Dexamethasone inhibits stemness maintenance and enhances chemosensitivity of hepatocellular carcinoma stem cells by inducing deSUMOylation of HIF­1α and Oct4.

It has been controversial whether patients with hepatocellular carcinoma (HCC) should receive glucocorticoid therapy during chemotherapy. Recent studies have demonstrated that glucocorticoids increase the therapeutic sensitivity of tumors to some chemotherapeutic drugs, but the specific mechanism remains unclear. In the present study, dexamethasone (Dex) was used to treat HCC stem cells. The results demonstrated that Dex reduced stemness maintenance and self­renewal of HCC stem cells, promoted epithelial­to­mesenchymal transition, inhibited migration and angiogenesis and, more importantly, increased cell sensitivity to the herpes simplex virus thymidine kinase/ganciclovir drug system in vitro and in vivo. Further mechanistic analyses demonstrated that Dex inhibited small ubiquitin­like modifier (SUMO) modification of several proteins in HCC stem cells, including hypoxia­inducible factor (HIF)­1α, an important hypoxia tolerance protein, and octamer­binding transcription factor 4 (Oct4), a crucial stemness maintenance protein. Inducing deSUMOylation of HIF­1α and Oct4 reduced their accumulation in the nucleus, thereby inhibiting tumor angiogenesis and stemness maintenance. These findings provide a new perspective to the study of the mechanism underlying the anti­hepatocarcinogenesis effects of Dex. Due to the few side effects of glucocorticoids at low doses and their anti­inflammatory effects, the appropriate combination of glucocorticoids and chemotherapeutic drugs is expected to improve the survival of HCC patients and their prognosis.

Cancer-type organic anion transporting polypeptide 1B3 is a target for cancer suicide gene therapy using RNA trans-splicing technology.

Cancer-type organic anion transporting polypeptide 1B3 (Ct-OATP1B3) has been identified as a cancer-specific transcript in various solid cancers, including colorectal cancer. Given its excellent cancer-specific expression profile, we hypothesized that Ct-OATP1B3 could represent a promising target for cancer-specific expression of the suicide gene, herpes simplex virus 1 thymidine kinase (HSV-tk), via a spliceosome-mediated RNA trans-splicing (SMaRT) approach. SMaRT technology is used to recombine two RNA molecules to generate a chimeric transcript. In this study, we engineered an RNA trans-splicing molecule carrying a translation-defective HSV-tk sequence (RTM44), which was capable of inducing its own trans-splicing to the desired Ct-OATP1B3 pre-mRNA target. RTM44 expression in LS180 cells resulted in generation of Ct-OATP1B3/HSV-tk fusion mRNA. A functional translation start site contributed by the target pre-mRNA restored HSV-tk protein expression, rendering LS180 cells sensitive to ganciclovir treatment in vitro and in xenografted mice. The observed effects are ascribed to accurate and efficient trans-splicing, as they were absent in cells carrying a splicing-deficient mutant of RTM44. Collectively, our data highlights Ct-OATP1B3 as an ideal target for the HSV-tk SMaRT suicide system, which opens up new translational avenues for Ct-OATP1B3-targeted cancer therapy.

The role of herpes simplex virus-1 thymidine kinase alanine 168 in substrate specificity.

Herpes simplex virus type 1 (HSV) thymidine kinase (TK) has been widely used in suicide gene therapy for the treatment of cancer due to its broad substrate specificity and the inability of the endogenous human TK to phosphorylate guanosine analogs such as ganciclovir (GCV). The basis of suicide gene therapy is the introduction of a gene that encodes a prodrug-activating enzyme into tumor cells. After administration, the prodrug is selectively converted to a toxic drug by the suicide gene product thereby bringing about the eradication of the cancer cells. A major drawback to this therapy is the low activity the enzyme displays towards the prodrugs, requiring high prodrug doses that result in adverse side effects. Earlier studies revealed two HSV TK variants (SR39 and mutant 30) derived by random mutagenesis with enhanced activities towards GCV in vitro and in vivo. While these mutants contain multiple amino acid substitutions, molecular modeling suggests that substitutions at alanine 168 (A168) may be responsible for the observed increase in prodrug sensitivity. To evaluate this, site-directed mutagenesis was used to individually substitute A168 with phenylalanine or tyrosine to reflect the mutations found in SR39 and mutant 30, respectively. Additionally, kinetic parameters and the ability of these mutants to sensitize tumor cells to GCV in comparison to wild-type thymidine kinase were determined.