Biomarkers : A Novel Approach for Targeted Cancer Therapy

Samad A

The progress in the understanding of cancer progression and early detection has been slow and frustrating due to the complex multifactorial nature and heterogeneity of the cancer syndrome.

Till date, no effective treatment is available for advanced cancers, which remain a major cause of morbidity and mortality. There is an urgent need to unravel novel biomarkers for early detection. Improvements in understanding the genetic and epigenetic alterations in the process of carcinogenesis are thus demanded in order to find new diagnostic approaches and targeted therapies. Due to the advances in molecular pathology the genetic characteristics of the early preinvasive lesions in carcinogenesis are already known. This offers contemporary approaches for the early detection and diagnosis of this disease. Some proteins are secreted and/or cleaved into the extracellular milieu and may represent valuable serum biomarkers for diagnosis purpose. It is estimated that the cancer proteome may include over 1.5 million proteins as a result of post translational processing and modifications. Such complexity clearly highlights the need for ultra-high resolution proteomic technology for robust quantitative protein measurements and data acquisition. Currently, it is estimated that cancer kills over 6 million people per year worldwide, with over 10 million new cases being diagnosed every year. Mortality is mainly attributed to dissemination of primary cancer to distant organs, on which no effective treatment is available.

What Are Biomarkers?

 “Biochemical, cellular, physiological or behavioural variations in the tissue or body fluids or at the level of whole organism that provide evidence of exposure to chemical pollutants, and may also indicate a toxic effect”

Cancer has proven to be one of the most intractable diseases to which humans are subjected, and as yet no effective treatment is available for advanced cancers, which remain a major cause of morbidity and mortality. Therefore, most pressing and the urgent need is to unravel novel biomarkers for early detection.

Detection Of Cancer Via Biomarkers: Current Scienario

Despite advances in diagnostic imaging technology, surgical management, and therapeutic modalities, cancer remains a major cause of mortality worldwide. Currently, it is estimated that cancer kills over 6 million people per year worldwide, with over 10 million new cases being diagnosed every year. Mortality is mainly attributed to dissemination of primary cancer to distant organs, on which no effective treatment is available. The dilemma in oncology practice is the large number of patients presenting macro or micro metastases at primary diagnosis, and the fact that in some cases (e.g. breast cancer) metastases are seen in patients free of metastasis-positive axillary lymph nodes¹.

In the past years, significant progress in microarray technology has provided encouraging results on genetic patterns, or “fingerprints”, that can predict cancer progression, drug response, and/or help cancer staging ^2,3,4,5,6,7. Nevertheless, comparative transcriptional profiling alone is unlikely to fully identify “the gold standard” biomarkers that can mirror the cancer phenotype. It is evident that most of the functional information on the genes resides in the proteome, which is the sum of multiple dynamic processes that include protein phosphorylation, protein trafficking and localization, and protein-protein interactions with secondary effectors (Fig.1). Functional proteomics is potentially more predictive than genomics. Unlike genomics, however, acquiring proteomic data faces technical challenges, particularly with regard to lack of standardized methodologies, sensitivity and reproducibility, and intra and interindividual tumor heterogeneity.

Nevertheless, these obstacles can be overcome with the current research efforts to develop high-resolution proteomic instrumentation for high throughput monitoring of protein changes that occur in cancer ^8,9.

Fig.1 Illustration of the information flow from genotype to phenotype. The framework for the regulatory network would encompass knowledge from gene sequence to protein sequence, to posttranslational modifications, to protein cellular and sub-cellular distribution and trafficking, and the protein-protein interaction pattern

Novel Biomarkers In Early Cancer Detection:

Lung cancer is the most common cause for cancer death in developed countries. The prognosis is dismal, with less than 15% of patients surviving 5 years after diagnosis, which is because of the lack of efficient diagnostic methods and successful treatment for metastatic disease. This led to a shift of the therapeutic paradigm towards asymptomatic pre invasive and early invasive cancer. Improvements in understanding the genetic and epigenetic alterations in the process of lung carcinogenesis are thus demanded in order to find new diagnostic approaches and targeted therapies. Due to the advances in molecular pathology the genetic characteristics of the early preinvasive lesions in lung carcinogenesis are already known. This offers contemporary approaches for the early detection and diagnosis of this disease.

Recent developments in molecular biology and gene technology provide a better understanding of the essence of the multistep process of lung carcinogenesis and offer new perspectives for lung cancer screening and early detection. Few of the recent biomarkers being utilized for early cancer detection may be summarized as below-

Ø Circulating DNA and RNA as possible markers in lung cancer patients

There are different studies evaluating the role of circulating nucleic acids in the blood of lung cancer patients. Despite this there is no clear concept about their possible clinical application because of the limited number of the patients, the absence or small number of controls and the lack of validated methods for detection.

