Hydroxyurea
Subj: Report on Hydrea
Date: Tue, Apr 2, 1996 1:48 AM EDT
From: MPD-SUPPORT-L@LISTSERV.AOL.COM
X-From: DAS155@PSUVM.PSU.EDU (Dave)
Hi everyone,
I posted a message a week or so ago inquiring about PV for a report I am
writing. I am in my junior year at Penn State studying (or at least making an
attempt) molecular and cell biology. Last semester, I wrote a report on
Hydrea (hydroxyurea) for another one of my classes. I thought there might be
some interest in it on this list, so I thought I would post it. If anyone has
any questions, comments, criticisms, etc, please feel free to write me. I
would appreciate and welcome it. The report was originally compiled on Word, so
I had to translate it to ascii. Thus, some of the font and type characteristics
were lost. Chemical equations lost subscripts (water = H20). Also, Greek
letters were used throughout the report and they were translated into their
corresponding Arabic counterpart. (a=alpha, b=beta, g=gamma, etc.). There are
others as well, but those are the biggies. I hope everyone is doing well and
happy holidays to all. Have a great day!
Dave Schlosser
Thanks to all who responded to my original posting. I will be in touch soon.
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a = alpha
b = beta
g = gamma
Hydroxyurea
A Rediscovered Miracle or Killer?
Presented to:
Joseph M. Bollinger, Ph.D.
Assistant Professor of Biochemistry and Molecular Biology
208 Althouse Laboratory
University Park, PA 16801
December 8, 1995
Introduction
"Invention is the mother of necessity."
- Thorstein Veblen
Nothing better describes the position that
hydroxyurea holds today in society's allopathic system
of medicine. First synthesized by Dr. W.F.C. Dresler
and Dr. R. Stein of Heidelberg, Germany in 1869, it
rested clincally idle for just less than one hundred
years before the world took notice. Little did
Dresler and Stein know they made one of the most
potentially important drugs of society. It's
therapeutic effect was not utilized until the early
1960's. Today, it is the accepted treatment for a
handful of ailments, however, ailments affecting
millions of people. Currently, it is used to treat a
variety of cancers and has been reasonably effective. In
the past two years, hydroxyurea also has been
indicated experimentally for sickle cell anemia and
shown to have an inhibitory effect on the Human
Immunodeficiency Virus Type 1 (HIV-1). For a drug over
125 years old, it's been a busy two years. However,
like all drugs, these benefits do not come without
substantial short and long term side effects.
This paper will discuss several facets of
hydroxyurea. Its different actions and mechanisms, as
well how cells that have defeated them, will be
overviewed. In addition, current and possible future
indications will be discussed and the side effects caused
by treatment.
Synthesis
Hydroxyurea (HU), marketed by Bristol
Meyers-Squibb (Princeton, NJ) as Hydrea, is a rather
simple compound (CH4N2O2) as illustrated below.
O
||
H2N - C - NH - OH
Dresler and Stein's method of synthesis involved many
different crystallization steps [21]. Today, it is a
simple synthesis reaction involving hydroxylamine HCL and
KCN [22]. Approximately 50% of an oral dose is converted
by the liver to respiratory CO2 and urea, a large
component of urine.
Indications
HU has been indicated by the Food and Drug
Administration (FDA) for several diseases. Currently, HU
is used to treat a variety of cancers. Among these are
chronic myeloid leukemia (CML), polycythemia vera
(PCV), and hypereosinophilic syndrome. Although some
research indicates that it possesses no anti-tumor
activity [4], most studies and references indicate that
it does [1-3, 6, 14]. It also causes temporary remissions
in metastatic malignant melanomas and other solid
turmors like carcinomas of the head, neck,
genitourinary systems, cervix, and lung. In addition, but
not yet indicated by the FDA, is treatment of sickle
cell anemia and possibly AIDS when used with AZT or
ddI.
Mechanisms and Applications
Cancer
HU's primary site of action in cancer is the
inhibition of the enzyme ribonucleoside diphosphate
reductase (RDR) [1-3]. RDR consists of two proteins,
R1 and R2. HU, sometimes called a "free radical
quencher", destroys a tyrosyl free radical that is
formed in the catalytic center of the enzyme.
This results in the destabilization of the iron
center in protein R2, rendering the enzyme inactive
[8]. RDR catalyzes the reductive conversion of
ribonucleotides to deoxyribonucleotides, the component
of DNA. This conversion is the rate limiting step in
DNA synthesis. HU therefore inhibits DNA synthesis,
however, it has been shown that it has no effect on
transcription or translation. This has a substantial
impact on cancer cell growth and disease progression.
