Abstract 452: Novel autophagy inhibitory strategies to overcome chemotherapy resistance in multiple myeloma

Multiple myeloma (MM) is an incurable disease. Classical chemotherapeutics including bortezomib, melphalan, lenalidomide and thalidomide have greatly enhanced survival times. Unfortunately, patients typically relapse and become refractory with an average survival of 5 years post-diagnosis. Our emerging studies demonstrate a novel role for ULK3 in regulating autophagy in MM, a key program that sustains cell survival under times of stress and has been implicated as a major mechanism of proteasome inhibitor (PI) resistance. MM is known to be highly dependent on autophagy and, currently, specific ULK3 inhibitors are lacking. We posit that by targeting this marker in chemotherapy resistant MM patients, we can circumvent alternative metabolic routes and resensitize to standard of care proapoptotic therapy. We performed RNASeq analysis of CD138+ MM cells derived from patients across the disease stages spectrum (n=815) to confirm the role of ULK3 in disease progression and resistance to chemotherapy. We developed novel inhibitors SG3014/MA9060 that target multiple kinases including ULK3 (EC50 90nM) as well as BRD4. BRD4 is a known driver of MYC and its expression is increased in refractory MM. The BRD4 inhibitor, JQ1, effectively impairs the tumorigenic potential of MM but resistance has also been noted. We determined the efficacy of MA9060 for the treatment of CD138+ MM isolated from naive and refractory patients using a novel ex vivo high throughput platform developed at Moffitt.ULK3 is highly associated with MM stage of the disease. Refractory MM patients have increased autophagy activity with significantly higher expression of ULK3 in refractory patients and in drug resistant cell lines (immunoblotting U266 vs U266-PSR; RPMI-8226 vs RPMI-8226-B25; ABNL vs V10 resistant cells).Genetic ablation of ULK3 by siRNA in U266 and 8226 cell lines results in rapid cessation of the downstream autophagy proteins (ULK1, ATG13, pATG13) and MM cell death within 72h of transduction. Increased concentrations of autophagy inhibitors MA9060/SG3014 progressively decreased CMYC and ULK3 levels, as measured by immunoblotting in U266 cells. In vivo preclinical model of U266Luc tail vein injection proved our drugs are highly effective in reducing tumor dissemination and extending overall survival (CTRL untreated n=65 days vs MA9060 n=110). Importantly, we noted no overt toxicity and protected effect against myeloma-induced bone disease. This novel class of drug works synergistically with PI and can re-sensitize PI resistant disease to these effective therapies. We also show by EMMA ex vivo platform that MA9060 is highly effective for the treatment of CD138+ MM cells isolated from patients with refractory disease.ULK3 represents a novel target for treatment of MM refractory disease. Our dual inhibitors can increase overall survival in vivo and ex vivo, therefore we expect to quickly translate our novel molecules to the clinic.

Citation Format: Marilena Tauro, Tao Li, Mark Meads, Praneeth R. Sudalagunta, Raghunandan R. Alugubelli, Nicholas J. Lawrence, Ernst Schonbrunn, Harshani Lawrence, Kenneth H. Shain, Conor C. Lynch. Novel autophagy inhibitory strategies to overcome chemotherapy resistance in multiple myeloma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 452.

Development of SOS1 Inhibitor-Based Degraders to Target KRAS-Mutant Colorectal Cancer

Direct blockade of KRAS driver mutations in colorectal cancer (CRC) has been challenging. Targeting SOS1, a guanine nucleotide exchange factor, has arisen as an attractive approach for KRAS-mutant CRC. Here, we describe the development of novel SOS1 degraders and their activity in patient-derived CRC organoids (PDO). The design of these degraders as proteolysis-targeting chimera was based on the crystal structures of cereblon and SOS1. The synthesis used the 6- and 7-OH groups of a quinazoline core as anchor points to connect lenalidomide. Fifteen compounds were screened for SOS1 degradation. P7 was found to have up to 92% SOS1 degradation in both CRC cell lines and PDOs with excellent specificity. SOS1 degrader P7 demonstrated superior activity in inhibiting CRC PDO growth with an IC₅₀ 5 times lower than that of SOS1 inhibitor BI3406. In summary, we developed new SOS1 degraders and demonstrated SOS1 degradation as a feasible therapeutic strategy for KRAS-mutant CRC.

Chronologically modified androgen receptor in recurrent castration-resistant prostate cancer and its therapeutic targeting

Resistance to second-generation androgen receptor (AR) antagonists such as enzalutamide is an inevitable consequence in patients with castration-resistant prostate cancer (CRPC). There are no effective therapeutic options for this recurrent disease. The expression of truncated AR variant 7 (AR-V7) has been suggested to be one mechanism of resistance; however, its low frequency in patients with CRPC does not explain the almost universal acquisition of resistance. We noted that the ability of AR to translocate to nucleus in an enzalutamide-rich environment opens up the possibility of a posttranslational modification in AR that is refractory to enzalutamide binding. Chemical proteomics in enzalutamide-resistant CRPC cells revealed acetylation at Lys609 in the zinc finger DNA binding domain of AR (acK609-AR) that not only allowed AR translocation but also galvanized a distinct global transcription program, conferring enzalutamide insensitivity. Mechanistically, acK609-AR was recruited to the AR and ACK1/TNK2 enhancers, up-regulating their transcription. ACK1 kinase-mediated AR Y267 phosphorylation was a prerequisite for AR K609 acetylation, which spawned positive feedback loops at both the transcriptional and posttranslational level that regenerated and sustained high AR and ACK1 expression. Consistent with these findings, oral and subcutaneous treatment with ACK1 small-molecule inhibitor, (R)-9b, not only curbed AR Y267 phosphorylation and subsequent K609 acetylation but also compromised enzalutamide-resistant CRPC xenograft tumor growth in mice. Overall, these data uncover chronological modification events in AR that allows prostate cancer to evolve through progressive stages to reach the resilient recurrent CRPC stage, opening up a therapeutic vulnerability.

Dual JAK2/Aurora kinase A inhibition prevents human skin graft rejection by allo-inactivation and ILC2-mediated tissue repair

Prevention of allograft rejection often requires lifelong immune suppression, risking broad impairment of host immunity. Nonselective inhibition of host T cell function increases recipient risk of opportunistic infections and secondary malignancies. Here we demonstrate that AJI-100, a dual inhibitor of JAK2 and Aurora kinase A, ameliorates skin graft rejection by human T cells and provides durable allo-inactivation. AJI-100 significantly reduces the frequency of skin-homing CLA⁺ donor T cells, limiting allograft invasion and tissue destruction by T effectors. AJI-100 also suppresses pathogenic Th1 and Th17 cells in the spleen yet spares beneficial regulatory T cells. We show dual JAK2/Aurora kinase A blockade enhances human type 2 innate lymphoid cell (ILC2) responses, which are capable of tissue repair. ILC2 differentiation mediated by GATA3 requires STAT5 phosphorylation (pSTAT5) but is opposed by STAT3. Further, we demonstrate that Aurora kinase A activation correlates with low pSTAT5 in ILC2s. Importantly, AJI-100 maintains pSTAT5 levels in ILC2s by blocking Aurora kinase A and reduces interference by STAT3. Therefore, combined JAK2/Aurora kinase A inhibition is an innovative strategy to merge immune suppression with tissue repair after transplantation.

Differential BET Bromodomain Inhibition by Dihydropteridinone and Pyrimidodiazepinone Kinase Inhibitors

BRD4 and other members of the bromodomain and extraterminal (BET) family of proteins are promising epigenetic targets for the development of novel therapeutics. Among the reported BRD4 inhibitors are dihydropteridinones and benzopyrimidodiazepinones originally designed to target the kinases PLK1, ERK5, and LRRK2. While these kinase inhibitors were identified as BRD4 inhibitors, little is known about their binding potential and structural details of interaction with the other BET bromodomains. We comprehensively characterized a series of known and newly identified dual BRD4-kinase inhibitors against all eight individual BET bromodomains. A detailed analysis of 23 novel cocrystal structures of BET-kinase inhibitor complexes in combination with direct binding assays and cell signaling studies revealed significant differences in molecular shape complementarity and inhibitory potential. Collectively, the data offer new insights into the action of kinase inhibitors across BET bromodomains, which may aid the development of drugs to inhibit certain BET proteins and kinases differentially.

Pacritinib Combined with Sirolimus and Low-Dose Tacrolimus for GVHD Prevention after Allogeneic Hematopoietic Cell Transplantation: Preclinical and Phase I Trial Results

PURPOSE

In this first-in-human, phase I, GVHD prevention trial (NCT02891603), we combine pacritinib (PAC), a JAK2 inhibitor, with sirolimus to concurrently reduce T-cell costimulation via mTOR and IL6 activity. We evaluate the safety of pacritinib when administered with sirolimus plus low-dose tacrolimus (PAC/SIR/TAC) after allogeneic hematopoietic cell transplantation.

PATIENTS AND METHODS

The preclinical efficacy and immune modulation of PAC/SIR were investigated in xenogeneic GVHD. Our phase I trial followed a 3+3 dose-escalation design, including dose level 1 (pacritinib 100 mg daily), level 2 (pacritinib 100 mg twice daily), and level 3 (pacritinib 200 mg twice daily). The primary endpoint was to identify the lowest biologically active and safe dose of pacritinib with SIR/TAC (n = 12). Acute GVHD was scored through day +100. Allografts included 8/8 HLA-matched related or unrelated donor peripheral blood stem cells.

