Usefulness of platelet-derived growth factor as a prognostic factor in pulmonary adenocarcinoma

PDGFRα expression as a novel therapeutic marker in well-differentiated neuroendocrine tumors

AIMS

To evaluate the biological significance of dense vascular networks associated with low-grade NENs, we assessed the impact of PDGFRα tissue expression in 77 GEP/NEN patients, associating PDGFRα expression with the morphological characterization in low-grade tumors.

METHODS AND RESULTS

Paraffin-embedded specimens of 77 GEP- NEN tissues, collected from January 2006 to March 2018, were evaluated for PDGFRα tissue expression and correlations with clinicopathological characteristics. PDGFRα tissue expression was significantly correlated with grade and the NEN growth pattern (p < 0.001) but not with gender, primary site or lymph nodes metastatic status. PDGFRα staining was mainly localized in the vascular pole of the neuroendocrine cells and in Enterochromaffin (EC) cells. In particular PDGFRα tissue expression was significantly more expressed in G2 (p < 0.001) than G1 and G3 cases (p 0.004; p < 0.0002;) and correlated with an insular growth pattern. PDGFRα tissue expression was associated with the Ki67 index and we found a significant negative trend of association with the Ki67 proliferation index (P < 0.001): thus PDGFRα expression is referred to morphological and not to proliferative data.

CONCLUSIONS

PDGFRα represents an effective target for new anti-angiogenic treatment in WD- GEP-NENs, in particular in G2 cases, and in G3 cases only when there is a mixed insular-acinar pattern. In this context, it is important to carefully delineate those tumors that might better respond to this type of treatment alone or in combination. Further investigation of the relationship between PD-L1 and PDGFRa is warranted, and may contribute to optimize the therapeutic approach in patients with GEP-NENs.

Targeting the PDGF signaling pathway in tumor treatment

Platelet-derived growth factor (PDGF) isoforms and PDGF receptors have important functions in the regulation of growth and survival of certain cell types during embryonal development and e.g. tissue repair in the adult. Overactivity of PDGF receptor signaling, by overexpression or mutational events, may drive tumor cell growth. In addition, pericytes of the vasculature and fibroblasts and myofibroblasts of the stroma of solid tumors express PDGF receptors, and PDGF stimulation of such cells promotes tumorigenesis. Inhibition of PDGF receptor signaling has proven to useful for the treatment of patients with certain rare tumors. Whether treatment with PDGF/PDGF receptor antagonists will be beneficial for more common malignancies is the subject for ongoing studies.

Platelet-derived growth factor (subtype BB) is elevated in patients with colorectal carcinoma

PURPOSE

Platelet-derived growth factor-BB plays a role in the development of vascular and lymphatic vessels in tumors. In this study plasma levels of platelet-derived growth factor-BB were assessed preoperatively in patients with adenomas and colorectal cancer to determine whether platelet-derived growth factor-BB is a useful marker or prognostic indicator.

METHODS

Patients with adenomas and colorectal cancer undergoing resection were assessed. Clinical and pathologic data and preoperative blood samples were collected. Plasma platelet-derived growth factor-BB levels (median, 95 percent confidence interval for median) were determined and the Kruskal-Wallis test and Mann-Whitney U test were used for analysis.

RESULTS

One hundred seventy-nine patients were studied (91 with colorectal cancer, 88 with adenomas). Preoperative colorectal cancer platelet-derived growth factor-BB levels were higher (1,771.1 pg/ml; confidence intervals, 1,429-2,065) than in the benign neoplasm group (1083 pg/ml; confidence intervals, 933-1,192, P < 0.001). In patients with colorectal cancer, a direct relationship was noted between platelet-derived growth factor-BB levels and disease severity. Despite the increase in platelet-derived growth factor-BB noted with increasing stage, the differences between the Stages 1, 2, 3, and 4 groups were not significant.

