Prostate Cancer Research Notes (Andrea Almonti, USI)

Prostate Cancer Prevalence and Challenges

Prostate cancer affects 1 in 9 men.
Early stages are curable with surgery +/- androgen deprivation therapy.
A subset of patients doesn't respond to standard treatments, leading to relapse and metastatic castration-sensitive or castration-resistant prostate cancer.
Effective therapies for these patients are lacking, impacting survival.
This accounts for 15% of prostate cancer patients, a significant number due to the high prevalence of the disease.
Prostate cancer is still a major cause of death for men in the Western world.
Research efforts focus on delaying castration-resistant prostate cancer, developing new therapies, and reversing castration resistance.

Transgenic Mouse Models in Prostate Cancer Research

Transgenic mouse models are used to mimic the evolution of prostate cancer from early to metastatic stages.
These models are used for preclinical trials to test novel therapeutics at different disease stages.
The p10 null prostate conditional mouse model spontaneously develops prostate cancer due to complete loss of P10, a potent tumor suppressor gene.
This model was developed in the lab of Pierre Paolo Pandolfi at Memorial Sloan Kettering.
The p10 null model has been intercrossed with p53, SMAD4, etc., to generate more aggressive prostate cancer models.
Other models overexpress CDCP1 or inactivate T1, combined with beta loss, to induce aggressive, metastatic prostate cancer.
The lab has a large collection of mouse models with different prostate tumors at various disease stages.
These models are used to study cancer biology and test novel therapeutics.

Cellular Senescence in Prostate Cancer

Research focuses on the role of cellular senescence and the tumor microenvironment in prostate cancer development and metastatic progression.
Cellular senescence is a state of permanent cell growth arrest.
Inactivation of PTEN in mouse models leads to benign tumors characterized by senescent cells.
In vitro, primary mouse embryonic fibroblasts with complete p10 loss exhibit growth arrest and senescence.
Paradoxically, inactivation of a tumor suppressor gene can inhibit growth due to P10's activation of the PI3K-AKT pathway.
mTOR, controlled by AKT activation, regulates p53 translation, which induces cellular senescence.
Cellular senescence is a permanent, irreversible growth arrest in primary and cancer cells, induced by oncogenic stress, chemotherapy, radiotherapy, or targeted therapies.
Senescent cells cannot easily re-enter the cell cycle, distinguishing them from quiescent cells.
Senescent cells can re-enter the cell cycle under specific circumstances.
Senescent cells have high lysosomal activity, detectable by beta-galactosidase assay (staining blue).
Senescent cells upregulate p16, p21, and p27, inhibitors of cell proliferation.
They are resistant to cell death and overexpress pro-survival factors like BCL2.
Zombie cells

Senescence-Associated Secretory Phenotype (SASP)

Senescent cells remain in tissues and secrete cytokines, growth factors, and metalloproteinases, known as SASP.
Apoptotic cells die without secreting factors, while senescent cells influence the microenvironment, immune response, etc.
SASP is a key hallmark of cellular senescence.
Early-stage tumors exhibit a lot of senescence, observed by beta-Gal positive senescent cells.
Prosenescence therapy aims to induce senescence in advanced cancers using pathways that drive primary aging cancer cells.
Small molecules can block gene upregulation in senescence or target downstream targets important for senescence.
Screening platforms have identified compounds that drive cellular senescence in cancer.
Some compounds effectively induce irreversible growth arrest, potentially curing different cancers, particularly prostate cancer.

Dual Role of Senescence in Cancer Progression

Senescent cells can be protective at early stages, as demonstrated by chemotherapy or anti-androgen therapy inducing senescence and cell arrest.
This activates a pro-inflammatory state in the tumor.
Immune responses may eliminate senescent cells, clearing the tumor completely.
If immune responses are suppressed, senescent cells persist, secreting inflammatory factors that promote tumor progression and metastasis.
Myeloid-derived suppressor cells (MDSCs) or immunosuppressive neutrophils influence whether senescent cells are eliminated.
Accumulation of these cells is associated with metastasis development.
Senescent tumor cells promote tumor proliferation by releasing secreted factors and mitochondrial DNA (mtDNA).
Senescent tumor cells release mtDNA into the cytosol, encapsulated in extracellular vesicles.
This mtDNA activates MDSCs in the microenvironment.
Senescent cells release mtDNA in conditioned media, caught by CD11b+LY6G+ cells (MDSCs or neutrophils).
Cross-species mtDNA transfer experiments show human prostate tumor cells injected into mice transfer mtDNA to murine immune cells.
Transferred mtDNA makes these cells immunosuppressive, driving tumor progression by releasing additional factors.

