Radioimmunotherapy involves coupling a radionuclide to monoclonal antibodies targeting tumor antigens. This allows targeted delivery of radiation to cancer cells while sparing healthy cells. Radionuclides like Yttrium-90 and Iodine-131 are attached to antibodies using chelators or chemical reactions. Low dose radiation is continuously delivered over days, inducing cell death through various radiobiological effects like the crossfire effect. Radioimmunotherapy has been used to treat hematologic malignancies like NHL and solid tumors. Clinical trials show radioimmunotherapy improves progression-free survival when used as consolidation after chemotherapy for follicular lymphoma.

1. RADIOIMMUNOTHERAPY
Presenter: Dr. Masthan Basha
Moderator: Dr. B.V. Subramanian

2. • Definition :
• Radioimmunotherapy(RIT) involves the coupling of a
radionuclide with monoclonal antibodies (mAbs) that are
targeted against tumor-associated antigens or antigens
expressed by cells of the tumor microenvironment.

3. Radioimmunotherapy (RIT)
Targeting and destroying cancer cells with radionuclide,
without damaging surrounding healthy cells.
Cancer cells express a
specific antigen
The chelator links
the antibody to the
isotope
The isotope
destroys
the cancer cell
The antibody
recognizes and
targets the cancer
cell’s antigen

4. Physics & Radiobiology of RIT
• RIT delivers radiation to the target tissue in a continuous low
dose rate (LDR) fashion.
• Typical dose rates for RIT are in the range of 10 to 20 cGy per
hour compared to EBRT with 100 to 500 cGy per hour
• The total dose delivered by RIT is in the range of 1,500 to
2,000 cGy with an effective half-life of 24 to 72 hours.

5. • The shoulder on the cell survival
curve is typically observed when
HDRs of radiation are employed
• In RIT, the dose rate is 1,000-fold
lower.
• So, the quadratic portion of the
curve will have a lower impact on
survival because many SSBs,
considered sublethal damage, will
be repaired during the more
lengthy delivery of LDR radiation.
• This will result in a “small” or
absent observable shoulder.
• Thus, when estimating cell
survival for RIT, α alone will
define the radiosensitivity of the
tumor.
Cell survival curves following treatment with
radiotherapy. The blue curve represents low dose
rate radiotherapy; the green curve represents high
dose rate radiotherapy.

6. • RIT is approx., 20% less effective than HDR EBRT.
• But it is relatively effective because of many radiobiologic
processes include low-dose/dose rate apoptosis, inverse dose
rate effect (G2 synchronization), radiation-induced biologic
bystander effect, and the crossfire effect.

7. Crossfire Effect
• The beta emissions from radioisotopes penetrate several
hundreds of cell layers, creates a crossfire effect useful for
inducing apoptosis in malignant cellls not directly bound to
the RIT
• This makes RIT helpful in treating bulky or poorly vascularised
tumor masses

8. Crossfire Enhances Efficacy
Unlabeled “Cold” Antibody Radiolabeled Antibody

9. Bystander effect
• Radiation induced bystander effect is the phenomenon in
which non irradiated cells exhibit effects as a result of signals
received from near by irradiated cells.
• Responses include changes in process of translation, gene
expression, cell proliferation, apoptosis and cell death.

10. Inverse dose rate
effect
• The dose-response curve for acute
exposures is characterized by a broad
initial shoulder.
• As the dose rate is reduced, the survival
curve becomes progressively more
shallow as more and more sublethal
damage is repaired, but cells are“ frozen”
in their positions in the cycle and do not
progress.
• As the dose rate is lowered further and
for a limited range of dose rates, the
survival curve steepens again because
cells can progress through the cycle to
pile up at a block in G2, a radiosensitive
phase, but still cannot divide.
• A further lowering of dose rate below this
critical dose rate allows cells to escape
the G2 block and divide; cell proliferation
then may occur during the protracted
exposure, and survival curves become
shallower as cell birth from mitosis offsets

11. RIT
• TARGETS( TUMOR ANTIGENS)
• CARRIERS( ANTIBODIES)
• RADIONUCLIDES
• RADIOCHEMISTRY

12. Tumor associated antigens(TAA)
• The targets for radioimmunotherapy (RIT) typically consist of
tumor-associated antigens (TAAs).
• To date, >2,000 TAAs have been identified.
• One of the main methodologies used to identify TAAs is
termed SEREX (serologic analysis of recombinant cDNA
libraries).

