S4-1.7 Jan. 5 Biological stoichiometry of tumors: a test of the growth rate hypothesis using paired biopsy samples of human tumors ELSER, JJ*; KYLE, M; SMITH, M; NAGY, J; Arizona State University; Arizona State University; University of Kansas Medical School; Scottsdale Community College email@example.com
The growth rate hypothesis proposes that there is a mechanistic association between growth rate and biological P requirement because increased growth rates generally require increased allocation to P-rich ribosomal RNA. This hypothesis has received wide support in previous physiological, ontogenetic, and inter-specific comparisons involving diverse biota from bacteria to fruitflies. Here we extend the hypothesis to the case of human cancer, as cancer usually results from accelerated proliferation of clonal cells. We determined the elemental composition and RNA/DNA contents of paired tumor and normal tissues for four organs (colon/rectum, liver, kidney, pancreas) using samples obtained via the NIH tumor tissue procurement network. Consistent with the growth rate hypothesis, tumor tissues had significantly higher P contents (% of dry weight) than paired normal tissues. RNA and DNA contents were also generally higher for tumor tissues and there were significant associations of P content with RNA content and with total nucleic acid content. However, the absolute magnitude of the contribution of P in RNA to overall P content (~10%) was relatively low compared to previous studies (~50%). This suggests that either our RNA determination method underestimates tumor RNA or that there is another pool of P-rich molecules at increased allocation in tumor cells. Our results suggest that tumor cells may be poor competitors for circulating P in the body and may be at a disadvantage, relative to normal tissues, if P supplies are limiting.