multidrug resistance essay
TRANSCRIPT
-
8/8/2019 Multidrug Resistance Essay
1/14
Multidrug Resistance Essay
Terms & Definitions and General Perspectives
Drug resistance:The ability of a cell or microorganism to withstand theeffects of a drug that is lethal to most members of theirequivalents.
Malignant neoplasmsvary in their response to cytotoxic drugs: some aresensitive, others resistant. Understanding of the biochemical basis of this resistance might lead
to the development of markers that would correlate with the clinical response to the drugs - or
even lead to ways of overcoming the resistance.
Multidrug resistance:
1 The resistance ofTumor cells to more than onechemotherapeutic agent. Resistance may be
attributed to a P-glycoprotein transmembrane pumpthat lowers the concentration of drugs in the cell.
2 The resistance of bacteria, especially
Mycobacterium tuberculosis, against more than two ofthe antibiotics that were once effective.
Multidrug resistance"multiple drug resistance in some
malignant cell lines"= Resistance to many structurally
unrelated chemotherapy agents in cells that were discovered
to have developed natural resistance to a single cytotoxic
compound.
-
8/8/2019 Multidrug Resistance Essay
2/14
Discovery
Multidrug resistance was first described in 1970 afterselection of Chinese hamster ovarian cancer cellsexposed to increasing concentrations of actinomycin
D.1 Though the cells had been selected by a singleagent, they proved to be resistant to a range ofclinically important anticancer drugs, including the
Anthracyclines (doxorubicin and daunomycin), theVinca alkaloids (vincristine, vinblastine, and
vindesine), Etoposide, and Colchicine.
Criteria of multidrug resistant cells
Riordan and Ling went on to show that the multidrug resistant cells had
lower concentrations of the drug
a drug accumulation deficit - and
that a membrane glycoprotein of 170 kDa was responsible.2
At first the deficit was thought to be due to a fault in Permeationand therefore theglycoprotein was named P glycoprotein (P-gp).3
Genetics
The gene for this, mdr-1, has been cloned andsequenced, and the amino acid has beensequenced and the amino acid sequence
derived.
4
P glycoprotein has1280
amino acids,and its structure suggests that it arose from thefusion of two closely related genes; it uses ATPas a source of energy.
The precise molecular mechanism whereby Pglycoprotein can transport such a wide range of
-
8/8/2019 Multidrug Resistance Essay
3/14
structurally diverse drugs is uncertain, andseveral models have been proposed.
P glycoprotein& multidrugresistance associated protein
(MRP).
P glycoprotein belongs to a superfamily of ATP bindingcassette transporters, whose members include the cystic
fibrosis transmembrane regulator, the chloroquine
transporter of Plasmodium falciparum, and a yeast
transporter.8
Recently a new memberof this family was cloned from a
human small cell lung cancer cell line, H69AR.
Though it was resistant to doxorubicin and vincristine, it did
not express P glycoprotein.9 This new protein has 1522 amino
acids and has been termed multidrug resistance associated
protein (MRP).
Cells with this type of resistance may not have accumulation
deficits of doxorubicin. One possible explanation is that
multidrug resistance associated protein facilitates the
sequestration of cytotoxic drugs into intracellular organelles.9
Whether this protein binds to the drugs against which it
confers resistance is not known, but the emergence of a
potential new target for modulation, if it is widely expressed inhuman tumours, is clearly an exciting development.
Several probes have been developed that can detect the P glycoprotein
gene, its mRNA, and its protein product.10,11
Studies have shown that the
gene expressed in normal gastrointestinal mucosal cells, renal tubular
cells, biliary canalicular cells, and adrenocortical cells .11
-
8/8/2019 Multidrug Resistance Essay
4/14
Tumours that are initially sensitive to chemotherapy but resistant on relapse commonly show
increases in expression of P glycoprotein.
Leukaemias with high concentrations of P glycoprotein tend to be resistant to inductive
treatment with chemotherapy based on anthracycline.12
Expression of P glycoprotein is an adverse factor in multivariate prognostic models for
childhood sarcoma and neuroblastoma.13,14
BEFORE LONG IT MAY BE PRACTICABLE TO TISSUE TYPE TUMOURS ACCORDING TO
EXPRESSION OF P GLYCOPROTEIN AND, PERHAPS, TO AVOID THE TOXICITY AND REDUCED
QUALITY OF LIFE ASSOCIATED WITH TREATMENT WITH INEFFECTIVE ANTICANCER DRUGS.
