Abstract 3230: In vitro evaluation of Her2 targeted N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer conjugates in combination treatment with tyrosine kinase inhibitor (PKI-166)
Authors: Lee Jun H. , Sabnis Gauri , Brodie Angela , Nan Anjan 
Published: June 2012

Abstract
Trastuzumab (TRZ) and tyrosine kinase inhibitors are useful in treating Her2 overexpressing cancers. However, due to low selectivity and non-specificity, side effects are a major concern along with development of resistance. We propose to overcome these challenges with a novel drug delivery approach. Water-soluble HPMA copolymer conjugate systems are well characterized and have demonstrated enhanced pharmacokinetic profiles in many anticancer therapies. The present study evaluates the potential of TRZ-HPMA copolymer conjugates and combination with PKI-166 to enhance the therapeutic index of Her2 targeted therapy. TRZ was conjugated to two types of HPMA copolymer structures with random (PHPMA) and semitelechelic (ST-PHPMA) backbone. Growth inhibition studies were performed with the conjugates, TRZ, PKI-166 and their combination against two Her2 positive human breast cancer cell lines (BT-474 and SK-BR-3). Her2 negative MDA-MB-231 cell line was used as a negative control. Cell viability after drug treatment was determined by the MTT assay. The growth inhibition effects of all TRZ-HPMA copolymer conjugates were concentration dependant. The IC50 of TRZ-PHPMA 1:1 conjugate (T/P 1/1) and TRZ-ST-PHPMA 1:1 (T/STP 1/1) in BT-474 and SK-BR-3 cells were comparable to free TRZ. These results suggested that the antibody retained its bioactivity upon conjugation. In each combination of T/P 1/1, T/STP 1/1 or free TRZ with free PKI-166 showed synergistic growth inhibition effects in both Her2+ve cell lines with combination index less than 1. Interestingly, combination treatments also reduced viability in the Her2-ve cell line. Activation of Her2 after treatments was measured by western immunoblotting on BT-474 cell line. Her2 phosphorylates and activates MAPK and Akt. Treatment with free TRZ downregulates pMAPK and pAkt to a greater extent than those of TRZ-HPMA polymer conjugates in 4h. However these effects were reversed by 72h. The pMAPK and pAkt levels of free TRZ treated cells increased at 72h while those of TRZ-HPMA polymer conjugates treated cells decreased further. This suggests that polymer conjugation prolonged the effect of TRZ on MAPK and Akt activity. As expected PKI-166 down-regulated pHer2, pMAPK and pAkt in both single and combination treatment. The results suggest that TRZ-HPMA copolymer conjugation may prolong activity of TRZ while retaining the efficacy. Active targeting to Her2 overexpressing breast cancer cells using this novel drug delivery system of TRZ could have advantages in patients developing rapid drug resistance from TRZ treatment. It provides rationale of further development of a novel anti-cancer drug delivery system containing dual mode of action drugs of TRZ and PKI-166 in same HPMA copolymer backbone.
Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 3230. doi:10.1158/1538-7445.AM2011-3230