Inclusion Criteria:

Subjects must meet all of the following criteria to be eligible to participate in this study:

1. Willing and able to comply with the protocol and provide written informed consent.
2. Age greater than or equal to 18 years.
3. Histologically and/or cytologically confirmed metastatic solid tumors which have progressed after treatment with approved therapies or for which there are no standard effective therapies available. Part B allows metastatic BRAF mutated melanoma and CNS metastases (treated or untreated from a primary melanoma).
4. Female subjects of childbearing potential must agree to use medically acceptable methods of contraception, such as abstinence, double-barrier method (e.g., condom and spermicide; condom, diaphragm, and spermicide), intrauterine device (IUD), or have a vasectomised partner. Female subjects who use hormonal contraceptives must also use an additional approved method of contraception (as described previously). Contraceptive measures must start either prior to or at Screening and continue throughout the entire study period and for 2 months after the last dose drug is administered. Pregnant and/or lactating females are excluded.
5. Male subjects must agree to use contraceptive methods such as abstinence, or double-barrier method (e.g., condom and spermicide; condom, diaphragm, and spermicide). Contraceptive measures must start either prior to or at Screening and continue throughout the entire study period and for 2 months after the last dose of study drug is administered.

6. Adequate bone marrow function defined as:

   • Absolute neutrophil count (ANC) greater than or equal to 1.5 x 10^9/L
   • Hemoglobin greater than or equal to 9.0 g/dL; however, a hemoglobin value < 9.0 g/dL is acceptable if it is corrected to greater than or equal to 9.0 g/dL by growth factor or transfusion before the start of treatment
   • Platelet count greater than or equal to 100 x 10^9/L.

7. Adequate renal function defined as:

   • Serum creatinine < 1.5 mg/dL or calculated creatinine clearance >50 mL/minute per the Cockcroft-Gault formula

8. Adequate liver function defined as:

   • Total Bilirubin within normal limits
   • Alkaline phosphatase (AP), alanine transaminase (ALT), and aspartate transaminase (AST) less than or equal to 2.5 x upper limit of normal (ULN)
   • AP, ALT, and AST less than or equal to 5 x ULN in the case of liver metastases and liver-specific AP less than or equal to 3 x ULN in the case of bone metastases
9. Eastern Cooperative Oncology Group (ECOG) performance status less than or equal to 1.
10. Life expectancy > 3 months.

Additionally, subjects enrolled in Part B (MTD expansion) of the study MUST meet the following criteria:

1. Have at least 1 tumor lesion at Screening measurable by Modified RECIST (Response Evaluation Criteria in Solid Tumors) criteria using either CT/MRI or photography (as appropriate) and which measures ≥1.5 cm in the longest dimension for a non-lymph node and ≥ 2.0 cm in the longest dimension for a lymph node.
2. Have at least 1 tumor lesion accessible to biopsy.
3. Have a B-type RAF kinase (BRAF)-mutated tumor (including brain metastases) as established either by a BRAF-gene analysis report from a qualified laboratory, or by a BRAF-gene analysis of archival tissue during the Screening Period, or by a BRAF-gene analysis of tumor biopsy tissue obtained at Screening.

Exclusion Criteria:

Subjects who meet any of the following criteria are not eligible to participate in this study:

1. Primary or metastatic central nervous system (CNS) tumors are not allowed in Part A unless treated and stable. Stability is proven by at least 2 contrast-enhanced CT or MRI scans obtained at least 8 weeks apart, with the most recent scan obtained within 28 days of the first infusion of E6201. In Part B, untreated or unstable metastatic brain tumors are allowed.
2. Known human immunodeficiency virus (HIV), hepatitis B or C, or severe/uncontrolled infections or intercurrent illness that is unrelated to the tumor.
3. Prior surgery, radiotherapy, chemotherapy, biologic therapy, or investigational agents within 4 weeks prior to the first infusion and prior immunotherapy, hormonal, or molecular-targeted therapy within 2 weeks prior to the first infusion. All acute toxicities related to prior treatments should have resolved.
4. For Part A, a history of malignancy other than the present diagnosis (except treated non-melanoma skin cancer or carcinoma in situ of the cervix), or stable primary CNS tumors, unless in complete remission and off all therapy for that disease for a minimum of 5 years. For Part B, untreated or unstable metastatic brain tumors are allowed.
5. QT interval corrected for rate (QTc) > 450 msec on the electrocardiogram (ECG) obtained at Screening (Day -14 to 0) using the Fridericia method for QTc analysis. For Part B, QTc > 450 msec on the electrocardiogram (ECG) obtained at Screening (Day -21 to 0) using the Fridericia method for QTc analysis.
6. History or substance or alcohol abuse which, in the opinion of the investigator, would prohibit participation in the study.
7. History of clinically significant cardiac impairment, congestive heart failure >New York Heart Association (NYHA) cardiac disease classification Class II, unstable angina, or myocardial infarction during the previous 6 months, or serious cardiac arrhythmia.
8. Current significant co-morbid disease which, in the opinion of the investigator, would exclude the subject from the study.