Purine Antimetabolites

Nam Deuk Kim, Ph.D.

Purine Antimetabolites

Contents



Guanine analogs



6-Mercaptopurine (6-MP), 6-Thioguanine (6-TG), Azathioprine



Adenosine analogs



Fludarabine, Pentostatin, Cladribine



Allopurinol



The amount of chemotherapeutic agent used

(항암제 분류)

Guanine analogs

3

1. Guanine analogs



6-MP

 Extensive hepatic, cellular metabolism after dosing

1) Activated intracellularly by hypoxanthine-guanine phosphoribosyl transferase (HGPRT) to form 6-thioinosine monophosphate (TIMP ; inhibit purine synthesis)  sequential metabolism to thioguanine monophosphate(TGMP), 6-TGTP  incorporated into DNA, RNA

 trigger programmed cell death by mismatch repair pathway

2) methylation ; antiproliferative property through inhibition of purine synthesis by methylmercaptopurine nucleotides



6-TG

 Converted to 6-thioguanylic acid (TGMP) by HGPRT   incorporated into DNA, RNA

 6-TG into thioguanine nucleotide ; fewer metabolic steps & higher cellular conc. than 6-MP

4

1) Guanine analogs : Mechanism of action (MOA)

5



Azathioprine

 Cleaved by nonenzymatic mechanisms to 6-MP &

imidazole derivatives

1) incorporation of false nucleotides into DNA, inhibition of purine synthesis

2) Modify immune response

 Inhibit T-lymphocyte activity than B-lymphocytes

 6-TGTP ; bind & inhibit Rac1 (small GTP-binding protein, major role in T cell development, differentiation, proliferation) 

mitogen-activated kinase (MEK), NF-κB I, bcl-X_L suppression  apoptosis

1) Guanine analogs : Mechanism of action

1) Guanine analogs : Mechanism of action

7



6-MP (1)

 Formulation ; 50 mg tab (Purinethol ^{Ⓡ 삼일제약})

 Use ; ALL (little role in solid tumor, myeloid leukemia), inflammatory bowel disease

 Dosage ; 75 mg/m² or Acute lymphoid leukemia (FDA labeled indication), as induction and maintenance therapy: induction, 2.5 mg/kg/day (100-200 mg) ORALLY ; if no clinical improvement after 4 weeks, may increase dose to 5 mg/kg daily

 Absorption ; bioavailability (BA) 5-37%

 Metabolism ; liver

 1) Oxidized to 6-thiouric acid (inactive) by xanthine oxidase (high in intestinal mucosa, liver  large 1st pass effect, low BA)

 2) S-methylation to 6-methyl mercaptopurine by thiopurine methyl transferase (TPMT)

2) Guanine analogs : Clinical pharmacology



6-MP(2)

 Drug interaction

 Allopurinol ; xanthine oxidase inhibitor, increase 6-MP BA by 500%

 MTX ; weak inhibitor of xanthine oxidase , small increase of BA

 Precaution ; Inherited deficiency of TPMT

 Marked myelosuppression with low activity

 Frequency ; one in 200-300 subjects has absent activity, 10% intermediate , the rest have high activity

 Race ; blacks, less activity than whites

 Eight TPMT polymorphism associated with reduced activity ; TPMT3 , the most common mutation genotype, more than 80% of heterozygotes

 Dosage adjustments in hepatic, renal function impairment

2) Guanine analogs : Clinical pharmacology

9



6-TG

 40 mg tab (Lanvis ^Ⓡ 삼일제약) / BA 14-46%

 Median half life ; 90 min

 Metabolism ; different from 6-MP

 Converted to 6-thioinosine (inactive) by guanase ※ not a substrate for xanthine oxidase

 Methylation by TPMT ; less active 2-amino-6-metylthiopurine than 6-TG, more extensive than 6-MP



Azathioprine

 Prodrug, metabolized to 6-MP by oxidation or methylation in the liver and erythrocytes

 Use ; immunosupressant in the renal transplant rejection, adjunct, autoimmune disease (rheumatoid arthritis, lupus, ulcerative colitis)

 50 mg tab (Imuran ^Ⓡ, Azafrin ^Ⓡ), IV (Imuran ^Ⓡ 100mg/20ml/vial)

2) Guanine analogs : Clinical pharmacology



6-MP

 Myelosuppression

 Dose-limiting, 1-4 weeks following the onset of therapy, reversible.

