The authors would like to thank Wade Koba for his assistance with micro computed tomography (S10RR029545), Vera DesMarais and Hillary Guzik of the Analytical Imaging Facility for their training and assistance with microscopy, the Einstein Montefiore Cancer Center, the National Cancer Institute (P30CA013330, R01CA21248, R01CA255153), the Gruss Lipper Biophotonics Center, the Integrated Imaging Program for Cancer Research, a Sir Henry Wellcome Postdoctoral Fellowship (221647/Z/20/Z), and a METAvivor Career Development Award.

All procedures described in this protocol have been performed in accordance with guidelines and regulations for the use of vertebrate animals, including prior approval by the Albert Einstein College of Medicine Institutional Animal Care and Use Committee.
Prior to surgery, lung metastases are to be generated in mice using cancer cells that express a photoconvertible/photo-switchable protein; several protocols for lung metastasis generation have been published26,</s...

Examining Tumor Cell Dissemination from Lung Metastases

<ol>
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In this paper, we describe a surgical protocol for the selective photoconversion of tumor cells in the lung. This technique enables researchers to selectively mark tumor cells in the lung and track their fate by reidentifying them throughout the body at a later time point, facilitating the study of metastasis from lung metastases. Using this protocol, it was possible to visualize photoconverted cells in the brain, liver, and non-photoconverted right lung of mice that had undergone the surgery with photoconversion, indica...

