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Posts Tagged ‘carrier’


Reproductive Genetic Testing

Reporter and Curator: Sudipta Saha, Ph.D.

Reproductive genetics, a field of medical genetics integrated with reproductive medicine, assisted reproduction, and developmental genetics, involves a wide array of genetic tests that are conducted with the intent of informing individuals about the possible outcomes of current or future pregnancies. The tests themselves can include the analysis of chromosomes, DNA, RNA, genes, and/or gene products to determine whether an alteration is present that is causing or is likely to cause a specific disease or condition.

Types of Tests

In general, reproductive genetic testing involves the following categories of tests:

Carrier testing is performed to determine whether an individual carries one copy of an altered gene for a particular recessive disease. The term recessive refers to diseases that will occur only if both copies of a gene that an individual receives have a disease-associated mutation; thus, each child born to two carriers of a mutation in the same gene has a 25 percent risk of being affected with the disorder. Examples of carrier tests include those for

Couples are likely to have carrier tests if they are at higher risk of having a child with a specific disorder because of their racial or ethnic heritage or family history. Carrier testing is often done in the context of family planning and reproductive health.

Preimplantation diagnosis is used following in vitro fertilization to diagnose a genetic disease or condition in a preimplantation embryo. Preimplantation genetic diagnosis is essentially an alternative to prenatal diagnosis, as it allows prenatal testing to occur months earlier than conventional tests such as amniocentesis on week 18th of pregnancy, even before a pregnancy begins. Doctors can test a single cell from an eight-cell embryo that is just days old to determine, among other things, whether it is a male or female. This can provide crucial information for genetic diseases that afflict just one sex. Preimplantation genetic diagnosis has been applied to patients carrying chromosomal rearrangements, such as translocations, in which it has been proven to decrease the number of spontaneous abortions and prevent the birth of children affected with chromosome imbalances. Preimplantation genetic diagnosis techniques have also been applied to

  • increase implantation rates,
  • reduce the incidence of spontaneous abortion, and
  • prevent trisomic offspring in women of advanced maternal age undergoing fertility treatment.

A third group of patients receiving preimplantation genetic diagnosis are those at risk of transmitting a single gene disorder to their offspring. The number of monogenic disorders that have been diagnosed in preimplantation embryos has increased each year. So far, at least 700 healthy babies have been born worldwide after undergoing the procedure, and the number is growing rapidly.

Prenatal diagnosis is used to diagnose a genetic disease or condition in a developing fetus.

The techniques currently in use or under investigation for prenatal diagnosis include

  • (1) fetal tissue sampling through amniocentesis, chorionic villi sampling (CVS), percutaneous umbilical blood sampling, percutaneous skin biopsy, and other organ biopsies, including muscle and liver biopsy;
  • (2) fetal visualization through ultrasound, fetal echocardiography, embryoscopy, fetoscopy, magnetic resonance imaging, and radiography;
  • (3) screening for neural tube defects by measuring maternal serum alpha-fetoprotein (MSAFP);
  • (4) screening for fetal Down Syndrome by measuring MSAFP, unconjugated estriol, and human chorionic gonadotropin;
  • (5) separation of fetal cells from the mother’s blood; and
  • (6) preimplantation biopsy of blastocysts obtained by in vitro fertilization.

The more common techniques are amniocentesis, performed at the 14th to 20th week of gestation, and CVS, performed between the 9th and 13th week of gestation. If the fetus is found to be affected with a disorder, the couple can plan for the birth of an affected child or opt for elective abortion.

Newborn screening is performed in newborns on a public health basis by the states to detect certain genetic diseases for which early diagnosis and treatment are available. Newborn screening is one of the largest public health activities in the United States. It is aimed at the early identification of infants who are affected by certain genetic, metabolic or infectious conditions, reaching approximately 4 million children born each year. According to the Centers for Disease Control and Prevention (CDC), approximately 3,000 babies each year in the United States are found to have severe disorders detected through screening. States test blood spots collected from newborns for 2 to over 30 metabolic and genetic diseases, such as

  • phenylketonuria,
  • hypothyroidism,
  • galactosemia,
  • sickle cell disease, and
  • medium chain acyl CoA dehyrogenase deficiency.

The goal of this screening is to identify affected newborns quickly in order to provide treatment that can prevent mental retardation, severe illness or death.

It is possible that somatic cell nuclear transfer (cloning) techniques could eventually be employed for the purposes of reproductive genetic testing. In addition, germline gene transfer is a technique that could be used to test and then alter the genetic makeup of the embryo. To date, however, these techniques have not been used in human studies.

