Cancer (3) Anticancer Agents 2 Flashcards
Drugs that exploit other aspects of tumour biology
Selective toxicity on the basis of rapid cell division is flawed
>leads to dose limiting side effect profile
Drugs based on some other difference in tumour biology should be
>more selective
>lesser side effects
>desired dose can be adminstered
Drugs that exploit other aspects of tumour biology
Hormones and related agents
Anti-angiogenesis agents
Inhibitors of signalling pathways
Hormones
Used when tumour growth known to depend on hormones
Oestrogens
>androgen-dependent prostatic tumours
Antioestrogens
>e.g. tamoxifen
>oestrogen-dependent breast cancer
Angiogenesis
Growth of new blood vessels from pre-existing vessels
Tightly controlled part of normal physiology
>late embryonic development
>menstrual cycle
>wound healing
Necessary for growth and spread of solid tumours
>”angiogenic switch”
Metastasis
1) Cancer cells invade surrounding tissues and vessels
2) Cancer cells are transported by circulatory system to distant sites
3) Cancer cells reinvade and grow at new loaction
Angiogenesis - a multistep process
Multistep process
Degradation of basement membrane by matrix metalloproteinases
Endothelial cell
>migration
>proliferation
Formation of new matrix
Stabilisation by pericytes
Endothelial cell proliferation
Under control of a variety of growth factors
Vascular endothelial growth factors (VEGF) are major contributors
>produced by tumour as part of angiogenic switch
>drive endothelial cell proliferation, thus permitting angiogenesis to occur
Angiogenesis
Necessary for growth and spread of solid tumours
New blood endothelial cells are required as part of process
>vascular endothelial growth factors (VEGFs) control endothelial cell proliferation
Inhibitors of VEGFs could be novel antitumour agents
VEGFs
Family of related growth factors
Ligands»_space; Receptors
1) Placental growth factor»_space; VEGFR-1
2) VEGF-A»_space; VEGFR-2 (blood vessels)
3) VEGF-B»_space; ?
4) VEGF-C»_space; VEGFR-3
5) VEGF-D»_space; VEGFR-3
VEGFRs are ALL receptor tyrosine kinases
VEGF inhibitors
Bind to ligand
>anti-VEGF monoclonal antibodies
Inhibit receptor
>tyrosine kinase inhibitors
>Competitive receptor antagonists
VEGF inhibitors
Bevacizumab
Monoclonal antibody to VEGF
>prevent binding of VEGF to its receptors
>stop endothelial cell proliferation
Best clinical effects seen in combination with cytotoxic drugs
>e.g. metastatic colon cancer
Bevacizumab -MOA
Mechanism of action
Induction of tumour hypoxia/starvation
Reduction in VEGF-mediated increase in vascular permeability
>reduced interstitial pressure
>improved drug delivery
Bevacizumab - side effects
Side effects
Proteinuria
Hypertension
Risk of thrombosis/bleeding
Impairment of wound healing
VEGF RTK inhibitors
Small molecules that bind to active site of tyrosine kinase domain
Sunitinib
>inhibits VEGFR-1, VEGFR-2, PDGFR
Sorafenib
>inhibits above receptors, + B-RAF
Promising in renal cell carcinoma, where inhibition of multiple tyrosine kinases may be important
Structure of VEGF
Disulphide-linked dimer
Solvent exposed loops
>form two “poles” of receptor binding
>mimetics of these should act as VEGF antagonists
VEGFR-2 Bioassay
Monomeric monocyclic peptides
Compound in preclinical development (vegenics Ltd)
Chronic Myeloid Leukaemia (CML)
Accounts for 15% of adult leukaemias
Patients express a constitutively active kinase (BCR-ABL kinase)
>chromosomal translocation event gives rise to “Philadelphia chromosome”
>results in fusion of two genes BCR and ABL
(ABL normally a tightly regulated tyrosine kinase)
>BCR-ABL essential for leukaemic cell survival
Poor prognosis (median survival 6 years)
Imatinib mesylate to treat CML
Small molecule tyrosine kinase inhibitor
Inhibits BCR-ABL kinase
>binds to kinase domain
>stabilises protein in closed, inactive conformation
Registered for use treatment of CML in US in May 2001
Imatinib mesylate efficacy
Inhibit growth of BCR-ABL Kinase expressing cells in vitro
Suppressed growth of BCR-ABL expressing human tumours in mice
Phase I trial
>normalisation of blood counts in 95% of patients (haematologic response)
>reduction in Philadelphia chromosome-positive cells
(cytogenic response)
Phase III
>found to be better (haematologic and cytogenic) than standard cytotoxic treatment
Clinical use of imatinib
Slows progression of CML
NOT a cure
Side effects not insignificant
>nausea, vomiting, muscle cramps
>liver toxicity, severe fluid retention
Resistance is common
Drug resistance
Common problem
Common problem
Primary
>when drug first given
Secondary
>develops during treatment
Need to increase dose for same killing effect
>therefore increased side effects
>eventually will limit effectiveness of chemotherapy
Drug resistance
Tumour cells primed to develop resistance
Tumour cells primed to develop resistance
High cell number
Rapid Growth rate
High mutation rate
>from result of loss of function to tumour suppressor genes
Drug treatment inherently selects for resistant cells
Drug resistance mechanisms
Decreased intracellular accumulation
Increased expression of drug transport protein P-glycoprotein
>protection against environmental toxins
>causes active efflux of drugs
>can pump out more than one type of drug, so can be responsible for resistance to multiple drug classes
Drug resistance mechanisms - contd
Reduced uptake by cell
>e.g. methotrexate and reduced expression of folate carrier
Reduced activation by cell
>e.g. 5-Fluorouracil and reduced activation by phosphorylation
Increased inactivation by cell
>inactivation of antimetabolites by deaminase