Anti-RB1 monoclonal antibody, clone 62C8

Introduction: Ovarian cancer remains the most lethal gynecologic cancer in women. Despite achievements in surgical and systemic therapy, most patients develop platinum resistance. Thus, new strategies to increase or reverse the platinum sensitivity in ovarian cancer patients are urgently needed. In this study, we aimed to investigate the anti-cancer effect of the leaves of Pistacia lentiscus L medicinal plants used in Algerian traditional medicine on ovarian cancer cells in vitro. Methods: Four newly established primary cell lines derived from ascites of patients with high-grade serous and clear cell ovarian cancer were used to test the anti-cancer effect of the leaves of Pistacia lentiscus L. An experimental study was performed to study the therapeutic effects of the plant leaves substances in patient derived models. The anti- proliferative activity of ethanolic, acetonic and methanolic plant leaves extracts was measured by cell viability assays, and the apoptotic effect assessed using flow cytometry analysis. The impact on constitutive active oncogenic pathways and cytokine release in cell culture supernatant were monitored by Western blotting and ELISA, respectively. Results: Sequencing analysis confirmed the presence of mutations in several genes, such as TP53, RB1, PIK3C, which are commonly mutated in high-grade serous ovarian cancer. Obtained results indicated a cytotoxic effect of the methanolic extract of P. lentiscus L (MEPL) on primary cell line cultures, inhibiting PI3K/AKT and MAPK/ERK signaling pathways, and decreasing the release of IL6 and VEGF by the malignant cells. Moreover, treatment with MEPL enhanced the sensitivity to platinum-based chemotherapy in our primary cell lines of patients. Conclusion: Methanolic extract of P. lentiscus L might be a promising candidate for novel therapeutic approaches in combination with classic chemotherapy for patients with high-grade serous ovarian cancer.

Purpose: Malignant peripheral nerve sheath tumors (MPNST) are deadly sarcomas that lack effective therapies. In most MPNSTs, the retinoblastoma (RB1) tumor suppressor is disabled by hyper-activation of cyclin-dependent kinases (CDK), commonly through loss of CDK-inhibitory proteins such as p27(Kip1). RABL6A is an inhibitor of RB1 whose role in MPNSTs is unknown. To gain insight into MPNST development and establish new treatment options, we investigated RABL6A-RB1 signaling and CDK inhibitor-based therapy in MPNSTs. Experimental Design: We examined patient-matched MPNSTs and precursor lesions by RNA sequencing (RNA-Seq) and IHC. Molecular and biological effects of silencing RABL6A and/or p27 in MPNST lines and normal human Schwann cells were determined. Tumor-suppressive effects of CDK inhibitors were measured in MPNST cells and orthotopic tumors. Results: RABL6A was dramatically upregulated in human MPNSTs compared with precursor lesions, which correlated inversely with p27 levels. Silencing RABL6A caused MPNST cell death and G(1) arrest that coincided with p27 upregulation, CDK downregulation, and RB1 activation. The growth-suppressive effects of RABL6A loss, and its regulation of RB1, were largely rescued by p27 depletion. Importantly, reactivation of RB1 using a CDK4/6 inhibitor (palbociclib) killed MPNST cells in vitro in an RABL6A-dependent manner and suppressed MPNST growth in vivo. Low-dose combination of drugs targeting multiple RB1 kinases (CDK4/6, CDK2) had enhanced antitumorigenic activity associated with potential MPNST cell redifferentiation. Conclusions: RABL6A is a new driver of MPNST pathogenesis that acts in part through p27-RB1 inactivation. Our results suggest RB1 targeted therapy with multiple pathway drugs may effectively treat MPNSTs.