RESULTS

In mice, we show that dual JAK2/mTOR inhibition significantly reduces xenogeneic GVHD and increases peripheral regulatory T cell (Treg) potency as well as Treg induction from conventional CD4⁺ T cells. Pacritinib 100 mg twice a day was identified as the minimum biologically active and safe dose for further study. JAK2/mTOR inhibition suppresses pathogenic Th1 and Th17 cells, spares Tregs and antileukemia effector cells, and exhibits preliminary activity in preventing GVHD. PAC/SIR/TAC preserves donor cytomegalovirus (CMV) immunity and permits timely engraftment without cytopenias.

CONCLUSIONS

We demonstrate that PAC/SIR/TAC is safe and preliminarily limits acute GVHD, preserves donor CMV immunity, and permits timely engraftment. The efficacy of PAC/SIR/TAC will be tested in our ongoing phase II GVHD prevention trial.

Structural Insights into JAK2 Inhibition by Ruxolitinib, Fedratinib, and Derivatives Thereof

The discovery that aberrant activity of Janus kinase 2 (JAK2) is a driver of myeloproliferative neoplasms (MPNs) has led to significant efforts to develop small molecule inhibitors for this patient population. Ruxolitinib and fedratinib have been approved for use in MPN patients, while baricitinib, an achiral analogue of ruxolitinib, has been approved for rheumatoid arthritis. However, structural information on the interaction of these therapeutics with JAK2 remains unknown. Here, we describe a new methodology for the large-scale production of JAK2 from mammalian cells, which enabled us to determine the first crystal structures of JAK2 bound to these drugs and derivatives thereof. Along with biochemical and cellular data, the results provide a comprehensive view of the shape complementarity required for chiral and achiral inhibitors to achieve highest activity, which may facilitate the development of more effective JAK2 inhibitors as therapeutics.

Mesenchymal stem cell-derived interleukin-28 drives the selection of apoptosis resistant bone metastatic prostate cancer

Bone metastatic prostate cancer (PCa) promotes mesenchymal stem cell (MSC) recruitment and their differentiation into osteoblasts. However, the effects of bone-marrow derived MSCs on PCa cells are less explored. Here, we report MSC-derived interleukin-28 (IL-28) triggers prostate cancer cell apoptosis via IL-28 receptor alpha (IL-28Rα)-STAT1 signaling. However, chronic exposure to MSCs drives the selection of prostate cancer cells that are resistant to IL-28-induced apoptosis and therapeutics such as docetaxel. Further, MSC-selected/IL-28-resistant prostate cancer cells grow at accelerated rates in bone. Acquired resistance to apoptosis is PCa cell intrinsic, and is associated with a shift in IL-28Rα signaling via STAT1 to STAT3. Notably, STAT3 ablation or inhibition impairs MSC-selected prostate cancer cell growth and survival. Thus, bone marrow MSCs drive the emergence of therapy-resistant bone metastatic prostate cancer yet this can be disabled by targeting STAT3.

Metabolic reprogramming augments potency of human pSTAT3-inhibited iTregs to suppress alloreactivity

Immunosuppressive donor Tregs can prevent graft-versus-host disease (GVHD) or solid-organ allograft rejection. We previously demonstrated that inhibiting STAT3 phosphorylation (pSTAT3) augments FOXP3 expression, stabilizing induced Tregs (iTregs). Here we report that human pSTAT3-inhibited iTregs prevent human skin graft rejection and xenogeneic GVHD yet spare donor antileukemia immunity. pSTAT3-inhibited iTregs express increased levels of skin-homing cutaneous lymphocyte-associated antigen, immunosuppressive GARP and PD-1, and IL-9 that supports tolerizing mast cells. Further, pSTAT3-inhibited iTregs significantly reduced alloreactive conventional T cells, Th1, and Th17 cells implicated in GVHD and tissue rejection and impaired infiltration by pathogenic Th2 cells. Mechanistically, pSTAT3 inhibition of iTregs provoked a shift in metabolism from oxidative phosphorylation (OxPhos) to glycolysis and reduced electron transport chain activity. Strikingly, cotreatment with coenzyme Q10 restored OxPhos in pSTAT3-inhibited iTregs and augmented their suppressive potency. These findings support the rationale for clinically testing the safety and efficacy of metabolically tuned, human pSTAT3-inhibited iTregs to control alloreactive T cells.

Targeting the BRD4-HOXB13 Coregulated Transcriptional Networks with Bromodomain-Kinase Inhibitors to Suppress Metastatic Castration-Resistant Prostate Cancer

Resistance to androgen receptor (AR) antagonists is a significant problem in the treatment of castration-resistant prostate cancers (CRPC). Identification of the mechanisms by which CRPCs evade androgen deprivation therapies (ADT) is critical to develop novel therapeutics. We uncovered that CRPCs rely on BRD4-HOXB13 epigenetic reprogramming for androgen-independent cell proliferation. Mechanistically, BRD4, a member of the BET bromodomain family, epigenetically promotes HOXB13 expression. Consistently, genetic disruption of HOXB13 or pharmacological suppression of its mRNA and protein expression by the novel dual-activity BET bromodomain-kinase inhibitors directly correlates with rapid induction of apoptosis, potent inhibition of tumor cell proliferation and cell migration, and suppression of CRPC growth. Integrative analysis revealed that the BRD4-HOXB13 transcriptome comprises a proliferative gene network implicated in cell-cycle progression, nucleotide metabolism, and chromatin assembly. Notably, although the core HOXB13 target genes responsive to BET inhibitors (HOTBIN10) are overexpressed in metastatic cases, in ADT-treated CRPC cell lines and patient-derived circulating tumor cells (CTC) they are insensitive to AR depletion or blockade. Among the HOTBIN10 genes, AURKB and MELK expression correlates with HOXB13 expression in CTCs of mCRPC patients who did not respond to abiraterone (ABR), suggesting that AURKB inhibitors could be used additionally against high-risk HOXB13-positive metastatic prostate cancers. Combined, our study demonstrates that BRD4-HOXB13-HOTBIN10 regulatory circuit maintains the malignant state of CRPCs and identifies a core proproliferative network driving ADT resistance that is targetable with potent dual-activity bromodomain-kinase inhibitors.

Abstract 4879: Mutation selectivity of the allosteric SHP2 inhibitor SHP099

SHP2 (PTPN11) mediates oncogenic signaling and gain-of-function (GOF) SHP2 mutations are associated with leukemias and other types of cancer. Recently, SHP099 was identified as a novel allosteric SHP2 inhibitor that displayed high potency and selectivity to the wildtype SHP2 in vitro and inhibited protein tyrosine kinase oncogene-driven cancer cells. However, it was unclear whether SHP099 inhibits SHP2 mutants. Using SHP2 mutant-dependent TF-1 leukemia cells, we determined sensitivities of four common oncogenic SHP2 mutants to SHP099. SHP2D61Y-, SHP2A72V-, and SHP2E76K-expressing TF-1 cells were resistant, whereas SHP2E69K-expressing TF-1 cells were sensitive to SHP099 with a potency similar to that of cytokine-stimulated TF-1 cells expressing the wildtype SHP2. Consistently, SHP099 reduced active ERK1/2 and Bcl-XL and induced apoptosis of SHP2E69K-dependent TF-1 cells, but had no effects on the other SHP2 mutant cell lines. SHP2 knockout cells were unresponsive to SHP099, demonstrating specificity. Like the wildtype SHP2, SHP2E69K PTP was inhibited by SHP099 in vitro with a sub-micromolar IC50, whereas micromolar IC50s of SHP099 were observed against SHP2D61Y, SHP2A72V, and SHP2E76K. These results indicate that SHP2D61Y, SHP2A72V, and SHP2E76K mutants are resistant to SHP099 and that SHP2E69K is a SHP099-sensitive oncogenic mutant.

Citation Format: Xiaojun Sun, Yuan Ren, Steven Gunawan, Peng Teng, Zhengming Chen, Harshani R. Lawrence, Jianfeng Cai, Nicholas J. Lawrence, Jie Wu. Mutation selectivity of the allosteric SHP2 inhibitor SHP099 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4879.

Ligand-mediated protein degradation reveals functional conservation among sequence variants of the CUL4-type E3 ligase substrate receptor cereblon

Upon binding to thalidomide and other immunomodulatory drugs, the E3 ligase substrate receptor cereblon (CRBN) promotes proteosomal destruction by engaging the DDB1-CUL4A-Roc1-RBX1 E3 ubiquitin ligase in human cells but not in mouse cells, suggesting that sequence variations in CRBN may cause its inactivation. Therapeutically, CRBN engagers have the potential for broad applications in cancer and immune therapy by specifically reducing protein expression through targeted ubiquitin-mediated degradation. To examine the effects of defined sequence changes on CRBN's activity, we performed a comprehensive study using complementary theoretical, biophysical, and biological assays aimed at understanding CRBN's nonprimate sequence variations. With a series of recombinant thalidomide-binding domain (TBD) proteins, we show that CRBN sequence variants retain their drug-binding properties to both classical immunomodulatory drugs and dBET1, a chemical compound and targeting ligand designed to degrade bromodomain-containing 4 (BRD4) via a CRBN-dependent mechanism. We further show that dBET1 stimulates CRBN's E3 ubiquitin-conjugating function and degrades BRD4 in both mouse and human cells. This insight paves the way for studies of CRBN-dependent proteasome-targeting molecules in nonprimate models and provides a new understanding of CRBN's substrate-recruiting function.

