The Effects of Cisplatin Binding to DNA

1
The Effects of Cisplatin Binding to DNA

• By
• Lesley Skelton

2
History of Cisplatin

• Cis-diamminedichloro platinum (II) commonly
  called Cisplatin is an excellent anticancer drug.
• Used to treat testicular ovarian lung bladder
  and head and neck cancers.
• First synthesized by Michel Peyrone in 1845 .
• Barnett Rosenberg discovered its effectiveness as
  an anticancer drug in 1969
• Approved as an anticancer drug by FDA in 1978

Cisplatin. (2007 April 11). In Wikipedia The
Free Encyclopedia. Retrieved April 15 2007
from http//en.wikipedia.org/w/index.phptitleCis
platinoldid122044175 McCormick. M. Chem. and
Eng. News. 1999 77 3-7.
3
Rosenberg and Cisplatin

• Designed experiments to measure effects of
  electrical currents on bacterial cell growth.
• Found that E. coli grew 300 times its normal
  length.
• Prevented cell division but not other growth
  processes.
• Due to cisplatin that was formed between the
  platinum electrodes and the solution containing
  the bacteria.

Smith A. Cisplatin Chem Cases. Retrieved April
15 2007 from Kennesaw State University Web
site http//chemcases.com/cisplat/htm. Keppler
Bernard Studies on the Tumor-inhibiting
Properties. Retrieved April 15 2007 from
University of Vienna Web site http//www.setforeu
rope.org/brno95/talks/Bernard_Keppler.pdf.
4
Cisplatin and Mammalian Cells

• Implanted transplanted tumors under the armpit of
  the mice.
• Tumors were allowed to grow for 8 days until mass
  was 1 gram.
• Found that it caused the cell to shrink and the
  mice to be cured.
• Animals immune system rejected the reimplanted
  tumors.

Smith A. Cisplatin Chem Cases. Retrieved April
15 2007 from Kennesaw State University Web
site http//chemcases.com/cisplat/htm.
5
Cellular Uptake of Cisplatin

• Administered intravenously
• Enters cell by passive diffusion or active uptake
  by the cell
• Once inside cell the complex is activated due to
  low chloride concentration

Smith A. Cisplatin Chem Cases. Retrieved April
15 2007 from Kennesaw State University Web
site http//chemcases.com/cisplat/htm.
6
Mechanism of Cisplatin

• When the chlorido ligands are replaced by aqua
  ligands the complex is activated due to the
  positive charge.
• The complex can thus bind to various cellular
  components specifically the N7 atom of guanine
  in DNA.

Liu S.M. Mechanism. Retrieved April 15 2007
from http//www2.mrc-lmb.cam.ac.uk/personal/sl/Htm
l/Mechanism.html.
7
Interaction with RNA

• Can coordinate to RNA but not important
  mechanistically in the body.
• Damaged RNA can be replaced by newly synthesized
  RNA.
• Does not affect synthesis of RNA.
• When used in vitro at lethal dose only 1-10 of
  RNA molecules are damaged.

Smith A. Cisplatin Chem Cases. Retrieved April
15 2007 from Kennesaw State University Web
site http//chemcases.com/cisplat/htm.
8
Interaction with DNA

• Coordinate DNA mainly through N7 atoms of
  purines-Adenine and Guanine
• N7 atoms do not hydrogen bond with any other DNA
  bases
• Can coordinate to the N3 of Cytosine and Uracil

Smith A. Cisplatin Chem Cases. Retrieved April
15 2007 from Kennesaw State University Web
site http//chemcases.com/cisplat/htm.
9
Possible Binding Modes of Cisplatin

• Binds 90 of the time through intrastrand
  crosslinks
• Monofunctional adducts of a single purine base
• Interstrand crosslinks
• DNA protein cross-linking

Liu S.M. Mechanism. Retrieved April 15 2007
from http//www2.mrc-lmb.cam.ac.uk/personal/sl/Ht
ml/Mechanism.html.
10
Coordination with DNA

• Bound mainly through 12-intrastrand cross-link
  due to the cis orientation of the leaving groups.
• Two chlorine ligands are replaced by purine
  nitrogen atoms on adjacent bases on the same
  strand of DNA.
• Usually two guanines are involved in these
  adducts but can be one guanine and one adenine.

