QRT-PCR A primer for patients

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This booklet provides an overview of the quantitative Reverse Transcriptase Polymerase Chain Reaction (qRT-PCR) test. It includes a description of the qRT-PCR International Standardisation (IS) project within the context of the recently updated (2013) ELNet Recommendations and NCCN Treatment Guidelines for the treatment and management of Ph+CML based on molecular testing by qRT-PCRIS.

Transcript of QRT-PCR A primer for patients

  • QRT-PCR

    Quantitative ReverseTranscription Polymerase Chain ReactionA primer for patients

  • www.cmlsupport.org.uk page 1

    1. Background

    Introduction

    Inside the cell

    Chronic Myeloid Leukaemia and thePhiladelphia Chromosome

    Genetic Tests used at diagnosis and inthe first months of TKI therapy

    2. Quantitative ReverseTranscriptase Polymerase ChainReaction (qRT-PCR)

    What the test measures and itsrelationship to other tests

    The BCR-ABL1 gene and its constituentmRNA, the protein tyrosine kinase Bcr-Abl1

    How the qRT-PCR test works inpractice

    Factors affecting the suitability of asample sent for testing

    3. Response to treatment: the role ofqRT-PCR testing

    Levels of Molecular Response

    Why results may differ between testinglaboratories

    4. The InternationalStandardisation Project (IS)

    Establishing an international standard

    The foundation of the IS method

    Conversion Factor: How a specific locallab value is calculated to allow forconversion to the IS

    The International Standard: itsusefulness as a prognostic tool

    Four key variables necessary foroptimal qRT-PCR testing

    Switching between testing laboratories

    5. Summary

    6. Ensuring an optimal response toTKI therapy

    Adherence, the importance of takingdaily therapy

    Drug resistant mutations

    7. The Future

    New and Advanced Monitoring: q-PCRtechniques; can we do better?

    Then and now: the post imatinib era

    8. Glossary

    9. Citations

    10. References and useful links

    11. CML Support Group

    Contents

  • page 2 www.cmlsupport.org.uk

    Acknowledgements

    We are grateful to the following people for providing not only theirmedical expertise and editorial assistance but also their support for thisproject, without which this booklet could not have been realised. Withthanks and immense gratitude to

    Professor Jane F. Apperley, MBChB, MD, FRCP, FRCPath, Chief ofService for Clinical Haematology and Chair of the Department ofHaematology at Imperial College Healthcare NHS Trust, London, UK

    Dr. Dragana Milojkovic, MB,BS, FRCPath, PhD, ConsultantHaematologist at Imperial College Healthcare NHS Trust, London, U K

    Professor Letizia Foroni, MD PhD FRCPath, Consultant Scientist,Head of Imperial Molecular Pathology Laboratory, Imperial AcademicHealth Sciences Centre, Hammersmith Campus, London, UK

    Professor Timothy P. Hughes, MD, FRACP, FRCPA, Head ofDepartment of Haematology at SA Pathology, ConsultantHaematologist Royal Adelaide Hospital, Clinical Professor of Medicine,University of Adelaide, Chair and co-founder International CMLFoundation (iCMLf)

    Associate Professor Susan Branford, PhD, FFSc (RCPA) Centrefor Cancer Biology, SA Pathology, Affiliate Associate Professor,School of Medicine; School of Molecular and Biomedical Science; Schoolof Pharmacy and Health Science; University of Adelaide

    This booklet is dedicated to the memory of Professor John MGoldman (1938-2013), DM, FRCP, FRCPath, FMedSci, EmeritusProfessor and Senior Research Investigator at the Division ofInvestigative Science Imperial College, London, UK, co-founder andChair of the International CML Foundation (iCMLf). John Goldmansmajor disease interest was CML. An erudite and profoundly empatheticman, many have benefited from his observant, elegant and ever curiousmind. For that gift we remain eternally grateful.

  • Background

    Introduction

    This booklet provides an overview of the quantitative ReverseTranscriptase Polymerase Chain Reaction (qRT-PCR) test. It includes a description of the qRT-PCR International Standardisation (IS)project within the context of the recently updated (2013) ELNetRecommendations and NCCN Treatment Guidelines for the treatmentand management of Ph+CML based on molecular testing by qRT-PCRIS.

    This primer provides a useful resource for patients and others with aninterest in this important topic and will contribute to the betterunderstanding and interpretation of qRT-PCR results and response totreatment. For simplicity the test is referred to as q-PCR throughout.

    We hope this primer also serves as an exemplar in a healthcareenvironment where patients face a lifetime on therapy, enabling an indepth understanding, not just of the disease and its current treatments,including those in development, but also test methodologies used tomonitor responses to therapy.

    This primer has been developed following a suggestion from patient self-educators as a way to encourage a better understanding of q-PCRtesting. The draft was further developed by Sandy Craine who is theauthor of the text on behalf of the CML Support Group.