 Platelet, granulocyte, erythrocyte

 Weekly monitoring of blood counts during the 1^st 2 months

 Related to TPMT phenotype ; excessive toxicity with TPMT deficiency or heterozygosity (65%)

 Gastrointestinal mucositis, stomatitis ; adults > children

 Nausea, vomiting, anorexia ; 25% / Pancreatitis

 Hepatotoxicity ; mild, reversible. Not associated TPMT

polymorphism, correlated with dose and methylated metabolite



6-TG

 Primary ; Myelosuppression

 GI toxicity ; less frequently than 6-MP Jaundice, hepatic veno-occlusive disease

3) Guanine analogs : Toxicity

11



Azathioprine

 similar to 6-MP

 Hypersensitivity ; fever, chills, severe nausea, diarrhea, hypertension, hepatic dysfunction

 Chronic immunosuppressive therapy ; 2ndary infection, malignant tumor risk

3) Guanine analogs : Toxicity

A. 6-Mercaptopurine

B. 6-Thioguanine

13

C. Azathioprine

2. Adenosine analogs

15

16



Monophosphate analog of adenosine arabinoside ; F-ara-AMP



MOA

 After IV, rapidly, completely dephosphorylated in plasma (5’ nucleotidase in erythrocyte, endothelial cell) to F-ara-A  enters cells via carrier-

mediated transport, phosphorylated to active form, F-ara-ATP

(fludarabine triphosphate) ; inhibit DNA replication by inhibiting DNA plymerase, ribonucleotide reductase, DNA primase, DNA ligase Ι

 F-ara-AMP ; incorporation into DNA as a false nucleotide  DNA chain terminator  apoptosis

 “S- phase agent” but, also active in non-dividing cells

 Inhibit RNA polymerase by incorporation into RNA

 Depletion of nicotinamide adenine dinucleotide (NAD)  cellular energy store ↓

 Interferance with normal DNA repair processes

1) Fludarabine :

1) Fludarabine

17

 Dosage form ; Fludara ^Ⓡ 10 mg tab, 50 mg vial (바이엘, 희귀약품)

 Use ; CLL 25-30 mg/m²

IV (40

orally )

hairy cell leukemia, non-Hodgkin’s lymphoma

 Absorption ; BA 70%(not affected by meal), Tmax 1.5 hrs orally

 Elimination ; terminal half life 7-33 hr

 F-ara-A is excreted primarily in the urine (50-60%) ; in renal impairment, dose reduction needed

 F-ara-ATP

 major intracellular metabolite, the only metabolite with known cytotoxicity, Tpk 4hr

 Long intracelluar half life ; 15 hr

1) Fludarabine : clinical pharmacology

19

 Myelosuppression

 Dose-limiting, reversible leukopenia, thrombocytopenia, lymphopenia

 Immunosuppression ; inhibition of signal transduction of lymphocyte activation

 Infection ; Dose-limiting, opportunistic infection ( CD4, CD8 T- lymphocyte↓)

 Fever of unknown origin(2/3), autoimmune hemolytic anemia, acute tumor lysis

 Neurotoxicity ; 16%

 Irreversible ; optic neuritis, encephalopathy, general seizure, coma

 Reversible ; lower doses, increased frequency

 Pulmonary ; fever, cough, hypoxia, diffuse interstitial pneumonitis (corticosteroid therapy)

1) Fludarabine : Toxicity

20

 MOA

 Potent adenosine deaminase (ADA) inhibitor ; tight ADA binding, Accumulation of deoxyadenosine, dATP  negative feedback on

ribonucleotide reductase  imbalance in deoxynucleotide pools  slows DNA synthesis, alter DNA replication, repair

 S-adenosylhomocysteine hydrolase inhibition ; block normal cellular methylation reactions

 Pharmacology

 Not orally bioavailable, stable at neutral pH (unstable at pH ≤5)

 Large Vd with little protein binding, cross BBB

 Terminal elimination T_1/2 6 hr

 Metabolism ; only a small amount

 Excreted in urine unchanged

 Dose reduction for patients with renal impairment

2) Pentostatin : 2’-deoxycoformycin (dCF)

21



Toxicity

 Neutropenia, increase risk of opportunistic infections

 Nausea & vomiting(12-72 hr after adm.), mild to moderate lethargy, rash, reactivation of herpes zoster

 Immunosuppression, conjunctivitis, hepatic enzyme elevation, renal impairment, CNS disturbances with higher doses

 Renal toxicity(10 to 20 days after), cardiac complications in older patients



Use ; no apparent advantage over standard therapy except hairy- cell leukemia (responses in over 90% of patients)