Liu S.M. Mechanism. Retrieved April 15 2007
from http//www2.mrc-lmb.cam.ac.uk/personal/sl/Htm
l/Mechanism.html.
11
DNA Alterations

• The cisplatin complexes bound to the purines
  cause unwinding of the double helix and a
  widening to the minor groove
• The 12-intrastrand cross-link causes a kink to
  the DNA molecule in the major groove
• Opens a hydrophobic pocket in the minor groove
  between the two guanine bases

Raber J. Zhu C. Eriksson L.A. J. Phys. Chem.
B. 2005 109 11006-11015.
12
(HMG)-domain Proteins

• A (HMG)-domain protein recognizes the hydrophobic
  pocket of the minor groove and the kink in the
  major groove.
• The protein inserts a phenyl group and binds
  tightly to the DNA causing it to bend.
• Researchers believe these proteins may aid in the
  cytotoxicity of cisplatin because they protect it
  from DNA repair enzymes.

McCormick. M. Chem. and Eng. News. 1999 77
3-7. Raber J. Zhu C. Eriksson L.A. J. Phys.
Chem. B. 2005 109 11006-11015.
13
Cell Death

• Cisplatin is phase-nonspecific in that it kills
  cells at any phase of the cell cycle
• It is believed that the 12-intrastrand
  cross-links are the cause of the drugs
  cytotoxicity
• Alterations to DNA structure prevent cell
  replication and activation of cellular repair
  mechanisms which leads to cell death

Liu S.M. Mechanism. Retrieved April 15 2007
from http//www2.mrc-lmb.cam.ac.uk/personal/sl/Htm
l/Mechanism.html.
14
Cell Death

• The link between structure alteration and cell
  death is due to prevention of DNA transcription
  which involve 3 mechanisms of action.
• 1.)Participation of HMG proteins
• 2.)Irreversible platinum binding to transcription
  factors
• 3.)Abortive Correction Repair

Liu S.M. Mechanism. Retrieved April 15 2007
from http//www2.mrc-lmb.cam.ac.uk/personal/sl/Htm
l/Mechanism.html.
15
Participation of (HMG)-proteins

• (HMG)-proteins have a greater affinity to bind to
  cisplatin-modified DNA than unmodified DNA
• Due to the bent formation of the DNA duplex which
  resembles its binding site
• Increase cytotoxicity by binding to DNA adducts
  obstructing cellular excision repair

Liu S.M. Mechanism. Retrieved April 15 2007
from http//www2.mrc-lmb.cam.ac.uk/personal/sl/Htm
l/Mechanism.html.
16
Irreversible binding factors

• Able to replace zinc (II) of regulatory proteins
  essential for the transcription of DNA with
  itself
• Usually the zinc cation coordinates to histidine
  and cysteine packing together the 9 small DNA
  binding domains into dense structures
• By replacing the zinc ion with platinum it
  disrupts the conformation and binds the zinc
  finger permanently to the DNA-polymerase-alpha
  which is the transcription enzyme for cell
  replication

Liu S.M. Mechanism. Retrieved April 15 2007
from http//www2.mrc-lmb.cam.ac.uk/personal/sl/Htm
l/Mechanism.html.
17
Abortive Correction Repair

• Generally involves single or double stranded
  breaks in the DNA that are caused by
  DNA-polymerase and post-replicative repair
  mechanisms
• DNA-polymerase breaks the DNA strands by
  colliding with the platinum adduct.
• Post-replicative repair mechanisms creates nicks
  and breaks in the DNA because it thinks the
  cisplatin adduct is a mismatched base pair
• This creates the upregulation of p53 due to the
  DNA strand breaks which leads to apoptosis.

Liu S.M. Mechanism. Retrieved April 15 2007
from http//www2.mrc-lmb.cam.ac.uk/personal/sl/Htm
l/Mechanism.html.
18
Why Guanine

• Both the hydrogen bond length and covalent
  binding energy lead to the stabilization and
  preference for cisplatin to bind to the
  GN7-cisPt-GN7 complex in DNA.

Robertazzi A. Platts J.A. Inorg. Chem. 2005
44 267-274.
19
Transplatin vs. Cisplatin

• Less mutagenic because it binds through
  interstrand cross-links instead of intrastrand
  cross-links
• Less able to form hydrogen bonds to Guanine or
  Adenine
• Forms cross-links slower
• Interstrand cross-links are easier to repair
  because kinetically more reactive

Smith A. Cisplatin Chem Cases. Retrieved April
15 2007 from Kennesaw State University Web
site http//chemcases.com/cisplat/htm.
20
Sulfur Containing Biomolecules

