Tozuleristide
A scorpion-venom peptide carrying a near-infrared dye to light up tumours during surgery
Tozuleristide, developed as BLZ-100 and nicknamed Tumor Paint, joins chlorotoxin, a peptide first isolated from scorpion venom, to indocyanine green, a dye that glows under near-infrared light. Injected hours before an operation, it gathers in tumour tissue so that a camera can show the surgeon where cancer is. It is not radioactive. Studies have run in adult and paediatric brain tumours, skin, breast and head-and-neck cancers; it is investigational.
Used in human trials: 24 mg, Single dose, 1-24 hours before surgery, Intravenous (Adult glioma, phase 2 (contrast-enhancing tumours)) Details ↓
Recommended Dosing
Used in human trials
No manufacturer dose exists for this use: these are amounts given in published trials, not recommendations.
What is it?
Surgeons removing brain and other solid tumours must judge by eye and touch where cancer ends, and leaving tumour behind raises the risk of recurrence. Fluorescence-guided surgery adds a dye that tumour tissue takes up, so a camera can show it. Tozuleristide uses chlorotoxin, a scorpion-venom peptide long known to bind gliomas and other tumours, to carry indocyanine green, a dye already used in medicine that emits near-infrared light, which passes through tissue better than visible light.
Before people, it was tested in mice, rats, dogs and monkeys. Single injections caused no adverse findings in rats or monkeys at many times the planned human dose, but dogs had histamine-driven allergic-type reactions. In dogs with natural cancers it gave usable contrast in carcinomas, mast cell tumours and especially soft tissue sarcomas, and in mouse models it marked head-and-neck cancers and high-grade precancerous lesions.
The human studies were small and focused on safety and signal. In 21 adults with skin cancers given 1 to 18 mg two days before excision, there were no serious adverse events and no maximum tolerated dose; most basal cell carcinomas and melanomas fluoresced at intermediate doses. In 17 adults with glioma given 3 to 30 mg, no dose-limiting toxicity occurred, the drug left the blood with a half-life of about 30 minutes, and high-grade tumours glowed more brightly. In 23 women with breast cancer, pathologists could see invasive and in situ cancer in fresh specimens. In children with brain tumours, 15 mg per m2 was chosen for later trials, with in-situ fluorescence in 70% of cases at that dose.
The phase 2 adult glioma study gives the clearest measure of accuracy. Fluorescence appeared in 30 of 33 contrast-enhancing tumours and none of six non-enhancing ones. Across 191 biopsies, a glowing sample was usually tumour (positive predictive value 0.85), but a dark sample often still contained tumour (negative predictive value 0.33). Surgeons did not use the signal to decide what to remove, so the study could not show better outcomes. A case series also found it lit up two cavernous vascular malformations, which are not tumours.
Tozuleristide is given only in operating theatres within studies. It has no FDA or EMA approval. Chlorotoxin has also been used to carry radioactive iodine and anticancer drugs, which are different molecules.
Mechanism of Action
Tozuleristide is a contrast agent for surgeons. It does not kill tumour cells; it marks them.
Chlorotoxin targeting
The peptide carries the dye into tumour tissue; proposed binding partners include matrix metalloproteinase-2 and annexin A2 (2021 report), and a 2019 study of another chlorotoxin conjugate pointed to neuropilin-1.
Near-infrared fluorescence
Indocyanine green emits near-infrared light seen with a dedicated camera during surgery (2019 phase 1).
Fast blood clearance
Serum half-life of about 30 minutes, while tumour signal persists for surgery hours later (2019 phase 1).
Limits of the signal
A dark area can still hold tumour: negative predictive value was 0.33 in glioma biopsies (2026 phase 2).
Published Research
These studies were read from their PubMed abstracts on October 29, 2026: six in people, four in animals and one on tissue in the laboratory.
