NSC606985 induces apoptosis, exerts synergistic effects with cisplatin, and inhibits hypoxia-stabilized HIF-1alpha protein in human ovarian cancer cells

Novel cancer treatment paradigm targeting hypoxia-induced factor in conjunction with current therapies to overcome resistance

Chemotherapy, radiotherapy, targeted therapy, and immunotherapy are established cancer treatment modalities that are widely used due to their demonstrated efficacy against tumors and favorable safety profiles or tolerability. Nevertheless, treatment resistance continues to be one of the most pressing unsolved conundrums in cancer treatment. Hypoxia-inducible factors (HIFs) are a family of transcription factors that regulate cellular responses to hypoxia by activating genes involved in various adaptations, including erythropoiesis, glucose metabolism, angiogenesis, cell proliferation, and apoptosis. Despite this critical function, overexpression of HIFs has been observed in numerous cancers, leading to resistance to therapy and disease progression. In recent years, much effort has been poured into developing innovative cancer treatments that target the HIF pathway. Combining HIF inhibitors with current cancer therapies to increase anti-tumor activity and diminish treatment resistance is one strategy for combating therapeutic resistance. This review focuses on how HIF inhibitors could be applied in conjunction with current cancer treatments, including those now being evaluated in clinical trials, to usher in a new era of cancer therapy.

Dual action of NSC606985 on cell growth and apoptosis mediated through PKCδ in prostatic cancer cells

Chemotherapy is a vital therapeutic strategy for castration-resistant prostate cancer (CRPC). We have previously shown that NSC606985 (NSC), a camptothecin (CPT) analog, induced cell apoptosis via interacting with topoisomerase I (Topo I) in prostate cancer cells. In the present study, the effect and mechanism of CPT analogs in LAPC4 cells were investigated. LAPC-4 cells were treated with NSC, CPT, and topotecan. Cell proliferation, apoptosis, and protein kinase Cδ (PKCδ) subcellular activation were measured at different doses and time-points, with or without PKCδ inhibition or knockdown of PKCδ expression. NSC at doses ranging from 10 to 100 nM induced a dose-dependent increase in viable cell number and DNA biosynthesis with mild cell apoptosis, whereas, at doses ranging from 500 nM to 5 mM, NSC produced a dose-dependent decrease in cell proliferation and DNA biosynthesis with a significant induction of cell apoptosis. Both NSC-induced cell proliferation and apoptosis were blocked by knockdown of PKCδ with a specific RNAi, or by the co-administration of rottlerin, a PKCδ inhibitor. Moreover, NSC produced a dose-dependent subcellular activation of PKCδ. The dose-dependent dual action of NSC is mediated at least in part through the differential subcellular activation of PKCδ in LAPC4 cells. The demonstration of a differential cell response to camptothecin analogs would facilitate the identification of biomarker(s) to CPT sensitivity and promote the personalization of CPT chemotherapy in CRPC.

SENP1 desensitizes hypoxic ovarian cancer cells to cisplatin by up-regulating HIF-1α

Hypoxia-inducible factor 1 alpha (HIF-1α) is closely related to chemoresistance of ovarian cancers. Although it is reported that HIF-1α can be regulated by Sentrin/SUMO-specific protease 1 (SENP1), the effects of SENP1 on HIF-1α is still controversial. In this study, we identified that SENP1 positively regulated the expression of HIF-1α by deSUMOylation and weakened the sensitivity of hypoxic ovarian cancer cells to cisplatin. These results indicate that SENP1 is a positive regulator of HIF-1α and plays a negative role in ovarian cancer chemotherapy.

BAY 87-2243, a novel inhibitor of hypoxia-induced gene activation, improves local tumor control after fractionated irradiation in a schedule-dependent manner in head and neck human xenografts

Background

The transcription factor hypoxia-inducible factor-1 (HIF-1) pathway plays an important role in tumor response to cytotoxic treatments. We investigated the effects of a novel small molecule inhibitor of mitochondrial complex I and hypoxia-induced HIF-1 activity BAY-87-2243, on tumor microenvironment and response of human squamous cell carcinoma (hSCC) to clinically relevant fractionated radiotherapy (RT) with and without concomitant chemotherapy.

Methods

When UT-SCC-5 hSCC xenografts in nude mice reached 6 mm in diameter BAY-87-2243 or carrier was administered before and/or during RT or radiochemotherapy with concomitant cisplatin (RCT). Local tumor control was evaluated 150 days after irradiation and the doses to control 50% of tumors (TCD₅₀) were compared between treatment arms. Tumors were excised at different time points during BAY-87-2243 or carrier treatment for western blot and immunohistological investigations.

Results

BAY-87-2243 markedly decreased nuclear HIF-1α expression and pimonidazole hypoxic fraction already after 3 days of drug treatment. BAY-87-2243 prior to RT significantly reduced TCD₅₀ from 123 to 100 Gy (p=0.037). Additional BAY-87-2243 application during RT did not decrease TCD₅₀. BAY-87-2243 before and during radiochemotherapy did not improve local tumor control.

Conclusions

Pronounced reduction of tumor hypoxia by application of BAY-87-2243 prior to RT improved local tumor control. The results demonstrate that radiosensitizing effect importantly depends on treatment schedule. The data support further investigations of HIF-1 pathway inhibitors for radiotherapy and of predictive tests to select patients who will benefit from this combined treatment.

