multiforme and lung cancer with brain metastases.
Ulixertinib was generally well tolerated, with manageable and reversible toxicity.The most common AEs were rash (most commonly acneiform), fatigue, and gastrointestinal AEs, including nausea, vomiting, and diarrhea.The safety profile of ulixertinib is consistent with its selective inhibition of the MAPK pathway; the AE profile overlaps considerably with MEK inhibitor experience (41).However, toxicities asso-ciated with any targeted therapy may include dependence on both the specific mechanism and the degree of target inhibition, as well as any off-target effects.
Durable responses by RAF and MEK inhibitors are often limited by intrinsic and eventual acquired resistance, with a common feature often involving reactivation of the ERK pathway (25)(26)(27)(28)(29)(30)(31)38).Thus, ERK inhibition with ulixertinib alone or in combination with other MAPK signaling pathway inhibitors may have the potential to delay the development of resistance to existing therapies and to benefit a broader patient population (42).The ability of ERK inhibitors, including ulixertinib, to retain their potency in BRAFand MEK-resistant cell lines provides preclinical evidence for their use in patients with acquired resistance to standard of care (BRAF/MEK inhibitor combination therapy; refs.34,35,39).Importantly, in this study, 9 of 19 patients with BRAFmutant melanoma previously treated with MAPK inhibitor therapy had either a PR or stable disease, including a patient with a PR while receiving ulixertinib whose cancer had progressed after experiencing stable disease when treated initially with a BRAF inhibitor (vemurafenib) and subsequently with dabrafenib.This patient remained on study for a total of 38.4 months as of the cutoff date of this publication.Based in part on the antitumor effects observed in this patient, the FDA has designated as a Fast Track development program the investigation of ulixertinib for the treatment of patients with unresectable or metastatic BRAF V600 mutation-positive melanoma that is refractory to or has progressed following treatment with a BRAF and/or MEK inhibitor(s).One potential explanation for this activity in patients with BRAF-mutant melanoma previously treated with MAPK pathway-targeted therapy is repopulation of the tumor following a break in treatment (43).However, in 2 of the 3 PRs and 5 of the 6 patients with stable disease, ulixertinib commenced within 6 weeks of the last BRAF and/or MEK inhibitor dose, with the majority treated within 4 weeks.In summary, we report initial data from the phase I study evaluating ulixertinib, a first-in-class ERK inhibitor, as a treatment for patients with advanced cancers.Continuous, twicedaily oral treatment with ulixertinib resulted in antitumor effects in subsets of patients with a variety of solid-tumor types, including patients either naïve to or having progressed on available MAPK pathway-targeted therapies.Ulixertinib generally was well tolerated in this population of patients with advanced cancer, and toxicities were manageable; the MTD and RP2D were 600 mg twice daily.Ulixertinib exposures increased linearly up to the RP2D, and robust pharmacodynamic effects were evident at this dose level.The preliminary efficacy shown in a variety of molecularly defined cohorts, hallmarked by MAPK activating alterations, supports the ongoing development of ulixertinib as a single agent as well as in combination.

Patients
Between April 4, 2013, and March 6, 2017, a total of 135 patients at 12 sites were consented and enrolled into the study, after local Institutional Review Board approval.All participants provided informed consent prior to initiation of any study procedures.Patients ages ≥18 years were eligible for participation if they had noncurable, histologically confirmed metastatic or advanced-stage malignant tumors; an ECOG PS of 0 or 1; adequate renal, hepatic, bone marrow, and cardiac function; and a life expectancy ≥3 months.Patients may have received up to two prior lines of chemotherapy for their metastatic disease.Exclusion criteria were known uncontrolled brain metastases; gastrointestinal conditions that could impair absorption of study medication; history or current evidence/risk of retinal vein occlusion or central serous retinopathy; and concurrent therapy with drugs known to be strong inhibitors of CYP1A2, CYP2D6, and CYP3A4, or strong inducers of CYP3A4.
Patients who received at least one dose of ulixertinib were included in the analysis.We used SAS (version 9.3) to support this study.The data cutoff was March 6, 2017.This study is registered with ClinicalTrials.gov(NCT01781429).