After an initial observation by Tsuruo et al,15
several groups
have shown that transport defect mediated by P glycoprotein
can be blocked by many non-cytotoxic drugs, including
nifedipine, verapamil, quinine, chloroquine, progestogens,tamoxifen, cyclosporin A and its analogues, reserpine and
tricyclic anti-depressants.16 Clinical trials have assessed the
combination of conventional chemotherapy with modulators
of P glycoprotein; in one study of relapsed non-Hodgkin's
lymphoma 13 of18 patients responded to infusional
chemotherapy with high doses of verapamil.17
Unfortunately,
the amounts of verapamil needed to reverse drug resistance
produced congestive cardiac failure and heart block.Research
groups are currently looking for potent, non-toxic modulators
of P glycoprotein to combine with conventional
chemotherapy. Cyclosporin A has been reported to reverse
clinical multidrug resistance in myeloma.18 The combination
of quinidine with the antineoplastic agent epirubicin was
recently assessed in a prospective, placebo controlled
randomised study in patients with advanced breast
cancer.19Tumour response rates and survival were similar in
the two arms of the trial, a finding that probably reflects the
low potency of quinidine to bind P glycoprotein.7
Another possible application of the genetics of P glycoprotein is in gene therapy. Transgenic
mice that express human P glycoprotein in their bone marrow are resistant to chemotherapy,20
so in theory if human bone marrow could be transfected with the gene that might protect it
against myelosuppression from anticancer chemotherapy.8
Novel, improved modulators of P glycoprotein seem likely to be developed in parallel with mechanistic
research on the function of the gene, and thus should lead to the rational design of inhibitor. Future
-
8/8/2019 Multidrug Resistance Essay
5/14
phase II clinical trials with new modulators of P glycoprotein must include pharmacokinetic studies since
interactions can occur with cytotoxic drugs - for example, Etoposide's activity is increased by80% when it is given in combination with cyclosporin A.21 These trials should focus onthose cancers that are known to express high concentrations of P glycoprotein (including
renal and colorectal cancers and sarcomas).
Since P glycoprotein is expressed in normal tissues there is
