The present invention provides compositions and methods useful for diagnostic and imaging techniques for detecting and localizing the biomarker Plectin-1. The present invention provides multimeric peptide ligand complexes for targeting Plectin-1, such as the multimeric peptide ligand complex having the formula (βAKTLLPTPGGS(PEG5000))4 KKKKDOTAβA-NH2, to which imaging agents and/or therapeutic agents can be conjugated.