Heme oxygenase inhibition in cancers: possible tools and targets.

Heme oxygenase-1 (HO-1, encoded by HMOX1 ) through degradation of pro-oxidant heme into carbon monoxide (CO), ferrous ions (Fe2+ ) and biliverdin, exhibits cytoprotective, anti-apoptotic and anti-inflammatory properties. All of these potentially beneficial functions of HO-1 may play an important role in tumors' development and progression. Moreover, HO-1 is very often upregulated in tumors in comparison to healthy tissues, and its expression is further induced upon chemo-, radio- and photodynamic therapy, what results in decreased effectiveness of the treatment. Consequently, HO-1 can be proposed as a therapeutic target for anticancer treatment in many types of tumors. Nonetheless, possibilities of specific inhibition of HO-1 are strongly limited. Metalloporphyrins are widely used in in vitro studies, however, they are unselective and may exert serious side effects including an increase in HMOX1 mRNA level. On the other hand, detailed information about pharmacokinetics and biodistribution of imidazole-dioxolane derivatives, other potential inhibitors, is lacking. The genetic inhibition of HO-1 by RNA interference (RNAi) or CRISPR/Cas9 approaches provides the possibility to specifically target HO-1; however, the potential therapeutic application of those methods are distant at best. In summary, HO-1 inhibition might be the valuable anticancer approach, however, the ideal strategy for HO-1 targeting requires further studies.