CONCLUSION

Platelet-derived growth factor-BB levels were greater in patients with colorectal cancer (vs. patients with adenoma) and rose with increasing disease severity. Unfortunately, however, the modest differences between categories do not permit accurate stage determination.

Serum PDGF-AB in pleural mesothelioma

Overexpression of platelet-derived growth factor (PDGF) has been observed in lung and pleural tumors. The aim of this study was to evaluate the diagnostic and prognostic role of serum PDGF in pleural mesothelioma (PM). Four groups of subjects were studied: 93 malignant PM patients, 33 primary non small cell lung cancer patients, 51 subjects exposed to asbestos, defined as high-risk controls, and 24 healthy controls. PDGF-AB mean concentration was higher in PM patients (45.8 ng/ml) than in high-risk controls (33.1 ng/ml) and healthy controls (26.8 ng/ml). Using the cut-off level of 49.8 ng/ml, corresponding to the mean+2SD of PDGF-AB in healthy controls, 43% of PM patients showed positive PDGF-AB levels. Survival was evaluated in 82 PM patients. At the end of the follow-up (median 9.8 months) 80.5% of patients had died. Median survival was 13.1 and 7.9 months for patients with PDGF-AB lower and higher than the cut-off, respectively. Adjusting for age, sex, histology and platelet count, positive PDGF-AB levels were associated with lower survival (OR=1.2, 95%CI: 0.9-1.6), even if not significantly so. In conclusion, serum PDGF may represent a useful additional parameter to prognostic factors already available for PM.

Activation of tyrosine kinases in cancer

Receptor and nonreceptor tyrosine kinases (TKs) have emerged as clinically useful drug target molecules for treating certain types of cancer. Epidermal growth factor receptor (EGFR)-TK is a transmembrane receptor TK that is overexpressed or aberrantly activated in the most common solid tumors, including non-small cell lung cancer and cancers of the breast, prostate, and colon. Activation of the EGFR-TK enzyme results in autophosphorylation, which drives signal transduction pathways leading to tumor growth and malignant progression. Randomized clinical trials of the EGFR-TK inhibitor gefitinib have demonstrated clinical benefits in patients with advanced non-small cell lung cancer whose disease had previously progressed on platinum- and docetaxel-based chemotherapy regimens. Bcr-Abl is a constitutively activated nonreceptor TK enzyme found in the cytoplasm of Philadelphia chromosome-positive leukemia cells. STI571 (imatinib mesylate) inhibits the Bcr-Abl TK, blocks the growth of these leukemia cells, and induces apoptosis. STI571 also inhibits other TKs, including the receptor TK c-kit, which is expressed in gastrointestinal stromal tumors. As TK inhibitors become available for clinical use, new challenges include predicting which patients are most likely to respond to these targeted TK inhibitors. Additional clinical trials are needed to develop the full potential of receptor and nonreceptor TK inhibitors for cancer treatment.

Activation of Stat3 by receptor tyrosine kinases and cytokines regulates survival in human non-small cell carcinoma cells

Overexpression of receptor tyrosine kinases including the epidermal growth factor receptor (EGF-R) as well as nonreceptor tyrosine kinases, such as Src, have been implicated in the formation of human lung cancers. In addition, cytokines like interleukin-6 (IL-6) have been demonstrated to modulate lung cancer cell growth and elevated levels of IL-6 have been shown to be an adverse prognostic factor for patients with lung cancer. Despite a large body of evidence pointing to their potential importance, few direct studies into the role of signal transducers and activators of transcription (STAT) pathways in human lung cancer have been undertaken. Here we demonstrate that multiple nonsmall cell lung cancer cell lines demonstrate constitutive Stat3 DNA-binding activity. Stat3 DNA-binding activity is specifically upregulated by the addition of epidermal growth factor (EGF), IL-6, and hepatocyte-derived growth factor (HGF). Furthermore, the stimulation of Stat3 DNA-binding activity by EGF requires the activity of EGF-R tyrosine kinase as well as Src-kinase, while the upregulation of Stat3 activity by IL-6 or HGF requires only Src-kinase activity. Treatment of A549 lung cancer cells with PD180970 or SU6656, both pharmacological inhibitors of Src-kinase, resulted in reduced Src and Stat3 activity, cell cycle arrest in G2, and reduced viability of cells accompanied by induction of apoptosis. Treatment of Stat3-positive A549 and H358 cells with antisense Stat3 oligonucleotides results in complete loss of Stat3 DNA-binding activity and apoptosis, while Stat3-positive H1299 cells remained healthy. Finally, an adenoviral vector expressing a dominant-negative Stat3 isoform results in loss of Stat3 DNA-binding activity, apoptosis, and reduced cellular viability. These results demonstrate a role of Stat3 in transducing survival signals downstream of tyrosine kinases such as Src, EGF-R, and c-Met, as well as cytokines such as IL-6, in human nonsmall cell lung cancers.