2) Pentostatin

2) Pentostatin

23



MOA

 Resistant to ADA

 Prodrug ; intracellular phosphorylation for activation ; cladribine 5’- triphosphate (2CdATP) accumulates in cells rich in deoxycytidine kinase

 Incorporated into DNA, DNA strand breaks, DNA synthesis inhibition

 Inhibition of DNA polymerase, ribonucleotide reductase →DNA synthesis &

repair impairment

 Apoptosis triggering in non-dividing cells ; interact with cytochrome C and protease activating factor-1(PAF-1) to initiate caspase cascade leading to DNA degradation

 Cladribine resistance ; by deficiency in deoxycytidine kinase, p53 mutation, multidrug resistance protein 4

3) Cladribine : 2-chlorodeoxyadenosine (2-CdA)

3) Cladribine

25

 Dosage form ; Leustatin ^Ⓡ 10mg/10ml /vial 바이엘, 희귀의약품

 Use ; similar to fludarabine

 Hairy cell leukemia, CLL, low grade NHL, AML

 Higher(several hundred fold) intracellular conc. than plasma conc.

 long intracellular T_1/2(9-30hr) ; intermittent administration

 Protein binding 20%

 BA ; 100% with sc. 40-50% with oral adm.

 Renal clearance 50% (20-30% unchanged drug)

 Drug interaction

 with cytarabine – increase intracellular accumulation of ara-CTP (active metabolite of cytarabine) by 40%

 increased frequency of drug rash with allopurinol

3) Cladribine : clinical pharmacology



Myelosuppression ; dose-limiting



Immunosuppression and opportunistic infection



Fever ; 2/3 of patients , mostly during neutropenia



Autoimmune hemolytic anemia, eosinophilia, nausea, fatigue

3) Cladribine : ^toxicity

3) Cladribine

27

 No antineoplastic activity, but frequently used in pts with leukemia, lymphoma to prevent hyperuricemia, uric acid nephropathy

 Available in 100 mg tab



MOA (Mechanism of action)

 Allopurinol (hypoxantine analog) & oxipurinol (major metabolic product of allopurinol, xanthine analog) ; inhibit xanthine oxidase, block conversion to uric acid  decrease total purine (xanthine, hypoxanthine, uric acid) excretion by 30-40%

 Allopurinol ; decreasing the rate of purine synthesis

3. Allopurinol

3. Allopurinol

29

Fig. 9.7 Feedback inhibition of de novo purine biosynthesis.

3. Allopurinol

3. Allopurinol

31



Toxicity

 Skin rash ; 2%

 Life-threatening hypersensitivity syndrome

 fever, eosinophilia, skin rash including toxic epidermal neurolysis (TEN), renal dysfunction, hepatic failure

 2-4 weeks after initiation

 Underlying renal failure when therapy in started  dose adjustment



Clinical use

 Gout

 Prevent marked increases in UA excretion after chemotherapy ; hydration & allopurinol before chemotherapy recommended

 Renal failure due to precipitation of urate crystals from sudden rise in UA after chemotherapy

 Interaction ; azathioprine, 6-MP to 6-thiouric acid(inactive) by

3. Allopurinol

4. 항암화학요법제 분류_심사평가원

33

 2군 항암제는 보건복지가족부장관이 정하여 고시하는 항암화 학요법제(분류번호 245, 247, 249, 313, 339, 392, 399, 421, 429, 617, 639)중 각 약제의 개발시기ㆍ재심사대상ㆍ희귀의약품 등을 기준으로 암질환심의위원회에서 2군으로 분류한 약제임

 위 분류에 해당하지 아니하는 경우는 1군으로 분류됨.

 항암화학요법의 투여대상, 투여단계, 투여요법은 1군 항암제

의 경우에는 진료의사의 의학적 판단에 따라 사용하며, 2군 항

암제

상, 투여단계, 투여요법을 적용함

주요항암제 심평원 EDI 청구현황

2010.9.16 *단위; 백만원

*EDI, Electronic Data Interchange (전자문서교환)

35

product Generic Class (use) product generic Class (use)

1 글리벡 Imatinib Protein tyrosine kinase

inhibitor(CML) 13 페마라정 Letrozole ^Aromatase

inhibitor 2 탁소텔 Docetaxel Anti-microtubule 14 벨케이드주 Bortezomib Proteosome

inhibitor 3 엘록사틴 Oxliplatin Platinum – alkylating

agent 15 아리미덱스 Anastrozole ^Aromatase

inhibitor 4 알림타주 Pemetrexed Antifolate (NSCLC) 16 수텐캡슐 Sunitinib Tyrosine kinase

inhibitor 5 캠푸토주 Irinotecan Topoisomerase inhibitor 17 ^티에스원

캡슐 Tegafur,gemeracil, Oteracil

Pyrimidine analog

6 젬자주 Gemcitabine antimetabolite

(deoxycytidine analog) 18 ^아그릴린

캡슐 Anagrelide Platelet reduction 7 허셉틴주 Trastuzumab Monoclonal antibody 19 다코젠주 Decitabine Pyrimidine analog

