PDT for Neovasculature

A number of diseases such as cancer and age-related macular degeneration (AMD), the leading cause of blindness, are closely related to angiogenesis, or the formation of new blood vessels.  Tumors are highly vascularized, and their growth is dependent on angiogenesis.  Similarly, macular degeneration occurs when new blood vessels grow inappropriately behind the retina.  Angiogenesis is regulated by the growth factor VEGF, and this growth factor is the target of many new treatments for cancer and AMD.

Conventional cancer treatments such as radiotherapy, chemotherapy, and photodynamic therapy (PTD) often control a tumor locally but raise the rate of metastasis.  It seems that cancer cells damaged but not killed by cancer therapy fight for life by secreting growth factors such as VEGF and by sometimes detaching from the original tumor.  It has been shown that the rate of metastasis after PTD is significantly reduced if PDT is delivered along with an anti-VEGF agent.  The effectiveness of PTD alone is also limited for AMD because revascularization behind the retina occurs relatively frequently, most likely because of VEGF.  Blocking VEGF in the eye after PTD has been shown to limit revascularization.

The current method of blocking VEGF is to intravenously deliver an anti-VEGF antibody known as Avastin or bevacizumab.  This approach seems promising, but so far, it has not been as successful as many people hoped.  It seems that the timing and delivery of Avastin need to be improved.  Studies have shown the effectiveness of Avastin depends on when it is delivered.  Researchers are also investigating ways to deliver Avastin and photosensitive drugs within nanoparticles.  It is hoped that this approach will increase the effectiveness of PTD. 

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