Herceptin: Taming of a bad gene

HER2/neu: what is it all about?

The HER2/neu gene is a proto-oncogene (mapped on chromosome 17q21) that directs the synthesis of a surface protein called Human Epidermal Growth Factor Receptor 2 (HER2 protein or receptor). It’s homology to the rat neu gene had led many investigators to use the term HER2/neu for the human gene. The HER2 receptor is a 185 KD transmembrane receptor (p185 ^HER2) with an extracellular ligand binding site, which transmits growth signals from outside of the cell to the nucleus.⁽¹⁾
The HER2 gene (also called C-erbB-2) is a member of HER gene family which is composed of four closely related genes designed as HER1 to HER4. All of these genes encode transmembrane growth factor receptors, which are tyrosine kinase type I receptors with growth stimulating potential. Once the HER receptors are activated by a ligand e.g. (Epidermal Growth Factor or neu differentiation factor) tyrosine autophosphorylation of cytoplasmic signal proteins occurs with transmission of signals to the nucleus, thus regulating aspects of cell growth, division, migration and differentiation (signal transduction). It is important to recognize that normal cells contain 2 copies of the HER-2 gene and it has a physiological role in a development of many organs including the breast and the heart.⁽²⁾
It should be emphasized that any particular HER receptor exists as a monomer (single structure) in equilibrium with another receptor (i.e. dimmer receptors) and they are stabilized by ligand binding. In fact HER2 is the preferred dimerisation partner with other HER family receptors, this allows HER2 to participate in signal transduction induced by all ligands of the other HER partner. This explains why the HER2 gene has a significant contribution in the biology and pathogenesis of certain malignant tumors, in spite of the fact that no growth factor is known to act as a specific ligand for HER2.⁽³⁾   
Amplification of HER2 results in overexpression of the HER2/neu receptors on the cell surface (10-100 fold increase in the HER2 receptors). This occurs when multiple copies of Her-2 gene are generated in the nucleus due to unknown DNA dysregularity mechanism.⁽⁴⁾
The consequence of HER2 receptor overexpression is that the receptors transmit excessive signals for cell proliferation to the nucleus. This may lead to oncogenic transformation and more aggressive growth characters of the transformed cell. 
In fact all the data on the HER2-transfected cells, as well as transgenic animals, support the hypothesis that this proto-oncogene directly contributes to the pathogenesis and clinical aggressiveness of tumors that overexpress HER2
This preclinical data was further confirmed in clinical studies that have almost consistently demonstrated poor prognosis in breast cancer patients over expressing Her2-neu.⁽⁴⁾
A series of studies have suggested that Her2-positive breast cancer may predict for  resistance to hormonal therapy, especially tamoxifen ⁽⁵⁾. Few recent studies have suggested a relative superiority of letrizole, compared to tamoxifen in these patients.
Evidence is also accumulating to support the role of Her2 positivity as a marker of enhanced tumor sensitivity to optimal doses of anthracyclins ⁽⁶⁾. Data with other commonly used chemotherapeutic agents and combinations as CMF and Taxanes are still less clear.⁽⁷⁾

Her2/neu: How much positive is a true positive?

A range of different assays have been employed to determine HER2 status, each of which has its relative advantages and disadvantages.
Immunohistochemistry (IHC) staining is the most frequently used method to determine HER2 status of tumor tissue and FDA approved kits have been already available for the laboratory studies (HERCEP test). According to the intensity of membrane stain by IHC, cases are subdivided into four scores: score Zero, score 1+ (both considered HER2 –ve), score 2+ (considered HER2 +ve by many investigators) and score 3+ (definite HER2 +ve). However, Immunohistochemistry assay for HER2 determination still suffer from some technical problems including tissue processing, selection of antibodies and the subjective nature of evaluation.
On the other hand, amplification of HER2 gene using FISH technique to determine the number of gene copies had been considered a more objectively reliable method (more than five copies of HER2 gene). In a recent large multicenter study in USA, the investigators advocated withdrawal of the score 2+ by IHC as a criterion for a HER2 positive status unless it is further confirmed by FISH technique ⁽⁸⁾. Till these problems are corrected, FISH technique should remain the preferred method for determining HER2 status. 
In recent clinical trials using the two methods, patient’s selection with FISH could predict improved treatment outcome from Herceptin therapy compared with selection by IHC assay. ⁽⁹⁾

The HER2 receptor as a target for cancer treatment

The HER2 receptor has been investigated as a target for more effective anti-cancer treatments. Its accessible location on the cell surface makes it particularly attractive for monoclonal antibodies against its extracellular domain.However, other approaches are being developed, including tyrosine kinase inhibitors; anti-sense approaches which downregulate expression of the HER2 gene, intracellular expression of single chain antibodies (ScFvs) to functionally inactivate the receptor, and immunization to boost anti-HER2 responses. By far the most widely studied approach is via inhibition of HER2 receptors by monoclonal antibodies (MAB) directed at a specific epitope along the extracellular domain of the receptor ⁽¹⁰⁾.
Herceptin is a chimeric antibody -FIGURE 1-  that binds specifically to HER2 protein leading to internalization of the receptor and inhibition of Epidermal Growth Factor binding to the receptor with subsequent interference in signal transduction pathways that facilitate malignant proliferation. It also induces a profound antibody dependent cellular cytotoxicity against HER2 overexpressing tumor cells.

