Microtubule Stabilizers

Report
New insights into the mechanisms of
action of microtubule targeting
agents that are effective against
metastatic breast cancer
Susan L. Mooberry, Ph.D.
Professor of Pharmacology
Cancer Therapy & Research Center
University of Texas Health Science Center at San Antonio
San Antonio, TX, 78229
Microtubules are Essential for
Normal Cell Functions
• Microtubules are involved in:
Separation of the chromosomes during cell
division
Cell motility
Cell shape and cellular junctions
Intracellular trafficking and secretion
Signal transduction
.
Jordan and Wilson, Nat Rev Cancer 2004, 4:253-265;
Dumontet and Jordan, Nat Rev Drug Discov. 2009, 9:790-802; Komlodi-Pasztor et al., 2011, Nat Rev Clin Oncol; 8:244-250.
Polymerization and Structure of
Microtubules
αβ tubulin
heterodimers
microtubule
nucleus
Polymerization and Structure of
Microtubules
αβ tubulin
heterodimers
microtubule
nucleus
growing
microtubule
Polymerization and Structure of
Microtubules
αβ tubulin
heterodimers
microtubule
nucleus
growing
microtubule
13 protofilaments
Adapted from Risinger et al., Cancer Treat Rev. 2009, 35: 255-261.
Microtubules are Intrinsically Dynamic
Dynamics are essential
for microtubule functions
Dynamic Instability- switching between
growth and shortening
Elongation-growth at + end
Catastrophe-rapid change from
growth to shrinkage
Pause-no change in length
Jordan and Wilson, Nat Rev Cancer 2004, 4:253-265.
Dynamic Instability
+
-
GTP cap-stabilizes
+ end
Dynamic Instability
Lose GTP capdestabilize microtubule
Microtubule Depolymerization
Microtubule Depolymerization
Microtubule targeting agents disrupt normal
microtubule dynamics in diverse ways
Measure effects of microtubule targeting
drugs on microtubule dynamics
Microtubule targeting drugs suppress microtubule
dynamics thereby perturbing microtubule function
Jordan and Wilson, Nat Rev Cancer 2004, 4:253-265.
Microtubule Targeted Agents
Important drugs used for the treatment of
metastatic breast cancer
Two classes:
• Microtubule Depolymerizers- inhibit polymerization,
cause loss of cellular microtubules (Vinca alkaloids;
vinblastine, vincristine, vinorelbine: halichondrins;
eribulin; maytansines;DM1)
• Microtubule Stabilizers –stimulate polymerization,
increase density of cellular microtubules (taxanes;
paclitaxel, docetaxel, nab-paclitaxel: epothilones;
ixabepilone)
Jordan and Wilson, Nat Rev Cancer 2004, 4:253-265. Dumontet and Jordan, Nat Rev Drug Discov. 2009, 9:790-802.
Microtubule Targeted Agents
• The effects of these drugs on interphase
microtubules are dramatic, but at the lowest
concentrations these drug inhibit mitosis and
are classified as antimitotics
• Mitotic spindle is highly dynamic-leading to
increased susceptibility to microtubule
targeting agents
Jordan and Wilson, Nat Rev Cancer 2004, 4:253-265. Dumontet and Jordan, Nat Rev Drug Discov. 2009, 9:790-802.
Mitotic spindle microtubules are targets
for anti-cancer drugs
Microtubule
dynamics increase
4-100 fold in
mitosis
S.L. Mooberry
S.L.M.
S.L. Mooberry
metaphase
S.L.M.
anaphase
Successful
cell division
Microtubule
Binding agent
Mitotic arrest
interphase
S.L.M.
Suppress microtubule dynamics
Formation of aberrant mitotic spindles
Unable to organize DNA
Jordan and Wilson, Nat Rev Cancer 2004, 4:253-265
Cell Death
New data suggests that interphase
microtubules are also important targets
Interphase Microtubules
Polarized array with + end at periphery
Key role in cellular metabolism
S.L. Mooberry
Pathways for intracellular trafficking
Komlodi-Pasztor et al., 2011, Nat Rev Clin Oncol; 8:244-250;
Microtubule Targeted Agents Are
Not the Same
• Bind to different binding sites on tubulin
and on microtubules
• Suppress microtubule dynamics by subtly
different mechanisms
• These differences may help explain lack of cross
resistance
Microtubule Targeted Agents Are
Not the Same
• Bind to different binding sites on tubulin
and on microtubules
Microtubule Targeted Agents
Bind to different sites on microtubules
Microtubule Depolymerizer
Vinblastine
Outside surface and + end
Microtubule Targeted Agents
Bind to different sites on microtubules
Microtubule Depolymerizer
Microtubule Stabilizer
Vinblastine
Paclitaxel
Outside surface and + end
Interior surface
Microtubule Stabilizing Agents
Taxane site
Binding pocket is in the interior of the microtubule
Multiple drug orientations possible
Taxane site agents:
paclitaxel
docetaxel
ixabepilone
Bind differently within the
taxane binding pocket
Microtubule Stabilizing Agents
Paclitaxel
Stabilizes both longitudinal dimer interactions
and lateral protofilament interactions
Xiao H et al., PNAS 2006, 103: 10166-73.
