Abstract
Lessons Learned
Afatinib and selumetinib can be combined in continuous and intermittent dosing schedules, albeit at lower doses than approved for monotherapy.
Maximum tolerated dose for continuous and intermittent schedules is afatinib 20 mg once daily and selumetinib 25 mg b.i.d.
Because the anticancer activity was limited, further development of this combination is not recommended until better biomarkers for response and resistance are defined.
Background
Antitumor effects of MEK inhibitors are limited in KRAS‐mutated tumors because of feedback activation of upstream epidermal growth factor receptors, which reactivates the MAPK and the phosphoinositide 3‐kinase–AKT pathway. Therefore, this phase I trial was initiated with the pan‐HER inhibitor afatinib plus the MEK inhibitor selumetinib in patients with KRAS mutant, PIK3CA wild‐type tumors.
Methods
Afatinib and selumetinib were administered according to a 3+3 design in continuous and intermittent schedules. The primary objective was safety, and the secondary objective was clinical efficacy.
Results
Twenty‐six patients were enrolled with colorectal cancer (n = 19), non‐small cell lung cancer (NSCLC) (n = 6), and pancreatic cancer (n = 1). Dose‐limiting toxicities occurred in six patients, including grade 3 diarrhea, dehydration, decreased appetite, nausea, vomiting, and mucositis. The recommended phase II dose (RP2D) was 20 mg afatinib once daily (QD) and 25 mg selumetinib b.i.d. (21 days on/7 days off) for continuous afatinib dosing and for intermittent dosing with both drugs 5 days on/2 days off. Efficacy was limited with disease stabilization for 221 days in a patient with NSCLC as best response.
Conclusion
Afatinib and selumetinib can be combined in continuous and intermittent schedules in patients with KRAS mutant tumors. Although target engagement was observed, the clinical efficacy was limited.
Keywords: Afatinib, Selumetinib, KRAS, Colorectal cancer, Non‐small cell lung cancer, Pancreatic cancer
Discussion
We demonstrated that selumetinib can be safely combined with afatinib without unacceptable toxicity, although not at full single agent doses because of dose‐limiting toxicities (Fig. 1). The RP2D was 20 mg afatinib QD and 25 mg selumetinib b.i.d. (21 days on/7 days off) for continuous afatinib dosing and also for intermittent dosing with both drugs in a 5 days on/2 days off regimen.
Figure 1.
Overview of dose levels and dose‐limiting toxicities.Abbreviations: AF, afatinib; SEL, selumetinib; QD, once daily; BID, twice daily; G, grade; RP2D, recommended phase II dose.
Stable disease was the best overall response with a median time on treatment of 64 days (Fig. 2). Although a patient with non‐small cell lung cancer had a tumor regression of –16% in dose level 3, treatment was discontinued because of intolerable toxicity. This illustrates what has been observed throughout the study: combining afatinib and selumetinib is potentially effective at higher doses, yet reaching these doses seems not clinically feasible. The intermittent regimens were expected to allow improvement of the efficacy‐to‐toxicity ratio. Unfortunately, patients still experienced unmanageable toxicities in the intermittent dose levels, which restricted dose escalation. Moreover, the RP2D for intermittent dosing was determined at exactly the same dose for both drugs as in the continuous regimen.
Figure 2.
Swimmer plot of treatment duration, by dose level. Doses of both drugs are in milligrams. Symbols at the end of each bar represent the reason for end of treatment for each individual patient. The dotted line represents the median time on treatment of 64 days.Abbreviations: A, afatinib; S, selumetinib; QD, once daily; BID, twice daily; 21/7, 21 days on/7 days off; 5/2, 5 days on/2 days off; CRC, colorectal cancer; NSCLC, non‐small cell lung cancer; PC, pancreatic cancer.
Despite relatively low plasma levels of both drugs, we observed pharmacodynamic effects in on‐treatment biopsies that were taken in the second week of treatment. The intratumoral levels of pERK and pS6 decreased by on average 52% and 39%, respectively. This indicates that relevant MEK and pan‐HER inhibition is reached during the treatment. Moreover, pERK modulation correlated with exposure to selumetinib. However, this did not translate into objective clinical responses. The best responses were observed in patients with NSCLC, including tumor regression of 16% and disease stabilization for 8 months. It is unknown if these patients had relevant target modulation because no paired biopsies were available. Additionally, no reliable pERK or pS6 stainings were available from the patients treated in dose level 5, which makes it unclear if relevant pharmacodynamic effects were established at RP2D for intermittent dosing.
