How Far Have We Come on Cancer Diagnosis?
How Far Have We Come on Cancer Diagnosis?
Joint research team led by Professor Youngsoo Kim at the Department of Biomedical Engineering of Seoul National University College of Medicine and Doctor Cheolju Lee at Korea Institute of Science and Technology (hereinafter referred to as Seoul team, headed by Professor Youngsoo Kim) developed quantitative technology for 319 target proteins with minimal amount of 1 μg (1/1000 mg) breast cancer cell specimen by using Multiple Reaction Monitoring (MRM) of Triple Quadrupole Mass Spectrometer.
With the support of National Cancer Institute, this research was jointly conducted by Dr. Amada Paoulovich at the US Fred Hutchinson Cancer Research Center (hereinafter referred to as Western US Seattle team) and Dr. Steven Carr at the BROAD Institute of Harvard and MIT (hereinafter referred to as Eastern US Boston team).
Genes and protein are one of the most important factors deciding the characters of our body’s cells. At present, gene information can be easily obtained thanks to the development of Next Generation Sequencing (NGS) but quantitative analysis on quantitative proteome (measuring the amount or concentration of specific proteins) is limited in its speed and scale.
As cancer multiplies, it produces unique protein of its own. Based on the idea, tumor marker test takes blood from a cancer patient and measures the amount of protein generated by cancer cells.
Tumor marker test taken at a clinical experiment is shown at [Table 1]. To have a more accurate check on cancer, we go through various medical tests such as CT, MRI and PET. However, patients cannot undergo such tests every month as they are expensive and have the risk of radiographic exposure. On the contrary, tumor marker test can be taken on a regular basis at an inexpensive price to check whether one has developed cancer or not.
With the present technology, tumor marker test measures concentration by using reaction between protein (antigen) which cancer cells generate and antibody. Yet it takes a lot of time and money as every tumor marker requires new method for analyzing antibody. Even though the same test is conducted, it is hard to get the same standardized outcome due to analytical deviation for each laboratory.
That is why the medical team came up with the Multiple Reaction Monitoring (MRM) using Triple Quadrupole Mass Spectrometer. By going through a test with minimal amount of 1 μg specimen just one time, approximately 100 to 300 target proteins can be quantified. If a certain protein is identified as a cancer marker, several kinds of cancers can be diagnosed with just one blood test.
The principle works like this. First, assume that there are 100 target proteins within one droplet of blood. Then go through chemical pretreatment on a certain protein to turn it into peptides and measure its mass (Q1) through electronic mass scanner. Then fragment the same peptide into product ions and measure their mass (Q3) through electronic mass scanner. Just like fingerprints, each protein has its own mass values for Q1/Q3, respectively. The research team enters the unique Q1/Q3 values for every 100 protein into the mass spectrometer in advance.
After putting the samples prepared from blood into the mass spectrometer, researchers analyze the mass by scanning peptides within the blood at msec (millisecond, a thousandth of a second) unit. Afterwards the result is compared with the unique Q1/Q3 values of the standard peptides entered in advance, respectively. Say that the Q1/ Q3 value for protein A is 400/200. If it turns out that 20 is corresponding to 400/200 for its Q1/ Q3 value, it means that the amount of the protein are 20.
The Q1/Q3 values for 319 proteins were measured in 30 breast cancer cell strains, where the 162 proteins were quantitated commonly in Seoul team, Western US Seattle team and Eastern US Boston team by using the same mass spectrometer and technology.
The result was that for each three site the change in the average of analysis on those 162 proteins was within 0.2%.
It means that the same quantification value for the protein can be obtained when using the same mass spectrometer and methods regardless of time and place. In other words, a new era of absolute analysis on massive target proteins has dawned as absolute quantitative proteomics has become possible on a massive scale globally.
Professor Youngsoo Kim said, “If massive target proteins can be analyzed with globally standardized absolute quantification values as we enter the age of individual-tailored medicine service, it will pave the way for common technological development, which I believe will make significant contribution to the analysis of target proteins and development of medical technology. It is expected that low-priced innovative medical analysis equipment will be developed if super-high speed multiple target protein analysis becomes possible by using the Triple Quadrupole Mass Spectrometer we used in this research.”
This research, with impact factor of 23, was introduced in December on-line version of Nature Methods, a renowned international scientific journal.