Microtubules are centrally involved in cell division, being the principal components of mitotic spindle. Tubulin, the constituent of microtubules, can be cyclically modified on its α-subunit by enzymatic removal of the COOH-terminal tyrosine residue by an ill-defined tubulin carboxypeptidase (TCP) and its readdition by tubulin tyrosine ligase (TTL). We and others have previously shown that suppression of TTL and resulting accumulation of detyrosinated tubulin are frequent in human cancers of poor prognosis. Explanations for the involvement of TTL and detyrosinated tubulin in tumor progression arise from the recent discovery that tubulin detyrosination leads to CAP-Gly protein mislocalization, which correlates with defects in spindle positioning during mitosis. Impaired control of spindle positioning is one factor favoring tumor invasiveness. Thus, TCP could be a target for developing novel therapeutic strategies against advanced stages of cancers. Inhibitors of TCP, by reversing abnormal detyrosinated tubulin accumulation in tumor cells, could impair tumor progression. TCP has never been isolated and this has hampered search of specific inhibitors. In this article, we describe a cell-based assay of TCP activity and its use to screen a library of natural extracts for their inhibitory potency. This led to the isolation of two sesquiterpene lactones. We subsequently found that parthenolide, a structurally related compound, can efficiently inhibit TCP. This inhibitory activity is a new specific property of parthenolide independent of its action on the nuclear factor-κB pathway. Parthenolide is also known for its anticancer properties. Thus, TCP inhibition could be one of the underlying mechanisms of these anticancer properties. [Cancer Res 2007;67(7):3371–8]

X-ray crystallography studies, as well as live-cell fluorescent imaging, have recently challenged the traditional view of protein kinase CK2. Unbalanced expression of catalytic and regulatory CK2 subunits has been observed in a variety of tissues and tumours. Thus the potential intersubunit flexibility suggested by these studies raises the likely prospect that the CK2 holoenzyme complex is subject to disassembly and reassembly. In the present paper, we show evidence for the reversible multimeric organization of the CK2 holoenzyme complex in vitro. We used a combination of site-directed mutagenesis, binding experiments and functional assays to show that, both in vitro and in vivo, only a small set of primary hydrophobic residues of CK2β which contacts at the centre of the CK2α/CK2β interface dominates affinity. The results indicate that a double mutation in CK2β of amino acids Tyr188 and Phe190, which are complementary and fill up a hydrophobic pocket of CK2α, is the most disruptive to CK2α binding both in vitro and in living cells. Further characterization of hotspots in a cluster of hydrophobic amino acids centred around Tyr188–Phe190 led us to the structure-based design of small-peptide inhibitors. One conformationally constrained 11-mer peptide (Pc) represents a unique CK2β-based small molecule that was particularly efficient (i) to antagonize the interaction between the CK2 subunits, (ii) to inhibit the assembly of the CK2 holoenzyme complex, and (iii) to strongly affect its substrate preference.

The emergence of tumor resistance to conventional microtubule-targeting drugs restricts their clinical use. Using a cell-based assay that recognizes microtubule polymerization status to screen for chemicals that interact with regulators of microtubule dynamics, we identified Pyr1, a cell permeable inhibitor of LIM kinase, which is the enzyme that phosphorylates and inactivates the actin-depolymerizing factor cofilin. Pyr1 reversibly stabilized microtubules, blocked actin microfilament dynamics, inhibited cell motility in vitro and showed anticancer properties in vivo, in the absence of major side effects. Pyr1 inhibition of LIM kinase caused a microtubule-stabilizing effect, which was independent of any direct effects on the actin cytoskeleton. In addition, Pyr1 retained its activity in multidrug-resistant cancer cells that were resistant to conventional microtubule-targeting agents. Our findings suggest that LIM kinase functions as a signaling node that controls both actin and microtubule dynamics. LIM kinase may therefore represent a targetable enzyme for cancer treatment. Cancer Res; 72(17); 4429–39. ©2012 AACR.

The alkyloid compound ellipticine derived from the berrywood tree is a topoisomerase II poison that is used in ovarian and breast cancer treatment. In this study, we report the identification of ellipticine derivatives and their tetracyclic angular benzopyridoindole analogues as novel ATP-competitive inhibitors of the protein kinase CK2. In vitro and in vivo assays showed that these compounds have a good pharmacologic profile, causing a marked inhibition of CK2 activity associated with cell cycle arrest and apoptosis in human cancer cells. Further, in vivo assays demonstrate antitumor activity in a mouse xenograft model of human glioblastoma. Finally, crystal structures of CK2–inhibitor complex provide structural insights on the molecular basis of CK2 inhibition. Our work lays the foundation for development of clinically useful CK2 inhibitors derived from a well-studied scaffold with suitable pharmacokinetics parameters. Cancer Res; 70(23); 9865–74. ©2010 AACR.

Protein kinase casein kinase 2 (CK2) is a serine/threonine kinase with evidence of implication in growth dysregulation and apoptosis resistance, making it a relevant target for cancer therapy. Several CK2 inhibitors have been developed showing variable efficiency, emphasizing the need to expand the chemical diversity of those inhibitors. We report the identification and characterization of 2,8‐difurandicarboxylic acid derivatives as a new class of nanomolar ATP‐competitive inhibitors. Selectivity profiling pointed out proviral insertion Moloney virus kinases (Pim kinases) as the only other kinases that are significantly inhibited. By combining structure‐activity relationship analysis with structural determination, we were able to determine the binding mode of these inhibitors for both kinases and to explain their strong inhibitory potency. Essential chemical features necessary for activity on both kinases were then identified. The described compounds are not cell permeable: however, they could provide a lead for developing novel inhibitors usable also in vivo . Given the similar but not redundant pathophysiological functions of CK2 and Pim family members, such inhibitors would provide new attractive leads for targeted cancer therapy. This work highlights that 2 functionally related kinases from different kinome branches display exquisite sensitivity to a common inhibitor.—López‐Ramos, M., Prudent, R., Moucadel, V., Sautel, C. F., Barette, C., Lafanechère, L., Mouawad, L., Grierson, D., Schmidt, F., Florent, J.‐C., Filippakopoulos, P., Bullock, A. N., Knapp, S., Reiser, J.‐B., Cochet, C. New potent dual inhibitors of CK2 and Pim kinases: discovery and structural insights. FASEB J . 24, 3171–3185 (2010). www.fasebj.org