         FIGURE1

Herceptin (95% of human protein origin and 5% of murine origin) was the first monoclonal antibody approved in the treatment in breast cancer (and all solid tumors). It may be also active against other tumors with HER2 overexpression.    
In large studies ^{(11) (12) (13) (14)} (three phase II and one phase III studies), Herceptin has shown very impressive efficacy either as a single agent in heavily pretreated⁽¹¹⁾ or previously untreated metastatic breast cancer ⁽¹⁴⁾. more importantly, the addition of Herceptin to chemotherapy could improve the overall survival compared to chemotherapy alone ^{(12) (13)}
The safety profile of Herceptin indicated that adverse events were mainly mild to moderate chills and fever occurring in approximately 40% of patients, particularly following the first administration of the drug. The only significant adverse event was an increased risk for cardiac dysfunction, especially in women receiving Herceptin and Adriamycin. ^{(12) (15)}
The data suggested that cardiotoxicity was not markedly enhanced in the presence of Paclitaxel or Docetaxel but toxicity was much greater among patients who received doxorubicin and Cyclophosphamide plus Herceptin. This may be related to synergistic effects between chemotherapeutic agents particularly doxorubicin and the Herceptin on the myoglobin. At the present time, it seems much safer to administer Herceptin with a Taxane than with an Anthracycline. ^{(12) (13) (15)}  

Herceptin in metastatic breast cancer: How can we do better?

During its preclinical development, it was evident that Herceptin can exert definite synergy with some chemotherapeutic drugs/or drugs combination. ^{(16) (17)}
Accordingly, some clinical studies were designed to explore what had been observed invitro concerning the beneficial synergistic interaction between Herceptin and chemotherapeutic drugs in the treatment of breast cancer patients. These studies showed that adding Herceptin to Navelbin, Taxanes or the combination of Taxanes and Platinum salts could result in extremely favorable treatment outcome with very infrequent cardiac events. ^{(18) (19) (20) (21)}
In one important randomized phase II study, Roberts et al. ⁽²⁰⁾could show that the addition of platinum salt (Carboplatin) to the combination of Herceptin/ Paclitaxel could significantly improve response rate and time to progression compared to Herceptin/ Paclitaxel alone specially in  fish +ve patients
Our group in Cairo Cure pioneered a phase II study testing the synergy between Herceptin and Cisplatin in combination with either weekly Paclitaxel or Navelbin (according to whether or not a Taxane had been previously used). The study design is shown in Table I

Table I

 The preliminary analysis of the first 15 cases in this phase II ongoing study showed an objective response in 9 cases (60%) with a median duration of 9 months. No cardiac dysfunction was seen in all patients. ⁽²¹⁾
The update of our results on 25 patients entered into the study till Jan 2004 will be updates soon. We confirm in this update what we have previously reported concerning the very high incidence of brain metastasis among these patients reaching 36% (9 cases out of 25).
Important lessons may be confidently concluded from all reported studies on Herceptin in metastatic breast cancer:

  - Herceptin may induce remission even in heavily pretreated patients confirming the validity of             the concept of targeting therapy.

        - The remissions encountered by Herceptin are characteristically of longer duration compared to         classic chemotherapy.

       - Herceptin therapy should be restricted to patients with Fish (+ve) or IHC score (3+). This would         render treatment more effective and more cost effective.

  - Novel combination including Platinum/Taxanes/Navelbin may improve the treatment outcome with     apparently  minimal cardiac events.

        - Treatment outcome obtained by Herceptin either alone or in combination with chemotherapy is apparently superior if Herceptin is used in the early course of the disease.

        - Moving Herceptin into the adjuvant phase of the disease is a very rationale approach, however an extreme caution should be made to monitor the cardiac events in such patients.

     Herceptin in the adjuvant setting of breast cancer: Early targeting may be a better job

 At the present time, 4 major adjuvant trials are testing the role of adjuvant Herceptin in primary breast cancer. (NSABP-B31, Intergroup N9831, BCIRG 006 and the HERA trial). Our group in Cairo Cure is involved in the BCIRG 006 study which has already finished recruitment in April 2004.
The results of these studies will not be made available before 1-2 years from today. Till then we don’t advise to give Herceptin for Her-2 +ve tumors in the adjuvant setting outside one of these large studies.

