Synthesis and biochemical evaluation of benzoylbenzophenone thiosemicarbazone analogues as potent and selective inhibitors of cathepsin L

Abstract

Upregulation of cathepsin L in a variety of tumors and its ability to promote cancer cell invasion and migration through degradation of the extracellular matrix suggest that cathepsin L is a promising biological target for the development of anti-metastatic agents. Based on encouraging results from studies on benzophenone thiosemicarbazone cathepsin inhibitors, a series of fourteen benzoylbenzophenone thiosemicarbazone analogues were designed, synthesized, and evaluated for their inhibitory activity against cathepsins L and B. Thiosemicarbazone inhibitors 3-benzoylbenzophenone thiosemicarbazone 1, 1,3-bis(4-fluorobenzoyl)benzene thiosemicarbazone 8, and 1,3-bis(2-fluorobenzoyl)-5-bromobenzene thiosemicarbazone 32 displayed the greatest potency against cathepsin L with low IC50 values of 9.9 nM, 14.4 nM, and 8.1 nM, respectively. The benzoylbenzophenone thiosemicarbazone analogues evaluated were selective in their inhibition of cathepsin L compared to cathepsin B. Thiosemicarbazone analogue 32 inhibited invasion through Matrigel of MDA-MB-231 breast cancer cells by 70% at 10 μM. Thiosemicarbazone analogue 8 significantly inhibited the invasive potential of PC-3ML prostate cancer cells by 92% at 5 μM. The most active cathepsin L inhibitors from this benzoylbenzophenone thiosemicarbazone series (1, 8, and 32) displayed low cytotoxicity toward normal primary cells [in this case human umbilical vein endothelial cells (HUVECs)]. In an initial in vivo study, 3-benzoylbenzophenone thiosemicarbazone (1) was well-tolerated in a CDF1 mouse model bearing an implanted C3H mammary carcinoma, and showed efficacy in tumor growth delay. Low cytotoxicity, inhibition of cell invasion, and in vivo tolerability are desirable characteristics for anti-metastatic agents functioning through an inhibition of cathepsin L. Active members of this structurally diverse group of benzoylbenzophenone thiosemicarbazone cathepsin L inhibitors show promise as potential anti-metastatic, pre-clinical drug candidates.

A Review of the Structure–Activity Relationship of Natural and Synthetic Antimetastatic Compounds

“…For example, inhibition of one of its members, cathepsin L, reduced cancer cell invasion and migration [14]. Benzoylbenzophenone thiosemicarbazone analogues were synthesised and tested as potential cathepsin L inhibitors [15]. Among the derivatives (Figure 4), compound 12 (3-benzoylbenzophenone thiosemicarbazone) was able to inhibit the activity of cathepsin L significantly at a half maximal inhibitory concentration (IC 50 ) value of 9.9 nM (Table 3).…”

“…Parker et al in 2013 carried out the synthesis of benzoylbenzophenone thiosemicarbazone derivatives and assessed the inhibitory activity against cathepsins L [15]. The activity was diminished when the compound was substituted with a methoxy group.…”

“…Benzoylbenzophenone thiosemicarbazone analogues were tested for the inhibition of cathepsins L [15]. It was observed that para substitution of hydroxy at the analogue 16 resulted in diminished anticancer activity.…”

“…The benzoylbenzophenone thiosemicarbazone analogues 17 and 19 exhibited a remarkable decrease of cathepsin L inhibition among all the analogues. Both of these compounds have m-bromo substituents on the outermost rings of the benzoylbenzophenone molecular template [15]. Moreover, analogue 14 with p-bromo substituted bis-thiosemicabazone was unable to inhibit cathepsin L even at a high concentration of 10,000 nM (Table 3).…”

Hydrazone Derivatives Enhance Antileishmanial Activity of Thiochroman-4-ones

“…In the search for new drugs against novel targets in Leishmania species Avery et al explored the cysteine proteases inhibitors, and a total of 241,000 compounds were screened, of which 24 showed inhibition of cysteine proteases or antileishmanial activity, and 16 out of the 24 compounds possess hydrazone or imine moieties [ 16 , 17 ]. Semicarbazones, thiosemicarbazones and thiosemicarbazone derivatives of thiochroman-4-ones are potent inhibitors of cysteine proteases, specifically of cathepsin L [ 20 , 21 , 22 , 23 , 24 ]. However, there are no reports on the antileishmanial or cytotoxic activities of these compounds.…”