Elucidating the role of primary and secondary senescence in liver cancer

Dr Kristina Kirschner, Dr Tom Bird, Professor Stuart Forbes

Senescence is a cell cycle arrest state characterised by a pro-tumorigenic secretome. Oncogene activation or exposure to DNA damaging therapy, such as chemotherapy causes accumulation of DNA damage and may trigger senescence. Through the secretion of factors like extracellular matrix proteases and interleukins and chemokines, senescent cells modulate tissue organisation and recruit immune cells, mediating their own clearance. Chronically, however the senescence associated secretory phenotype (SASP) accelerates inflammation and cancer progression. In addition, SASP factors can act in a paracrine fashion to induce secondary senescence in otherwise healthy surrounding cells and tissues (Nelson et al, Aging cell 2012, Bird and Forbes STM 2018). More recently, cell-contact mediated juxtacrine Notch signalling has also been implicated in mediating secondary senescence induction (Teo et al Cell Reports 2019, Hoare et al. Nat Cell Biol 2016). The roles of secondary senescence in-vitro and in-vivo remain elusive since its discovery. We previously showed that these two senescent populations differ in their gene expression profiles and secretomes (Teo et al 2019), hinting at functional differences in heterogeneous senescence populations. From this we hypothesise that these different senescence forms have distinct roles in cancer with relevance for cancer formation and prevention. We will investigate the role of stromal cell primary and secondary senescence in liver cancer initiation, progression and resistance to chemotherapy in the context of therapy induced senescence.

Aim 1: Elucidate the role of primary and secondary senescence on tumorigenesis in-vitro.

We will elucidate the role of secondary senescence on tumorigenesis in-vitro. Using a co-culture system previously described (Teo et al 2019), we will produce primary senescent fibroblasts and secondary senescent stromal cells and characterise their gene expression and senescence profiles.

We will sort primary and secondary senescent cells for co-culture with liver cancer cell lines to test senescence impact on tumoral properties and response to chemotherapy by senescence profiling on a molecular and cellular level (including single cell RNA-seq).

Aim 2: Elucidate the role of primary and secondary senescence on tumorigenesis in-vivo

To investigate the role of senescence of stromal cells on acute tumorigenesis, we will co-inject senescent cell populations with liver cancer cells into mice characterising tumours, their environment and their response to chemotherapy. To investigate the role of senescence in tumour initiation and progression, we will inject senescent cell populations into the liver of transgenic mouse models susceptible to cancer and characterise precancerous lesions and tumours.

Aim 3: Test senolytics on primary and secondary senescence interacting with cancer cells in-vitro and in-vivo

Senolytics drugs specifically eliminate senescent cells. In the previous in-vitro and in-vivo models, we will test if senolytics counteract the effects of primary and secondary senescence on cancer, using standard chemotherapy with and without senolytics combination therapy.

In conclusion, this project will characterise the responses of secondary and primary senescence to therapy and provide a rationale for using senolytics to target each population as cancer therapy.

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