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Breast cancer (BCA) is the most frequently diagnosed cancer in women, with distant metastases to lung, liver, bone and skin occurring in approximately 40% of cases. Radiation therapy (RT) has been successfully employed for the treatment of BCA; however, multiple rounds of RT are associated with undesirable cutaneous side effects. This study explores PDT as a therapeutic alternative, to be given alone or in combination with RT and chemotherapy. Earlier, we had developed differentiation-enhanced combination photodynamic therapy (cPDT) using a neoadjuvant (5-fluorouracil; 5FU) prior to PDT. The neoadjuvant increases the levels of PpIX, leading to better efficacy following aminolevulinate (ALA)- based PDT. Here, to avoid the toxicity of systemic 5FU, we used a nontoxic 5FU precursor (Capecitabine; CPBN) in a new cPDT regimen. CBPN, a standard chemotherapeutic for BCA, is metabolized to 5FU specifically within tumor tissue. Murine (4T1) BCA cells were injected into breast fat pads of nude mice. CPBN was administered by oral gavage followed by intraperitoneal ALA and red light for PDT. CPBN pretreatment of 4T1 tumors led to increased tumor cell differentiation (3.5 fold), homogenous elevation of intratumoral PpIX levels (4.5 fold), and enhanced tumor cell death post-PDT (5 fold), relative to vehicle control. Using an in vivo imaging system (IVIS), a decline in tumor growth following CPBN-PDT was observed. Results showing the effect of CPBN-PDT on distant metastases of BCA to lung, lymph nodes and skin will be presented. In summary, CPBN-PDT, a novel combination approach, has a significant potential for translation into the clinic.
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