Research Grants Awarded
Overcoming Primary Herceptin Resistance In Breast Cancer
Rationale: Despite the enormous clinical success of Herceptin, major challenges remain in the treatment and management of ErbB2-positive breast cancer patients. For example, roughly half of patients do not respond to Herceptin treatment (primary resistance), and those who do initially respond eventually progress (secondary resistance). This is an important clinical problem, and we are, therefore, interested in the mechanisms of primary Herceptin resistance. To study this problem we have used ErbB2-positive, Herceptin-resistant breast cancer cell lines as a model of primary patient resistance. Five of five Herceptin resistant cell lines, when cultured long-term with Herceptin (primary resistant, Herceptin treated: PRHT), exhibited substantial reprogramming of ErbB expression patterns despite the lack of Herceptin-induced growth inhibition. Specifically, EGFR and ErbB3 expression were greatly increased in PRHT breast carcinoma cell lines when compared to parental cell lines. We recognize the potential exploitative value of these two receptors as potential targets for therapeutic intervention in Herceptin resistant breast cancer patients (e.g., EGFR upregulation in response to Herceptin, may be correlated with de novo gefitinib [Iressa] or lapatinib [Tykerb] sensitivity.)
Hypothesis: Based on our observation that Herceptin treatment reprograms the ErbB expression pattern of both Herceptin-sensitive and resistant breast cancer cell lines, we believe we are in a unique position to challenge the very definition of Herceptin resistance. We hypothesize that Herceptin may remain a viable treatment for primary Herceptin-resistant breast cancer via modulation of related signaling pathways. Specifically, we hypothesize that Herceptin-mediated upregulation of EGFR and ErbB3 in PRHT breast carcinoma cell lines may sensitize previously unresponsive cell lines to both EGFR and ErbB3 ligands (e.g., EGF, heregulin) and inhibitors (e.g., erlotinib, gefitinib). Furthermore, we hypothesize that these alterations in ErbB receptor expression in response to Herceptin in PRHT cell lines is indicative of similar altered patterns in ErbB expression following Herceptin treatment in vivo
Specific Aim 1. Evaluate the expression of ErbB family members in primary Herceptin-resistant breast carcinoma cell lines. Our preliminary studies have focused on five breast carcinoma cell lines. While all five Herceptin-resistant, ErbB2-positive breast cancer cell lines showed similar patterns of alterations in ErbB expression following Herceptin treatment, to achieve statistical significance and also to confirm and expand our studies, here we propose analogous studies in additional cell lines. ErbB family receptor expression will be assayed by standard immunological methods in each PRHT breast carcinoma cell line, following long-term Herceptin treatment, and this pattern of expression will be compared to parental cells.
Specific Aim 2. Determine the sensitivity of Herceptin treated, primary Herceptin resistant breast cancer cell lines to ErbB ligands and ErbB-targeted inhibitors. To establish that the observed alterations in ErbB receptor expression in PRHT breast cancer cell lines vs. parental cell lines are functional, we propose to treat these same cell lines with a series of ErbB-targeted (EGFR and ErbB3) inhibitors e.g,, does upregulation of EGFR in PRHT breast carcinoma cell lines sensitize these cell lines to EGF, TGF-?, gefitinib, erlotinib, and/or cetuximab treatment.
Specific Aim 3. Correlate changes in ErbB expression patterns in breast cancer patient tumors before and after Herceptin treatment with clinical response. The goal of this aim is, therefore, to examine ErbB expression patterns in vivo, in breast tumors both prior to and following Herceptin treatment, to: 1) confirm that Herceptin-mediated ErbB reprogramming also occurs in Herceptin primary resistant breast tumors in vivo, and 2) to determine if these changes can be correlated with primary Herceptin resistance vs. sensitivity.
Design: To address these hypotheses, we propose a series of in vitro studies using primary Herceptin sensitive vs. resistant cell lines, cultured continuously in Herceptin, with matched parental controls. We will analyze Herceptin-induced alterations in ErbB expression patterns, as well as the responsiveness of these cell lines to ErbB-targeted ligands and inhibitors (i.e., examine the functional implications of changes in ErbB expression patterns in these same cell lines). Finally, we will confirm Herceptin-induced changes in ErbB expression patterns in vivo by comparing expression patterns in biopsies of breast tumors before and after Herceptin treatment.
Impact: The long term goal of this project is to challenge the existing dogma associated with primary Herceptin resistance in breast cancer, based on our strong preliminary data, which suggest that while some Herceptin-treated breast cancer derived cell lines may be Herceptin ?resistant?, they are not necessarily unresponsive to Herceptin. The logical extension of this in vitro observation is that breast tumors that exhibit primary resistance to Herceptin, may, in fact, be sensitized to treatment with other biologically-directed therapeutics (e.g., lapatinib). Together, these observations have obvious implications for patient stratification prior to treatment, since approximately half of patients with ErbB2-positive breast cancer exhibit primary resistance to Herceptin.
For decades, the standard treatment for breast cancer patients has been chemotherapy that damages all tissues of the body, rather than specifically targeting the tumor. Over the past decade, so-called ?biologically-targeted? therapeutics have come into the clinic, with the promise of greater effectiveness against the tumor with few side effects. The crowning jewel in breast cancer therapeutics has been the development of one such biologically-targeted therapeutic called Herceptin, which has saved the lives of tens of thousands of women. This new drug has been much more successful than other drugs because it was designed to specifically inhibit a key growth regulator in breast cancer cells called ?HER2? (also called ?ErbB2?). However, only about 20-25% of all breast cancers depend on HER2 for their growth. Therefore, for the past several years scientists and physicians have been trying to direct this expensive drug treatment to only those women who will respond to it (hence, the term ?personalized medicine?), by using special assays (3 or 4 different methods) to determine which tumors have HER2. But in spite of over a decade?s worth of work on these HER2 assays, we still cannot accurately predict who will show the most benefit from Herceptin treatment. Perhaps most unsettling is the fact that roughly half of patients do not respond at all to Herceptin, despite having the clinical criteria of patients that do respond to Herceptin.
Physicians are left with the difficult question of what to do with breast cancer patients who do not respond to Herceptin. Our preliminary studies have shown for the first time that breast cancers that do not stop growing when treated with Herceptin do, nonetheless, ?respond? to Herceptin in subtle ways. Here we propose that these subtle changes actually render Herceptin-resistant breast cancers dependent on another regulator for continued growth. Using this fellowship award, if I can demonstrate this to be the case, we may have a whole new method for taking out cancer cells, while leaving normal cells intact. The beauty of our approach is that we will still use Herceptin clinically, but will instead use it to sensitize breast tumors to a new type of cancer growth inhibitor.
In summary, the experiments outlined here challenge existing notions of the basis for Herceptin resistance, while at the same time have profound implications for how patients are tested for Herceptin therapy, how Herceptin therapy is applied, follow up treatment after Herceptin therapy, and how we should define ?success? in terms of breast cancer treatment. Finally, these results may greatly advance Herceptin treatment by finally addressing the difficult question of how to treat HER2-positive breast cancers that do not respond to the most effective treatment available.