Targeting anti-cancer drugs intracellularly via TRP channels
Selective introduction of charged anti-proliferative molecules into cancer cells by permeation through TRP channels, which are expressed in a number of types of cancer cells.
The strategy promises to open up a large new chemical space of potential anti-cancer agents, i.e. cationic molecules that are too poorly permeant to be effective unless introduced by permeation through TRP channels.
Many cancer cells express in their plasma membrane large-pore cation channels such as TRP channels and P2X-receptor channels. Mining existing gene expression profiling data from patients with a variety of cancer types, a sub-group of basal-like breast cancers have increased expression of TRPM8, as do a number of prostate cancers, some of which also have increased expression of TRPV1 channels. This in silico analysis has also revealed that melanomas have increased expression of TRPV2 channels and neuroblastomas express P2X7 channels, which are large-pore channels gated by ATP. Work assessing the ability of agonists of TRPM8 and TRPV1 to functionally activate these channels in a number of breast and prostate cancer cell lines is ongoing.
Innovations and Advantages
Recent results show that TRPV1 channels form pores that are sufficiently large to allow entry of a charged derivative of lidocaine, which can be selectively introduced into TRPV1-expressing pain-sensing neurons by co-application with capsaicin, an agonist that opens TRPV1 channels. Evidence for expression of a variety of TRP channels in cancer cells, including TRPV1 and TRPM8 channels in prostate cancer cells, TRPM8 channels in basal-like breast cancer cells, and TRPV2 channels in melanomas exists in the literature. Data suggests that adriamycin, a positively charged anti-proliferative agent, can permeate through TRPV1 channels when the channels are opened by capsaicin. Synthesis and screening for novel charged molecules with cytotoxic or anti-proliferative properties that are unable to enter cells except when TRP channels are activated by a co-applied agonist is possible, thus targeting them selectively to TRP-expressing cancer cells.
A method to selectively introduce charged sodium channel blocking molecules into pain-sensing neurons by way of TRPV1 channels, which are strongly expressed in nociceptors but have little expression in other types of neurons has recently been developed. Data shows that the pore of TRP channels is large enough pass QX-314, a charged derivative of lidocaine that is ineffective from the outside but blocks sodium channels (and therefore excitability) from the inside of cells. This allows selective inhibition of pain signals without producing general numbness or blocking motor neurons.
With the knowledge that a variety of cancer cells express TRP channels and other large-pore cation channels such as P2X7 ATP-gated channels, a similar strategy to selectively introduce into cancer cells charged molecules that are cytotoxic or antiproliferative when inside the cells but relatively innocuous outside. Co-applying such a compound together with an agonist for TRP or other large-pore channels present on the tumor cell would preferentially potentiate cytotoxicity in tumor cells that overexpress the large-pore channel, but have less effect on normal cells that either do not express such channels or express them at lower density.
Doxorubicin (Adriamycin) is a widely used chemotherapeutic agent that is relatively small (543 daltons) and is positively charged, making it an excellent candidate for transport via TRP channels or other large-pore cation channels. Although adriamycin is highly effective in many diseases (e.g., leukemia, breast cancer), the total dose that can be given is limited by a cumulative cardiotoxicity. Therefore, preferentially facilitating tumor cell uptake may improve the therapeutic index of this very important chemotherapeutic agent.
As a proof-of-concept, the Bean/Woolf labs have performed preliminary experiments testing whether it is possible to enhance adriamycin entry into cells through TRP channels (See Figure below). With a brief exposure to a low concentration of adriamycin applied together with capsaicin, there is entry of adriamycin into N1E-115 neuroblastoma cells that have been transfected with TRPV1. Adriamycin enters only cells that have been successfully transfected with TRPV1, and entry requires exposure to capsaicin (not shown). The simplest interpretation is that adriamycin enters directly through activated TRPV1 channels.
We are currently testing for enhanced cell death produced by adriamycin entry through TRP channels natively expressed in several types of cancer cells, starting with prostate cancer cells that endogenously express TRPV1. Another early focus will be basal-like breast cancer cells that express TRPM8 channels, using agonists for TRPM8 applied with adriamycin, since adriamycin is already used clinically against such cancers. Even a small increase in the potency of adriamycin's action produced by enhanced entry through TRP channels would be very important clinically due to the low margin of safety with this drug.
Intellectual Property Status: This technology is available for worldwide, exclusive licensing and/or a collaborative research program with the Bean and Woolf laboratories.
Bean, Bruce P.
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Reference Harvard Case #3059