Metastasis is the leading cause of cancer-related deaths1.&#160;Metastatic cancer arises when cells from the primary tumor disseminate throughout the body and proliferate into clinically detectable tumors in distant organs2,3.
Although metastasis is commonly thought of as a unidirectional process wherein tumor cells disseminate from the primary tumor and colonize distant organs4, increasing clinical and experimental evidence suggests that a more complex, multi-directional process is at play. It has been shown that circulating tumor cells can reseed the primary tumor (if still in place)5,6,7,8,9, and tumor cells from existing metastatic foci can travel to tertiary sites and give rise to new lesions10,11,12,13. Indeed, evidence from recent genomic analyses suggests that some metastatic lesions arise not from the primary tumor, but from other metastases-a phenomenon known as &#34;metastasis-from-metastases&#34; or &#34;metastasis-to-metastasis seeding&#34;14,15,16. Metastasis-to-metastasis seeding can perpetuate the disease process even after removal of the primary tumor, increasing metastatic burden, and decreasing patient quality of life and survival. Therefore, understanding the processes behind metastasis-to-metastasis seeding is crucial to refining treatment strategies for patients with metastatic disease.
Despite the potentially severe clinical implications, little is known about metastasis-to-metastasis seeding, due in part to logistical and technological limitations. Human studies are limited by a paucity of clinical samples. Clinical resection and biopsy of metastatic lesions are uncommon, as is the biopsy of seemingly healthy organs, where single disseminated tumor cells may lurk. This means that human studies are typically only possible using autopsy samples from individuals whose primary tumors are either still in place or were previously resected but are still available to researchers. When such samples are available, lineage analyses of cancer progression must be performed using sequencing methods14. However, bulk sequencing of matched primary tumors and metastases does not have the sensitivity needed for comprehensive lineage tracing. For instance, bulk sequencing of one lesion may reveal a subclone that is undetectable in any of its matched lesions. In this case, one would be unable to determine the origin of this subclone. It may have been present in the primary tumor or another metastasis at a frequency below the limit of detection, or it may have arisen after the initial colonization of the metastatic lesion it was found in. Single-cell sequencing provides increased sensitivity, but its high cost limits the large-scale application of this technique. The retrospective nature of these studies also means that they provide limited insight into transient metastatic events and the disease landscape at different time points.
In animal models, recent technological advances now allow for prospective phylogenetic mapping with high spatial and temporal resolution17,18,19,20. These techniques utilize CRISPR/Cas9 genome editing to engineer cells with an evolving barcode - heritable mutations that accumulate over time. Upon sequencing, the lineage of each cell can be traced based on the mutational profile of its barcode17,18,19,20. Indeed, such technology is already being used to map metastasis-to-metastasis seeding. In a recent paper, Zhang et al. demonstrated that breast and prostate cancer cells in bone metastases redisseminate from the bone to seed secondary metastases in multiple organs21.
While these novel methods have great potential to generate detailed, high-resolution phylogenetic maps of cancer progression, they are highly impractical for those studying the exact timing of metastasis-to-metastasis seeding events and what promotes or prevents them. Filling these knowledge gaps is crucial to refining our understanding and treatment of metastatic cancer, but there is a noticeable lack of technologies to facilitate such studies. To address this need, we recently developed - and present herein - a novel technique that allows us to specifically mark tumor cells via photoconversion in a metastatic site (the lung) and subsequently reidentify them in tertiary organs. Using this technique, we recently showed that breast cancer cells do redisseminate from lung metastases and seed tertiary organs13. This technique may also be used to determine the timing of redissemination events within a narrow window and quantify redisseminated tumor cells, facilitating the study of organotropism of redisseminated cells and what promotes/prevents redissemination.
While photoconversion and locally inducible cre/lox systems that permanently replace one fluorescent protein with another have been previously used to mark and track tumor cells11,22,23, to our knowledge, no approach for spatiotemporal marking of tumor cells has been optimized to target the lung - one of the most common sites of metastasis among men and women diagnosed with any of the 14 most common cancers24. Any cancer cell type and any protocol for lung metastasis generation may be used with our procedure, making it broadly useful for metastasis researchers. All cancer cells used to generate lung metastases should express a photoconvertible or photo-switchable protein, and researchers may choose which protein to use based on their specific needs and resources. In this study, we used 6DT1 breast cancer cells that stably expressed the photoconvertible green-to-red fluorescent protein Dendra2 (6DT1-Dendra2 cells)25 tagged to the histone H2B. We injected 5.0 &#215; 104 6DT1-Dendra2 cells into the fourth mammary fat pad of female Rag2-/- mice. Primary tumors were palpable between 12 and 16 days after injection and were not resected for the duration of the experiment. Spontaneous lung metastases developed between 19 and 26 days after tumor cell injection. Photoconversion surgeries were performed between 26 and 29 days after tumor cell injection. Mice were sacrificed by 72 h post surgery due to lung metastasis burden.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>0-30 V, 0-3 A Power Supply</td>