Experiments reveal there is a direct correlation between
the relative growth of rat hepatomas and RDR activity,
supporting HU as part of an anti-cancer regimen.
HU is specific only for cells in the S phase of the
cell cycle and is lethal to normally radioresistant S-
phase cells. Cell cultures treated with HU arrest at
the G1-S interface, the point in the cell cycle where
cells are most susceptible to irradiation. This
gives synergistic toxicity when HU and irradiation
therapy are used simultaneously.
HU also seems to induce apoptosis [14]. Chronic
myeloid leukemia (CML) infected lymphocytes treated with
HU developed morphological changes characteristic of
apoptosis. After a 24 hour culture with HU, cell
shrinkage became evident, the chromatin condensed, the
cell membrane became flaccid, and cellular damage and DNA
fragmentation into the oligonucleosomal ladder of 180bp
multiples were apparent. These are all changes that have
been observed in cells undergoing apoptosis.
HIV-1
Studies also indicate that HU disperses pools of
dTTP (thymidine 5'-triphosphate) by 65% [6, 7, 23].
This makes AZT (3' Azido-3'-deoxythymidine), a
thymidine analog, more accessible to the DNA
synthesis operation. This results in more AZT
incorporation and thus increases viral inhibition. AZT
and HU create a synergistic inhibitory effect because
more AZT is being utilized as a false substrate for DNA
synthesis. This data suggests that HU has some anti-viral
effect. HU also blocks HIV-1 replication in acutely
infected primary human lymphocytes (quiescent and
activated) and macrophages. In addition, it blocks
replication in blood cells infected in vivo obtained from
individuals with AIDS. This anti-viral effect is achieved
at non-toxic levels, lower than those used currently in
other HU therapies. In addition, combination therapy with
didanosine (ddI) also produces a synergistic inhibitory
effect without increasing toxicity. Unlike most effects
caused by HU in other applications, HIV-1 inhibition by
HU was sometimes irreversible even after several weeks of
treatment suspension. These actions combined not only
result in less viral DNA produced, but the majority of
the DNA are incomplete chains. This is a very promising
advance in HIV-1 research.
Sickle Cell Anemia
Sickle Cell Anemia (SCA) is a disease caused by the
sickling of red blood cells (RBC's). Sickling is caused
by the polymerization of molecules of deoxygenated
hemoglobin S (a2b2S) into rigid, rod like polymers called
sickles. Fetal hemoglobin (a2g2), however, lacks b-globin
chains. This inhibits sickling in vitro by interfering
with the polymerization of hemoglobin S.
Recent clinical trials by NIH have resulted in
promising news with respect to SCA. High, sub-toxic
levels of HU seems to increase the level of fetal
hemoglobin (HbF) several fold [9]. In addition, total
Hb, cellular concentration of HbF, and mean RBC volume
also increase. Increased levels of HbF prevent RBC's
from becoming rigid sickle cells, preventing painful
crises and vaso-occlusion (blocked blood vessels)
ever so routine to many SCA patients [10]. Beneficial
effects of HU are not seen for several months, however,
and continuous therapy is necessary to maintain elevated
HbF levels [20]. This is the first effective treatment
for reducing these crises, and results so far have been
so successful that trials have been halted. There have
been some exceptions, however. Two SCA patients are noted
that had a five to tenfold increase in HbF and died of
SCA complications they experienced prior to HU therapy as
well [12]. Both patients' HbF levels exceeded 20%, a
concentration often observed to prevent SCA
complications. Due to the other studies, however, it is
likely that HU will eventually be approved by the FDA for
the treatment of SCA.
Resistance
Some cells seem to develop the ability to resist
HU's actions. There are several hypotheses explaining
this development. Some think that there is a loss of
RDR affinity for HU or cells somehow acquire RDR's with
decreased sensitivity to HU [1-4].
Other studies indicate that some cells produce more
RDR due to gene amplification [8]. Compared to wild-type
cells, HU-resistant mouse cells had elevated R2 gene
amplification, elevated R2 RNA levels, increased total
cellular R2 protein concentrations, and increased
enzyme activity. In addition, HU-resistant cells had
elevated levels of light chain (L-chain) ferritin RNA
and total cellular heavy chain (H-chain) protein
levels. Ferritin, a iron protein complex, maintains
iron in an available soluble form to be used in oxygen
activation, electron transfer, and, importantly, DNA
synthesis. It is the result of a polymerization of the
products of the ferritin H-chain and ferritin L-chain
genes. It facilitates free radical generation, which
may be linked to the synthesis of RDR. In fact,
elevations in RDR were associated with increases in
ferritin gene expression [13].
