Repotrectinib (TPX-0005) Is a Next-Generation ROS1/TRK/ALK Inhibitor That Potently Inhibits ROS1/TRK/ALK Solvent- Front Mutations.

The use of tyrosine kinase inhibitors (TKI) with activity against ALK, ROS1, or TRKA-C can result in significant clinical benefit in patients with diverse tumors harboring ALK, ROS1, or NTRK1-3 rearrangements; however, resistance invariably develops. The emergence of on-target kinase domain mutations represents a major mechanism of acquired resistance. Solvent-front substitutions such as ALKG1202R, ROS1G2032R or ROS1D2033N, TRKAG595R, and TRKCG623R are among the most recalcitrant of these mechanisms. Repotrectinib (TPX-0005) is a rationally designed, low-molecular-weight, macrocyclic TKI that is selective and highly potent against ROS1, TRKA-C, and ALK. Importantly, repotrectinib exhibits activity against a variety of solvent-front substitutions in vitro and in vivo As clinical proof of concept, in an ongoing first-in-human phase I/II trial, repotrectinib achieved confirmed responses in patients with ROS1 or NTRK3 fusion-positive cancers who had relapsed on earlier-generation TKIs due to ROS1 or TRKC solvent-front substitution-mediated resistance.Significance: Repotrectinib (TPX-0005), a next-generation ROS1, pan-TRK, and ALK TKI, overcomes resistance due to acquired solvent-front mutations involving ROS1, NTRK1-3, and ALK Repotrectinib may represent an effective therapeutic option for patients with ROS1-, NTRK1-3-, or ALK-rearranged malignancies who have progressed on earlier-generation TKIs. Cancer Discov; 8(10); 1227-36. ©2018 AACR. This article is highlighted in the In This Issue feature, p. 1195.

Combined inhibition of EGFR and CK2 augments the attenuation of PI3K-Akt-mTOR signaling and the killing of cancer cells.

Ser/Thr protein kinase CK2 regulates multiple processes that play important roles in the sensitivity of cancer to epidermal growth factor receptor targeting therapeutics, including PI3K-Akt-mTOR signaling, Hsp90 activity, and inhibition of apoptosis. We hypothesized that top-down inhibition of EGFR, combined with lateral suppression of multiple oncogenic pathways by targeting CK2, would create a pharmacologic synthetic lethal event and result in an improved cancer therapy compared to EGFR inhibition alone. This hypothesis was tested by combining CX-4945, a first-in-class clinical stage inhibitor of CK2, with the EGFR tyrosine kinase inhibitor, erlotinib, in vitro and in vivo in models of non-small cell lung carcinoma, NCI-H2170, and squamous cell carcinoma, A431. Our results demonstrate that combination of CX-4945 with erlotinib results in enhanced attenuation of the PI3K-Akt-mTOR pathway. We also observed an increase in apoptosis, synergistic killing of cancer cells in vitro, as well as improved antitumor efficacy in vivo. Taken together, these data position CK2 as a valid pharmacologic target for drug combinations and support further evaluation of CX-4945 in combination with EGFR targeting agents.

CK2 inhibitor CX-4945 suppresses DNA repair response triggered by DNA-targeted anticancer drugs and augments efficacy: mechanistic rationale for drug combination therapy.

Drug combination therapies are commonly used for the treatment of cancers to increase therapeutic efficacy, reduce toxicity, and decrease the incidence of drug resistance. Although drug combination therapies were originally devised primarily by empirical methods, the increased understanding of drug mechanisms and the pathways they modulate provides a unique opportunity to design combinations that are based on mechanistic rationale. We have identified protein kinase CK2 as a promising therapeutic target for combination therapy, because CK2 regulates not just one but many oncogenic pathways and processes that play important roles in drug resistance, including DNA repair, epidermal growth factor receptor signaling, PI3K/AKT/mTOR signaling, Hsp90 machinery activity, hypoxia, and interleukin-6 expression. In this article, we show that CX-4945, a clinical stage selective small molecule inhibitor of CK2, blocks the DNA repair response induced by gemcitabine and cisplatin and synergizes with these agents in models of ovarian cancer. Mechanistic studies show that the enhanced activity is a result of inactivation of XRCC1 and MDC1, two mediator/adaptor proteins that are essential for DNA repair and that require phosphorylation by CK2 for their function. These data position CK2 as a valid pharmacologic target for intelligent drug combinations and support the evaluation of CX-4945 in combination with gemcitabine and platinum-based chemotherapeutics in the clinical setting.

