Elevated Phospholipase A2 Activities in Plasma Samples from Multiple Cancers.

Only in recent years have phospholipase A2 enzymes (PLA2s) emerged as cancer targets. In this work, we report the first detection of elevated PLA2 activities in plasma from patients with colorectal, lung, pancreatic, and bladder cancers as compared to healthy controls. Independent sets of clinical plasma samples were obtained from two different sites. The first set was from patients with colorectal cancer (CRC; n = 38) and healthy controls (n = 77). The second set was from patients with lung (n = 95), bladder (n = 31), or pancreatic cancers (n = 38), and healthy controls (n = 79). PLA2 activities were analyzed by a validated quantitative fluorescent assay method and subtype PLA2 activities were defined in the presence of selective inhibitors. The natural PLA2 activity, as well as each subtype of PLA2 activity was elevated in each cancer group as compared to healthy controls. PLA2 activities were increased in late stage vs. early stage cases in CRC. PLA2 activities were not influenced by sex, smoking, alcohol consumption, or body-mass index (BMI). Samples from the two independent sites confirmed the results. Plasma PLA2 activities had approximately 70% specificity and sensitivity to detect cancer. The marker and targeting values of PLA2 activity have been suggested

Plk1 Phosphorylation of Orc2 and Hbo1 Contributes to Gemcitabine Resistance in Pancreatic Cancer

Although gemcitabine is the standard chemotherapeutic drug for treatment of pancreatic cancer, almost all patients eventually develop resistance to this agent. Previous studies identified Polo-like kinase 1 (Plk1) as the mediator of gemcitabine resistance, but the molecular mechanism remains unknown. In this study, we show that Plk1 phosphorylation of Orc2 and Hbo1 mediates the resistance to gemcitabine. We show that the level of Plk1 expression positively correlates with gemcitabine resistance, both in pancreatic cancer cells and xenograft tumors. Overexpression of Plk1 increases gemcitabine resistance, while inhibition of Plk1 sensitizes pancreatic cancer cells to gemcitabine treatment. To validate our findings, we show that inhibition of Plk1 sensitizes tumors to gemcitabine treatment in a mouse xenograft study. Mechanistically, we find that Plk1 phosphorylation of Orc2 maintains DNA replication on gemcitabine treatment. Furthermore, Plk1 phosphorylation of Hbo1 transcriptionally increases cFos expression and consequently elevates its target multidrug resistance 1 (MDR1), which was previously reported to confer chemotherapeutic drug resistance. Knockdown of cFos or MDR1 sensitizes gemcitabine-resistant cells to gemcitabine treatment. Finally, pancreatic cancer cells expressing Plk1-unphosphorylatable mutants of Orc2 or Hbo1 are more sensitive to gemcitabine than cells expressing wild-type Orc2 or Hbo1. In short, our study provides a mechanism for Plk1-mediated gemcitabine resistance, suggesting that Plk1 is a promising target for treatment of gemcitabine-resistant pancreatic cancer

Clinical characteristics and PLA₂ activities in the CRC cases.

*<p>Student <i>t</i>-test.</p>**<p>One-way ANOVA.</p><p>CT: chemotherapy; RT: radiotherapy.</p

Demographic data for participants from IUSM and HOG study.

<p>CRC: colorectal cancer; LC: Lung cancer; BC: Bladder cancer; PC: Pancreatic cancer; SD, standard deviation; HOG: Hoosier Oncology Group.</p><p>In the HOG set: • For gender, the overall <i>P</i> value is 0.0339. • For Age, the overall <i>P</i> value is <0.0001. • For race, the overall <i>P</i> value is 0.2352. Since it was not significant, it was not recommended to perform pair-wise comparisons. Nonetheless, <i>P</i> values for pair-wise comparisons are given to be consistent with the other two variables. All pair-wise comparisons are against healthy controls.</p

ROC curves of plasma PLA₂ activities with additional parameters.

<p>CRC cases vs. healthy subjects. A. All cancer cases vs. healthy subjects in the second set. B. Lung cancer vs. healthy subjects. C. Bladder cancer vs. healthy subjects. D. Pancreatic cancer vs. healthy subjects. E. All cancers vs. all healthy subjects with combined two sets.</p

ROC curves of plasma PLA₂ activities in different groups.

<p>CRC cases vs. healthy subjects. A. All cancers vs. healthy subjects in the 2nd set. B. Lung cancer vs. healthy subjects. C. Bladder cancer vs. healthy subjects. D. Pancreatic cancer vs. healthy subjects. E. All cancers vs. all healthy subjects with combined two sets.</p

Smoking and alcohol consumption status of participants from HOG study.

<p>LC: Lung cancer; BC: Bladder cancer; PC: Pancreatic cancer.</p><p>All <i>P</i> values are comparisons between the cancer group and the healthy group.</p

Comparison of PLA₂ activities among different BMI groups.

<p>The subjected in healthy and CRC groups were divided into two groups: BMI 18.5 to <25 (For all subjects, n = 43) and BMI>25 (For all subjects, n = 80). A. The subjected in healthy and other cancer groups were divided into two groups: BMI≤25 (For all subjects, n = 80) and BMI>25 (For all subjects, n = 148).</p

Comparison of two independent sets of healthy controls.

<p>Comparison of two independent sets of healthy controls.</p