DHFR and cancer: We would also like to thank Dr. Paul A. Spengler (University of Rochester) and Dr. Margot Ip (Roswell Park Cancer Institute – RPCI, Buffalo, NY) for critically reading and revising the manuscript, and Dr. Lili Tian (SUNY at Buffalo/RPCI) for acting as a statistics consultant, Dr. Bruce Dolnick (RPCI) for providing the DHFR antibody, Dr. Allen C. Gao (University of California, Davis), Dr. Daniel Chan (University of Colorado, Denver, CO) and Dr. Kunle Odunsi (RPCI) for providing several cancer cell lines, and Dr. Dario C. Altieri (Wistar Institute Cancer Center) for the pcDNA3-XIAP vector.