some concern that its modulators might alter the cellular
transport of physiological metabolites such as bilirubin and
thereby delay the clearance of cytotoxic drugs that undergo
hepatobiliary excretion. These clinical trials should therefore
be performed in units used to handling the toxicity associated
with intensive chemotherapy.
Oxford Journals
y Volume95, Issue4
y Pp. 255-257.
Multidrug Resistance: Can New Drugs Help
Chemotherapy Score Against Cancer?
%UXFH*ROGPDQ)RUWKHYDVWVWUHWFKRIHYROXWLRQDU\WLPHSUHFHGLQJUHIULJHUDWLRQUXQQLQJZDWHUDQGDLUWLJKWSDFNDJLQJ
OLIHZDVVKRUWDQGIRRGZDVGLUW\,QWRGD\VLQGXVWULDOL]HGZRUOGWKLQJVDUHGLIIHUHQW %XWWKH
PHFKDQLVPVWKDWHYROYHGLQOLYLQJFHOOVWRSURWHFWWKHPIURPGDQJHURXVVXEVWDQFHVLQWURGXFHGWKURXJK
LQJHVWLRQLQKDODWLRQDQGLQIHFWLRQUHPDLQLQWDFW
3URPLQHQWDPRQJWKHVHPHFKDQLVPVLVDIDPLO\RIFHOOPHPEUDQHDQFKRUHGSURWHLQVWKDWDFWDV
JRDOLHVIRUWKHFHOOGHQ\LQJHQWU\WRIRUHLJQWR[LQVWKDWZRXOGRWKHUZLVHGLIIXVHWKURXJKWKHFHOO
PHPEUDQH7KHILUVWVXFKSXPSWREHLGHQWLILHG3JO\FRSURWHLQRUVLPSO\3JSLVFRPPRQLQWKHJXW
OLYHUDQGNLGQH\ZKHUHWR[LQVDERXQGDVZHOODVWKHWHVWHVDQGEORRGEUDLQEDUULHU
7KLVJRDOLHLVXOWUDYHUVDWLOH$YDULHW\RIVWUXFWXUDOO\GLYHUVHFKHPLFDOVDUHVXEVWUDWHVIRU3JSZKLFK
PDNHVJRRGHYROXWLRQDU\VHQVHEHFDXVHWKHUHDUHQRWHQRXJKJHQHVWRFRGHIRUDOOWKHSXPSVWKDW
ZRXOGEHUHTXLUHGLIHDFKZHUHQDUURZO\VSHFLILF8QIRUWXQDWHO\PDQ\ZLGHO\XVHGFKHPRWKHUDS\
GUXJVDUHH[SHOOHGE\3JSEHIRUHWKH\FDQGRWKHLUMRERIGDPDJLQJWKHFHOOEH\RQGDOOKRSHRIUHSOLFDWLRQ,QDWXPRUFORQHVRIFHOOVFDQVSRQWDQHRXVO\DULVHWKDWSURGXFHODUJHDPRXQWVRI3JSDQG
WKHUHE\DFTXLUHFKHPRUHVLVWDQFH2WKHUWXPRUVGHULYHGIURPWLVVXHVH[SUHVVLQJ3JSDUHUHVLVWDQWWR
EHJLQZLWK
*LYHQWKHVHREVHUYDWLRQVLWLVUHDVRQDEOHWRDVN&DQEORFNLQJ3JSWULSSLQJWKHJRDOLHVDIHO\DQG
HIIHFWLYHO\UHYHUVHDWXPRUVFKHPRWKHUDS\UHVLVWDQFH"$IWHUPRUHWKDQWZRGHFDGHVRIIRFXVHG
DWWHQWLRQWKHUHKDVEHHQQRGHILQLWLYHDQVZHUWRWKLVTXHVWLRQODUJHO\EHFDXVHRIWKHDEVHQFHRILGHDO
3JSLQKLELWLQJGUXJVWKDWZRXOGSURYLGHXQDPELJXRXVUHVXOWV
-
8/8/2019 Multidrug Resistance Essay
6/14
Redundant Mechanisms
9LUWXDOO\DOORIWKHURXJKO\KDOIPLOOLRQDQQXDOFDQFHUGHDWKVLQWKH8QLWHG6WDWHVFDQEHVDLGWRKDYH
RFFXUUHGEHFDXVHFKHPRWKHUDS\IDLOHGVDLG7LWR)RMR0'3K'DVHQLRULQYHVWLJDWRUDWWKH
1DWLRQDO&DQFHU,QVWLWXWHV&HQWHUIRU&DQFHU5HVHDUFK6XFKIDLOXUHVKDSSHQEHFDXVHSDWLHQWVWXPRUV
HLWKHUZHUHUHVLVWDQWDWWKHRXWVHWRUHYHQWXDOO\GHYHORSHGUHVLVWDQFHDIWHUH[SRVXUHWRWKHGUXJV
,V3JSWKHPDMRUGHWHUPLQDQWRIFKHPRWKHUDS\UHVLVWDQFH"9LFWRU/LQJ3K'QRZYLFHSUHVLGHQWRI
