SAN DIEGO—Experiments conducted in the lab and the clinic suggest the enzyme heparanase enhances resistance to chemotherapy in multiple myeloma (MM).
Researchers first found that expression of heparanase, an endoglycosidase that cleaves heparan sulfate, is highly elevated in MM patients after chemotherapy.
The team then used MM cell lines to investigate the mechanism behind this phenomenon.
Their results indicate that, by inhibiting heparanase, we might be able to prevent or delay relapse in MM.
Vishnu Ramani, PhD, of the University of Alabama Birmingham, and his colleagues conducted this research and presented the results at the AACR Annual Meeting 2014 (abstract 1708).
Several years ago, Dr Ramani’s colleagues (in the lab of Ralph Sanderson, PhD) identified heparanase as a master regulator of aggressive MM. Since then, research has suggested that heparanase fuels aggressive MM by upregulating the expression of pro-angiogenic genes, driving osteolysis, upregulating prometastatic molecules, and controlling the tumor microenvironment.
“We have done a lot of work on the biology of how this molecule works in myeloma, but the one thing I was really interested in was its role in drug resistance,” Dr Ramani said.
So he and his colleagues decided to study heparanase levels in 9 MM patients undergoing chemotherapy. The team isolated tumor cells from patients before and after 2 rounds of chemotherapy and compared heparanase levels at the different time points.
“What we find—and this is really remarkable—is that the expression of heparanase over rounds of therapy goes up several thousand-fold, and this is in the majority of patients,” Dr Ramani said. “In 8 out of 9 patients that we studied, at the end of chemotherapy, the cells that survive have extremely high levels of heparanase.”
To gain more insight into this phenomenon, the researchers studied it in MM cell lines. The team introduced bortezomib to RPMI-8226 and CAG cells and found that heparanase levels increased “dramatically” after treatment.
“The treatment is not only increasing the heparanase expression inside the cell,” Dr Ramani explained. “What the cells do is that, if you continue the treatment, they die, but they don’t take the heparanase with them. They leave it out in the media, and this can be taken in by other cells. So this can activate other cells to promote aggressive tumor growth too.”
Additional investigation revealed that the NF-κB pathway plays a role—namely, chemotherapy activates the pathway to upregulate heparanase. But inhibiting NF-κB activity can prevent that increase in heparanase.
The researchers tested the NF-κB inhibitors BAY 11-7085 and BMS345541 in combination with bortezomib. And they found that both agents prevented bortezomib from elevating heparanase expression in CAG cells.
Dr Ramani and his colleagues also evaluated heparanase levels in chemoresistant MM cell lines. Heparanase levels were 4-fold higher in a doxorubicin-resistant MM cell line and 10-fold higher in a melphalan-resistant cell line, when compared to a wild-type MM cell line.
Next, the researchers compared MM cells with high heparanase expression to those with low heparanase expression. And they discovered that high heparanase levels protect cells from chemotherapy.
After treatment with bortezomib, cells with high heparanase expression were significantly more viable than those with low expression (P<0.05). And there was a significantly higher percentage of apoptotic cells among the low-heparanase population compared to the high-heparanase population (P<0.05).
“If you take cells that have high heparanase and another group of cells that have low heparanase and expose both of them to therapy, the cells with high heparanase always survive better because the heparanase upregulates certain pathways, like the MAP kinase pathway, which helps the cells to survive the onslaught of chemotherapy,” Dr Ramani said. “So myeloma cells are actually hijacking the heparanase pathway to survive better after therapy.”
Building upon that finding, the researchers decided to assess whether inhibiting ERK activity might help cells overcome heparanase-mediated chemoresistance. And experiments showed that the ERK inhibitor U0126 can sensitize cells with high heparanase levels to treatment with bortezomib.
To take this research to the next level, Dr Ramani and his colleagues are collaborating with a company called Sigma Tau, which is developing a heparanase inhibitor called SST-0001. A phase 1 study of the drug in MM patients has been completed, and phase 2 studies are currently recruiting patients in Europe.
Dr Ramani is now conducting experiments in mice to determine how the inhibitor might work in combination with chemotherapy and when it should be administered in order to overcome treatment resistance. He is also looking for other molecular pathways that could be involved in heparanase-related treatment resistance.
