J-4: a novel and typical preclinical anticancer drug targeting protein kinase C ζ

FBXW7 in breast cancer: mechanism of action and therapeutic potential

Breast cancer is one of the frequent tumors that seriously endanger the physical and mental well-being in women. F-box and WD repeat domain-containing 7 (FBXW7) is a neoplastic repressor. Serving as a substrate recognition element for ubiquitin ligase, FBXW7 participates in the ubiquitin-proteasome system and is typically in charge of the ubiquitination and destruction of crucial oncogenic proteins, further performing a paramount role in cell differentiation, apoptosis and metabolic processes. Low levels of FBXW7 cause abnormal stability of pertinent substrates, mutations and/or deletions in the FBXW7 gene have been reported to correlate with breast cancer malignant progression and chemoresistance. Given the lack of an effective solution to breast cancer's clinical drug resistance dilemma, elucidating FBXW7's mechanism of action could provide a theoretical basis for targeted drug exploration. Therefore, in this review, we focused on FBXW7's role in a range of breast cancer malignant behaviors and summarized the pertinent cellular targets, signaling pathways, as well as the mechanisms regulating FBXW7 expression. We also proposed novel perspectives for the exploitation of alternative therapies and specific tumor markers for breast cancer by therapeutic strategies aiming at FBXW7.

Combination therapy of PKCζ and COX-2 inhibitors synergistically suppress melanoma metastasis

Background

Metastatic malignant melanoma is one of the most aggressive malignancies and its treatment remains challenging. Recent studies demonstrate that the melanoma metastasis has correlations with the heightened activations of protein kinase C ζ (PKCζ) and cyclooxygenase-2 (COX-2) signaling pathways. Targeted inhibitions for PKCζ and COX-2 have been considered as the promising strategies for the treatment of melanoma metastasis. Thus, the PKCζ inhibitor J-4 and COX-2 inhibitor Celecoxib were combined to treat melanoma metastasis in this study.

Methods

The Transwell assay, Wound-healing assay and Adhesion assay were used to evaluate the inhibition of combined therapy of J-4 and Celecoxib on melanoma cells invasion, migration and adhesion in vitro, respectively. The impaired actin polymerization was observed by confocal microscope and inactivated signal pathways about PKCζ and COX-2 were confirmed by the Western blotting assay. The B16-F10/C57BL mouse melanoma model was used to test the inhibition of combined therapy of J-4 and Celecoxib on melanoma metastasis in vivo.

Results

The in vitro results showed that the combination of J-4 and Celecoxib exerted synergistic inhibitory effects on the migration, invasion and adhesion of melanoma B16-F10 and A375 cells with combination index less than 1. The actin polymerization and phosphorylation of Cofilin required in cell migration were severely impaired, which is due to the inactivation of PKCζ related signal pathways and the decrease of COX-2. The combined inhibition of PKCζ and COX-2 induced Mesenchymal-Epithelial Transition (MET) in melanoma cells with the expression of E-Cadherin increasing and Vimentin decreasing. The secretion of MMP-2/MMP-9 also significantly decreased after the combination treatment. In C57BL/6 mice intravenously injected with B16-F10 cells (5 × 10⁴ cells/mouse), co-treatment of J-4 and Celecoxib also severely suppressed melanoma lung metastasis. The body weight monitoring and HE staining results indicated the low toxicity of the combination therapy.

Conclusions

This study demonstrates that the combination therapy of PKCζ and COX-2 inhibitors can significantly inhibit melanoma metastasis in vitro and in vivo, which will be an efficient strategy for treatment of melanoma metastasis in clinics.