UHVHDUFKDWWKH%ULWLVK&ROXPELD&DQFHU$JHQF\LQ9DQFRXYHU%&GLVFRYHUHG3JSLQWKHODWHV
ZKHQDIWHUKHFKDOOHQJHGFXOWXUHGWXPRUFHOOVZLWKWKHF\WRWR[LFGUXJFROFKLFLQHVRPHFHOOVEHFDPH
UHVLVWDQWQRWRQO\WRFROFKLFLQHEXWDOVRWRFKHPLFDOO\XQUHODWHGGUXJV+RZHYHUVHYHUDOPROHFXODU
SXPSVVLPLODUWR3JSQRWWRPHQWLRQVHYHUDOXQUHODWHGPHFKDQLVPVKDYHQRZEHHQLPSOLFDWHGLQ
GUXJUHVLVWDQFH2QHVXFKSXPSLV053IRUPXOWLGUXJUHVLVWDQFHSURWHLQGLVFRYHUHGLQE\
6XVDQ&ROH3K'DQG5RJHU'HHOH\3K'053LVGLVWULEXWHGIDLUO\XEL TXLWRXVO\LQDOPRVWDOO
QRUPDOWLVVXHVXVXDOO\DWORZOHYHOVVDLG&ROHSURIHVVRURISDWKRORJ\RQFRORJ\DQGWR[LFRORJ\DW
4XHHQV8QLYHUVLW\LQ.LQJVWRQ2QWDULR
7KHUHDUHUHGXQGDQWWR[LQH[SHOOLQJV\VWHPVLQWKHGLJHVWLYHWUDFW,QFRORUHFWDODQGUHQDOFDQFHUWKH
ODUJHPDMRULW\RIWXPRUVH[SUHVV3JSVDLG%UDQLPLU6LNLF0'DQRQFRORJLVWSURIHVVRURIPHGLFLQHDQGSURJUDPGLUHFWRURI6WDQIRUG8QLYHUVLW\0HGLFDO&HQWHUV&OLQLFDO5HVHDUFK&HQWHU$QGZHNQRZ
WKDWXQLIRUPO\3JSUHODWHGFDQFHUGUXJVDUHQWDFWLYHLQWKRVHWXPRUV
-
8/8/2019 Multidrug Resistance Essay
7/14
FRPSRXQGVVORZLQJWKHLUFOHDUDQFHDQGLQFUHDVLQJWKHLUWR[LFLW\WRKHDOWK\WLVVXHV7RFRPSHQVDWH
RQFRORJLVWVUHGXFHGGRVDJHVRIWKHF\WRWR[LFVDGPLQLVWHUHGLQODWHSKDVHWULDOV%XWHDFKSDWLHQWV
PHWDEROLVPLVGLIIHUHQWWKHUHIRUHVRPHSDWLHQWVZHUHHIIHFWLYHO\UHFHLYLQJWRRPXFKDQGRWKHUVWRR
OLWWOHRIWKHLUFKHPRWKHUDS\GUXJV
New Drugs, New Trials7KHHDUO\3JSEORFNHUVORZSRWHQF\SRRUVSHFLILFLW\VKRUWGXUDWLRQRIDFWLRQDQGSKDUPDFRNLQHWLF
LQWHUDFWLRQVEHGHYLOHGHIIRUWVWRPDNHWKHLQKLELWRUVDIHDVLEOHDGGLWLRQWRWKHFOLQLF%XWDQHZ
JHQHUDWLRQRI3JSEORFNHUVZKRVHDWWULEXWHVVKRXOGDOORZULJRURXVWHVWLQJRIWKHK\SRWKHVLVWKDW3JS
UHYHUVDOFDQUHVWRUHHQKDQFHRUSURORQJFKHPRWKHUDSHXWLFGUXJVHQVLWLYLW\LVPRYLQJWRFHQWHUVWDJH
7ZRWKLUGJHQHUDWLRQFDQGLGDWHVWDULTXLGDU;HQRYD6ORXJK8.DQG]RVXTXLGDU(OL/LOO\
,QGLDQDSROLVDUHH[WUHPHO\SRWHQWDQG3JSVSHFLILF1HLWKHUGUXJEORFNV053RUH[KLELWVGLUHFW
WR[LFLW\7DULTXLGDULVSDUWLFXODUO\ORQJDFWLQJ,QRQHDVVD\HPSOR\LQJFLUFXODWLQJQDWXUDONLOOHUFHOOV
WKDWH[SUHVV3JSLQKLJKDPRXQWVWDULTXLGDUFRPSOHWHO\EORFNHG3JSIRUDWOHDVWKRXUVDIWHUD
KDOIKRXULQIXVLRQVDLGWKH1&,V%DWHV&KHPRWKHUDSHXWLFGUXJVDGPLQLVWHUHGDQ\WLPHGXULQJWKDW
EORFNDGHFDQQRWEHH[SHOOHGE\3JS
7KHVHDJHQWVGRQRWDSSHDUWRLQWHUIHUHZLWKWKHPHWDEROLVPRIWKHFKHPRWKHUDS\GUXJVWKHPVHOYHV
7DULTXLGDUKDVEHHQWHVWHGLQFOLQLFDOWULDOVZLWKSDFOLWD[HOGR[RUXELFLQDQGYLQRUHOELQHEHVWVHOOLQJUHSUHVHQWDWLYHVRIWKUHHGLVWLQFWFDWHJRULHVRIFKHPRWKHUDSHXWLFGUXJVWD[DQHVDQWKUDF\FOLQHVDQG
