Inducement, Characterization and Targeting of Human Cancer Stem Cells
Stem cells undergo a process termed differentiation that consists of producing different types of cells. These stem cells multiply into several copies of the original cell(s) which is called self-renewal. However, this self-renewal is a regulated process and only the necessary numbers of copies of these stem cells are produced in the human or animal body. On the contrary, cancer cells self-renew in an unregulated manner and undergo uncontrolled proliferation. Both the stem cells and cancer cells express certain characteristic proteins termed as marker antigens. A cancer stem cell (CSC) is a cell that expresses both the stem cell and cancer cell proteins. CSCs are expected to be sparse when the tumors are formed but are drug resistant and cause cancer anew even when the non-CSC tumor cells are killed.
We have identified stem cell markers such as CD133 in certain but not all of a panel of human ovarian cancer cells. These CSCs and their counterpart cancer cells that do not express CD133 will be tested for the formation of secondary tumors to further characterize the CSC from a cancer cell. We will also use the Melanoma-624 (cancer of the skin or eye) tumor cells which are negative for CD133, in parallel experiments to ovarian cancer cells. We will also study the possibility of inducement of CSCs anew by these ovarian and Mel-624 tumor cells and also their susceptibility to killing by vaccines which require immune responses as in humans.
For this purpose, we will use immunodeficient mice transplanted with human thymus and liver tissues (NOD/SCID-hu mice) to produce stem cells contained in blood/bone marrow/liver and white blood cells that that generate immune responses similar to those in humans. We will engraft/transplant the ovarian or Mel-624 CSCs and cancer cells separately in parallel experiments in these NOD/SCID-hu mice to induce secondary tumors for further characterization of CSCs. We will also induce CSCs by transfer of genes involved in self-renewal of these stem cells into the transplanted and developed human tissue of these mice. The characterization of the tumor formation will include the possible generation of new CSCs due to the stem cell-cancer cell contact in the human tissue of these mice. We will compare the potency of generation of CSCs or cancer cells due to the influence of secondary tumors.
Finally, we will determine if the CSCs are more resistant to killing by our nanoparticle (tiny particles)-based vaccines than the cancer cells that do not express stem cell markers (not CSCs). In other words, we will determine if the CSCs can evade the immune responses that are produced in these mice to target the cancer cells. Thus these studies will reveal important information on the role of CSCs in cancers and help in appropriate targeting to attack the CSCs through development of additional vaccines in the event the CSCs are resistant to our presently available vaccines.
The cancer incidence in the state of California is almost on the same par as the rest of the nation. Non-Hispanic White females have a higher incidence rate followed by African Americans among females of different ethnicities. Among the males, African Americans followed by Non-Hispanic White population have the highest incidence and also mortality. The same trend exists in the mortality rates among females of African American and Non-Hispanic White populations. Males in general have a higher incidence and mortality than females. (All these data are summarized from Cancer in California, 2005, California Cancer Registry, Dept of Health Services).
The cancer incidence of Melanoma is at least 50% lower than among Non-Hispanic Whites compared to African American, Asian/Pacific Islander and Hispanic populations between the years 1998-2002. Melanoma cancer is one of the very few cancers the incidence of which is at a much higher rate among the Non-Hispanic White population. Incidentally, this grant proposal deals also with Melanoma in addition to Ovarian cancer. The estimated prevalence of cancer of Melanomas of the Skin in 2005 is 40,700 (Male-20,300, Female 20,400) and Ovarian cancer is 22,500. In 2005, the expected new cases of cancer of the Melanomas of the Skin were stated to be 5,810 (Male-3,340, Female-2,455) and expected deaths were 845 (Male-570, Female-280); expected new cases of Ovarian cancer were to be 2,260 and expected deaths were 1,570.
The estimated prevalence of cancer in California in 2005 for all races combined is 950,000 (Male-402,800, Female-547,100). The expected new case at that time were 136,875 (Male-69,780, Female-66,855) and expected deaths were 54,300 (Male-27,485, Female-26,855).
Our proposed research deals with attacking two of the more prevalent cancers that include Melanoma and Ovarian cancer in the state of California. The main objective of this proposal is to study the early formation of the cancer stem cells (CSCs). In addition, we will attempt to target specifically CSCs utilizing our novel receptor-targeted nanoparticle-based vaccines. Therefore, the findings of this study will not only help in understanding the (stem cell) origin of cancer, but could also be used in translational and clinical programs that will benefit many patients with cancer.
The ability to prospectively identify, isolate and study cancer stem cells will significantly alter the way we think about, prevent, and treat cancer. Our novel approach to studying the CSCs and the design of nanoparticle vaccines targeting cancer stem cells is highly innovative and holds great promise. This approach has never been applied to the prevention or treatment of any type of cancer. Therefore, the findings of this study will be translated to clinical applications, which will benefit many patients with cancer and will reduce the human suffering and the impact of this disease in California.