Prognostic value of platelet-derived growth factor-A (PDGF-A) in gastric carcinoma

OBJECTIVE

Because our previous study indicated that PDGF-A mRNA expression in biopsy specimens might identify a subgroup of high-risk patients with gastric carcinoma, in this study we analyzed the prognostic value of platelet-derived growth factor-A (PDGF-A) gene expression in gastric carcinoma biopsy specimens.

METHODS

Reverse transcriptase-polymerase chain reaction (RT-PCR) was used to analyze the PDGF-A gene expression in 65 gastric carcinoma endoscopic biopsy specimens. The 65 patients were divided into a PDGF-A-positive group (29 patients) and a PDGF-A-negative group (36 patients).

RESULTS

On the basis of 2-year follow-up data, the PDGF-A-positive group demonstrated a shorter overall survival rate compared with the PDGF-A-negative group (p < 0.0001). A similar correlation was found in 34 advanced-stage patients (p = 0.003) and in 24 advanced-stage patients who underwent a curative resection (p = 0.003). Multivariance analysis indicated that the transcription of PDGF-A gene is a potent prognostic factor that is independent of the traditional pathologic parameters.

CONCLUSIONS

Expression of PDGF-A mRNA in gastric biopsy specimens may be a new preoperative prognostic parameter in gastric carcinoma.

Growth factor PDGF-B/v-sis confers a tumorigenic phenotype to human tumor cells bearing PDGF receptors but not to cells devoid of receptors: evidence for an autocrine, but not a paracrine, mechanism

Numerous established human tumor lines co-express platelet-derived growth factor (PDGF) and cognate receptors, suggesting that an autocrine and/or paracrine growth mechanism may be a causal or contributing mechanism to their transformed phenotype. Indeed, it is known that a PDGF-autocrine system is functional in several established tumor lines, especially in human gliomas, and a model for a functional paracrine mechanism has been established in a human melanoma line. However, at least 168 human cell lines representing 26 different human tumor types have been reported to continuously express PDGF-A and/or -B chains, and 55 of these also express PDGF receptors. For the majority of these cases, the significance of co-expression and the relative roles of autocrine and paracrine mechanisms in transformation remains unclear. Here, we show that human glioblastoma T98G cells co-express PDGF-B/c-sis and moderate levels of the cognate beta-type PDGF receptor (PR-beta) but are not tumorigenic in athymic mice. In contrast, human breast carcinoma MCF-7 cells do not express PR-beta and are tumorigenic. Clonal lines of each cell type with greatly increased secretion of p16w(T98Gsis and MCF-7sis cells) were characterized. T98Gsis cells are 85% tumorigenic and occasionally develop pulmonary metastases, showing that endogenous PR-beta can mediate complete transformation upon sufficient stimulation. In contrast, MCF-7sis cells exhibit some growth slowing in vitro and an exactly proportional decrease in tumor growth rate. We conclude that a PDGF-autocrine, and not a paracrine, mechanism best accounts for the acquired tumorigenicity of T98Gsis cells, thereby emphasizing the potential significance of expression of even moderate levels of PR-beta by human tumor cells.