P16

Klinipath BV is de Nederlandse distributeur van de marker p16INK4

Hierbij kunt u de p16 flyer "CINtec® p16: The Breakthrough in Managing ASC-US And LSIL Cytology Results" downloaden

- Use of p16-INK4A overexpression to increase the specifi city of human papillomavirus testing: a nested substudy of the NTCC randomised controlled trial

Francesca Carozzi, et al.

Summary: Background Human-papillomavirus (HPV) testing is more sensitive, but less specifi c, than conventional cytology for

detecting high-grade cervical intraepithelial neoplasia (CIN). We assessed whether HPV testing with triage by

p16-INK4A overexpression can increase specifi city while maintaining sensitivity. download

- Via bijgaande link kunt u zowel de histologische- als cytologische beelden met de p16INK4a in de digitale atlas beoordelen. http://www.mtmlabs.com/cda/atlas/content-120306.html

Uitgebreide literatuur over p16INK4a is te vinden op: http://www.mtmlabs.com/cda/science_technology/literature/content-118651.html

CINtec Cytologiekit p16INK4a download

CINtec Histologiekit p16INK4a download

p16INK4a

p16INK4a is the biomarker mtm is targeting with its patent protected products to develop sensitive diagnostics for cervical cancer. This cyclin-dependent kinase inhibitor demonstrates marked over-expression in cancerous and precancerous cervical tissue making it an ideal candidate as a biomarker for the disease.

Cervical cancer is known to be caused by persistent infections from high-risk Human Papilloma Virus (HR-HPV) types. The over-expression of p16INK4a is linked to the oncogenic transformation caused by persistent HR-HPV infection. However, unlike the detection of the pure presence of HR-HPV, the detection of p16INK4a over-expression points to the inactivation of the cell-cycle control mediated by the HR-HPV oncoproteins, that is the main disease process in cervical cancer.

Scientific background to cellular proliferation

Cell replication is controlled through a complex mechanism involving many regulatory pathways within the cell. One of these pathways, the retinoblastoma protein (pRB) pathway, controls cell cycle progression, and thus cellular proliferation. Under normal conditions pRB binds to the transcription factor E2F. This has the effect of blocking the transcription of genes promoting cell cycle progression and proliferation, but also the gene encoding for the cyclin-dependent kinase inhibitor, p16INK4a. In this way, under normal conditions, binding of the transcription factor E2F by pRB is one of the critical control mechanisms to prevent cells from continuous replication and proliferation.

When E2F is released from pRB, the blocking effect on the transcription of the p16INK4a gene is lost, leading to the production of functional p16INK4a protein within the cell. The p16INK4a protein ("INK4a", originating from "inhibitor of kinase 4") now in turn inhibits the phosphorylating activity of the cdk4/6 - cyclin D complex, thus shifting the balance from phosphorylated (inactive; not able to bind E2F) pRB back to non-phosphorylated (functional; able to bind E2F) pRB. This complex feedback control represents one of the key mechanisms of how cells effectively establish the fine balance between cell cycle progression/proliferation, and cell cycle arrest.

The role of p16INK4a in cervical cancer

Chronic infection with HR-HPV can in time result in the disruption of the functional protein complex pRB-E2F. One of the proteins expressed by the virus within the cell is the oncogenic protein E7. The main oncogenic activity of E7 is to impair the function of pRB. In this way pRB does not bind to the transcription factor E2F, leading to the transcription of genes that promote cell proliferation. Only in transforming HPV infections where the oncogenic process has been started, levels of E7 protein are usually elevated in replication competent cells. For that reason p16INK4a is a more accurate predictor of cervical cancer than the presence of HR-HPV.

p16INK4a as a marker independent of HR-HPV type and patient age

Since p16INK4a is a cellular protein, it can serve as a biomarker that is independent of the individual HR-HPV type and indicative of the cervical cancer disease process in action. There are several types of HR-HPV but in each case the effect of the E7 oncoproteins is the same in blocking pRB and leading to the over-expression of p16INK4a. Over-expression of p16INK4a is a direct marker of the oncogenic activity of all the various high-risk HPV types.

The presence of HPV does not mean certain future cervical cancer, and prevalence in young women can be as high as 30%. HPV testing is therefore of little use in pinpointing disease in younger women. By contrast, p16INK4a is only expressed in the oncogenic process of cervical cancer and does not show greater prevalence in young women.

In order to selectively detect p16INK4a in cervical tissue, mtm's diagnostic kits make use of the clinically validated proprietary E6H4™ antibody clone, which is highly selective and sensitive to the presence of p16INK4a. Detection with E6H4™ does not show the cross reactivity with Trichomonas (a protozoal infection of the vagina) which gives rise to a high rate of false positives with other antibody candidates. The GMP manufactured kit components in combination with the optimized antibody ensures the reproducible quality and results in assessing a wide variety of biological specimens.

Finally, mtm's p16INK4a tests are assessing the over-expression of only one cellular molecule that is revealed in cervical tissue from any woman with cancer. The test is therefore fairly simple. In contrast, tests focused on HPV DNA or HPV capsid proteins need various probes or antibody cocktails against the individual HR-HPV types, making the test necessarily more complex and error prone.

Conclusion

mtm's p16INK4a tests allow one to go one step beyond mere virus detection, which may or may not be indicative of developing cancer, to demonstrate when and only when the virus is "in oncogenic action".

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