Although target engagement was demonstrated, no complete or partial responses were observed. Therefore, we do not recommend further exploration of this combination until relevant biomarkers for response and resistance are defined to optimize patient inclusion.
Trial Information
| Disease | Colorectal cancer |
| Disease | Lung cancer – NSCLC |
| Stage of Disease/Treatment | Metastatic/advanced |
| Prior Therapy | No designated number of regimens |
| Type of Study | Phase I, 3+3 |
| Primary Endpoint | Safety |
| Secondary Endpoint | Efficacy |
| Additional Details of Endpoints or Study Design | |
| Phase I multicenter open‐label proof of concept study, consisting of a phase I pharmacological dose‐ and schedule‐finding study. The primary objective was to determine the recommended phase II dose and schedule of the selumetinib/afatinib combination in patients with KRAS mutant and PIK3CA wild‐type non‐small cell lung cancer and colorectal cancer. Secondary objectives were (a) to characterize the safety and tolerability of afatinib in combination with selumetinib, as assessed by the incidence and severity of adverse events; (b) to determine the antitumor activity as assessed by overall response rate and duration of response; and (c) to determine the pharmacokinetic profile of afatinib and selumetinib in this combination, as measured by plasma concentrations of both drugs and relevant metabolites. Exploratory objectives were to (a) explore determinants (gene alteration/expression) and mode of response to the selumetinib‐afatinib combination, as measured by baseline and on‐therapy molecular status in tumor tissue of potential and indicative markers of tumor response; (b) explore the potential mechanism of resistance, as measured by gene alterations/expression profiles in tumor tissue upon progression; and (c) to obtain tumor genomic data to investigate potential mechanisms of resistance and genomic markers for unresponsiveness. | |
| Investigator's Analysis | Drug tolerable, efficacy indeterminant |
Drug Information
| Drug 1 | |
| Generic/Working Name | Afatinib |
| Drug Type | Small molecule |
| Drug Class | Her‐2 / Neu |
| Dose | 20 milligrams (mg) per flat dose |
| Route | Oral (p.o.) |
| Schedule of Administration | The RP2D was 20 mg afatinib QD and 25 mg selumetinib b.i.d. (21 days on/7 days off) for continuous afatinib dosing and for intermittent dosing with both drugs 5 days on/2 days off |
| Drug 2 | |
| Generic/Working Name | Selumetinib |
| Drug Type | Small molecule |
| Drug Class | MEK |
| Dose | 25 milligrams (mg) per flat dose |
| Route | Oral (p.o.) |
| Schedule of Administration | The RP2D was 20 mg afatinib QD and 25 mg selumetinib b.i.d. (21 days on/7 days off) for continuous afatinib dosing and for intermittent dosing with both drugs 5 days on/2 days off |
Dose Escalation Table
| Dose level | Dose of drug: afatinib | Dose of drug: selumetinib | Number enrolled | Number evaluable for toxicity |
|---|---|---|---|---|
| 1 | 20 mg QD | 25 mg b.i.d. (21 days on/7 days off) | 6 | 6 |
| 2 | 20 mg QD | 50 mg b.i.d. (21 days on/7 days off) | 5 | 5 |
| 3 | 30 mg QD | 25 mg b.i.d. (21 days on/7 days off) | 4 | 4 |
| 4 | 30 mg QD (5 days on/2 days off) | 25 mg b.i.d. (5 days on/2 days off) | 2 | 2 |
| 5 | 20 mg QD (5 days on/2 days off) | 25 mg b.i.d. (5 days on/2 days off) | 5 | 5 |
Abbreviation: QD, once daily.