References

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2-       Schroeder W, Lee DC. Dynamic expression and activation of ErbB receptors in the developing mouse mammary gland. Cell Growth Differ 1998:9:451-64

3-       Van Der Geer P, Hunter T, Lindberg RA. Receptor protein tyrosine kinases and their signal transduction pathways. Annu Rev Cell Dev Biol 1994;10:251-337

4-       Slamon DJ, Clark GM, Wong SG, et al; Human breast cancer: correlation of relapse and survival with amplification of the Her2-neu oncogene. Science 1987:235:177-82

5-       De Laurntiis M, Arpino G, Masarelli E, et al; A metanalysis of the interaction between Her2 and the response to endocrine therapy (ET) in metastatic breast cancer (MBC). Proc Am Soc Clin Oncol 2000;19:78a (abstract 300)

6-       Ravdin PM, Green S, Albain KS, et al; Initial report of the SWOG biological correlative study od c-erbB-2 expression as a predictor of outcome in a trial comparing adjuvant CAF T with tamoxifen (T) alone. Proc Am Soc Clin Oncol 1998;17:97a (abstract 374)

7-       Picart MJ, Di Leo A, Hamilton A. Her2: a “predictive factor” ready to use in the daily management in breast cancer patients? Eur. J Cancer, 2000; 36:1755-61

8-       Tubbs R, Roche P, Stoler M, et al; Discrepancies in laboratory assessment of eligibility for Herceptin therapy: the message matters. Proc Am Soc Cli Oncol 2000:19:77a

9-       Vogel CL, Cobleigh MA, Tripathy D, et al; Superior outcomes with (Herceptin) trastuzumab (H) in fluorescence in situ hybridization (FISH)-selected patients. Proc Am Soc Clin Oncol 2001a;20:22a (abstract 86)

10-   Lewis GD, Figari I, Fendly B, et al; differential responses of human tumor cell lines to anti-p185^HER2 monoclonal antibodies. Cancer Immunol Immunother 1993;37:255-63

11-   Cobleigh MA, Vogel CL, Tripathy D, et al; Multinational study of the efficacy and safety of humanized anti-Her2 monoclonal antibody in women who have her2 overexpressing breast cancer that has progressed after chemotherapy for metastatic diseases. J Clin Oncol 1999; 17:2639-48

12-   Slamon DJ, Leyland-Jones B, Shak S, et al; Use of chemotherapy plus a monoclonal antibody against Her2 for metastatic breast cancer that overexpresses Her2. N Engl J Med 2001 a; 344:783-92

13-   Extra J.M, Cognetti F, Chan S et al; Randomized phase II trail (M77001) of trastuzumab (Herceptin) plus Docetaxel versus Docetaxel alone as first line therapy in patients with HER2 positive metastatic breast cancer. EJC abs 672 Vol1, 2003

14-   Vogel CL, Cobleigh MA, Tripathy D, et al; Efficacy and safety of trastuzumab (Herceptin) as a single agent in first line treatment of Her2-overexpressing metastatic breast cancer. J Clin Oncol 2001b

15-   Tripathy D Seidman A, Hudis C, et al; Effect of cardiac dysfunction on treatment outcome in the Herceptin (trastuzumab) (H) pivotal trial. Proc Am Soc Clin Oncol 2001;20:49a (abstract 191)

16-   Pietras RJ, Frendly BM, Chazin VR, et al; Antibody to Her2-neu receptor blocks DNA repair after cisplatinum in human breast and ovarian cancer cells. Oncogene 1994;54:1829-38

17-   Pegram M, Hsu S, Lewis G, et al; inhibitory effects of combinations of Her2-Neu antibody and chemotherapeutic agents used for treatment of human breast cancers. Oncogene 1999; 18:2241-51

18-   Brustein HJ, Kuter I, Campos SM, Gelman RS, et el; Clinical activity of trastuzumab and venorelbine in women with Her2 overexpressing breast cancer. J Clin Oncol 2001;19:2722-30

19-   Nabholtz JM, Pienkowski T, Northfelt D, et al; Results of two open label multicenter phase II pilot studies (BCIRG 101 and 102) with Trastuzumab (Herceptin) in combination with docetaxel and platinum salts (cis- or Carboplatin) (THC) as therapy for advanced breast cancer IN WOMEN OVEREXPRESSING THE Her2-neu proto-oncogene (abstract 695) Eur J Cancer 2001;37:S190

20-   Roberts et al. proceedings SABCC Abs 520, 2002

21-   Azim H, Salam A. M, Mubarak N, Her2-Neu overexpression: from poor prognosis to improved survival. J of Chemoth; 2002, V14, suppl. 1

Other Breast Cancer Articles:

    - Docetaxel/cisplatinum metastatic breast cancer previously exposed To anthracycline

    - Combination of Herceptin, Cisplatinum and Taxotere in Metastatic Breast Cancer

    - Temodal in the treatment of brain metastasis of mammary origin