- Monoclonal antibodies (MAbs) are identical antibodies produced from a single clone that can be produced in large quantities with high purity. Early MAbs had limited effectiveness due to immunogenicity and inefficient effector functions as they were of murine origin. - Later generations of chimeric, humanized, and fully human MAbs have improved effectiveness by reducing immunogenicity issues. MAbs can induce tumor cell killing through mechanisms like antibody-dependent cellular cytotoxicity and complement-dependent cytotoxicity. - Examples of approved unconjugated MAbs for solid tumors include trastuzumab for HER2-positive breast cancer, cetuximab and panitumumab for colorectal and head/neck cancers,

1. Dr. Suhail Qureshi
Monoclonal Antibodies

2. Journey so far…
 1st generation of MAbs : limited effectiveness in
trials
 Concerns : Imunogenicity & inefficient effector
functions
 Murine origin  Development of human
antimouse antibody responses
 Engineered chimeric, humanized and fully human
MAbs redefining cancer therapeutics

3. Monoclonal Antibodies
 Monoclonal antibodies (MAbs) are antibodies that
are identical because they are produced by one type
of immune cell, all clones of a single parent cell.
 Hybridoma technology (Kohler & Milstein ; Nobel
prize winners 1984) made it possible to produce
large quantities of antibodies with high purity and
monospecificity for single binding region (epitope)
on an antigen
 Antibody based conjugates employ targeting
specificity of antibodies to deliver toxic compounds
like chemotherapy drugs specifically to the tumour
site

4. Immunoglobulin structure

5. Immunoglobulin structure
 Fab domains mediate the binding of IgG to their
cognate Antigens
 Each chain in the Fab domain has variable & constant
regions
 Variable region contains the hypervariable or
complementarity determining regions (CDRs)
 Ag contact residues reside in the CDRs
 The heavy & light chain variable regions each contain
three CDRs (CDR 1, 2 &3)
 All 6 CDRs combine to form the antigen-binding
pocket
 CDR3 plays a dominant role

6. Immunoglobulin structure
 Fab = Fragment, antigen binding
 Fc = Fragment, crystalline
 Fc domain : defines the different isotypes of
immunoglobulins
 The Fc fragment specifies other biological activities of
the molecule & determines how an antibody mediates
its effector functions. For example, the Fc fragment
may determine whether the antibody simply prevents
signaling through a receptor, or causes the cell’s
destruction through complement fixation or targeting
immune effector cells.

7. Unfulfilled Promise?
 Early antibodies displayed insufficient activation of
human effector functions (i.e. the antibodies did not kill
the infecting organism or cell)
 Production of human anti-mouse antibodies (HAMA)
 Antigen distribution of malignant cells is highly
heterogeneous, so some cells may express tumor
antigens, while others do not.
 Tumor blood flow is not always optimal
 High interstitial pressure within the tumor can prevent
the passive monoclonal antibody from binding.
 Insufficient tumour specificity of target antigens

8. Types of MAb designed
 Murine source: Rodent MAbs with excellent affinities &
specificities, generated using conventional hybridoma
technology. Clinical efficacy compromised by HAMA
response, which lead to allergic or immune complex
herpersensitivities.
 Chimeric : Chimers combine the human constant
regions with the intact rodent variable regions. Affinity
and specificity unchanged. Also cause human anti-
chimeric antibody response (HACA) (30% murine
resource)
 Humanized : Contain only the CDRs of the rodent
variable region grafted onto human variable region

9. Evolution of Therapeutic Antibodies

10. Nomenclature of MAbs
PRODUCT SOURCE IDENTIFIERS
 -e-
 -a-
 -i-
 -o-
 -xi-
 -zu-
 -u-
 Hamster
 Rat
 Primate
 Mouse
 Chimeric
 Humanized
 Human