Protein Kinase C (PKC) Isozymes and Cancer

Protein kinase C (PKC) is a family of phospholipid-dependent serine/threonine kinases, which can be further classified into three PKC isozymes subfamilies: conventional or classic, novel or nonclassic, and atypical. PKC isozymes are known to be involved in cell proliferation, survival, invasion, migration, apoptosis, angiogenesis, and drug resistance. Because of their key roles in cell signaling, PKC isozymes also have the potential to be promising therapeutic targets for several diseases, such as cardiovascular diseases, immune and inflammatory diseases, neurological diseases, metabolic disorders, and multiple types of cancer. This review primarily focuses on the activation, mechanism, and function of PKC isozymes during cancer development and progression.

Effects of combined Tan IIA and 5-FU on cell proliferation, apoptosis, and the expression of HIF-1α and mutant P53 in human gastric cancer cell line SGC7901 under hypoxia

AIM: To investigate the effects of combined tanshinone IIA (Tan IIA) and 5-fluorouracil (5-FU) on cell proliferation, apoptosis, and the expressions of hypoxia-inducible factor-1 alpha (HIF-1α) and mutant P53 (mt P53) in human gastric cancer cell line SGC7901 under hypoxia.

METHODS: Hypoxia was induced in SGC7901 cells by cobalt dichloride treatment. SGC7901 cells under hypoxia were treated with different concentrations of Tan IIA in combination with 10.0 mg/L of 5-FU for 24, 48 and 72 hours. Cell proliferation was detected by methyl thiazolyl tetrazolium (MTT) assay. Cell apoptosis was detected by Hoechst staining. The expression of HIF-1α and mt P53 proteins was detected by immunocytochemistry.

RESULTS: Combined Tan IIA and 5-FU significantly inhibited the proliferation of SGC7901 cells (all P < 0.01) in a dose- and time-dependent manner under hypoxia. The reduced proliferation rate of cells incubated with Tan IIA at a concentration of 10 mg/L and 5-FU for 72 hours was 67.46%. Hoechst staining showed that Tan IIA in combination with 5-FU promoted the apoptosis of SGC7901 cells in a dose- and time-dependent manner under hypoxia (all P < 0.01). Immunocytochemical staining revealed that the expression levels of HIF-1α and mt P53 proteins in SGC7901 cells under hypoxia were evidently higher than those in SGC7901 cells under normal conditions (t = 22.786 and 13.914, respectively; both P < 0.01). However, Tan IIA in combination with 5-FU significantly downregulated the expression of HIF-1α and mt P53 proteins in SGC7901 cells under hypoxia (F = 182.234 and 130.062, respectively; both P < 0.01). A significant positive correlation was noted between the expression of HIF-1α and mt P53 in SGC7901 cells (n = 5, r = 0.995, P < 0.01).

CONCLUSION: Tan IIA can significantly enhance 5-FU-mediated growth inhibition and apoptosis induction in SGC7901 cells under hypoxia perhaps by downregulating HIF-1α and mt P53 protein expression.

Downregulation of ANP32B, a novel substrate of caspase-3, enhances caspase-3 activation and apoptosis induction in myeloid leukemic cells

The acidic leucine-rich nuclear phosphoprotein 32 (ANP32)B has been reported to regulate gene expression by acting as a histone chaperone or modulate messenger RNA trafficking by serving as a HuR ligand. However, its exact cellular functions are poorly understood. By utilizing a proteomics-based approach, in this work, we identify that the human ANP32B protein is cleaved during apoptosis induction by NSC606985, a novel camptothecin analog. Further investigation shows that various apoptosis inducers cause a decrease of full-length ANP32B in multiple cell lines with a concomitant increase of an approximately 17 kDa fragment. The proteolytic cleavage of ANP32B is inhibited by a specific caspase-3 inhibitor Z-DEVD-fmk, and it cannot be seen in NSC606985-induced death of caspase-3-deficient MCF-7 cells. In vitro caspase cleavage assay and mutagenesis experiment reveal that ANP32B is a direct substrate of caspase-3 and it is primarily cleaved at the sequence of Ala-Glu-Val-Asp, after Asp-163. Additionally, the reduced expression of endogenous ANP32B by specific small interfering RNA enhances caspase-3 activation and apoptosis induction by NSC606985 and etoposide. These results suggest that ANP32B is a novel substrate for caspase-3 and acts as a negative regulator for apoptosis, the mechanism of which remains to be explored.

Nuclear translocation of dihydrofolate reductase is not a pre-requisite for DNA damage induced apoptosis

Dihydrofolate reductase (DHFR) is a key enzyme for the synthesis of thymidylate, and therefore, of DNA. By applying subcellular proteomic analysis, we identified that the DHFR protein was translocated from cytoplasm into the nucleus when apoptosis was induced by NSC606985, a camptothecin analogue. The nuclear translocation of DHFR protein during apoptosis was independent of the cellular context, but it was more sensitive in cell death induction by DNA damaging agents such as doxorubicin, etoposide and ultraviolent radiation than endoplasmic reticulum stressors (brefeldin-A and tunicamycin) and anti-microtubule agents (paclitaxel and nocodozole). The addition of methotrexate almost completely blocked the nuclear translocation of DHFR protein. Further investigations showed that the nuclear translocation of DHFR was not a pre-requisite for DNA damage induced apoptosis. Therefore, its potential biological significance remains to be further explored.