Ethical Issues

Any procedure that provides information that could lead to a decision to terminate a pregnancy is not without controversy. Although prenatal diagnosis has been routine for nearly 20 years, some ethicists remain concerned that the ability to eliminate potential offspring with genetic defects contributes to making society overall less tolerant of disability. Others have argued that prenatal diagnosis is sometimes driven by economic concerns because as a society we have chosen not to provide affordable and accessible health care to everyone. Thus, prenatal diagnosis can save money by preventing the birth of defective and costly children. For reproductive genetic procedures that involve greater risk to the fetus, e.g., preimplantation diagnosis, concerns remain about whether the diseases being averted warrant the risks involved in the procedures themselves. These concerns are likely to escalate should

  • cloning or
  • germline gene transfer

be undertaken as a way to genetically test and select healthy offspring.

SOURCE:

http://www.genome.gov/10004766

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Author: Tilda Barliya PhD

Title: Factors affecting the PK of the nanocarrier.

Category: Nanotechnology in drug delivery

A plethora of new products are emerging as potential therapeutic agents. This calls for detailed studies of their unique pharmacologic characteristics and mechanisms of action in humans. This review written by Caron WP et al (Zamboni’s group) provides a major overview of the factors that affect the pharmacokinetics (PK) and pharmacodynamics (PD) of nanoparticle carries in preclinical models and patients (1). I will use this article as the main source as it was so nicely written yet many other references are added within.

The disposition of carrier-mediated agents (CMAs) is dependent on the carrier and not on the parent drug, until the drug is released from the carrier into the system and includes encapsulated (the drug within or bound to the carrier), released (the active drug that gets released from the carrier), and sum total (encapsulated drug plus released drug).

After the drug has been released from its carrier, it is pharmacologically active and subjected to the same routes of metabolism and clearance (CL) as the non-carrier form of the drug (1,2).

In theory, the PK disposition of the drug after it is released from the carrier should be the same as after administration of the small-molecule or standard formulations. Therefore, the pharmacology and PK of CMAs are complex and call for comprehensive analytical studies to assess the disposition of encapsulated and released forms of the drug in plasma and tumor.

Interindividual variability in drug exposure, represented by area under the plasma concentration– time curve (AUC) of the encapsulated drug and several factor can potentially affect it:

  • Physical characteristics of the CMA (size, charge, surface modification). Figure 1
  • Host-associated characteristics such as gender and age as well as the host mononuclear phagocyte system (MPS), which is a collective term for the immune cells.

F3.large.jpg (1280×843)

Figure 1 here (=figure 3 in the original paper. ref 1) : Nanoparticle clearance and biocompatibility are dependent on various factors including physical characteristics of the carrier as well as physiologic parameters such as the mononuclear phagocyte system (MPS) (reticuloendothelial system (RES)) recognition and enhanced permeability and retention (EPR) effect. There are qualitative relationships between the independent variables, namely, particle size, particle zeta-potential (surface charge), and solubility, and the dependent variable, namely, biocompatibility. Biocompatibility, or extent of exposure (area under the plasma concentration–time curve), includes the route of uptake and clearance (shown in green as the EPR effect and renal and biliary clearance), cytotoxicity (shown in red, can represent either efficacy or toxicities/ adverse events in anticancer treatment), and MPS/RES recognition (shown in blue).

The effect on the immune cells is divided into two categories:  (i) responses to nanoparticles that are specifically modified to stimulate the immune system (e.g., vaccine carriers) and (ii) undesirable interactions and/or side-effects.

Immune cells that participate in nanoparticle uptake are circulating monocytes, platelets, leukocytes, and dendritic cells in the bloodstream (3,4).  In addition, nanoparticles can be taken up in tissues by phagocytes, e.g., by Kupffer cells in the liver, by dendritic cells in the lymph nodes, by B cells in the spleen, and by macrophages

Uptake mechanisms may occur through different pathways and can often be facilitated by the adsorption of opsonins to the nanoparticle surface

Physical characteristics:

  • Particle size: In one study of liposomes, particles that had a hydrodynamic diameter between 100 and 200 nm had a fourfold higher rate of uptake in tumors than particles <50 nm or >300 nm.
  • Surface modification: Conjugated PEG polymer onto the surface- is known to minimize opsonization and thus subsequent decreased rate of MPS uptake overall plasma exposures of drugs contained within PEGylated liposomes were six fold higher than those contained within non-PEGylated liposomes
  • Surface charge: Uncharged liposomes have lower CLs than either positively or negatively charged liposomes (probably due to reduced opsonization by MPS. rate of CL from blood was significantly higher for negatively charged particles than for uncharged particles

It can be summarized as for their rate of clearance from highest (left) to lowest (right) as:

positive>negative> neutral

Note: PEGylation can alter the alter this rate significantly for example,

Levchenko et al. showed that the negative charge on liposomes can be shielded with this physical alteration, leading to a significantly reduced rate of liver uptake and consequent prolongation of their presence in circulating blood (5).