YLQFDDONDORLGVDQGVKRZQQRWWRQHFHVVLWDWHDQ\FKDQJHVLQFKHPRWKHUDSHXWLFGRVLQJVFKHGXOHV
=RVXTXLGDUDQGWDULTXLGDUDUHLQSKDVH,,,WULDOVLQUHVSHFWLYHO\$0/DQGQRQVPDOOFHOOOXQJFDQFHU
16&/&WZRGLVHDVHVZLWKYHU\VKRUWPHGLDQVXUYLYDOWLPHVDQGWKHSURVSHFWRIUHODWLYHO\IDVW
UHVXOWV,PSRUWDQWO\ERWKWULDOVHPSOR\3JSEORFNHUVDVILUVWOLQHWKHUDS\LQFRPELQDWLRQZLWK
FKHPRWKHUDS\ZLWKWKHLQWHQWLRQRIGHVWUR\LQJWXPRUVEHIRUHWKH\HYROYHUHVLVWDQFHPHFKDQLVPV
%HFDXVHWKHHPHUJHQFHRIUHVLVWDQWFORQHVPD\EHSUHYHQWHGE\WKHGHVWUXFWLRQRIMXVWDIHZ3JS
H[SUHVVLQJFHOOVWLPHWRUHODSVHDQGRYHUDOOVXUYLYDOQRWWXPRUVKULQNDJHZLOOEHNH\HQGSRLQWV
7KH]RVXTXLGDUWULDOOHGE\/DUU\&ULSH0'GLUHFWRURIFOLQLFDODIIDLUVDW,QGLDQD8QLYHUVLW\&DQFHU
&HQWHUZLOOIRFXVRQROGHUSDWLHQWVZKRVHWUDQVIRUPHGOHXNRF\WHVDUHJH QHUDOO\NQRZQWREHPRUH
OLNHO\WRH[SUHVVKLJKDPRXQWVRI3JSWKDQWKRVHRI\RXQJHUSDWLHQWV$ERXWSDWLHQWVZLWK$0/
ZLOOEHUDQGRPO\DVVLJQHGWRUHFHLYHKRXULQIXVLRQVRIHLWKHUDSODFHERRU]RVXTXLGDUSOXVWKHFKHPRWKHUDS\GUXJVGDXQRUXELFLQD3JSVXEVWUDWHDQGF\WDUDELQH5HVXOWVDUHH[SHFWHGLQDERXW
\HDUV&ULSHVDLG1XPHURXVVWXGLHVRI$0/SDWLHQWVSXEOLVKHGVLQFHKDYHVKRZQDQDVVRFLDWLRQ
EHWZHHQ3JSH[SUHVVLRQRQFKHPRWKHUDS\UHFLSLHQWVWXPRUVDQGFOLQLFDORXWFRPHV+RZHYHU
GDXQRUXELFLQLVDVXEVWUDWHIRUERWK3JSDQG0537KLVFRXOGFRPSOLFDWHDWWHPSWVWRUHYHUVH
UHVLVWDQFHE\EORFNLQJ3JSEHFDXVH053LVIDLUO\FRPPRQRQWKHOHXNRF\WHVLQZKLFK$0/DULVHV
,QWKHFOLQLFDOWULDORIWDULTXLGDUSDWLHQWVZLWK16&/&ZLOOUHF HLYHDWDULTXLGDULQIXVLRQIRUDERXWRQH
KDOIKRXUSUHFHGLQJFKHPRWKHUDS\ZLWKSDFOLWD[HODQGFDUERSODWLQLQRQHSDWLHQWWULDODQGZLWK
YLQRUHOELQHLQDQRWKHUHTXDOVL]HGVWXG\IRUSRRUHUSHUIRUPLQJSDWLHQWV$VZLWK$0/053DERXQGV
LQ1&6/&WXPRUV%XWSDFOLWD[HODVWURQJ3JSVXEVWUDWHKDVOLWWOHDIILQLW\IRU053053V
DSSHWLWHIRUYLQRUHOELQHLVQRW\HWFOHDU)LQDOGDWDVKRXOGEHDYDLODEOHLQVDLG*UDHPH%RQLIDFH
3K'GLUHFWRURIUHVHDUFKIRURQFRORJ\DW4/79DQFRXYHU%&WKHFRPSDQ\WRZKLFK;HQRYD
OLFHQVHGWDULTXLGDUIRUFDQFHULQGLFDWLRQV
7KHUHLVPXFKGHEDWHDVWRZKHWKHU3JSDSSHDUVRQ16&/&WXPRUVIUHTXHQWO\HQRXJKWRSURYLGH
VWDWLVWLFDOO\PHDQLQJIXOWULDOUHVXOWV$UJXLQJWKDWWKHEHQHILWVRI3 JSLQKLELWRUVDUHOLPLWHGWRWXPRUV
H[SUHVVLQJ3JSVRPHDXWKRULWLHVSURSRVHVWXGLHVWKDWHQUROORQO\SDWLHQWVZKRVHWXPRUVDUHDOUHDG\3
JSSRVLWLYH)RMRDQGRWKHUVFRXQWHUWKDWFXUUHQWGHWHFWLRQPHWKRGVODFNUHOLDELOLW\WHQGWR
XQGHUHVWLPDWHWKHLQFLGHQFHRI3JSH[SUHVVLRQLQ1&6/&DQGIDLOWRGLVWLQJXLVKEHWZHHQWXPRUVZLWK
]HUR3JSH[SUHVVLRQDQGWKRVHZLWKORZH[SUHVVLRQ%XWWKHODWWHUWXPRUVPD\VWLOOEHSURQHWRGHYHORS
UHVLVWDQFHDQGWKHUHIRUHPD\EHUHVSRQVLYHWRFRDGPLQLVWUDWLRQRIDEORFNLQJDJHQWDORQJZLWK
