Learners to know the role of metal complexes to play anticancer activity.

1. Anticancer Activity of
Metal Complexes
By
Dr. G. Balakrishnan
Assistant Professor
Department of Chemistry
Vivekananda College
Madurai, Tamil Nadu

3. Medicinal Inorganic Chemistry
The introduction of metal ion or metal complex
into a biological system for the treatment of
disease - subdivision of bioinorganic chemistry.
The field of knowledge concerned with the
application of inorganic chemistry to therapy or
diagnosis of disease - medicinal inorganic
chemistry.
Intentional introduction of metal complex into
the human biological system - useful to early
detection of disease through imaging of the living
body.

4. Cancer
 Cancer - one of the leading causes of death in developed
countries.
 Almost 600 000 cancer deaths estimated in 2016 in the
United States ~ 13% of all deaths.
 Biologically – cancer represents a vastly heterogenic group
of diseases sharing several common traits.
 One of the hallmarks – sustained proliferation resulting in
uncontrolled cellular growth and multiplication(spread) of
abnormal cells.
 Such cells have unlimited replicative potential and evade
apoptosis- the process of programmed cell death-
deregulation of apoptosis is closely associated with cancer
 Cancer survival rates tend to be poor because of late stage
diagnosis and limited access to timely and standard
treatment.

5. Cancer biomarker
Schematic illustration of various cancer biomarkers.

6. Cisplatin as anticancer drug
 Cis-diammine-dichloroplatinum(II) – a square
planar metal complex.
 In 1978 – cisplatin approved as an anticancer drug
for clinical use(Discovered in 1965 by Rosenberg)
 This discovery opened new avenue for the
application of metal complexes in cancer therapy.
 One of the most successful therapeutic
metallodrugs even today.
 Among the top revenue – generating licensed
product.
 Provided Michigan State University with a large
gross revenue from licensing royalty.

7. Cisplatin
Pt(II) drugs have serious side effects.
The main reason for this – their action
mechanism.
Pt(II) drugs are not able to distinguish
tumor from normal cells.
The mode of action and efficacy of
chemotherapeutic agents is fundamentally
influenced by localization and uptake in
the target cells.

8. Main interaction sites of anticancer metal complexes with
cellular redox and oxidative stress pathways.

9. Clinically approved Pt(II) drugs

10. Scheme of the reaction pathway leading to the formation of adducts between
cisplatin (a) and DNA. One chloride ligand is displaced by water to form the
aqua-complex (b) which interacts with DNA forming the monofunctional
adduct (c). This last might exchange the chloride ligand with one molecule of
water forming the hydrated monofunctional adduct (d). Both the
monofunctional adduct (c) and its hydrated form (d) lead to the formation of
the bifunctional adduct (e).

11.  This coordination leads to a significant
distortion of the helical DNA structure resulting
in inhibition of DNA replication and
transcription.
 Further, several signaling pathways are
activated which—as a final consequence—lead to
cell cycle arrest and/or apoptosis.
 Apoptosis plays a crucial role in developing and
maintaining the health of the body by

12. Drug and redox processes
 Due to the Pt center of cisplatin, it is reasonable that the
drug reacts not only with DNA but also with donor atom
containing proteins with particularly high affinity to sulfur
and seleno amino acids.
 This is supported by the fact that less than 1% of
intravenously administered cisplatin reaches DNA.
Therefore, several other cellular targets have been
suggested.
 Such DNA damage-independent mechanisms might
involve, redox reaction consequently, activation of FAS-
mediated apoptosis.
 Cisplatin detoxification is at least partially based on
formation of cisplatin-GSH conjugates, which leads to
intracellular GSH pool depletion and increased levels of
intracellular ROS, particularly hydroxyl radical generation.

13. Role of Metal Ions
 Metal ions play important biological functions.
 Fe2+, Zn2+, Cu2+, Mn2+, Co2+, Ni2+
 Cell signalling, metabolism, energy production, catalysis,
and the immune response.
 Cells require tight regulation of the intracellular redox
balance and consequently of reactive oxygen species(ROS)
for proper redox signaling and maintenance of metal (e.g.,
of iron and copper) homeostasis.
 In several diseases, including cancer, this balance is
disturbed.

14. Oxidative Stress
 Excessive production of ROS or an imbalance between ROS and
antioxidants, that is ROS concentrations exceeding the antioxidant
capacity of the cell, can lead to a common pathophysiological situation
termed oxidative stress.
 This cellular condition with altered oxidation-reduction (redox)
homeostasis may determine oxidative modification of cellular
macromolecules, modify their function, and eventually promote cell
death.
 A global imbalance of prooxidants and antioxidants, has been recently
updated as “an imbalance between oxidants and antioxidants in favor of
the oxidants, leading to a disruption of redox signaling and control and/or
molecular damage”.