14. overexpressed on cancer cells
Uniformly expressed
Not found to any significant level
in normal tissue
Not shed into the circulation
Exhibits an important role in
tumor growth and progression
antigen densities ≥105 receptors on each cell
for adequate targeting
Nonuniform activity distributions
↓effectiveness of RIT , heterogeneous dose
distributions
Ab binds to Ag in circulation,
Rapid clearance , less effectve treatment
disruption of growth pathways important
for tumor growth
Ideal target

15. Carriers(Targeting Constructs)
• Commonly used are antibodies, antibody fragments
• In humans, there are five classes or isotypes of antibodies
(IgA, IgD, IgE, IgG, and IgM).
• IgG is the most commonly used mAb for RIT because it is the
most prevalent antibody in serum and has the longest serum
half-life (approx., 23 days).
• IgG is further divided into four subtypes, IgG1–4.
• IgG antibodies are large glycoprotein macromolecules, with an
atomic mass of approx.,150 kDa.

16. Carriers
• The “y-shaped structure” consists
of two Fab fragments (fragment
antigen binding) and an Fc
fragment (crystallizable fragmen).
• The “tip” of each Fab fragment has
a variable amino acid sequence,
from one mAb to another.
• Accordingly, each tip is an antigen
binding site (ABS) and is
responsible for antigen
recognition.

17. Carriers
• Each ABS forms a noncovalent bond (electrostatic
forces, van der Waals forces, hydrophobic
interactions, and hydrogen bonds) with the target or
antigen.
• The specific region of an antigen, which binds to the
ABS, is referred to as an epitope.
• Peptides, affibodies, aptamers, and nanostructures
(i.e., liposomes, nanoparticles, microparticles,
nanoshells, and minicells) are under investigation.

18. IDEAL
• MORE TUMOR UPTAKE
• LESS TIME TO ACCRETION AND FASTER CLEARANCE
Carriers

19. Radionuclides

20. Radiochemistry
• Labeling the targeting construct(carrier) with the appropriate
radionuclide is the radiochemistry
• It is more important and complex procedure.
• Radionuclides are attached to targeting constructs by either
using a “linker” molecule, termed a bifunctional chelating
agent (BCA) or by a chemical reaction that forms a covalent
bond between the radionuclide and the targeting construct.

21. • In general, metallic radionuclides will require a BCA for
labeling, and radiohalogens will require a chemical reaction
(halogenation).
• The most prevalent therapeutic radionuclides used in RIT are
90Y (metallic radionuclide) and 131I (radiohalogen).
• Tiuxetan, a modified DTPA molecule, is used as a linker
molecule to chelate 90Y to ibritumomab
• The halogenation reaction that bonds 131I to the targeting
construct (131I tositumomab; Bexxar, GlaxoSmithKline,
Philadelphia, PA) is called iodination.

22. METALLIC RADIONUCLIDES –
BIFUNCTIONAL CHELATING AGENT
(Tixuetan)
RADIOHALOGEN I 131------
HALOGENATION REACTION
Radiochemistry

23. • To improve radiation delivery and therapeutic efficacy
• Strategies:
• Using pretargeting techniques
• Modulating the tumor microenvironment
• Extracorporeal delivery
• Fractionation
• Multiple radionuclides (radionuclide cocktail)
• Increasing antibody mass
• Alteration of the physical properties (size and affinity) of the
targeting construct

24. • Pretargeting techniques
• a) Bispecific monoclonal antibody
• b) Streptavidin-biotin system

25. Bispecific monoclonal antibody
• A portion of the antibody has affinity for the
tumor (antitumor) & another portion has
affinity for the radionuclide carrier ligand or
hapten-peptide (antihapten).
• Initially (step 1), a large “saturation” dose of
the unlabeled bsmAb is administered, and
the antibody localizes in the tumor over
several days.
• Subsequently (step 2), a radionuclide
conjugated to a hapten-peptide is
administered.
• This step results in a rapid distribution of
the radionuclide in the tumor.
• Because the hapten-peptide has a small
molecular weight, it will clear rapidly from
the body and result in a low bone marrow
exposure to radiation.