Microtubule Stabilizing Agents
Paclitaxel
Stabilizes both longitudinal dimer interactions
and lateral protofilament interactions
Changes lateral interactions resulting in
microtubule with 12 protofilaments
Khrapunovich-Baine M et al., J Biol Chem 2011, 286:11765-78. Matesanz R. et al., Biophysical J 2011, 101: 2970-80
Microtubule Stabilizing Agents
Paclitaxel
Stabilizes both longitudinal dimer interactions
and lateral protofilament interactions
Changes lateral interactions resulting in
microtubule with 12 protofilaments
Binding within β-tubulin transduces changes in
structure of α-tubulin and site of motor and
microtubule associated protein (MAP) binding
Khrapunovich-Baine M et al., J Biol Chem 2011, 286:11765-78 . Xiao H. et al., 2012, ACS Chem Biol. 7:744-52.
Microtubule Stabilizing Agents
Docetaxel
Stabilizes both longitudinal dimer interactions
and lateral protofilament interactions
Changes lateral interactions resulting in
microtubule with 13 protofilaments
Difference in orientation as compared to
paclitaxel
Matesanz R. et al., Biophysical J 2011, 101: 2970-80
Microtubule Stabilizing Agents
Ixabepilone
Stabilizes longitudinal dimer interactions and but
less effect on lateral protofilament interactions
Difference in orientation as compared
to paclitaxel engaging different protein
moieties in β-tubulin
Khrapunovich-Baine M. et al., J Biol Chem 2011, 286:11765-78
Microtubule Stabilizing Agents
Taxane site
Bind on interior surface of formed microtubule
Stabilize longitudinal and lateral interactions
Drugs bind with different poses within the site
Contacts with different peptides in β-tubulin and
distinct poses may initiate different interactions
with microtubule associated proteins
Xiao H et al., PNAS 2006, 103: 10166-73. Matesanz R. et al., Biophysical J 2011, 101: 2970-80
Khrapunovich-Baine M et al., J Biol Chem 2011, 286:11765-78 . Xiao H. et al., 2012, ACS Chem Biol. 7:744-52.
Microtubule Destabilizing Agents
Vinca Domain
Located on β-tubulin
Binding site on exterior of microtubules
Multiple drug orientations possible
Vinca domain binding agents:
Vinca alkaloids: vinblastine, vinorelbine
halichrondrins: eribulin
maytansines: maytansine, DM-1
Bind with distinct orientations in binding site
Microtubule Destabilizing Agents
Vinca Alkaloids
• Bind
at + end and along
length of microtubule
• Can
also bind heterodimers
in solution at higher
concentrations
Microtubule Destabilizing Agents
Eribulin
• Eribulin
binds only to the ends of microtubules
14.7 eribulin molecules bind per microtubule
• Few molecules of eribulin are needed
to inhibit microtubule growth
At the concentration that inhibits growth 50%,
only 0.5 molecules of eribulin are bound per microtubule
Smith et al. Biochemistry 2010;19:1331-1337.
Microtubule Destabilizing Agents
DM1
• DM1 is an “end poison”
binds preferentially to the ends of
microtubules
37 molecules bind per microtubule
• Inhibits both microtubule shrinking and
growth
.Lopus M et al. Mol Cancer Ther. 2010;99:2689-99.
Microtubule Destabilizing Agents
Vinca Domain Binding Drugs
Suppress microtubule dynamics
Bind with distinct orientations in binding site
Subtle differences in how they inhibit microtubule
dynamics
Lopus M et al. Mol Cancer Ther. 2010;99:2689-99 Smith et al. Biochemistry 2010;19:1331-1337.
Microtubule Targeted Agents
• Suppress normal microtubule dynamics
• Disrupt microtubules and
• Prevent normal microtubule functions
• Resulting in apoptosis
• They all are mechanistically distinct
In Conclusion:
Microtubule Targeting Agents
●
Effective drugs used in the treatment of breast cancer
●
Mechanistic differences among microtubule targeting drugs
● All suppress microtubule dynamics and lead to mitotic
arrest and ultimately apoptosis
● A recent hypothesis suggests that interruption of
interphase microtubules might also be important
● New opportunities for the future by targeting microtubule
disrupting agents to tumor-directed antibodies, T-DM1

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