PARP-1 and Prostate Cancer

 

Edited by:Mohammad  Hezarkhani  MD,Urologist

Board-Certified of Urology,Tehran  University ,The Member  of  Iranian  Urological  Association

http://www.facebook.com/#!/mohammad.hezarkhani.1

11/october/2012 

Prostate cancer (PCa) is the leading cancer diagnosed in men, with one out of seven developing PCa and a quarter of those progressing to an advanced stage of the disease. Intense research is ongoing to be able to predict the probability of disease progression. As current nomograms are solely composed of clinico-pathological factors, the inclusion of molecular markers may potentially increase their precision. The over-expression of poly(ADP-ribosyl) polymerase-1 (PARP-1) is associated with colorectal cancer progression as well as a poor prognosis in ovarian and breast cancers. researchers hypothesized that the proportion of PARP-1 positive (+) nuclei would increase with PCa progression. The present study evaluated the value of PARP-1 in predicting biochemical recurrence (BCR) in PCa patients.

Poly(ADP-ribose) polymerase-1 (PARP-1) is an abundant nuclear enzyme that modifies substrates by poly(ADP-ribose)-ylation.

PARP1 works:

• By modifying nuclear proteins by poly ADP-ribosylation.
• In conjunction with BRCA, which acts on double strands; members of the PARP family act on single strands; or, when BRCA fails, PARP takes over those jobs as well.

PARP1 is involved in:

• Differentiation, proliferation, and tumor transformation
• Normal or abnormal recovery from DNA damage
• May be the site of mutation in Fanconi anemia
• May participate in the pathophysiology of type I diabetes.

PARP1 is activated by:

• Helicobacter pylori in the development and proliferation of gastric cancer.

Role in DNA damage repair

PARP1 has a role in repair of single-stranded DNA (ssDNA) breaks. Knocking down intracellular PARP1 levels with siRNA or inhibiting PARP1 activity with small molecules reduces repair of ssDNA breaks.

In the absence of PARP1, when these breaks are encountered during DNA replication, the replication fork stalls, and double-strand DNA (dsDNA) breaks accumulate. These dsDNA breaks are repaired via homologous recombination (HR) repair, a potentially error-free repair mechanism. For this reason, cells lacking PARP1 show a hyper-recombinagenic phenotype (e.g., an increased frequency of HR), which has also been observed in vivo in mice using the pun assay. Thus, if the HR pathway is functioning, PARP1 null mutants (cells without functioning PARP1) do not show an unhealthy phenotype, and in fact, PARP1 knockout mice show no negative phenotype and no increased incidence of tumor formation.

Interaction with BRCA1 and BRCA2

However, both BRCA1 and BRCA2 are at least partially necessary for the HR pathway to function. Therefore, cells that are deficient in BRCA1 or BRCA2 have been shown to be highly sensitive to PARP1 inhibition or knock-down, resulting in cell death by apoptosis, in stark contrast to cells with at least one good copy of both BRCA1 and BRCA2. Many breast cancers have defects in the BRCA1/BRCA2 HR repair pathway due to mutations in either BRCA1 or BRCA2, or other essential genes in the pathway (the latter termed cancers with "BRCAness"). Tumors with BRCAness are hypothesized to be highly sensitive to PARP1 inhibitors, and it has been demonstrated in mice that these inhibitors can both prevent BRCA1/2-deficient xenografts from becoming tumors and eradicate tumors having previously formed from BRCA1/2-deficient xenografts.

The team, led by Karen E. Knudsen, Ph.D., Professor in the Departments of Cancer Biology, Urology, & Radiation Oncology at Thomas Jefferson University, found that functions of PARP-1 not only include DNA damage repair but also androgen receptor (AR) regulation in advanced prostate cancer growth and progression. PARP inhibition in various models was found to suppress AR activity, which fuels prostate growth.

Researchers believe that the dual functions of PARP-1 -- as both a regulator of AR as well as critical for DNA damage repair -- could be leveraged for therapeutic benefit. PARP inhibitors could slow down advanced-stage prostate cancer and shrink tumors, the team surmises.