FKHPRWKHUDS\
-
8/8/2019 Multidrug Resistance Essay
8/14
$WWKH1&,)RMRDQG%DWHVDUHGHYHORSLQJEHWWHUVXUURJDWHDVVD\VXVLQJUDGLRDFWLYHG\HVWRGLDJQRVH
3JSH[SUHVVLRQDQGPRQLWRU3JSLQKLELWLRQLQFHOOVDQGWLVVXHV$QXOWLPDWHJRDOWRFDWDORJHDFK
WXPRUFHOOIRUDOOPHFKDQLVPVRIUHVLVWDQFHDQGWDLORUWUHDWPHQWDFFRUGLQJO\ZLWKKLJKO\WDUJHWHGDJHQWV
0HDQZKLOHZLWKWKHDGYHQWRIKLJKO\VSHFLILF3JSLQKLELWRUVWKHVWDJHLVQRZVHWWRVHHLIWULSSLQJWKH
JRDOLHZLOOZRUN*LYHQFKHPRWKHUDS\VSUHVHQWIDLOXUHUDWHHYHQDVPDOOEXWVLJQLILFDQWUHGXFWLRQLQ
GUXJUHVLVWDQFHPD\WXUQLQWRWKRXVDQGVRIOLYHVVDYHG
y 2[IRUG8QLYHUVLW\3UHVV
Nanoparticles may play a role in inhibiting the multidrug resistance in
chemotherapy
(Nanowerk Spotlight) Multidrug resistance, the principal mechanism by which many
cancers develop resistance to chemotherapy drugs, is a major factor in the failure of
many forms of chemotherapy. New research by Chinese scientists suggests that
nanoparticle surface chemistry and size as well as the unique properties of the
magnetic nanoparticles themselves may contribute to a synergistic enhanced effectof drug uptake of targeted cancer cells. These findings could result in promising
biomedical applications for cancer therapy.
ProfessorXuemei Wang from the the State Key Laboratory of Bioelectronics (Chien -
Shiung Wu Laboratory) in Nanjing, PR China, together with several of her col leagues
from Southeast University, recently published a paper titled "Synergistic
enhancement effect of magnetic nanoparticles on anticancer drug accumulation in
cancer cells" in the June 26, 2006 online issue of Nanotechnology.
In it, the researchers describe their investigation of the synergistic effect of threekinds of magnetic nanoparticles, nano Fe 3O4, Ni and Fe2O3, on the drug uptake of
anticancer drug daunorubicin in leukemia K562 cells.
They show how Fe3O4 nanoparticles could remarkably enhance the uptake or
diffusion efficiency of anticancer drugs into target cancer cells (especially drug
resistance cancer cells). If Fe3O4 nanoparticles, which are biocompatible and very
stable, are fixed at the ailing area by using external magnetic field during the tumor
treatment, the chemotherapy effect could be considerably enhanced by combination
of the application of the new magnetic nanoparticles in drug delivery systems for
achieving the targeting and controlled drug release.