First in humans: skin cancers
Twenty-one adults received 1, 3, 6, 12 or 18 mg by vein two days before excision. No serious adverse events, deaths or withdrawals; headache and nausea were the only effects in more than one person. Blood levels rose more than proportionally with dose. At 3-12 mg, 4 of 5 basal cell carcinomas and 4 of 4 melanomas fluoresced.
Phase 1 in adults with glioma
Seventeen patients received a single 3-30 mg dose 3-29 hours before surgery. No dose-limiting toxicity and no related adverse events. Terminal serum half-life was about 30 minutes at 9 mg and above. High-grade tumours fluoresced more than low-grade ones, with signal rising with dose.
Phase 1 in children with brain tumours
Twenty-nine children (32 operations) received 1.7-17.3 mg per m2. No dose-limiting toxicity, allergic reactions or deaths within 30 days. At 13.9-17.3 mg per m2, tumours fluoresced about five times more brightly and in-situ signal was seen in 69.6%; ex vivo sensitivity was 81% and PPV 93%.
Phase 2 in glioma
Thirty-nine adults received 24 mg (enhancing tumours) or 36 mg (non-enhancing) 1-24 hours before surgery. Fluorescence showed in 30 of 33 enhancing and 0 of 6 non-enhancing tumours. Across 191 biopsies: sensitivity 0.735, specificity 0.50, PPV 0.847, NPV 0.333. Fluorescence did not guide resection, so efficacy is unproven.
Breast cancer specimens
Twenty-three women received 6 or 12 mg at least an hour before surgery. Pathology staff saw bright focal signal in invasive cancers and fainter, diffuse signal in in situ disease, in ductal and lobular types and at all grades, and could relate cancer to the margins in fresh tissue.
Unexpected glow in vascular malformations
Two children in the paediatric phase 2/3 study had suspected gliomas that turned out to be cavernous malformations; both fluoresced strongly and were fully removed. The authors link this to matrix metalloproteinase-2 and annexin A2, proposed binding partners also found in these lesions.
Toxicology across four species
Single doses were well tolerated in rats and monkeys, with no-adverse-effect levels over 100 times a 3 mg human imaging dose. Dogs developed allergic-type reactions linked to histamine release, not related to dose; these were not seen in other species or in human studies to that date.
Dogs with natural tumours
Given before surgery to pet dogs with spontaneous cancers, it gave usable contrast in adenocarcinomas, squamous cell carcinomas, mast cell tumours and soft tissue sarcomas, with sarcomas brightest.
Head-and-neck cancer and precancer
In mice with tongue tumours, signal-to-background was 2.51 and at the tumour edge a cut-off gave 95% sensitivity and 91% specificity. In hamsters, high-grade dysplasia glowed more than mild-to-moderate dysplasia (2.31 vs 1.51).
Glioma in mice and a low-cost camera
A camera built from a standard CCD detected the agent down to about 50 nM. Mice with implanted human glioma injected 48 hours earlier showed strong tumour uptake against normal brain.
Seeing deeper with photoacoustics
In beef muscle, photoacoustic-ultrasound scanning detected 20 µM tozuleristide at estimated depths up to about 34 mm, beyond the roughly 5 mm limit of fluorescence alone, suggesting the two methods could be combined.
Dosing Data
Tozuleristide has no approved label. It is given once by vein before surgery; rows are from the carded human studies.
Educational information, not medical advice. Each dose above is tagged with its source: an approved label, a published human study, animal data, or amounts reported by users. None is a recommendation for you. An unapproved compound has no established safe or effective human dose, and products sold for “research use only” are not made or tested for people. Talk to a doctor before acting on anything on this site, including before you start, stop or change any medicine or dose. Full medical disclaimer.
What a Buyer Needs to Know
What is sold, how it is mixed, stored and taken, and what is known about its safety, quality and legal status. Each part names its source. Where we have none, it says unknown.
