Search

B-RAF selective inhibitors, including vemurafenib, were recently developed as effective therapies for melanoma patients with B-RAF V600E mutation. However, most patients treated with vemurafenib eventually develop resistance largely due to reactivation of MAPK signaling. Inhibitors of MAPK signaling, including MEK1/2 inhibitor trametinib, failed to show significant clinical benefit in patients with acquired resistance to vemurafenib. Here, we describe that cell lines with acquired resistance to vemurafenib show reactivation of MAPK signaling and upregulation of cyclin D1 and are sensitive to inhibition of LY2835219, a selective inhibitor of cyclin-dependent kinase (CDK) 4/6. LY2835219 was demonstrated to inhibit growth of melanoma A375 tumor xenografts and delay tumor recurrence in combination with vemurafenib. Furthermore, we developed an in vivo vemurafenib-resistant model by continuous administration of vemurafenib in A375 xenografts. Consistently, we found that MAPK is reactivated and cyclin D1 is elevated in vemurafenib-resistant tumors, as well as in the resistant cell lines derived from these tumors. Importantly, LY2835219 exhibited tumor growth regression in a vemurafenib-resistant model. Mechanistic analysis revealed that LY2835219 induced apoptotic cell death in a concentration-dependent manner in vemurafenib-resistant cells whereas it primarily mediated cell-cycle G1 arrest in the parental cells. Similarly, RNAi-mediated knockdown of cyclin D1 induced significantly higher rate of apoptosis in the resistant cells than in parental cells, suggesting that elevated cyclin D1 activity is important for the survival of vemurafenib-resistant cells. Altogether, we propose that targeting cyclin D1–CDK4/6 signaling by LY2835219 is an effective strategy to overcome MAPK-mediated resistance to B-RAF inhibitors in B-RAF V600E melanoma. Mol Cancer Ther; 13(10); 2253–63. ©2014 AACR.

Skeletal muscle wasting occurs in a great majority of cancer patients with advanced disease and is associated with a poor prognosis and decreased survival. Myostatin functions as a negative regulator of skeletal muscle mass and has recently become a therapeutic target for reducing the loss of skeletal muscle and strength associated with clinical myopathies. We generated neutralizing antibodies to myostatin to test their potential use as therapeutic agents to attenuate the skeletal muscle wasting due to cancer. We show that our neutralizing antimyostatin antibodies significantly increase body weight, skeletal muscle mass, and strength in non–tumor-bearing mice with a concomitant increase in mean myofiber area. The administration of these neutralizing antibodies in two preclinical models of cancer-induced muscle wasting (C26 colon adenocarcinoma and PC3 prostate carcinoma) resulted in a significant attenuation of the loss of muscle mass and strength with no effect on tumor growth. We also show that the skeletal muscle mass– and strength-preserving effect of the antibodies is not affected by the coadministration of gemcitabine, a common chemotherapeutic agent, in both non–tumor-bearing mice and mice bearing C26 tumors. In addition, we show that myostatin neutralization with these antibodies results in the preservation of skeletal muscle mass following reduced caloric intake, a common comorbidity associated with advanced cancer. Our findings support the use of neutralizing antimyostatin antibodies as potential therapeutics for cancer-induced muscle wasting. Mol Cancer Ther; 14(7); 1661–70. ©2015 AACR.

LY573636-sodium (tasisulam) is a small molecule antitumor agent with a novel mechanism of action currently being investigated in a variety of human cancers. In vitro, tasisulam induced apoptosis via the intrinsic pathway, resulting in cytochrome c release and caspase-dependent cell death. Using high content cellular imaging and subpopulation analysis of a wide range of in vitro and in vivo cancer models, tasisulam increased the proportion of cells with 4N DNA content and phospho-histone H3 expression, leading to G2–M accumulation and subsequent apoptosis. Tasisulam also blocked VEGF, epidermal growth factor, and fibroblast growth factor–induced endothelial cell cord formation but did not block acute growth factor receptor signaling (unlike sunitinib, which blocks VEGF-driven angiogenesis at the receptor kinase level) or induce apoptosis in primary endothelial cells. Importantly, in vivo phenocopying of in vitro effects were observed in multiple human tumor xenografts. Tasisulam was as effective as sunitinib at inhibiting neovascularization in a Matrigel plug angiogenesis assay in vivo and also caused reversible, non G2–M–dependent growth arrest in primary endothelial cells. Tasisulam also induced vascular normalization in vivo. Interestingly, the combination of tasisulam and sunitinib significantly delayed growth of the Caki-1 renal cell carcinoma model, whereas neither agent was active alone. These data show that tasisulam has a unique, dual-faceted mechanism of action involving mitotic catastrophe and antiangiogenesis, a phenotype distinct from conventional chemotherapies and published anticancer agents. Mol Cancer Ther; 10(11); 2168–78. ©2011 AACR.

B-RAFV600E mutation is found in approximately 50% of melanoma patients. It activates the MEK/ERK pathway and drives tumor progression. Vemurafenib, a B-RAF selective inhibitor was recently approved as an effective therapy for metastatic melanoma with B-RAF V600E mutation. However, most patients treated with vemurafenib eventually develop resistance in an average of 6-7 months. We and others have found that MAPK reactivation is a common mechanism of vemurafenib resistance. However, inhibitors of MAPK pathway, such as the MEK inhibitor trametinib, showed minimal clinical benefit in patients who had previously developed resistance to vemurafenib. Thus, overcoming resistance to vemurafenib remains an urgently unmet medical need. In this report, we have developed several in vitro models and an in vivo model resistant to vemurafenib and found that, in addition to MAPK reactivation, Cyclin D1 upregulation is common in these models. We demonstrated that these resistant cells are sensitive to inhibition of the Cyclin D1-CDK4/6 axis by LY2835219, a selective CDK4/6 inhibitor. LY2835219 inhibited growth of melanoma A375 xenografts, and delayed tumor recurrence in combination with vemurafenib. We further developed a vemurafenib-resistant xenograft model by continuous dosing of vemurafenib in A375 xenografts. Consistent with our in vitro observation, we found that Cyclin D1 is elevated and the MAPK pathway is reactivated in the resistant tumors, as well as in the cell lines generated from these tumors. Importantly, treatment with LY2835219 induced significant growth inhibition in these vemurafenib-resistant tumors. Additional mechanistic analysis demonstrated that LY2835219 preferably induced apoptosis in vemurafenib-resistant cells, while it primarily arrested cells in G1 phase in the parental A375 cells. Similar to CDK4/6 inhibition by LY2835219, Cyclin D1 knockdown by siRNA also induced a significantly higher rate of apoptotic cell death in the resistant cells, suggesting that Cyclin D1 may play an important role in the survival of resistant cells. Altogether, our data suggest that inhibition of the Cyclin D1-CDK4/6 axis by LY2835219 represents an effective strategy for overcoming resistance to B-RAF inhibition in melanoma patients with oncogenic BRAF mutation. Citation Information: Mol Cancer Ther 2013;12(11 Suppl):C88. Citation Format: Vipin Yadav, Teresa F. Burke, Lysiane Huber, Robert D. Van Hoen, Youyan Zhang, Sean Buchanan, Edward M. Chan, James J. Starling, Richard P. Beckmann, Sheng-Bin Peng. The CDK4/6 inhibitor LY2835219 overcomes vemurafenib resistance resulting from MAPK reactivation and cyclin D1 upregulation. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr C88.