Study Design and Objectives
This was an open-label, phase I study to assess the safety, pharmacokinetics, and pharmacodynamics of escalating doses of ulixertinib in a capsule formulation in patients with advanced malignancies.The dosing regimen combined both accelerated titration and standard cohort 3 + 3 dose-escalation schema, which were used jointly to identify the MTD and RP2D of ulixertinib in patients with advanced solid tumors.One to 6 patients per treatment cohort were assigned to receive sequentially higher oral doses of ulixertinib administered twice daily (12-hour intervals) continuously in 21-day cycles at the following doses: 10 mg (n = 1); 20 mg (n = 1); 40 mg (n = 1); 75 mg (n = 1); 150 mg (n = 1); 300 mg (n = 4); 600 mg (n = 7); 900 mg (n = 7); and 750 mg (n = 4).In the cohort-expansion phase, patients were enrolled to one of six cohorts until at least 15 patients per cohort were expected to be evaluable for response to therapy.The six cohorts were defined as patients without prior MAPK targeted therapy that had BRAF-mutant colorectal (17 enrolled/11 evaluable), lung (16/12), or other cancers (24/21), NRAS-mutant melanoma (22/18), or any tumor type with a MEK mutation (8/4), and patients with melanoma who had prior BRAF and/or MEK inhibitor treatment (21/15).Notably, the cohort of patients with MEK mutations was closed after enrollment of only 8 patients, due to slow accrual.
Patients received ulixertinib until disease progression, unacceptable toxicity, or a clinical observation satisfying another withdrawal criterion.Dose escalations occurred in up to 100% increments in single-patient cohorts until 1 patient experienced at least a grade 2 toxicity (excluding alopecia or diarrhea).Cohorts were then expanded to at least 3 patients each, and subsequent dose-escalation increments were reduced from up to 100% to a maximum of 50%.When at least 1 patient in a 3-patient cohort experienced a DLT, up to 3 additional patients were treated at this dose level.When more than 1 DLT occurred in ≤6 patients, this dose level was defined as the nontolerated dose, and dose escalation was stopped.Intrapatient dose escalation was allowed, provided the patients receiving the highest current dose had been observed for at least 3 weeks and dose-limiting AEs were reported in fewer than 2 of 6 patients assigned to that dose.Patients experiencing DLTs or unacceptable toxicity had their treatment interrupted until the toxicity returned to grade 1 or lower.Resumption of ulixertinib treatment was then initiated at the next lower dose level tested or at a 20% to 30% dose decrease, aligning with capsule strength.
The primary objective of the study was to define the safety and tolerability of ulixertinib by determining the DLTs, the MTD, and the RP2D.The secondary objectives included the determination of the pharmacokinetic profile of ulixertinib and the investigation of any preliminary clinical effects on tumor response, as assessed by physical or radiologic examination using RECIST v1.1.The exploratory objectives included evaluation of pharmacodynamic marker (biomarker) measures.

MTD, DLT, and RP2D
MTD was defined as the highest dose cohort at which ≤33% of patients experienced ulixertinib-related DLTs in the first 21 days of treatment.DLT was defined as a ulixertinib-related toxicity in the first 21 days of treatment that resulted in a grade 4 or higher hematologic toxicity for >1 day; grade 3 hematologic toxicity with complications (e.g., thrombocytopenia with bleeding); grade 3 or higher nonhematologic toxicity, except untreated nausea, vomiting, constipation, pain, and rash (these become DLTs if the AE persisted despite adequate treatment); or a treatment interruption exceeding 3 days in cycle 1 (or the inability to be in cycle 2 for >7 days) due to ulixertinib-related toxicity.
The RP2D could be as high as the MTD and was determined in discussion with the clinical investigators, medical monitor, and sponsor.Observations related to pharmacokinetics, pharmacodynamics, and any cumulative toxicity observed after multiple cycles were included in the rationale supporting the RP2D.

Safety Assessments
Patients who received ulixertinib and experienced any untoward medical occurrence had their AE defined as per the MedDRA coding dictionary, regardless of causal relationship with test article.The AEs were graded according to the National Cancer Institute Common Terminology Criteria for Adverse Events, Grading Scale, version 4.03.Investigators assessed the relationship of AEs to study drug as either unrelated, possibly related, or related, and followed up until event resolution or stabilization or the AE was judged to no longer be clinically significant.An SAE was defined as any untoward medical occurrence that resulted in death, was life-threatening, required inpatient hospitalization or prolongation of existing hospitalization, or resulted in persistent or significant disability/incapacity or a congenital anomaly/birth defect.
Safety evaluations were conducted at baseline, on days 8, 15, 22, 29, 36, and 43, and, in patients who continued treatment, every 3 weeks or if clinically indicated thereafter.Each evaluation included a physical examination and clinical laboratory studies.Electrocardiograms were repeated if clinically significant and at the discretion of the investigator.Holter monitoring (12 ± 2 hours) was performed in a subset of patients in cycle www.aacrjournals.orgdays) and Holter ECG analyses were conducted by BioClinica.An ophthalmologic assessment was also conducted at screening, at the end of study, and at other visits by an ophthalmologist if clinically indicated.