TIMP1 and Senescence-Driven Metastasis

Inactivation of p10 drives senescence, and TIMP1, an inhibitor of metalloproteinases, blocks metalloproteinases overexpressed in senescent tumor cells.
Removing TIMP1 in the p10 null mouse model leads to aggressive, metastatic tumors because metalloproteinases become active.
Senescent tumor cells promote neighboring tumor cell metastasis by secreting pro-inflammatory, pro-metastatic factors.
Metalloproteinases shape the secretory phenotype of senescent cells.
Chemotherapy (docetaxel) in the TIMP1-expressing mouse model shrinks tumors and increases senescence.
In the model lacking TIMP1, docetaxel increases senescent cells, pushing neighboring cells to metastasize, accelerating tumor progression.
Genetic background determines whether senescence is tumor-suppressive or tumor-promoting.

Senescence Index Tool (SIT)

Using the mouse model where senescence pushes metastasis formation and 10x single-cell transcriptome data, a new tool was designed to identify senescent tumor cells: Senescence Index Tool (SIT).
SIT is a bioinformatic method to identify senescent tumor cells within a tumor.
Senescent tumor cells are heterogeneous, forming different clusters.
These cells rely on NCL1 for survival, and NCL1 inhibitors are in clinical trials.
Senescent tumor cells express NCL1 to remain in the tumor microenvironment.
NCL1 inhibitors are used to eliminate senescent tumor cells after docetaxel therapy.
Docetaxel induces cellular senescence in a human mouse model of prostate cancer (PC3 cells, p10/p53 loss, TIMP1 inactivation).
Mice develop metastasis only after docetaxel therapy.
Semolytic compounds (killing senescent cells) are administered concomitantly.
Eliminating senescent tumor cells decreases the number of liver/lung metastases.
Semolytic therapy, considered useful for aging, can also prevent metastatic dissemination in oncology.

Adapalin and Favorable Senescence Response

Specific drugs can induce a favorable senescence response even in advanced tumors.
A screening platform identifies drugs that induce cellular senescence, aiming for a secretory phenotype that doesn't promote tumor growth or activates the immune response.
Adapalin, a retinoid, induces a favorable senescence response.
Combining adapalin with docetaxel (which gives rise to an unfavorable senescence response) leads to tumor proliferation arrest and activation of an anti-tumor immune response.
Docetaxel-induced senescent tumor cells produce tumor-promoting factors, while adapalin changes the secretory phenotype.
Adapalin combined with docetaxel reduces bad factors and increases secreted factors that activate the immune response, particularly NK cells.
The combination promotes growth arrest and recruits NK cells to the tumor microenvironment.
Senescent tumor cells treated with the combination upregulate activating NK markers like MICA-1.
Upregulated MICA-1 allows NK cells to recognize and kill tumor cells through NKG2D receptor.
Blocking NKG2D reverses the killing effect, confirming NKG2D dependence.

Enhancement of NK Cell Therapy

Allogeneic infusion of NK cells is used to treat different diseases.
Phase 2/3 studies are ongoing with genetically modified NK cells (NK CAR-T) and allogeneic NK cell infusions.
In mice with aggressive prostate cancer, NK cell infusion alone has little response.
The combination of docetaxel and adapalin enhances NK cell capability to kill PC3 SH-shp9 tumors.
This approach could enhance the efficacy of allogeneic infusion of NK cells.

Targeting the Tumor Microenvironment: Immunosuppressive Neutrophils

Research focuses on developing therapies targeting the tumor microenvironment.
Polymorphonuclear myeloid cells (immunosuppressive neutrophils) infiltrate prostate cancer at different stages.
The presence of myeloid cells in the tumor microenvironment promotes prostate cancer growth.
This has been reproduced by multiple research groups in both mouse and human prostate cancer.
Metastases from patients with castration-sensitive or resistant prostate cancer are infiltrated by these immune cells.
Myeloid cells originate from the bone marrow and are recruited by tumor-released factors.
CXCR2 receptor on these cells is key for migration into the tumor, as tumor cells produce CXCL chemokines that bind to this receptor.
Inhibiting CXCR2 interferes with cell migration into the tumor.
Inhibiting MDSCs in prostate cancer treated with chemotherapy activates senescent surveillance, promoting tumor inhibition by reactivating Th1 and NK cells.
These cells drive tumor progression by interfering with innate/adaptive immune responses and producing tumor microenvironment factors like IL-23.
IL-23 binds to the IL-23 receptor, activating a signaling pathway that promotes prostate tumor cell growth even in the absence of androgens.
Inhibitors of this receptor are used to interfere with the recruitment of these cells into the tumor.
The inhibitor was effective in different mouse models, prolonging survival by blocking immunosuppressive neutrophils' presence in the tumor.