PKCζ Promotes Breast Cancer Invasion by Regulating Expression of E-cadherin and Zonula Occludens-1 (ZO-1) via NFκB-p65

Atypical Protein Kinase C zeta (PKCζ) forms Partitioning-defective (PAR) polarity complex for apico-basal distribution of membrane proteins essential to maintain normal cellular junctional complexes and tissue homeostasis. Consistently, tumor suppressive role of PKCζ has been established for multiple human cancers. However, recent studies also indicate pro-oncogenic function of PKCζ without firm understanding of detailed molecular mechanism. Here we report a possible mechanism of oncogenic PKCζ signaling in the context of breast cancer. We observed that depletion of PKCζ promotes epithelial morphology in mesenchymal-like MDA-MB-231 cells. The induction of epithelial morphology is associated with significant upregulation of adherens junction (AJ) protein E-cadherin and tight junction (TJ) protein Zonula Occludens-1 (ZO-1). Functionally, depletion of PKCζ significantly inhibits invasion and metastatic progression. Consistently, we observed higher expression and activation of PKCζ signaling in invasive and metastatic breast cancers compared to non-invasive diseases. Mechanistically, an oncogenic PKCζ– NFκB-p65 signaling node might be involved to suppress E-cadherin and ZO-1 expression and ectopic expression of a constitutively active form of NFκB-p65 (S536E-NFκB-p65) significantly rescues invasive potential of PKCζ-depleted breast cancer cells. Thus, our study discovered a PKCζ - NFκB-p65 signaling pathway might be involved to alter cellular junctional dynamics for breast cancer invasive progression.

PKCζ and PKMζ are overexpressed in TCF3-rearranged paediatric acute lymphoblastic leukaemia and are associated with increased thiopurine sensitivity

Both tumour suppressor and oncogenic functions have been ascribed to the atypical zeta isoform of protein kinase C (PKCζ), whereas its constitutively active form PKMζ is almost exclusively expressed in the brain where it has a role in long-term memory. Using primers unique for either isoform, we found that both PKCζ and PKMζ were expressed in a subset of paediatric acute lymphoblastic leukaemia (ALL) cases carrying a TCF3 (E2A) chromosomal rearrangement. Combined PKCζ and PKMζ (PKC/Mζ) protein as well as phosphorylation levels were elevated in ALL cases, especially TCF3-rearranged precursor B-ALL cases, compared with normal bone marrow (P<0.01). Furthermore, high PKC/Mζ expression in primary ALL cells was associated with increased sensitivity to 6-thioguanine and 6-mercaptopurine (P<0.01), thiopurines used in ALL treatment. PKCζ is believed to stabilize mismatch-repair protein MSH2, facilitating thiopurine responsiveness in T-ALL. However, PKC/Mζ knockdown in a TCF3-rearranged cell line model decreased MSH2 expression but did not induce thiopurine resistance, indicative that the link between high PKC/Mζ levels and thiopurine sensitivity in paediatric precursor B-ALL is not directly causal. Collectively, our data indicate that thiopurine treatment may be effective, especially in paediatric TCF3-rearranged ALL and other patients with a high expression of PKC/Mζ.

Association of PKCζ expression with clinicopathological characteristics of breast cancer

The protein kinase C (PKC) family has been functionally linked to cancer. It has been suggested that atypical PKCs contribute to cell proliferation and cancer progression. With respect to breast cancer, PKCζ has been found to play a key role in intracellular transduction of mitogenic and apoptotic signals using mammary cell lines. However, little is known about its function in vivo. Here we examined the correlation between PKCζ protein levels and important clinicopathologic factors in breast cancer using patient samples. To conduct the study, 30 invasive ductal carcinoma cases and their paired normal tissues were used for tissue microarray analysis (TMA) and 16 were used for western blot analysis. In addition, the correlation between PKCζ expression levels and clinicopathologic characteristics was determined in 176 cases with relevant clinical data. Finally, the correlation between PKCζ and epithelial growth factor receptor 2 (HER2) expressions was determined using three breast cancer cell lines by western blot analysis. Both TMA and western blot results showed that PKCζ protein was highly expressed in primary tumors but not in paired normal tissue. The correlation study indicated that high PKCζ levels were associated with premenopausal patients (p = 0.019) and worse prognostic factors, such as advanced clinical stage, more lymph node involvement and larger tumor size. Both disease-free survival and overall survival rates were lower in the high PKCζ group than those in the low PKCζ group. No correlation was observed between PKCζ levels and age, histological grade, or estrogen or progesterone receptor expression status. A positive correlation between PKCζ and HER2 levels was observed in both tumor samples and cell lines. Our observations link PKCζ expression with factors pointing to worse prognosis, higher HER2 levels and a lower survival rate. This suggests that PKCζ protein levels may serve as a prognostic marker of breast cancer.