Crystal structure of the Eg5 - K858 complex and implications for structure-based design of thiadiazole-containing inhibitors

Abstract

The thiadiazole scaffold is an important core moiety in a variety of clinical drug candidates targeting a range of diseases. For example, the 2,4,5-substituted 1,3,4-thiadiazole scaffold is present in a lead compound and at least two clinical candidates targeting the human motor protein Eg5, against neoplastic diseases. An inhibitor named K858 has in vivo activity in various mouse xenografts whereas the clinical candidates (S)-ARRY-520 and (R)-Litronesib have entered clinical trials with the former one in phase III clinical trials either alone or in combination with a proteasome inhibitor against relapsed/refractory multiple myeloma. Astonishingly, structural data are lacking for all thiadiazole-containing Eg5 inhibitors. Here we report the structure determination of two crystal forms of the ternary Eg5-ADP-K858 complex, locking the motor in the so-called final inhibitor bound state, thus blocking ADP release, a crucial stage for Eg5 activity. K858 acts at the established allosteric inhibitor-binding pocket formed of helix α2, loop L5 and helix α3. The structure of the complex has far reaching consequences for thiadiazole containing Eg5 inhibitors. For example, we could rationalise the structure-activity relationship in the crucial 5-position of the thiadiazole scaffold and the complex will serve in the future as a basis for strucutre-based drug design.

Kinesin Eg5 Targeting Inhibitors as a New Strategy for Gastric Adenocarcinoma Treatment

“…As reported in the literature, Eg5 inhibition results in the formation of monoaster spindles which is thought to lead to mitotic catastrophe and apoptosis [22]. This aspect, which is dose-dependent, is clearly demonstrated in our experimental model where compounds 2 , 41 and K858 , by inhibiting Eg5 protein, lead to the formation of several monopolar spindles [12]. Mitotic braking, due to an improper mitotic spindle formation, may result in the induction of apoptosis by activating several pro-apoptotic factors, among which Bax and Caspases are included [23].…”

“…Potent kinesin Eg5 inhibitors, compounds 2 , 4 , 26 , 30 , 31 , 41 , and 44 , characterized by the thiadiazoline nucleus present in the structure of K858 and endowed with different substituents at C5 (Figure 1), were enrolled in this study on the basis of the reported in vitro inhibition of the basal Eg5 ATPase activity in the range 0.84 < IC 50 (μM) < 7.5 [12].…”

“…Based on this knowledge, starting from monastrol, the first Eg5 inhibitor discovered in 1999 [10], a number of Eg5 inhibitors were then discovered, synthetized, and used in basic and clinical research [11]. In our laboratory, seven novel kinesin Eg5 inhibitors ( 2 , 4 , 26 , 30 , 31 , 41 , and 44 ) were synthesized keeping constant the thiadiazoline core nucleus and modifying the C5 substituents of K858 , the most common Eg5 inhibitor used in cancer therapies, due to their promising inhibition of the basal Eg5 ATPase activity (0.84 < IC 50 (μM) < 7.5) in vitro [12].…”

Therapeutic targeting of KSP in preclinical models of high-risk neuroblastoma

“…Both compounds contain a main 1,3,4-thiadiazole ring with a 5-phenyl group ( fig. S5A and B), which is important for binding to the hydrophobic pocket of the KSP allosteric site (34). Both compounds have nanomolar IC50 values for KSP enzymatic activity in vitro and subnanomolar IC50 values for reducing viability of cells in culture (21,22), and each exhibits a maximum tolerated dose in mg/kg in mice (20,23), fig.…”

Cancer drug therapy and stochastic modeling of &ldquo;nano-motors&rdquo;

“…47 Evidence is available in the literature, supporting the fact that different inhibitors target Eg5 differently, 48 in normal, aberrant, and degenerative manner; furthermore, novel drug development strategies are under clinical trials. 49,50 Chen et al 41 contrasting effects of a group of inhibitors on Eg5 motor proteins.…”