BIOPRECURSOR PRODRUGS

The presentation provides the brief description about bioiprecursor prodrugs and site specific drug delivery approach.

1. PRODRUGS With Special Reference to ( Bioprecursors and Site Specific Drug Delivery) Presented by:- Sobhi Gaba

2. PRODRUGS The reversibly modified compound usually inactive in itself and releases the active compound as a metabolite is called a PRODRUG OR Prodrug is defined as biologically inactive derivative of a parent drug molecules that usually requires a chemical or enzymatic transformation within the body to release the active drug and possess improved delivery properties over parent molecule

3. OR A prodrug is a medication or compound that after administration is metabolised (in body) into pharmacologically active drug. PRODRUG ACTIVE DRUG MOEITY For Example:- Sulfasalazine Amino Salicylic Acid+ Sulfapyridine CHEMICAL OR ENZYMATIC ATTACK

4. CLASSIFICATION OF PRODRUGS ON THE BASIS OF STRUCTURAL ASSOCIATION

5. ON THE BASIS OF SITES OF CONVERSION INTO ACTIVE DRUG FORM

6. BIOPRECURSORS A Bioprecursor prodrug is a prodrug that does not imply the linkage to a carrier group , but results from a molecular modification of the active principle itself. This modification generates new compound, able to be transformed metabolically or chemically , the resulting compound being the active principle. These types of prodrugs not only need hydrolysis to get converted to its active compound bound but also requires oxidation or reduction reactions(PHASE 1 Metabolism Reaction)

7. ORIGIN OF BIOPRECURSORS The birth of bioprecursor prodrugs occurred when it was demonstrated that the antibacterial agent “ PRONTOSIL ” was active only in vivo because it was metabolised to the actual drug ” SULFANILAMIDE ” PRONTOSIL(Azo Prodrug) SULFANILAMIDE(Amine sulfa drug)

8. ACTIVATION OF BIOPRECURSOR PRODRUGS The bioprecursor prodrug show their action after undergoing metabolism reaction in the body (in vivo). The activation of these prodrugs can be by following pathways:- PROTON ACTIVATION ELIMINATION ACTIVATION OXIDATIVE ACTIVATION REDUCTIVE ACTIVATION PHOSPHORYLATION ACTIVATION DECARBOXYLATION ACTIVATION

9. I. PROTON ACTIVATION Some bioprecursors activates in the body through proton activation mechanism . For example: OMEPERAZOLE (Proton Pump Inhibitor) It is used in the treatment of gastric ulceration.

10. PROTON ACTIVATION OF OMEPERAZOLE CYSTEINE RESIDUE BLOCKS PROTON PUMP

11. MECHANISM OF ACTION OF OMEPERAZOLE

12. PROTON PUMP IS BLOCKED AND THUS GASTRIC ACID SECRETION IS INHIBITED

13. II. ELIMINATION ACTIVATION LEFLUNAMIDE METABOLITE (Used in treatment of rheumatoid arthritis) Leflunamide is not itself active It undergoes elimination and gets converted to its metabolite and show antiarthritic activity . The metabolite inhibit the synthesis of pyrimidine.

14. MECHANISM OF ACTION OF LEFLUNAMIDE LEFLUNAMIDE

15. (INACTIVE) (ACTIVE) SHOWS ANTI ARTHRITIC ACTIVITY MECHANISM OF ELIMINATION REACTION OF LEFLUNAMIDE

16. III. OXIDATIVE ACTIVATION The most common pathway for the action of several bioprecusors is oxidation . The various types of oxidation occurring in the compounds are as follows:- N and O Dealkylation Oxidative Deamination N-Oxidation S-Oxidation

17. 1. N AND O DEALKYLATION N DEALKYLATION:- Open ring analogues of benzodiazepines such as anxiolytic drug “ALPRAZOLAM” and sedative “TRIAZOLAM”, undergoes metabolic N- dealkylation and spontaneous cyclization.