    Inside the cell

    Normally each of us inherits 23 pairs of homologous chromosomes (twin pairs with the same basic structure) one set from our father and one set from our mother, making 46 chromosomes in total. Each pair is numbered from 1 to 22 according to size. Number 23 is the pair thatdefines gender, containing either an X and a Y chromosome in men, or two X chromosomes in women.

    All 23 pairs are found in the nucleus or engine of all blood cells apart from red cells.

    www.cmlsupport.org.uk page 3

    1.

  • 23 23

    1

    9

    17

    or

    18

    2

    10

    7

    15

    8

    16

    3

    11

    19

    6

    14

    22

    12

    20

    4

    13

    21

    5

    Sex ChromosomesAutosomesXX (female) XY (male)

    Each chromosome has a constriction point (centromere) dividing it intotwo sections or arms. The short arm is labelled the p arm (for petite); q (chosen as the next letter after p in the alphabet) indicates the long arm.The location of the centromere gives each chromosome its characteristicshape and helps describe where specific genes are located. Changes to thebasic structure of chromosomes can sometimes occur, possibly throughexposure to ionizing radiation, environmental toxins or for other unknownreasons. A Genome describes a complete set of DNA code; the humangenome has been estimated to contain approximately 30,000 genes.

    Normal human karyotype shows 2 sets of 23 chromosomes

    Chromosomes are not visible in the nucleus unless the cell is in its dividingphase. They are actually long strands of DNA which, during the process ofcell division become tightly packed; only then are they visible under amicroscope. Most of what we know about chromosomes was learned byresearchers observing cells during the dividing cycle.

    page 4 www.cmlsupport.org.uk

  • BCR

    #9 #22

    ABL1

    ABL1BCR

    der 9 PhiladelphiaChromosome 22

    Before translocation After translocationDuring translocation

    Chronic Myeloid Leukaemia and the Philadelphia Chromosome

    The Philadelphia chromosome is an acquired abnormality and is thedefinitive marker for CML. It is formed when chromosomes 9 and 22 swopone part each with the other. It is not yet understood why this happens. CMLis not an inherited condition and as such cannot be passed on to children.

    Known as a reciprocal translocation, a piece containing the ABL1 genefrom the bottom part of chromosome 9 breaks off and attaches to a regionon chromosome 22 where the BCR gene is located, thus forming a newchromosome 22 containing the abnormal fusion gene BCR-ABL1

    The new shortened chromosome 22 is called the Philadelphiachromosome. You might also see it written as t(9; 22). The BCR-ABL1.fusion gene makes a protein called a tyrosine kinase. These kinds ofproteins are located on or near the surface of cells and send signals thatspeed up cell division.

    Ph+CML is a rare disease with an incidence of 1 to 1.5 new cases per100.000 people each year. It is very rare in young people under 19 andultra-rare in young children.

    A reciprocal translocation of ABL1 and BCR results in an abnormalchromosome 22 The Philadelphia Chromosome

    www.cmlsupport.org.uk page 5

  • In approximately 95% of cases, the Ph chromosome is detected bycytogenetic analysis. In around 5% of the remaining suspected cases, thePh chromosome is not visible. However, the BCR-ABL1 fusion gene can beidentified by molecular testing with q-PCR in approximately half of thosecases. For simplicity, any disease that contains the BCR-ABL1 fusion geneis referred to as Ph+ CML. If you do not have the Ph chromosome orevidence of the BCR-ABL1 gene then you do not have CML.

    It has been shown that the BCR-ABL1 fusion gene is the single definitivemarker for Ph+ CML and remains the key abnormality throughout thechronic phase of the disease.

    The BCR-ABL1 fusion gene translates as a protein tyrosine kinase,referred to as Bcr-Abl1. The activity of tyrosine kinases is typicallycontrolled by other molecules, but the mutant tyrosine kinase producedby the BCR-ABL1 gene means the signal for cell division is alwaysswitched on. Its continuous activity sets up a cascade of events thatallows for unregulated cell division (cancer). Over time the Ph+ cellsoverpopulate the marrow, crowding out normally functioning cells.

    Since the introduction of targeted therapy with tyrosine kinase inhibitors(TKIs), it is increasingly evident that, at least in chronic phase, when cellscontaining the BCR-ABL1 gene are reduced to very low levels, the risk ofdisease progression is significantly reduced.

    Genes are denoted with italicized capitals as in ABL1 ; BCR etc., whereasproteins are denoted with non-italicized capitals, sometimes followed bylower case, as in Bcr-Abl1.

    page 6 www.cmlsupport.org.uk

  • nucleus

    cell

    cytoplasm

    chromosome DNA

    mRNA

    A cell nucleus showing chromosomes, DNA and its duplicate mRNA (visibleinside the two strands)

    Genetic Tests used at diagnosis and in the first months of