| Summary: | A proportion of patients with osteoporosis, Paget’s disease and bone associated cancers show no reduction in disease-indicating markers after treatment with N-BPs, and resistance to bisphosphonates has been documented . We have examined whether polymorphic or isoforms variation in the FPPS gene could influence the ability of N-BPs to inhibit this enzyme and affect the clinical response to treatment. Sequencing revealed a novel (T→C) polymorphism in exon 11, resulting in an amino acid change from Val 364 to A1a (V364A), with an allele frequency of 0.08 for the C allele and 0.92 for the T allele. Kinetic values for isoprenoid substrates GPP and IPP were found to be similar to previously published values. Enzymes did not differ in the IC50 values for inhibition by the N-BPs risedronate, pamidronate, alenodonate, ibandronate and zoledronate. Splice variant analysis revealed the presence of two distinctly spliced and targeted isoforms of FPPS. Overexpression plasmids containing the different isoforms of FPPS were used to elucidate the intracellular localisation of the different isoforms. Furthermore, polyclonal antiserum was produced to use as a specific tool for detection of FPPS. Detection and co-localisation of the peroxisomally targeted isoform of FPPs with the peroxisomes was shown 48h post-transfection, while the mitochondrially targeted isoform of FPPS was undetectable. Overexpression of the cytosolic or peroxisomal isoform of FPPS was unable to induce resistance to N-BPs, even though it has been shown that overexpression of FPPS is in part responsible for the induction of resistance to N-BPs.
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