This document discusses antibody-directed enzyme-prodrug therapy (ADEPT) for cancer treatment. ADEPT involves administering an antibody-enzyme fusion protein that localizes an enzyme to the tumor, followed by a prodrug that is non-toxic until converted to a cytotoxic drug by the localized enzyme. The document outlines the mechanism of ADEPT, various enzymes and prodrugs used, advances like improved antibody-enzyme complexes and clearance, phase I clinical trials results, and mathematical models to optimize ADEPT dosing and pharmacokinetics. It concludes that while clinical trials proved ADEPT's potential, further research is still needed to address toxicities in order to develop ADEPT as a successful

1. GE-511
PRESENTED BY
GANDRATHI KULDEEP KUMAR
M.S.(PHARM), I SEMESTER
DEPARTMENT OF PHARMACEUTICS
NATIONAL INSTITUTE OF PHARMACEUTICAL EDUCATION AND RESEARCH
1

2. Introduction
Antibody-Directed Enzyme-Prodrug Therapy
Advances in ADEPT
Conclusion
2

3.  Many therapies are used for the treatment of cancer
 These therapies suffer from many limitations
 Limitation to the on-going treatments is due to
 Drug resistance
 Lack of selectivity
 Pathway redundancy
 Many chemotherapeutic agents-narrow therapeutic
index
 A more efficient approach is needed
3

4.  It was proposed by Dr. Bagshawe et al
 Advantageous over conventional therapies
 Involves 2 steps:
 Administration and localization of antibody-enzyme
complex in tumor cell
 Selective conversion of prodrug by antibody-enzyme
fusion protein
4
Afshar, S et al., Molecular cancer therapeutics 8, 185.

5. TUMOR CELL
Mechanism of ADEPT
5

6. 6
Bagshawe, K.D et al., 1999. Current opinion in immunology 11, 579-583.

7.  Better understanding of the therapy
 Identification of antigen
 Penetration of antibody-enzyme fusion protein
 Elimination of biological molecules might be
non-linear
 Enzyme specific prodrug activation
7
Fang et al., 2008. Drug Metabolism and Disposition 36, 1153-1165.

8. Use of different
enzymes in
ADEPT
Modifications in
antibody-enzyme
complexes
Phase-I clinical
studies
Optimization of
ADEPT- mathematical
models
ADVANCEMENTS IN ADEPT
8

9. 9
Enzymes
employed
in ADEPT
Non-human
enzymes
Intracellular
human
enzymes
Engineered
human
enzymes

10. 10
 Vast number of prodrugs can be designed
 Bacterial enzymes are generally employed
 Many studies were reported on bacterial
carboxypeptidase G2
 Limited by their immunogenecity
 Modified, in the recent times, to reduce immunogenecity
Example: Reduction in immunogenecity of β-lactamase

11. 11
Contd...
 Non-human enzymes are more efficient compared to
human enzymes
Example:
Activation of prodrug CPT-11 to the active drug
SN-38 is very fast using rabbit carboxylesterases
compared to the human enzymes

12. 12
 These are produced by inducing mutations in human
enzymes
 Less immunogenic compared to non human
enzymes
 Substrate specificity of wild type enzymes is altered
Example:
Double mutant (hDM) of human Poly Nucleoside
Phosphorylase (hPNP)
Afshar, S et al., Molecular cancer therapeutics 8, 185.

13. 13
 They are present only within the cell
 No systemic activation of prodrugs will be observed
 Recent strategy employed in ADEPT
 Less immunogenic compared to non human enzymes
and engineered human enzymes
Example: Post Proline cleaving endopeptidase
N-Protected
glycine-
proline
dipeptide
doxorubicin
Doxorubicin
Heinis, C et al., 2004. Biochemistry 43, 6293-6303.