(골수이형성) 8 타쎄바정 Erlotinib Tyrosine kinase inhibitor

(NSCLC) 20 테모달캡슐 Temozolomide Alkylating agent

(astrocytoma) 9 맙테라주 Rituximab Monoclonal antibody 21 하이캄틴주 Topotecan Topoisomerse1

inhibitor 10 젤로다정 Capecitabine Antimetabolite ; breast,

colorectal Ca 22 캄토벨주 Belotecan Other (SCLC)

11 이레사정 Gefitinib Tyrosine kinase inhibitor

(NSCLC) 23 넥사바정 Sorafenib Raf kinase

inhibitor 12 탁솔주 Paclitaxel Anti-microtubule

1군 항암제

2군 항암제

product generic Class (use) product generic Class (use)

1 토뮤덱스 Raltitrexed Antimetabolite(folat e analog) (colorectal Ca)

12 ^선플라주 Heptaplatin Platinum analog

2 부설펙스주 Busulfan Alkylating agent 13 ^{맵캠파스주} alemtuzumab Monoclonal antibody (CLL) 3 탈리도마이

드 thalidomide immunosuppressant 14 ^{스프라이셀정 Dasatinib} Tyrosine kinase

inhibitor

4 ^비다자주 Azacitidine Pyrimidine analog

(골수이형성) 15 ^{케릭스주 Loposomal}

doxorubicin

anthracycline

5 ^{류스타틴주} Cladribine Purine analog 16 ^{자베도스캡슐} Idarubicin anthracycline

6 ^{부몬주 Tenipocid} podophyllotoxin 17 ^{제바린키트} (ibritumomab

tiuxetan

Other (NHL)

7 ^선라빈주 Enocitabine Pyrimidine analog 18 ^{아바스틴주} bevacizumab Monoclonal antibody

8 ^{프로류킨주} Aldesleukin-2 T-cell growth factor 19 ^{얼비툭스주 cetuximab} Monoclonal antibody

9 ^플루다라 Fludarabine Purine analog 20 ^{나벨빈캡슐} Vinorelbine Vinca alkaloid

10 ^{베스타틴 Ubenimex other} 21 ^{마일로타그주} gemtuzumab Monoclonal

2군 항암제

37

Product class product class product class

Ifosfamide (Holoxan)

Alkylating agent

carboplatin Platinum – alkylating agent

dacarbazine Alkylating agent

Melphalan (Alkeran)

Alkylating agent

cisplatin Platinum – alkylating agent

Actinomycin D Antitumor antibiotic 6-MP

(Purinethol)

Purine analog

6-TG (Lanvis)

Purine analog Daunorubicin Antitumor antibiotic Methotrexat

e (MTX)

antifolate Cyclo

phosphamide

Alkylating agent Doxorubicin (Adriamycin)

Antitumor antibiotic Mitomycin Antitumor

antibiotic

cytarabine DNA polymerase inhibitor

Epirubicin(Pha rmorubicin)

Antitumor antibiotic Chlorambuc

il(Leukeran)

Alkylating agent

Etoposide (Lastet)

Epipodophyllo toxin

Fluorouracil (5-FU)

Pyrimidine analog Thiotepa Alkylating

(Bladder)

Hydroxyurea (Hydrea)

Pyrimidine antagonist

idarubicin Antitumor antibiotic vincristine Vinca

alkaloid

flutamide antiandrogen Goserelin GnRH analog

tamoxifen SERM Toremifen (Fareston)

SERM azathioprine Purine analog

Chemotherapy regimen (example)



Metastatic colorectal cancer

 FOLFOX 3

 Oxaliplatin 85 mg/m² IV day 1

 Folinic acid 200 mg/m² IV day 1

 5-FU 400 mg/m² then 600 mg/m² IV days 1-2 q2 weeks



Breast cancer

 CAF

 Cyclophophamide 500 mg/m² IV day 1

 Doxorubicin 50 mg/m² IV day 1

 Fluorouracil 500 mg/m² IV day 1, 8 q3 weeks

 CMF

 Cyclophophamide 100 mg/m² PO day 1-14

 Methotrexate 40 mg/m² IV day 1, 8