Abstract: Constructs comprising pH low insertion peptide and variants thereof conjugated to monomethyl auristatins and analogs thereof are described. These constructs are useful, for example, in the treatment of solid tumors, including the treatment of breast cancer and prostate cancer, as well as other cancers such as pancreatic cancer, ovarian cancer, cervical cancer, uterine cancer, lung cancer, skin cancer, kidney cancer, and colon cancer. The constructs inhibit tumor cell proliferation and reduce tumor volume, particularly in a low pH tumor environment.