Metarrestin (ML-246) in Subjects With Metastatic Solid Tumors

* INCLUSION CRITERIA: * Adult (\>= 18 years) subjects with: * histologically or cytologically confirmed solid tumors (Phase IA). OR --histologically or cytologically confirmed pancreatic, colorectal, or breast cancer (Phase IB) OR * Pediatric (\>=12 and \< 18 years) subjects with histologically or cytologically confirmed solid tumors other than rhabdomyosarcoma (RMS) including embryonal, alveolar, spindle cell/sclerosing, and pleomorphic subtypes of RMS (Phase IB). * Subjects must have disease that: * is not amenable to potentially curative resection, * spread at least to one other organ system other than primary tumor or recurred after removal of primary tumor, * has site measurable per RECIST 1.1 (Phase IB only). * progressed on or after at least one line of standard systemic chemotherapy (Phase IA and IB1) * have no standard therapy option available (Phase IB2) * Patients must have recovered from any acute toxicity related to prior therapy or surgery or disease to a grade 1 or less. * Performance status * Karnofsky \>= 70% (for patients \>= 16 years old), Lansky \>= 70% (for patients \<16 years old) * Adequate hematological function defined by: * absolute neutrophil count (ANC) \>= 1.0 x 10(9)/L, * transfusion-independent platelet count \>= 100 x 10(9)/L, * Hgb \>= 9 g/ dL (patients who have received \<= 2 PRBC transfusions within 48 hours are eligible) * Adequate coagulation as defined by: --INR\<1.5 (or \< 3.0 if subjects are currently taking anticoagulated medications) Note: increase of the upper limit of INR is restricted only to subjects who are receiving anticoagulation for medical reasons (DVT/PE prophylaxis, treatment for a thromboembolic event) and have increased INR because of these medications. Patients who have an elevated INR due to compromised liver function or any other medical conditions remain excluded * Adequate hepatic function defined by: --a total bilirubin level \<= 1.5 x ULN, (total bilirubin \<= 2.0 x ULN in case of prior diagnosis of Gilbert syndrome) * an AST level \<= 3xULN * an ALT level \<= 3 xULN * Adequate renal function defined by: --Creatinine OR Measured or calculated creatinine clearance (CrCl) (eGFR may also be used in place of CrCl)\* ---\< 1.5x institution upper limit of normal OR ---\>= 45 mL/min/1.73 m\^2 for participant with creatinine levels \>= 1.5 X institutional ULN \*Creatinine clearance (CrCl) or eGFR should be calculated per institutional standard. * The effects of the study treatment on the developing human fetus are unknown; thus, individuals of childbearing potential and individuals who can father children must agree to use adequate contraception (hormonal or barrier method of birth control; abstinence) prior to study entry, for the duration of study therapy and up to 120 days after the last dose of the study drug. * Nursing participants must be willing to discontinue nursing at the time of the study treatment initiation. * Weight: \>= 35 kg (\>= 18 years old) or \>=40 kg (\>= 12 and \< 18 years old). * Ability of subject or parent/guardian to understand and the willingness to sign a written informed consent document. * Subjects must have lesion(s) accessible for biopsy (other than used for measurement of disease) and be willing to undergo mandatory study biopsies (Cohort IB1 only). * Ability to swallow oral capsules. EXCLUSION CRITERIA: * Anticancer treatment within designated period before treatment initiation including: * minor surgical procedure (such as biliary stenting) within 14 days. Note: if liver function tests after biliary stenting or renal function tests after ureteral stenting return to normal, within 5 days after biliary or ureteral stenting; * major surgical procedure or curative radiation treatment within 28 days; * palliative radiation treatment within 14 days; * chemotherapy or experimental drug treatment with published half-life known to be 72 hours or less within 14 days; * experimental drug treatment with unpublished or half-life greater than 72 hours within 28 days; * chemotherapy regimen containing an alkylating antineoplastic agent (cyclophosphamide, chlorambucil, melphalan, or ifosfamide), alkylating-like (platinumbased chemotherapeutic drugs, platinum analogues), and non-classical alkylating agent (dacarbazine, temozolomide) within 28 days. * Patients receiving any medications or substances that are moderate and strong inhibitors or inducers of CYP3A4 and are not able to safely stop these medications are excluded from this study; patients must stop strong CYP3A4 inhibiting/inducing medications within 5 published half-lives and moderate within 3 published half-lives prior to the treatment initiation. Note: dihydropyridine calcium - channel blockers are permitted for management of underling disease. * Patients receiving medications known to carry a high to moderate risk to lower seizure threshold within 2 weeks prior to treatment initiation. * Subjects with cardiomyopathy diagnosed within 6 months prior to treatment initiation including but not limited to the following: * hypertrophic cardiomyopathy * arrhythmogenic right ventricular cardiomyopathy * abnormal ejection fraction (echocardiogram \[ECHO\]) \<= 53% (if a range is given then the upper value of the range will be used) * previous moderate or severe impairment of left ventricular systolic function (LVEF \<45%) * severe valvular heart disease * atrial fibrillation with a ventricular rate \>100 bpm on EKG at rest * Fridericia's corrected QT interval (QTcF) \>= 480 msec (adults) or \>= 460 msec (pediatric subjects, aged 12 to \<18 years) or other factors that increase the risk of QT prolongation or arrhythmic events (e.g., heart failure, hypokalemia, family history of long QT interval syndrome. * HIV, HCV, HBV positive patients on antiviral drugs are excluded due to the absence of previous experience with concurrent use of antiviral medications and the investigational drug