			<td>MPJA</td>
			<td>9616 PS</td>
			<td></td>
		</tr>
		<tr>
			<td>12 VDC, 1.2 A Unregulated Plug Supply</td>
			<td>MPJA</td>
			<td>17563 PD</td>
			<td></td>
		</tr>
		<tr>
			<td>28 G 1 mL BD Insulin Syringe</td>
			<td>BD</td>
			<td>329410</td>
			<td></td>
		</tr>
		<tr>
			<td>400 nm light emitting diode array lamp</td>
			<td>LedEngin Inc.</td>
			<td>897-LZPD0UA00</td>
			<td>Photoconversion lamp, custom-built (individual parts included below)</td>
		</tr>
		<tr>
			<td>5-0 braided silk suture with RB-1 cutting needle</td>
			<td>Ethicon, Inc.</td>
			<td>774B</td>
			<td></td>
		</tr>
		<tr>
			<td>9 cm 2-0 silk tie</td>
			<td>Ethicon, Inc.</td>
			<td>LA55G</td>
			<td></td>
		</tr>
		<tr>
			<td>Baytril 100 (enrofloxacin)</td>
			<td>Bayer (Santa Cruz Biotechnology)</td>
			<td>sc-362890Rx</td>
			<td>Antibiotic used in drinking water</td>
		</tr>
		<tr>
			<td>Buprenorphine</td>
			<td>Hospira</td>
			<td>0409-2012-32</td>
			<td>Analgesic</td>
		</tr>
		<tr>
			<td>Cables (Cable Assemblies) 2.1 DC JACK-STRAIGHT 72&#34;&#160; BLACK/ZIP CORD</td>
			<td>Mouser</td>
			<td>172-7426-E</td>
			<td></td>
		</tr>
		<tr>
			<td>Cables (Cable Assemblies) 2.5 JK-ST 72&#34; ZIP CD</td>
			<td>Mouser</td>
			<td>172-0250</td>
			<td></td>
		</tr>
		<tr>
			<td>Chlorhexidine solution</td>
			<td>Durvet</td>
			<td>7-45801-10258-3</td>
			<td>Chlorhexidine Disinfectant Solution</td>
		</tr>
		<tr>
			<td>Compressed air canister</td>
			<td>Falcon</td>
			<td>DPSJB-12</td>
			<td></td>
		</tr>
		<tr>
			<td>Extra Fine Micro Dissecting Scissors 4&#34; Straight Sharp/Sharp 24 mm</td>
			<td>Roboz Surgical</td>
			<td>RS-5912</td>
			<td>Sharp Micro Dissecting Scissors</td>
		</tr>
		<tr>
			<td>Fiber-optic illuminator</td>
			<td>O.C. White Company</td>
			<td>FL3000</td>
			<td>Used during mouse intubation</td>
		</tr>
		<tr>
			<td>Gemini Cautery Kit</td>
			<td>Harvard Apparatus</td>
			<td>726067</td>
			<td>Cautery pen</td>
		</tr>
		<tr>
			<td>Germinator 500</td>
			<td>CellPoint Scientific</td>
			<td>GER&#160;5287-120V</td>
			<td>Bead Sterilizer</td>
		</tr>
		<tr>
			<td>Graefe forceps</td>
			<td>Roboz</td>
			<td>RS-5135</td>
			<td></td>
		</tr>
		<tr>
			<td>High power LEDs - single color ultraviolet 90 watts</td>
			<td>Mouser</td>
			<td>LZP-D0UA00</td>
			<td></td>
		</tr>
		<tr>
			<td>Infrared heat lamp</td>
			<td>Braintree Scientific</td>
			<td>HL-1</td>
			<td></td>
		</tr>
		<tr>
			<td>Isoflurane SOL 250 mL PVL</td>
			<td>Covetrus</td>
			<td>29405</td>
			<td>Anesthetic</td>
		</tr>
		<tr>
			<td>Isoflurane vaporizer</td>
			<td>SurgiVet</td>
			<td>VCT302</td>
			<td></td>
		</tr>
		<tr>
			<td>Jacobson needle holder with lock</td>
			<td>Kalson Surgical</td>
			<td>T1-140</td>
			<td></td>
		</tr>
		<tr>
			<td>Labeling tape</td>
			<td>Fisher Scientific</td>
			<td>S68702</td>
			<td></td>
		</tr>
		<tr>
			<td>LED Lighting Reflectors CREE MP-L SNGL LENS REFLECTOR &#38; LOC PIN</td>
			<td>Mouser</td>
			<td>928-C11395TM</td>
			<td></td>
		</tr>
		<tr>
			<td>Long cotton tip applicators</td>
			<td>Medline Industries</td>
			<td>MDS202055</td>
			<td></td>
		</tr>
		<tr>
			<td>Masscool / Soccket 478 / Intel Pentium 4/Celeron up to 3.4GHz / Ball Bearing / Copper Core / CPU Cooling Fan</td>
			<td>CompUSA</td>
			<td>#S457-1023</td>
			<td></td>
		</tr>
		<tr>
			<td>Micro Dissecting Scissors 4&#34; Straight Blunt/Blunt</td>
			<td>Roboz Surgical</td>
			<td>RS-5980</td>
			<td>Blunt Micro Dissecting Scissors</td>
		</tr>
		<tr>
			<td>Murine ventilator</td>
			<td>Kent Scientific&#160;</td>
			<td>PS-02</td>
			<td>PhysioSuite</td>
		</tr>
		<tr>
			<td>Nair Hair Removal Lotion</td>
			<td>Amazon</td>
			<td>B001RVMR7K</td>
			<td>Depilatory cream</td>
		</tr>
		<tr>
			<td>Personnet mini retractor</td>
			<td>Roboz</td>
			<td>RS-6504</td>
			<td>Retractor</td>
		</tr>
		<tr>
			<td>Phosphate Buffered Saline 1x</td>
			<td>Fisher Scientific</td>
			<td>14190144</td>
			<td>PBS</td>
		</tr>
		<tr>
			<td>pLenti.CAG.H2B-Dendra2.W</td>
			<td>Addgene</td>
			<td>51005</td>
			<td>Dendra2 lentivirus</td>
		</tr>
		<tr>
			<td>Puralube</td>
			<td>Henry Schein Animal Health</td>
			<td>008897</td>
			<td>Eye Lubricant</td>
		</tr>
		<tr>
			<td>Rodent intubation stand</td>
			<td>Braintree Scientific</td>
			<td>RIS 100</td>
			<td></td>
		</tr>
		<tr>
			<td>Small animal lung inflation bulb</td>
			<td>Harvard Apparatus</td>
			<td>72-9083</td>
			<td></td>
		</tr>
		<tr>
			<td>SurgiSuite Multi-Functional Surgical Platform for Mice, with Warming</td>
			<td>Kent Scientific</td>
			<td>SURGI-M02</td>
			<td>Heated surgical platform</td>
		</tr>
		<tr>
			<td>Test Leads 48&#34; TEST LEAD BANANA - Black</td>
			<td>Mouser</td>
			<td>565-1440-48-0</td>
			<td></td>
		</tr>
		<tr>
			<td>Test Leads 48&#34; TEST LEAD BANANA - Red</td>
			<td>Mouser</td>
			<td>565-1440-48-2</td>
			<td></td>
		</tr>
		<tr>
			<td>Tracheal catheter&#160;</td>
			<td>Exelint International</td>
			<td>26746</td>
			<td>22 G catheter</td>
		</tr>
		<tr>
			<td>Wound closing system veterinary kit</td>
			<td>Clay Adams</td>
			<td>IN015</td>
			<td>Veterinary surgical stapling kit</td>
		</tr>
	</tbody>
</table>