Targeting Aurora kinase A and JAK2 prevents GVHD while maintaining Treg and antitumor CTL function

Graft-versus-host disease (GVHD) is a leading cause of nonrelapse mortality after allogeneic hematopoietic cell transplantation. T cell costimulation by CD28 contributes to GVHD, but prevention is incomplete when targeting CD28, downstream mammalian target of rapamycin (mTOR), or Aurora A. Likewise, interleukin-6 (IL-6)-mediated Janus kinase 2 (JAK2) signaling promotes alloreactivity, yet JAK2 inhibition does not eliminate GVHD. We provide evidence that blocking Aurora A and JAK2 in human T cells is synergistic in vitro, prevents xenogeneic GVHD, and maintains antitumor responses by cytotoxic T lymphocytes (CTLs). Aurora A/JAK2 inhibition is immunosuppressive but permits the differentiation of inducible regulatory T cells (iT_regs) that are hyperfunctional and CD39 bright and efficiently scavenge adenosine triphosphate (ATP). Increased iT_reg potency is primarily a function of Aurora A blockade, whereas JAK2 inhibition suppresses T helper 17 (T_H17) differentiation. Inhibiting either Aurora A or JAK2 significantly suppresses T_H1 T cells. However, CTL generated in vivo retains tumor-specific killing despite Aurora A/JAK2 blockade. Thus, inhibiting CD28 and IL-6 signal transduction pathways in donor T cells can increase the T_reg/T_conv ratio, prevent GVHD, and preserve antitumor CTL.

ACK1/TNK2 Regulates Histone H4 Tyr88-phosphorylation and AR Gene Expression in Castration-Resistant Prostate Cancer

The androgen receptor (AR) is critical for the progression of prostate cancer to a castration-resistant (CRPC) state. AR antagonists are ineffective due to their inability to repress the expression of AR or its splice variant, AR-V7. Here, we report that the tyrosine kinase ACK1 (TNK2) phosphorylates histone H4 at tyrosine 88 upstream of the AR transcription start site. The WDR5/MLL2 complex reads the H4-Y88-phosphorylation marks and deposits the transcriptionally activating H3K4-trimethyl marks promoting AR transcription. Reversal of the pY88-H4 epigenetic marks by the ACK1 inhibitor (R)-9bMS-sensitized naive and enzalutamide-resistant prostate cancer cells and reduced AR and AR-V7 levels to mitigate CRPC tumor growth. Thus, a feedforward ACK1/pY88-H4/WDR5/MLL2/AR epigenetic circuit drives CRPC and is necessary for maintenance of the malignant state.

Potent Dual BET Bromodomain-Kinase Inhibitors as Value-Added Multitargeted Chemical Probes and Cancer Therapeutics

Synergistic action of kinase and BET bromodomain inhibitors in cell killing has been reported for a variety of cancers. Using the chemical scaffold of the JAK2 inhibitor TG101348, we developed and characterized single agents which potently and simultaneously inhibit BRD4 and a specific set of oncogenic tyrosine kinases including JAK2, FLT3, RET, and ROS1. Lead compounds showed on-target inhibition in several blood cancer cell lines and were highly efficacious at inhibiting the growth of hematopoietic progenitor cells from patients with myeloproliferative neoplasm. Screening across 931 cancer cell lines revealed differential growth inhibitory potential with highest activity against bone and blood cancers and greatly enhanced activity over the single BET inhibitor JQ1. Gene drug sensitivity analyses and drug combination studies indicate synergism of BRD4 and kinase inhibition as a plausible reason for the superior potency in cell killing. Combined, our findings indicate promising potential of these agents as novel chemical probes and cancer therapeutics. Mol Cancer Ther; 16(6); 1054-67. ©2017 AACR.

Inhibition of Shp2 suppresses mutant EGFR-induced lung tumors in transgenic mouse model of lung adenocarcinoma

Epidermal growth factor receptor (EGFR) mutants drive lung tumorigenesis and are targeted for therapy. However, resistance to EGFR inhibitors has been observed, in which the mutant EGFR remains active. Thus, it is important to uncover mediators of EGFR mutant-driven lung tumors to develop new treatment strategies. The protein tyrosine phosphatase (PTP) Shp2 mediates EGF signaling. Nevertheless, it is unclear if Shp2 is activated by oncogenic EGFR mutants in lung carcinoma or if inhibiting the Shp2 PTP activity can suppress EGFR mutant-induced lung adenocarcinoma. Here, we generated transgenic mice containing a doxycycline (Dox)-inducible PTP-defective Shp2 mutant (tetO-Shp2CSDA). Using the rat Clara cell secretory protein (CCSP)-rtTA-directed transgene expression in the type II lung pneumocytes of transgenic mice, we found that the Gab1-Shp2 pathway was activated by EGFRL858R in the lungs of transgenic mice. Consistently, the Gab1-Shp2 pathway was activated in human lung adenocarcinoma cells containing mutant EGFR. Importantly, Shp2CSDA inhibited EGFRL858R-induced lung adenocarcinoma in transgenic animals. Analysis of lung tissues showed that Shp2CSDA suppressed Gab1 tyrosine phosphorylation and Gab1-Shp2 association, suggesting that Shp2 modulates a positive feedback loop to regulate its own activity. These results show that inhibition of the Shp2 PTP activity impairs mutant EGFR signaling and suppresses EGFRL858R-driven lung adenocarcinoma.

Abstract 4547: Preparation of peptide-based Shp2 substrates with phosphatase activity-dependent fluorescence

The Shp2 protein tyrosine phosphatase mediates signal transduction of growth factor receptors and regulates cellular activities critical to tumor growth and metastasis. Shp2-activating mutations are associated with several types of leukemias and solid tumors, making Shp2 an attractive target for anticancer development. While there are reports of Shp2 inhibitors, there is a need for compounds with higher potency and improved selectivity. One approach to the discovery of new Shp2 inhibitors is via high throughput screening (HTS) of small molecule libraries. The small molecule probe 6,8-difluoro-4-methylumbelliferyl phosphate (DiFMUP) is currently a widely used substrate for phosphatases and has been used to assay Shp2 activity. However, DIFMUP binds only the catalytic site of the phosphatase and is unlikely to reveal compounds that are selective for Shp2 in an HTS. There is clearly a need to develop probes that are more sensitive and more specific for a particular phosphatase to identify Shp2 selective inhibitors and to measure Shp2 activity. We have developed a new phosphopeptide-like Shp2 substrate that becomes fluorescent upon enzyme-mediated hydrolysis, based on a phosphopeptide sequence that has high affinity for Shp2. We will report details of the novel Shp2 activity probe and its use as a reagent for HTS and determination of Shp2 inhibitor potency. We will also report on its suitability for HTS and preliminary results from screening and its potential for the discovery of novel Shp2 inhibitors. We will discuss the binding mode of the probe, based on novel co-crystal structures of related peptides with Shp2.

Citation Format: Steven Gunawan, Yunting Luo, Yuan Ren, Harshani R. Lawrence, Jerry Wu, Nicholas J. Lawrence. Preparation of peptide-based Shp2 substrates with phosphatase activity-dependent fluorescence. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4547. doi:10.1158/1538-7445.AM2015-4547

Abstract 3643: Targeting the acetyl-lysine binding site of BRD4 with dual nanomolar BET-JAK2 inhibitors: A new anticancer therapeutic strategy

Bromodomain (BRD)-containing proteins are essential for the recognition of acetylated lysine residues of histones during transcriptional activation. The BRD-containing proteins have emerged as promising drug targets for a number of diseases, including many cancers, that are characterized by changes in the epigenetic cell signature. Recent reports have shown that targeting BRD4 with small molecules may represent a new way to treat prostate and breast cancer, acute myeloid leukemia and melanoma. We have identified many type 1 and type 2 kinase inhibitors which also inhibit BRD4 by robotic co-crystallization screening of kinase inhibitor libraries against BRD4. In each case the co-crystal structure unambiguously revealed the inhibitor bound to the acetyl lysine site of BRD4-1. The identified BRD4 ligands were subjected to differential scanning fluorimetry (DSF) and AlphaScreen assay to assess their binding and inhibitory potentials against BRD4. As shown previously for other BRD-inhibitor-protein complexes, the melting temperatures of BRD4-kinase inhibitor complexes were logarithmically proportional to their IC50 values. We now report the design, synthesis, structural analysis and biological evaluation of next-generation nanomolar BET-selective and nanomolar dual-activity BET-JAK2 inhibitors, based on the initial co-crystallization screening hits. Structure activity relationships were developed using both DSF and co-crystallization of the ligands with BRD4, to assess binding potential and binding modes, respectively. We report initial evaluation of the anticancer potential of compounds possessing dual potent BRD4 and JAK2 inhibitory properties. In addition to myeloma cell lines, this includes the evaluation of dual BRD4-JAK2 inhibitor compounds against JAK2-driven myeloproliferative neoplasm cell lines and primary cells from patients.

Citation Format: Steven Gunawan, Ayaz Muhammad, Stuart W. J. Ember, Jin-Yi Zhu, Rebecca A. Jacobsen, Norbert Berndt, Que T. Lambert, Gary W. Reuther, Harshani R. Lawrence, Ernst Schonbrunn, Nicholas J. Lawrence. Targeting the acetyl-lysine binding site of BRD4 with dual nanomolar BET-JAK2 inhibitors: A new anticancer therapeutic strategy. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3643. doi:10.1158/1538-7445.AM2015-3643

Abstract 3697: Development of a focused non-hydrolyzable phosphopeptide library based on a high affinity SHP2 substrate

The Src homology-2 domain containing protein tyrosine phosphatase-2 (SHP2), a widely expressed cytoplasmic tyrosine phosphatase with two src-homology 2 (SH2) domains, has received much attention in the signal transduction field. SHP2 is a transducer of growth factor, cytokine, integrin, and hormone signaling pathways that regulate processes such as cell proliferation, differentiation, adhesion, migration, and apoptosis and plays a pivotal role in growth factor and cytokine signaling. Gain-of-function SHP2 mutations are associated with several types of leukemias, and solid tumors; this makes SHP2 is an attractive target for cancer therapy Several small molecules have been developed for inhibition of this important phosphatase, which serve as chemical tools to probe the role of SHP2 in disease and lead compounds for optimization. Nevertheless it is challenging to improve these lead compounds with better potency, selectivity and cell permeability. To gain structural insights for development of potent and selective SHP2 inhibitors, we synthesized a non-hydrolyzable phosphotyrosine peptide mimetic based on reported SHP2 substrate peptide sequence (10-mer). The non-hydrolyzable phosphopeptide, containing the phosphotyrosyl surrogate difluoromethylphosphonate, was synthesized using solid phase peptide synthesis methods from the known building block N-FMOCF2Pmp and we improved the coupling reaction conditions to generate a peptide library of difluoromethylphosphonate to understand the SHP2 affinity. We will present the synthesis of the peptide library, analysis of SHP2 phosphatase inhibition, and the binding mode (X-ray crystal structure) of the phosphopeptide mimic to SHP2.