-
8/8/2019 Multidrug Resistance Essay
9/14
Microscopy images (200 m 200 m) of Fe3O4 incubated leukemia cells in the
absence and presence of a magnetic field. The cells numbered in the images
illustrate the movement of the cells, while squared cells in the left image wereobserved to move out of vision after the external magnetic field was applied, and the
cycled cells in the right image appeared upon application of the external m agnetic
field. The arrows indicate the direction of the magnetic field and the picture was
captured after the magnetic field was applied for 5 s. (Reprinted with permission from
IOP Publishing)
"Our results illustrate that the presence of magnetic nanopar ticles could facilitate the
drug accumulation of daunorubicin inside leukemia cells and the enhancement effect
of nano Fe3O4 is much stronger than that of the other two magnetic nanoparticles"
Wang explains the findings to Nanowerk. "These observations are consistent with the
results of our recent biological experimental studies, which indicates that the
presence of Fe3O4 nanoparticles could apparently inhibit the growth of the respective
leukemia cells (Interestingly, the Fe 3O4 nanoparticle itself could al so inhibit the cell
growth somehow); especially, when treated the target cells by anticancer drug
daunorubicin together with Fe 3O4 nanoparticles, the growth of leukemia cells could
be much more remarkably inhibited than that with only daunorubicin or other
nanoparticles. Since these three kinds of nanoparticles were all capped with the
tetraheptylammonium, our observations suggest that both the size and the unique
properties of magnetic nanoparticles themselves may contribute to the synergistic
enhanced effect of the drug uptake of targeted cancer cells."
The magnetic targeting offers a unique opportunity to treat tumors without systemic
toxicity. It is known that the cure efficiency of cancer chemotherapy depends not only
on the anticancer drug itself but also on how it is delivered to its targets. As already
reported in some literature, it has been observed that the magnetic particles can be
targeted and concentrated in some tumor tissue at significantly high level.
-
8/8/2019 Multidrug Resistance Essay
10/14
"Our observations indicate that magne tic nanoparticles with different size and surface
chemistry have different ability to enter target cells and thus the relative efficiency of
the drug delivery systems by the conjugation of drugs with nanoparticles will be
critically dependent upon nanopart icle surface chemistry and size of the
functionalized nanoparticles" says Wang.
"Based on these observations, our future research with regard to cancer therapy may
focus on the relative mechanisms of new magnetic nanoparticles" Wang describes a
possible direction for her group's future research. "Magnetic nanomaterials are
especially promising for the early diagnosis of some cancers and for efficiently
targeting chemotherapy.
Multidrug resistance
Mechanism and function of multidrug transporters in pro- and eukaryoticcells
The development of resistance to multiple drugs is a major problem in the treatment of
cancer cells and infections by pathogenic microorganisms. One of the mechanisms by
which human cells and bacteria can acquire multidrug resistance involves the expression of
membrane proteins which mediate the active extrusion of drugs from the cell. Current
research focuses on the molecular properties of four distinct multidrug transport proteins.
Multidrug transporter LmrP
InLactococcuslactisLmrP mediates drug resistance by extruding amphiphilic, organic
compounds from the inner leaflet of the cytoplasmic membrane.LmrP is a secondary
multidrug transporter which is typical for prokaryotes. The antibiotic specificity ofLmrP is
exceptionally broad and includes tetracyclins, quinolones, aminoglucosides, lincosamides,
macrolides, streptogramins and others. To facilitate functional and structural studies,
histidine-tagged LmrPprotein was overexpressed inL. lactis, solubilized with
dodecylmaltoside, purified to homogeneity by nickel chelate affinity chromatography, and
functionally reconstituted in proteoliposomes. Interestingly, LmrP is able to transport
detergents such as Triton X-100. Therefore, the choice of the detergent used for
solubilization of the protein was critical.
