Alkylating agents

Question 1

What are alkylating agents

Answer 1

• add alkyl group to acceptor molecules
  -small molecule drug which covalent bond with bio-molecules (DNA)
• Kill cancer cells (cure/palliation)

Question 2

How does alkylating agents effect DNA

Answer 2

Forms DNA adducts N7/O6 guanine and N3 adenine
- monofunctional /bifunctional
- Cross link (BF) interstrand, intrastrand and DNA-Protein
== Stops transcription and replication

Question 3

what are archetypal alkylating agents

Answer 3

Typical of nitrogen mustard related compounds
- Initial reaction = activation
- Further reaction = inactivation monoadduct

Question 4

What is the mechanism of cell death linked to alkylating agent

Answer 4

Inhibition of replication
Lethal repair (Mismatch repair)
Induction of apoptotic pathways (P53)

Question 5

How do tumour cells become resistance to alkylating agents

Answer 5

• Decreased Transport
• Inactivation (Glutathione conjugates, Role of GST ?)
• Repair of adducts (MMR Deficiency, MGMT)
• Downstream events (P53 mutation +Deficient apoptotic pathway)

Question 6

What are the adverse effects of alkylating agents

Answer 6

• Drug specific organ toxicities = Bladder toxicity associated with cyclophosphamide and ifosfamide
• Common toxicities = Hematopoietic and immuno supression, Nausea & vomiting, Alopecia, Infertility, Teratogenesis and Carcinogenesis

Question 7

Give an example of oxazaphosphorines

Answer 7

• Prodrugs
  Ifosfamide & cyclophosphamide

Question 8

What are the clinical indications for ifosfamide

Answer 8

sarcoma, metastatic BC, lung cancer and paediatric tumours [sarcoma]

Question 9

What are the clinical indications for cyclophosphamide

Answer 9

adjuvant breast, leukaemia/lymphomas and paediatric tumours

Question 10

what are the regimens of oxazaphosphorines

Answer 10

• Intravenous, short or prolonged infusion (100-600 mg/m2)
• Cyclophosphamide also oral (Ifosfamide neurotoxic orally)
• High dose cyclophosphamide (up to 9 g/m2)

Question 11

What are the toxicities surrounding oxazaphosphorines use

Answer 11

• Myelosuppression
• Haemorrhagic cystitis (MESNA)
• Secondary malignancy (AML)
• Cardiotoxicity (high-dose cyclo)

Question 12

Cyclophosphamide are activated by _
to _

Answer 12

CYP2B6,2C9,2C19,3A4,2A5
4-Hydroxycyclophosphamide

Question 13

4-Hydroxycyclophosphamide can be activated further by _

Answer 13

Reversibly to Aldophosphamide
-> phosphoramide mustard + acrolein

Question 14

How are cyclophosphamide and its activated product inactivated

Answer 14

• Cyclophosphamide - 2-Dechloroethylcyclophosphamide + chloroacetaldehyde (via CYP3A4/3A5)
• 4-Hydroxycyclophosphamide into 4-glutathionylcyclophosphamide (via GSTA1/P1) and 4-Ketocyclophosphamide
• phosphoramide mustard into Diglutathionylphosphoramide mustard via (GSTA1)

Question 15

How is oxazaphosphorine metabolism induced

Answer 15

• Anticonvulsants (carbamazepine, phenytoin)
• Steroids (prolonged treatment with dexamethasone = 80% increase in CP clearance)
• Autoinduction

Question 16

What inhibits oxazaphosphorine metabolism

Answer 16

Fluconazole (azole antifungal)

Question 17

The AUC of cyclophosphamide patients who developed _ was lower than patients that didn’t developed _.

Answer 17

cardiotoxicity

Question 18

Tumour response durability was significantly longer is cyclophosphamide patients who _

Answer 18

had lower AUCs (had cardio toxicity)

Question 19

How does pharmacogenetics effect cyclophosphamide

Answer 19

CYP2C19
2 decreased cyclophosphamide elimination
CYP2B6
2,9,4 decrease overall survival in breast cancer

Question 20

What is Mitomycin C

Answer 20

Naturally synthesised antibiotic (usually in non-small cell lung and head/neck cancer)
Main clinical use is superficial bladder cancer
Prototype bio-reductive drug

Question 21

What causes enzymatic reduction of MMC

Answer 21

NQO1 (NAD(P)H Qunone Oxidoreductase 1)
NQO2 (NAD(P)H Qunone Oxidoreductase 1)
Xanthine dehydrogenase
P450 reductase
Cytochome b5 reductase
Xanthine oxidase

Question 22

high expression of MQO1 in tumour cells confer _

Answer 22

tumour specificity novel drugs

Question 23

What is E09 (alkylating agents)

Answer 23

Mitomycin C analogues - substrate for NQO1 which produces interstrand cross links
- Caused tumour regression in high NQO1 expressing xenograft models following IP administration.
- Phase II trials showed compund was ineffective following IV admin
- DLT was renal toxicity

Question 24

What is RH1 (alkylating agent)

Answer 24

NQO1 substrate
Dose-limiting toxicity = hematotoxicity
No efficacy
NO correlation between NQO1 expression and DNA damage

Question 25

Give some examples of monofunctional alkylators and what do they do

Answer 25

Temozolomide
Dacarbazine
- both add methyl groups to DNA = mismatched bases

Question 26

Give an outline of temozolomide use

Answer 26

Clinical use:
- Oral administration – high bioavailability
- 200 mg/m2/day for 5 days, every 4 weeks
- Good penetration of blood brain barrier
- Glioma, astrocytoma
Modest activity in melanoma
- 10-15% response rate
- Comparable to dacarbazine (but more expensive)

Question 27

what is the mechanism of action of temozolomide

Answer 27

• Spontaneous activation reaction
• Methylates O6 or N7 of guanine and N3 of adenine
• Augmented by low expression of MGMT

Question 28

Explain the link between MGMT expression and survival in paediatric brain tumours

Answer 28

O6-methylguanine-DNA methyltransferase over expression had been linked to decreased probability of overall survival

Question 29

How does MGMT methylation effect survival in glioblastomas and why?

Answer 29

Unmethylation decreases cumulative survival why methylation did cause a decrease in survival however later on
Methylation of gene promoter silences expression

Question 30

How are alkyltransferase inhibited

Answer 30

Lomeguatrib inhibits MGMT
pre-clinical studies + phase I clinical trials

Question 31

what occurs in lomeguatrib phase II trials

Answer 31

disappointing
- No difference in response

Question 32

Alkylating agents are superseded by _

Answer 32

BRAF inhibitors
(in 50% melonama)