Host characteristics

  • Age: In some cases, age-related effects on the PK of some PEGylated liposomal agents have been reported, where in younger male patients (<60) there was a higher rate of clearance of two different agents (Doxil and CDK602) compared to older patients (>60). In other words, in older age, the CL rate was lower and therefore higher AUC/dose. No relation to age was observed for female patients, in the same study.

Alterations in the PK and PD of CMAs may involve accerelated decline in immune system functioning, specifically the association between aging and the functioning of monocytes (6). In theory, there is a loss of MPS activity or function in elderly patients, and this decreases the CL of CMAs by the MPS, leading to increased drug exposures and toxicity in elderly patients. In terms of efficacy, greater age was inversely proportional to progression-free survival; however, no correlation was found between age and overall survival.

  •  Gender: In similar study to the one presented above, female patients had overall lower CL of DOXIL, IHL-305 and CDK602 compared to male patients of the same age.

The basis for the gender-related differences in the PK and PD of CMAs is unclear. It has been hypothesized that some of the differences may be attributed to the effects of sex hormones such as testosterone and estrogen on immune cell function.

Delivery of CMAs Into Tumor

Major advances in the understanding of tumor biology have led to the discovery of targeted agents that can deliver drugs to the desired site while minimizing exposure in normal tissues, thereby minimizing the associated adverse effects. Whereas conventional drugs encounter numerous obstacles en route to their target, CMAs can take advantage of a tumor’s leaky vasculature to extravasate into tissue, via the enhanced permeability and retention effect (EPR).

Note: The extend of the EPR effect is highly debated since although passive targeting through the EPR effect has been a key concept in delivering CMAs to tumors, it does not ensure uniform delivery to all regions of tumor. Furthermore, not all tumors exhibit an EPR effect, and the permeability of vessels may not be the same across any single tumor.

Active targeting may overcome these limitations. The CMAs can be enabled to bind to specific cells in a tumor by using surface attached ligands that are capable of recognizing and binding to cells of interest.

Antibody-mediated targeting has been the method of choice, other targeting strategies using nucleic acids, carbohydrates, peptides, aptamers, vitamins, and other agents are also being evaluated.

Other major points that can affect the PK disposition

  • The linearity and nonlinearity of the CLs of a drug (might be associated with the dose like with S-CKD602)(7).
  • Drug-drug interaction (single agent vs combination)
  • Body composition (Body surface area, body weight)

There are a multitude of properties of CMAs that differ from those of the active small-molecule drugs they contain. These differences lead to significant variability in the PK and PD of carrier- mediated drugs. It has been shown that physical properties, the MPS, the presence of tumors in the liver, EPRs, drug–drug interactions, age, and gender all contribute in varying degrees to the PK disposition and PD end points of CMAs in patients.

Areas of research that can aid in an understanding of how these agents should be used and how we may predict their actions in patients include pharmacogenomics, cellular function (probing the MPS), more sensitive and accurate analytical PK methods, and identification of the optimal preclinical (animal and in vitro) models.

References:

1. W P Caron, G Song, P Kumar, S Rawal and W C Zamboni.Interpatient PK and PD variability of carrier-mediated anticancer agent.  Clinical Pharmacology and Therapeutics 2012 91, 802-812 http://www.nature.com/clpt/journal/vaop/ncurrent/full/clpt201212a.html

2. Zamboni, W.C. Liposomal, nanoparticle, and conjugated formulations of anticancer agents. Clin. Cancer Res. 11, 8230–8234 (2005).

http://clincancerres.aacrjournals.org/content/11/23/8230.long

http://clincancerres.aacrjournals.org/content/11/23/8230.full.pdf+html

3. Dobrovolskaia, M.A., Aggarwal, P., Hall, J.B. & McNeil, S.E. Preclinical studies to understand nanoparticle interaction with the immune system and its potential effects on nanoparticle biodistribution. Mol. Pharm. 5, 487–495 (2008). http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2613572/

4. Dobrovolskaia, M.A. & McNeil, S.E. Immunological properties of engineered nanomaterials. Nat. Nanotechnol. 2, 469–478 (2007). http://www.ncbi.nlm.nih.gov/pubmed/18654343

5. Levchenko, T.S., Rammohan, R., Lukyanov, A.N., Whiteman, K.R. & Torchilin, V.P. Liposome clearance in mice: the effect of a separate and combined presence of surface charge and polymer coating. Int. J. Pharm. 240, 95–102 (2002). http://www.ncbi.nlm.nih.gov/pubmed/12062505

6. Lloberas, J. & Celada, A. Effect of aging on macrophage function. Exp. Gerontol. 37, 1325–1331 (2002). http://www.ncbi.nlm.nih.gov/pubmed/12559402

7. Zamboni, W.C. et al. Pharmacokinetic study of pegylated liposomal CKD-602 (S-CKD602) in patients with advanced malignancies. Clin. Pharmacol. Ther. 86, 519–526 (2009). http://www.nature.com/clpt/journal/v86/n5/abs/clpt2009141a.html

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