Multidrug transporter LmrA
A second protein in L. lactis, LmrA, mediates antibiotic resistance via a similar mechanism,
and with a similar specificity as the secondary multidrug transporter LmrP. Unlike other
known bacterial multidrug resistance proteins, LmrA is an ATP-binding cassette (ABC)
transporter.LmrA is homologous to the human multidrug resistance P-glycoprotein,
encoded by the MDR1 gene, overexpression of which is one of the major causes of
resistance of human cancers to chemotherapy. In collaboration with Prof. C.F. Higgins in
Oxford, LmrA was expressed in human lung fibroblast cells to compare the
pharmacological properties ofLmrA with those ofP-glycoprotein. Surprisingly, LmrA was
-
8/8/2019 Multidrug Resistance Essay
11/14
targeted to the plasma membrane and conferred typical multidrug resistance on these
human cells. The pharmacological characteristics ofLmrA and P-glycoprotein- expressing
lung fibroblasts were very similar, and the affinities of both proteins for vinblastine and
magnesium-ATP indistinguishable. Blockers ofP-glycoprotein-mediated multidrug
resistance also inhibited LmrA-dependent drug resistance. Kinetic analysis of drug
dissociation from LmrA, expressed in plasma membranes of insect cells, revealed the
presence of two allosterically-linked drug binding sites indistinguishable from those ofP-
glycoprotein. These findings have implications for the reversal of antibiotic resistance in
pathogenic microorganisms. Taken together, these observations demonstrate that
bacterial LmrA and human P-glycoprotein are functionally interchangeable and that this
type of multidrug resistance efflux pump is conserved from bacteria to man.LmrA has
been overexpressed in L. lactis up to a level of 35% of total membrane protein. This
protein is functional, and has been purified and reconstituted into proteoliposomes to
facilitate detailed structure-function analyses. Currently, mg quantities of reconstituted
LmrA can be obtained rather easily.
Multidrug transporter HorA
LactococcalLmrA is homologous to other prokaryotic ABC transporters such as the hop-
resistance protein HorA in the beer-spoilage bacterium Lactobacillus brevis. To study HorA
in more detail, the protein was functionally expressed in L. lactis. Studies in whole cells
and membrane vesicles derived thereof demonstrate that HorA is a multidrug transporter
able to transport hop compounds (iso-a-acids), with a substrate specificity similar to that
ofLmrA. Recently, the protein has been purified and reconstituted into proteoliposomes.
Cholatetransporter
Micro-organisms able to colonize the gastrointestinal tract in mammals must tolerate high
levels of bile salts, powerful detergents that disrupt biological membranes.Physiological
evidence has been obtained for the presence of an ATP-dependent cholate transporter in L.
lactis. Interestingly, this transport activity may be related to the transport activities for
fluorescent anionic dyes BCECF and FTUG in this organism. Current work aims at the
isolation of the gene(s) encoding the cholate transporter.
Multidrug resistance-associated protein
Multidrug resistance in humans is caused by the overexpression of two multidrug
transporters: P-glycoprotein and the Multidrug Resistance-Associated Protein (MRP1).
Although MRP1 contains two nucleotide binding domains (NBDs), it is not known whether
both NBDs can function as an active ATPase, and whether drug-protein interactions inthese domains play a role in the drug-stimulated ATPase activity of MRP1. The NBDs of
MRP1 were expressed in fusion with glutathione S-transferase, purified by affinity
chromatography, cleaved from the fusion partner by thrombine, and purified to
homogeneity by gel filtration. Both NBDs hydrolyze ATP, with a Km of 340 mM Mg-ATP and
Vmax of 6.0 nmol Pi/mg/min for NBD1, and a Km of 910 mM Mg-ATP and Vmax of 7.5
nmol Pi/mg/min for NBD2. The properties of NBD1 were further studied. Surprisingly, the
Vmax of the NBD1 ATPase reaction was stimulated more than 3-fold by the MRP substrate
-
8/8/2019 Multidrug Resistance Essay
12/14
decyl glutathione but not by decylmaltoside or decanol, whereas the Km of the reaction
was not affected. The interaction between S-alkyl glutathione conjugates and NBD1 was
analyzed by using the intrinsic tryptophan fluorescence of NBD1 as a reporter. The
tryptophan fluorescence was quenched in a concentration-dependent manner by S-alkyl
glutathione conjugates, but not by alkyl maltosides or alkanols. The apparent KD of NBD1
for S-alkyl glutathione conjugates decreased with an increasing length of the alkyl chain.
Thus, NBD1 is suggested to have a high-affinity binding site for S-alkyl glutathione
conjugates.
-
8/8/2019 Multidrug Resistance Essay
13/14
-
8/8/2019 Multidrug Resistance Essay
14/14