∙ Age

• Participant must meet the following age requirements at the time the informed consent form (ICF) (and assent form, if applicable) is signed:

‣ Phase 1 Part 1: participants must be ≥ 2 to \< 18 years of age.

⁃ Phase 2: participants must be ≥ 2 to ≤ 30 years of age.

∙ Type of Participant and Disease Characteristics

• Participant has a confirmed solid tumor

• The participant has a Lansky/Karnofsky performance status score of ≥ 50%.

• The participant has adequate liver function, evidenced by the following laboratory values:

‣ Aspartate aminotransferase (AST), alanine aminotransferase (ALT) ≤ 2.5 × upper limit of normal (ULN).

⁃ Total bilirubin ≤ 1.5 × institutional ULN (with the exception of participants with Gilbert's syndrome who must have bilirubin \< 3 × institutional ULN).

• The participant has adequate bone marrow function, evidenced by the following:

‣ Absolute neutrophil count (ANC) ≥ 1.0 × 109/L (independent of growth factor support within 1 week of screening laboratories).

• Platelets ≥ 100 × 109/L (without platelet transfusion within previous 7 days of screening laboratories).

‣ Hemoglobin ≥ 8 g/dL (note: may have been transfused).

• The participant has an adequate renal function:

‣ Calculated creatinine clearance (use Cockcroft-Gault formula for participants ≥ 18 years; Schwartz equation for participants \< 18 years) ≥ 60 mL/min.

• The participant has an adequate cardiac function:

‣ Left ventricular ejection fraction or shortening fraction per institutional norm ≥ institutional lower level of normal.

• The participant has creatine phosphokinase ≤ 2.5 × institutional ULN.

∙ Weight

• The participant has body weight ≥ 15 kg.

∙ Sex and Contraceptive/Barrier Requirements

∙ Male participants:

∙ Male participants are eligible to participate if they agree to the following during the study intervention period and for at least 4 months after the last dose of study intervention:

• Refrain from donating sperm.

∙ PLUS, either:

• Be abstinent from heterosexual intercourse as their preferred and usual lifestyle (abstinent on a long-term and persistent basis) and agree to remain abstinent.

∙ OR

• Must agree to use contraception/barrier as detailed below:

‣ Agree to use a male condom with female partner and use of an additional highly effective contraceptive method with a failure rate of \< 1% per year when having sexual intercourse with a Woman of childbearing potential (WOCBP) who is not currently pregnant.

⁃ Note: male participants who are azoospermic (vasectomized or due to a medical cause) are still required to follow the protocol-specified contraception/barrier criteria.

∙ Female participants:

∙ A female participant is eligible to participate if she is not pregnant or breastfeeding, and one of the following conditions applies:

• Is a Woman of nonchildbearing potential (WONCBP). OR

• Is a WOCBP and using an acceptable contraceptive method during the study intervention period (at least 7 months after the last dose of study intervention). The investigator should evaluate the potential for contraceptive method failure (eg, noncompliance, recently initiated) in relationship to the first dose of study intervention.

• A WOCBP must have a negative highly sensitive pregnancy test (urine or serum as required by local regulations) within 7 days before the first dose of study intervention.

‣ If a urine test cannot be confirmed as negative (eg, an ambiguous result), a serum pregnancy test is required. In such cases, the participant must be excluded from participation if the serum pregnancy result is positive.

• Additional requirements for pregnancy testing during and after study intervention.

• The investigator is responsible for review of medical history, menstrual history, and recent sexual activity to decrease the risk for inclusion of a woman with an early undetected pregnancy.

∙ Informed Consent

• Capable of giving signed informed consent, which includes compliance with the requirements and restrictions listed in the ICF and in this protocol.