The Effect of PARP Inhibitor Radiosensitization on the mRNA Translational Regulation of T Cell Chemokines

PURPOSE/OBJECTIVE(S)

Immunotherapy has modestly improved survival for small cell lung cancer (SCLC) patients. Low response rate and rapid disease progression remain an intractable challenge. One of the factors that contribute to immunotherapy resistance is the lack of cytotoxic T cell infiltration. The expression of chemoattractant cytokines, like CCL5 and CXCL10, are essential for T cell infiltration. The control of chemokine expression is not fully understood, but both transcriptional and translational control pathways could play a major role. Previous studies have shown a correlation between DNA damage and chemokine expression and that PARP inhibitors (PARPi) are radiosensitizers for SCLC that increases DNA damage. The objectives of this study were to define this potential PARPi immunogenic radiosensitizing relationship.

MATERIALS/METHODS

We identified doses of olaparib+ radiation treatment (RT) that conferred radiosensitization in SCLC cell-lines by cell viability and/or clonogenic assays. Olaparib+RT induced CCL5 and CXCL10 mRNA expression was measured by qPCR across SCLC cell-lines. Protein level of chemokines was assessed by immunoblotting. SBC5 cells were treated with olaparib+RT and submitted for RNA sequencing analysis. Genes with adjusted p value<0.05 were considered significant. Protein level changes and target gene knock-out (KO) were confirmed by immunoblotting. Chemokine CXCL10 mRNA and protein level in wildtype (WT) and KO cells were measured by qPCR and western blot, respectively. A mRNA decay assay and dual-luciferase reporter assay was used to identify the region of CXCL10 mRNA that confers mRNA stability control. In vivo anti-tumor efficacy and tumor T cell infiltration studies were done in B6129F mice bearing KP1 tumors. And the T cell infiltration was measured by immune profiling.

RESULTS

In vitro, olaparib+RT significantly increased CXCL10 mRNA in all four SCLC subtype cell-lines in comparison to vehicle control. Consistently, the increase of CXCL10 protein levels (3-fold) was observed in SBC5 cells. By RNA-Seq, a top-ranking translational repressor was EIF4E2 (4EHP) mRNA. The downregulation of EIF4E2 protein by olaparib+RT was validated in four SCLC subtypes by western blot. EIF4E2 KO in HEK293 and SBC5 cells increased CXCL10 mRNA and protein level. By mRNA decay assay and western blot, the absence of EIF4E2 stabilized CXCL10 mRNA and increased CXCL10 protein levels. The dual-luciferase assay demonstrated EIF4E2 destabilizes CXCL10 mRNA via the 3'UTR of CXCL10. In vivo, immune profiling showed olaparib+RT significantly increased the total T cell and CD8+ T cell infiltration. Finally, anti-PD-L1 inhibition potentiated olaparib + IR to improve tumor control in KP1 allograft.

CONCLUSION

Our study demonstrated olaparib + RT increases CXCL10 protein levels through downregulating EIF4E2 to subsequently increase T cell infiltration. Olaparib + RT enhanced anti-PD-L1 immunotherapy efficacy and has therapeutic potential as an immunogenic radiosensitizer.

Beta-globin gene cluster haplotypes and HbF levels are not the only modulators of sickle cell disease in Lebanon

Sickle cell disease (SCD) is an inherited autosomal recessive disorder of the beta-globin chain. Despite the fact that all subjects with SCD have the same single base pair mutation, the severity of the clinical and hematological manifestations is extremely variable. This study examined for the first time in Lebanon the correlation between the clinical manifestation of SCD and the beta-globin gene haplotypes. The haplotypes of 50 patients diagnosed with SCD were determined using polymerase chain reaction amplification of fragments containing nine polymorphic restriction sites around and within the epsilon-Ggamma-Agamma-psibeta-delta-beta-globin gene complex. Most reported haplotypes were found in our population with the Benin haplotype as the most prevalent one. When the patients were divided according to their HbF levels into three groups (Group A: HbF < 5%, Group B: HbF between 5 and 15%, and Group C: HbF > 15%), surprisingly, the highest levels of HbF were associated with the most severe clinical cases. Our findings suggest that fetal hemoglobin levels are important but not the only parameters that affect the severity of the disease. In addition, the high levels of HbF in patients with CAR haplotypes did not seem to ameliorate the severity of symptoms, suggesting that genetic factors other than haplotypes are the major determinants of increased HbF levels in Lebanon.