Fyn and SRC are effectors of oncogenic epidermal growth factor receptor signaling in glioblastoma patients.

Activating epidermal growth factor receptor (EGFR) mutations are common in many cancers including glioblastoma. However, clinical responses to EGFR inhibitors are infrequent and short-lived. We show that the Src family kinases (SFK) Fyn and Src are effectors of oncogenic EGFR signaling, enhancing invasion and tumor cell survival in vivo. Expression of a constitutively active EGFR mutant, EGFRvIII, resulted in activating phosphorylation and physical association with Src and Fyn, promoting tumor growth and motility. Gene silencing of Fyn and Src limited EGFR- and EGFRvIII-dependent tumor cell motility. The SFK inhibitor dasatinib inhibited invasion, promoted tumor regression, and induced apoptosis in vivo, significantly prolonging survival of an orthotopic glioblastoma model expressing endogenous EGFRvIII. Dasatinib enhanced the efficacy of an anti-EGFR monoclonal antibody (mAb 806) in vivo, further limiting tumor growth and extending survival. Examination of a large cohort of clinical samples showed frequent coactivation of EGFR and SFKs in glioblastoma patients. These results establish a mechanism linking EGFR signaling with Fyn and Src activation to promote tumor progression and invasion in vivo and provide rationale for combined anti-EGFR and anti-SFK targeted therapies.

BMS-214662 potently induces apoptosis of chronic myeloid leukemia stem and progenitor cells and synergizes with tyrosine kinase inhibitors.

Chronic myeloid leukemia (CML), a hematopoietic stem-cell disorder, cannot be eradicated by conventional chemotherapy or the tyrosine kinase inhibitor imatinib mesylate (IM). To target CML stem/progenitor cells, we investigated BMS-214662, a cytotoxic farnesyltransferase inhibitor, previously reported to kill nonproliferating tumor cells. IM or dasatinib alone reversibly arrested proliferation of CML stem/progenitor cells without inducing apoptosis. In contrast, BMS-214662, alone or in combination with IM or dasatinib, potently induced apoptosis of both proliferating and quiescent CML stem/progenitor cells with less than 1% recovery of Philadelphia-positive long-term culture-initiating cells. Normal stem/progenitor cells were relatively spared by BMS-214662, suggesting selectivity for leukemic stem/progenitor cells. The ability to induce selective apoptosis of leukemic stem/progenitor cells was unique to BMS-214662 and not seen with a structurally similar agent BMS-225975. BMS-214662 was cytotoxic against CML blast crisis stem/progenitor cells, particularly in combination with a tyrosine kinase inhibitor and equally effective in cell lines harboring wild-type vs mutant BCR-ABL, including the T315I mutation. This is the first report of an agent with activity in resistant and blast crisis CML that selectively kills CML stem/progenitor cells through apoptosis and offers potential for eradication of chronic phase CML.

Targeting multiple kinase pathways in leukemic progenitors and stem cells is essential for improved treatment of Ph+ leukemia in mice.

It is generally believed that shutting down the kinase activity of BCR-ABL by imatinib will completely inhibit its functions, leading to inactivation of its downstream signaling pathways and cure of the disease. Imatinib is highly effective at treating human Philadelphia chromosome-positive (Ph(+)) chronic myeloid leukemia (CML) in chronic phase but not Ph(+) B cell acute lymphoblastic leukemia (B-ALL) and CML blast crisis. We find that SRC kinases activated by BCR-ABL remain fully active in imatinib-treated mouse leukemic cells, suggesting that imatinib does not inactivate all BCR-ABL-activated signaling pathways. This SRC pathway is essential for leukemic cells to survive imatinib treatment and for CML transition to lymphoid blast crisis. Inhibition of both SRC and BCR-ABL kinase activities by dasatinib affords complete B-ALL remission. However, curing B-ALL and CML mice requires killing leukemic stem cells insensitive to both imatinib and dasatinib. Besides BCR-ABL and SRC kinases, stem cell pathways must be targeted for curative therapy of Ph(+) leukemia.

Identification of novel functional inhibitors of 17beta-hydroxysteroid dehydrogenase type III (17beta-HSD3).

BACKGROUND: Endocrine therapy of prostate cancer (PCa) relies on agents which disrupt the biosynthesis of testosterone in the testis and/or by direct antagonism of active hormone on the androgen receptor (AR) in non-gonadal target tissues of hormone action such as the prostate. METHODS: In an effort to evaluate new therapies which could inhibit gonadal or non-gonadal testosterone biosynthesis, we developed high throughput biochemical and cellular screening assays to identify inhibitors of 17beta-hydroxysteroid dehydrogenase type III (17beta-HSD3), the enzyme catalyzing the conversion of androstenedione (AdT) to testosterone. RESULTS: Initial screening efforts identified a natural product, 18beta-glycyrrhetinic acid, and a novel derivative of AdT, 3-O-benzylandrosterone, as potent inhibitors of the enzyme. Further efforts led to the identification of several classes of non-steroidal, low molecular weight compounds that potently inhibited 17beta-HSD3 enzymatic activity. One of the most potent classes of 17beta-HSD3 inhibitors was a series of anthranilamide small molecules identified from a collection of compounds related to non-steroidal modulators of nuclear hormone receptors. The anthranilamide based 17beta-HSD3 inhibitors were exemplified by BMS-856, a compound displaying low nanomolar inhibition of 17beta-HSD3 enzymatic activity. In addition, this series of compounds displayed potent inhibition of 17beta-HSD3-mediated cellular conversion of AdT to testosterone and inhibited the 17beta-HSD3-mediated conversion of testosterone necessary to promote AR-dependent transcription. CONCLUSIONS: The identification of non-steroidal functional inhibitors of 17beta-HSD3 may be a useful complementary approach for the disruption of testosterone biosynthesis in the treatment of PCa.

Structure based approach to the design of bicyclic-1H-isoindole-1,3(2H)-dione based androgen receptor antagonists.

A novel series of isoindoledione based compounds were identified as potent antagonists of the androgen receptor (AR). Co-crystallization of members of this family of inhibitors was successfully accomplished with the T877A AR LBD. A working model of how this class of compounds functions to antagonize the AR was created. Based on this model, it was proposed that expanding the bicyclic portion of the molecule should result in analogs which function as effective antagonists against a variety of AR isoforms. In contrast to what was predicted by the model, SAR around this new series was dictated by the aniline portion rather than the bicyclic portion of the molecule.

Identification of a novel class of androgen receptor antagonists based on the bicyclic-1H-isoindole-1,3(2H)-dione nucleus.

A novel series of isoindoledione based compounds were identified as potent antagonists of the androgen receptor (AR). SAR around this series revealed dramatic differences in binding and function in mutant variants (MT) of the AR as compared to the wild type (WT) receptor. Optimization of the aniline portion revealed substitution patterns, which yielded potent antagonist activity against the WT AR as well as the MT AR found in the LNCaP and PCa2b human prostate tumor cell lines.

The synthesis and evaluation of [2.2.1]-bicycloazahydantoins as androgen receptor antagonists.

A novel series of [2.2.1]-azahydantoins has been designed and synthesized in an enantiospecific manner. The ability of these compounds to act as antagonists to the androgen receptor was investigated and several were found to have potent activity in vitro.