26. In the streptavidin-biotin system, streptavidin is conjugated to the
initial pretargeting macromolecule, and biotin is conjugated to the
radionuclide.
Streptavidin and biotin have a very high affinity for each other .
The tumor/blood ratios of the targeting agent are significantly
increased
Streptavidin-Biotin system

27. RIT - Applications
• NHL, Hodgkin lymphoma
• Leukemia
• Multiple myeloma
• Colorectal carcinoma
• Hepatocellular carcinoma (HCC)
• Central nervous system (CNS) malignancies
• Medullary thyroid cancer
• Ovarian cancer
• Head and neck cancer
• Prostate cancer
• Renal cell carcinoma
• Osteosarcoma,
• NETs
• Melanoma, pediatric malignancies.

28. Haematology

29. Approved Therapeutic Agents

30. Regulatory Status of Anti-CD20 Radioimmunotherapy
• Y-90 ibritumomab tiuxetan
– 2002 FDA approval: relapsed or refractory follicular or low
grade NHL
– 2009 FDA approval: treatment of previously untreated
follicular NHL in patients who achieve a partial or complete
response to first-line chemotherapy
• I-131 tositumomab
– 2003 FDA approval: treatment of patients with CD20 antigen-
expressing relapsed/refractory follicular or transformed NHL,
including rituximab-refractory NHL
• Not indicated for first-line treatment of CD20+ NHL

31. Relapse Setting

32. Relapse Setting
• Witzig TE, et al. J Clin Oncol 2002;20:2453-63 A phase III study
comparing Zevalin versus rituximab for patients with relapsed
or refractory low-grade follicular B-cell NHL or transformed
NHL was performed.
• A single intravenous (IV) dose of Zevalin 0.4 mCi/kg (n = 73)
• IV rituximab 375 mg/m2 weekly for four doses (n = 70).
• Patients in both arms of the study received two prior
chemotherapy regimens.
• With a median folllowup of 14.2 months,
• The ORR was 80% for Zevalin and 56% for rituximab (p =
0.002).
• The CR rates were 30% and 16% (p = 0.04), respectively, in the
Zevalin and rituximab group.

33. Frontline Therapy

34. RIT Consolidation
FIT(Frontline Indolent Trial)
90Y-ibritumomab
(n = 207)
Rituximab 250 mg/m2 days −0,7
90Y-ibritumomab (0.4 mCi/kg)
[max 32 mCi] day 0
CONSOLIDATION
No further treatment
(n = 202)
CONTROL
R
A
N
D
O
M
IZ
A
TI
O
N
Start of study
6-12 weeks after last
dose of induction
CVP = cyclophosphamide, vincristine, prednisone; CHOP = cyclophosphamide, doxorubicin,
vincristine, prednisone; CR = complete response; CR/u = unconfirmed CR; PR = partial response; NR
= no response; PD = progressive disease.
Morschhauser et al. J Clin Oncol. 2008;26:5156-5164.
INDUCTION
Patients with previously
untreated FL
First-line therapy with CVP,
CHOP, CHOP-like, chlorambucil,
fludarabine combination, or
rituximab combination
NR
PD
CR/CRu
or PR
Not Eligible
Response

35. The 5-year overall PFS was 29% in the control arm compared with 47% in the 90Y-
ibritumomab arm: HR = 1.95 (95% CI: 1.52 – 2.50); P < 0.001
Hagenbeek, et al. Blood (ASH Annual Meeting Abstracts), Nov 2010; 116: 594
25
50
75
100
0 12 24 36 48 60
Proportion
Progression
Free
PFS From Time of Randomization (months)
90Y-ibritumomab
Control
207 174
117
133
83
113
67
98
65
80
46
At risk:
202
90Y-ibritumomab: n = 207
Median PFS: 49 mo
Control: n = 202
Median PFS: 15 mo
0
N F
Control 202 144
90Y-ibritumomab 207 108
RIT consolidation: FIT