"Our data show that PARP-1 plays a major role in controlling AR function and that, when suppressed with inhibitors, enhanced anti-tumor effects of castration and delayed onset to castration resistance. " 

Today, PARP-1 is seen as a valuable target because of its involvement in DNA damage repair for cancer cells. The therapy has been successful when combined with DNA-damaging drugs because it heightens the apoptotic activity of these drugs. In other words, it helps halt tumor growth by stopping DNA repair in various cancers.

Prostate cancer is dependent on AR activity for growth and survival, and is largely resistant to standard chemotherapy. AR-directed therapies are the first-line intervention for patients with advanced disease; however, recurrent tumors arise when AR is reactivated, a common occurrence in the castrate-resistant stage of the disease.

Therefore, there is a dire need to develop means to suppress the AR function in these patients. With this new role defined, PARP inhibitors targeting both functions could sensitize prostate cancer cells to DNA damage, and potentially improve the efficacy of AR-directed therapies in these patients, the researchers suggest in the paper. Almost 40 percent of men with prostate cancer progress into an advanced stage, termed castrate-resistant prostate cancer, where chemotherapy and other therapies have little to no effect.

Finally, in a novel explant system of primary human tumors, targeting PARP-1 potently suppresses tumor cell proliferation. Collectively, these studies identify novel functions of PARP-1 in promoting disease progression, and ultimately suggest that the dual functions of PARP-1 can be targeted in human PCa to suppress tumor growth and progression to castration-resistance.

Reference:

1. M. J. Schiewer, J. F. Goodwin, S. Han, J. C. Brenner, M. A. Augello, J. L. Dean, F. Liu, J. L. Planck, P. Ravindranathan, A. M. Chinnaiyan, P. McCue, L. G. Gomella, G. V. Raj, A. P. Dicker, J. R. Brody, J. M. Pascal, M. M. Centenera, L. M. Butler, W. D. Tilley, F. Y. Feng, K. E. Knudsen. Dual roles of PARP-1 promote cancer growth and progression. Cancer Discovery, 2012; DOI: 10.1158/2159-8290.CD-12-0120

2-Implication of PARP-1 expression in prostate cancer progression.

 E. Thomas, P. O. Gannon, I. H. Koumakpayi, M. Latour, A. Mes-Masson, F. Saad; CRCHUM-Institut du Cancer de Montreal, Montreal, QC, Canada; Research Center of the Universite de Montreal Hospital Center (CRCHUM) - Institut du Cancer de Montreal, Montreal, QC, Canada; CHUM - Hopital Notre Dame, Montreal, QC, Canada; Centre Hospitalier de l'Université de Montréal, Montreal, QC, Canada; Research Center of the Universite de Montreal Hospital Center, Institut du Cancer de Montreal, Montreal, QC, Canada; University of Montreal Hospital Center, Montreal, QC, Canada . J Clin Oncol 29: 2011

3- Wikipedia, The Free Encyclopedia  12/December/2011 

 

 

 

 

 

 

Epothilones: tubulin polymerization as a novel target for prostate cancer therapy

 

 Nature Clinical Practice Oncology | February 1, 2009 | Lee, James J.; Kelly, W. Kevin 

KEY POINTS

* Microtubules are an excellent target for anticancer drugs

* Microtubule-stabilizing agents such as taxanes and epothilones exert cytotoxic effects by stabilization of microtubule dynamics

* Several epothilones are currently in active clinical development: ixabepilone, patupilone, BMS-310705, KOS-862, KOS-1584, and ZK-EPO

* Epothilones have shown important antitumor activity in several tumor types, including prostate cancer

* Ixabepilone and patupilone have shown encouraging clinical activity in patients with castrate metastatic prostate cancer

INTRODUCTION

Microtubules are vital and dynamic cellular organelles, and have a critical role in cellular functions such as cell division and transport of vesicles and organelles. Microtubules are hollow tubes composed of linear, polymerized [alpha][beta]-tubulin protofilaments. The unique polymerization features of microtubules enable specific biologic functions, and several agents can target their polymerization function. Agents such as taxanes and epothilones exert their cytotoxicity by stabilizing microtubules and promoting the assembly of [alpha][beta]-tubulins.  

