Personalizing cancer treatment in the age of global genomic analyses: PALB2 gene mutations and the response to DNA damaging agents in pancreatic cancer

Abstract

Metastasis and drug resistance are the major causes of mortality in patients with pancreatic cancer. Once developed, the progression of pancreatic cancer metastasis is virtually unstoppable with current therapies. Here, we report the remarkable clinical outcome of a patient with advanced, gemcitabine-resistant, pancreatic cancer who was later treated with DNA damaging agents, on the basis of the observation of significant activity of this class of drugs against a personalized xenograft generated from the patient's surgically resected tumor. Mitomycin C treatment, selected on the basis of its robust preclinical activity in a personalized xenograft generated from the patient's tumor, resulted in long-lasting (36+ months) tumor response. Global genomic sequencing revealed biallelic inactivation of the gene encoding PalB2 protein in this patient's cancer; the mutation is predicted to disrupt BRCA1 and BRCA2 interactions critical to DNA double-strand break repair. This work suggests that inactivation of the PALB2 gene is a determinant of response to DNA damage in pancreatic cancer and a new target for personalizing cancer treatment. Integrating personalized xenografts with unbiased exomic sequencing led to customized therapy, tailored to the genetic environment of the patient's tumor, and identification of a new biomarker of drug response in a lethal cancer.

Trial registration: ClinicalTrials.gov NCT00276744.

Conflict of interest statement

Disclosure of Potential Conflicts of Interest: Siân Jones, Ralph H. Hruban, James R. Eshleman and Alison Klein are co-inventors on PLAB2- related intellectual property managed by Johns Hopkins University and have the potential to receive royalty payments for the PALB2 invention. The other authors disclosed no potential conflicts of interest

©2010 AACR.

Figures

Figure 1. Images of Clinical Outcome

A) Pet-CT obtained at the first postoperative visit showing an enlarged left supraclavicular lymph node with increase FDG uptake (arrowhead). A biopsy of this lymph node showed metastatic adenocarcinoma; B) CT revealing extensive locoregional recurrent disease after four cycles of gemcitabine; C) Late pulmonary progression with a left upper lesion that developed 22 months of follow up after the initial treatment with MMC (arrowhead); D) Decrease in pulmonary lesion size after two additional courses of MMC (arrowhead).

Figure 2. CA 19-9 restores to normal levels with MMC treatment

Time-course of CA 19-9 showing disease progression while on gemcitabine and complete normalization with MMC. Y-axis is log-scale of CA19-9 concentration presented in Units/mL;

Figure 3. MMC and cisplatin treatment remarkably suppressed the tumor growth of patient’s pancreatic carcinoma grown in nu/nu mice xenografts

Tumor growth curves indicating resistance to gemcitabine and remarkable response to MMC and cisplatin in the patient’s own xenografts (JH033). Panc 185, a pancreatic cancer xenograft with wild-type PALB2 wass presented as a control. Mice were treated and tumor volumes were monitored over time (days) as indicated in the materials and methods. Tumor growth is expressed as mean tumor volume ± SEM.

Figure 4. Mechanistic Studies

A) Location of somatic mutation in the PALB2 gene. The patient had somatically acquired a transition mutation (C to T) at a canonical splice site for exon 10 (IVS10+2). Exons are represented as black boxes and introns as black lines; B) Co-immunoprecipitation with a monoclonal antibody against BRCA1 of the BRCA1-BRCA2 complex. No complex is identified in the PALB2 mutant tumor JH033 as compared to the wild type Panc185 tumor used as a control; C) Western blot of FANCD2 ubiquitination. The upper band represents the ubiquitinated or long form (PFANCD2 Lys561) and the lower band represents the short, non ubiquitinated form. JH033 has competent proximal FA complex similar to the MMC resistant Panc185 control.