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A specimen of the Other drawer Drawer G · Other

225Ac-DOTA-LM3

Investigational

An alpha-emitting radiolabeled somatostatin receptor antagonist for peptide receptor radionuclide therapy (PRRT) in neuroendocrine tumors. Unlike conventional beta-emitting Lu-177 therapies and SSTR agonists, 225Ac-DOTA-LM3 combines the higher cell-killing power of alpha particles with antagonist binding for enhanced tumor targeting. Clinical stage investigational therapy showing promise in Lu-177-refractory patients.

Actinium-225-DOTA-LM3 · 225Ac-DOTA-JR11 · Alpha-PRRT · Ac-225 LM3

Research evidence
Moderate

18 human studies

Preclinical
36%
Clinical
64%

Based on 28 cited sources

Evidence Score57/100
Early / limited
Research Depth49/100
Mechanism80/100
Plausibility88/100
Global Coverage48/100
Community Experience11/100
Effectiveness66/100

clinically demonstrated · low confidence

Demonstrated effect magnitude — not a recommendation or safety claim.

Research Depth: multiple uncontrolled retrospective/observational human cohorts (Heidelberg n=35 + NEN-G3 rescue + TANDEM), no RCT. Mechanism: SSTR2 target with binding + functional antagonist confirmation and a fully mapped alpha-radiobiology chain. Plausibility: full mechanism->dosimetry->outcome chain, coherent with PRRT oncology, strong same-class analogy (Lutathera). Global Coverage: clinical work concentrated in one German/Swiss cluster, ~28 studies, investigational only. Community Experience: dossier confirms no meaningful community/user reports (hospital-administered investigational). Effectiveness basis clinical (low confidence): quantified human efficacy for the antagonist DOTA-LM3 class (85.1% disease control, 36.2% PR in the n=51 177Lu-DOTA-LM3 first-in-humans study) plus a 35-patient 225Ac-DOTA-LM3 Lu-177-refractory salvage series.

Scored May 2026 How we rate →
~
Evidence Level
moderate
Not approved for human use by any regulatory agency
Limited human clinical trial data
Consult a healthcare provider before use
Not FDA Approved WADA Prohibited
Identity
SCALE · 1:1 N-TERMINUS C-TERMINUS 8 AA · ~3,500 Da (peptide + chelator)
Also Known As
Actinium-225-DOTA-LM3 • 225Ac-DOTA-JR11 • Alpha-PRRT • Ac-225 LM3
Class
Radiolabeled octapeptide antagonist
Length
8 amino acids
Mol. weight
~3,500 Da (peptide + chelator)
Sequence
Cpa-c[DCys-Aph(Hor)-DAph(Cbm)-Lys-Thr-Cys]-DTyr-NH2
Molecular Structure
Cpa
DCys
Aph(Hor)
DAph(Cbm)
Lys
Thr
Cys
DTyr
Hydrophobic
Polar
Positive
Negative

The mechanism of 225Ac-DOTA-LM3 is well-characterized based on extensive preclinical studies and growing clinical experience.

How It Works (Simplified)

225Ac-DOTA-LM3 acts as a precision “smart bomb” for neuroendocrine tumors:

Receptor Targeting

LM3 peptide locks onto SSTR2 receptors highly expressed on NET cells. As an antagonist, it binds without triggering internalization, accessing 2-4x more receptor sites than agonists.

Alpha Emission

Actinium-225 decays releasing 4 alpha particles (helium nuclei) with ~28 MeV total energy. These heavy, high-energy projectiles are 400x more ionizing than beta particles.

DNA Destruction

Alpha particles cause clustered double-strand DNA breaks that are essentially irreparable. Unlike beta radiation damage, cells cannot recover from this level of destruction.

Precision Kill

Alpha particles travel only 50-100 microns (less than a hair width), destroying tumor cells without damaging distant healthy tissue. Ideal for micrometastases.

Key Research: Perrone E, Baum RP et al. (2025) reported a 35-patient retrospective series of 225Ac-DOTA-LM3 PRRT (as monotherapy and as Lu-177 TANDEM), describing acceptable safety and promising survival in patients progressing after Lu-177 DOTATATE/DOTATOC. PMID:41008911

Important Limitations

  • Investigational therapy not approved by any regulatory agency
  • Limited to specialized nuclear medicine centers with Ac-225 access
  • Actinium-225 supply remains constrained globally
  • Xerostomia (dry mouth) occurs in 30-50% due to salivary gland uptake
  • Long-term safety data and survival outcomes still being established
  • Optimal dosing, number of cycles, and patient selection criteria not standardized
i. SSTR2 Antagonist Binding · Tumor Targeting
225Ac-DOTA-LM3SSTR2 binding (antagonist)No receptor internalizationProlonged surface retentionHigher tumor uptake
ii. Alpha Particle Radiobiology · Cell Killing
225Ac decay4 alpha particles (28 MeV total)High LET (80-100 keV/micron)Clustered DNA double-strand breaksIrreparable damageCell death
iii. Ac-225 Decay Cascade · Sustained Radiation
225Ac (t1/2 = 9.92 days)221Fr217At213Bi209Pb209Bi (stable)alphaalphaalphabeta/alpha 5.83 MeV 6.34 MeV 7.07 MeV 8.38 MeV
Mechanism SSTR2 antagonist binding without receptor internalization, providing prolonged tumor surface retention
Established 8 direct studies
Benefit shown to achieve higher tumor uptake than agonist-based therapies
Evidence Level
Moderate
4 Human
6 Animal
3 In Vitro
Mechanism Alpha particle emission causing irreparable DNA double-strand breaks with high linear energy transfer (80-100 keV/micron)
Established 12 direct studies
Benefit may overcome radioresistance seen with beta-emitting therapies
Evidence Level
Moderate
6 Human
5 Animal
4 In Vitro
Mechanism Actinium-225 decay cascade releasing 4 alpha particles with ~28 MeV total energy over 10-day half-life
Established 10 direct studies
Benefit shown to provide sustained high-dose radiation to tumor cells
Evidence Level
High
8 Human
6 Animal
5 In Vitro
Mechanism Short alpha particle range (50-100 microns) limiting collateral damage to adjacent normal tissue
Established 8 direct studies
Benefit shown to minimize off-target radiation exposure
Evidence Level
Moderate
5 Human
4 Animal
3 In Vitro
Mechanism Confidence
Established
Supported
Emerging
Evidence Level
High
Moderate
Low
Very Low
Phase 01 1
Day 0-7