Taxanes remain one of the most effective chemotherapy agents, and have a broad spectrum of antitumor activity in prostate, breast, and non-small-cell lung cancer. Since the introduction of taxanes, a great deal of effort has been made to understand and overcome their limitations, particularly the development of drug resistance. One of the main mechanisms of resistance to taxanes is the development of multidrug resistance, which is mainly mediated by overexpression of the ATP-binding cassette family of transmembrane transporters, among which P-glycoprotein is the best known. The alteration of tubulin structure, as a result of point mutations, is suspected to be another important mechanism for taxane resistance on the basis of in vitro and in vivo data.   

The great success of taxane therapy provided the rationale to develop novel agents with similar mechanisms of action and improved properties in relation to multidrug resistance, efficacy, and safety profiles. Epothilones are macrolides that were isolated from the myxobacterium Sorangium cellulosum in 1987.  Subsequently, epothilones were found to be strong promoters of tubulin polymerization in vitro, and to induce G2-M cell-cycle arrest and cytotoxicity.  Epothilones have strong cytotoxic effects against several human cancer types in cell culture systems and mouse xenograft models.  

Although epothilones are similar to taxanes in terms of their mechanism of action , they have several advantages over taxanes that govern their clinical application.  First, epothilones are less likely to induce multidrug resistance than taxanes; they have strong anti-proliferative activity in human cancer cells with high expression of genes involved in the development of resistance such as ABCB1 (previously known as MDR), especially those that also express high levels of P-glycoprotein.

 Epothilones have also demonstrated antiproliferative activity in taxane-resistant human cancer cell lines,  and in malignant cells that have become resistant to taxanes because of tubulin mutations.  The clinical implication of this observation is not clear yet. Second, epothilones are more water-soluble than taxanes, and so require little or no formulation vehicle such as Cremophor[R] (BASF Aktiengesellschaft, Germany). Thus, epothilone-treated patients require less premedication with sensitizing agents such as dexamethasone than taxane-treated individuals. These characteristics of epothilones have generated great interest.  

Several epothilones are currently in active clinical development: ixabepilone, patupilone, BMS-310705, KOS-862, KOS-1584, and ZK-EPO (Table 1).  This Review will summarize the existing preclinical and clinical information about epothilones, and will focus on the role of epothilones in the management of castrate metastatic prostate cancer (CMPC).  

MECHANISM OF ACTION OF EPOTHILONES

In vitro, epothilones induce tubulin polymerization into microtubules, and have kinetics similar to those of paclitaxel. Epothilone A and epothilone B are natural products that share the same structure, except for an additional methyl group on the C12 of epothilone B . Epothilone A and epothilone B have similar kinetics for the competitive inhibition of binding of paclitaxel to mammalian tubulin in vitro, which suggests that all three agents have a common binding site on tubulins. The inhibition constant is 0.6 [micro]M for epothilone A and 0.4 [micro]M for epothilone B, as assessed by Dixon analysis. 

 Epothilones and paclitaxel, however, have different activity against microtubules isolated from yeast, which indicates that they might have different characteristics in relation to tubulin binding. Epothilone B causes a stronger growth inhibition in human cancer cells in vitro than epothilone A, especially in cancer cells such as the human colon cancer cell line SW620 (I[C.sub.50] [the concentration needed to achieve 50% growth inhibition] 0.1 versus 2.0 nM) and the human ovarian cancer cell line 1A9 (I[C.sub.50] 0.06 versus 2.00 nM).  

Epothilones enhance microtubule stability and bundling in vitro. In a cell-culture system, epothilone A and epothilone B induced cell-cycle arrest at the G2-M transition and exerted cytotoxic effects similar to those of paclitaxel. Suppression of microtubule dynamics by epothilones is associated with mitotic arrest. In cell-culture systems, epothilone B suppressed microtubule dynamics in a concentration-dependent manner, similarly to paclitaxel.  

KIDNEYS

 

Edited by:Mohammad  Hezarkhani  MD,Urologist

Board-Certified of Urology,Tehran  University ,The Member  of  Iranian  Urological  Association

http://www.facebook.com/#!/mohammad.hezarkhani.1

6/october/2012 

Gross Appearance

Bilateral bean shaped retroperitoneal organ lie along lat. borders of psoas muscles and are therefore obliquely placed (lower pole lat.).

liver → RK lower than LK.