Side Effects
Like all drugs, the benefits of HU do not come
without side effects. HU should not be used without
serious consideration. The best known side effects are
short term effects. ALL patients experience, within two
weeks, hematopoietic depression, including leukopenia
(leukocyte reduction). However, reversal is eminent on
withdrawal of therapy. Common immediate effects include
drowsiness, fever, chills, malaise (general discomfort),
and renal impairment. There are also a host of others
that occur only rarely. Dizziness, hallucinations,
convulsions, and dysuria (painful urination) are just a
few. No interactions with other drugs have been observed.
One 1994 study reported no long term major side
effects [9]. However, all other studies, also recent,
reported otherwise [5, 15-19]. There are serious long
term effects that are only now being discovered. All of
these effects have developed under therapy levels
consistent with prescribed instructions and common
practice.
HU is now generally considered a leukemogenic agent.
In a 1993 study of fifty patients with polycythemia vera
(PCV), 20% patients developed leukemia with a mean
treatment start time of 8.4 years [5]. Eight additional
studies in the past ten years also have yielded similar
results. This classification is now obviously a serious
issue to consider before therapy. HU therapy also causes
chromosomal abnormalities in PCV patients similar to
those that occur after treatment with 32P [17]. These
abnormalities, -5/5q- and -7/7q- are consistent with
those considered typical for secondary leukemia [18, 19].
HU also is reported to cause other problems. In a
1991 report, it seemed to cause acute interstitial lung
disease, a life-threatening condition, in a non-smoking
female with myeloproliferative syndrome [16]. The problem
subsided immediately after therapy was discontinued. Long
term maintenance therapy also has been demonstrated to
cause pigmentation and atrophy of the skin as well as a
host of skin tumors [15]. These lesions are further
exaggerated after exposure to ultraviolet light. Some of
them resolve after discontinuing HU, but most do not.
Although it has been successful in a few cases, it
is not recommended that HU be used during pregnancy due
to its unknown toxicity to fetal development [2].
New Indications
It is evident that HU is being noticed as a very
powerful and versatile drug. HU research is becoming
widespread very quickly. Evidence of this is the release of
an article a few months ago suggesting HU as possible
treatment in rheumatoid arthritis in conjunction with
irradiation [24]. The mechanism of this action is currently
not known.
Conclusion
It is obvious that HU is a very powerful chemical. HU
has went from a "chemical on the bench" to a drug used to
treat millions of people in a short period of time.
Justifiable indications are arising every few years, a
growth not seen with many other drugs. Interacting with
cells in a myriad of different ways, it becomes extremely
beneficial in a variety of environments. However, many of
these same interactions seem to cause very serious problems
as well. Although recent research holds, possibly, a very
promising future in AIDS and especially SCA treatment, it is
important to examine and balance the benefits with the
hazards of therapy.
References
1. Gilman, Alfred G., M.D., Ph.D., ed. The Pharmacological
Basis of Therapeutics. 8th ed. New York: Perganon
Press, 1990, p1251-1252.
2. Physician's Desk Reference. 48th ed. Montvale, NJ:
Medical Economics Data Production Company, 1994, p1064-
1065.
3. Olin, Bernie R., Pharm.D., ed. Drug Facts and
Comparisons. St. Louis: Facts and Comparisons, Inc.,
1991, p2362-2363.
4. Blumenreich, Martin S., M.D., Kellihan, Michael J.,
Pharm.D., Joseph, U. Geetha, M.D., et. al. Long-term
Intravenous Hydroxyurea Infusions in Patients with
Advanced Cancer. Cancer. 1993; 71:2828-2831.
5. Weinfeld, A., Swolin, B., and Westin, J. Acute leukaemia
after hydroxyurea therapy in polycythemia vera and
allied disorders: Prospective study of efficacy and
leukaemigenicity with therapeutic implications. European
Journal of Haematology. 1994; 52:134-139.
6. Tosi, P., Ottaviani, E., Tura, S., and Darnowski, J.W.
Hydroxyurea enhances 3'-azido-3'deoxythymidine (AZT)
cytotoxicity in human chronic myeloid leukemia models.
European Journal of Haematology. 1994; 52:291-295.
7. Lori, F., Malykh, A., Cara, A., et. al. Hydroxyurea as an
Inhibitor of Human Immunodeficiency Virus-Type 1
Replication. Science. 1994; 266:801-804.
8. Hurta, R.A.R., Wright, J.A. Correlation between levels of
ferritin and the iron- containing component of
ribonucleotide reductase in hydroxyurea-sensitive, -
resistant, and -revertant cell lines. Biochemistry and
Cell Biology. 1991; 69: 635- 642.
