Abstract Submission: AACR Abstract La Jolla Conference September 2005

Drug response indicators in cancer cells provide the bases of personalized anticancer chemotherapy (PAC) for breast cancer (BC). Ts’o, P.O.P.¹, Lesko, S.A.¹, Lum, Z.P.¹, Deamond, S.F.¹, Shan, E.¹, Zhou, D.B.¹, Daniel, J.R.¹, Tkaczuk, K.H.², Tait, N.S.², Feldman, F.², Van Echo D.A.³. 1. CCC Diagnostics, LLC, 2. University of Maryland Greenebaum Cancer Center, 3. Harbor View Cancer Center, Baltimore, Maryland.

Targeted therapy designed against specific cellular components (receptors, enzymes) or processes (repair, mitotic division) coupled with the diagnostic tools to measure the target status in tumors from individual patients (pts.) forms the basis of PAC.

PAC requires the integration of three strategic steps. Step I is the measurement of several targets simultaneously in the tumor quantitatively. The targets termed drug response indicators (DRI) can be evaluated by immunofluorescence utilizing monoclonal antibodies and a computerized fluorescence microscope. Quantitative values can be derived and normalized to a reference standard for inter-laboratory comparison.

Step II establishes a statistically significant correlation of DRI expression with the cytotoxic response of tumor cells to a related drug. This allows for interpretation of quantitative DRI data. Seven BC cell lines with different sensitivities to various anticancer drugs were utilized. The effect of tamoxifen, paclitaxel, and trastuzumab on the proliferation of BC cell lines in culture was determined as well as the DRI for each drug in these cell lines.

The cytotoxic response of various BC cell lines: to trastuzumab correlated inversely with the level of HER-2/neu expression evidenced by a Spearman rank correlation coefficient (SRCC) of (-1); to tamoxifen correlated with estrogen receptor expression shown by a SRCC of (-.995); to paclitaxel correlated with beta tubulin III expression shown by SRCC of +.995. These in-vitro results provide for the design of a confirmatory clinical trial.

Step III: Technology for obtaining cancer cells from individual cancer pts. For metastatic tumors, circulating cancer cells (CCC) from peripheral blood were obtained using a negative selection procedure, enumerated, and stained with labeled trastuzumab to quantify the HER-2/neu expression. Ninety-one BC pts. were studied and 347 blood samples drawn; med. number of samples drawn per pt. was 3 (1-6). CCC are related to distant metastasis; 88% of Stage IV pts. have CCC at some point during sampling (59% of samples). CCC numbers ranged from 1-1283 per sample.

Fifteen pts. had sufficient number of CCC to test for HER-2 expression and also had available tumor tissue data. In eleven pts., the CCC and primary tumor data concurred (73%) with 4 positive in HER-2 and 7 negative in HER-2. Three pts. had negative results for HER-2 in tumor tissue but found positive for HER-2 in CCC. One patient had positive HER-2 in tumor tissue and negative HER-2 in CCC.

Conclusion: Therapy (trastazumab) – diagnostics (HER-2 expression) coupling was the first model approved by FDA for PAC for BC. Unfortunately, 60-70% of HER-2 positive pts. do not respond to standard trastazumab though HER-2 negative pts. are significantly much less responsive to trastazumab. Improvement of DRI measurements in BC tumor tissue and CCC may lead to more predictable treatment and outcomes in BC pts.

Research supported in part by NCI SBIR Grant CA081903 awarded to CCC Diagnostics, LLC.