11. Mechanisms of anti-tumour effects of
MAbs
 Cell mediated cytotoxicity
(ADCC-Antibody dependent cellular cytotoxicity)
 Complement dependent cytotoxicity
 Immunomodulation
E.g. CTLA-4 Inhibitory receptor of T-cell activation
Abs directed against CTLA-4Increase CD8+ & CD4+
immune
response & induce tumour regression
• Altering signal transduction (Bevacizumab-Anti
VEGF)

12. Immunoconjugates
 Immunotoxins(Eg. BL22)
Highly potent, Catalytic action, well defined biology
& chemistry
 Drug Immunoconjugates (Eg. Gemtuzumab)
Proven efficacy of antineoplastic component, well
defined efficacy & toxicity, Bystander effect,
Internalization not reqd
 Radioimmunoconjugates(Eg. Ibritumomab)
Multiple available isotopes permit customized
approaches, Internalization not reqd, Predictable
toxicity based on dosimetry

13. Anti-tumour effects of MAbs

14. Unconjugated Antibodies
approved for use in Solid
tumours

15. Trastuzumab (Herceptin)
 Herceptin is an anti-cancer antibody that acts on
HER2/neu (c-erbB-2) receptor, a member of the EGFR
family which is overexpressed in 25% breast cancer.
 Only cells overexpressing this receptor are susceptible.
 Such cells, when treated with Herceptin, undergo arrest
in the G1 phase of the cell cycle and experience a
reduction in proliferation.
 This can reduce the rate of relapse of breast cancer by
50% during the first year in the adjuvant setting
 Combination with chemotherapy shows improved
responses than chemotherapy alone
 Myocardial dysfunction seen with increased frequency

16. Cetuximab (Erbitux)
 Targets the EGFR & inhibits ligand induced activation
of this tyrosine kinase receptor
 Approved for Colorectal Ca & Sq. Cell Ca of Head &
Neck
 CRC : Combination of Erbitux with Irinotecan
increased overall response & median duration of
response as compared to Erbitux alone
 Patients with KRAS mutations in codon 12 or 13
should not receive anti-EGFR therapy

17. Panitumumab (Vectibix)
 Binds to EGFR with a higher affinity than Cetuximab
 Interferes with EGFR-Ligand (EGF, TGF α)
interactions
 Setting : Metastatic CRC
 Patients with Metastatic CRC who have KRAS
mutations in codon 12 or 13 should not receive this
therapy

18. Bevacizumab (Avastin)
 Recombinant humanized monoclonal antibody against
VEGF-A
 Approved in 2004 for use in combination therapy with 5-
FU based regimens in the Rx of mCRC
 Other approvals: GBM (Prog.disease), Metastatic RCC
(with IFN-α) and in combination with Pacli/Carbo for 1st
line Rx of unresectable, locally advanced, recurrent or
metastatic non-squamous, NSCLC
 Binds VEGF & prevents its interaction with its EC
receptors (Flt-1)
 Side effects : Grade 3 HT, Grade 1 or 2 proteinuria, a
slight increase in grade 3 or 4 bleeding & impaired
surgical wound healing.

19. Rituximab
 Rituximab is a chimeric monoclonal antibody that
targets the CD20 B-cell antigen.
 This antigen is expressed on 90% of B-cell neoplasms
 The precise biological functions of CD20 are uncertain,
but the antibody is believed to function by flagging the
B-cells for destruction by the body’s own immune
system, including ADCC, CDC, and apoptosis.
 This antibody thus leads to the elimination of all B-cells
from the body (including cancerous ones), allowing
new, healthy B-cells to be produced from lymphoid
stem cells.

20. Gemtuzumab ozogamicin
(Mylotarg)
 This monoclonal antibody is conjugated to the
cytotoxic agent calicheamycin
 It is used to treat relapsed CD33+ acute myeloid
leukemia (AML),
 This monoclonal antibody attacks the CD33 receptor,
which is found in most leukemic blast cells, but not in
normal hematopoietic stem cells
 Represents the only FDA-approved immunodrug
conjugate

21. THANK YOU