What is sold
Unknown: we hold no regulator's label that says in what form Tozuleristide is supplied. It is prepared and given by clinical staff, not bought and mixed at home: the next part says where.
Mixing a vial: a worked example
Nothing to mix at home, and no syringe units to work out: Tozuleristide is prepared and given by clinical staff, in hospital, before tumour surgery.
In the carded studies it was given once into a vein hours before an operation, so the surgeons could see tumour tissue glow under near-infrared light.
Source: PMID 31069381 and PMID 40882241 (studies carded under Research below).
Storage before and after mixing
Unknown: no label on file says how Tozuleristide is stored. It is kept and prepared by the hospital or clinic that gives it (see the part above); the home rules for a mixed vial in the mixing guide do not apply to it.
How it is taken
As it was given in human studies: Intravenous (Single dose, 1-24 hours before surgery; Adult glioma, phase 2 (contrast-enhancing tumours)).
Source: Used in human trials: the route and frequency of each row in Dosing Data below.
What to expect, and when
How long it stays in the body: a half-life of about 30 minutes, terminal serum half-life at doses of 9 mg and above (PMID 31069381). After about five half-lives almost none is left.
How long the doses were given: Adult glioma, phase 2 (contrast-enhancing tumours): Once; Adult glioma, phase 2 (non-enhancing tumours): Once; Children with brain tumours, phase 1 expansion dose: Once.
When effects appear: unknown; no source on this page gives a time to effect for Tozuleristide. Results reported in the studies are under Published Research.
Source: half-life: PMID 31069381; Used in human trials, the duration of each row in Dosing Data below.
Side effects, and when to stop or get help
From the Side Effects section: No dose-limiting toxicity in adult or paediatric phase 1 studies; Headache and nausea (two people each) in the skin cancer study; No allergic reactions in 29 children; allergic-type, histamine-driven reactions were seen in dogs. Full list and cautions ↓
When to stop or get help: unknown; no label or trial on file sets rules for stopping Tozuleristide. Treat a severe or unexpected reaction as a reason to stop and see a doctor.
Source: the Side Effects section below (“From the human studies above”).
Interactions
Unknown: a PubMed search for human interaction studies of Tozuleristide (reviewed 2026-10-28) found none. Unknown is not the same as safe to combine.
Every peptide's record, with its source: the interaction matrix.
Checking what you bought
Unknown: no published independent test of Tozuleristide products is in our lab-results database yet, so how products sold under this name measure up is not known.
To read a certificate of analysis, paste it into the COA decoder; it checks the measured mass against Tozuleristide's expected mass, 4,766.0 Da, from this entry's molecular data. Trust & Verification explains what independent testing can and cannot show.
Legal status
US: In Clinical Trials (Not approved: Drugs@FDA and the EMA medicines list hold no record (searched October 28, 2026)). Sport: Prohibited (S0 catch-all).
Country by country ↓ · Regulatory tracker
Source: this entry's approval status and the WADA Prohibited List, as in Legal Status below.
Side Effects & Contraindications
Reported Side Effects
From the human studies above.
Contraindications & Cautions
No approved label exists, so there are no official contraindications. Points from the studies:
Legal Status
Tozuleristide is investigational in every jurisdiction checked.
Frequently Asked Questions
?What is tozuleristide?
Chlorotoxin, a peptide from scorpion venom, joined to the near-infrared dye indocyanine green. It is a surgical imaging agent, also known as BLZ-100 or Tumor Paint.
?Is it radioactive?
No. It works by fluorescence, read with a near-infrared camera.
?Does it improve surgery?
Not yet shown. In the phase 2 glioma study the signal was not used to guide resection, and a dark area could still contain tumour.
?Is it approved?
No. It has been given only in trials.
