A novel ACTH-inducible P450, cytochrome P450RAP, is responsible for polycyclic aromatic hydrocarbon (PAH) metabolism in male rat adrenal microsomes. P450RAP is present at similar levels in male and female adrenal microsomes and is immunochemically distinct from P450IA1. Anti-P450RAP immunoblots a protein present in ovarian and testicular microsomes that is the same size as P450RAP and which coelutes with the P450 fraction during chromatography on an immobilized artificial membrane column made with phosphatidylcholine. Rat adrenal, ovarian, and testicular microsomes exhibit similar regioselectivities in the metabolism of two polycyclic aromatic hydrocarbons, dimethylbenz(a)anthracene (DMBA) and benzo(a)pyrene (BP). Unlike P450IA1, these microsomes form little or no 7-OH-DMBA and BP-4,5-diol but do catalyze the formation of a high proportion of the presumptive procarcinogen, DMBA-3,4-diol. The relative activities of PAH metabolism by untreated adrenal, testicular, and ovarian microsomes are approximately 60, 20, and 6 pmol/mg microsomal protein/min, respectively. PMSG induced PAH metabolism 2- to 5-fold in ovarian microsomes and also increased the P450RAP immunoblot. Hypophysectomy reduced PAH metabolism 3-fold in testicular microsomes while also decreasing the P450RAP immunoblot. This close correlation between PAH metabolism and expression of P450RAP indicates the involvement of the cytochrome in this activity. DMBA and BP metabolism by PMSG-treated rat ovarian microsomes and untreated testicular microsomes are each completely inhibited by anti-P450RAP but are not inhibited by anti-P450IA1. Essentially all of the PAH metabolism in rat adrenal, testis, and ovary is, therefore, catalyzed by P450RAP, which is hormonally elevated in each tissue by a variety of possible mechanisms, including induction and selective proliferation of cells that express this protein.

Objectives To further elucidate anti-cancer mechanisms of metformin again pancreatic cancer, we evaluated inhibitory effects of metformin on pancreatic tumorigenesis in a genetically-engineered mouse model, and investigated its possible anti-inflammatory and anti-angiogenesis effects. Methods Six-week old LSL-KrasG12D/+;Trp53F2-10 mice (10 per group) were administered once daily intraperitoneally with saline (control) for one week or metformin (125 mg/kg) for one week (Met_1wk) or three weeks (Met_3wk) prior to tumor initiation. All mice continued with their respective injections for six weeks post-tumor initiation. Molecular changes were evaluated by quantitative polymerase chain reaction (PCR), immunohistochemistry, and Western blotting. Results At euthanasia, pancreatic tumor volume in Met_1wk (median, 181.8 mm3) and Met_3wk (median, 137.9 mm3) groups was significantly lower than the control group (median, 481.1 mm3) (P = 0.001 and 0.0009, respectively). No significant difference was observed between Met_1wk and Met_3wk groups (P = 0.51). These results were further confirmed using tumor weight and tumor burden measurements. Furthermore, metformin treatment decreased the phosphorylation of nuclear factor κB (NFκB) and signal transducer and activator of transcription 3 (STAT3) as well as the expression of Sp1 transcription factor and several NFκB-regulated genes. Conclusions Metformin may inhibit pancreatic tumorigenesis by modulating multiple molecular targets in inflammatory pathways.

The steroidogenic acute regulatory protein (STAR) participates in steroidogenesis through the mitochondrial transfer of cholesterol to cytochrome P450scc. The rat adrenal Star gene is transcribed as a 3.5-kilobase pair (kb) and 1.6-kb mRNA with the larger mRNA predominating (ϳ85% of total) in vivo. Hypophysectomy (HPX) produced a 3-5-fold decrease in Star mRNA along with a loss of adrenal steroids, whereas P450scc mRNA decreased by less than 2-fold.

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