Projection Description
Approximately 75% of all patients diagnosed with invasive breast cancer have hormone receptor positive disease, which means that hormones such as estrogen and progesterone act as fuel for their cancer cells to grow. There are a number of anti-hormonal agents in clinical practice that can effectively block the growth of these tumors. These drugs include Tamoxifen, Fulvestrant and aromatase inhibitors.

While the ubiquitous application of antihormone drugs for treatment and prevention of breast cancer has significantly advanced patient care, the consequence of prolonged treatment with antihormonal therapy is the development of drug resistant disease in a significant proportion of patients. Most women who reach the stage of hormone-receptor positive drug resistance succumb to their disease, as there are few lines of evidence available to suggest an effective treatment strategy in the Stage IV setting.

Today, through two decades of pioneering research by Professor V. Craig Jordan, it is becoming accepted that there are two distinct phases of anti-hormone-resistant breast cancer; Phase I resistant-tumors grow in response to estrogen, or anti-estrogen (classical resistance). Phase II resistant-tumors, however, paradoxically undergo estrogen-induced cell death. The Jordan laboratory, in collaboration with our laboratory, believe the reason for this is because breast tumor cells that are struggling to survive in an estrogen-free environment through the many years of anti-hormonal therapy, “evolve” over time. This evolution involves the tumors acquiring genetic changes that provide alternative routes for breast tumor cell survival that circumvent the need for estrogen, which is no longer available. Importantly, in doing so, the tumor cells become super-sensitized to the cell death-promoting effects that can be elicited by estrogen. Given these observations, if we are able to determine which women undergoing anti-hormonal therapy reach the stage of Phase II drug resistance, we would have a phenomenal opportunity to provide estrogen-based therapy to these women, to selectively kill their hormone receptor positive, Phase II-resistant breast cancer.

Our laboratory at TGen has a strong collaboration with Dr. V. Craig Jordan, Scientific Director Lombardi Comprehensive Cancer Center, Georgetown University Medical Center. Dr. Jordan’s laboratory has developed a laboratory model of estrogen receptor positive, Phase II resistant breast cancer cell line model called MCF7:5C. These immortalized cancer cells grow robustly in the absence of estrogen, mimicking the situation observed in post-menopausal women with hormone receptor positive breast cancer treated exhaustively with anti-hormone therapy. Importantly, when MCF7:5C cells are given estrogen, they die within 48-72h. This cell line therefore mimics the observed responses in advanced breast cancer patients, and can be exploited as a laboratory model to understand key biomarkers of Phase II resistance, and the mechanism by which estrogen is lethal in this cancer cell context.

The goal of this study is to comprehensively define the molecular characteristics of phase 2 resistant breast cancer cells to define what constitutes Phase II resistance at the genetic and molecular level. We are optimistic this will allow us to develop a rationale for effective treatment strategies for advanced breast cancer patients with hormone receptor positive anti hormone treatment-refractory breast cancer.

Our first aim is to compare and contrast the Phase II resistant breast cancer cells with the hormone-responsive cells. The genetic material has been extracted from these two cell lines and is currently being examined using state-or-the-art tumor profiling technologies at TGen. All experiments were successful in generating optimal data for this analysis. Preliminary evidence shows dramatic evolution of the DNA material in the Phase II resistant breast cancer cells compared to the hormone-responsive cells, indicating that estrogen deprivation has lead to dramatic changes in the tumor DNA over time. This is likely to therefore be occurring in patient tumors during a course of antihormone therapy.

We are currently meeting our budget projections based on workflow timelines.

The second aim of this proposal is to systematically block the function of up to 7000 genes known to play a role in cancer progression in the Phase II resistant cells, to determine whether any of these genes play a role in the ability of estrogen to kill these cells. This process involves optimization of several experimental parameters including cell density and chemical toxicity. Optimization steps will be completed in approximately 4 months.

1) An immortalized laboratory model of Phase II resistance to anti-hormone therapy has been collaboratively obtained from Professor V. Craig Jordan’s laboratory. 2) DNA and RNA have been isolated from Phase II resistance breast cancer cells and compared to the DNA and RNA from the original hormone-responsive cells using two forms of genomic profiling technology. Striking changes have been identified in the Phase II resistant cells which highlight an important alternative pathway operating in these cells.