Oncogenic Addiction of Fibrolamellar Hepatocellular Carcinoma to the Fusion Kinase DNAJB1-PRKACA

Abstract

Purpose: Gene fusions are drivers of many pediatric tumors. In fibrolamellar hepatocellular carcinoma (FLC), a fusion of DNAJB1 and PRKACA is the dominant recurrent mutation. Expression of the DNAJB1-PRKACA fusion gene in mice results in a tumor that recapitulates FLC. However, it is not known whether transient expression of DNAJB1-PRKACA is sufficient only to trigger tumor formation or whether ongoing expression is necessary for maintenance and progression. Experimental Design: We screened shRNAs tiled over the fusion junction and identified several potent and specific candidates in vitro and two independent FLC patient-derived xenografts (PDXs). Results: We show that continued DNAJB1-PRKACA expression is not only required for continued tumor growth, but additionally its inhibition results in cell death. Inhibition of DNAJB1-PRKACA by an inducible shRNA in cells of PDX of FLC resulted in cell death in vitro. Induction of the shRNA inhibits FLC tumors growing in mice with no effect on xenografts from a hepatocellular carcinoma (HCC) cell line engineered to express DNAJB1-PRKACA. Conclusion: Our results validate DNAJB1-PRKACA as the oncogene in FLC and demonstrate both a continued requirement for the oncogene for tumor growth as well as an oncogenic addiction that can be exploited for targeted therapies. We anticipate our approach will be useful for investigations of other fusion genes in pediatric cancers and spur development of precision therapies.

Fighting rare cancers: lessons from fibrolamellar hepatocellular carcinoma

“…Once we could measure the FLC tumour growing in the mice, we induced production of the shRNA. The DNAJB1-PRKACA fusion disappeared from the cells, and the tumours stopped growing and then shrank 36 . The same virus and shRNA had no effect on other tumour types 36 .…”

“…The DNAJB1-PRKACA fusion disappeared from the cells, and the tumours stopped growing and then shrank 36 . The same virus and shRNA had no effect on other tumour types 36 . This showed that DNAJB1-PRKACA was needed for the FLC tumour to continue to grow.…”

“…In the coming year, we hope to have drugs that are already in the clinic 'repurposed' for FLC. In the near future, there will be therapies targeted directly against the driver 36 or towards recruitment of the immune system 43,46 . Still, it does not feel like a moment to celebrate.…”

CDK7 is a Novel Therapeutic Vulnerability in Fibrolamellar Carcinoma

“…They uncovered that not only is DNAJB1-PRKACA sufficient for FLC development, but that it is required for tumor cells to survive. 12 They subsequently showed the efficacy in targeting DNAJB1-PRKACA with shRNA in human-relevant models, but translating this approach will require minimizing off-target effects of native PKA and ensuring effectiveness in situ. 12 Another group exploited the FLC-specific nature (i.e., exclusively in tumor cells) of the immunogenic neoepitopes from the DNAJ-PKAc chimera to pioneer an innovative immune targeting strategy.…”

“…12 They subsequently showed the efficacy in targeting DNAJB1-PRKACA with shRNA in human-relevant models, but translating this approach will require minimizing off-target effects of native PKA and ensuring effectiveness in situ. 12 Another group exploited the FLC-specific nature (i.e., exclusively in tumor cells) of the immunogenic neoepitopes from the DNAJ-PKAc chimera to pioneer an innovative immune targeting strategy. 13 The authors performed a series of elegant studies to reveal that a personalized chimeric protein-derived peptide vaccine in conjunction with a toll-like receptor 1/2 agonist resulted in sustained immune response in a patient with multiple prior recurrences.…”