Protein kinase CK2 modulates IL-6 expression in inflammatory breast cancer.

Inflammatory breast cancer is driven by pro-angiogenic and pro-inflammatory cytokines. One of them Interleukin-6 (IL-6) is implicated in cancer cell proliferation and survival, and promotes angiogenesis, inflammation and metastasis. While IL-6 has been shown to be upregulated by several oncogenes, the mechanism behind this phenomenon is not well characterized. Here we demonstrate that the pleotropic Serine/Threonine kinase CK2 is implicated in the regulation of IL-6 expression in a model of inflammatory breast cancer. We used siRNAs targeted toward CK2 and a selective small molecule inhibitor of CK2, CX-4945, to inhibit the expression and thus suppress the secretion of IL-6 in in vitro as well as in vivo models. Moreover, we report that in a clinical trial, CX-4945 was able to dramatically reduce IL-6 levels in plasma of an inflammatory breast cancer patient. Our data shed a new light on the regulation of IL-6 expression and position CX-4945 and potentially other inhibitors of CK2, for the treatment of IL-6-driven cancers and possibly other diseases where IL-6 is instrumental, including rheumatoid arthritis.

Anticancer activity of CX-3543: a direct inhibitor of rRNA biogenesis.

Hallmark deregulated signaling in cancer cells drives excessive ribosome biogenesis within the nucleolus, which elicits unbridled cell growth and proliferation. The rate-limiting step of ribosome biogenesis is synthesis of rRNA (building blocks of ribosomes) by RNA Polymerase I (Pol I). Numerous kinase pathways and products of proto-oncogenes can up-regulate Pol I, whereas tumor suppressor proteins can inhibit rRNA synthesis. In tumorigenesis, activating mutations in certain cancer-associated kinases and loss-of-function mutations in tumor suppressors lead to deregulated signaling that stimulates Pol I transcription with resultant increases in ribosome biogenesis, protein synthesis, cell growth, and proliferation. Certain anticancer therapeutics, such as cisplatin and 5-fluorouracil, reportedly exert, at least partially, their activity through disruption of ribosome biogenesis, yet many prime targets for anticancer drugs within the ribosome synthetic machinery of the nucleolus remain largely unexploited. Herein, we describe CX-3543, a small molecule nucleolus-targeting agent that selectively disrupts nucleolin/rDNA G-quadruplex complexes in the nucleolus, thereby inhibiting Pol I transcription and inducing apoptosis in cancer cells. CX-3543 is the first G-quadruplex interactive agent to enter human clinical trials, and it is currently under evaluation against carcinoid/neuroendocrine tumors in a phase II clinical trial.

Anilinodialkoxyquinazolines: screening epidermal growth factor receptor tyrosine kinase inhibitors for potential tumor imaging probes.

The epidermal growth factor receptor (EGFR), a long-standing drug development target, is also a desirable target for imaging. Sixteen dialkoxyquinazoline analogues, suitable for labeling with positron-emitting isotopes, have been synthesized and evaluated in a battery of in vitro assays to ascertain their chemical and biological properties. These characteristics provided the basis for the adoption of a selection schema to identify lead molecules for labeling and in vivo evaluation. A new EGFR tyrosine kinase radiometric binding assay revealed that all of the compounds possessed suitable affinity (IC50 = 0.4-51 nM) for the EGFR tyrosine kinase. All of the analogues inhibited ligand-induced EGFR tyrosine phosphorylation (IC50 = 0.8-20 nM). The HPLC-estimated octanol/water partition coefficients ranged from 2 to 5.5. Four compounds, 4-(2'-fluoroanilino)- and 4-(3'-fluoroanilino)-6,7-diethoxyquinazoline as well as 4-(3'-chloroanilino)- and 4-(3'-bromoanilino)-6,7-dimethoxyquinazoline, possess the best combination of characteristics that warrant radioisotope labeling and further evaluation in tumor-bearing mice.