18. MECHANISM OF ACTION OF ALPRAZOLAM

19. O-DEALKYLATION:- The example of bioprecursor prodrug that is activated by O- dealkylation is an analgesic drug i.e. “PHENACITIN” PHENACITIN ACETAMINOPHEN (Has more affinity to bind with COX2) O DEALKYLATION

20. 2. OXIDATIVE DEAMINATION Various antitumour agents gets activated by this mechanism These anti tumour compounds donot act only by hydrolysis but they need activation by liver enzymes. For example:- CYCLOPHOPHAMIDE (Nitrogen Mustard). The liver enzymes CYP450 cause deamination of cyclophosphamide and then phosphoramidase enzyme in tumour cells helps the intermediate formed to bind with N7 guanine molecule of DNA of tumour cells and thus causing death of tumour cells.

21. MECHANISM OF OXIDATIVE DEAMINATION IN CYCLOPHOPHAMIDE

22. 3. N OXIDATION For example:- PRALIDOXIME (antidote for poisoning by organophosphorous compounds) BIOPRECURSOR PRODRUG ACTIVE FORM

23. MECHANISM OF ACTION OF PRALIDOXIME ACETYLCHOLINESTERASE CATALYZED HYDROLYSIS OF ACETYL CHOLINE

24. PHOSPHORYLATION OF ACETYLCHOLINESTERASE BY DIISOPROPYL PHOSPHOROFLUORIDATE(ORGANOPHOSPHOROUS COMPOUND ) Acetylcholinesterase gets blocked by organophosphorous compound thus increasing the concentration of acetyl choline and high cholinergic activity is observed

25. REACTIVATION OF PHOPHORYLATED ACETYL CHOLINESTERASE BY PRALIDOXIME CHLORIDE PRALIDOXIME is not able to cross BBB but PLARIDOXIME CHLORIDE can. Pralidoxime chloride after crossing the BBB gets converted to Pralidoxime through N Oxidation which further acts with phosphorous to treat organophophorous poisoning

26. 4. S OXIDATION BREFELDIN A is an antitumour and antiviral antibiotic, has poor bioavailability and is rapidly cleared. A series of sulphide prodrugs were prepared having greater aqueous solubilities than BREFELDIN A. The prodrugs were converted back to BREFELDIN A by S Oxidation to the sulfoxide.

27. IV. REDUCTIVE ACTIVATION Bioprecursors can be activated through reduction too. The functional groups which undergoes reduction for activation are as follows:- AZO REDUCTION SULFOXIDE REDUCTION DISULFIDE REDUCTION

28. 1. AZO REDUCTION The most common example for azo reduction is PRONTOSIL from where the discovery of bioprecursor prodrug occurred. Prontosil is not active but its metabolite “ SULFANILAMIDE ” has antibacterial activity SULFANILAMIDE (ANTIBACTERIAL ACTION)

29. Another example of azo reduction is the reduction of SULFASALAZINE to active drug SULGAPYRIDINE and 7-amino salicylic acid. SULFASALAZINE is itself inactive as it has azo group and not free amino group which binds with the enzyme DIHYDROFOLATE REDUCTASE and inhibits FOLIC ACID synthesis in bacterial cell but on the other hand the metabolite of sulfasalazine has free amino group.

30. 2. SULFOXIDE REDUCTION The most common example of sulfoxide reduction is SULINDAC SULINDAC is a Non Steroidal Antinflammatory Drug (NSAID) and is used in treatment of arthritis. The sulfoxide group present in SULINDAC doesnot allow the drug to bind with COX2. The drug on reduction gets converted to its corresponding sulphide which is active.

31. 3. DISULFIDE REDUCTION To diminish the toxicity of the antimalarial drug PRIMAQUINE and target it for cells that contain the malarial parasite, a macromolecular drug delivery system was designed. The LACTOSE LINKED ALBUMIN was used for improved intake in the liver via ASILAOGLYCOPROTEIN RECEPTOR SYSTEM

32. V. PHOPHORYLATION ACTIVATION The drug undergoing phosphorylation activation is ACYCLOVIR. It is highly effective against genital HERPES SIMPLEX VIRUS and VARICELLA ZOSTER VIRUS infection.

