Background: Rac is a central regulator of cancer cell migration/invasion and metastasis. Results: EHop-016 inhibits Rac activity with an IC 50 of 1 M. EHop-016 blocks Rac interaction with the Rac exchange factor Vav2, lamellipodia extension, and cell migration. Conclusion: EHop-016 is an effective Rac inhibitor. Significance: EHop-016 has potential as a metastasis therapeutic and for investigations of Rac-regulated cellular responses.

Metastatic disease still lacks effective treatments, and remains the primary cause of cancer mortality. Therefore, there is a critical need to develop better strategies to inhibit metastatic cancer. The Rho family GTPase Rac is an ideal target for anti-metastatic cancer therapy, because Rac is a key molecular switch that is activated by a myriad of cell surface receptors to promote cancer cell migration/invasion and survival. Previously, we reported the design and development of EHop-016, a small molecule compound, which inhibits Rac activity of metastatic cancer cells with an IC50 of 1 μM. EHop-016 also inhibits the activity of the Rac downstream effector p21-activated kinase (PAK), lamellipodia extension, and cell migration in metastatic cancer cells. Herein, we tested the efficacy of EHop-016 in a nude mouse model of experimental metastasis, where EHop-016 administration at 25 mg/kg body weight (BW) significantly reduced mammary fat pad tumor growth, metastasis, and angiogenesis. As quantified by UPLC MS/MS, EHop-016 was detectable in the plasma of nude mice at 17 to 23 ng/ml levels at 12 h following intraperitoneal (i.p.) administration of 10 to 25 mg/kg BW EHop-016. The EHop-016 mediated inhibition of angiogenesis In Vivo was confirmed by immunohistochemistry of excised tumors and by In Vitro tube formation assays of endothelial cells. Moreover, EHop-016 affected cell viability by down-regulating Akt and Jun kinase activities and c-Myc and Cyclin D expression, as well as increasing caspase 3/7 activities in metastatic cancer cells. In conclusion, EHop-016 has potential as an anticancer compound to block cancer progression via multiple Rac-directed mechanisms.

Simple and efficient Grignard procedures are reported for the syntheses of B-allenyl-10-(phenyl)-9-borabicyclo[3.3.2]decane (1) and its B-(gamma-trimethylsilylpropargyl) counterpart (2) in both enantiomeric forms. Both add selectively to ketones, providing propargyl- and alpha-silylallenyl 3-degree-carbinols, respectively (i.e., 6 (61-93% ee) and 9 (64-98% ee)). The air-stable boron byproduct is efficiently recovered and recycled back to either 1 or 2. The ozonolysis and bromination of 9 provide nonracemic alpha-hydroxy acids and gamma-bromopropynyl carbinols, respectively.

Based on the efficacy of EHop-016 as an inhibitor of migration and Rac1 activation, a new series of carbazole derivatives has been synthesized. Cytotoxic and anti-migratory effects of these compounds were evaluated in MCF-7 and MDA-MB-231 breast cancer cell lines. Preliminary investigations of their anticancer activity demonstrated that several compounds have moderate antiproliferative effects on cancer cell lines with GI values in the range of 13-50 µM. Furthermore, compounds 3b and 11b inhibit migration activity of metastatic cell line MDA-MB-231 by 32% and 34%, respectively. Compound 11b was shown to inhibit activation of the Rho GTPase Rac1 by 55% at 250 nM in both MDA-MB-231 and MDA-MB-435 cell lines. Compared with the IC of Rac1 inhibition by lead compound EHop-016 of 1.1 µM, compound 11b demonstrates 4X improved in vitro efficacy.

[reaction: see text] The asymmetric propargylboration of aldehydes at -78 degrees C in <3 h with 1 provides silylated alpha-allenyl carbinols 6 (60-87%) in high ee (94% to >98% ee). The reagents 1 are easily prepared in both enantiomeric forms with a simple Grignard procedure and air-stable borinate complexes 2. The ozonolysis of 6 proceeds smoothly through an acylsilane intermediate to give a TMS ester, which is hydrolyzed to the alpha-hydroxy acid quantitatively with water.

The Rac inhibitor EHop-016 was developed as a compound with the potential to inhibit cancer metastasis. Inhibition of the first step of metastasis, migration, is an important strategy for metastasis prevention. The small GTPase Rac acts as a pivotal binary switch that is turned "on" by guanine nucleotide exchange factors (GEFs) via a myriad of cell surface receptors, to regulate cancer cell migration, survival, and proliferation. Unlike the related GTPase Ras, Racs are not usually mutated, but overexpressed or overactivated in cancer. Therefore, a rational Rac inhibitor should block the activation of Rac by its upstream effectors, GEFs, and the Rac inhibitor NSC23766 was developed using this rationale. However, this compound is ineffective at inhibiting the elevated Rac activity of metastatic breast cancer cells. Therefore, a panel of small molecule compounds were derived from NSC23766 and screened for Rac activity inhibition in metastatic cancer cells. EHop-016 was identified as a compound that blocks the interaction of Rac with the GEF Vav in metastatic human breast cancer cells with an IC50 of ~1μM. At higher concentrations (10μM), EHop-016 inhibits the related Rho GTPase Cdc42, but not Rho, and also reduces cell viability. Moreover, EHop-016 inhibits the activation of the Rac downstream effector p21-activated kinase, extension of motile actin-based structures, and cell migration. Future goals are to develop EHop-016 as a therapeutic to inhibit cancer metastasis, either individually or in combination with current anticancer compounds. The next generation of EHop-016-based Rac inhibitors is also being developed.

The asymmetric allylboration of N-H aldimines, generated from either N-trimethylsilyl or N-diisobutylalanyl precursors, with B-allyl-9-borabicyclo[3.3.2]decane is described. The desired homoallylic amines are obtained efficiently (60-90 %) and selectively (60-89 % ee). A non-oxidative work-up procedure has also been developed for this new method, which permits the recovery of the air-stable pseudoephedrine (PE) complex (50-70 %), which is conveniently converted back to B-allyl-9-borabicyclo[3.3.2]decane (98 %) with allylmagnesium bromide in ether for its reuse in the asymmetric allylboration process. Additional studies were conducted to better understand these processes and the origin of the observed enantioselectivity.

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