• Sulfur containing biomolecules like
  metallothionein and glutathione are found inside
  cells
• Have been linked to drug resistance in the cell
• Production is increased by presence of heavy
  metal ions in the cells
• Both are involved in the detoxification of heavy
  metal ions in the cell
• Aid in the removal of heavy metal ions from the
  cell

Smith A. Cisplatin Chem Cases. Retrieved April
15 2007 from Kennesaw State University Web
site http//chemcases.com/cisplat/htm.
21
Drug Resistance

• Believe cancer cells develop mechanisms to remove
  or keep cisplatin out of the cells
• Increase ability to remove cisplatin DNA adducts
• Repair damaged DNA
• Concentration of nuclear proteins like ERCC1 and
  XPE-BF have been known to increase as tumor cells
  become resistant to cisplatin

Smith A. Cisplatin Chem Cases. Retrieved April
15 2007 from Kennesaw State University Web
site http//chemcases.com/cisplat/htm.
22
Problems with Cisplatin

• Lacks selectivity to tumor tissue which leads to
  severe toxicities and side effects
• Renal Impairment
• Neurotoxicity
• Ototoxicity (Loss of balance and hearing)
• Only affects a narrow range of tumors
• Development of resistance to the drug

Smith A. Cisplatin Chem Cases. Retrieved April
15 2007 from Kennesaw State University Web
site http//chemcases.com/cisplat/htm.
23
Criteria for Cisplatin Analogues

• Electroneutrality- ability to diffuse through
  non-polar substances like cell membranes.
• Two good leaving groups that are cis to one
  another
• Inert carrier ligand such as a non-tertiary
  amines that increase adduct stabilization due to
  hydrogen bonding with nearby bases.
• Ability to differentiate between cancerous and
  normal cells
• Ability to arrive intact at the cellular target.
• 
  

24
Carboplatin

• Approved by FDA in 1989 for ovarian cancer
• Forms 12-intrastrand cross-links like cisplatin
• Less toxic to kidneys and peripheral nervous
  system
• Contains bidentate dicarboxylate ligand that
  slows down the breakdown of carboplatin into
  harmful derivatives

Liu S.M. Mechanism. Retrieved April 15 2007
from http//www2.mrc-lmb.cam.ac.uk/personal/sl/Htm
l/Mechanism.html. Carboplatin. (2007 March 14).
In Wikipedia The Free Encyclopedia. Retrieved
April 15 2007 from http//en.wikipedia.org/w/ind
ex.phptitleCarboplatinoldid115106892
25
Discussion

• Cisplatin is an effective anticancer drug because
  it binds to DNA causing kinks and unwinding of
  the major and minor groove.
• 12-intrastand crosslinks of DNA specically to
  the N7 of guanine is believed to cause
  cytotoxicity
• Interactions with the (HMG)-domain proteins also
  lead to cisplatins cytotoxicity because they
  protect the DNA-cisplatin complex from DNA repair
  enzymes
• Prevents DNA replication and transcription which
  eventually leads to apoptosis.
• Both cis and transplatin bind to DNA covalently
  but cisplatin is more cytotoxic and has greater
  preference for tumor cells over normal ones.
• Cisplatin and its analogs are the only inorganic
  complexes used in cancer therapy.

26
References

• Cisplatin. (2007 April 11). In Wikipedia The
  Free Encyclopedia. Retrieved April 15 2007
  from http//en.wikipedia.org/w/index.phptitleCis
  platinoldid122044175.
• Carboplatin. (2007 March 14). In Wikipedia The
  Free Encyclopedia. Retrieved April 15 2007
  from http//en.wikipedia.org/w/index.phptitleCar
  boplatinoldid115106892.
• McCormick. M. Chem. and Eng. News. 1999 77 3-7.
• Robertazzi A. Platts J.A. Inorg. Chem. 2005
  44 267-274.
• Liu S.M. Mechanism. Retrieved April 15 2007
  from http//www2.mrc-lmb.cam.ac.uk/personal/sl/Htm
  l/Mechanism.html.
• Smith A. Cisplatin Chem Cases. Retrieved April
  15 2007 from Kennesaw State University Web
  site http//chemcases.com/cisplat/htm.
• Keppler Bernard Studies on the Tumor-inhibiting
  Properties. Retrieved April 15 2007 from
  University of Vienna Web site http//www.setforeu
  rope.org/brno95/talks/Bernard_Keppler.pdf.
• Kasparkova J. Delalande O. Stros M.
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• Raber J. Zhu C. Eriksson L.A. J. Phys. Chem.
  B. 2005 109 11006-11015.