SIRT1 is an actionable target to restore p53 function in HPV-associated cancer therapy

BACKGROUND

Our aim was to evaluate the efficacy and anti-cancer action of a precision medicine approach involving a novel SIRT1-dependent pathway that, when disrupted, leads to the restoration of a functional p53 in human papillomavirus (HPV)-transformed cells.

METHODS

The anticancer potential of inhibiting SIRT1 was evaluated by examining the effects of the specific SIRT1 inhibitor EX527 (also known as Selisistat) or genetic silencing, either individually or in conjunction with standard chemotherapeutic agents, on a range of HPV+ cancer cells and a preclinical mouse model of HPV16-induced cancer.

RESULTS

We show that SIRT1 inhibition restores a transcriptionally active K382-acetylated p53 in HPV+ but not HPV- cell lines, which in turn promotes G0/G1 cell cycle arrest and inhibits clonogenicity specifically in HPV+ cells. Additionally, EX527 treatment increases the sensitivity of HPV+ cells to sublethal doses of standard genotoxic agents. The enhanced sensitivity to cisplatin as well as p53 restoration were also observed in an in vivo tumorigenicity assay using syngeneic C3.43 cells harbouring an integrated HPV16 genome, injected subcutaneously into C57BL/6J mice.

CONCLUSIONS

Our findings uncover an essential role of SIRT1 in HPV-driven oncogenesis, which may have direct translational implications for the treatment of this type of cancer.

The RIG-I agonist M8 triggers cell death and natural killer cell activation in human papillomavirus-associated cancer and potentiates cisplatin cytotoxicity

Although the activation of innate immunity to treat a wide variety of cancers is gaining increasing attention, it has been poorly investigated in human papillomavirus (HPV)-associated malignancies. Because these tumors harbor a severely impaired cGAS-STING axis, but they still retain a largely functional RIG-I pathway, another critical mediator of adaptive and innate immune responses, we asked whether RIG-I activation by the 5'ppp-RNA RIG-I agonist M8 would represent a therapeutically viable option to treat HPV+ cancers. Here, we show that M8 transfection of two cervical carcinoma-derived cell lines, CaSki and HeLa, both expressing a functional RIG-I, triggers intrinsic apoptotic cell death, which is significantly reduced in RIG-I KO cells. We also demonstrate that M8 stimulation potentiates cisplatin-mediated cell killing of HPV+ cells in a RIG-I dependent manner. This combination treatment is equally effective in reducing tumor growth in a syngeneic pre-clinical mouse model of HPV16-driven cancer, where enhanced expression of lymphocyte-recruiting chemokines and cytokines correlated with an increased number of activated natural killer (NK) cells in the tumor microenvironment. Consistent with a role of RIG-I signaling in immunogenic cell killing, stimulation of NK cells with conditioned medium from M8-transfected CaSki boosted NK cell proliferation, activation, and migration in a RIG-I-dependent tumor cell-intrinsic manner. Given the highly conserved molecular mechanisms of carcinogenesis and genomic features of HPV-driven cancers and the remarkably improved prognosis for HPV+ oropharyngeal cancer, targeting RIG-I may represent an effective immunotherapeutic strategy in this setting, favoring the development of de-escalating strategies.

How Autophagy Shapes the Tumor Microenvironment in Ovarian Cancer

Ovarian cancer (OC) is characterized by a high mortality rate due to the late diagnosis and the elevated metastatic potential. Autophagy, a lysosomal-driven catabolic process, contributes to the macromolecular turnover, cell homeostasis, and survival, and as such, it represents a pathway targetable for anti-cancer therapies. It is now recognized that the vascularization and the cellular composition of the tumor microenvironment influence the development and progression of OC by controlling the availability of nutrients, oxygen, growth factors, and inflammatory and immune-regulatory soluble factors that ultimately impinge on autophagy regulation in cancer cells. An increasing body of evidence indicates that OC carcinogenesis is associated, at least in the early stages, to insufficient autophagy. On the other hand, when the tumor is already established, autophagy activation provides a survival advantage to the cancer cells that face metabolic stress and protects from the macromolecules and organelles damages induced by chemo- and radiotherapy. Additionally, upregulation of autophagy may lead cancer cells to a non-proliferative dormant state that protects the cells from toxic injuries while preserving their stem-like properties. Further to complicate the picture, autophagy is deregulated also in stromal cells. Thus, changes in the tumor microenvironment reflect on the metabolic crosstalk between cancer and stromal cells impacting on their autophagy levels and, consequently, on cancer progression. Here, we present a brief overview of the role of autophagy in OC hallmarks, including tumor dormancy, chemoresistance, metastasis, and cell metabolism, with an emphasis on the bidirectional metabolic crosstalk between cancer cells and stromal cells in shaping the OC microenvironment.