Citation Format: Harshani R. Lawrence, Yunting Luo, Steven Gunawan, Andreas Becker, Yuan Ren, Ernst Schonbrunn, Jie Wu, Nicholas J. Lawrence. Development of a focused non-hydrolyzable phosphopeptide library based on a high affinity SHP2 substrate. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3697. doi:10.1158/1538-7445.AM2015-3697

Development of novel ACK1/TNK2 inhibitors using a fragment-based approach

The tyrosine kinase ACK1, a critical signal transducer regulating survival of hormone-refractory cancers, is an important therapeutic target, for which there are no selective inhibitors in clinical trials to date. This work reports the discovery of novel and potent inhibitors for ACK1 tyrosine kinase (also known as TNK2) using an innovative fragment-based approach. Focused libraries were designed and synthesized by selecting fragments from reported ACK inhibitors to create hybrid structures in a mix and match process. The hybrid library was screened by enzyme-linked immunosorbent assay-based kinase inhibition and (33)P HotSpot assays. Systematic structure-activity relationship studies led to the identification of compound (R)-9b, which shows potent in vitro (IC50 = 56 nM, n = 3, (33)P HotSpot assay) and in vivo (IC50 < 2 μM, human cancer cell lines) ACK1 inhibition. Both (R)-9b and (S)-9b were stable in human plasma and displayed a long half-life (t(1/2) > 6 h).

Dual Aurora A and JAK2 kinase blockade effectively suppresses malignant transformation

Aurora A and JAK2 kinases are involved in cell division and tumor cell survival, respectively. Here we demonstrate that ectopic expression of Aurora A and JAK2 together is more effective than each alone at inducing non-transformed cells to grow in an anchorage-independent manner and to invade. Furthermore, siRNA silencing or pharmacological inhibition of Aurora A and JAK2 with Alisertib and Ruxolitinib, respectively, is more effective than blocking each kinase alone at suppressing anchorage-dependent and –independent growth and invasion as well as at inducing apoptosis. Importantly, we have developed dual Aurora and JAK inhibitors, AJI-214 and AJI-100, which potently inhibit Aurora A, Aurora B and JAK2 in vitro. In human cancer cells, these dual inhibitors block the auto-phosphorylation of Aurora A (Thr-288) and the phosphorylation of the Aurora B substrate histone H3 (Ser-10) and the JAK2 substrate STAT3 (Tyr-705). Furthermore, AJI-214 and AJI-100 inhibit anchorage dependent and independent cell growth and invasion and induce G2/M cell cycle accumulation and apoptosis. Finally, AJI-100 caused regression of human tumor xenografts in mice. Taken together, our genetic and pharmacological studies indicate that targeting Aurora A and JAK2 together is a more effective approach than each kinase alone at inhibiting malignant transformation and warrant further advanced pre clinical investigations of dual Aurora A/JAK2 inhibitors as potential anti tumor agents.

Abstract 2511: New inhibitors the tyrosine kinase ACK1/TNK2 active in prostate, breast and pancreatic cancer

ACK1, is a non-receptor tyrosine kinase that is aberrantly activated, over expressed or mutated in many cancer cell types. It interacts with several important ligand-activated receptor tyrosine kinases (RTKs), for example, EGFR, MerTK, HER2, PDGFR and insulin receptor to initiate intracellular signaling cascades. ACK1 activation has been reported in various cancers including prostate, breast and pancreatic tumors. We have shown that the androgen receptor (AR) and AKT are two major downstream effectors of ACK1. ACK1 directly phosphorylates AKT at Tyr176 resulting in AKT membrane localization and activation. We have also found that in prostate cancer cells ACK1 phosphorylates AR at Tyr-267 in an androgen-independent manner. Tyr284-phosphorylated-ACK1, Tyr176-phosphorylated-AKT and Tyr267-phosphorylated-AR levels are positively correlated with the severity of disease progression, and inversely correlated with the survival of patients with prostate cancer. Similarly, ACK1 mediated AKT tyrosine phosphorylation was found to correlate positively with breast cancer progression. Further, we have shown that a 5,6-biaryl-furo[2,3-d]pyrimidine inhibitor of ACK1 (AIM-100) inhibits ACK1 activation and suppresses pTyr267-AR phosphorylation and AKT Tyr176-phosphorylation, inhibiting AR and AKT activity. These findings indicate that Ack1 is prognostic of progression of prostate, breast and pancreatic cancer and inhibitors of ACK1 activity have potential as novel cancer therapeutic agents.

We will discuss the development of new potent ACK1 inhibitors by fragment-recombination and structure-based design by incorporating fragments of key ACK1 inhibitors. Focused chemical libraries were developed and structure activity relationships will be described. The work described has produced compounds capable of inhibiting ACK1 in vitro at low nanomolar concentrations. We have used an ELISA based assay that measures the ability of ACK1 to phosphorylate a peptide derived from AKT, as a primary screening assay. ACK1 inhibition of hits was confirmed in the 33P ATP “Hotspot” assay platform. Selected compounds from the library have been shown to inhibit ACK1 autophosphorylation and the phosphorylation of AR at Tyr267, a surrogate for ACK1 inhibition in vivo. Furthermore we will show that ACK1 is a promising drug target for cancer therapy.

Citation Format: Harshani R. Lawrence, Yunting Luo, Daniel Zhang, Nathan Tindall, Sevil Ozcan, Miles Huseyin, Sakib Kazi, Sayantani Bandyopadhyay, Kiran Mahajan, Nupam P. Mahajan, Nicholas J. Lawrence. New inhibitors the tyrosine kinase ACK1/TNK2 active in prostate, breast and pancreatic cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2511. doi:10.1158/1538-7445.AM2014-2511

Abstract 2518: Development of a non-hydrolysable phosphotyrosine mimetic peptide based on a high affinity SHP2 substrate

The Src homology-2 domain containing protein tyrosine phosphatase-2 (SHP2) is a transducer of growth factor, cytokine, integrin, and hormone signaling pathways that regulate processes such as cell proliferation, differentiation, adhesion, migration, and apoptosis and plays a pivotal role in growth factor and cytokine signaling. Gain-of-function SHP2 mutations are associated with several types of leukemias, and solid tumors. This makes SHP2 an attractive target for developing new anticancer therapy. Several small molecules have been developed for inhibition of this important phosphatase, which serve as chemical tools to probe the role of SHP2 in disease and lead compounds for optimization. Nevertheless improvements are required to improve these lead compounds with better potency, selectivity and cell permeability. To gain structural insights for development of potent and selective Shp2 inhibitors, we synthesized a non-hydrolysable phosphotyrosine peptide mimetic, based on reported Shp2 substrate peptide sequences. The non-hydrolyzable phosphopeptide, containing the phosphotyrosyl surrogate difluoromethylphosphonate, was prepared by solid phase peptide synthesis methods from the known building block N-FMOCF2Pmp. We will present the synthesis of the peptide, analysis of Shp2 phosphatase inhibition, and binding of the phosphopeptide mimic to SHP2 by micro isothermal calorimetry. We will present a model for the binding mode of the peptide and its implications for the design of selective Shp2 inhibitors.

Citation Format: Harshani R. Lawrence, Yiyu Ge, Andreas Becker, Yuan Ren, Yunting Luo, Jie Wu and Nicholas J. Lawrence. Development of a non-hydrolysable phosphotyrosine mimetic peptide based on a high affinity SHP2 substrate. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2518. doi:10.1158/1538-7445.AM2014-2518

ACK1 tyrosine kinase interacts with histone demethylase KDM3A to regulate the mammary tumor oncogene HOXA1

Hormone therapy with the selective estrogen-receptor modulator tamoxifen provides a temporary relief for patients with estrogen receptor α (ER)-positive breast cancers. However, a subset of patients exhibiting overexpression of the HER2 receptor tyrosine kinase displays intrinsic resistance to tamoxifen therapy. Therefore, elucidating the mechanisms promoting the estrogen (E2)-independent ER-regulated gene transcription in tamoxifen-resistant breast tumors is essential to identify new therapeutic avenues to overcome drug resistance and ameliorate poor prognosis. The non-receptor tyrosine kinase, ACK1 (also known as TNK2), has emerged as a major integrator of signaling from various receptor tyrosine kinases including HER2. We have uncovered that heregulin-mediated ACK1 activation promoted ER activity in the presence of tamoxifen, which was significantly down-regulated upon ACK1 knockdown or inhibition of ACK1 by small molecule inhibitors, AIM-100 or Dasatinib. We report that ACK1 phosphorylates the ER co-activator, KDM3A, a H3K9 demethylase, at an evolutionary conserved tyrosine 1114 site in a heregulin-dependent manner, even in the presence of tamoxifen. Consistent with this finding, ACK1 activation resulted in a significant decrease in the deposition of dimethyl H3K9 epigenetic marks. Conversely, inhibition of ACK1 by AIM-100 or Dasatinib restored dimethyl H3K9 methylation marks and caused transcriptional suppression of the ER-regulated gene HOXA1. Thus, by its ability to regulate the epigenetic activity of an ER co-activator KDM3A, ACK1 modulates HOXA1 expression in the absence of E2, conferring tamoxifen resistance. These data reveal a novel therapeutic option, suppression of ACK1 signaling by AIM-100 or Dasatinib, to mitigate HOXA1 up-regulation in breast cancer patients displaying tamoxifen resistance.

