“Porphyrin uptake in lung cancer cells by dynamin-mediated endocytosis: a novel marker of dysregulated endocytosis in cancer”

American Society of Cell Biology Annual Meeting, December 2015

D. Elzi, PhD, UTHSCSA; P. Fatland, UTHSCSA; B. Karia, PhD, bioAffinity; M. Iza, MD, UTHSCSA; A. Pertsemlidis, PhD, UTHSCSA; V. Rebel, MD, PhD, UTHSCSA
Porphyrins are dynamic molecules involved in many biological processes, including oxygen and electron transport. Porphyrins have also been known to incorporate more readily into cancer cells compared to non-cancerous cells, and this property of porphyrins is being explored for diagnostic and therapeutic applications in cancer patients. The mechanism of how porphyrins are selectively incorporated into cancer cells is poorly understood, but the literature suggests that dysregulated endocytotic pathways may be a mechanism for porphyrin uptake. In addition, previous studies have suggested that porphyrins interact with the low-density lipoprotein receptor (LDLR) to incorporate into cells. We have examined the mechanism of incorporation of the porphyrin tetrakis(4-carboxyphenyl)porphyrin (TCPP) in lung cancer cells. We hypothesized that TCPP uptake in lung cancer cells is mediated by an endocytotic pathway through the LDLR.

We analyzed TCPP uptake by flow cytometry in a panel of human lung cancer cell lines, including, HCC15, H157, and H358, while manipulating clathrin-dependent and independent endocytosis by chemical inhibitors. We found that sucrose and cold temperature moderately inhibited TCPP uptake in lung cancer cells. The dynamin inhibitor chlorpromazine, an antagonist of clathrin-mediated endocytosis, inhibited TCPP uptake by up to 80%, while the clathrin-independent endocytosis inhibitor filipin had no effect on TCPP uptake. To examine LDLR contribution on TCPP uptake, we pre-treated lung cancer cells with an anti-LDLR neutralizing antibody, which reduced TCPP uptake by 20%. Interestingly, TCPP uptake in human fibroblasts with or without functional LDLR showed no significant difference. These data suggest additional receptors and/or mechanisms are involved in TCPP uptake. In summary, our results show that the porphyrin TCPP is incorporated into lung cancer cells by a dynamin-mediated endocytotic pathway. Studies are underway to discover additional mediators of porphyrin uptake in these cancer cells. TCPP may provide a novel marker for monitoring dysregulated endocytosis in lung cancer and other cancers.