Visit our Expo - Redox and Inflammation signaling 2012

Protein Kinase C alpha as a potential target in the treatment of acquired antiestrogen
resistance of human breast cancer.
Jan. S. Jepsen 1 , Lisa Frankel 1 , Bo Hansen 2 , Anne E. Lykkesfeldt 1
1 Danish Cancer Society, Strandboulevarden 49, DK-2100, Copenhagen, Denmark.
2 Santaris Pharma A/S, Bøge Allé 3, DK-2970, Hørsholm, Denmark.
E-mail: jsj@cancer.dk, lfr@cancer.dk, bh@santaris.com, al@cancer.dk
Initially, antiestrogen therapy is an efficient treatment of hormone-dependent breast cancer.
However, many patients eventually acquire resistance. This presents a serious therapeutic
problem and current research aims at elucidating the underlying molecular mechanisms in
order to identify new targets in treatment of patients with resistant tumors.
The Protein Kinase C alpha (PKC alpha) level is increased in several cancer types. However,
limited information is available on the involvement of PKC alpha in antiestrogen resistance.
We screened nine different antiestrogen resistant breast cancer cell lines and found that
elevated PKC alpha expression was a general phenomenon. Two of the resistant cell lines
were chosen for further studies: MCF-7/TAM R -1 and MCF-7/182 R -6, resistant to tamoxifen
and ICI 182,780 (faslodex), respectively. These two cell lines posses highly elevated PKC
alpha protein expression and kinase activity levels in comparison to parental MCF-7 cells.
A potent and relatively specific PKC alpha inhibitor, Ro-32-0432, resulted in a significant
growth inhibition of these antiestrogen resistant cell lines relative to MCF-7. Moreover,
specific down-regulation of PKC alpha by transient transfection of antisense oligonucleotides
resulted in a 30-40% growth inhibition of TAM R -1 and 182 R -6, while MCF-7 remained
unaffected. Additionally, using small hairpin RNA, we generated stable PKC alpha knockdown
cells with almost no PKC alpha protein expression and found that PKC alpha knock
down restored the sensitivity of TAM R -1 to tamoxifen. Finally, preliminary results indicate
that MCF-7 clones which overexpress PKC alpha are more resistant to antiestrogen mediated
growth inhibition than parental MCF-7 cells. These results suggest that PKC alpha may be
causally involved in the growth of antiestrogen resistant cells and that PKC is a potential
therapeutic target in the treatment of antiestrogen resistant breast cancer.
Recent papers (papers from 2004, 2005)
Frogne T, Jepsen JS, Larsen SS, Fog CK, Brockdorff BL and Lykkesfeldt AE. Antiestrogenresistant
human breast cancer cells require activated protein kinase B/Akt for growth. Endocr
Relat Cancer. 2005 12(3): 599-614.
Christensen GL, Jepsen JS, Fog CK and Lykkesfeldt AE. Sequential versus combined
treatment of human breast cancer cells with antiestrogens and the vitamin D analogue
EB1089 and evaluation of predictive markers for vitamin D treatment. Breast Cancer
Research and Treatment. 2004 85(1):53-63.
Juncker-Jensen A, Lykkesfeldt AE, Worm J, Ralfkiær U, Espelund U and Jepsen JS. Insulinlike
growth factor binding protein 2 is a marker for antiestrogen resistant human breast cancer
cell lines but is not a major growth regulator. Submitted to Growth Hormone & IGF Reseach
Jepsen JS, Pfundheller HM and Lykkesfeldt AE: Specific down regulation of p21 (WAF1/CIP1)
and the estrogen receptor " in MCF-7 cells by antisense oligonucleotides containing locked
nucleic acid (LNA). Oligonucleotides. 2004 14(2): 147-156.
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