Module 8

Theranostics & Radio-Ligand Therapy

Theranostics pair a diagnostic imaging agent with a therapeutic radio-ligand targeting the same receptor. Pluvicto (¹⁷⁷Lu-PSMA-617, 2022) and Lutathera (¹⁷⁷Lu-DOTATATE, 2018) have transformed metastatic prostate cancer and neuroendocrine tumour treatment. Alpha-emitters (²²⁵Ac,²²³Ra) are the next wave.

1. The Theranostic Pair

The platform uses the same small-molecule or peptide ligand conjugated to either an imaging radionuclide (⁶⁸Ga, ¹⁸F PET) or a therapeutic radionuclide (¹⁷⁷Lu, ²²⁵Ac). Baseline⁶⁸Ga-PSMA-11 PET identifies tumour-expressed target; patients with sufficient uptake qualify for ¹⁷⁷Lu-PSMA-617 therapy. Response is monitored by repeat PET. This closed-loop “see-treat-see” model is uniquely precise among oncology modalities.

2. Beta vs. Alpha Emitters

¹⁷⁷Lu emits beta particles (~500 keV, ~2 mm tissue range) with a 6.65-day half-life. The longer range and lower linear energy transfer (LET) suit larger tumour deposits. ²²⁵Ac and ²²³Ra emit alpha particles (~5–8 MeV, ~50–80 µm range) with ~200× higher LET — ideal for single-cell micrometastases and radio-resistant disease. Pharmacokinetics differ: alpha emitters require tighter receptor residency because of their half-life and short range.

Simulation: Decay & LET Profiles

Python

script.py41 lines

import numpy as np, matplotlib
matplotlib.use('Agg')
import matplotlib.pyplot as plt

# Decay curves for therapeutic radionuclides
t = np.linspace(0, 30, 500)  # days
iso = {
    'Lu-177': 6.65,      # beta, days
    'I-131':  8.0,       # beta, days
    'Y-90':   2.67,      # beta, days
    'Ac-225': 10.0,      # alpha, days
    'Ra-223': 11.43,     # alpha, days
}
fig, (ax1, ax2) = plt.subplots(1, 2, figsize=(14, 5), facecolor='#0a0a1a')
for ax in (ax1, ax2):
    ax.set_facecolor('#111827'); ax.tick_params(colors='#cbd5e1')
    for s in ax.spines.values(): s.set_color('#334155')
    ax.grid(True, color='#334155', alpha=0.3)

for k, (lbl, half) in enumerate(iso.items()):
    ax1.plot(t, 0.5**(t/half)*100, lw=2.4, label=f'{lbl} t1/2 {half}d')
ax1.set_xlabel('Days', color='#cbd5e1')
ax1.set_ylabel('% activity remaining', color='#cbd5e1')
ax1.set_title('Radionuclide decay', color='#5eead4', fontweight='bold')
ax1.legend(facecolor='#1e293b', edgecolor='#334155', labelcolor='#cbd5e1')

# Alpha vs beta LET
distance = np.linspace(0, 100, 200)
alpha_dose = np.where(distance < 80, 100*np.exp(-distance/40), 0)
beta_dose = 100 * np.exp(-distance/500)
ax2.plot(distance, alpha_dose, color='#dc2626', lw=2.5, label='225Ac alpha (few cell diameters)')
ax2.plot(distance, beta_dose, color='#2dd4bf', lw=2.5, label='177Lu beta (mm range)')
ax2.set_xlabel('Distance (um)', color='#cbd5e1')
ax2.set_ylabel('Dose deposited (relative)', color='#cbd5e1')
ax2.set_title('Alpha vs beta LET profiles', color='#5eead4', fontweight='bold')
ax2.legend(facecolor='#1e293b', edgecolor='#334155', labelcolor='#cbd5e1')

plt.tight_layout()
plt.savefig('output.png', dpi=120, bbox_inches='tight', facecolor='#0a0a1a')
print('Pluvicto (177Lu-PSMA-617) 2022: mCRPC radio-ligand therapy')
print('Alpha emitters (225Ac) higher LET, short range - ideal for single-cell disease')

Click Run to execute the Python code

Code will be executed with Python 3 on the server

3. Approved Theranostics

Lutathera (¹⁷⁷Lu-DOTATATE, 2018): somatostatin-receptor-expressing neuroendocrine tumours.
Pluvicto (¹⁷⁷Lu-PSMA-617, 2022): metastatic castration-resistant prostate cancer after androgen-receptor-pathway inhibitor failure.
Xofigo (²²³Ra-dichloride, 2013): bone-metastatic mCRPC; targets calcium-hydroxyapatite.
Zevalin / Bexxar (⁹⁰Y / ¹³¹I anti-CD20): lymphoma radioimmunotherapy (mostly historical).

4. Synthesis of the Course

Eight modules surveyed the modern modality landscape: DNA-origami logic gates, PROTACs, antibody-drug conjugates, CAR-T cells, mRNA + LNPs, CRISPR editing, AAV gene therapy, and theranostics. Each extends the druggable genome in a distinct direction. The progression from small molecules (80% of historical approvals) to molecularly-targeted, genome-modifying, and radiolabelled precision therapies reflects the broader arc of 21st-century medicine: more targeted, more expensive per dose, and increasingly curative rather than chronic. Cost, access, and manufacturing remain the open problems as the modalities mature.

Key References

• Sartor, O. et al. (2021). “Lutetium-177-PSMA-617 for metastatic castration-resistant prostate cancer.” N. Engl. J. Med., 385, 1091–1103.

• Strosberg, J. et al. (2017). “Phase 3 trial of ¹⁷⁷Lu-DOTATATE for midgut neuroendocrine tumors.” N. Engl. J. Med., 376, 125–135.

• Kratochwil, C. et al. (2016). “²²⁵Ac-PSMA-617 for PSMA-targeted alpha-radiation therapy of metastatic castration-resistant prostate cancer.” J. Nucl. Med., 57, 1941–1944.

• Parker, C. et al. (2013). “Alpha emitter radium-223 and survival in metastatic prostate cancer.” N. Engl. J. Med., 369, 213–223.

Share:X Reddit LinkedIn

← Module 7 Course Overview →