Patient Characteristics
| Number of Patients, Male | 13 |
| Number of Patients, Female | 13 |
| Stage | metastatic |
| Age | Median (range): 63 (47–77) years |
| Number of Prior Systemic Therapies | One or more |
| Performance Status: ECOG |
0 — 20 1 — 6 2 — 0 3 — 0 Unknown — |
| Cancer Types or Histologic Subtypes | Colorectal cancer, 19; non‐small cell lung cancer, 6; pancreatic cancer, 1. |
Primary Assessment Method
| Number of Patients Screened | 29 |
| Number of Patients Enrolled | 26 |
| Number of Patients Evaluable for Toxicity | 22 |
| Number of Patients Evaluated for Efficacy | 19 |
| Evaluation Method | RECIST 1.1 |
| Response Assessment CR | n = 0 (0%) |
| Response Assessment PR | n = 0 (0%) |
| Response Assessment SD | n = 10 (53%) |
| Response Assessment PD | n = 9 (47%) |
| (Median) duration Assessments Duration of Treatment | 138 days |
Adverse Events: Dose‐Limiting Toxicities
| Dose level | Number enrolled | Number evaluable for toxicity | Number with a dose‐limiting toxicity | Dose‐limiting toxicity information |
|---|---|---|---|---|
| 1 | 6 | 6 | 1 | Diarrhea and decreased appetite |
| 2 | 5 | 5 | 2 | Diarrhea, nausea/vomiting, and dehydration |
| 3 | 4 | 4 | 2 | Mucositis and dehydration |
| 4 | 2 | 2 | 1 | Diarrhea |
| 5 | 5 | 5 | 0 |
Assessment, Analysis, and Discussion
| Completion | Study completed |
| Investigator's Assessment | Drug tolerable, efficacy indeterminant |
In this clinical trial, the recommended phase II dose with continuous afatinib administration was found to be 25 mg b.i.d. selumetinib (21 days on/7 days off) and 20 mg afatinib continuously, which is 33% and 50% of their monotherapy doses. At these doses, plasma concentration‐time curves show that relatively low plasma levels are reached. For selumetinib, a concentration of 352 ng/mL is needed for 50% of pERK inhibition in peripheral blood mononuclear cells, as reported in a previous phase I trial. In this study, this concentration was reached for only 17% of each 12‐hour dosing interval in the 21 days on/7 days off regimen. For afatinib, the concentration needed for 50% inhibition of cell proliferation in preclinical setting was determined as approximately 30 ng/mL, which is also supported by clinical efficacy in patients in whom these plasma concentrations were reached [1]. This target concentration was consistently reached only in patients treated with continuous afatinib 30 mg, which was not tolerable in combination with selumetinib in the applied schedule. Although the relevance of target levels in this combination setting is uncertain because these target levels are based on single‐agent use, we assumed that the probability of response increases when the target levels of both drugs are more consistently reached. Based on this, it was decided to explore other regimens with the aim of increasing the plasma levels and exposure, starting with a 5 days on/2 days off regimen with doses of 30 mg afatinib once daily (QD) and 25 mg selumetinib b.i.d. Unfortunately, de‐escalation of the afatinib dose from 30 mg to 20 mg QD (5 /2) was necessary to manage toxicity, which resulted in not reaching afatinib concentrations needed for sufficient target engagement.
Although we observed target engagement in some patients, we found a poor correlation with clinical response. This poor correlation could be due to a variety of mechanisms. First, intermetastatic heterogeneity may play an important role because the pharmacodynamic analyses were based on a single lesion only. Insight into the relevance of this mechanism may be obtained by correlating the radiological response of the biopsied lesion to the pERK/pS6 modulation. For this study, data were not sufficient to perform these analyses.
Secondly, the observed pathway modulation may be transient or insufficient, meaning that resistance mechanisms occur shortly after the on‐treatment biopsy which was performed in the second week. Several resistance mechanisms could play a role. Corcoran et al. reported that upon MEK inhibition, resistance occurs via expression of antiapoptotic proteins BCL‐XL [2]. Therefore, addition of a third agent such as the BCL‐XL inhibitor navitoclax could be of interest, if clinically feasible. Furthermore, Burgess et al. showed that KRAS copy numbers, KRAS expression levels, and the ratio of KRAS mutant to wild type can explain resistance to MEK inhibition [3], and Sun et al. showed that high tumor expression of HER2/HER3 at baseline increased the probability of response on MEK and pan‐HER inhibition [4]. Conversely, upregulation of HER2/HER3 during treatment could theoretically cause treatment resistance via pathway reactivation. Another important biomarker might be the nature of the KRAS mutation. Recent studies demonstrated that KRAS G12C mutations are more dependent on upstream signaling than other KRAS mutations. in vitro and in vivo, these KRAS G12C mutations are more sensitive to combined pan‐HER and MEK inhibition [5, 6]. An ongoing phase I study with the specific KRASG12C inhibitor AMG510 shows a partial response in three out of 225 patients and stable disease in 13 patients with KRAS G12C mutant solid tumors [7].
