The invention relates to novel cyclic compounds (cyclic peptides), linkers useful as beta-turn promoters in cyclic peptides, and methods for treatment of malignant cells in vitro or in vivo using one or more linear and cyclic peptides. The peptides can act as integrin interaction inhibitors and may be used in the treatment of cancers as monotherapies or in combination with other anti-cancer agents, such as proteasome inhibitors, inhibitors of autophagy, alkylating agents, MEK inhibitors, FAK/PYK2 inhibitors, and EGFR inhibitors. The invention further concerns a method of predicting the binding of a cyclic or linear HYD1 peptide to a cancer cell by assessing overexpression of biomarkers such as CD44, VLA-4 integrin, basigin, CD138 (syndecan 1), NCAM, ICAM1, ICAM3, and CD59. The invention further concerns a method of detecting one or more members of a complex comprising CD44, VLA-4 integrin, basigin, CD138 (syndecan 1), NCAM, ICAM1, ICAM3, and CD59, using a linear or cyclic HYD1 peptide bearing a detectable moiety.