14. S.No Enzyme Prodrug Drug
1 DT diaphorase 5-(Aziridin-1-yl)-2,4-
nitrobenzamide (CB 1954)
5-(Aziridin-1-yl)-4-
hydroxyl amino-2-
nitrobenzamide.
2 Plasmin Peptidyl-p-phenylene diamine-
mustard
Phenylenediamine-
mustard
3 Carboxypeptidase G2 Benzoic acid mustard
glutamates
Benzoic acid
mustards (various)
4 Thymidine kinase (viral) Ganciclovir* Ganciclovir
triphosphate
5 Cytosine deaminase 5-Fluorocytosine* 5-Fluorouracil
6 β –Glucosidase Amygdalin Cyanide
7 β –Lactamase Nitrogen-mustard-
cephalosporin
Nitrogen mustards
(various)
8 Alkaline phosphatase Phenol mustard phosphatase*
Doxorubicin phosphatase*
Phenol mustard
Doxorubicin
9 Cytochrome P-450 Cyclophosphamide
Ifosfamide
Phosphoamide
mustard
(+ acrolein)
14
Enzymes and prodrugs proposed for cancer therapy

15. 15
 Use of humanized antibodies and enzymes
Example: humanized disulfide-stabilized anti
p185HER2 Fv-β-lactamase fusion protein
 Accelerated clearance of Ab-E fusion protein
 Usage of clearance antibody
 Hypermannosylation of recombinant antibody-
enzyme fusion protein
Rodrigues et al., 1995. Cancer Res 55, 63-70.

16. 16
 Produced via post translational modifications in
Pichia pastoris
 Elimination is well understood
 Complex eliminates via mannose receptors
 Macrophages (spleen) and endothelial cells (liver) are
mainly responsible for the elimination of complex

17. 17
 With A5CP conjugate and CMDA prodrug
 It required additional clearance antibody
 100% patients developed HAMA and 97% HACA
 With recombinant MFECP1 and Bis-iodo phenol
prodrug
 Only 31 patients were taken
 36% patients developed HACA and none of them developed HAMA

18. 18
Treatment with MFECP1
(units/m2) and BIP prodrug
(mg/m2 X3)
No. of patients Toxicity
5000 MFECP1 + 12.42 BIP
prodrug
Plasma CPG2
0.0111units/mL (median)
3 G3 thrombocytopenia (1), G3
neutropenia (1), G3 leukopenia (1)
5000 MFECP1 + 1075 BIP
prodrug
Plasma CPG2
<0.002units/mL
1 G4 ALT/AST, G3 GGT, G4 Cr/urea,
G3 anemia, G3 leukopenia, G3
thrombocytopenia
3000 MFECP1 + 537.6 BIP
prodrug
Plasma CPG2
<0.002units/mL
2 G4 ALT/AST (1), G3 anemia (1), G3
thrombocytopenia (1), G3
leukopenia (1), G3 fatigue
1500 MFECP1 +200 BIP
prodrug
1 G3 thrombocytopenia (1)
Abbrevations: G3 :Grade 3, G4: Grade 4, ALT: Alanine aminotransferase, AST: Aspartate aminotransferase
GGT: ϒ-glutamyl transferase
Dose escalation and toxicity of BIP prodrug
Mayer, A. et al., 2006. Clinical cancer research 12, 6509-6516.

19. 19
 To predict therapeutic outcome before preclinical
and clinical studies
 Two models were applied:
 Compartmental model: Failed to describe pharmacokinetic
properties of biological molecules
 Physiology based Pharmacokinetic (PBPK) model: Applied to
analyse each compartment or organ.
Galluppi et al., 2001. Clinical pharmacology and therapeutics 69, 387.

20. 20
For an effective ADEPT
 Optimal clearance of Ab-E is 1.5X10-3 ml/min
 Optimal Emax of Ab-E for prodrug conversion is 600 min-1
 Optimal Permeability of prodrug is 1.4 X 10-4 cm/sec
 Optimal dosing interval of Ab-E and prodrug is 5 days
Galluppi et al., 2001. Clinical pharmacology and therapeutics 69, 387.

21. 21
 ADEPT was proved to be a potential therapy for the
treatment of cancer. Clinical trials of ADEPT proved
this fact but the therapy is limited by toxic effects,
many of which were being addressed in the recent
years
 Further research has to be encouraged in the future
as ADEPT has the potential of being the successful
therapy in the treatment of cancer in the future

22. 22