Treatment administration at specialized nuclear medicine center. Amino acid co-infusion for renal protection. Actinium-225 begins alpha decay cascade. Nausea possible on treatment day; managed with antiemetics.

PMID:41008911
Phase 02 2
Week 1-4

Continued alpha particle emission as Ac-225 decays (9.92-day half-life). Mild fatigue common. Hematologic parameters monitored. Tumor irradiation ongoing from internalized and surface-bound radioactivity.

PMID:41008911
Phase 03 3
Week 4-6

Hematologic nadir typically occurs 4-6 weeks post-treatment. Transient grade 1-2 cytopenias common. Blood count monitoring recommended. Some patients may experience onset of xerostomia.

PMID:41008911
Phase 04 4
Week 8-12

Hematologic recovery in most patients. Restaging imaging (68Ga-DOTATATE PET/CT) to assess response. Next treatment cycle considered if tolerated and indicated. Disease control assessment.

PMID:41008911
Phase 05 5
Cycle 2-6

Additional cycles administered at 8-12 week intervals based on response and tolerance. Cumulative kidney dose monitored. Xerostomia may develop or worsen with repeated cycles. Long-term monitoring for secondary malignancy.

PMID:41008911

Research-based observations

This timeline reflects observations from published clinical and preclinical studies. Individual responses may vary significantly. This is not a guarantee of effects or a dosing schedule. Consult qualified healthcare providers for personalized guidance.

Good Signs (6 indicators)
Administered at accredited nuclear medicine facility
Proper SSTR-positive tumor confirmation via 68Ga-DOTATATE PET/CT
Individualized dosimetry performed for kidney dose estimation
Amino acid co-infusion protocol followed for renal protection
Multidisciplinary tumor board review prior to treatment
Certificate of analysis for radiopharmaceutical preparation
Warning Signs (5 indicators)
Limited prior imaging to confirm SSTR expression
No dosimetry performed between cycles
Inadequate hydration or amino acid protection
Treatment at facility with limited PRRT experience
Insufficient time between cycles (<8 weeks)
Bad Signs (6 indicators)
Administration without confirmed SSTR-positive disease
No renal function monitoring before treatment
Skipping amino acid renal protection protocol
Treatment in setting of severe renal impairment (eGFR <30)
No baseline hematologic assessment
Facility without proper radiation safety protocols
Positive quality indicator
Requires evaluation
Potential quality issue

For Research Evaluation Only

These quality indicators are general guidelines based on typical peptide characteristics. Professional laboratory testing (HPLC, mass spectrometry) provides definitive quality verification. This checklist is for initial visual evaluation only.

Synergistic
Compatible
Caution
Avoid

Semaglutide

Compatible
Compatible

No overlapping receptor targets. GLP-1 agonists do not affect SSTR2 binding. Can be safely used in diabetic NET patients receiving PRRT.

Lutathera

Caution
Caution

Sequential use may be appropriate (Lu-177 first-line, Ac-225 at progression). TANDEM therapy protocols combine both for complementary beta and alpha radiation effects. Coordinate with nuclear medicine specialist.

BPC-157

Caution
Caution

BPC-157's gastroprotective effects may theoretically interact with GI tract radiation effects. No clinical data on combination. Consult treating physician.

Octreotide

Avoid
Avoid

Both target SSTR2. Octreotide (agonist) would compete for receptor binding and reduce 225Ac-DOTA-LM3 tumor uptake. Must discontinue octreotide before PRRT administration.

Lanreotide

Avoid
Avoid

Similar SSTR agonist that would compete for receptor binding. Requires washout period before 225Ac-DOTA-LM3 therapy to ensure optimal tumor targeting.

Research Note: Interaction data is based on published literature, mechanistic understanding, and theoretical considerations. Most peptide combinations lack direct clinical study. This information is for educational purposes only and does not constitute medical advice. Always consult qualified healthcare providers.

28 Sources 18 Human 10 Preclinical

Key Studies Cited

Human Wild D et al. 2014
PMID:24963127
Animal Ginj M et al. 2006
PMID:17056720
Human Baum RP et al. 2021
PMID:33674401
In Vitro Stanley FKT et al. 2020
PMID:33010172
Human Perrone E et al. 2025
PMID:41008911
Human Kratochwil C et al. 2016
PMID:27390158
Human Delker A et al. 2015
PMID:25790773

Full reference list available on request. All citations link to PubMed for verification.

This dossier synthesizes available evidence from peer-reviewed literature, regulatory documents, and clinical trial registries. Evidence strength ratings follow a modified GRADE approach.

For complete methodology details, see our Methodology page.

Important Disclaimer

This dossier is for educational purposes only and does not constitute medical advice. Always consult a qualified healthcare provider before making health decisions.

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