Sinicrope, Frank A.

Abstract Background. Mutation of the BRAF(V600E) oncogene occurs in ~8% of human colorectal cancers (CRC) and its inhibition is associated with treatment resistance that is due, in part, to paradoxical re-activation of MEK/ERK signaling. Recently, pathway analysis identified cyclin-dependent kinase 1 (CDK1) upregulation in a subset of human BRAFV600E CRCs. We determined whether CDK1 antagonism can enhance the efficacy of MEK inhibition in BRAFV600E CRC cell lines. Methods. Manipulation of gene expression was achieved by siRNA and/or ectopic expression, or using isogenic cell pairs. Cells were treated with the CDK1 selective inhibitor RO-3306 or dinaciclib (CDK1,2,5,9 inhibitor) alone or combined with the MEK inhibitor cobimetinib. Apoptosis was quantified by Annexin V staining with flow cytometry; apoptotic signaling was analyzed by immunoblotting of caspase-8 phosphorylation and caspase cleavage. Long-term cell survival was evaluated by clonogenic assay. In vivo efficacy of the drug combination was determined in a murine flank xenograft model. Results. BRAFV600E CRC cell lines expressed CDK1 whose siRNA knockdown or pharmacological inhibition by RO-3306 or dinaciclib was shown to sensitize them to apoptosis (annexin V labeling). The combination of RO-3306 or dinaciclib with cobimetinib cooperatively enhanced apoptosis and reduced clonogenic survival compared to drug monotherapy. Cells isogenic or ectopic for BRAFV600E displayed apoptosis resistance to CDK inhibitors, as did cells with ectopic expression of constitutively active MEK. CDK1 inhibition by RO-3306 or dinaciclib induced a caspase-8-dependent apoptosis shown by caspase-8 restoration in deficient NB7 cells that enhanced dinaciclib-induced caspase-3 cleavage. Furthermore, CDK inhibitors suppressed procaspase-8 phosphorylation at S387 shown by drug withdrawal that restored phospho-S387 and increased cell mitosis. In a CRC xenograft model, dinaciclib plus cobimetinib produced significantly greater tumor growth inhibition in association with a caspase-dependent apoptosis than did either drug alone. Analysis of TCGA datasets revealed overexpression of CDK1 in human CRCs compared to normal colonic tissue. An inverse relationship existed between expression of CDK1 and the cell cycle inhibitor p16. In CRC cells, ectopic p16 was shown to downregulate CDK1 expression. In conclusion, our data establish CDK1 as a novel mediator of apoptosis resistance in BRAFV600E CRC cells lines whose combined targeting with CDK and MEK/ERK inhibitors may represent an effective therapeutic strategy. Citation Format: Peng Zhang, Hisato Kawakami, Weizhen Liu, Xiangyu Zeng, Klaus Stebhardt, Kaixiong Tao, Shengbing Huang, Frank A. Sinicrope. Targeting CDK1 and MEK/ERK overcomes apoptosis resistance in BRAFV600E human colorectal cancer cells [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 2336.

Background and Aims: The benefit of adjuvant chemotherapy for stage II colorectal cancer (CRC) patients remains unclear, emphasizing the need for improved prognostic biomarkers to identify patients at risk of metastatic recurrence. To address this unmet clinical need, we examined the expression and phosphorylation status of the vasodilator-stimulated phosphoprotein (VASP) in CRC tumor progression. VASP, a processive actin polymerase, promotes the formation of invasive membrane structures leading to extracellular matrix remodeling and tumor invasion. Phosphorylation of VASP serine (Ser) residues 157 and 239 regulate VASP function, directing subcellular localization and inhibiting actin polymerization, respectively. Methods: The expression levels of VASP protein, pSer157-VASP, and pSer239-VASP were determined by immunohistochemistry in tumors and matched normal adjacent tissue from 141 CRC patients, divided into 2 cohorts, and the association of VASP biomarker expression with clinicopathologic features and disease recurrence was examined. Results: We report that changes in VASP expression and phosphorylation were significantly associated with tumor invasion and disease recurrence. Furthermore, we disclose a novel 2-tiered methodology to maximize VASP positive and negative predictive value performance for prognostication. Conclusion: VASP biomarkers may serve as prognostic biomarkers in CRC and should be evaluated in a larger clinical study.

