The present invention provides a new 18-residue homodimerized peptide, designated PIP [59-67] dimer (SEQ ID NO: 1), which is a mutant of the optimized anti-inflammatory peptide P-NT.II, the patent for which has recently been filed [1]. P-NT.II has the potential to modulate both the inflammatory and bone damaging components of rheumatoid arthritis, and was originally designed on the basis of the primary structure of the anti-inflammatory protein termed `Phospholipase Inhibitor from Python (PIP)` [2]. Using solid phase chemistry, variants of P-NT.II were designed and examined for inhibitory activity against secretory phospholipase A2 (sPLA2), a key enzyme involved in the inflammatory pathway, and matrix metalloproteinases (MMPs) that are involved in the remodeling and degradation of the extracellular matrix in rheumatoid arthritis (RA) and cancer. Among the family of mutants tested, the dimerized peptide was found to be the most potent inhibitor against sPLA2 as well as the human recombinant MMP-1. This invention provides the utility of the peptide analogue PIP [59-67] dimer as a potential therapeutic agent for modulation of inflammatory diseases such as rheumatoid arthritis, and cancer. This invention relates to all the polypeptide analogues (SEQ ID NO: 1 to 3) and polynucleotides (SEQ ID NO: 4), and to the use of those polypeptides and polynucleotides, their synthetic chemical analogues or variants that inhibit activity and synthesis of sPLA2 and MMPs, in the diagnosis, study, prevention and treatment of rheumatoid arthritis and/or cancer.