9. Voskaridou, E., Kalotychou, V., and Loukopoulos, D.
Clinical and laboratory effects of long-term
administration of hydroxyurea to patients with sickle-
cell/b- thalassaemia. British Journal of Haematology.
1995; 89:479-484.
10. Marwick, C. Trial Halted as Sickle Cell Treatment Proves
Itself. Journal of the American Medical Association.
1995; 273:611.
11. Mehta, Mukesh, R.Ph., ed. PDR Guide to Drug
Interactions, Side Effects, and Indications. Montvale,
NJ: Medical Economics Data Production Company, 1994,
p482.
12. Vichinsky, E.P., and Lubin, B.H. A Cautionary Note
Regarding Hydroxyurea in Sickle Cell Disease. Blood.
1994; 83(4):1124-1128.
13. McClarty, G.A., Tonin, A.K., Choy, B.K., and Wright,
J.A. Increased ferritin gene expression is associated
with increased ribonucleotide reductase gene expression
and the establishment of hydroxyurea resistance in
mammalian cells. Journal of Biological Chemistry. 1990;
265:7539-7547.
14. Shubna, A., Verma, H., Kumar, L., and Singh, N.
Induction of apoptosis in chronic myelogenous leukemia
lymphocytes by hydroxyurea and adriamycin. Cancer
Letters. 1995; 88:101-105.
15. Stasi, R., Cantonetti, M., Abruzzese, E., et. al.
Multiple skin tumors in long-term treatment with
hydroxyurea. European Journal of Haematology. 1992;
48(2):121-122.
16. Kavuru, M.S., M.D., Gadsden, T., M.D., Lichtin, A.,
M.D., and Gephardt, G., M.D. Hydroxyurea-Induced Acute
Interstitial Lung Disease. Southern Medical Journal.
1994; 87(7):767-769.
17. Diez-Martin, J.D., Graham, D.L., Petitt, R.M., and
Dewald, G.W. Chromosome studies in 104 patients with
polycythemia vera. Mayo Clinic Proceedings. 1991;
66:287-299.
18. Pedersen-Bjergaard, J. Incidence, previous treatment,
and chromosome characteristics of secondary acute non-
lymphocytic leukemia. Cancer Treatment Review. 1985;
12:65-75.
19. Johansson, B., Mertens, F., Heim, S., et. al. Cytogenics
of secondary myelodysplasia (sMDS) and acute
nonlymphocytic leukemia (sANLL). European Journal of
Haematology. 1991; 47:17-27.
20. Charache, S., M.D., Terrin, M.L., M.D., Moore, R.D.,
M.D., et. al. Effect of Hydroxyurea on the Frequency of
Painful Crises in Sickle Cell Anemia. The New England
Journal of Medicine. 1995; 332(20):1317-1322.
21. Dresler, W.F.C and Stein, R. Uber den Hydroxylharnstoff.
Justus Liebigs Ann Chemie. 1869; 150:242-252.
22. Windholz, M., ed. The Merck Index. Rahway, NJ: Merck &
CO., Inc., 1983, p4772.
23. Gao, W., Mitsuya, H., Driscoll, J.S., Johns, D.G.
Enhancement by Hydroxyurea of the Anit-Human
Immunodeficiency Virus Type 1 Potency of 2'-b-Fluoro-
2',3'-Dideoxyadenosine in Peripheral Blood
Mononuclear Cells. Biochemical Pharmacology. 1995;
50(2):274-276.
24. Ehrlich, L.S., Thalji, K., Whitman, K., Albert, D.A. A
preliminary evaluation of hydroxyurea for the
treatment of rheumatoid arthritis. Journal of
Rheumatology. 1995; 22(9):1646-1650.
***
Please note this from a fellow subscriber:
>To: mpd-support-L@listserv.aol.com
>From: Norman Freeburg <freeburg@ftn.net> >Subject: incorrect hydrea stats
>
>Robert,
> I noticed on the hydrea paper that you reprinted that the student author has an incorrect stat on hydrea. He cites that "in a 1993 study of 50 patients with PV, 20% developed leukemia...." I have the journal article he uses for this reference ("Acute leukemia after hydroxyurea therpy in PV,....." - European Journal of Haematology. 1994; 52:134-139.) His statement is incorrect as it relates to that article. The 50 HU treated patients include MF, ET, and PV - ten of these did develop acute leukemia or 20% (3 of these had prior myelosuppression other than HU). HOWEVER, when HU is considered with PV and ET only (not the MF patients) AND without previous alkylating agents, the incidence of leukemia is 10.5% (4 of 38). > I guess that's a little less frightening. However, as my doctor frequently says, "We don't know of a cancer drug that doesn't cause cancer." >(Speaking of chemotherapy, of course, not biological like IFN.)
***