Inhibiting the interaction of cMET and IGF-1R with FAK effectively reduces growth of pancreatic cancer cells in vitro and in vivo

Pancreatic cancer is one of the most lethal diseases with no effective treatment. Previously, we have shown that FAK is overexpressed in pancreatic cancer and plays a key role in cancer cell survival and proliferation. FAK has been shown to interact with growth factor receptors including cMET and IGF-1R. As a novel therapeutic approach, we targeted the protein interaction of FAK with growth factor receptors to block tumor growth, alter signaling pathways and sensitize cells to chemotherapy. We have selected a small molecule compound (INT2-31) that decreases phosphorylation of AKT via disrupting interaction of FAK with cMET and IGF-1R. Our results demonstrate that interaction of a small molecule compound with FAK decreases phosphorylation of FAK Y397 while increasing FAK Y407 phosphorylation, without inhibiting the kinase activity of FAK and dramatically reduces downstream signaling to AKT. Our lead compound, INT2-31, demonstrates significant inhibition of tumor cell growth in two orthotopic models of pancreatic cancer. In addition, INT2-31 increases sensitivity to gemcitabine chemotherapy in a direct fresh biopsy xenograft model of pancreatic cancer growth.

Lysophosphatidic acid acyltransferase beta regulates mTOR signaling

Lysophosphatidic acid acyltransferase (LPAAT-β) is a phosphatidic acid (PA) generating enzyme that plays an essential role in triglyceride synthesis. However, LPAAT-β is now being studied as an important regulator of cell growth and differentiation and as a potential therapeutic target in cancer since PA is necessary for the activity of key proteins such as Raf, PKC-ζ and mTOR. In this report we determine the effect of LPAAT-β silencing with siRNA in pancreatic adenocarcinoma cell lines. We show for the first time that LPAAT-β knockdown inhibits proliferation and anchorage-independent growth of pancreatic cancer cells. This is associated with inhibition of signaling by mTOR as determined by levels of mTORC1- and mTORC2-specific phosphorylation sites on 4E-BP1, S6K and Akt. Since PA regulates the activity of mTOR by modulating its binding to FKBP38, we explored the possibility that LPAAT-β might regulate mTOR by affecting its association with FKBP38. Coimmunoprecipitation studies of FKBP38 with mTOR show increased levels of FKBP38 associated with mTOR when LPAAT-β protein levels are knocked down. Furthermore, depletion of LPAAT-β results in increased Lipin 1 nuclear localization which is associated with increased nuclear eccentricity, a nuclear shape change that is dependent on mTOR, further confirming the ability of LPAAT-β to regulate mTOR function. Our results provide support for the hypothesis that PA generated by LPAAT-β regulates mTOR signaling. We discuss the implications of these findings for using LPAAT-β as a therapeutic target.

Selective disruption of rb-raf-1 kinase interaction inhibits pancreatic adenocarcinoma growth irrespective of gemcitabine sensitivity

Inactivation of the retinoblastoma (Rb) tumor suppressor protein is widespread in human cancers. Inactivation of Rb is thought to be initiated by association with Raf-1 (C-Raf) kinase, and here we determined how RRD-251, a disruptor of the Rb-Raf-1 interaction, affects pancreatic tumor progression. Assessment of phospho-Rb levels in resected human pancreatic tumor specimens by immunohistochemistry (n = 95) showed that increased Rb phosphorylation correlated with increasing grade of resected human pancreatic adenocarcinomas (P = 0.0272), which correlated with reduced overall patient survival (P = 0.0186). To define the antitumor effects of RRD-251 (50 μmol/L), cell-cycle analyses, senescence, cell viability, cell migration, anchorage-independent growth, angiogenic tubule formation and invasion assays were conducted on gemcitabine-sensitive and -resistant pancreatic cancer cells. RRD-251 prevented S-phase entry, induced senescence and apoptosis, and inhibited anchorage-independent growth and invasion (P < 0.01). Drug efficacy on subcutaneous and orthotopic xenograft models was tested by intraperitoneal injections of RRD-251 (50 mg/kg) alone or in combination with gemcitabine (250 mg/kg). RRD-251 significantly reduced tumor growth in vivo accompanied by reduced Rb phosphorylation and lymph node and liver metastasis (P < 0.01). Combination of RRD-251 with gemcitabine showed cooperative effect on tumor growth (P < 0.01). In conclusion, disruption of the Rb-Raf-1 interaction significantly reduces the malignant properties of pancreatic cancer cells irrespective of their gemcitabine sensitivity. Selective targeting of Rb-Raf-1 interaction might be a promising strategy targeting pancreatic cancer.

Abstract 2467: Development of new N-Arylbenzamides as STAT3 dimerization inhibitors

The association of aberrant STAT3 activation with many types of human malignancies and solid tumors makes STAT3 an attractive molecular target for the development of novel cancer therapeutics. STAT3 dimerization via two reciprocal phosphotyrosine (pTyr)-Src-homology 2 (SH2) interaction is required for its binding to specific DNA-response elements in the promoters of target genes. This dimerization process offers a potentially selective way to directly target STAT3. Nevertheless the design of small molecules capable of disrupting protein-protein interactions remains a significant challenge to medicinal chemistry. We describe the development of a new class of small molecule capable of disrupting the STAT3:STAT3 protein-protein interaction. We identified the STAT3 inhibitor S3I-201 (NSC-74859) from the NCI chemical collection by using structure-based virtual screening with a model based on the X-ray crystal structure of the STAT3β homodimer. We developed a series of phosphonic and salicylic acids based on the structure of S3I-201 incorporating an N-arylbenzamide scaffold. The series of phosphonic and salicylic acids with a shorter amide linker lacking the O-tosyl group has improved STAT3 inhibitory activity [as measured by a competitive, fluorescence-polarization (FP)-based assay]. The equivalent in vitro potencies observed by the replacement of phosphonic acid moiety of with 5-amino-2-hydroxybenzoic acid group validates 5-amino-2-hydroxybenzoic acid as a phosphotyrosine mimic in this series. The binding mode of selected compounds, as predicted by molecular modeling, will be discussed. Our docking studies indicated that the phosphonic and salicylic acid groups interact in the pTyr-705 binding site in a broadly similar manner, while the other substituents occupy the STAT3 pY+1 and pY-X hydrophobic pockets. One of the most potent compounds in vitro (in the FP assay) inhibits STAT3 dimerization in intact cells and suppresses malignant transformation in human cancer cells that depend on STAT3. The in vitro and cell based potency of the N-arylbenzamides warrants further development of this scaffold as STAT3 inhibitors.

Citation Format: Nicholas J. Lawrence, Roberta Pireddu, Yiyu Ge, Murali K. Urlam, Xiaolei Zhang, Ying Sun, Harshani R. Lawrence, Wayne C. Guida, Said Sebti. Development of new N-Arylbenzamides as STAT3 dimerization inhibitors. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2467. doi:10.1158/1538-7445.AM2013-2467

Abstract 2470: Identification and evaluation of small molecule inhibitors of lysophosphatidic acid acyltransferase-beta

Abstract: Lysophosphatidic acid acyltransferase-beta (LPAAT-β) catalyzes the production of phosphatidic acid (PA) from lysophosphatidic acid (LPA). PA is a lipid cofactor that contributes to the activation of c-Raf, BRAF, mTOR and PKC-ζ. LPAAT-β expression is a prognostic factor in gynecologic malignancies and is being investigated as a therapeutic target in a variety of tumor types. We previously reported that knockdown of LPAAT-β by siRNA led to a significant inhibition of both anchorage-dependent and -independent growth in pancreatic cancer cell lines. Having thus established LPAAT-β as a valid therapeutic target in pancreatic cancer, we screened small molecule libraries for compounds which block LPAAT-β enzymatic activity in vitro.

Methods: We utilized a 96-well plate screening assay for LPAAT-β enzymatic activity modified from Aguado and Campbell, J Biol Chem 273(7):4096-4105, 1998. Briefly, compounds were introduced into a mixture containing full-length, recombinant, baculovirus-produced LPAAT-β (Blue Sky Biotechnology), oleoyl-LPA, and oleoyl coenzyme A. The ability of the compound to inhibit the enzyme activity was assayed by the measurement of the reaction of the thiol group of the released coenzyme A with the DTNB, resulting in an increase in the optical density of the sample when read at an absorbance of 413 nm. To rule out non-specific compounds identified from the DTNB plate assay, we confirmed activity using a secondary thin layer chromatography (TLC) assay that directly measures the ability of LPAAT-β to catalyze the synthesis of PA from oleoyl-LPA and a fluorochrome-labeled (NBD) palmitoyl coenzyme A.

Results: We screened a total of ten libraries containing 11204 compounds, and achieved a 1.2% hit rate for inhibition of &gt;50% at the tested concentration (100μM for nine libraries; 10μM for one library). Further testing identified several compounds with IC50s ranging from 0.1-15 μM. One hit identified with an IC50 of 100 nM was chosen for further investigation and for synthesis of analogs to optimize potency and undertake SAR. We verified the activity of this hit and its analogs against LPAAT-β by determining their inhibitory activity of the synthesis of NBD-labeled PA in a TLC assay. Finally, we demonstrated that the best analog from this group inhibited the proliferation of several pancreatic cancer cell lines.

