Dosimetry evaluation in a phase I study of intravenous 131I-TM601 in patients with recurrent or refractory somatic and/or cerebral metastatic solid tumors

Objectives TM601, or Chlorotoxin, is a peptide derived from scorpion venom that specifically binds to tumors. Previous Phase 1 & 2 trials of intracranially infused ¹³¹I-TM601 in glioma patients have shown promise. This trial is to determine tumor and normal organ uptake of IV infused ¹³¹I-TM601.

Methods Twenty patients (7 glioma, 7 melanoma, 2 lung, 1 prostate, 1 colon, 1 breast, 1 pancreatic) were analyzed in this ongoing study. All patients received a tracer dose of 10 mCi ¹³¹I-TM601 followed by 5 whole body scans and 1 SPECT. Triple energy windows were used to correct scatter. Patients showing tumor uptake by whole body or SPECT imaging treated with 30 mCi ¹³¹I-TM601 one week later.

Results Scatter correction improved tumor visualization. Seven out of 7 glioma, 6 out of 7 melanoma, and 4 out of 6 other somatic solid tumor patients demonstrated tumor specific uptake. Normal organ dose estimates were similar among all 20 patients. Mean radiation dose was 4.8, 2.9, 1.2, 0.52, 0.27 cGy/mCi for kidneys, thyroid, stomach, marrow, body, respectively (n=20). Mean tumor dose was 1.4 cGy/mCi for glioma and melanoma patients (n=13) with tumor volume defined by MRI T1 post contrast. Dose limiting toxicity was not observed.

Conclusions ¹³¹I-TM601 administered IV crosses the blood brain barrier and can target glioma as well as other solid tumor types. These results support future dose escalation trials for safety and efficacy to treat glioma and melanoma.