Size: 12 X 6 X 3 cm

weight = 150 g.

 

Renal Hilum is shallow depression at cenre of medial border, transmits:

• renal vein: ant.
• Renal artery: middle
• Renal pelvis: posterior (post. segmental pass behind upper part of pelvis)
• & lymphatics & pelvis pass.

Renal sinus is space interior to hilum, contain major vessels, pelvis, majr calyces, minor calyces & sinus fat.

Coverings  

1-Renal capsule (fibrous & adherent to parenchyma)

2-Perinephric fat: inside Gerota’s f.

3- Perirenal (Gerota’s) fascia: ·surround kidney, perinephric fat & adrenal

·2 laminae:

Ø  anterior lamina ® fascia of Toldt (thin)

Ø  posterior lamina ® fascia of Zuckerkandl (thicker)

·encloses the kidney on all sides except inferiorly (remains an open potential space) ·Medially: fuse with the contralateral side across the midline.

4-aranephric fat: outside Gerota’s f.

 

Supported

Kidney is supported by:

1-coverings (as above)

2-renal vascular pedicle,

3-abdominal muscle tone,

4-bulk of the abdominal viscera.

 Supporting Tissue

The renal stroma is composed of loose connective tissue and contains blood vessels, capillaries, nerves, and lymphatics.

average descent on inspiration or upright position = 4-5 cm.

Lack of mobility = abnormal fixation (eg, perinephritis),

extreme mobility = not necessarily pathologic.  

Longitudinal section: composed of:

Renal capsule: thick & penetrated by capsular vessels

Renal parenchyma

1-cortex (outer), homogeneous appearance. columns of Bertin are parts of cortex projecting between the papillae and fornices toward renal sinus.

2-medulla (central), formed of pyramids (converging collecting renal tubules), their tips called papillae → drain into the minor calices (at tip of papillae or into pelvis itself).

3-Pelvicalyceal system: internal calices and pelvis.

Relations:

Posterior (both kidneys)

Above: diaphragm

Below: psoas ms, quadratus lumburum & transversus abdominis (from med. To lat.)

 

Anterior (different bet. Rt & LT)

Rt kidney	Lt kidney
Above: suprarenal, Liver (Rt lobe) Hilum: duodenum 2^nd part Below: Rt colic flex., jejunum	Above: suprarenal, stomach, spleen Middle: pancreas Below: Lt colic flexure, jejunum

 

Microscopic anatomy

Cortex is 

Microscopic anatomy

Cortex is composed mainly of nephrons

Medulla is composed mainly of collecting ducts

Nephron

The functioning unit of the kidney composed of a tubule that has both secretory and excretory functions

1- secretory part of nephron: in the cortex and consists of:

a) renal corpuscle is composed of the vascular glomerulus + Bowman's capsule.

b) secretory part of the renal tubule: PCT, LH & DCT

2- excretory part of nephron: in the medulla  = collecting tubule (CD), continuous with DCT. It empties its contents through the tip (papilla) of a pyramid into a minor calyx.

Nephrons are 2 types:

Cortical nephrons: all parts in cortex

Juxtamedullary nephrons: glomerulus close to cortico-medullary junction & other parts in medulla.

Renal corpuscle:

1-glomerulus (capillary tuft) projects into Bowman’s capsule, supplied by afferent a. (from interlobular a.) & drained by efferent a. (to peritubular capillaries)

2-Bowman's capsule: concave  consists of 2 layers:

Visceral (inner): endothelium & epithelial cells (podocytes)→ foot processes(pedicles) that cover endothelial pores

Parietal (outer): simple squamous epith.Bowman space: space bet. both layers, continuous with epithelium of PCT. PCT: (longest part): cuboidal epith. covered by microvilli LH: 2 limbs

thin descending limb: descend to medulla thick ascending limb: cuboidal & columnar epith. DCT: cuboidal epith.has straight part (contain macula densa cells adjacent to glomerulus) & convoluted part, ends in CD.

