Inositol trisphosphate (ITPP) causes normalization of tumor vasculature and is a particularly effective cancer therapy when a second chemotherapeutic agent is administered following partial vascularization. ITPP also treats, alone or in combination, multi-drug resistant cancers. ITPP can also be used to reduce the amount of a second chemotherapeutic drug required for anticancer activity. In addition, ITPP enhances immune response and treats hyperproliferative disorders.