Prodrug AST-003 Improves the Therapeutic Index of the Multi-Targeted Tyrosine Kinase Inhibitor Sunitinib

A Novel AKR1C3 Specific Prodrug TH3424 With Potent Antitumor Activity in Liver Cancer

Overexpression of AKR1C3, an aldo-keto reductase, was recently discovered in liver cancers. In this study, an inverse correlation between AKR1C3 expression and survival of patients with liver cancer was observed. AKR1C3 inhibitors, however, failed to suppress liver cancer cell growth. The prodrug TH3424, which releases a DNA alkylating reagent upon reduction by AKR1C3, was developed to target tumors with overexpression of AKR1C3. TH3424 showed specific killing of liver cancer cells with AKR1C3 overexpression both in vitro and in vivo. In patient-derived mouse xenograft models, TH3424 at doses as low as 1.5 mg/kg eliminated liver tumors with no apparent toxicity. Therefore, TH3424 is a promising drug candidate for liver cancer and other types of cancers overexpressing AKR1C3.

Protective Effect of RIVA Against Sunitinib-Induced Cardiotoxicity by Inhibiting Oxidative Stress-Mediated Inflammation: Probable Role of TGF-β and Smad Signaling

Sunitinib (SUN) is an oral tyrosine kinase inhibitor approved in 2006 as a first-line treatment for metastatic renal cell cancer. However, weak selectivity to kinase receptors and cardiotoxicity have limited the use of sunitinib. Rivaroxaban (RIVA) is a Factor Xa inhibitor with cardioprotective action. It inhibits atherosclerosis and numerous inflammatory cascades. The present study was designed to investigate the cardioprotective effects of RIVA in sunitinib-induced cardiotoxicity. Thirty male Wistar rats were divided into five groups. Group 1 was the normal control (control). Group 2 was administered i.p. SUN 25 mg kg^-1 thrice weekly for 3 weeks. Groups 3 and 4 received the same treatment as Group 2 followed by the administration of RIVA 5 mg kg^-1 day^-1 and 10 mg kg^-1 day^-1, respectively, for 3 weeks. Group 5 received only 10 mg kg^-1 day^-1 RIVA for 3 weeks. Serum levels of Ca²⁺, Mg²⁺, Fe³⁺/Fe²⁺, lipid profiles, and cardiac enzymes were measured. Cardiac tissues were isolated for the measurements of oxidant/antioxidant balance gene and protein expressions. Relative to the controls, the administration of SUN significantly altered serum levels of (Ca²⁺, Mg²⁺, Fe³⁺/Fe²⁺, lipid profiles, and cardiac enzymes), intracellular antioxidant enzymes, and the expression levels of the genes encoding certain proteins. RIVA treatment significantly restored these parameters to near-normal levels. RIVA treatment significantly mitigated SUN-induced cardiac injuries by restoring antioxidant enzyme levels and attenuating the proinflammatory cascades resulting from SUN-induced cardiac injuries.

A targeted transforming growth factor-beta (TGF-β) blocker, TTB, inhibits tumor growth and metastasis

Transforming growth factor beta (TGF-β) promotes cancer growth in late stage cancers. To inhibit the TGF-β pathway, we investigated a tumor-targeting TGF-β receptor blocker, TTB, and its role in tumor progress. The targeted TTB comprised of the extracellular domain of the TGF-β receptor II, the endoglin domain of TGF-β receptor III, and the human immuno-globin IgG1 constant fragment (Fc). To enhance tumor microenvironment targeting, a RGD peptide was fused at the N-terminal of TTB. The targeted TTB exhibited potent TGF-β neutralization activities, and inhibited cancer cell migration and invasion as well as colony formation. In xenograft models, the TTB had potent tumor inhibition activities. The TTB also attenuated the TGF-β1-induced Smad2 phosphorylation and epithelial to mesenchymal transformation (EMT), and suppressed breast cancer metastasis. Thus, the TTB is an effective TGF-β blocker with a potential for blocking excessive TGF-β induced pathogenesis in vivo.

Targeting a Targeted Drug: An Approach Toward Hypoxia-Activatable Tyrosine Kinase Inhibitor Prodrugs

Tyrosine kinase inhibitors (TKIs), which have revolutionized cancer therapy over the past 15 years, are limited in their clinical application due to serious side effects. Therefore, we converted two approved TKIs (sunitinib and erlotinib) into 2-nitroimidazole-based hypoxia-activatable prodrugs. Kinetics studies showed very different stabilities over 24 h; however, fast reductive activation via E. coli nitroreductase could be confirmed for both panels. The anticancer activity and signaling inhibition of the compounds against various human cancer cell lines were evaluated in cell culture. These data, together with molecular docking simulations, revealed distinct differences in the impact of structural modifications on drug binding to the enzymes: whereas the catalytic pocket of the epidermal growth factor receptor (EGFR) accepted all new erlotinib derivatives, the vascular endothelial growth factor receptor (VEGFR)-inhibitory potential in the case of the sunitinib prodrugs was dramatically diminished by derivatization. In line, hypoxia dependency of ERK signaling inhibition was observed with the sunitinib prodrugs, while oxygen levels had no impact on the activity of the erlotinib derivatives. Overall, proof of principle could be shown for this concept, and the results obtained are an important basis for the future development of tyrosine kinase inhibitor prodrugs.