36. The 5-year OS was 89% in the control arm compared with 93% in the 90Y-ibritumomab
arm: HR = 1.26 (95% CI: 0.68 – 2.35); P = 0.465
Hagenbeek, et al. Blood (ASH Annual Meeting Abstracts), Nov 2010; 116: 594
90Y-ibritumomab
Control
At risk:
207
202
202
194
195
192
185
182
172
171
146
135
0
25
50
75
100
0 12 24 36 48 60
Proportion
Alive
OS From Time of Randomization (months)
90Y-ibritumomab
Control
207
202
18
22
N F
90Y-ibritumomab: n = 207
Median PFS: > 98 mo
Control: n = 202
Median PFS: > 101 mo
RIT consolidation: FIT

37. FIT Trial: Conclusions…
• 90Y-Ibritumomab consolidation resulted in:
– High conversion rates from PR toCR: 78%
– High overall CR rate: 87%
• Significantly prolonged median PFS
• 90Y-Ibritumomab consolidation was well-tolerated with manageable
hematologic adverse events
• For patients who relapse:
– 90Y-Ibritumomab consolidation does not (appear to) rule out any
second-line treatment approach, including ASCT
• At current follow-up: no significant difference in OS between Rx arms
Morschhauser et al. JClin Oncol. 2008;26:5156-5164

38. RIT consolidation: SWOG 0016
• Untreated
follicular
lymphoma
• PS 0-2
• Stage III-IV
R
A
N
D
O
M
I
Z
E
CHOP21 x 6 +
R x 6 (4 pre, 2 post)
CHOP21 x 6 +
131I tositumomab post
N=279
N=276

39. RIT consolidation: SWOG 0016 (PFS)
0%
20%
40%
60%
80%
100%
0 2 4 6 8 10
Years from Registration
CHOP I-131
CHOP-R
At Risk
265
267
Relapse
or Death
86
106
2-Year
Estimate
80%
76%
2-sided, multivariate p = .11
S0016
CHOP-RIT
CHOP-R
Median FU 4.9y

40. Overall Survival: S0016
0%
20%
40%
60%
80%
100%
0 2 4 6 8 10
CHOP I-131
CHOP-R
At Risk
265
267
Deaths
40
26
2-Year
Estimate
93%
97%
2-sided, multivariate p = .08
Years from Registration
CHOP-R
CHOP-RIT
Median FU 4.9y

41. Solid Tumors

42. Lung Cancer:
131I-chTNT
• Iodine-131-chimeric tumor necrosis treatment (131I-
chTNT)was the first solid tumor TRIT agent in the world
approved for therapy
• Approved by the Chinese State Food and Drug Administration
to treat refractory bronchogenic carcinoma.
• Progressive and recurrent glioblastoma multiforme (Phase 1
trail)

43. HCC :
131I-METUXIMAB( LICARTIN)
• Is an antibody fragment F(ab’)2, that targets HAb18G/CD147,
a HCC TAA.
• The Chinese State Food and Drug Administration has
approved Licartin as adjuvant therapy after OLT for HCC in
2005

44. • CNS tumors:
• Studies done on new or recurrent/refractory cases of
glioblastomas, astrocytomas.
• Not satisfactory.

45. There was no survival benefit for 90Y-HMFG1 IP instillation as consolidation treatment
for EOC, an improved control of IP disease was found, which appeared to be offset by
increased extraperitoneal recurrences.
EOC

46. RIT Safety precautions Y-90
• 90Y-Zevalin is a pure beta
emitter
• To administer y-90
plexiglass(1cm) shielded
syringe is needed
• Radiation exposure for
patient family and for the
treatment team is minimal

47. Shielding for the patient’s family and for the health care team
due to gamma emissions and longer half-life of 131I-Bexxar.
Lead bricks or custom shielding infusion syringe or infusion
pump
Isolated or shielded location for the treatment
RIT Safety precautions I-131

48. RIT Toxicity
• Minor allergic responses to the protein components of the
cold antibody
• Asthenia and nausea
• Post treatment hypothyroidism occurs in approximately 10%
to 20% of patients treated with 131I-tositumomab despite
physiologic thyroid blocking maneuvers
• Neutropenia and thrombocytopenia
• Second Malignancies After RIT( MDS)

49. THANK U