AbstractBackground: Prior studies have supported an inverse association between physical activity and colon cancer risk and suggest that higher physical activity may also improve cancer survival. Among participants in a phase III adjuvant trial for stage III colon cancer, we assessed the association of physical activity around the time of cancer diagnosis with subsequent outcomes.Methods: Before treatment arm randomization (FOLFOX or FOLFOX + cetuximab), study participants completed a questionnaire including items regarding usual daily activity level and frequency of participation in recreational physical activity (N = 1,992). Using multivariable Cox models, we calculated HRs for associations of aspects of physical activity with disease-free (DFS) and overall survival (OS).Results: Over follow-up, 505 participants died and 541 experienced a recurrence. Overall, 75% of participants reported recreational physical activity at least several times a month; for participants who reported physical activity at least that often (vs. once a month or less), the HRs for DFS and OS were 0.82 [95% confidence interval (CI), 0.69–0.99] and 0.76 (95% CI, 0.63–0.93), respectively. There was no evidence of material effect modification in these associations by patient or tumor attributes, except that physical activity was more strongly inversely associated with OS in patients with stage T3 versus T4 tumors (Pinteraction = 0.03).Conclusions: These findings suggest that higher physical activity around the time of colon cancer diagnosis may be associated with more favorable colon cancer outcomes.Impact: Our findings support further research on whether colon cancer survival may be enhanced by physical activity. Cancer Epidemiol Biomarkers Prev; 27(6); 696–703. ©2018 AACR.

Abstract The BRAFV600E mutation occurs in approximately 8% of human colorectal cancers and is associated with therapeutic resistance that is due, in part, to reactivation of MEK/ERK signaling cascade. Recently, pathway analysis identified cyclin-dependent kinase 1 (CDK1) upregulation in a subset of human BRAFV600E colorectal cancers. Therefore, it was determined whether CDK1 antagonism enhances the efficacy of MEK inhibition in BRAFV600E colorectal cancer cells. BRAFV600E colorectal cancer cell lines expressing CDK1 were sensitized to apoptosis upon siRNA knockdown or small-molecule inhibition with RO-3306 (CDK1 inhibitor) or dinaciclib (CDK1, 2, 5, 9 inhibitors). Combination of RO-3306 or dinaciclib with cobimetinib (MEK inhibitor) cooperatively enhanced apoptosis and reduced clonogenic survival versus monotherapy. Cells isogenic or ectopic for BRAFV600E displayed resistance to CDK1 inhibitors, as did cells with ectopic expression of constitutively active MEK. CDK1 inhibitors induced a CASP8-dependent apoptosis shown by caspase-8 restoration in deficient NB7 cells that enhanced dinaciclib-induced CASP3 cleavage. CDK inhibitors suppressed pro-CASP8 phosphorylation at S387, as shown by drug withdrawal, which restored p-S387 and increased mitosis. In a colorectal cancer xenograft model, dinaciclib plus cobimetinib produced significantly greater tumor growth inhibition in association with a caspase-dependent apoptosis versus either drug alone. The Cancer Genome Atlas (TCGA) transcriptomic dataset revealed overexpression of CDK1 in human colorectal cancers versus normal colon. Together, these data establish CDK1 as a novel mediator of apoptosis resistance in BRAFV600E colorectal cancers whose combined targeting with a MEK/ERK inhibitor represents an effective therapeutic strategy. Implications: CDK1 is a novel mediator of apoptosis resistance in BRAFV600E colorectal cancers whose dual targeting with a MEK inhibitor may be therapeutically effective. Mol Cancer Res; 16(3); 378–89. ©2017 AACR.

