Micronutrients attenuate progression of prostate cancer by elevating the endogenous inhibitor of angiogenesis, platelet factor-4

Abstract

Background: Longstanding evidence implicates an inadequate diet as a key factor in the onset and progression of prostate cancer. The purpose herein was to discover, validate and characterize functional biomarkers of dietary supplementation capable of suppressing the course of prostate cancer in vivo.

Methods: The Lady transgenic mouse model that spontaneously develops prostate cancer received a diet supplemented with a micronutrient cocktail of vitamin E, selenium and lycopene ad libitum. A proteomic analysis was conducted to screen for serum biomarkers of this dietary supplementation. Candidate peptides were validated and identified by sequencing and analyzed for their presence within the prostates of all mice by immunohistochemistry.

Results: Dietary supplementation with the combined micronutrients significantly induced the expression of the megakaryocyte-specific inhibitor of angiogenesis, platelet factor-4 (P = 0.0025). This observation was made predominantly in mice lacking tumors and any manifestations associated with progressive disease beyond 37 weeks of life, at which time no survivors remained in the control group (P < 0.0001). While prostates of mice receiving standard chow were enlarged and burdened with poorly differentiated carcinoma, those of mice on the supplemented diet appeared normal. Immunohistochemical analysis revealed marked amplifications of both platelet binding and platelet factor-4 within the blood vessels of prostates from mice receiving micronutrients only.

Conclusion: We present unprecedented data whereby these combined micronutrients effectively promotes tumor dormancy in early prostate cancer, following initiation mutations that may drive the angiogenesis-dependent response of the tumor, by inducing platelet factor-4 expression and concentrating it at the tumor endothelium through enhanced platelet binding.

Figure 1

Validation and identification of serum PF-4. Serum was harvested from Lady mice receiving either a standard diet (black) (n = 10) or a E/S/L-supplemented diet (red) (n = 10) at the study endpoint (37 weeks). A standard comparison was made using the SELDI-ToF biomarker discovery method. A spectral readout from SELDI-ToF MS between the two groups is presented here in gel-view format with a specific emphasis on the banding pattern related to the peptide candidate with an apparent molecular weight of 8960 Da.

Figure 2

Peptide purification and sequencing. Intensity differences of the bands are reflective of the serum concentrations of the peptide in each mouse. This peptide was later purified and sequenced according to Materials and Methods and identified as murine CXCL4 (PF-4). Contaminating peptides from serum processing and handling are shown as well in the sequencing readout.

Figure 3

Histopathology and immunohistochemistry of platelet binding and PF-4 in prostates of the Lady mouse. Prostate glands from Lady mice receiving either standard diet or an E/S/L-supplemented diet were excised and processed for histomorphology and immunohistochemistry according to Materials and Methods. H&E staining reveals tumor burden with poorly differentiated carcinoma in prostates of mice receiving a standard diet, while a normal prostate architecture is evident in mice receiving an E/S/L-supplemented diet (Panel A, 20× magnification). Distinct intravascular staining for PF-4 is evident in prostates of Lady mice receiving E/S/L compared to that of the control group (red arrows, Panel B-20X and Panel C-40X magnification, respectively). No positive staining for PF-4 is evident in the lymphatics (blue arrows). Distinct intravascular staining for platelets is evident in prostates of Lady mice receiving the test diet compared to that of the control group (red arrows, Panel D-20X magnification). No platelet binding is evident in the lymphatics (blue arrows).