Stromal disrupting effects of nab-paclitaxel in pancreatic cancer

Abstract

Background: Nab-paclitaxel and gemcitabine have demonstrated a survival benefit over gemcitabine alone in advanced pancreatic cancer (PDA). This study aimed to investigate the clinical, biological, and imaging effects of the regimen in patients with operable PDA.

Methods: Patients with operable PDA received two cycles of nab-paclitaxel and gemcitabine before surgical resection. FDG-PET and CA19.9 tumour marker levels were used to measure clinical activity. Effects on tumour stroma were determined by endoscopic ultrasound (EUS) elastography. The collagen content and architecture as well as density of cancer-associated fibroblasts (CAFs) were determined in the resected surgical specimen and compared with a group of untreated and treated with conventional chemoradiation therapy controls. A co-clinical study in a mouse model of PDA was conducted to differentiate between the effects of nab-paclitaxel and gemcitabine.

Results: A total of 16 patients were enrolled. Treatment resulted in significant antitumour effects with 50% of patients achieving a >75% decrease in circulating CA19.9 tumour marker and a response by FDG-PET. There was also a significant decrement in tumour stiffness as measured by EUS elastography. Seven of 12 patients who completed treatment and were operated had major pathological regressions. Analysis of residual tumours showed a marked disorganised collagen with a very low density of CAF, which was not observed in the untreated or conventionally treated control groups. The preclinical co-clinical study showed that these effects were specific of nab-paclitaxel and not gemcitabine.

Conclusion: These data suggest that nab-paclitaxel and gemcitabine decreases CAF content inducing a marked alteration in cancer stroma that results in tumour softening. This regimen should be studied in patients with operable PDA.

Figure 1

Antitumour effects of nab-paclitaxel and gemcitabine in PDA. Panels (A–C) show waterfall plots of changes from baseline variation in the levels of the CA19.9 tumour marker, SUV FDG uptake and elastrography strain ratio of patients treated with nab-paclitaxel and gemcitabine. Studies were performed at baseline, before treatment, and after two 4 weeks cycles of treatment and best response is shown. As depicted, in all patients but one, there was evidence of antitumour effects, which was marked in more than half of the patients. Panels (D) and (E) show a scatter plot graph of the change from baseline in FDG SUV and elastography strain ratio with CA19.9 levels, respectively, which is an accepted parameter of clinical efficacy. As shown, improvement in both imaging parameters were correlated with improvement in CA19.9 with a P=0.05 and 0.01, respectively.

Figure 2

Tissue effects of nab-paclitaxel and gemcitabine in human PDA. Panel (A) shows confocal microscopy analysis of type I collagen immunofluorescence as main component of extracellular matrix in untreated sample, a sample of a patient treated with chemoradiation, and a sample of a patient treated with nab-paclitaxel and gemcitabine ( × 20, top, and the same field at × 40, bottom; scale bar=100 μM, × 20 field, and 50 μM, × 40 field). Panel (B) shows the effects of treatment in CAF stained for αSMA (red) and vimentin (green) immunofluorescence for quantification of activated and total fibroblasts in untreated sample (left), sample treated with chemoradiation (middle) and sample treated with nab-paclitaxel and gemcitabine (right; × 40; scale bar=50 μM). Panel (C) shows a quantification of total and activated CAFs in untreated samples, primary PDA tumours treated with chemoradiation, primary tumour PDA tumours treated with nab-paclitaxel and gemcitabine in two (20 steps) × 40 HCX PL APO CS (1.25 NA) oil immersion objectives high-power fields. Samples treated with nab-paclitaxel and gemcitabine show a statistically significant lower activated CAF (Mann–Whitney tests were used for statistical analysis: *P=0.037). Panel (D) represents the average CAF density index determined by dividing the number of CAF by proportion of stromal content in two × 40 HCX PL APO CS (1.25 NA) oil immersion objectives high-power fields. As shown, nab-paclitaxel and gemcitabine-treated groups have a statistically significant lower activated CAF density (Mann–Whitney tests were used for statistical analysis: *P=0.037; **P=0.015).

Figure 3

Antitumour effects of nab-paclitaxel and gemcitabine in GEMM of PDA. Panel (A) shows tumour growth inhibition of individual mouse treated with gemcitabine, nab-paclitaxel, or the combination. As depicted, the combined treatment was more effective than treatment with either gemcitabine alone (P=0.01) or nab-paclitaxel (P=0.001). Panel (B) shows representative microphotograph of caspase 3 expression showing increased level of apoptosis in the treated tumours. Panel (C) shows the quantification of caspase 3-positive cells in the different treatment groups showing a statistically significant increased in the combination treated group compared with control (*P=0.047, assessed by Student's t-test related to the untreated group).

Figure 4

Tissue effects of treatment regimens in GEMM of PDA. Panel (A) shows confocal microscopy analysis of type I collagen immunofluorescence as main component of extracellular matrix in untreated tumours and tumours treated with gemcitabine, nab-paclitaxel, and the combination ( × 20, top, and detail of collagen network at × 20, bottom; scale bar=75 μM, × 20 field). Panel (B) shows the effects of treatment in CAF stained for αSMA (red) and vimentin (green) immunofluorescence for quantification of activated and total fibroblast in samples of mice treated with the indicated agents ( × 40, scale bar=50 μM). Panel (C) shows a quantification of total and activated CAFs in untreated tumours and tumours treated with gemcitabine, nab-paclitaxel and the combination in two (20 steps) × 40 HCX PL APO CS (1.25 NA) oil immersion objectives high-power fields. Statistical analysis was not significant because of heterogeneity of samples.