33. VI.DECARBOXYLATION ACTIVATION The removal of carboxylic group group from the drug lead to an active metabolite. For example:- LEVODOPA AND DOPAMINE Levodopa is a bioprecursor produg for dopamine In Parkinson disease, the concentration of dopamine is decreased, which can be treated by increasing level of DOPAMINE DOPAMINE is impermeable to BBB and will have no effect. So LEVODOPA ( bioprecursor prodrug) is used which has high permeability into brain through BBB. After entering into brain it gets converted to DOPAMINE and thus PARKINSON DISEASE can be treated.

34. MECHANISM OF ACTION OF LEVODOPA

35. SITE SPECIFIC DRUG DELIVERY MECHANISMS Several strategies, under the rubric of ENZYME PRODRUG THERAPIES, have been developed to achieve selective activation of prodrugs at a desired site, typically in TUMUOR CELLS . COMMON PROCEDURE FOR THIS APPROACH:- STEP 1- A prodrug activating enzyme is incorporated into the target tumour cells STEP 2- A non toxic prodrug, which is a substrate of the exogenous enzyme that was incorporated into the tumour cells, is administerd systemically. STEP 3- The prodrug is actively converted into the the active anticancer drug in high local concentration inside the tumour cells

36. DIFFERENT APPROACHES The different approaches used for site specific drug delivery into tumour cells are as follows:- ADEPT (ANTIBODY DIRECTED ENZYME PRODRUG THERAPY) GDEPT (GENE DIRECTED ENZYME PRODRUG THERAPY) VDEPT (VIRUS DIRECTED ENZYME PRODRUG THERAPY)

37. CERTAIN CRITERIAS FOR THESE APPROACHES TO BE EFFECTIVE The prodrug-activating enzyme should be either of non human origin or a human protein that is absent or expressed only at lower concentrations in normal tissues. The prodrug-activating enzyme must achieve adequate expression in the targeted tumour cells and have high catalytic activity The prodrug should be a good substrate for the enzyme incorporated in the tumours but nit be activated by endogeneous enzymes outside the tumours

38. IV. The prodrug must be able to cross the tumour cell membrane for intracellular activation. V. The cytotoxicity difference between the prodrug and its corresponding active drug should be high. VI. The activated drug should be highly diffusible or be actively taken up by adjacent non expressing cancer cells (BYSTANDER KILLER EFFECT i.e. the ability of the drug to kill neighbouring non expressing cells). VII. The half life of the active drug should be long enough to induce a BYSTANDER KILLING EFFECT but short enough to avoid the drug leaking out of tumour cells and causing damage elsewhere .

39. ADEPT (ANTIBODY DIRECTED ENZYME PRODRUG THERAPY )

40. MECHANISM OF ACTION OF ADEPT

41. EXAMPLE OF ADEPT NITROGEN MUSTARD ACTIVATION BY CARBOXYPEPTIDASE G2 (BACTERIAL ENZYME) FOR USE CONJUGATED WITH HUMANIZED MONOCLONAL ANTIBODIES

42. ADVANTAGES AND DISADVANTAGES OF ADEPT ADVANTAGE INCREASED SELECTIVITY OF FOR THE RELEASE OF HIGH CONCENTRATION OF DRUG AT TARGETED CELLS. (Advantage is only evident if enough time is allowed for the clearance of antibdody enzyme conjugate that is not bound to tumor cells. DISADVANTAGE:- REJECTION OF ANTIBODY ENZYME CONJUGATE THE POTENTIAL FOR LEAKBACK OF THE ACTIVE DRUG REQUIREMENT OF I.V ADMINISTRATION

43. GDEPT (GENE DIRECTED ENZYME PRODRUG THERAPY) Also called SUICIDE GENE THERAPY

44. MECHANISM OF ACTION OF VDEPT

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