Ø Total DNA

The total amount of DNA in lung cancer patients is assessed quantitatively by different methods in a number of studies and it varies between 50% and 70%, because of the lack of sensitive methods for detection ^10,11 . The largest study of Sozzi et, al.¹² included 100 slung cancer patients and 100 controls of heavy smokers. The circulating amount of DNA is determined with real time PCR which led to a specifi city of 95% and a sensitivity of 78% ¹².

Ø Circulating Gene Mutations

The most commonly investigated mutations in circulating DNA of lung cancer patients are ras and p53. The number of ras and p53 mutations range between 0-30% and 10-30% respectively¹³. K-ras point mutations in blood are identical to those in lung cancer tissue but are not always found despite their presence in tumor¹⁴. In contrast to this p53 mutations are detected in 41% of lung cancer tissue and the identical mutations are also present in 78% in the blood of the tumor positive patients ¹⁵.

Ø Microsatellite Alterations

Loss of heterozygosity and allelic shift have been the aim of investigation of different studies. DNA alterations in cancer tissue were detected in appoximately 60% (range 50%-80%). The same aberrations are detected in blood of 70% (range 55% - 90%) of the patients, which proves its tumor origin. To increase the percentage of abnormal findings two to nine markers have been used. Microsatellite alterations are present in 24%-71% in the plasma of patients ^16,17,18,19.

Validation Of Biomarkers: Need Of The Hour

The end result of proteomic analysis is to have appropriate validation before the marker can reach clinical applications. Once a putative biomarker has been identified, validation using additional measurements and compound identification is necessary^20,21. For example, one can repeat the analysis at additional time points and determine the temporal correlation of putative biomarkers with the progression of the disease. Determining the timing of the appearance of a biomarker has been shown to be important in assessing a biomarker’s prognostic utility. For example, ovarian cancer is accompanied by elevated serum osteopontin levels²², though its diagnostic utility is inferior to CA125 (the only currently validated biomarker for ovarian cancer) as a biomarker for postoperative monitoring. However, serum osteopontin was shown to rise earlier than CA125 in patients suffering from recurrent ovarian cancer. This fact illustrates the utility of simultaneous measurement of multiple biomarkers.

Critical issues that need to be addressed for the validation studies include the specificity and reproducibility of the marker. In the case of cancer tissues and biological fluids, this is further complicated by intra and intercell heterogeneity. The use of tumor tissues or needle biopsies may be problematic because multiple and representative tissue sampling is not always feasible, e.g. tumors in non-accessible sites. Furthermore, protein profiling can differ between a given area of the tumor mass. To address these problems, a proteomic study by on the most prevalent transitional cell carcinoma of the bladder has combined proteomics and immunohistochemistry with clinical data gathered over a 5-year period and correlated the protein database to cancer cell heterogeneity within normal urothelium with recurrence²³. The study reported that tumor lesions displaying phenotypic alterations in the basal, proliferative compartment of the urothelium have the highest incidence of recurrence.

Biomarkers: Future Prospects

Current clinical and pathological markers poorly predict early disease development and response to treatment. Standard diagnostic methods, including tissue histopathology are now shifting rapidly toward molecular diagnosis due to the rapid progress in proteomic instrumentation. This powerful technology can identify all proteins and their post translational modifications in disease conditions, and hence will greatly accelerate progress toward novel diagnostic and predictive tools to track early disease and tailor treatments to specific patients.

Conclusion:

Due to the rapid emergence of high tech proteomic instrumentation, novel biomarkers are gaining massive attention for the conventional clinical and pathological markers. Biomarkers are proving themselves as inevitable detection tools helping a lot in early detection as well as the subsequent targeted therapy of various types of cancers .In nutshell the concept of biomarkers can be exploited to put a check on the transformation of primary cancer into an advanced one.

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About Authors:

Samad A, Lecturer, D.J.College of Pharmacy, Niwari Road, Modinagar (U.P.)-201204

Kamal Dua, Lecturer, D.J.College of Pharmacy, Niwari Road, Modinagar (U.P.)-201204

Vijay Kumar Sharma, Assistant Professor, D.J.College of Pharmacy, Niwari Road, Modinagar (U.P.)-201204.

Pranav Sharma, Lecturer, D.J.College of Pharmacy, Niwari Road, Modinagar (U.P.)-201204.

Sunil Prajapati, Lecturer, D.J.College of Pharmacy, Niwari Road, Modinagar (U.P.)-201204.

V.P. Yadav, Lecturer, D.J.College of Pharmacy, Niwari Road, Modinagar (U.P.)-201204.