In parallel with this trial, two other studies with combined MEK and pan‐HER inhibition were conducted in patients with KRAS mutant tumors [8, 9]. Emerging combined data from these trials showed a trend toward preferential activity in non‐small cell lung cancer (NSCLC) compared with colorectal cancer (CRC) and pancreatic cancer. These clinical observations are supported by previous clinical studies that show that MEK inhibition added to second‐line docetaxel in patients with NSCLC can lead to improved responses, whereas in CRC the addition of a MEK inhibitor to second‐line irinotecan did not result in clinical benefit [10, 11].
For patients treated in the three trials investigating the combination of pan‐HER and MEK inhibition, tumor material is being analyzed for a broad spectrum of biomarkers in a translational study on paired biopsies. DNA and RNA sequencing, multiplex immunohistochemistry stainings, and reverse phase protein arrays are being used to explore the true mechanisms of response and resistance. The final results of these analyses are expected soon and may give us new insights into the differences of responses in different tumor types and rational use of MEK and pan‐HER inhibitors in the clinic.
To improve treatment options for patients with a KRAS mutation, triple combinations could also be effective to overcome resistance mechanisms. Potentially, synergistic effects may allow the use of relatively low doses of all agents, which is supported by preliminary data of MEK and pan‐HER inhibition in KRAS mutant CRC organoids (unpublished). The same unpublished data show that the dual combination, probably in combination with a chemotherapeutic agent, might provide an effective treatment option for patients with KRAS wild‐type tumors.
Disclosures
Carla van Herpen: Bayer, Bristol‐Myers Squibb, Ipsen, Merck Sharp & Dohme, Regeneron, TRK Fusion Cancer Medical Education Steering Committee (C/A); Neeltje Steeghs: AIMM Therapeutics, Boehringer Ingelheim, Ellipses Pharma (C/A), AB Science, Abbvie, Actuate Therapeutics, Amgen, Array, AstraZeneca/MedImmune, Bayer, Blueprint Medicines, Boehringer Ingelheim, Bristol‐Myers Squibb, Cantargia, Cytovation, Deciphera, Genentech/Roche, GlaxoSmithKline, Incyte, InteRNA, Lilly, Merck Sharp & Dohme, Merus, Novartis, Pfizer, Pierre Fabre, Roche, Sanofi, Taiho, Takeda (RF‐institutional); Kim Monkhorst: Lilly, Boehringe, Bayer (C/A), AstraZeneca (RF); Jos Beijnen: Modra Pharmaceuticals (E, OI), Patent on oral taxane pharmaceutical formulations (IP), PharmaMar, Roche, Astex (RF‐institutional); Jan Schellens: Byondis, Modra Pharmaceuticals (E), Patent for oral taxanes (IP), Modra Pharmaceuticals (OI). The other authors indicated no financial relationships.
(C/A) Consulting/advisory relationship; (RF) Research funding; (E) Employment; (ET) Expert testimony; (H) Honoraria received; (OI) Ownership interests; (IP) Intellectual property rights/inventor/patent holder; (SAB) Scientific advisory board
Acknowledgments
We are grateful to Boehringer Ingelheim and AstraZeneca for providing the study drugs and an unrestricted grant.
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Footnotes
- ClinicalTrials.gov Identifier: NCT2450656
- Sponsor: Netherlands Cancer Institute
- Principal Investigator: Frans Opdam
- IRB Approved: Yes
Contributor Information
Sanne Huijberts, Email: s.huijberts@nki.nl.
Frans Opdam, Email: f.opdam@nki.nl.
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