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PARP Inhibitors to Treat Certain Cancers

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楼主
发表于 12-6-2018 15:02:23 | 只看该作者 回帖奖励 |倒序浏览 |阅读模式
(1) Denise Roland and Kimberly Chin, Glaxo Makes Big Cancer-Drug Bet; Deal for Tesaro thrusts British company into highly competitive arera. Wall Street Journal, Dec 4, 2018
https://www.wsj.com/articles/gla ... -billion-1543842554

five consecutive paragraphs:

In an announcement made on Monday, Dec 3, "Britain's Glaxo agreed to pay $75 a share in cash for the Waltham, Mass-based company, a premium of 61% on its closing price Friday. Including debt, the deal is valuated at $5.1 billion.

"The acquisition hands Glaxo Tesaro's ovarian cancer drug Zejula, which went on sale in the US and Europe last year. Zejula is one of a new class of drugs known as PARP inhibitors, which have increased survival rates for women with recurrent ovarian cancer. PARP inhibitors are also showing promise in other forms of cancer, such as lung, breast and prostate.

"But in buying Zejula, Glaxo is entering a competitive arena.

"AstraZeneca PLC's Lynparza is the market leader, and a third PARP inhibitor from Boulder, Colo-based biotech company Clovis Oncology is also jostling for market share. * * *

"Zejula's sales have lagged behind rivals, with doctors and industry officials saying the treatment's side-effect profile is worse than the other drugs.

My comment: The report is available to the public, but there is no need to read the rest.
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沙发
 楼主| 发表于 12-6-2018 15:03:56 | 只看该作者
本帖最后由 choi 于 12-6-2018 16:37 编辑

(2)
(a) Poly (ADP-ribose) polymerase (PARP) is a family of about 17 members (proteins, coded by respective genes -- says PARP1 protein coded by PARP1 gene in humans) , whose founder (the first to be identified and most import) is PARP1.
(b) PARP1 wanders around in a cellular nucleus to detect single-stranded break (SSB) of DNA, which is double helix. Once finding SSB, PARP1 uses "nicotinamide adenine dinucleotide" (NAD+; the plus sign indicates it carries a positive charge (thus capable of receiving an electron to turn into NADH, its oxidation and reduction being its dominant role that is not deployed here) as substrate to generate "ADP-ribose" -- and then "poly (ADP-ribose) polymer" (PAR; that is, multiple moieties of ADP-ribose). The polymer (ie, PAR) acts as a signal to attract certain DNA-repairing enzymes which actually fix the SSB. Left unfixed, SSB will becomes double-stranded break (DSB) and the chromosome breaks into two. Wait until (2)(d)(i) to see chemical structure of ADP-ribose.
(c) All "PARP inhibitors" so far are "NAD+ analog." In other words, these analogs pretend to be NAD+, enter the catalytic pocket in PARP1 that is meant for NAD+ and remains there. Normally NAD+ enters the pocket and is quickly hydrolyzed to become "ADP-ribose" plus nicotinamide, with the latter two quickly leaving the pocket; but BAD+ analog can not be hydrolyzed.
(d) The following is a schematic representation of many players mentioned om (2)(b) and (c).
(i) Langelier, M-F et al, NAD+ Analog Reveals PARP-1 Substrate-Blocking Mechanism and Allosteric Communication from Catalytic Center to DNA-Binding Domains. Nature Communications, 9: 844 (2018).
https://www.nature.com/articles/s41467-018-03234-8
(A) Figure 1 shows -- in (a) (whose heading is "Non-hydrolyzable NAD+ analog binding and inhibition of PARP-1") -- the PARP1 (a protein; specifically an enzyme) is stretched out like a stick (rather than its correctly folded 3-D structure), composed from left to right of three zinc fingers -- skipping the middle two domains -- and, on the right, the catalytic domain (CAT) made up of HD and ART. The HD and ART stands for "alpha-helical sub-domain" and "ADP-ribosyl transferase;" ART is the part of PARP1 that carries out the enzymatic function (hydrolyse NAD+ to form "ADP-ribose" besides nicotinamide). The jargon and convention in biology, when a protein is stretched out like a rod, is "N-terminal" at the left end and "C-terminal" at the right end.