Abstract BRAFV600E mutation occurs in ~10% of human colorectal cancers (CRC) where it is associated with treatment resistance and poor prognosis. Data from TCGA and a clinical trial cohort identified a distinct subset of BRAF mutant colon cancers with deregulation of the cell cycle and overexpression of CDK1 (Barras D, et al, Clin Cancer Res. 2016). We tested the hypothesis that CDK1 inhibition can enhance apoptosis in BRAFV600E CRC cells. Since BRAF mutant cells show p-ERK activation, combined inhibition of CDK1 and MEK/ERK was evaluated. Using isogenic colon cancer cells, BRAF mutant alleles were shown to confer resistance to the CDK1 inhibitor, R0-3306, in a gene dose-dependent manner that was associated with reduced cleavage of caspase-3 and downstream PARP, and decreased pH2AX (DNA fragmentation marker). Ectopic BRAFV600E or constitutively active MEK mutant also conferred resistance to R0-3306. CDK1 siRNA was shown to increase cobimetinib-induced apoptosis, including annexin V labeling, and increased pH2AX. Furthermore, ERK siRNA or cobimetinib treatment attenuated CDK1 protein expression and increased R0-3306-induced pH2Ax. Moreover, treatment with R0-3306 plus cobimetinib significantly enhanced a caspase-dependent apoptosis and markedly reduced colony formation vs either drug alone in two CRC cell lines. Caspase-3 cleavage by R0-3306 + cobimetinib was dependent upon caspase-8. Mechanistically, CDK1 inhibition by R0-3306 suppressed the phosphorylation of procaspase-8 at Ser-387 shown by R0-3306 withdrawal which restored p-C8-S387 coincident with expression of the mitotic marker, pH3S10. In conclusion, inhibition of CDK1 can significantly augment apoptosis induction by MEK/ERK inhibition in BRAFV600E CRC cells, suggesting a novel therapeutic strategy to overcome mutant BRAF-mediated resistance. Apoptosis induction by CDK1 inhibitor (R0-3306) ± MEK/ERK inhibitor cobimetinibTreatmentTreatmentTreatementTreatmentCRC cell linesDMSOR0-3306 (5 µM)cobimetinib (5 µM)combinationAnnexin V+ (%)RKO13.43 ± 1.4132.55 ± 2.9315.04 ± 0.2652.72 ± 3.16Annexin V+ (%)HT-2911.22 ± 1.8442.44 ± 2.7025.29 ± 0.1665.62 ± 4.11 Citation Format: Hisato Kawakami, Shengbing Huang, Frank A. Sinicrope. Targeting CDK1 and MEK/ERK overcome mutant BRAF-mediated apoptosis resistance in human colorectal cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2173. doi:10.1158/1538-7445.AM2017-2173

Abstract Evidence suggests that up to one fifth of colorectal carcinomas develop from serrated polyps, named for their pattern of colonic crypts, and include the sessile serrated adenoma/polyp (SSA/P) that has malignant potential. SSA/Ps are typically located in the proximal colon and have molecular features of hypermethylation of CpG islands in gene promoters and activating point mutations (V600E) in the BRAF oncogene. Both of these features are seen in sporadic colorectal carcinomas with microsatellite instability (MSI) which is potentially consistent with an origin of these cancers from precursor SSA/Ps. Dysplasia is detected in a subset of SSA/Ps with a high risk of progression to carcinoma. An uncommon serrated polyp is the traditional serrated adenoma that is typically found in the left colon, has a tubulovillous architecture, and frequently harbors mutant KRAS. To date, the epidemiology of these serrated lesions is poorly understood, and limited observational data suggest a potential chemopreventive benefit of nonsteroidal anti-inflammatory drugs. The current primary strategy to reduce the risk of colorectal carcinoma from serrated polyps is to enhance their detection at colonoscopy and to ensure their complete removal. This review provides insight into the epidemiologic, clinical, histopathologic, and molecular features of serrated polyps and includes data on their endoscopic detection and chemoprevention. Cancer Prev Res; 10(5); 270–8. ©2017 AACR.