Novel Pactamycin Analogs Induce p53 Dependent Cell-Cycle Arrest at S-Phase in Human Head and Neck Squamous Cell Carcinoma (HNSCC) Cells

Abstract

Pactamycin, although putatively touted as a potent antitumor agent, has never been used as an anticancer drug due to its high cytotoxicity. In this study, we characterized the effects of two novel biosynthetically engineered analogs of pactamycin, de-6MSA-7-demethyl-7-deoxypactamycin (TM-025) and 7-demethyl-7-deoxypactamycin (TM-026), in head and neck squamous cell carcinoma (HNSCC) cell lines SCC25 and SCC104. Both TM-025 and TM-026 exert growth inhibitory effects on HNSCC cells by inhibiting cell proliferation. Interestingly, unlike their parent compound pactamycin, the analogs do not inhibit synthesis of nascent protein in a cell-based assay. Furthermore, they do not induce apoptosis or autophagy in a dose- or a time-dependent manner, but induce mild senescence in the tested cell lines. Cell cycle analysis demonstrated that both analogs significantly induce cell cycle arrest of the HNSCC cells at S-phase resulting in reduced accumulation of G2/M-phase cells. The pactamycin analogs induce expression of cell cycle regulatory proteins including master regulator p53, its downstream target p21Cip1/WAF1, p27kip21, p19, cyclin E, total and phospho Cdc2 (Tyr15) and Cdc25C. Besides, the analogs mildly reduce cyclin D1 expression without affecting expression of cyclin B, Cdk2 and Cdk4. Specific inhibition of p53 by pifithrin-α reduces the percentage of cells accumulated in S-phase, suggesting contribution of p53 to S-phase increase. Altogether, our results demonstrate that Pactamycin analogs TM-025 and TM-026 induce senescence and inhibit proliferation of HNSCC cells via accumulation in S-phase through possible contribution of p53. The two PCT analogs can be widely used as research tools for cell cycle inhibition studies in proliferating cancer cells with specific mechanisms of action.

Sodium fluoride causes hepatocellular S-phase arrest by activating ATM-p53-p21 and ATR-Chk1-Cdc25A pathways in mice

“…Cdc25A promotes cell cycle progression by activating cyclin-dependent protein kinases, and its production is associated with entry of cells into the S phase [ 42 – 44 ]. Moreover, exposure to novel pactamycin analogs also triggers p53-dependent S-phase cell cycle arrest in human head and neck squamous cell carcinoma (HNSCC) [ 45 ]. To determine whether the Cdc25A and p53 pathway is involved in NaF-induced cell cycle arrest, we examined the expression of ATR-Chk1-Cdc25A and ATM-p53-p21 pathway members at both the protein and mRNA levels [ 43 , 46 , 47 ].…”

“…Our results demonstrate conclusively that NaF up-regulates ATM and its downstream target p53, thus activating the ATM signal transduction pathways (Figures 15 and 16 ). These findings are similar to those of Guha et al ., who demonstrated that novel pactamycin analogs can cause S-phase arrest in human head and neck squamous cell carcinoma (HNSCC) cells by increasing p53 activity, up-regulating expression of the cyclin kinase inhibitors p27 and p21, slightly reducing cyclin D1 expression, and moderately increasing cyclin E expression; no changes were observed in the expression of cyclin B, CDK2, or CDK4 [ 45 ]. Treatment with the novel anthraquinone derivative IMP1338 also increased p53-dependent cell cycle arrest in the S phase in human cancer cells [ 59 ].…”

Mitochondrial complex I inhibitor deguelin induces metabolic reprogramming and sensitizes vemurafenib‐resistant BRAFV600E mutation bearing metastatic melanoma cells

“…ICC was performed as previously described . Briefly, cells were seeded onto 0.1% gelatin‐coated glass coverslips (Fisher Fisher Scientific) in six‐well plates (Falcon) at 200 000 cells/well.…”

“…ICC was performed as previously described. 17 we examined the potency of both compounds against normal human melanocytes in vitro and no effect on viability was observed ( Figure S1C). In further experiments, we chose to focus on the activity of deguelin as our model inhibitor of cancer cell metabolism due to rotenone's known toxicity in vivo .…”

Synthesis of an Orthogonally Protected Polyhydroxylated Cyclopentene from l‐Sorbose

“…In addition, advanced intermediate 7 can be also used for the preparation of biologically active cyclopentitols or cyclopentenols. These are polyhydroxylated cyclopentanes that display a plethora of biological activity such as found for the glycosidase inhibitors trehazolin and mannostatin, the anticancer and antibiotic pactamycin, and the insecticide ryanodine . In addition, cyclopentenols are also important because of their presence in numerous biologically active targets such as the antibiotic pentenomycin, the anti‐inflammatory monotropein, and the anticancer compound (−)‐neplanocin A …”