Conclusions: We have developed a library of compounds which show inhibitory activity against LPAAT-β in a screening assay, and have confirmed their ability to inhibit LPAAT-β directly in a TLC assay which monitors the production of PA. These compounds show low micromolar activity against LPAAT-β in vitro, and micromolar activity against the proliferation of pancreatic cancer cell lines in culture.

Citation Format: Michelle A. Blaskovich, Harsukh Gevariya, Nicholas J. Lawrence, Saïd Sebti, Gregory Springett. Identification and evaluation of small molecule inhibitors of lysophosphatidic acid acyltransferase-beta. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2470. doi:10.1158/1538-7445.AM2013-2470

Abstract 350: Inhibition of SHP2 impairs oncogenic activity of EGFR mutants in non-small cell lung cancer

Activating mutations of epidermal growth factor receptor (EGFR) are found in 5-15% of non small cell lung carcinomas (NSCLC) and are targets of NSCLC treatment. However, most patients treated with EGFR tyrosine kinase inhibitors eventually acquire drug resistance, pointing to the need of evaluating other molecules as potential targets for developing new therapy for NSCLC. The protein tyrosine phosphatase (PTP) SHP2 mediates signaling of growth factor receptors including that of EGFR. SHP2 is activated by EGFR mutants in lung adenocarcinoma. Inhibition of SHP2 with the SHP2 PTP inhibitor SPI-112Me or SHP2 knockdown suppressed proliferation of EGFR-dependent HCC827 and H1975 cells. To assess the role of Shp2 in the transgenic mouse model of EGFR mutant-driven lung cancer, we generated transgenic mice carrying a doxycycline (dox)-inducible, PTP-defective SHP2 (tetO-SHP2CSDA). Bitransgenic CCSP-rtTA/tetO-SHP2CSDA mice were crossed with tetO-EGFRL858R mice. F1 offspring of dox-induced transgenic mice were analyzed. Erk1/2 and Src were activated by EGFRL858R in bitransgenic CCSP-rtTA/tetO-EGFRL858R mice. Both of them were suppressed by SHP2CSDA in CCSP-rtTA/tetO-EGFRL858R/tetO-SHP2CSDA tritransgenic mice. Importantly, expression of SHP2CSDA significantly inhibited EGFRL858R-induced lung tumor in the tritransgenic mice. These results suggest that SHP2 is critical for lung tumorigenesis mediated by EGFR mutations.

Citation Format: Valentina E. Schneeberger, Yuan Ren, Noreen Luetteke, Hartmut Berns, Liwei Chen, Harshani R. Lawrence, Nicholas J. Lawrence, Alex S. Lopez, Eric B. Haura, Domenico Coppola, Jie Wu. Inhibition of SHP2 impairs oncogenic activity of EGFR mutants in non-small cell lung cancer. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 350. doi:10.1158/1538-7445.AM2013-350

Abstract 3254: Discovery of S3I-1757, a STAT3-STAT3 dimerization disruptor that inhibits STAT3 activity, tumor survival, migration and invasion

The ability of STAT3 to translocate to the nucleus, bind DNA and transcriptionally regulate STAT3 target genes depends on tyrosine phosphorylation STAT3-STAT3 dimerization. Our chemistry efforts led to the discovery of S3I-1757 that disrupts STAT3-STAT3 dimerization. Fluorescence polarization assays and molecular modeling show that S3I-1757 interacts with Y-705 binding site in the STAT3-SH2 domain and displaces fluorescein-labelled GpYLPQTV phosphotyrosine peptide from binding to STAT3. Furthermore, using co-immunoprecipitation and co-localization studies we show that S3I-1757 inhibits STAT3 dimerization and STAT3-EGF receptor binding in intact cells. Treatment of human cancer cells with S3I-1757 (but not a closely related analogue, S3I-1756, that does not inhibit STAT3 dimerization), inhibits selectively the phosphorylation of STAT3 over Akt and Erk1/2, nuclear accumulation of P-Y705-STAT3, STAT3-DNA binding and transcriptional activation and suppresses the expression levels of STAT3 target genes such as Bcl-xL, survivin, cyclin D1 and MMP9. Furthermore, S3I-1757 but not S3I-1756 inhibits anchorage-dependent and -independent growth, migration and invasion of human cancer cells which depend on STAT3 selectively over those that do not. Finally, STAT3-C, a genetically engineered mutant of STAT3 that forms a constitutively dimerized STAT3, rescues from S3I-1757 effects. Our results warrant further development of S3I-1757 as a STAT3-STAT3 dimerization inhibitor capable of blocking hyper activated STAT3 and suppressing malignant transformation of STAT3-dependent human tumors.

Citation Format: Xiaolei Zhang, Ying Sun, Roberta Pireddu, Hua Yang, Murali K. Urlam, Harshani R. Lawrence, Wayne C. Guida, Nicholas J. Lawrence, Said M. Sebti. Discovery of S3I-1757, a STAT3-STAT3 dimerization disruptor that inhibits STAT3 activity, tumor survival, migration and invasion. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3254. doi:10.1158/1538-7445.AM2013-3254

A novel inhibitor of STAT3 homodimerization selectively suppresses STAT3 activity and malignant transformation

STAT3-STAT3 dimerization, which involves reciprocal binding of the STAT3-SH2 domain to phosphorylated tyrosine-705 (Y-705), is required for STAT3 nuclear translocation, DNA binding, and transcriptional regulation of downstream target genes. Here, we describe a small molecule S3I-1757 capable of disrupting STAT3-STAT3 dimerization, activation, and malignant transforming activity. Fluorescence polarization assay and molecular modeling suggest that S3I-1757 interacts with the phospho-Y-705-binding site in the SH2 domain and displaces fluorescein-labeled GpYLPQTV phosphotyrosine peptide from binding to STAT3. We generated hemagglutinin (HA)-tagged STAT3 and FLAG-tagged STAT3 and showed using coimmunoprecipitation and colocalization studies that S3I-1757 inhibits STAT3 dimerization and STAT3-EGF receptor (EGFR) binding in intact cells. Treatment of human cancer cells with S3I-1757 (but not a closely related analog, S3I-1756, which does not inhibit STAT3 dimerization), inhibits selectively the phosphorylation of STAT3 over AKT1 and ERK1/2 (MAPK3/1), nuclear accumulation of P-Y705-STAT3, STAT3-DNA binding, and transcriptional activation and suppresses the expression levels of STAT3 target genes, such as Bcl-xL (BCL2L1), survivin (BIRC5), cyclin D1 (CCND1), and matrix metalloproteinase (MMP)-9. Furthermore, S3I-1757, but not S3I-1756, inhibits anchorage-dependent and -independent growth, migration, and invasion of human cancer cells, which depend on STAT3. Finally, STAT3-C, a genetically engineered mutant of STAT3 that forms a constitutively dimerized STAT3, rescues cells from the effects of S3I-1757 inhibition. Thus, we have developed S3I-1757 as a STAT3-STAT3 dimerization inhibitor capable of blocking hyperactivated STAT3 and suppressing malignant transformation in human cancer cells that depend on STAT3.

Development of new N-Arylbenzamides as STAT3 Dimerization Inhibitors

The O-tosylsalicylamide S3I-201 (10) was used as a starting point for design and synthesis of novel STAT-3 dimerization inhibitors with improved drug-like qualities. The phosphonic acid 12d and salicylic acids 13f, 13g with a shorter amide linker lacking the O-tosyl group had improved STAT-3 inhibitory activity. The equivalent potencies observed by the replacement of phosphonic acid moiety of 12d with 5-amino-2-hydroxybenzoic acid group as in 13f further validates 5-amino-2-hydroxybenzoic acid as a phosphotyrosine mimic. The salicylic acid 13f displayed improved whole cell activity. The focused library of salicylic acids 13 with benzamide linker indicated that hydrophobic heptyl and cyclohexyl are the best tolerated R groups and a biphenyl ether (as the Ar group) significantly contributes to STAT3 inhibitory activity. Our docking studies indicated that the acidic groups of 12d, 13f and 13g interact in the p-Tyr-705 binding site in a broadly similar manner, while the phenoxybenzoyl group and the cyclohexylbenzyl group occupying pY+1 and pY-X hydrophobic pockets respectively. The in vitro and cell based potency of 13f warrants further development of this scaffold as STAT3 inhibitors.

Regulation of interlocking gene regulatory network subcircuits by a small molecule inhibitor of retinoblastoma protein (RB) phosphorylation: cancer cell expression of HLA-DR

The induction of the major histocompatibility (MHC), antigen-presenting class II molecules by interferon-gamma, in solid tumor cells, requires the retinoblastoma tumor suppressor protein (Rb). In the absence of Rb, a repressosome blocks the access of positive-acting, promoter binding proteins to the MHC class II promoter. However, a complete molecular linkage between Rb expression and the disassembly of the MHC class II repressosome has been lacking. By treating A549 lung carcinoma cells with a novel small molecule that prevents phosphorylation-mediated, Rb inactivation, we demonstrate that Rb represses the synthesis of an MHC class II repressosome component, YY1. The reduction in YY1 synthesis correlates with the advent of MHC class II inducibility; with loss of YY1 binding to the promoter of the HLA-DRA gene, the canonical human MHC class II gene; and with increased Rb binding to the YY1 promoter. These results support the concept that the Rb gene regulatory network (GRN) subcircuit that regulates cell proliferation is linked to a GRN subcircuit regulating a tumor cell immune function.

