The PI3/Akt/mTOR kinase signaling pathway is a major signaling pathway in eukaryotic cells, and dysregulation of this
signaling pathway has been implicated in tumorigenesis and malignancy in several cancers including prostate cancer.
We assessed the effects of combination PI3K pathway inhibition on the efficacy of PDT in human prostate tumor cell
line (PC3) and SV40-transformed mouse endothelial cell line
(SVEC-40). Combination of PDT and BEZ 235 (BEZ), a
pan-PI3/ mTOR kinase inhibitor additively enhanced efficacy of
sub-lethal PDT in both cell lines. The combination of
the pan-PI3/ mTOR kinase inhibitor LY294002 (LY) with PDT also enhanced efficacy of PDT in PC3 in an additive
manner but synergistically in SVEC. In order to determine the mechanism of enhancement of efficacy, we assessed
apoptosis and autophagy following PDT. PDT-mediated apoptosis was enhanced in endothelial cells, by both BEZ and
LY rapidly after treatment. Compared to SVEC, PC3 cells are
apoptosis-deficient and apoptosis was not significantly
enhanced by either LY or BEZ. However, lethal PDT of PC3 cells induced a delayed autophagic response which may be
enhanced by combination, depending on PI3K inhibitor and dose.
Vascular targeting photodynamic therapy (vPDT) is currently in clinical trial for prostate cancer (PCa)
treatment. In order to study the effect of vPDT on tumor metastasis, GFP-PC3 or PC-3 xenografts were
treated with verteporfin (BPD) PDT. Vascular function was assessed by ultrasound imaging; lymph node and
lung metastasis were assessed by fluorescence imaging. vPDT significantly reduced tumor blood flow within
30minutes to 2 hours of treatment. Sub-curative treatment resulted in re-perfusion within 2 weeks of treatment
and increased lymph node metastasis. With curative doses, no metastasis was observed.
In order to identify cellular or matrix factors and cytokines implicated, conditioned medium from BPD PDTtreated
endothelial cells was incubated with PC3 cells in vitro. Tumor cell proliferation and migration was
assessed. By immunoblotting, we evaluated the change in mediators of intracellular signaling or that may
determine changes in tumor phenotype. Low sub-curative dose (200ng/ml BPD) of endothelial cells was
associated with ~15% greater migration in PC3 cells when compared with control. This dose was also
associated with sustained activation of Akt at Ser 473, an upstream effector in the Akt/ mTOR pathway that
has been correlated with Gleason scores in PCa and with survival and metastasis in vitro and in vivo. In
conclusion, the study implicates efficacy of PDT of endothelial cells as an important determinant of its
consequences on adjacent tumor proliferation and metastasis.
Tumor vasculature is an attractive target for cancer therapy due to its accessibility to blood-borne therapeutic agents and
the dependence of tumor cells on a functional blood supply for survival and growth. Vascular targeting photodynamic
therapy (vPDT) is a novel modality based on the selective laser light activation of photosensitizers localized inside tumor
vasculature to shutdown tumor vascular function. Although this vascular targeting therapy is showing great promise for
cancer treatment, tumor recurrence has been observed in both preclinical and clinical studies. In this study, we intend to
enhance the therapeutic outcome of vascular targeting PDT by combining it with combretastatin A4 phosphate (CA4P), a
blood flow inhibitor. We found that the combination of CA4P and vPDT significantly increased endothelial cell
apoptosis than each single therapy. Western blot analysis suggests that myosin light chain kinase (MLCK) is a common
target of CA4P and vPDT. In a PC-3 prostate tumor model, we found that CA4P was able to greatly enhance tumor
response to vPDT. These results demonstrate that CA4P and vPDT can be combined to enhance the therapeutic effect.
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