Pharmacokinetic Analysis
The pharmacokinetic population consisted of patients who received at least 1 dose of ulixertinib and had evaluable pharmacokinetic data for plasma and/or urine.Blood samples were collected prior to dosing, and then at 0.5 (± 5 minutes), 1 (± 5 minutes), 2 (± 10 minutes), 4 (± 10 minutes), 6 (± 10 minutes), 8 (± 10 minutes), and 12 (±2 hours) hours on day 1 (visit 2; baseline/initiation of treatment) and day 15 (visit 4; at steady state).On day 22, prior to dose administration, a final blood sample was collected for pharmacokinetic analyses.Urine samples were collected pre-dose and at the 1-to 6-hour and 6-to 12-(± 2) hour intervals post-dose on days 1 and 15.Plasma and urine samples were analyzed for ulixertinib and metabolites using validated LC/MS-MS methods.Standard pharmacokinetic parameters were obtained using Phoenix WinNonlin (Pharsight) with a noncompartmental method.Relationship between dose and exposure was calculated using standard least-squares regression analysis.

Pharmacodynamic Confirmation of Target Inhibition by Ulixertinib
ERK inhibition by ulixertinib was determined by measuring pRSK/RSK as a target biomarker in human whole-blood samples obtained from patients who had received ulixertinib during the phase I study.To establish a ulixertinib-dependent RSK1-phosphorylation calibration curve, healthy donor blood was treated with serial dilutions of ulixertinib (DMSO control) for 2 to 3 hours followed by stimulation with 100 nmol/L PMA for 20 minutes at room temperature.Peripheral blood mononuclear cells were isolated, lysed, and flash-frozen prior to measurement of pRSK and total RSK by ELISA (PathScan).
A plot of the pRSK/RSK ratio as a function of ulixertinib concentration was used as a standard curve for determination of ERK activity.Maximum (100%) inhibition was defined as the pRSK/RSK value obtained in the presence of 10 μmol/L ulixertinib: Baseline inhibition was defined as the pRSK/RSK value obtained in untreated and unstimulated blood.The EC 50 for ulixertinib was determined to be ∼200 ng/mL.Patient samples were evaluated using this methodology, with each patient serving as their own control for maximal and minimal stimulation.Pre-and post-ulixertinib treatment samples were collected at day 1 and steady state.

Antitumor Response
Tumor measurements based on physical examination occurred at baseline and on the first day of each treatment cycle.CT and other assessments were made every 2 to 3 cycles.Findings were assessed in accordance with RECIST v1.1: Complete response was defined as disappearance of all target lesions; PR was defined as a ≥30% decrease in the sum of the longest diameters of target lesions, taking baseline measurements as reference; stable disease was defined as being of neither sufficient shrinkage to qualify for PR nor sufficient increase to qualify for progressive disease, taking as reference the baseline measurement.CT scans were performed per routine site protocols and assessed by site radiologists; no central read assessments were included in this analysis.

Figure 2 .
Figure 2. Pharmacokinetics and pharmacodynamics of ulixertinib.Plasma concentrations of ulixertinib as a function of time and dose level following dosing on day 1 (A) and at steady state (B).AUC as a function of dose level following dosing on day 1 (C) and at steady state (D).The data for dose levels 10 to 150 mg twice daily (b.i.d.) represent a single patient at each dose level.Plasma levels and pharmacodynamic effects of ulixertinib are shown as a function of the dose level (E).Ulixertinib plasma levels from patients dosed with 600 mg/kg, twice daily, are shown at day 1 and steady state (F).

Figure 3 .
Figure 3. Dose-escalation patient response.Individual patient's target lesion response (A) and time on study (B) are shown as a function of initial dose level.C, A representative sustained partial tumor response in a melanoma patient that was refractory to prior BRAF inhibitor therapy.Horizontal red line in A depicts RECIST v1.1 partial response threshold.b.i.d., twice daily.

Figure 4 .
Figure 4. Cohort expansion patient response.Target lesion responses (A) and time on study (B), grouped by cohort, are shown for each evaluable patient initially dosed with 600 mg of ulixertinib twice daily in the expansion phase of the study.Specific genetic mutations are also indicated (A, B).C, Tumor response data for patients with atypical (non-V600) BRAF mutations, with specific mutations indicated.Data are further discriminated by color based on the literaturereported MAPK pathway activity, as indicated by pERK levels.CRC, colorectal cancer; NSCLC, non-small cell lung cancer.

Figure 5 .
Figure 5. Representative patient responses to ulixertinib.Longitudinal radiographic scans from a subset of patients who responded to ulixertinib are shown.A, A patient with gallbladder adenocarcinoma with a BRAF L485W mutation who experienced partial response in two lesions (green circles) over 12 weeks.B, A patient with glioblastoma multiforme with a BRAF V600E mutation who experienced a 64% reduction of their tumor (green circles) after 10 cycles of treatment with ulixertinib.