15. Redox environment within a cell
Strongly differs in diverse intracellular
compartments.
• The most redox active parts of the cell are the
mitochondria – the major intracellular
generators of ROS. The high reactivity of ROS
makes their tight regulation necessary for cell
survival.
• Apoptosis involves multiple intracellular and
extracellular events such as release of
cytochrome c from mitochondria

16. Mitochondria
 Mitochondria are the major source of cellular ROS in
cells.
 Under normal cellular conditions, less than 1% of the
mitochondrial electron flow leads primarily to the
formation of O2
•− .
 Interference with electron transport can dramatically
increase O2
•− production.
 Superoxide is rapidly converted within the cell to H2O2
and O2 by superoxide dismutase (SOD) enzymes
 H2O2 can react with reduced transition metals, via the
Fenton reaction
 Redox reaction also produces the highly reactive OH•, a
far more damaging molecule to the cell.

17. Enzymes
 The living organism constantly maintains a complex
oxidant–antioxidant homeostasis system with diverse ROS
generating and degrading systems in different compartments
of the cell.
 There are several regulatory levels for maintenance of redox
balance in the cell involving enzymatic (such as superoxide
dismutases, catalase, thioredoxin reductases [TrxR],
glutathione reductases [GR], and glutathione peroxidases
[GPx]) as well as nonenzymatic antioxidants (such as
glutathione [GSH], thioredoxin [Trx], and several vitamins)

18. Production of ROS. (A) The electronic structure of O2 favors its
reduction by addition of one electron at a time, leading to the
generation of oxygen radicals causing cellular damage.

19. General overview on the role of ROS in the activity
of anticancer metal drugs.

20. Ruthenium drugs. KP1019 and NAMI-A have been already evaluated in
clinical trials, whereas all others are under preclinical investigation.

21. Ru(II) and Ru(III) complexes
 Among the best studied non-platinum metal complexes
with anticancer activity.
 Ru complexes have DNA binding properties similar to
Pt complexes.
 Ru(III) are characterized by a high affinity to serum
proteins – crucial for drug accumulation into the tumor
tissue.
 Besides GSH, Ru(III) complexes also interact with NO˙
known as intracellular and intercellular messenger for
diverse physiological processes.

22. PLIM imaging of live MCF-7 cells pretreated with Ru(II) complex
(500 mm, 1 h, serum-free media).

23. Other metal complexes
 Fe, Cu, V, Co and Mn complexes also play important
role as anticancer agents.
 Re(I) complexes have been used for DNA binding and
as anticancer agents Mr. Balakrishnan
 Ru(III) complexes for the generation of ROS
Dr.Thiruppathi
 Dr. Nagaraj used Co(III) and Cu(II) complexes
 Other candidates used Fe and V complexes.

24. Distinct imaging of mitochondrial TrxR in living HeLa cells by
TPP2a. Scale bar: 5 μm.

25. Confocal fluorescence image, bright field image and their overlay of living
HeLa cells incubated with 25 μM of Ru1 in PBS (pH = 7.4) for 1 h at 37 °C,
followed by 50 nM of MTG, respectively. (A) confocal fluorescence image of
MTG; (B) confocal fluorescence image of Ru1; (C) overlay of A and B; (D)
bright field image; (E) overlay of A, B and D.

26. Confocal fluorescence images of the cells were incubated in the absence or
presence of 10 μM CCCP for 1 h, and then stained with 50 nM MTG for 30
min and 25 μM Ru1 for 1 h.

27. Cytochrome-c translocation induced by the metal complexes on MCF7 cells. The
cells were seeded on a cover glass for 24 h followed by the treatment of the
complexes at the IC50 concentration for another 16 h. The cells were fixed with
formaldehyde followed by immune-staining with anti-cytochrome-c and FITC
labelled secondary antibodies, and viewed under a fluorescence microscope. Panels
(left to right) denote DAPI staining of the cell nucleus, cytochrome-c translocation,
overlay, and differential interference contrast (DIC) images, respectively. The
control panel indicates cells treated with DMSO.

28. Re(I) complex
Time series of confocal fluorescence microscopy images of Re(I) complex
incubated with MCF-7 cells.

30. A) Confocal microscopic images of HeLa cells co-labeled with Re1–Re4 (20 mm, 2 h)
and LTDR (50 nm, 0.5 h). B) Confocal microscopy images of HeLa cells co-labeled
with Re1–Re4 (20 mm, 2 h) and MTDR (150 nm, 0.5 h). Scale bar: 20 mm.

31. Confocal fluorescence microscopy images of Dox (1 mm),
Cp-Dox (5 mm), and Cp-N-Dox (5 mm) in HeLa cells after 2 h
of incubation. Excitation at 488 nm, emission above 600 nm.
Scale bars: 20 mm.
Magnified images showing an overlay of Cp-Dox autofluoresnce and MitoTracker
fluorescence in HeLa cells, suggesting an accumulation of the Dox conjugate in the
mitochondrial membrane.