Targeting platelet-derived growth factor receptor on endothelial cells of multidrug-resistant prostate cancer.
BACKGROUND
Inhibiting phosphorylation of platelet-derived growth factor receptor (PDGFR) by treatment with the PDGFR kinase inhibitor imatinib and the chemotherapeutic agent paclitaxel reduces the incidence and size of human prostate cancer bone lesions in nude mice. Because tumor cells and tumor-associated endothelial cells express activated PDGFR, the primary target for imatinib has been unclear.


METHODS
We selected multidrug-resistant human PC-3MM2 prostate cancer cells (termed PC-3MM2-MDR cells) by culturing them in increasing concentrations of paclitaxel. PC-3MM2-MDR cells were implanted into one tibia of 80 nude mice. Two weeks later, the mice were randomly assigned to receive distilled water (control group), paclitaxel, imatinib, or imatinib plus paclitaxel for 10 weeks (20 mice per group). Tumor incidence and weight, bone structure preservation and osteolysis, and the incidence of lymph node metastasis were determined. The phosphorylation status of PDGFR on tumor cells and tumor-associated endothelial cells and levels of apoptosis were examined with immunohistochemical analyses. Microvessel density was assessed as the number of cells expressing CD31/platelet endothelial cell adhesion molecule 1 (PECAM-1). All statistical tests were two-sided.


RESULTS
PC-3MM2-MDR cells were resistant to paclitaxel and imatinib in vitro. Treatment of implanted mice with imatinib plus paclitaxel led to statistically significant decreases in bone tumor incidence (control = 19 mice with tumors of 19 mice total; imatinib plus paclitaxel = four of 18 mice; P < .001), median tumor weight (control = 1.3 g, interquartile range [IQR] = 1.0-1.9; imatinib plus paclitaxel = 0.1 g, IQR = 0-0.3; P < .001), bone lysis, and the incidence of lymph node metastasis (control = 19 of 19 mice total; imatinib plus paclitaxel = three of 18 mice; P < .001). Treatment with imatinib alone had similar effects, and imatinib treatment also inhibited phosphorylation of PDGFR on tumor cells and tumor-associated endothelial cells and increased the level of apoptosis of endothelial cells, but not tumor cells. Treatment with imatinib and more so with imatinib and paclitaxel decreased mean vessel density (three CD31/PECAM-1-positive cells, 95% confidence interval [CI] = 0 to 9; and control group = 38 CD31/PECAM-1-positive cells, 95% CI = 17 to 59) (P < .001), which was followed by apoptosis of tumor cells.


CONCLUSIONS
Tumor-associated endothelial cells, rather than tumor cells themselves, appear to be the target for imatinib in prostate cancer bone metastasis.
Kim
Sun-Jin
SJ
Department of Cancer Biology, The University of Texas M. D. Anderson Cancer Center, Houston, TX 77030, USA.
Uehara
Hisanori
H
Yazici
Sertac
S
Busby
Joseph Erik
JE
Nakamura
Toru
T
He
Junqin
J
Maya
Marva
M
Logothetis
Christopher
C
Mathew
Paul
P
Wang
Xuemei
X
Do
Kim-Anh
KA
Fan
Dominic
D
Fidler
Isaiah J
IJ
D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology*; D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects; D001549:Benzamides; D015153:Blotting, Western; D001859:Bone Neoplasms / Q000098:blood supply / Q000737:chemistry / Q000517:prevention & control* / Q000556:secondary*; D018432:Drug Resistance, Multiple; D019008:Drug Resistance, Neoplasm; D042783:Endothelial Cells / Q000187:drug effects* / Q000378:metabolism; D005455:Fluorescent Antibody Technique; D006801:Humans; D000068877:Imatinib Mesylate; D007150:Immunohistochemistry; D020287:In Situ Nick-End Labeling; D008207:Lymphatic Metastasis / Q000517:prevention & control; D008297:Male; D051379:Mice; D008819:Mice, Nude; D008833:Microcirculation / Q000187:drug effects; D009368:Neoplasm Transplantation; D009389:Neovascularization, Pathologic / Q000517:prevention & control; D017239:Paclitaxel / Q000494:pharmacology*; D010766:Phosphorylation / Q000187:drug effects; D010879:Piperazines / Q000494:pharmacology*; D011471:Prostatic Neoplasms / Q000188:drug therapy* / Q000473:pathology*; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors; D011743:Pyrimidines / Q000494:pharmacology*; D011897:Random Allocation; D017479:Receptors, Platelet-Derived Growth Factor / Q000037:antagonists & inhibitors; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013977:Tibia / Q000187:drug effects / Q000473:pathology; D014407:Tumor Cells, Cultured
D000970:Antineoplastic Agents; D000972:Antineoplastic Agents, Phytogenic; D001549:Benzamides; D010879:Piperazines; D047428:Protein Kinase Inhibitors; D011743:Pyrimidines; D000068877:Imatinib Mesylate; D011505:Protein-Tyrosine Kinases; D017479:Receptors, Platelet-Derived Growth Factor; D017239:Paclitaxel