STAT3 as a novel therapeutic target for glioblastoma multiformeBackground: Glioblastoma multiforme is the most common and most aggressive of the primary brain tumors. Glioblastoma multiforme continues to have very poor prognosis despite advances in chemotherapy and radiation therapy. Few patients with glioblastoma multiforme survive longer than 3 years and only a handful survive 5 years. The 5 year survival rate of the disease has remained unchanged over the past 30 years, and stands at less than three percent. Therefore, there is an urgent need to develop more effective treatments. Designing new therapies targeting glioblastoma multiforme specific oncogene products that are involved in cancer progression is a new area of research in novel cancer drug discovery. Many cases of glioblastoma multiforme from patients as well as from established human glioblastoma multiforme cell lines express constantly activated (persistently turn on) Stat3. Stat3 is an oncogene product because persistently activated Stat3 can induce normal murine cells or non-malignant human cells to form tumors in nude mice. Persistent activation of Stat3 signaling participates in tumor development and progression by stimulating cancer cell growth, suppressing host immune cells to recognize tumor cells, promoting tumor angiogenesis and resistance to cancer cell death induced by conventional therapies. Inhibition of persistently activated Stat3 dramatically induced cell death in cancer cells, demonstrating that constant Stat3 signaling is crucial for the survival and growth of tumor cells. It also indicates that Stat3 is a highly important and true therapeutic target for glioblastoma multiforme, because once Stat3 pathway is inhibited, cancer cells die quickly. Since Stat3 is frequently activated in glioblastoma multiforme and could contribute to glioblastoma multiforme progression, development, and survival, there is an important need to develop small molecular compounds that block persistently activated Stat3 pathway.
Preliminary studies: We have recently developed a new cell permeable, non-peptide low molecular weight compound (termed STA- 21) which is a natural product extract that inhibits Stat3 to form dimers and opened a new door for more effective and selective treatment of glioblastoma multiforme. In order for Stat3 to be activated, Stat3 must first form dimers through their SH2 domains and translocate to the nucleus to activate targeted genes that promote cell growth and survival. STA-21 binds to the SH2 domain of Stat3 and blocks the dimerization of Stat3 as well as inhibits cell growth and induces cell death of human glioblastoma multiforme cell lines, U373, U87, and U251. However STA-21 does not induce cell death in normal human bladder and skeletal muscle cells that do not express persistently activated Stat3 suggesting it is selective to cancer cells with persistently activated Stat3 but not normal human cells without persistently activated Stat3.
We further used structure-based strategy to select LLL-3 as the first STA-21 structural analogue and docking simulation showed identical binding mode as STA-21. LLL-3 has a much higher potential to generate a focused small molecule library because it is much easier to be synthesized than STA-21 and LLL-3 inhibits Stat3-dependent transcription activity and cell viability and induces cell death in human glioblastoma multiforme U373, U87, and U251 cell lines that express persistently activated Stat3.
Research design and Methods: Our first aim is to determine the efficacy of new Stat3 inhibitors, LLL-7 and LLL-8 that were derived from the new low molecular weight Stat3 inhibitor, STA-21 in glioblastoma multiforme cells. We will examine the potency of these new inhibitors to induce cell death of glioblastoma multiforme with persistently activated Stat3. We will also examine the selectivity of these new inhibitors in normal human cells without persistent activation of Stat3. Based upon our preliminary results with STA-21 and its first structural analogue, LLL-3, we predict that these new inhibitors sould be very effective to induce cell death of glioblastoma multiforme with persistently activated Stat3 but have much less toxicity in normal cells without persistent activation of Stat3.
Our second aim is to investigate the combination effects of our pharmacological Stat3 inhibitors, LLL-3, LLL- 7, and LLL-8 with commonly used anti-glioblastoma multiforme chemotherapeutic drugs. Persistent activation of Stat3 mediates the survival of cancer cells and confers resistance to cell death induced by chemotherapeutic drugs, vincristine and temozolomide in cancer cells. We will examine the combination of new Stat3 inhibitors with vincristine and temozolomide that have already shown clinical utility in the therapy of glioblastoma multiforme.
We hypothesize that blocking Stat3 surival pathway in cancer should switch drugresistant glioblastoma multiforme cells to become drug-sensitive cells and re-sensitize them to vincristine andtemozolomide. Such an approach should reduce adverse side effects to normal cells that are associated with conventional, aggressive chemotherapeutic drugs and may increase the therapeutic efficacy of each agent and improve the overall responses. We predict that our new pharmacological Stat3 inhibitors will sensitize and significantly enhance anti-glioblastoma multiforme drugs to induce cell death of glioblastoma multiforme cells.
Our long-range goal is to develop potent pharmacological agents that inhibit Stat3 in glioblastoma multiforme as a promising therapeutic approach. We anticipate that these proposed studies will pave the way for future clinical studies of pharmacological Stat3 inhibitor in combination with anti-glioblastoma multiforme chemotherapeutic drugs, as an entirely new class of anti-cancer therapy, with the ultimate goal of therapy for glioblastoma multiforme.
Innovation: Stat3 is a novel therapeutic target for glioblastoma multiforme. Our studies propose to target activated Stat3 in glioblastoma multiforme using novel non-peptide, cell-permeable small molecules that disrupt the dimerization of Stat3 protein and block Stat3 functions is innovative.
Expected impact and benefits of the proposed research: Glioblastoma multiforme continues to have very poor prognosis despite advances in chemotherapy and radiation therapy. The outcome of this research has potential to make a significant impact leading to the translation of novel agents targeting Stat3 into the future clinical trials for glioblastoma multiforme and improve the outcome of glioblastoma multiforme treatment. The proposed research should fulfill the mission of the James S. McDonnell Foundation in brain cancer research. The funding from the James S. McDonnell Foundation will provide critical seed money for our laboratories to complete this promising research project.
