Dose Escalation Study of CLR 131 in Children and Adolescents With Relapsed or Refractory Malignant Brain Cancer, Neuroblastoma, Rhabdomyosarcoma, Ewings Sarcoma, and Osteosarcoma

Even with standard, highly toxic multimodality therapies and salvage regimen, most pediatric
patients with primary metastatic or relapsed solid tumors are confronted with a poor
prognosis. For these patients there is currently no accepted successful treatment regimen.
There is a need for new drugs, including targeted radiopharmaceuticals, preferably with
cancer-specific uptake and broad applicability for these rare pediatric malignancies.

CLR 131 is a radioiodinated therapeutic that exploits the selective uptake and retention of
phospholipid ethers (PLEs) by malignant cells. Cellectar Biosciences' novel cancer-targeted
small-molecule compound (CLR1404) is radiolabeled with the isotope iodine-131 (I-131). CLR
131 has demonstrated tumor selective uptake across numerous adult and pediatric cancer cell
types. Therapeutic efficacy has been demonstrated in various pediatric and adult-type cancer
xenograft models, confirming the ability of CLR 131 to target tumors.

Based on the critical unmet medical need for effective agents with novel mechanisms of action
in relapsed pediatric cancers and initial preclinical and clinical experience with
radioiodinated CLR1404, Cellectar Biosciences has chosen to assess CLR 131 in a phase 1
pediatric trial.

Inclusion Criteria:

All Patients

- Previously confirmed (histologically or cytologically) pediatric solid tumor (e.g.,
neuroblastoma, sarcoma), lymphoma (including Hodgkin's lymphoma), or malignant brain
tumors that are clinically or radiographically suspected to be relapsed, refractory,
or recurrent for which there are no standard treatment options with curative potential

- ≥ 2 years of age and ≤ 21 years of age at time of consent/assent

- If ≥ age 16, Karnofsky performance status of ≥ 60. If < age 16, Lansky performance
status ≥ 60

- Platelets ≥ 75,000/µL (last transfusion, if any, must be at least 1 week prior to
study registration, and, unless deemed medically necessary, no transfusions are
allowed between registration and dosing)

- Absolute neutrophil count ≥ 750/µL

- Hemoglobin ≥ 10 g/dL (last transfusion must be at least 1 week prior to study
registration, and, unless deemed medically necessary, no transfusions are allowed
between registration and dosing)

- Using the bedside Schwartz formula, age-based serum creatinine within 2 x upper limit
of normal (ULN)

- Alanine aminotransferase < 3 × ULN

- Bilirubin < 2 × ULN

- Patients who have undergone autologous bone marrow transplant must be at least 3
months from transplant.

- Patients enrolling at dose levels > 30 millicurie (mCi)/m2 must have availability or
ability to collect an autologous stem cell back-up product prior to CLR 131
administration. At minimum, 2 x 10^6/kg cryopreserved CD34+ cells/kg must be
available.

- Patient or his or her legal representative is judged by the Investigator to have the
initiative and means to be compliant with the protocol.

- Patient or his or her legal representative has the ability to read, understand, and
provide written informed consent for the initiation of any study-related procedures.

- Female patients of childbearing potential must have a negative pregnancy test at
screening and within 24 hours of dosing. It is recommended that female caregivers of
childbearing potential have a negative pregnancy test within one week of dosing.

- Patients of childbearing potential must practice an effective method of birth control
while participating on this study to avoid possible damage to the fetus.

Patients with Pediatric Solid Tumor or Lymphoma

- At least 1 measurable lesion with longest diameter of at least 15 mm. Patients with a
lesion(s) that are determined to be Metaiodobenzylguanidine (MIBG) or positron
emission tomography (PET) positive may be enrolled at the investigator's discretion,
even if not associated with a measurable lesion of at least 15 mm.

- Patients with known brain metastases must have completed any radiotherapy or systemic
treatments for brain metastases prior to enrollment; by investigator assessment be
considered stable with no new signs or symptoms for at least 1 month, and on a stable
dose of steroids (unchanged for three weeks prior to screening).

Patients with Recurrent or Refractory Brain Tumors

- At least 1 measurable lesion with longest diameter of at least 10 mm on any imaging
sequence.

- Patients with neurological deficits must be clinically stable at time of enrollment
and able to complete all study related procedures. Patients with documented or newly
diagnosed neurological deficits will be enrolled at the investigator's discretion.

- Patients must be on a stable dose of steroids (unchanged for three weeks prior to
screening)

Exclusion Criteria:

- Patients receiving active treatment for brain metastases or those that are likely to
require active treatment during anticipated participation in this trial.

- Central nervous system involvement unless previously treated with surgery, systemic
therapy, or radiotherapy with the patient neurologically stable.

- Antitumor therapy or investigational therapy, within 2 weeks of registration. For
certain types of radiation (craniospinal, total abdominal, whole lung [spot
irradiation to skull-based metastases is not considered craniospinal radiation for the
purposes of this study]), at least 3 months must have elapsed.

- Patients previously treated with iodine-131 (131I)-MIBG who have already received a
cumulative I-131 dose > 54 mCi/kg or who would exceed 54 mCi/kg by participating in
this trial, are not eligible.

- History of hypersensitivity to iodine

- Any other concomitant serious illness or organ system dysfunction (including cardiac
and pulmonary dysfunction) that in the opinion of the Investigator would either
compromise patient safety or interfere with the evaluation of the safety of the test
drug.

- Major surgery within 6 weeks of enrollment

- Known history of human immunodeficiency virus or uncontrolled, serious, active
infection

- Pregnancy or breast-feeding