tracking tumor cell dissemination from lung metastases using photoconversion

Metastasis - the systemic spread of cancer - is the leading cause of cancer-related deaths. Although metastasis is commonly thought of as a unidirectional process wherein cells from the primary tumor disseminate and seed metastases, tumor cells in existing metastases can also redisseminate and give rise to new lesions in tertiary sites in a process known as &#34;metastasis-from-metastases&#34; or &#34;metastasis-to-metastasis seeding.&#34; Metastasis-to-metastasis seeding may increase the metastatic burden and decrease the patient&#39;s quality of life and survival. Therefore, understanding the processes behind this phenomenon is crucial to refining treatment strategies for patients with metastatic cancer.
Little is known about metastasis-to-metastasis seeding, due in part to logistical and technological limitations. Studies on metastasis-to-metastasis seeding rely primarily on sequencing methods, which may not be practical for researchers studying the exact timing of metastasis-to-metastasis seeding events or what promotes or prevents them. This highlights the lack of methodologies that facilitate the study of metastasis-to-metastasis seeding. To address this, we have developed - and describe herein - a murine surgical protocol for the selective photoconversion of lung metastases, allowing specific marking and fate tracking of tumor cells redisseminating from the lung to tertiary sites. To our knowledge, this is the only method for studying tumor cell redissemination and metastasis-to-metastasis seeding from the lungs that does not require genomic analysis.

Author Spotlight: Decoding Metastasis-to-Metastasis Seeding Using a New In Vivo Technique for Tracking Breast Cancer Spread 

Tracking Tumor Cell Dissemination from Lung Metastases Using Photoconversion

Recent evidence suggests that existing metastatic lesions can act as a source of disseminating tumor cells that give rise to new lesions. This process is called metastasis to metastasis seeding and can increase tumor burden and decrease the quality of life and survival of cancer patients. Our method was developed to study metastasis to metastasis seeding and the factors that influence it.This technique has helped our lab establish that breast cancer cells can spread from lung metastases and enabled us to investigate factors that promote or prevent metastasis. These findings may guide future research on slowing the progression of metastatic cancer. The lungs are a common site of metastasis, but very few techniques allow for the study of tumor cell dynamics in vivo.This technique enables the tracking of tumor cells in live mice facilitating the study of lung metastasis specific dissemination pathways and therapies. Metastatic cancer is often an incurable and fatal disease. This technique can be used to study ways to reduce its spread leading to therapies that extend the lives of patients.

The steps of the surgery described in this protocol are illustrated in Figure 1. In brief, the mouse is anesthetized, and hair is removed from the left thorax. The mouse is then intubated and ventilated, which allows the mouse to receive oxygen while the thoracic cavity is open. Soft tissue is removed to expose the ribcage, and an incision is made in the 6th or 7th intercostal muscle. A retractor is inserted in the intercostal breach and released to spread the adjacent ...

Watch this Scientific Journal Video about Decoding Metastasis-to-Metastasis Seeding Using a New In Vivo Technique for Tracking Breast Cancer Spread at JoVE.com

We present a method for studying tumor cell redissemination from lung metastases involving a surgical protocol for the selective photoconversion of lung metastases, followed by the identification of redisseminated tumor cells in tertiary organs.

Metastasis - the systemic spread of cancer - is the leading cause of cancer-related deaths. Although metastasis is commonly thought of as a unidirectional ...

tracking-tumor-cell-dissemination-from-lung-metastases-using