Targeting of S-phase kinase associated protein 2 stabilized tumor suppressors leading to apoptotic cell death in squamous skin cancer cells.

S-phase kinase-associated protein 2 (Skp2) is an F-box protein overexpressed in human cancers and linked with poor prognosis. It triggers cancer pathogenesis, including stemness and drug resistance. In this study, we have explored the potential role of Skp2 targeting in restoring the expression of tumor suppressors in human cutaneous squamous cell carcinoma (cSCC) cells. Our results showed that genetic and pharmacological Skp2 targeting markedly suppressed cSCC cell proliferation, colony growth, spheroid formation, and enhanced sensitization to chemotherapeutic drugs. Further, western blot results demonstrated restoration of tumor suppressor (KLF4) and CDKI (p21) and suppression of vimentin and survivin in Skp2-knocked-down cSCC cells. Importantly, we also explored that Skp2 targeting potentiates apoptosis of cSCC cells through MAPK signaling. Moreover, co-targeting of Skp2 and PI3K/AKT resulted in increased cancer cell death. Interestingly, curcumin, a well-known naturally derived anticancer agent, also inhibits Skp2 expression with concomitant CDKI upregulation. In line, curcumin suppressed cSCC cell growth through ROS-mediated apoptosis, while the use of N-acetyl cysteine (NAC) reversed curcumin-induced cell death. Curcumin treatment also sensitized cSCC cells to conventional anticancer drugs, such as cisplatin and doxorubicin. Altogether, these data suggest that Skp2 targeting restores the functioning of tumor suppressors, inhibits the expression of genes associated with cell proliferation and stemness, and sensitizes cancer cells to anticancer drugs. Thus, genetic, and pharmacological ablation of Skp2 can be an important strategy for attenuating cancer pathogenesis and associated complications in skin squamous cell carcinoma.

Pristimerin mediated anticancer effects and sensitization of human skin cancer cells through modulation of MAPK signaling pathways.

Squamous cell carcinoma is a frequent skin cancer still demanding to understand the underlying mechanisms for better clinical outcomes. Pristimerin, a natural quinonemethide triterpenoid, has shown promising therapeutic outcome due to its anti-cancer activity and multi-targeting potential. We explored the underlying mechanisms of pristimerin-induced programmed cell death of primary (A431) and metastatic (A388) cutaneous squamous cell carcinoma (cSCC) cells. Our results show that pristimerin inhibits growth and proliferation of cSCC through JNK activation. Moreover, pristimerin causes cell cycle arrest and induces cell death via apoptosis and autophagy. Interestingly, use of apoptosis (z-VAD-FMK) and autophagy (3-methyladenine) inhibitors confirmed vital role of programmed cell death in pristimerin-mediated anti-cancer actions. JNK inhibitor, SP600125, also mitigated pristimerin-induced apoptotic and autophagic actions. Moreover, pristimerin-mediated anti-cancer activity acts by generating reactive oxygen species (ROS) thereby inducing JNK signaling. Use of N-acetyl cystine (NAC), a universal ROS scavenger, significantly reversed pristimerin-induced programmed cell death through downregulation of JNK. Pristimerin sensitized skin cancer cells to conventional anticancer drugs cisplatin, azacytidine and doxorubicin through JNK activation, as confirmed by SP600125. Our results indicate that pristimerin mediates programmed cell death and sensitized skin cancer cells to conventional anti-cancer drugs via ROS-mediated JNK activation.

F-box proteins in cancer stemness: An emerging prognostic and therapeutic target.

Cancer is a complex heterogenic disease with significant therapeutic challenges. The presence of cancer stem cells (CSCs) in cancer tissue orchestrates tumor growth, progression, and metastasis, the tumor heterogeneity, disease relapse, and therapeutic resistance. Hence, it is imperative to explore how progenitor or cancer-initiating cells acquire stemness features and reprogram different biological mechanisms to maintain their sustained oncogenicity. Interestingly, deregulation of F-box proteins (FBPs) is crucial for cancer stemness features, including drug resistance and disease relapse. In this review, we highlight recent updates on the clinical significance of targeting FBPs in cancer therapy, with emphasis on eliminating CSCs and associated therapeutic challenges. Moreover, we also discuss novel strategies for the selective elimination of CSCs by targeting FBPs.