The purpose of this study is to assess the safety and tolerability of ASP8273 and to determine the maximum tolerated dose (MTD) and/or recommended Phase 2 dose (RP2D). This study will also determine the pharmacokinetics (PK) of ASP8273, evaluate the potential inhibition of CYP3A4 by ASP8273 and the antitumor activity of ASP8273 as well as determine the effect of food on the bioavailability of ASP8273.

This study is composed of 2 parts: part 1 is the dose escalation phase and part 2 is the recommended Phase 2 dose (RP2D) phase, Food Effect (FE) cohort and Exon 20 cohort.

Inclusion Criteria:

• Non-child bearing potential or able to follow birth control requirements

• Eastern Cooperative Oncology Group (ECOG) ≤ 1

• Life expectancy ≥ 12 weeks

• Laboratory criteria as:

  • Neutrophil count ≥ 1,500/mm3
  • Platelet count ≥ 7.5 x 104 /mm3
  • Hemoglobin ≥ 9.0 g/dL
  • Lymphocyte count ≥ 500/mm3
  • Serum creatinine < 1.5 x institutional Upper Limit of Normal (ULN) or an estimated glomerular filtration rate (eGFR) of > 50 ml/min as calculated by the Modification of Diet in Renal Disease (MDRD) equation
  • Total bilirubin < 1.5 x ULN (except for subjects with documented Gilbert's syndrome)
  • Aspartate aminotransferase (AST) and alanine aminotransferase (ALT) < 3.0 x ULN

• Dose escalation subjects: Epidermal Growth Factor Receptor (EGFR) activating mutation by local testing: exon 18 G719X, exon 19 deletion, exon 21 L861Q, exon 21 L858R or exon 20 insertion; and received prior treatment with EGFR Tyrosine Kinase Inhibitor (TKI)

• Response expansion/RP2D expansion/ FE Cohort subjects: disease progression on or was intolerant to prior EGFR TKI; activating mutation as above AND T790M mutation; tumor sample subsequent to EGFR TKI is available for central testing; at least one measurable lesion per Response Evaluation Criteria in Solid Tumors (RECIST) 1.1

Inclusion Criteria for Exon 20 cohort:

• Subject on any line of treatment and has an EGFR exon 20 insertion mutation on examination of an NSCLC tissue or cellular specimen. Local testing may determine eligibility and a tumor sample should also be sent for central testing.
• Subjects must have at least 1 measurable lesion based on RECIST version 1.1.

Exclusion Criteria:

• Any ongoing toxicity ≥ Grade 2 attributable to prior Non-Small-Cell Lung Cancer (NSCLC) treatment
• Prior EGFR inhibitor within 6 days; received prior treatment with any other agent with antitumor activity chemotherapy, radiotherapy, or immunotherapy within 14 days; any investigational therapy within 28 days or 5 half-lives, whichever is shorter; blood transfusion or hemopoietic factor within 14 days; major surgery within 14 days; any strong CYP3A4 inhibitors within 7 days
• Positive hepatitis B surface antigen (HBsAg) or hepatitis C antibody (anti-HCV) or Human Immunodeficiency Virus (HIV)
• Symptomatic Central Nervous System (CNS) metastasis
• Active infection requiring systemic therapy within 14 days
• Severe or uncontrolled systemic diseases including uncontrolled hypertension
• History of or active interstitial lung disease
• Screening QTcF >450 msec or current medication known to prolong QT
• ≥ Grade 2 cardiac arrhythmia or uncontrolled atrial fib of any grade; Class 3 or 4 New York Heart Association congestive heart failure; history of severe/unstable angina, myocardial infarction or cerebrovascular accident within 6 months
• History of gastrointestinal ulcer or bleeding within 3 months; any digestive tract dysfunction
• Concurrent corneal disorder or ophthalmologic condition making subject unsuitable
• RP2D cohort subjects: contraindications to midazolam, any other midazolam within 7 days, or any medications or supplements known to be strong CYP3A inhibitors within 7 days or inducers within 12 days
• Any other malignancy requiring treatment

Access to anonymized individual participant level data collected during the study, in addition to study-related supporting documentation, is planned for studies conducted with approved product indications and formulations, as well as products terminated during development. Studies conducted with product indications or formulations that remain active in development are assessed after study completion to determine if Individual Participant Data can be shared. Further details on Astellas' data sharing policy can be found at https://www.clinicaltrials.astellas.com/transparency/.

Access to participant level data is offered to researchers after publication of the primary manuscript (if applicable) and is available as long as Astellas has legal authority to provide the data.

Researchers must submit a proposal to conduct a scientifically relevant analysis of the study data. The research proposal is reviewed by an Independent Research Panel. If the proposal is approved, access to the study data is provided in a secure data sharing environment after receipt of a signed Data Sharing Agreement.