Loeb, Lawrence

The major focus of our research is the relationship between mutations and human cancer. We wish to identify the sources of spontaneous mutations in normal cells and whether there is an exponential increase in mutations during the growth of human cancers. Do cancer cells display a mutator phenotype and is this phenotype the basis for the progressive ability of tumors to divide where they ought not, to invade and to metastasize? Our current research efforts are in: Fidelity of DNA Replication: We are continuing to measure the mechanism(s) by which DNA polymerases can copy DNA with phenomenally high accuracy, approaching one error in every 10^7 nucleotides polymerized. Our approach is to copy biologically active DNA in vitro and then analyze the frequency and types of mutations generated after transfection of the copied DNA into cells. An analysis of mutations produced by polymerases is key to evaluating the contribution of errors in DNA replication to spontaneous mutations. Our goal is to reconstruct a human DNA replication system that accurately copies DNA, and then ask whether and how this system is defective in cancer cells.

HIV Reverse Transcriptase: We have extended the study on DNA polymerization to the reverse transcriptase in the AIDS virus and to yeast. The exceptionally high error rate of HIV reverse transcriptase in copying both RNA and DNA templates suggests that this enzyme is responsible for the hypervariability of the AIDS virus and provides a basis for the design of antiviral nucleosides.

Our studies on HIV indicate that the incorporation of mutagenic nucleoside analogs can be used to increase the mutation frequency of the virus leading to an error catastrophy with the obliteration of the viral population. We now asked if a similar approach can be used to preferentially kill malignant cells.