Development of o-chlorophenyl substituted pyrimidines as exceptionally potent aurora kinase inhibitors

The o-carboxylic acid substituted bisanilinopyrimidine 1 was identified as a potent hit (Aurora A IC(50) = 6.1 ± 1.0 nM) from in-house screening. Detailed structure-activity relationship (SAR) studies indicated that polar substituents at the para position of the B-ring are critical for potent activity. X-ray crystallography studies revealed that compound 1 is a type I inhibitor that binds the Aurora kinase active site in a DFG-in conformation. Structure-activity guided replacement of the A-ring carboxylic acid with halogens and incorporation of fluorine at the pyrimidine 5-position led to highly potent inhibitors of Aurora A that bind in a DFG-out conformation. B-Ring modifications were undertaken to improve the solubility and cell permeability. Compounds such as 9m with water-solubilizing moieties at the para position of the B-ring inhibited the autophosphorylation of Aurora A in MDA-MB-468 breast cancer cells.

RKI-1447 is a potent inhibitor of the Rho-associated ROCK kinases with anti-invasive and antitumor activities in breast cancer

The Rho-associated kinases ROCK1 and ROCK2 are critical for cancer cell migration and invasion, suggesting they may be useful therapeutic targets. In this study, we describe the discovery and development of RKI-1447, a potent small molecule inhibitor of ROCK1 and ROCK2. Crystal structures of the RKI-1447/ROCK1 complex revealed that RKI-1447 is a Type I kinase inhibitor that binds the ATP binding site through interactions with the hinge region and the DFG motif. RKI-1447 suppressed phosphorylation of the ROCK substrates MLC-2 and MYPT-1 in human cancer cells, but had no effect on the phosphorylation levels of the AKT, MEK, and S6 kinase at concentrations as high as 10 μmol/L. RKI-1447 was also highly selective at inhibiting ROCK-mediated cytoskeleton re-organization (actin stress fiber formation) following LPA stimulation, but does not affect PAK-meditated lamellipodia and filopodia formation following PDGF and Bradykinin stimulation, respectively. RKI-1447 inhibited migration, invasion and anchorage-independent tumor growth of breast cancer cells. In contrast, RKI-1313, a much weaker analog in vitro, had little effect on the phosphorylation levels of ROCK substrates, migration, invasion or anchorage-independent growth. Finally, RKI-1447 was highly effective at inhibiting the outgrowth of mammary tumors in a transgenic mouse model. In summary, our findings establish RKI-1447 as a potent and selective ROCK inhibitor with significant anti-invasive and antitumor activities and offer a preclinical proof-of-concept that justify further examination of RKI-1447 suitability as a potential clinical candidate.

HG-829 is a potent noncompetitive inhibitor of the ATP-binding cassette multidrug resistance transporter ABCB1

Transmembrane drug export mediated by the ATP-binding cassette (ABC) transporter P-glycoprotein contributes to clinical resistance to antineoplastics. In this study, we identified the substituted quinoline HG-829 as a novel, noncompetitive, and potent P-glycoprotein inhibitor that overcomes in vitro and in vivo drug resistance. We found that nontoxic concentrations of HG-829 restored sensitivity to P-glycoprotein oncolytic substrates. In ABCB1-overexpressing cell lines, HG-829 significantly enhanced cytotoxicity to daunorubicin, paclitaxel, vinblastine, vincristine, and etoposide. Coadministration of HG-829 fully restored in vivo antitumor activity of daunorubicin in mice without added toxicity. Functional assays showed that HG-829 is not a Pgp substrate or competitive inhibitor of Pgp-mediated drug efflux but rather acts as a noncompetitive modulator of P-glycoprotein transport function. Taken together, our findings indicate that HG-829 is a potent, long-acting, and noncompetitive modulator of P-glycoprotein export function that may offer therapeutic promise for multidrug-resistant malignancies.

Pyridylthiazole-based ureas as inhibitors of Rho associated protein kinases (ROCK1 and 2)

Potent ROCK inhibitors of a new class of 1-benzyl-3-(4-pyridylthiazol-2-yl)ureas have been identified. Remarkable differences in activity were observed for ureas bearing a benzylic stereogenic center. Derivatives with hydroxy, methoxy and amino groups at the meta position of the phenyl ring give rise to the most potent inhibitors (low nM). Substitutions at the para position result in substantial loss of potency. Changes at the benzylic position are tolerated resulting in significant potency in the case of methyl and methylenehydroxy groups. X-Ray crystallography was used to establish the binding mode of this class of inhibitors and provides an explanation for the observed differences of the enantiomer series. Potent inhibition of ROCK in human lung cancer cells was shown by suppression of the levels of phosphorylation of the ROCK substrate MYPT-1.

Ack1-mediated androgen receptor phosphorylation modulates radiation resistance in castration-resistant prostate cancer

Androgen deprivation therapy has been the standard of care in prostate cancer due to its effectiveness in initial stages. However, the disease recurs, and this recurrent cancer is referred to as castration-resistant prostate cancer (CRPC). Radiotherapy is the treatment of choice; however, in addition to androgen independence, CRPC is often resistant to radiotherapy, making radioresistant CRPC an incurable disease. The molecular mechanisms by which CRPC cells acquire radioresistance are unclear. Androgen receptor (AR)-tyrosine 267 phosphorylation by Ack1 tyrosine kinase (also known as TNK2) has emerged as an important mechanism of CRPC growth. Here, we demonstrate that pTyr(267)-AR is recruited to the ATM (ataxia telangiectasia mutated) enhancer in an Ack1-dependent manner to up-regulate ATM expression. Mice engineered to express activated Ack1 exhibited a significant increase in pTyr(267)-AR and ATM levels. Furthermore, primary human CRPCs with up-regulated activated Ack1 and pTyr(267)-AR also exhibited significant increase in ATM expression. The Ack1 inhibitor AIM-100 not only inhibited Ack1 activity but also was able to suppress AR Tyr(267) phosphorylation and its recruitment to the ATM enhancer. Notably, AIM-100 suppressed Ack1 mediated ATM expression and mitigated the growth of radioresistant CRPC tumors. Thus, our study uncovers a previously unknown mechanism of radioresistance in CRPC, which can be therapeutically reversed by a new synergistic approach that includes radiotherapy along with the suppression of Ack1/AR/ATM signaling by the Ack1 inhibitor, AIM-100.

A novel mechanism by which small molecule inhibitors induce the DFG flip in Aurora A

Most protein kinases share a DFG (Asp-Phe-Gly) motif in the ATP site that can assume two distinct conformations, the active DFG-in and the inactive DFG-out states. Small molecule inhibitors able to induce the DFG-out state have received considerable attention in kinase drug discovery. Using a typical DFG-in inhibitor scaffold of Aurora A, a kinase involved in the regulation of cell division, we found that halogen and nitrile substituents directed at the N-terminally flanking residue Ala273 induced global conformational changes in the enzyme, leading to DFG-out inhibitors that are among the most potent Aurora A inhibitors reported to date. The data suggest an unprecedented mechanism of action, in which induced-dipole forces along the Ala273 side chain alter the charge distribution of the DFG backbone, allowing the DFG to unwind. As the ADFG sequence and three-dimensional structure is highly conserved, DFG-out inhibitors of other kinases may be designed by specifically targeting the flanking alanine residue with electric dipoles.

Abstract 3904: Pyridylthiazole-based ureas as inhibitors of Rho-associated protein kinases

Rho GTPase is a small G-protein which plays a critical role in signaling pathways and controls cell growth and division. Rho-associated protein kinase (known as ROCK or Rho kinase) is a Ser/Thr protein kinase activated by GTP-bound Rho and phosphorylates target proteins involved in various signal transduction pathways. Rho and the Rho-kinase signalling pathways are implicated in cell morphology, motility, smooth muscle contraction, formation of stress fibres, focal adhesion and cell transformation. ROCKs have been subject to growing attention, having been implicated in a range of therapeutic areas including cardiovascular diseases, CNS disorders, and cancer. Further, the pharmacological inhibition of ROCKs has been suggested as a promising strategy in the prevention of cell invasion, a central event in the process of metastasis. Potent ROCK inhibitors of a new class of 1-benzyl-3-(4-pyridylthiazol-2-yl)ureas have been identified. Remarkable differences in activity were observed for ureas bearing a benzylic stereogenic center. Derivatives with hydroxy, methoxy and amino groups at the meta position of the phenyl ring give rise to the most potent inhibitors (low nM). Substitutions at the para position result in substantial loss of potency. Changes at the benzylic position are tolerated resulting in significant potency in the case of methyl and methylenehydroxy groups. X-ray crystallography was used to establish the binding mode of this class of inhibitors and provides an explanation for the observed differences of the enantiomer series. Potent inhibition of ROCK in human lung cancer cells was shown by suppression of the phosphorylation levels of the ROCK substrate MYPT-1. One of the series, RKI-1447 inhibits migration, invasion and anchorage-independent tumor growth of breast cancer cells and is discussed in an accompanying poster.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3904. doi:1538-7445.AM2012-3904

Abstract 2942: RKI-1447, a potent ROCK inhibitor with anti-tumor and anti-invasive activities in breast cancer

Rho-associated kinases 1 and 2 (ROCKs) are intimately involved in metastasis and this prompted the development of ROCK inhibitors (RKIs) as anti-metastatic agents. Here, we describe the development of RKI-1447 which inhibits ROCK 1 and 2 potently in vitro (IC50s; 14 and 6 nM, respectively) and suppresses the phosphorylation of ROCK substrates MLC2 and MYPT1 in human breast cancer cells (IC50; 100 nM). The crystal structure of the RKI-1447-ROCK1 complex reveals that RKI-1447 binds the hinge region in the ATP binding site. RKI-1447 is highly selective and does not affect the phosphorylation levels of Akt, Erk, Mek and S6. RKI-1447 is also highly selective at inhibiting ROCK-mediated cytoskeleton re-organization (actin stress fiber formation) following LPA stimulation, but does not affect PKA-meditated lamelipodia and filopodia formation following PDGF and bradykinin stimulation, respectively. RKI-1447 inhibits migration, invasion and anchorage-independent tumor growth of breast cancer cells. A structurally-related analog RKI-1313 that is inactive against ROCKs in vitro (IC50 &gt; 10 µM) has little effects on migration, invasion and anchorage-independent growth. Finally, RKI-1447 is highly effective at inhibiting the growth of ErbB2-driven breast tumors in a transgenic animal model.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2942. doi:1538-7445.AM2012-2942