Figure 1(b) displays chemical structures of, on the left, "nicotinamide adenine dinucleotide" (NAD+: constituents are a 5-ring ribose 核糖 at the bottom whose right arm holds up adenine and whose left arm, via two phosphates, nicotinamide). This report uses "non-hydrolyzable NAD+ analog benzamide adenine dinucleotide (BAD)" -- shown in Fig 1(b) middle -- whose only difference is that C (carbon atom) in benzamide substitutes the N (nitrogen atom) in nicotinamide.  Nicotinamide and benzamide are amides of, respectively, nicotinic acid and of benzoic acid. The Fig 1(b)'s extremely right demonstrates "ADP-ribose," where ADP is "adenosine diphosphate" (components: adenine, ribose and two phosphates); it is called "ADP-ribose," because there is one ADP (with its own ribose) AND one ribose at the far end (top) of diphosphate -- altogether two riboses in one "ADP-ribose."
(B) Figure 2(a) has BAD in the pocket of PARP1's catalytic domain (CAT). The heading of Fig 2 is "Crystal structure of PARP-1 CAT ΔHD bound to NAD+ analog BAD," where Δ is uppercase of Greek letter delta, whose first letter d signifies "deletion" (that is, CAT without HD -- plainly the ART in preceding paragraph).
(C) Jump to Figure 6 whose right lower corner shows a cartoon of PART1 tethered to SNA with a SSB. Take notice of three zinc fingers (Zn1 to Zn3), HD, ART and BAD.

A zinc finger (in 3-D) looks like a finger stabilized with a zinc ion. View the top graph only, in
https://en.wikipedia.org/wiki/Zinc_finger

A zinc finger is found in proteins, which may have a couple of zinc fingers (as here) to grab/ take hold of the DNA, so that other part of the same protein can work on the DNA.
(D) Returns to Figure 5(c), showing two nearly identical images for 3-D viewing (with 3-D glasses). One can see, in the 6 o'clock, an SSB; three zinc fingers, HD and ART (without BAD).
(ii) In case you are interested, a "poly (ADP-ribose) polymer" is shown in Figure 1 of

Anthony KL Leung, Poly(ADP-Ribose): An Organizer of Cellular Architecture. Journal of Cell Biology, 205: 613 (2014)  
jcb.rupress.org/content/205/5/613
http://jcb.rupress.org/content/205/5/613

, where the ribose in the "ADP-ribose" is in the correct position -- upside down. The (2)(d)(i)(A) has that particular in the wrong position (upside up) in Fig 1(b)'s extremely right.
(e)
(i) An SSB will stall DNA replication that occurs before mitosis. Moreover, an SSB may progress to a DSB. In a cellular nucleus, there are other enzymes called BRCA 1 or 2 *where BRCA stands for BReast CAncer), that will repair a DSB in the absence of PARP.
(ii) A PARP inhibitor suppresses PARP, leaving SSB unfixed. So this might harm a normal call, but a cancerous cell (which multiplies frequently) even more -- if and only if the cancerous cell lacks BRCA 1 or 2 (there is a test for that).  
(f) As of now, Food and Drug Administration (FDA) requires use of PARP inhibitors in limited kind of cancers (breast and ovarian so far) whose BRCA genes (1 or 2) are deficient thanks to mutation(s) --either genomic (born with the mutation, inherited from parents, and every cell in the body have the same BRCA mutation), or somatic (only cancerous cells, which are prone to mutations, loses BRCA function after accumulating mutations in a BRCA gene).
(g) "The cancer risk caused by BRCA1 and BRCA2 mutations are inherited in a dominant fashion even though usually only one mutated allele is directly inherited."  en.wikipedia.org for "BRCA mutation."
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板凳
 楼主| 发表于 12-6-2018 15:04:41 | 只看该作者
(3) Pamela Munster, My Father's Fight Against the Breast-Cancer Gene; My grandmother and I both survived the disease, and knowing our genetic legacy turned out to be crucial in saving him. Wall Street Journal, Sept 29, 2018.
https://www.wsj.com/articles/my- ... cer-gene-1538146392

Quote:

"I was 7 years old when my dad's mom, Gertrud, was diagnosed with breast cancer. It was 1971, and she had just turned 65. Grandma lived in Berlin * * * After living for another two decades—having survived breast cancer—she died of pancreatic cancer when I was in my last year of medical school.  In April 2012, as I prepared to undergo a double mastectomy * * * following an unlikely breast cancer diagnosis at the age of 48. Despite my years as a practicing oncologist—specializing in breast cancer, of all things—I was not prepared for it to come to me.

