NOS2 and neoplasm: Administration of 1400 W or GW274150 during this period slowed growth even further, consistent with iNOS/NO-dependent resistance; a light-only control was unresponsive to 1400 W. Immunoblot and NO analyses on post-PDT samples revealed a progressive increase in iNOS expression and NO output, each response reaching 5–6-fold over starting level at 6 h post-PDT; thus, in addition to stimulating resistance, NO from overexpressed iNOS after a PDT challenge acted in tumor-supporting fashion, with pre-existing iNOS/NO having no significant effect.