Trial Information

Cisplatin, Carboplatin, and Oxaliplatin Interactions With Plasma Proteins

Cisplatin, cis-[Pt(NH3)2Cl2], is a widely used antitumor agent for the treatment of
testicular and ovarian cancers. Carboplatin is used extensively for small cell, non small
cell lung cancer and ovarian cancer. Oxaliplatin has recently been approved in the US for
treatment of colorectal cancer. All of these analogues are administered by intravenous
injection, and within one day, 65-98% of the platinum in the blood plasma is bound to
protein. Binding of cisplatin to proteins reduces urinary excretion of platinum, and causes
deposition of platinum in tissues. Binding of cisplatin to proteins and enzymes is generally
believed to be the cause of several severe side effects exhibited by these drugs, especially
ototoxicity and nephrotoxicity.

Despite numerous studies of platinum-protein binding in the last few decades, the roles of
platinum-protein adducts in drug action, and in toxicity of these drugs are not known.
Although cisplatin-protein adducts are widely believed to cause the drug's side effects,
there are also claims that platinum-protein adducts are important for the drug's activity.
Therefore, a better understanding of the molecular mechanism of platinum-protein
interactions may have an impact on the optimization of strategies for platinum treatment. It
is important to understand basic principles that govern formation and reactivity of
platinum-protein adducts because these adducts may be important in defining the therapeutic
profile of these drugs. In this quest, the first goal is to develop a reliable technique for
these studies. To date, ultraviolet/visible (UV-Vis), fourier transform infrared (FT-IR),
and nuclear magnetic resonance (NMR) studies of cisplatin-protein interactions have provided
only low-resolution information on the mechanism of the binding or on the nature of the
adducts. The researchers propose to investigate the role of platinum-protein adducts in the
mechanisms of the drug action and their contributions towards the toxicity of these drug.
The short-term objective is to investigate platinum interaction with serum proteins using
both nanoelectrospray mass spectrometry (nanoESI-MS) and a combination of size exclusion
high performance liquid chromatography with inductively coupled plasma mass spectrometry
(HPLC/ICP-MS). The long-term objective of this research is to develop biomarkers based on
platinum-protein adducts for clinical monitoring.

Initially, metallothionein and human hemoglobin were used as model proteins to develop
nESI/MS and HPLC/ICP-MS techniques for studying cisplatin-protein interactions in vitro. The
researchers have demonstrated that the combination of size exclusion HPLC/ICP-MS and
nanoESI/MS provided new information on the adduct formation and potential reaction
mechanism. The size exclusion HPLC with ICP-MS enables monitoring of cisplatin-protein
binding under physiological conditions. Nanospray tandem MS offers information on formation
of specific complexes and on characteristics of binding. This information is useful for a
better understanding of drug toxicity and treatment resistance. The information on
platinum-protein interactions allows us to evaluate the utility of both nanoESI/MS and size
exclusion HPLC/ICP-MS techniques in providing mechanistic, kinetic and structural
information on the binding of platinum to other proteins. The methodology will be further
validated by studying the platinum-blood protein adducts in cancer patients undergoing
chemotherapeutic treatments. The correlation between the levels of platinum-protein adducts
and clinical outcomes will be studied.

The successful completion of this research program should provide the researchers with a
better understanding of mechanisms of the drug action and toxicity. This knowledge will be
of great importance in clinical monitoring of cancer patients to assist doctors to improve
cancer chemotherapy.