"By the following summer [of the same year], I was back in control—past the diagnosis and multiple surgeries. In November 2012, we had discovered that I carried the BRCA2 gene, one of the two hereditary cancer genes named BRCA because they indicate a very high risk for breast cancer. In 2012, only women from high-risk families, with multiple members diagnosed under the age of 50, were getting tested for BRCA mutations. The test then cost several thousand dollars (it now costs as little $100 and can be obtained easily).  More tests confirmed that my mutation came from my father's side, at last putting into perspective the two different cancers of his mother—and, likely, the early death of his own grandmother at 29.  BRCA mutations leave women with about a 70% chance of breast cancer and up to a 40% chance of ovarian cancer. Many female carriers will ultimately choose to have their breasts and ovaries removed by their mid-forties [as a pre-emptive strike, doing it before their organs turn cancerous]. What is less well known is that BRCA mutations do not spare men, increasing their risk, even at a young age, for breast, prostate and pancreatic cancer.  Life had barely returned to normal when, during one of our weekly calls, my father mentioned that he was having a bit of stomach trouble.

"My father was then 78, and in men his age, digestive problems are common. But I did not think of ulcers or constipation. My mind went directly to pancreatic cancer.  Pancreatic cancer is much feared for very good reason. It is one of the deadliest cancers we know, partly because it is rarely detected early.

"For someone with a BRCA2 mutation, the risk for pancreatic cancer is up to 10 times higher than for those without the mutation. Pancreatic cancer is the third most common cancer with BRCA mutations for both men and women

"Knowing that Papa was a BRCA2 carrier drastically raised my concern that this could be pancreatic cancer, but in 2013, at the time of his diagnosis, there were no recommendations to regularly screen someone with a BRCA2 mutation for pancreatic cancer. My own circumstances and my knowledge of the mutation were undoubtedly part of what saved him.  An exhaustive battery of tests confirmed my suspicion, and despite his acting on his first symptoms and taking immediate action, his pancreatic cancer was already advanced.

Going to Switzerland where her father had lived, "I accompanied him to his doctor's visits. Dr. Bruno Schmied, a seasoned pancreatic surgeon in the city of St. Gallen, explained to us with compassion and finality that surgery wasn’t an option. Both my father's age and the advanced nature of the tumor made it a very dangerous, and likely futile, endeavor.  I asked Dr Schmied whether he would reconsider surgery if we got Papa's tumor to shrink. I pointed out the special circumstances of the BRCA mutation * * * After a long pause [due to his skepticism], he [Dr Schmied] said that such an effect on the tumor was highly unlikely…but in principle, yes, if I could make it happen, he would reconsider.

"A week later, he received the first dose of a combination of aggressive chemo treatments that Dr. Stefan Greuter, the oncologist in Switzerland, had agreed to—only because Papa had a BRCA mutation (and an extremely persuasive, medically trained daughter). * * * I was back at work again in San Francisco when I received an excited phone call from Dr Greuter: After eight weeks of chemotherapy, the tumor was less than half its original size.  Ten weeks after starting treatment, we returned to the surgeon, Dr Schmied, who clearly had not expected to see us back in his office. He was even more surprised when he saw my father's response to the chemotherapy. * * * As I told him [Dr Schmied], the same defect that makes people with BRCA mutations more likely to have cancer is also the Achilles' heel of the tumors. Cancer cells often escape the effects of chemotherapy by efficiently repairing the damage it inflicts on them. Cancer cells with mutated BRCA genes cannot repair DNA damage and thus are particularly vulnerable to chemotherapy agents that cause DNA damage. * * * The relationship between BRCA2 and pancreatic cancer and the excellent response some patients can have to therapy was much less understood then. * * * My father underwent surgery, and his tumor was removed.  But his journey did not end there. Within two years, the pancreatic cancer was back, requiring further chemotherapy and then two courses of radiation therapy. Thankfully, each course of treatment brought his tumor back under control, without more surgery, and he has now marked the five-year anniversary since his diagnosis.

"since his diagnosis, an entirely new type of therapy has been developed and approved, called PARP inhibitors, which are specifically tailored for those with BRCA mutations.

"—This essay is adapted from Dr Munster's new book, 'Twisting Fate: My Journey with BRCA—From Breast Cancer Doctor to Patient, and Back,' published by The Experiment. She is a professor of medicine at the University of California, San Francisco.

My comment:
(a) This article did not say what kind(s) of chemotherapy her father received, but probably not PARP inhibitor according to the penultimate quotation.
(b) Gertrude (given name)
https://en.wikipedia.org/wiki/Gertrude_(given_name)
(c) The German or Dutch surname Munster, Münster is from name of places of the same respective spellings, "derived from Latin [noun neuter] monasterium monastery."
(d) "1 in 40 people of Ashkenazi Jewish descent" carries a mutation in either BRCA gene.
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