References
- [other] PubChem CID 121488172, Tozuleristide: formula C203H296N58O52S12, molecular weight 4766. Read October 28, 2026. https://pubchem.ncbi.nlm.nih.gov/compound/121488172
- [registry] ClinicalTrials.gov API v2, read October 28, 2026: NCT03579602 (phase 2/3, paediatric CNS tumours, completed); NCT04743310 (phase 2, adult CNS tumours, completed); NCT05316688 (phase 1/2, oral cavity cancer, terminated).
- [clinical-trial] Yamada M, et al. "A first-in-human study of BLZ-100 (tozuleristide) demonstrates tolerability and safety in skin cancer patients." Contemp Clin Trials Commun, 2021;23:100830. PMID: 34401600.
- [clinical-trial] Patil CG, et al. "Phase 1 Safety, Pharmacokinetics, and Fluorescence Imaging Study of Tozuleristide (BLZ-100) in Adults With Newly Diagnosed or Recurrent Gliomas." Neurosurgery, 2019;85(4):E641-E649. PMID: 31069381.
- [clinical-trial] Lee A, et al. "Phase 1 and expanded imaging study of tozuleristide in patients with pediatric primary central nervous system tumors." J Neurosurg Pediatr, 2025;36(5):582-592. PMID: 40882241.
- [clinical-trial] Fox RC, et al. "Tozuleristide Fluorescence-Guided Resection of Gliomas: Results of a Phase II Investigator-Initiated Study." Oper Neurosurg, 2026. PMID: 42788739.
- [clinical-trial] Dintzis SM, et al. "Real-time Visualization of Breast Carcinoma in Pathology Specimens From Patients Receiving Fluorescent Tumor-Marking Agent Tozuleristide." Arch Pathol Lab Med, 2019;143(9):1076-1083. PMID: 30550350.
- [pubmed] Kobets AJ, et al. "Unexpected Binding of Tozuleristide "Tumor Paint" to Cerebral Vascular Malformations: A Potentially Novel Application of Fluorescence-Guided Surgery." Neurosurgery, 2021;89(2):204-211. PMID: 33826729.
- [pubmed] Parrish-Novak J, et al. "Nonclinical Profile of BLZ-100, a Tumor-Targeting Fluorescent Imaging Agent." Int J Toxicol, 2017;36(2):104-112. PMID: 28403743.
- [pubmed] Fidel J, et al. "Preclinical Validation of the Utility of BLZ-100 in Providing Fluorescence Contrast for Imaging Spontaneous Solid Tumors." Cancer Res, 2015;75(20):4283-91. PMID: 26471914.
- [pubmed] Baik FM, et al. "Fluorescence Identification of Head and Neck Squamous Cell Carcinoma and High-Risk Oral Dysplasia With BLZ-100, a Chlorotoxin-Indocyanine Green Conjugate." JAMA Otolaryngol Head Neck Surg, 2016;142(4):330-8. PMID: 26892902.
- [pubmed] Butte PV, et al. "Near-infrared imaging of brain tumors using the Tumor Paint BLZ-100 to achieve near-complete resection of brain tumors." Neurosurg Focus, 2014;36(2):E1. PMID: 24484247.
- [pubmed] Shang R, et al. "Complementary fluorescence and photoacoustic imaging of tozuleristide in muscle tissue in vitro- toward optically-guided solid tumor surgery: feasibility studies." Sci Rep, 2026;16(1). PMID: 42069900.
- [pubmed] McGonigle S, et al. "Neuropilin-1 drives tumor-specific uptake of chlorotoxin." Cell Commun Signal, 2019;17(1):67. PMID: 31208428.
Sources & Citations
Studies were read from their PubMed records on October 29, 2026. Regulatory status comes from Drugs@FDA and the EMA medicines list (searched October 28, 2026) and trial listings from ClinicalTrials.gov (October 29, 2026). Grey Peptides sells nothing and links to no vendor.
Medical Disclaimer: This content is for educational and informational purposes only. It is not medical advice, and nothing here is an instruction to obtain or use any compound. Talk to a licensed clinician about your own situation.