We succeeded in the design and synthesis of multifunctional chemical probes of the HIF-1alpha inhibitor carboranylphenoxyacetanilide (1) that combine photoaffinity labeling and click reaction to identify the target protein. HSP60 was identified as a primary target protein of 1 using the chemical probes 2 and 3. Furthermore, HSP60 inhibitor 4 suppressed hypoxia-induced HIF activation, indicating that HSP60 affects HIF-1alpha accumulation directly or indirectly.

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The indenopyrazole framework was investigated as a new class of HIF-1α inhibitors. Indenopyrazole 2l was found to most strongly inhibit the hypoxia-induced HIF-1α transcriptional activity (IC50 = 0.014 μM) among all of the known compounds having relatively simple structures, unlike manassantins. Indenopyrazole 2l suppressed HIF-1α transcriptional activity without affecting both HIF-1α protein accumulation and HIF-1α/HIF-1β heterodimerization in nuclei under the hypoxic conditions, suggesting that 2l probably affected the transcriptional pathway induced by the HIF-1α/HIF-1β heterodimer.

Heat shock proteins (HSPs) are ubiquitous and evolutionary conserved proteins induced by cell stress. HSP60, in particular, is a typical mitochondrial molecular chaperone that is known to assist nascent polypeptides to reach a native conformation. HSP60 is also known to interact with HSP10. In the last decade, HSP60 has been detected in the cytosol, the cell surface, the extracellular space, and biological fluids. HSP60 elicits potent proinflammatory response in cells of the innate immune system and serves as a danger signal of stressed or damaged cells. As cytosolic HSP60 levels gradually increase or decrease during carcinogenesis in various organs, HSP60 can be used as a biomarker for the diagnosis and prognosis of preneoplastic and neoplastic lesions. In this review, we summarize recent discoveries on the important roles of HSP60 in various diseases ranging from autoimmune diseases to tumors. Furthermore, small molecules targeting HSP60, which were the target of intensive investigations in the last few years, are also summarized. The possibility of utilizing HSP60 as a new drug target for the treatment of certain diseases is examined.

Diaromatic-substituted ortho- and meta-carboranes were synthesized as mimics of manassantin A. Among the carboranes synthesized, compounds 1 and 2 showed significant inhibition of hypoxia-induced HIF-1 transcriptional activity, with IC(50) values of 3.2 and 2.2 μM, respectively. Compounds 1 and 2 similarly suppressed hypoxia-induced HIF-1α accumulation in a concentration-dependent manner without affecting the expression level of HIF-1α mRNA. The hypoxia-induced accumulation and translocation of HIF-1α into nuclei were not observed in HeLa cells treated with compounds 1 and 2 by immunofluorescence analysis, revealing that the inhibition of hypoxia-induced HIF-1 transcriptional activity is induced by compounds 1 and 2 through a degradation pathway of the HIF-1α protein under hypoxic conditions.