The hyaluronan (HA) receptor CD44 is a single pass transmembrane glycoprotein involved in cell-cell and cell-matrix adhesion. Alternative splicing in human CD44 pre-mRNA results in expression of different transcript variants (CD44v), leading to variation in the length and function of extracellular domain. CD44, particularly CD44v isoforms, are known to be cancer stem cell (CSC) markers and critical regulators of tumor initiation and metastasis and CD44v are expressed in a broad range of cancers in advanced stages. In addition, the expression of different CD44 variants on endothelial cells may be implicated in tumor angiogenesis affecting HA-binding.
Our main aim is to identify specific CD44 variants expressed by prostate cancer (PCa) and testicular cancer (TGCT) cells with CSC and metastatic traits in different microenvironment by using various cell lines and cultured sample of primary prostate tumors and paraffin-embedded section from testicular tumors. Interestingly, CD44 can function as co-receptor for the receptor tyrosine kinase (RTK) c-MET. Thus, the role of CD44v in c-MET activated cell pathways that promote tumorigenic functions will be investigated in our models.
We have previously identified a scanty CD44-negative cell population isolated from human PCa cell line PC3 that rapidly converts to CD44-highly positive cells expressing specific CD44v8-10 isoform and displaying high clonogenic and invasive potential (Di Stefano C et al Oncotarget 2018). At present, CAR-T technology development is a big challenge for the treatment of malignant solid tumors including prostate cancer. Therefore, we aim to identify CD44v8-10 as a novel marker of aggressiveness to use it as target of CAR-based therapeutic strategy.
We therefore believe that any progress in the knowledge of CD44 variants specifically expressed on CSC-like very aggressive PCa and TGCTs may constitute an important proof-of concept on the potential efficacy of adoptive immunotherapy.
The innovative contribution of this research consists in the identification of CD44 variants specifically expressed on prostate cancer (PCa) and Testicular Germ Cell Tumors (TGCTs) CSC-stem-like and/or in endothelial cells as markers and/or targets in male urogenital cancers.
In PCa, radiotherapy (RT) generally results in excellent initial response, but some patients relapse locally and/or systemically, indicating that a resistant population of cancer cells survives RT (Hayden AJ Curr. Oncol. 2010, Baumann M. Nat Rev Cancer 2016). In fact, accumulating evidence demonstrate that radiation can induce selection and/or generation of cancer stem cells (CSC) accompanied by cancer recurrence and metastasis. To improve the efficacy of treatments, there is increasing interest in combining radiotherapy with novel targeted therapies. Due to a cellular heterogeneity and stroma complexity of prostate cancer, the development of successful combined therapy, which is the convergence of more than one anti-tumor mechanism, might be needed to overcome radiotherapy resistance. Different CD44v isoforms have been identified as CSC markers and critical players in regulating tumor progression metastases and treatment resistance in many cancers (Ishimoto T Cancer Cell 2011, Sosulski A PLoS ONE 2016). Moreover, CD44v8-10 is a gastric CSC marker having a low expression in normal tissues hence considered an ideal target to eliminate gastric CSCs (Lau WM Cancer Res. 2014). A number of studies validate the potential of CD44 as a therapeutic target in various tumor types. Current therapeutic strategies include neutralizing antibody, peptide mimetics, aptamers, natural compounds that suppress CD44 expression, HA-directed targeting of bioconjugates and nanoparticles, HA oligomers, and CD44 decoys (Chen C Journal of Hematology & Oncology 2018). In addition, the chimeric antigen receptor T cell (CAR-T) therapy has currently gained great attention due to the advantages of CAR-T cells in the treatment of malignant tumors of the blood system (Gill S Immunol Rev 2015), but the potentialities of this approach in solid tumors are still object of intense research (Zuo S Mol Immunol. 2017, Guo X Sci. Rep 2017). At present, CAR-T technology development is a big challenge for the treatment of malignant solid tumors including prostate cancer. So far, there are only two ongoing clinical trials for prostate cancer CAR-T therapy. One is a Phase I trial of prostate-specific membrane antigen (PSMA)-targeted CAR-T in mCRPC patients (NCT01140373). Another one (NCT03089203) is a Phase I trial of ¿CART-PSMA-TGFßRDN Cells for CRPC¿ evaluating the safety and feasibility of intravenously administered, lentivirally transduced, dual PSMA-specific/TGFß-resistant, CAR-modified autologous T cells (Yu H OncoTargets Ther 2019). Interestingly, the significant preclinical antitumor efficacy of anti-CD44v6 CAR-T cells against acute myeloid leukemia and multiple myeloma was recently reported (Casucci M, BLOOD 2013). Moreover, it has been recently proposed a new immunotherapy for high grade soft tissue sarcomas (STS) based on cytokine-induced killer cells (CIK) redirected with a chimeric antigen receptor (CAR) against the tumor promoting antigen CD44v6 (Leuci V Oncoimmunology 2018).
Based on these data, this project intends to identify CD44 variants specifically expressed on CSC-like very aggressive PCa and TGCTs. As ultimate goal, the project aims to provide novel markers of aggressiveness to use as targets of CAR-based therapeutic strategy.