Abstract 3902: Development of Aurora A inhibitors with ortho-halophenyl substituted pyrimidines: Unusual potency, SAR and X-ray crystallography studies

The Aurora kinases are a family of serine-threonine kinases that play an important role in the regulation of cell division. The three members of the Aurora family Aurora A, B and C share a high degree of structural homology in their kinase domain but each kinase plays a different role in the control of mitosis. Aurora A and B have received the most attention to date as anticancer targets. Detailed studies have shown Aurora A and B are over expressed in a variety of cancers and are implicated in many aspects of tumor development. Aurora A is frequently over-expressed in tumors and cancer cell lines and has characteristics of an oncogene. Aurora B is also over expressed in many cancer types but does not have oncogenic properties. Aurora B plays important roles in M phase to ensure correct chromosome-microtubule alignment and attachment and chromosomal cytokinesis. Therefore, inhibition of Aurora kinase A and B is emerging as target-based therapy in cancer treatment. From our previous work HLM-8598 was identified from an in-house chemical library as a potent and highly selective inhibitor for Aurora A (IC50 value of 0.073 ± 0.002 μM) over Aurora B (IC50 = 5.4 ± 1.8 μM). X-ray crystallography studies of HLM-8598 bound to Aurora A confirmed HLM-8598 is a type-1 kinase inhibitor that interacts with the ATP binding site of the enzyme. The HLM-8598 bound to Aurora A structure-assisted synthesis of new analogs with IC50 &lt; 2.5 nM affinity. We will present the synthesis of new analogs that contain an ortho-halogen substituted phenyl moiety, structure activity relationship studies as a part of our efforts to identify unusually potent Aurora A kinase inhibitors. We will discuss the use of kinase structural elements to rationally guide compound synthesis and improve design strategy. The in vitro and in vivo activities of ortho-halogen phenyl substituted pyrimidines will be presented as unusually potent Aurora A inhibitors and potential anti-cancer agents.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3902. doi:1538-7445.AM2012-3902

Abstract 1854: Lysophosphatidic Acid Acyltransferase-Beta contributes to proliferation and anchorage-independent growth in pancreatic adenocarcinoma

Abstract: Lysophosphatidic acid acyltransferase-beta (LPAAT-α) catalyzes the production of phosphatidic acid (PA) from lysophosphatidic acid (LPA). PA is a lipid cofactor that contributes to the activation of c-Raf, BRAF, mTOR and PKC-α. LPAAT-α expression is a prognostic factor in gynecologic malignancies and is being investigated as a therapeutic target in a variety of tumor types. We previously reported that LPAAT-α is expressed in pancreatic cancer cell lines and in human pancreatic adenocarcinoma tissues. We employed siRNA knockdown of LPAAT-α expression in pancreatic cancer cells in vitro. We find that reduction in the expression of LPAAT-α protein is associated with decreased proliferation and impairment in anchorage dependent growth of pancreatic cancer cells. Methods: MiaPaCa and Panc-1 cells were transfected with two different siRNAs targeted to LPAAT-α at 10 nM and 25 nM for 48 hrs and 72 hrs. A non-targeting siRNA was used as a control. The cells were then plated on tissue culture dishes or in soft agar and allowed to proliferate. Proliferation on plastic dishes was measured using Alamar Blue. Colony formation in soft agar was determined by directly counting macroscopic colonies. Results: Transfection of MiaPaCa and Panc-1 cells with siRNA at 25 nM for 72 hours achieved almost 100% inhibition of LPAAT-α protein expression by Western blotting. Under these conditions there was a 50% reduction in proliferation and colony formation. Studies to determine the effects of depleting LPAAT-α on the levels of p-PKC-α, p-MEK, p-4E-BP1 and p-S6Kinase are ongoing and will be presented. Conclusions: Suppression of expression of LPAAT-α protein in pancreatic cancer cell lines reduces proliferation and anchorage independent growth. This contributes to the validation of LPAAT-α as a therapeutic target in pancreatic cancer.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1854. doi:1538-7445.AM2012-1854

Abstract 2912: Development of potent SHP2 inhibitors for in vivo studies

The Src homology-2 domain-containing protein tyrosine phosphatase-2 (SHP2) is a positive transducer of growth factor, cytokine, integrin, and hormone signaling pathways which regulates processes such as cell proliferation, differentiation, adhesion, migration, and apoptosis and plays a pivotal role in growth factor and cytokine signaling. Gain-of-function SHP2 mutations are associated with various kinds of leukemia, and solid tumors. This makes SHP2 an attractive target for anticancer therapy. We are developing SHP2 inhibitors as novel anticancer drugs. Previously, we have reported on SPI-112 and its methyl ester prodrug SPI-112Me. However, the poor solubility of SPI-112Me has become an obstacle for in vivo studies. In ongoing study, we generate SPI-112 analogs to further improve physicochemical properties of these SHP2 inhibitors, such as solubility and cell permeability. To this aim, we synthesized SPI-112 derivatives containing various phosphotyrosine mimics and their prodrugs. SPI-112 derivatives of SHP2 inhibitors having improved properties have been obtained in this effort.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2912. doi:1538-7445.AM2012-2912

Fragment-based and structure-guided discovery and optimization of Rho kinase inhibitors

Using high concentration biochemical assays and fragment-based screening assisted by structure-guided design, we discovered a novel class of Rho-kinase inhibitors. Compound 18 was equipotent for ROCK1 (IC(50) = 650 nM) and ROCK2 (IC(50) = 670 nM), whereas compound 24 was more selective for ROCK2 (IC(50) = 100 nM) over ROCK1 (IC(50) = 1690 nM). The crystal structure of the compound 18-ROCK1 complex revealed that 18 is a type 1 inhibitor that binds the hinge region in the ATP binding site. Compounds 18 and 24 inhibited potently the phosphorylation of the ROCK substrate MLC2 in intact human breast cancer cells.

Ack1 tyrosine kinase activation correlates with pancreatic cancer progression

Pancreatic cancer is a significant cause of cancer mortality worldwide as the disease has advanced significantly in patients before symptoms are evident. The signal transduction pathways that promote this rapid progression are not well understood. Ack1 or TNK2, an ubiquitously expressed oncogenic non-receptor tyrosine kinase, integrates signals from ligand-activated receptor tyrosine kinases to modulate intracellular signaling cascades. In the present study, we investigated the Ack1 activation profile in a pancreatic cancer tumor microarray, and observed that expression levels of activated Ack1 and pTyr284-Ack1 positively correlated with the severity of disease progression and inversely correlated with the survival of patients with pancreatic cancer. To explore the mechanisms by which Ack1 promotes tumor progression, we investigated the role of AKT/PKB, an oncogene and Ack1-interacting protein. Ack1 activates AKT directly in pancreatic and other cancer cell lines by phosphorylating AKT at Tyr176 to promote cell survival. In addition, the Ack1 inhibitor AIM-100 not only inhibited Ack1 activation but also suppressed AKT tyrosine phosphorylation, leading to cell cycle arrest in the G1 phase. This effect resulted in a significant decrease in the proliferation of pancreatic cancer cells and induction of apoptosis. Collectively, our data indicate that activated Ack1 could be a prognostic marker for ascertaining early or advanced pancreatic cancer. Thus, Ack1 inhibitors hold promise for therapeutic intervention to inhibit pancreatic tumor growth.

Nicotine-mediated induction of E-selectin in aortic endothelial cells requires Src kinase and E2F1 transcriptional activity

Smoking is highly correlated with enhanced likelihood of atherosclerosis by inducing endothelial dysfunction. In endothelial cells, various cell-adhesion molecules including E-selectin, are shown to be upregulated upon exposure to nicotine, the addictive component of tobacco smoke; however, the molecular mechanisms underlying this induction are poorly understood. Here we demonstrate that nicotine-induced E-selectin transcription in human aortic endothelial cells (HAECs) could be significantly blocked by α7-nAChR subunit inhibitor, α-BT, Src-kinase inhibitor, PP2, or siRNAs against Src or β-Arrestin-1 (β-Arr1). Further, chromatin immunoprecipitations show that E-selectin is an E2F1 responsive gene and nicotine stimulation results in increased recruitment of E2F1 on E-selectin promoter. Inhibiting E2F1 activity using RRD-251, a disruptor of the Rb-Raf-1 kinase interaction, could significantly inhibit the nicotine-induced recruitment of E2F1 to the E-selectin promoter as well as E-selectin expression. Interestingly, stimulation of HAECs with nicotine results in increased adhesion of U937 monocytic cells to HAECs and could be inhibited by pre-treatment with RRD-251. Similarly, depletion of E2F1 or Src using RNAi blocked the increased adhesion of monocytes to nicotine-stimulated HAECs. These results suggest that nicotine-stimulated adhesion of monocytes to endothelial cells is dependent on the activation of α7-nAChRs, β-Arr1 and cSrc regulated increase in E2F1-mediated transcription of E-selectin gene. Therefore, agents such as RRD-251 that can target activity of E2F1 may have potential therapeutic benefit against cigarette smoke induced atherosclerosis.