DCT lie adjacent to afferent arteriole → modify cells of both forming JGA (juxtaglomerular apparatus) formed by: macula densa cells (in DCT) + juxtaglomerular cells (in afferent arteriole) +CD: straight, in renal pyramid (medulla) →open into papillae in terminal duct of Bellini Tubule is name of parts covered by cuboidal epith.

Blood Supply

Very important bec. main function of kidney is regulation of volume & composition of blood & for nephrectomy & nephrolithotomy.

Renal arteries carry 20% of COP

A. Arterial

renal artery is a branch of the aorta at T2 (just below sup.mes.a.)

→ branch before it reaches renal hilum → 2 branches (post. segmental (1^st) & ant. segmental) → branches lie in hilum between renal vein (anterior) & pelvis (posterior).

·Posterior segmental branch (no branches)→ mid segment of the posterior surface (first it lies bet. RV & pelvis →then→ pass post to upper part of pelvis).

·Anterior segmental branch → upper and lower poles + entire anterior surface via 3-4 branches:

Ø  apical,

Ø  upper,

Ø  middle,

Ø  lower (basal)

→ Inside parenchyma, main branches further divides into → interlobar arteries, which ascend in the columns of Bertin (between the pyramids) → arcuate arteries (arch along the base of the pyramids) → interlobular arteries→ afferent arterioles → glomeruli → efferent arterioles → peritubular capillaries → supply blood to rest of nephron → Vasa recta are long vessels parallel to LH.

·kidney has 4 vascular segments:

Ø  anterior

Ø  posterior  

Ø  apical 

Ø  basal 

·The renal arteries are all end arteries, If ligated → infarction

·Brodel avascular white line: longitudinal true avascular plane between the posterior and anterior segmental & lies just posterior to the lateral aspect of the kidney (on post. surface of kidney). (Variable position)

·In duplication: each segment have its own arterial supply (2 branches from aorta).

B. Venous

paired with the arteries, but intercommunicating (any of them will drain the entire kidney if the others are ligated).

Peritubular capillaries → interlobular veins → arcuate vs → interlobar vs → segmental vs (3-5)→ main renal vein

Rt renal vein: no tributaries outside kidney (+/-)

Lt renal vein: tributaries, Lt adrenal (above) & Lumbar veins (behind) & Lt gonadal (below)

accessory renal vessels are common & may compress ureter → UPJO.

Nerve Supply (autonomic)

from the renal plexus. (over aorta just above renal a.) which receives:

Ø  Sympathetic from T11- L2

Ø  Parasympathetic from vagus

enter through hilum & accompany the renal a. in renal parenchyma.

Kidney share autonomic innervation with other organs → GIT S/S with GUT ds

Lymphatics

3 lymphatic plexuses (parenchymal, subcapsular & perinephric) → Lumbar(Retroperitoneal)  L.N.s (Rt → interaortocaval, precaval & Lt → paraaortic). 

CALYCES, RENAL PELVIS  

Gross Appearance

1. Calices: tips of the minor calices (8-12) indented (cupped) by pyramids→ unite to form 2 or 3 major calices, → unite to form renal pelvis (calyx may enclose >1 papillae)

   - Calyx neck = infundibulum.

2. Renal pelvis: may be entirely intrarenal or partly intrarenal and partly extrarenal. Inferomedially, it tapers to form the ureter.  

Relations

1. Calices: are intrarenal and intimately related to renal parenchyma.

2. Renal pelvis: If partly extrarenal, it lies along lateral border of psoas muscle and on quadratus lumborum muscle; the renal vascular pedicle is placed just anterior to it.

left pelvis lies at the level of L1 or L2

right pelvis is a little lower (L2).

Calyceal anatomy on IVU (LAMP)

Lateral calyces → Anterior

Medial calyces → Posterior

End-on calyces → posterior

Histology

Mucosa: transitional epith. over lamina propria (loose connective and elastic tissue).

Musculosa: helical and longitudinal smooth muscle fibers. not arranged in definite layers.

Adventitia: fibrous connective tissue.

Blood Supply

A. Arterial

from renal arteries

B. Venous

The veins are paired with the arteries.

Lymphatics

renal calices, pelvis, and upper ureters → lumbar lymph nodes.